Friction Stir Channeling Industrial Applications

Prototype Design and Production

Miguel Filgueiras Soares Ferraz

Dissertation for the Degree of Master in

Mechanical Engineering

Jury

Chairperson: Professor Doutor Rui Manuel dos Santos Oliveira Baptista

Supervisor: Professor Doutor Pedro Miguel dos Santos Vilaça da Silva

Members: Professora Doutora Rosa Maria Mendes Miranda

Professora Doutora Virgínia Isabel Monteiro Nabais Infante

May 2012

i

Agradecimentos

Venho por este meio expressar a minha profunda gratidão ao meu orientador, Professor

Pedro Miguel dos Santos Vilaça, por me ter convidado para integrar um projecto tão desafiante e

pioneiro no seio do seu talentoso grupo de trabalho, o iStir. Como também pelo seu apoio pessoal,

tempo investido, material, equipamento e input técnico crucial. Agradeço com a maior das

sinceridades todo o seu empenho e interesse.

Um sincero obrigado à Professora Luisa Coutinho pelo seu apoio a nível de escrita e compilar

um relatório bem estruturado e detalhado de todo o trabalho desenvolvido pelo autor.

O especial agradecimento ao Mestre João Gandra por toda o seu conhecimento, dedicação e

valor acrescido que deu para o desenvovlvimento deste trabalho como também ao grupo iStir, mas

especialmente por todo o seu apoio e amizade.

O meu profundo obrigado ao Mestre Filipe Nascimento por toda a sua ajuda prestada durante

o trabalho experimental decorrido na Secção de Tecnologia Mecânica, Instituto Superior Técnico,

como também do seu know-how na tecnologia deste trabalho mas acima de tudo o seu apoio

incondicional em qualquer altura.

Um sincero obrigado ao Mestre José Pedro por toda a sua motivação inspiradora e

disponibilidade em arranjar soluções para os mais variados problemas.

Agradeço à Mestre Catarina Vidal pela ajuda prestada durante todo o desenvolvimento deste

trabalho como também na fase de concepção de ferramentas para o mesmo.

Expresso também o meu apreço pelo Sr. João Luís por um excelente trabalho de produção

das ferramentas e de outros componentes projectados.

Aos meus colegas e futuros Mestres Tiago Carneiro, Miguel Passanha, Manuel Hall, Luís

Lobo da Costa, André Coutinho, João Avelar, Martim Teixeira, João Jeremias e Rui Pedro Silva entre

muitos outros, expresso a minha profunda consideração pela forte amizade que se desenvolveu ao

longo destes 5 anos e todo o apoio sistemático durante a realização deste trabalho.

ii

Acknowledgments

I would like to express deep gratification to my supervisor, Professor Pedro Miguel dos Santos

Vilaça da Silva, for inviting me to join such a challenging project, giving me the opportunity to work in

the development of a state of art technology with such a talented group of people as his iStir work

group. As well as for providing material, equipment, crucial technical support and time invested.

Honest thanks for all the commitment and personal interest.

The author would also like to express his gratitude to Professora Luisa Coutinho for the final

aid in compiling a well structured and detailed report on the work developed by the author.

A special thank to MSc. João Gandra for his constant teachings and contribution to the

development of the present work and the whole iStir work goup, but especially for all of his support

and close friendship.

My sincere appreciation to MSc. Filipe Nascimento for his precious help concerning the

experimental work performed at Secção de Tecnologia Mecânica, Instituto Superior Técnico. As well

as, all of the know-how he shared with me on the technological implementation of the present work.

A truthful gratitude to MSc. José Pedro for his availability and inspiring motivation to find

solutions for any kind of obstacle encountered throughout the present work.

Honest thank you to MSc. Catarina Vidal for the help given during all the development of the

present work and in the actual tool design.

The author expresses his appreciation to Mr. João Luís for an excellent job in tool

manufacturing.

To future MSc. Tiago Carneiro, Miguel Passanha, Manuel Hall, Luis Lobo da Costa, André

Coutinho, João Avelar, Martim Teixeira, João Jeremias, Rui Pedro Silva and many others colleagues,

the author expresses deep appreciation for the strong friendship and support provided during this

work.

iii

Resumo

A presente investigação teve como objectivo avaliar potenciais aplicações industriais da

tecnologia de abertura de canais por fricção linear (FSC), com enfâse na indústria dos moldes.

O FSC é um processo tecnológico inovador de fabrico no estado sólido capaz de produzir

canais contínuos internos em placas maciças. Os canais obtidos por FSC podem ter qualquer

caminho e dimensões variáveis ao longo desse caminho.

O facto dos canais feitos por FSC poderem ter qualquer caminho, abre portas para o FSC ser

uma tecnologia de fabrico de canais de aquecimento/refrigeração para a indústria dos moldes. No

presente trabalho, foram produzidos dois moldes protótipos para avaliar de facto o potencial do FSC.

O primeiro protótipo foi um molde de injecção de plásticos. Tendo em conta que, os tempos

de refrigeração são 70-80% do seu ciclo produtivo, é muito importante que esta fase seja eficiente. A

tecnologia FSC consegue produzir canais que se adaptam à geometria dos componentes a produzir

optimizando e uniformizando o tempo de refrigeração.

O segundo protótipo foi um molde de apoio ao processo de cura de um componente

compósito. Neste caso, os tempos de aquecimento/refrigeração são mais elevados e assim os canais

já podem ser mais compridos pois a temperatura tem mais tempo para estabilizar, possibilitando um

menor número de canais.

As conclusões indicam que o FSC tem potencial para ser uma tecnologia alternativa na

indústria dos moldes. No entanto, ainda existe trabalho para efectuar a nivel de I&D tecnológico

sustentável.

Palavras-Chave

Tecnologia de Abertura de Canais por Fricção Linear

Aquecimento/Refrigeração Adaptativa

Indústria dos Moldes

Superfície Moldante

Ligas de Alumínio

iv

Abstract

The current investigation envisages to evaluate the potential of Friction Stir Channeling (FSC)

to be industrially applied with a main focus on the mould industry.

FSC is an innovative technological process within solid-state manufacturing technologies able

to produce continuous internal channels in monolithic plates. Friction Stir (FS) channels can have any

path and variable dimensions along that path. FSC shows high potential for application in several

technical fields and offers significant advantages for existing and future industrial applications.

The features of FSC enable it to be successfully applied in the production of heating/cooling

conformal channels for moulds. In order to withstand such statement two mould prototypes were

designed and produced in the present work.

The first prototype was an injection mould for polymers, which relies on a rapid cooling

process that is 70-80% of its producing cycle time. The main aspects are i) uniform distance to

moulding surface and ii) short length of the FS channels to assure fast and uniform cooling processes,

for adequate surface quality and short cycle times.

The second prototype was a mould designed for a curing process of a composite component,

which is a slow heating/cooling process. The major focus is the workpiece surface quality, which can

be accomplished with a uniform heating/cooling cycle. In this case the conformal channels can have

greater channel lengths, since the heating/cooling fluid temperature in FS channels stabilizes with

time.

As a conclusion, FSC can be an alternative technology for the mould industry. However, FSC

still needs thorough investigation and sustainable technological development.

Keywords

Friction Stir Channeling

Conformal Heating/Cooling

Mould Industry

Moulding Surface

Aluminum Alloy

v

Table of Contents

Agradecimentos .........................................................................................................................................i

Acknowledgments .................................................................................................................................... ii

Resumo ................................................................................................................................................... iii

Palavras-Chave ....................................................................................................................................... iii

Abstract.................................................................................................................................................... iv

Keywords ................................................................................................................................................. iv

Table of Contents .....................................................................................................................................v

List of Figures ........................................................................................................................................ viii

List of Tables .......................................................................................................................................... xii

Nomenclature ........................................................................................................................................ xiii

Abbreviations ..................................................................................................................................... xiii

Greek Symbols .................................................................................................................................. xiv

1 Introduction ...................................................................................................................................... 1

1.1 Scope ....................................................................................................................................... 1

1.2 Objectives ................................................................................................................................ 2

1.3 Structure of Thesis .................................................................................................................. 3

2 State of Art ....................................................................................................................................... 4

2.1 Friction Stir Channeling ........................................................................................................... 4

2.1.1 The Process Concept ...................................................................................................... 4

2.1.1.1 Evolution from FSWelding ........................................................................................... 4

2.1.1.2 Preliminary Findings of FSC ........................................................................................ 7

2.1.1.3 Initial Version of FSC ................................................................................................... 7

2.1.1.4 Development of FSC ................................................................................................... 8

2.1.2 The Channel Formation ................................................................................................. 10

vi

2.1.3 The Channel Shape ....................................................................................................... 12

2.1.4 The Channel Size .......................................................................................................... 16

2.1.5 Surface Roughness ....................................................................................................... 17

2.1.6 Mechanical Properties ................................................................................................... 20

2.2 Alternative Technologies ....................................................................................................... 23

2.2.1 Drilling ............................................................................................................................ 23

2.2.2 EDM ............................................................................................................................... 25

2.2.3 Milling ............................................................................................................................. 27

2.3 Industrial Applications ............................................................................................................ 29

2.3.1 Mould Production ........................................................................................................... 29

2.3.1.1 Conformal Cooling ..................................................................................................... 29

2.3.1.2 Rapid Prototyping ...................................................................................................... 30

2.3.2 Heat Exchanger Production ........................................................................................... 33

2.3.3 Other Applications ......................................................................................................... 34

3 Competitive Analysis with Alternative Technologies ..................................................................... 36

3.1 FSC vs Drilling ....................................................................................................................... 37

3.2 FSC vs EDM .......................................................................................................................... 38

3.3 FSC vs Milling ........................................................................................................................ 39

3.4 Discussion ............................................................................................................................. 40

4 FSC Applications ........................................................................................................................... 41

4.1 Experimental Set-up .............................................................................................................. 42

4.1.1 Materials Characterization ............................................................................................. 42

4.1.2 Equipment ...................................................................................................................... 43

4.1.3 Tool Design .................................................................................................................... 44

4.1.4 Fixturing System ............................................................................................................ 46

vii

4.1.5 Testing Description ........................................................................................................ 47

4.1.5.1 Injection Mould Prototype .......................................................................................... 47

4.1.5.2 Curing Process Mould Prototype ............................................................................... 48

4.2 Injection Mould Prototype ...................................................................................................... 49

4.2.1 Formulation of Objectives .............................................................................................. 51

4.2.2 Computational Development of Solution ....................................................................... 52

4.2.3 Technological Implementation ....................................................................................... 53

4.2.4 Result Analysis .............................................................................................................. 56

4.3 Curing Process Mould Prototype ........................................................................................... 57

4.3.1 Formulation of Objectives .............................................................................................. 58

4.3.2 Computational Development of Solution ....................................................................... 61

4.3.3 Technological Implementation ....................................................................................... 70

4.3.4 Result Analysis .............................................................................................................. 73

5 Global Analysis of Performed Developments ................................................................................ 74

6 Conclusions ................................................................................................................................... 76

7 References .................................................................................................................................... 79

viii

List of Figures

Figure 2.1 – Schematic representation of Friction Stir Welding (FSW) [3]. ............................................ 4

Figure 2.2 – 4 main steps in completing a FSW weld: 1) Define weld starting position, 2) Probe

penetration until shoulder is in full contact with workpiece, 3) Establish adequate thermo-mechanical

conditions, 4) Relative linear movement is initiated. ............................................................................... 5

Figure 2.3 – Location of defects in welded zone [5]. ............................................................................... 6

Figure 2.4 – Schematic representation of FSC “new version” process (cross section view) [9]. ............ 9

Figure 2.5 – Example of a cross section macrograph of a FS channel showing channel (Ch), nugget

(N), base material (BM), advancing side (A.S.) and retreating side (R.S.) localization [9]. .................. 10

Figure 2.6 – Cross section showing FS channel shapes produced by Balasubramanian with different

processing parameters: (a) 1100 rpm, 2.11 mm/sec, and (b) 1100 rpm, 2.96 mm/sec [7]. .................. 12

Figure 2.7 – Cross section macrograph showing channel geometries produced with different FSC

processing parameters: (A) 600rpm, 80mm/min., (B) 600rpm, 150mm/min., (C) 800rpm, 80mm/min.

and (D) 800rpm, 150mm/min [9]. .......................................................................................................... 14

Figure 2.8 - Schematic representation of a cross-section (above) and a plan (below) views of the

friction stir channeled solid block [9]. ..................................................................................................... 15

Figure 2.9 - Longitudinal cross section of a FS channel conducted by Balasubramanian showing the

roughness on the channel ceiling produced with the following process parameters: (a) 1200 rpm, 2.11

mm/sec, (b) 800 rpm, 1.27 mm/sec, (c) 800 rpm, 0.42 mm/sec [7]. ..................................................... 18

Figure 2.10 - Longitudinal cross sections of a channel produced in FSC condition B (ω=600rpm;

v=150mm/min) showing the roughness on the retreating side (a) and on the advancing side (b) of the

channel [11]. .......................................................................................................................................... 19

Figure 2.11 - Cross section showing the roughness on the bottom and on the retreating side of the

channel at 4 different FSC (conditions A, B, C & D) processing parameters [11]................................. 19

Figure 2.12 - Cross section showing the roughness on the ceiling and on the advancing side of the

channel at 4 different FSC (conditions A, B, C & D) processing parameters [11]................................. 20

Figure 2.13 – Fracture localization of specimens tested under bending test condition (x) referred in

Table 2.6 [9]. .......................................................................................................................................... 21

Figure 2.14 - Microhardness profile across the FSC processed zone for FCS condition C (ω=800rpm;

v=80mm/min) [11]. ................................................................................................................................. 22

ix

Figure 2.15. – EDM hole drilling process schematic demonstration [19]. ............................................. 25

Figure 2.16 – Broad classification of industrial heat exchangers based on heat transfer area density

and channel size [37]. ............................................................................................................................ 33

Figure 4.1 - ESAB LEGIOTM 3UL Friction Stir Welding machine. Degrees of freedom representation

[42]. ........................................................................................................................................................ 43

Figure 4.2 - iSTIRtool_v3 model views, (a) Model views and (b) section view. 1 – Tool body; 2 –

Probe; 3 – Shoulder; 4 – Probe fixation screw; 5 – Shoulder fixation screw [44]. ................................ 45

Figure 4.3 - iSTIRtool_v3 tool version assembly. Probe and shoulder fastening (a) and several tool

geometry combinations (b-e): (b) & (c) cylindrical probes; (d) & (e) conical probes [44]. ..................... 45

Figure 4.4 - Cross section view of tool assembly with probe (pin) adjustment system [44]. ................. 46

Figure 4.5 – Two different configurations of fixturing system for FSC process. .................................... 47

Figure 4.6 – Modular tool with internal refrigeration used in FSC trials of injection mould prototype with

conical probe and 2 striates shoulder [45]. ............................................................................................ 47

Figure 4.7 – Modular tool with internal refrigeration and with special insert for surface finishing “add-in”

used in FSC trials of curing process mould prototype with cylindrical probe and 1 striate shoulder. ... 48

Figure 4.8 – Solidworks design of injection mould prototype (cavity and male). .................................. 50

Figure 4.9 – Solidworks assembly of injection mould prototype: male assembled with cavity of mould.

............................................................................................................................................................... 50

Figure 4.10 – Part to be produced from injection mould prototype. ...................................................... 50

Figure 4.11 – Simulation of cooling fluid flowing through the injection mould prototype with fluid

progressing along one of the FS channels. ........................................................................................... 52

Figure 4.12 – Cross section view of the injection mould prototype with the part placed on top of the

cavity mould, this procedure was performed in Solidworks software. ................................................... 53

Figure 4.13 – Simulation of different velocities of cooling fluid flowing through one FS channel of the

injection mould prototype....................................................................................................................... 53

Figure 4.14 – FS channels of injection mould prototype top views right after being produced, before

the mould cavity was manufactured. ..................................................................................................... 54

Figure 4.15 – Injection mould prototype top view. ................................................................................. 54

Figure 4.16 – Injection mould prototype cross section view. ................................................................. 55

x

Figure 4.17 – Perspective view of injection mould prototype with corresponding FS channels as well

as 4 sections demonstrating the FS channel cross sections. ............................................................... 55

Figure 4.18 – Solidworks design of curing process prototype (mould and workpiece). ........................ 57

Figure 4.19 – FS channels configuration of curing process mould prototype. ...................................... 58

Figure 4.20 – 3D dimensions of curing process mould prototype and corresponding workpiece. ........ 59

Figure 4.21 – 2D dimensions of curing process mould prototype and corresponding workpiece. ........ 60

Figure 4.22 – Block model developed in Abaqus software. .................................................................. 62

Figure 4.23 – Block model with workpiece square unit on top. ............................................................. 62

Figure 4.24 – Block model with interface between block and workpiece square unit. .......................... 63

Figure 4.25 – Temperature distribution of block model heated up to 80°C (perspective). .................... 63

Figure 4.26 – Temperature distribution of block model heated up to 80°C (front view). ....................... 64

Figure 4.27 – Channel configurations of all 3 Case Studies. ................................................................ 64

Figure 4.28 – Different FS channels configurations for curing process mould prototype, tested before

using final FS channels configuration (Case Study 3). ......................................................................... 65

Figure 4.29 – Temperatures versus time of Optimal curing process. ................................................... 67

Figure 4.30 – Properties distribution of curing process prototype computational simulation. ............... 67

Figure 4.31 – Properties distributions and values for mould component [49]. ...................................... 68

Figure 4.32 – Cross sections of the longitudinal (longer) side of the 3 components at the end of the

curing process prototype computational simulation with the corresponding temperature distribution for

all of the 3 Case Studies........................................................................................................................ 69

Figure 4.33 – Cross sections of the transversal (short) side of the 3 components at the end of the

curing process prototype computational simulation with the corresponding temperature distribution for

all of the 3 Case Studies (Case Study = CS). ....................................................................................... 69

Figure 4.34 - FS channels of curing process mould prototype with serpentine and contour paths (top

views) immediately after being produced and before the moulding surface was manufactured. ......... 70

Figure 4.35 – Two FS channels of curing process mould prototype immediately after being

manufactured. ........................................................................................................................................ 71

xi

Figure 4.36 – FS channels immediately after being produced at “colder conditions” leaving processed

surface at same level as before being processed just with a slight roughness variation, a) serpentine

path and b) straight path........................................................................................................................ 72

Figure 4.37 – Top view of initial FSC trials for curing process mould prototype and 2 cut pieces

demonstrating the corresponding FS channel cross sections............................................................... 72

xii

List of Tables

Table 2.1 – Variable parameters of FS channels produced by Balasubramanian [5]. .......................... 12

Table 2.2 – Different FSC process parameters [7]. ............................................................................... 13

Table 2.3 – Geometric parameters of internal channels produced with different FSC process

parameters [9]. ...................................................................................................................................... 15

Table 2.4 – FS channel areas (mm2) for different FSC conditions [9]. .................................................. 16

Table 2.5 – Heat indexes of three FSC trials performed by Balasubramanian. .................................... 18

Table 2.6 – Maximum load (kN) results for different FSC conditions [9]. .............................................. 21

Table 4.1 - AA5083 aluminum alloy chemical composition [40]. ........................................................... 42

Table 4.2 - AA5083 aluminum alloy physical properties [40]. ............................................................... 42

Table 4.3 - AA5083-H111 aluminum alloy mechanical properties [40]. ................................................ 42

Table 4.4 - AA5083-O aluminum alloy mechanical properties [41]. ...................................................... 42

Table 4.5 – FSC process parameters for injection mould prototype. .................................................... 48

Table 4.6 – FSC process parameters for curing process mould prototype. .......................................... 48

Table 4.7 - Properties values for the interface (defined by the author) and the workpiece component

[48] [50]. ................................................................................................................................................. 68

xiii

Nomenclature

Abbreviations

A Channel Area

AA Aluminum Alloy

A.S. Advancing Side of Channel

BM Base Material

CAD Computer-aided Design

COP Coefficient of Performance

CS Case Study

d Channel Depth

D Closing layer thickness

DASR Depth Averaged Surface Roughness

EDM Electrical Discharge Machining

EW Electrode Wear

FS Friction Stir

FSC Friction Stir Channeling

FSP Friction Stir Processing

FSSW Friction Stir Spot Welding

FSW Friction Stir Welding

HSTR High Strength Temperature Resitant

IST Instituto Superior Técnico

LM Layer Manufacturing

MCHX Mini-channel Heat Exchanger

MRF Metal Removal Fluid

xiv

MRR Material Removal Rate

N Nugget

RM Rapid Manufacturing

RP Rapid Prototyping

R.S. Retreating Side of Channel

SEM Scanning Electron Microscope

SLA Stereolithography

SLS Selective Laser Sintering

STL Standard Tessellation Language (file format)

SWOT Strengths Weaknesses Opportunities Threats

t Block Thickness

TMAZ Thermo-mechanically Affected Zone

TWI The Welding Institute

UTL Universidade Técnica de Lisboa

v Tool Travel Speed

Greek Symbols

Shear Angle of Channel Advancing Side

Tool Rotation Speed

1

1 Introduction

1.1 Scope

The FSC process was initially based on converting an internal defect in Friction Stir Welding

(FSW) joints: the “wormhole” defect, into a manufacturing technique where all the material extracted

from the workpiece laid on the processed zone below the shoulder, within a clearance between the

shoulder and the workpiece.

Recent developments made by P. Vilaça and C. Vidal, allows promoting distinct material flow,

where a controlled amount of material from the workpiece, flows out from the processed zone

producing the internal channel. Thus, the material flowing from the interior of the solid workpiece is not

deposited on the processed surface but directed outside from the processed zone in the form of toe

flash. The position and size of the channels can therefore be controlled and the processed surface can

be left at the same initial level. It is also possible to integrate in the FSC tool, a surface finishing

feature.

The Friction Stir (FS) channels result from the application in the visco-plasticized workpiece

material of an upward action along the threaded probe combined with an outward action along the

scrolled shoulder. The FS channels can be controlled by selecting the adequate processing

parameters and tool geometry.

To soften and deform the workpiece material enabling the creation of a continuous internal

channel, the FSC process relies not only on the frictional heat generated between the tool and the

workpiece, but mainly on the heat energy generated from dissipation during plastic deformation and

internal viscous dissipation during the material flow, similarly to heat generation during FSW.

The know-how related to FSC technology exists and is abundant. This shows that, FSC clearly

needs a boost to materialize its industrial applications. The capabilities to be a manufacturing

technology exist. The possibilities are also available, especially in the mould industry. However, as in

all industries, it is always difficult to overcome the following idea: fear of the unknown. Any industry is

in general reluctant to be the first in applying a different or alternative technology, even of clear added

value, due to the risk of failure.

The capability of FSC to produce internal channels with any desirable path and simultaneously

vary its size along that same path is not achievable by any other technology at such a moderate cost.

In addition to those two unique capabilities of FSC, there is a possibility of varying the channel depth

along that same path.

2

1.2 Objectives

The main objective of this study is to determine the adequate industrial application for FSC and

determine how FSC manufacturing technology can be implemented in those industries. Summarizing,

this study aimed at conducting a first research approach with the following objectives:

1. Summarize Friction Stir Channeling (FSC) technology know-how until present day.

2. Evaluate potential of FSC in various industries; acknowledge its advantages and

disadvantages.

3. Compare strengths, weaknesses, opportunities and threats (SWOT analysis) of FSC with

alternative technologies that are already implemented in the industry.

4. Based on previous results determine FSC industrial applications.

5. Produce prototypes that clearly demonstrate the potential of FSC to be a manufacturing

technology for its corresponding industrial applications.

6. Spot areas of FSC technology that need to be improved to increase the possibilities and

number of industrial applications.

7. Determine new possibilities for FSC to develop and evolve as a manufacturing

technology.

8. Define procedures to be implemented in future studies on FSC technology.

Due to timeline constraints inherent to an MSc thesis, the present work consists mainly of a

preliminary investigation of the main industrial application for FSC with the corresponding production

of two small mould prototypes. However, a follow-up is needed for the development of the FSC

technology and consequent introduction in the referred industries. Obviously, these ambitious

objectives ultimately raised further research work for future investigations.

3

1.3 Structure of Thesis

The current work is structured to address the following topics in each chapter:

Chapter 2 describes the current state of art, addressing the discovery and consequent birth of

FSC from a FSW defect.

Chapter 3 focuses on competitive SWOT analysis with alternative technologies to FSC, which

include drilling, electrical discharge machining (EDM) and milling. The three SWOT analyses reflect

the strengths, weaknesses, opportunities and threats that FSC has, compared to the three referred

technologies.

Chapter 4 presents the two Case Studies of this investigation as well as the experimental set-up

inherent to the fabrication of the two FSC applications. Before developing the FSC applications, the

whole experimental set-up is explained at a very detailed level. The first Case Study is a mould

prototype for injection moulding with its corresponding cooling channels being produced with FSC

technology. The second FSC application is a mould prototype for a curing process. The channel

configurations were both determined by the author after testing other channel configurations and

defining the one that best suits the objectives of the current investigation, with the aid of computational

simulations and thermal analysis. Each prototype has its corresponding objectives, computational

development and technological implementation as well as the corresponding result analysis.

Chapter 5 discusses the major results of this study. A global analysis of the performed

developments is executed to provide the reader with a technical insight on the current situation of the

FSC technology.

Main conclusions and proposals for future work developments are presented in Chapter 6.

4

2 State of Art

2.1 Friction Stir Channeling

2.1.1 The Process Concept

2.1.1.1 Evolution from FSWelding

Friction Stir Welding (FSW) is a solid-state joining process invented and patented [1] by The

Welding Institute (TWI) of the United Kingdom in December 1991 [2]. The development of this

technology is considered to be the most important achievement in the ‘welding world’ of the last

decade. The FSW is a non-consumable process and does not need any additional material. The non-

consumable cylindrical tool rotates, in the joint defined by the two pieces that are going to be joined,

and simultaneously the tool has a downward force that pushes it against the joint and a linear speed

that permits it to complete the welding process. Figure 2.1 demonstrates the tool and the workpiece in

a FSW process.

Figure 2.1 – Schematic representation of Friction Stir Welding (FSW) [3].

One important factor of FSW is that the metallic joining is done at temperatures inferior to the

fusion temperature of the involved material. This factor makes the difference in comparison with other

fusion joining techniques. It is an advantage to other fusion joining techniques because it results in

less distortions and residual stresses, due to the smaller heat transfer implicated [4].

5

The body of the tool is defined by a shoulder (cylinder) in which comes out a probe from its

center with a length a bit smaller than the desired penetration. The probe is also a cylinder but much

smaller in diameter and with a slight radial inclination, similar to a geometry of a conical screw. First,

the position of the tool is defined, which should be the start of the desired joint. After defining its

position, the rotating tool is pressured against the workpiece with an axial downward compression

force. This force is maintained until the probe has fully penetrated the workpiece and the shoulder is in

full contact with the surface of the workpiece. The joint is formed by the two workpieces that should be

firmly constrained, typically in butt joint of straight borders or lap joint. After the adequate thermo-

mechanical conditions are established, the relative linear movement is initiated between the pieces to

be joined and the tool, which maintains its rotating velocity. The movement of the tool along the joint

generates heat, owing to the plastic flow of materials imposed by the rotating probe in their interiors

(viscous dissipation due to internal friction) and also due to the superficial friction developed between

the materials that are supposed to be welded and the probe of the FSW tool. The transportation of

material due to plastic flow is imposed by the shoulder and due to a special configuration of the probe

that forges and extrudes the material that surrounds it, directing it to the retailing part of the tool,

promoting the mixture and resulting in the weld. This process is stationary, and occurs submitted to a

vertical forging force applied by the tool shoulder. This force must be kept constant throughout the

whole process [5].

Figure 2.2 – 4 main steps in completing a FSW weld: 1) Define weld starting position, 2) Probe

penetration until shoulder is in full contact with workpiece, 3) Establish adequate thermo-

mechanical conditions, 4) Relative linear movement is initiated.

FSW is a process that when the determination of the parameters is adequate, it is possible to

obtain welded joints with great qualities and defect free. However, some variations in the established

conditions in the productive cycle can originate joints with defects [5], which type and magnitude

depend on the nature of the variation in case. Changes in the welding parameters, structural

modifications in the base material (BM), different preparations of the welded joints or problems in the

exact position of the pieces that are going to be welded are some of the incidents that can be at the

origin of these variations.

6

The 4 major defects in FSW that occur with the welding process, in a range of established

parameters and in realistic industrial production conditions are [5]:

Defects in the bead root:

1. Lack of penetration (kissing bond)

2. Particle alignment

Defects in the bead interior:

3. Wormholes

4. Particle alignments (2nd

phase particles and oxides)

In Figure 2.3, in the transversal section of the welding bead, the previously mentioned defects are

demonstrated:

Figure 2.3 – Location of defects in welded zone [5].

FSW has a lot of other techniques that have evolved from it by utilizing basic FSW principles.

Some of these applications are Friction Stir Processing, Friction Stir Surfacing, Friction Stir

Microforming and Frcition Stir Spot Welding. Basically, these are technologies based on different

friction stir processes. Friction Stir Channeling, which appeared recently, is one more variant of FSW.

However, it is certainly one of the most innovative and with evident possibilities of being as successful

as Friction Stir Welding. Its “birth” is ironic because it started from a FSW defect, but now it has a

promising future ahead of it and its vast applicability make it very attractive to various industries

around the world. Let’s start with the preliminary findings of the FSC process.

Retreating Side Advancing Side

Tool base

7

2.1.1.2 Preliminary Findings of FSC

The defect “wormhole”, mentioned in the previous section, led to the invention of a new

welding process called Friction Stir Channeling (FSC). A “wormhole” occurs when the tool shoulder

contact and the processing parameters are not adequate. FSC was developed by determining, which

were the causes of this defect, so that a proper channel could be obtained instead of a small hole, or

“wormhole”. After determining the corresponding parameters that affect the channel formation, FSC

could now be considered a manufacturing process. FSC is based on making the formation of this FSW

defect into a manufacturing process. FSC will enable concepts such as [6]:

Production of integral channels in plates, dies and permanent moulds.

Incorporation of cooling or heating channels on curved surfaces of a solid component.

Design of single piece heat exchangers.

Mishra has shown that by selecting the optimal processing parameters and reversing the

material flow pattern of FSW, it is possible to produce continuous channels. So, Mishra, was the

inventor of FSC, and created a patent for it in 2005. However, since 2005 this innovative

manufacturing process has evolved considerably, with two authors in particular: Nagarajan

Balasubramanian and Pedro Vilaça.

2.1.1.3 Initial Version of FSC

Following the teachings of Mishra, a PhD student named Balasubramanian developed a “first

version” of FSC, and its main aspects are [7]:

The profiled tool is rotated such that the material flow is upwards towards the tool shoulder

An initial clearance is provided between the shoulder and the workpiece, where the material

from the base of the probe is deposited; and

This distance between the tool shoulder and the workpiece can be adjusted to control the

shape, size and integrity of the channel.

Throughout the FSC process, an upward force is generated by rotating a right-hand threaded tool

clockwise (or a left-hand threaded tool counter-clockwise). A channel is formed due to a separation of

the plasticized material around the probe with the plasticized material under the base of the probe.

The material around the probe moves upwards owing to the rotation of the probe and the orientation of

the threads, and it is deposited on the top of the nugget underneath the shoulder surface. The

clearance between the shoulder and the workpiece enhanced the formation of the “wormhole” defect.

Owing to the fact that, this defect occurred due to bad shoulder contact, this clearance was essential

8

for the channel formation. Another aspect of FSC, which enhanced the channel formation, was the aid

of the rotation in the opposite direction of the one performed in FSW. All of these factors enabled the

production of a continuous channel with any size, depth or path within the FSC tool limits. Hence, the

shape and size of the channel can be controlled by varying the following parameters [7]: the clearance

between the workpiece and the tool shoulder, the tool rotation speed, the tool travel speed and the

tool design.

Balasubramanian et al. [7] have also discussed and demonstrated the applicability of the FSC

concept to create continuous channels along linear and curved profiles, as well as the possibility of

manufacturing Mini-Channel Heat Exchangers (MCHX). The high flexibility and low production costs of

this innovative manufacturing process provide this technology with a great potential to be successfully

introduced in various industries. However, FSC still needs to have a considerable development to

prove its industrial applicability.

2.1.1.4 Development of FSC

Recently, in Instituto Superior Técnico (IST), FSC was patented and re-invented by Pedro

Vilaça and Catarina Vidal, being the referred patent: Modular adjustable tool and correspondent

process for opening continuous internal channels in solid components, national patent pending N.º

105628 T on April 15 of 2011 [8]. An evolution of the FSC tool was developed, which enables the

material removed by the process to be cleared out as the channel is being produced leaving the

workpiece with the same level and surface finish as it had before the channel was produced. The

major step given by P. Vilaça et al. in the development of FSC reinforces the great potential of this

manufacturing process in industrial applications such as the automotive, aerospace and railway

industry, as well as conformal cooling systems and heat exchangers, as it was mentioned by

Balasubramanian et al. The strong potential and vast applicability of FSC will be demonstrated, and

proven, throughout this work.

Balasubramanian et al. [7] stated that the presence of the gap between the shoulder and the

workpiece was a major difference between the FSC and the normal FSW or Friction Stir Processing

(FSP). It is important to recognize that FSW and FSP are performed with the bottom of the shoulder in

contact with the workpiece, to generate the forging action required, to produce defect free welding or

processing. However, the “new version” of FSC produced in IST by P. Vilaça et al. suggests some

modifications from FSC initial version of Balasubramanian:

No initial clearance is provided between the shoulder and the workpiece, so the material from

the base of the probe is deposited on the sides and back of the shoulder (to create the

channel).

The main parameters of the process (tool travel speed, tool rotation speed, size of probe and

shoulder) can be adjusted to control the shape, size, and integrity of the channel.

Comment [U1]: SWOT analysis

9

Recent developments made by P. Vilaça et al. [8] promoting distinct material flow, where a

controlled amount of material from the workpiece, flows out from the processed zone and ends up

producing the internal channel. However, the material flowing from the interior of the solid workpiece is

not deposited on the processed surface but directed outside of the processed zone in the form of toe

flash. The scrolls on the tool shoulder enable this material flow from under the shoulder to the

periphery of the processed zone. The position and size of the channels can therefore be controlled

and the processed surface is left at the same initial level. It is also possible to integrate in the tool, a

surface finishing feature. The Friction Stir (FS) channels result from the application, in the visco-

plasticized workpiece material, of an upward action along the threaded probe combined with an

outward action along the scrolled shoulder. The FSC process can be controlled by selecting the

adequate processing parameters.

Figure 2.4 – Schematic representation of FSC “new version” process (cross section view) [9].

Summarizing, the material that comes from the base of the probe is pushed outwards by the

scrolls on the shoulder because there is no clearance between shoulder and workpiece. This major

difference also has an impact on the characteristics of the channel: size, shape, roughness and

mechanical properties, compared to the FS channels produced by Balasubramanian. The

development made by P. Vilaça et al. created this “new version”, which allows FSC to have channels

of greater dimension, rougher surfaces and bigger “wet surfaces”. Consequently, all of the mentioned

features enable more industrial applications for FSC. Nonetheless, it is essential to understand how

these continuous channels are developed, to realize how easily the channels can be produced.

10

2.1.2 The Channel Formation

The production of a FS channel can only be fully understood, by analyzing the zones of a

channel’s transversal cross section. Figure 2.5 shows the transversal cross section of a FS channel

manufactured in IST.

Figure 2.5 – Example of a cross section macrograph of a FS channel showing channel (Ch),

nugget (N), base material (BM), advancing side (A.S.) and retreating side (R.S.) localization [9].

The nugget (N) demonstrates the material flow pattern during the process, after the tool has

passed over the region. The direction of the tool rotation is counter clockwise and the travel direction

is outside from the plane of the paper’s front side. To understand the channel formation, it is

necessary to distinguish among the different regions of the channel cross section, which are

demonstrated in Figure 2.5. The nugget consists of the stirred zone and the channel below; its limits

are defined by a black line in Figure 2.5. The base material (BM) is the unprocessed parent material

that did not have its properties altered [9]. Obviously, in order for a channel to be formed, material

must be removed from the stirred zone. Due to the orientation of the probe threads and the direction of

the tool rotation, the plasticized region at the bottom of the channel is pushed upwards on the

advancing side (the side where the velocity vector of the tool rotation has the same direction as the

travel direction), represented by A.S. on Figure 2.5. The upward force produced by the probe threads

obliges the plasticized material to be pushed upward. After being pulled upward, the stirred material is

then pushed outwards by the scrolls of the shoulder in the “new version” of FSC. Another important

difference to the initial version of FSC is that this process of pulling material upwards is aided by the

vertical downward forging force that creates a pressure on the nugget and helps the channel to be

compact and also enhances the material flow. This major difference explains the upgrade that having

no clearance between the shoulder and the workpiece represented to the FSC developed by P. Vilaça

et al. Owing to the shoulder rotation and shoulder base design, the material in the upper region of the

workpiece is pushed inward and deposited mainly on the retreating side (R.S.). A further distinction in

the conditions of the process is that better results are obtained with “colder” conditions. An additional

layer surrounds the nugget, as a thermo-mechanically affected zone (TMAZ), where the amount of

grain refinement is insignificant. TMAZ is unclear in Figure 2.5.

11

On the other hand, in the FSC version of Balasubramanian et al. the material that is pulled

upwards by the threads and the tool rotation is deposited in the clearance between the shoulder and

the workpiece. Consequently, the material is not deposited around the shoulder, but instead under the

shoulder. In this case, the material that is being pulled is not assisted by the downward forging force,

once again due to the gap between the workpiece and the shoulder. The absence of this aid reduces

the quantity of material that is pulled by the threads, which ends up being significantly less. As a

result, the channels from the two “versions” tend to be different in shape and size.

As any other manufacturing process, FSC is not defect free. Consequently, after various tests

and thorough analysis, a range of process parameters was developed, where continuous and stable

channels were created repeatedly. In this case the defects in both versions were slightly different but

the concept ended up being similar. In the initial version of Balasubramanian, two types of defects

were determined: defective channels (open channels) or discontinuous channels were observed when

the process parameters were outside the optimal process range. Open channels were created when

the processing conditions were extremely colder and this could be due to the inadequate flow of

material from the probe base to the shoulder region and the extruded material being insufficient to fill

the shoulder-work material clearance. This leads to a situation where the shoulder is unable to

process the material and distribute it evenly over the top of the channel, which results in the non-

closure of the flow arm along the advancing side [10], and an open and defective channel.

Discontinuous channels were created when the processing parameters were hotter and outside the

optimal zone.

The same situation happens with the “new version” of FSC. When the process parameters are

outside a certain range, open or discontinuous channels are created. Colder conditions, in other words

low heat indexes, caused defects more easily. On the other hand, when producing channels with

hotter conditions the most common problem was the probe breakage. Discontinuous channels almost

never occurred, due to the fact that the FSC performed by P. Vilaça et al. apparently removes more

material than the one executed by Balasubramanian. Consequently, there is always enough material

removed throughout the whole process to produce a channel, even if it is smaller than usual. An

optimal zone for this new version of FSC was also created. C. Vidal and P. Vilaça obtained specific

process parameters, which optimized the manufacturing process. However, three main reasons can

be defined until now for discontinuous channels in this “new version” of FSC:

1. Tool travel speed

2. Shoulder pressure

3. Base material (actual substrate)

Later on, in the current work, the different FSC conditions will be discussed with the process

parameters that were already established.

12

2.1.3 The Channel Shape

The differences in the FSC process between the two versions also caused a consequent

difference in the channel shapes. The shape of the channel obtained from FSC initial version is closer

to an ellipse or oval shape. The author stated that the channel shapes usually vary nonlinearly with the

process parameters (the tool rotation speed and tool travel speed). Figure 2.6 shows the variation of

the channel shape by changing the process parameters in the FSC initial version. As it can be

observed in Figure 2.6, including (a) and (b) below, the channel produced with a high heat index

process condition is visibly well-structured as compared with the channel from the lower heat index

process condition. In this case, Balasubramanian [7] defined heat index as a relative term defined as

the ratio of the square of the tool rotational speed to the tool travel speed. This ratio is used as a

representation to differentiate the various processing conditions. For a high heat index run, the volume

of material displaced from the probe base is high due to the high tool rotation speed, or alternatively, a

low travel speed. Another aspect that can be easily spotted in the channel shape is the shape of the

channel side walls, which are clearly influenced by the probe features.

Figure 2.6 – Cross section showing FS channel shapes produced by Balasubramanian with

different processing parameters: (a) 1100 rpm, 2.11 mm/sec, and (b) 1100 rpm, 2.96 mm/sec [7].

Table 2.1 – Variable parameters of FS channels produced by Balasubramanian [7].

FSC Condition

Tool rotation speed (rpm)

Tool travel speed (mm/sec)

Tool travel speed (mm/min)

Heat Index (rpm

2/(mm/min))

(a) 1100 2.11 126.6 9557.7

(b) 1100 2.96 177.6 6813.1

Table 2.1 was built to demonstrate the difference in heat indexes of the two runs. The heat

index is a parameter that aids in determining the stress, or harsh conditions, the probe and the

workpiece are going through in the process. A major feature in FSC is the heat up of the FSC tool. As

the FSC tool advances and produces the channel, the frictional heat increases at the tool-workpiece

interface making the material that is being processed softer, as well as heating up the probe

considerably. This heat increase is a problem that P. Vilaça et al. have faced in the development of

the FSC process. Balasubramanian et al. [7] stated that “a closer observation of the process forces

and channel shapes show that as the magnitude of the process forces reduces, the shape of the

channel is well-structured. It can be inferred that the shape of the channel is influenced by the

13

downward forging force applied by the shoulder on the material. The magnitude of the vertical force is

low due to high frictional heat. The structural integrity of the channel walls and roof indicates that the

force applied by the shoulder is insufficient to cause them to collapse”. The lack of this downward

forging force was the only defect of the FSC executed by Balasubramanian et al. and that is where the

developments performed by P. Vilaça et al. were critical to solve this technological disadvantage FSC

had. The inclusion of a downward forging force enables FSC to have larger channels with lower heat

indexes, which permits longer continuous channels with less demanding conditions for the FSC tool.

As it was mentioned before, these demanding conditions are concentrated especially on the probe of

the FSC tool, which is subject to harsh conditions and due to its small size, it needs to be made of an

extremely hard and resistant material.

Consequently, some changes were verified in the “new version” FSC, which relies on a

consistent downward forging force. The channel does not have an elliptical or oval shape anymore. In

this case, the shape is more like a trapezoid turned upside down. In contrast with the FSC version of

Balasubramanian, the channel shape does not have significant variations, when produced with

diverging process parameters. Four standard FSC conditions were determined, each with specific

parameters, to demonstrate the influences of the different process parameters on the channel

features. Even with a significant variation of the heat index for each FSC condition, the shape of the

channel does not change abruptly for any of the different conditions.

The process parameters, presented in Table 2.2, were tested and determined by P. Vilaça et

al. [9]. After a thorough analysis, 4 different FSC conditions were defined. These conditions and the

corresponding values will be referred to throughout this section of the work. After Table 2.2, images of

channel cross sections are displayed in Figure 2.7, which correspond to 4 different FSC conditions

that are mentioned in Table 2.2.

Table 2.2 – Different FSC process parameters [9].

FSC Condition

Tool rotation speed (rpm)

Tool travel speed (mm/min)

Heat Index (rpm

2/(mm/min))

A 600 80 4500

B 600 150 2400

C 800 80 8000

D 800 150 4266.7

14

Figure 2.7 – Cross section macrograph showing channel geometries produced with different

FSC processing parameters: (A) 600rpm, 80mm/min., (B) 600rpm, 150mm/min., (C) 800rpm,

80mm/min. and (D) 800rpm, 150mm/min [9].

The channel shape in the “new version” FSC can be attributed to the volume of processed

material that is displaced from the base of the probe for every rotation of the tool and also the

compacting force that is applied on the channel ceiling during the linear forward movement performed

by the shoulder [9]. Nonetheless, a trend can be spotted in the 4 different conditions of the “new

version” FSC. Condition B has by far the smallest heat index, and it has the channel with the least

defined shape. On the other hand, conditions A and D have very similar heat indexes but the channel

ceiling of condition D demonstrates a very irregular surface maybe due to a very large amount of

frictional heat produced and an excessive softening of the workpiece material. A possible cause of this

situation is the elevated value of tool rotation speed, as well as a large magnitude for the tool travel

speed. However, it is clear that the channel shape has small variations compared to the considerable

modification of the process parameters values. In order to standardize the characteristics of the

channel shape and to spot possible trends in the channel shape change with the variation of the

process parameters, two characteristics of the channel were determined by P. Vilaça et al. [9]: the

closing layer thickness (D) and the shear angle (α). In Figure 2.8, these geometric parameters are

demonstrated in a FS channel cross section.

15

Figure 2.8 - Schematic representation of a cross-section (above) and a plan (below) views of

the friction stir channeled solid block [9].

Table 2.3 – Geometric parameters of internal channels produced with different FSC process

parameters [9].

FSC Condition A (mm2) D (mm) α (º)

A 13.49 2.5 13

B 14.01 2.3 12

C 12.75 3.1 13

D 12.88 2.8 14

The closing layer thickness and the shear angle were defined by P. Vilaça et al. [9] for the

“new version” FSC. Both aspects are demonstrated above, in Figure 2.8, for a better understanding of

the preceding analysis. The closing layer thickness results are consistent with those obtained for the

channel area, as it is visible in Table 2.3. In other words, as the channel area increases, the closing

layer thickness decreases. On the other hand, the shear angle has no direct comparison to the values

of channel areas or even with the closing layer thicknesses for the different FSC conditions. The

results obtained are not conclusive for any of the two characteristics. Perhaps, this situation occurred

due to the low amount of samples that were analyzed. Nonetheless, the channel area is always an

important parameter to be analyzed, to understand the actual dimensions of the channels. The

channel dimensions are of great importance to the various industries FSC could be applied to, as well

as to determine its various industrial applications.

16

2.1.4 The Channel Size

In general terms, according to Balasubramanian et al. the channel size depends on the

following [7]: “for any tool, the maximum possible channel area is the maximum volume of material

that can be displaced by the probe at any given instance, over a unit length. The tool with the

maximum surface area of probe features theoretically is expected to generate a channel with the

largest cross-sectional area for a particular plunge depth”.

To prove this principle and to analyze this theory, it is important to demonstrate actual results

of channel areas and compare them with the process parameters. The channel areas for the 4

different FSC conditions, obtained by P. Vilaça et al., are shown in Table 2.4. At first sight, it is

possible to realize that the biggest channel areas correspond to FSC conditions A and B, in

comparison to conditions C and D. However, in both cases for the same tool travel speed, the channel

area increases significantly as tool rotation speed decreases. Taking into consideration a first insight,

in which Balasubramanian [7] considers that the channel area is directly related to the key process

parameters: tool rotation and travel speeds at each plunge depth. In fact, it is possible to verify by

observing Table 2.4 that the channel area decreases with an increase in the tool rotation speed.

Another pattern that can be determined is that for the same tool rotation speed, the channel area

increases slightly with an increase in the tool travel speed.

Table 2.4 – FS channel areas (mm2) for different FSC conditions [9].

FSC Condition A (mm2)

Tool rotation speed (rpm)

Tool travel speed (mm/min)

A 13.49 600 80

B 14.01 600 150

C 12.75 800 80

D 12.88 800 150

In conclusion, the channel size varies a lot, as it is noticeable from the values above. In

agreement with the vision of Balasubramanian, channel size varies due to the same concept. The

variation of the process parameters enables the possibility to vary the channel size. According to the

values of Table 2.4 and the research developed by Balasubramanian et al., it is possible to verify that

the channels obtained by P. Vilaça et al. are significantly bigger in size. In numerical values, the

difference is approximately 10 mm2, from about 13 mm

2 to 3 mm

2. In terms of percentage, it is an

increment of about 330%. However, the channel areas between the two versions are not comparable

due to the different sizes of FSC tools that were used as well as different base materials and process

parameters. A possibility to explain the great difference in the channel size of these two versions is the

application of the vertical downward forging force in “new version” FSC. Obviously, the growth of the

channel size permits a wider range of functions and a larger flexibility to maximize its potential

introduction in the mould or heat exchanger industry, as well as other major industries. P. Vilaça et al.

clearly improved the initial version of Balasubramanian and opened up new doors for FSC.

17

2.1.5 Surface Roughness

The surface roughness inside any fluid passage is a critical parameter in fluid flow

applications. The surface roughness pattern and the roughness dimensions affect significantly the

pressure drop inside the flow passages. Balasubramanian et al. [7] sectioned the FS channels along

the tool travelling direction, to determine their roughness features. Figure 2.9, including (a), (b) and (c),

shows longitudinal cross sections of channels produced by Balasubramanian FSC using three

different process parameters, which are also demonstrated in Table 2.5. The roughness properties of

the channels vary abruptly at the lower and upper surfaces. The bottom of the channel is relatively

smooth and flat due to the flat nature of the tool probe base. The ceiling of the channel is rough and

undulated and the orientation of its roughness points is in the tool travel direction.

The surface roughness of the channel ceiling can be easily determined and such an analysis

was performed by Balasubramanian et al. The referred authors [7] determined that the roughness of

the channel upper surface is uniformly spaced, and its periodicity matches the amount of material that

is being displaced with each rotation, i.e., the process pitch. For example for Figure (a) the distance

between two successive peaks is equal to 0.107 mm and the pitch of the run was determined to be

0.106 mm/rot. Similarly for Figures (b) and (c) the distance between successive peaks was 0.091 and

0.033 mm and their pitches were 0.095 and 0.032 mm/rot, respectively.

18

Figure 2.9 - Longitudinal cross section of a FS channel conducted by Balasubramanian

showing the roughness on the channel ceiling produced with the following process

parameters: (a) 1200 rpm, 2.11 mm/sec, (b) 800 rpm, 1.27 mm/sec, (c) 800 rpm, 0.42 mm/sec [7].

The heat indexes, as well as the process parameters, of these three trials performed by

Balasubramanian et al. are the following:

Table 2.5 – Heat indexes of three FSC trials performed by Balasubramanian.

FSC Condition

Tool rotation speed (rpm)

Tool travel speed (mm/sec)

Tool travel speed (mm/min)

Heat Index (rpm

2/(mm/min))

(a) 1200 2.11 126.6 11374.4

(b) 800 1.27 76.2 8398.95

(c) 800 0.42 25.2 25396.8

A major difference between the two versions of FSC is the value of the heat index during the

manufacturing process. These three runs that were performed to demonstrate the roughness features

of channels manufactured by Balasubramanian, reinforce the high values of heat indexes used by the

“old version” FSC. Having a higher heat index means working in hotter conditions, which also means

higher fatigue on the materials and higher demand on the FSC tool. Once again, this is another proof

that P. Vilaça et al. developed some disadvantages of the FSC process and had a major contribution

on the evolution of this innovative technology.

Figure 2.10 shows the longitudinal cross sections of a channel produced using the FSC

executed by P. Vilaça et al. In this case, the channel in Figure 2.10 was produced using FSC condition

B parameters. The upper surface of the channel (channel ceiling) is rough and wave shaped and the

orientation of this surface roughness points to the direction of the tool linear movement.

19

Figure 2.10 - Longitudinal cross sections of a channel produced in FSC condition B

(ω=600rpm; v=150mm/min) showing the roughness on the retreating side (a) and on the

advancing side (b) of the channel [11].

However, in discordance with Balasubramanian the channel side walls present different

roughness characteristics. The channel advancing side (shear side) does not exhibit any significant

roughness comparing to the retreating one. First of all, the bottom of the channel is relatively smooth

and flat due to the flat nature of the tool probe base, as it was mentioned by Balasubramanian et al.

Figures 2.11 and 2.12 present cross sections of the “new version” FSC, which were obtained by P.

Vilaça et al. to determine the roughness properties of the side walls of the FS channels. It is possible

to observe in Figure 2.11 that, for the same tool travel speed, the roughness of the retreating side is

similar, i.e. FSC conditions A and C present similar roughness conditions in the retreating side, as well

as conditions B and D. Consequently, the same logic is applied to Figure 2.12. In Figure 2.12 it is

visible that, for the same tool rotation speed, the ceiling has similar roughness characteristics [11].

Figure 2.11 - Cross section showing the roughness on the bottom and on the retreating side of

the channel at 4 different FSC (conditions A, B, C & D) processing parameters [11].

20

Figure 2.12 - Cross section showing the roughness on the ceiling and on the advancing side of

the channel at 4 different FSC (conditions A, B, C & D) processing parameters [11].

According to Balasubramanian et al., the channel side walls do not show any roughness

properties along the length of the channel. On the contrary, the IST version of FSC has different

results in terms of surface roughness, in certain aspects. Obviously, the lower surface is also flat due

to the flat surface of the probe base, but the lateral walls demonstrate certain roughness

characteristics. One of the walls, the advancing side one, presents a flat surface, very similar to the

bottom of the channel. However, the retreating side wall has a random surface roughness that will

increase the pressure drop and consequently enhance the heat transfer from the liquid flowing inside

the channel and its surroundings. Once again, an improvement to FSC caused by P. Vilaça et al.,

which can be of major relevance in any industrial application that involves heat transfer. A specific

example of that are the mould and heat exchanger industries. However, the industries are very exigent

in terms of mechanical properties of its products.

2.1.6 Mechanical Properties

The mechanical properties of the FS channels are an important feature of this manufacturing

process, to ensure a sustainable introduction into the industry. Following this logic, the influences of

the processing conditions on the bending and internal pressure resistance of the channels were

analyzed by P. Vilaça et al [9]. The referred author studied the influences on the mechanical

properties of the channel by varying the tool rotation speed and the tool traverse speed. A patented

modular concept of a FSW tool that enables internal forced refrigeration was used to produce all

channels. This tool is based on three main components: body; shoulder and probe. It was selected, for

all the runs, a conical probe with a 5mm bottom diameter and left-handed threads along its length and

a plane shoulder with two spirals striates scrolling an angle of 360º with outer and inner diameters of

20mm and 9mm, respectively. In-plane bending tests were carried out to two types of channels:

transversal and longitudinal. The span distance (distance between the centers of support rolls) was

21

59mm. Support rolls diameter was 10mm and mandrel radius was 5mm. Mandrel velocity used

throughout the trial was 1mm/min. From each condition two specimens were taken and bended. The

base material and three different conditions of FS channeled specimens were tested: (x) specimens

with a transversal channel with the processing zone (channel ceiling) under tensile stress, (y)

specimens with a longitudinal channel with the processing zone (channel ceiling) under tensile stress

and (z) specimens with a longitudinal channel with the non-processing zone (channel bottom) under

tensile stress. All mechanical trials were performed at room temperature. The values listed in Table

2.6 were determined by P. Vilaça et al. [9].

Table 2.6 – Maximum load (kN) results for different FSC conditions [9].

Base Material 76.65

Bending test condition

FSC Condition (x) (y) (z)

A 28.06 53.31 72.44

B 26.40 51.39 72.19

C 34.39 40.49 56.72

D Not tested 40.61 58.69

From the bending tests executed by P.Vilaça et al., it is possible to verify that the tool rotation

speed has a greater influence in the FSC specimens bending strength than the tool traverse speed.

For bending tests, specimens with a transversal channel with the processing zone under tensile

stress, when the tool rotation speed increases the maximum bending load also increases. A specific

fact needs to be mentioned, which is that all of the specimens with a transversal channel fractured at

the advancing side. Figure 2.13 demonstrates the place where the fracture occurred for the

experimental condition (x), which reinforces that the advancing side is the most fragile zone of the FS

channels. According to the bending tests, results of the specimens with a longitudinal channel with the

processing zone (channel ceiling) and with the non-processing zone (channel bottom) under tensile

stress, the channel bottom is more resistant than the channel ceiling.

Figure 2.13 – Fracture localization of specimens tested under bending test condition (x)

referred in Table 2.6 [9].

22

The internal pressure tests performed by P. Vilaça et al. [9] gave surprising results due to the

elevated pressures that FS channels were able to support before leaking points arose. The authors

also concluded that by increasing the tool rotation speed, for the FSC conditions tested, the minimum

pressure that leaking points arise also increases. In this specific case, by comparing FSC conditions C

and A, in other words by increasing 200 rpm and maintaining tool travel speed, the value of the

minimum pressure obtained without any leakage duplicated.

Figure 2.14 - Microhardness profile across the FSC processed zone for FCS condition C

(ω=800rpm; v=80mm/min) [11].

Last but not least, the hardness of FS channels was analyzed. Figure 2.14 shows the micro

hardness profile measured across the cross section of the channel processed zone produced with the

parameters of FSC condition C. It can be seen that the hardness values are higher in the stirred zone

- the channel nugget – in which the higher grain refinement contributes to the increase of hardness.

However, these hardness values are lower than the hardness values of the BM, which is about 194

HV0.5. The overall softening of the processed region is caused by coarsening/dissolution of

strengthening precipitates during the thermal cycle of the friction stir process [7].

23

2.2 Alternative Technologies

FSC is an innovative technology that has high potential to be introduced in various industries

that already have established technologies to perform the same task, FSC is able to perform.

However, FSC has some advantages to these established technologies, but that will be analyzed later

on in this work. First of all, it is essential to acknowledge which are the concurrent technologies of

FSC. The existing technologies that are able to produce continuous internal channels can be resumed

to three main technologies: Drilling, EDM and Milling. Each one of these technologies has its own

advantages and disadvantages, but all of them can be a threat to FSC, therefore they should be taken

into consideration.

2.2.1 Drilling

The main technology established throughout the world as the number one manufacturing

process to perform internal channels in solid blocks is: Drilling. Drilling constitutes about 40% of all

metal-cutting operations. Applications that involve drilling large number of holes encompass industries

such as the aerospace, automotive, and potentially many other industries [12]. Considering this fact,

these same industries would benefit largely from drilling holes at significantly faster rates. Aggressive

drilling can be summarized as combinations of properly set high cutting speed and tool feed resulting

in proportionally large material removal rate. The main benefits of aggressive drilling include higher

productivity, a synergistic effect in reducing the specific cutting power (and drilling forces) while

removing substantial amounts of material. The primary challenges for aggressive drilling include

spindle power, accelerated tool wear, set up rigidity, hole quality, chip evacuation, and high

acceleration/deceleration demands on the spindle drives. It is essential to understand how different

aluminum alloys behave when drilled. These differences include chip formation and tool wear rates.

This includes classifying the work aluminum as both wrought or cast alloy and then sub-classifying to

understand the subtle variations. This situation can be reflected on the evolution of FSC. A complete

comprehension of the material behavior in an innovative is imperative and such an analysis should be

performed for FSC. At this moment, the major difference between drilling and FSC is the speed at

which it produces channels. Nonetheless, drilling can only be performed in a straight path and FSC

can produce a hole with any desired path. If a drill tries to deviate or curve slightly, certainly it will

cause uneven wear in the drilling tool and lose its effectiveness. Drilling has this specific limitation and

FSC can be the solution for that limitation.

Drilling as we know it involves drilling holes of a considerable size. In order to relate drilling to

FSC, it is essential to acknowledge that drilling can be performed in very small holes. Zelinski et al.

[13] suggest that microdrilling is doable and more efficient than EDM hole making and in their

perspective, microdrilling simply requires more care than conventional-size drilling, however hole

straightness is easier to control with drilling than it is with EDM hole drilling. In some cases, the

Comment [U2]: SWOT analysis

Comment [U3]: SWOT analysis

Comment [U4]: SWOT analysis

24

straightness and position of the tiny holes in the workpiece (part) are critical. The holes in the case of

Zelinski et al. can be machined in a comparable critical part with a 0.51 mm diameter and 38.1 mm

deep. When the work material changed from super-alloy to stainless steel, small-hole EDM was

substituted by a small CNC machining center utilizing microdrilling. Clearly, an established quality of

drilling is its reliability in hole straightness and stability. It is also common sense that drilling can be

performed in almost any material, which is still not the case of FSC. However, drilling has other

limitations such as the need to refrigerate the drilling tool due to the growing heat index along the

manufacturing process.

At present, as mentioned before, there is a great deal of discussion about the use of lubricants

in machining. Industry and research institutions are looking for ways to reduce the use of lubricants

because of ecological and economical reasons. Due to high costs, infrastructure demands, and

environmental concerns, there is motivation to move toward dry machining, i.e., machining without the

use of a metal removal fluid (MRF). The rising costs associated with the use and disposal of cutting

fluid have forced engineers to concern themselves more intensively with questions of cooling

technology. While there are established applications of dry turning and milling, dry drilling presents

special difficulties due to the problems of swarf clearance from the drill flutes and consequent heat

build-up and clogging. Aluminum, as used in light-duty engines and transmissions, is particularly

difficult to machine dry because of its tendency to adhere to the tool as the temperature rises.

Machining performance suffers when machining is done without a MRF. For example, tool life during

drilling is reduced from > 10,000 holes/drill with MRF to about 40 holes/drill without a MRF (dry). As

Dasch et al. mentioned the challenge, then, is to reduce the heat build-up through improved

tribological surfaces on the tool. A solution according to the referred authors is to coat the drills with

specific materials. Consequently, their study involved the evaluation of a variety of carbon-based

coatings on drills to determine their performance in both bench and machining tests. The best coatings

gave a significant improvement in performance compared to an uncoated drill [14] [15]. These results,

demonstrate the limitations of drilling to produce long mini channels, which is a process that rapidly

overheats the tool when drilling material like aluminum. The need for specific coatings for each drill is

also another setback owing to the fact that it increases the technological cost. Another important

aspect is the need for MRF in drilling, which is not needed in FSC. The need for technologies that do

not need lubricants is increasing, and FSC can be the solution for this issue, as well as other issues

such as tool wear in conventional drilling techniques.

The temperature generated by friction and plastic deformation in a manufacturing process

strongly controls tool wear. At lower cutting speeds tool wear is not severe as long as the temperature

is not relevant. When the cutting speed is increased, there is a transition in wear mechanisms from

abrasion and/or adhesion to diffusion. The cutting tests performed by Nouari et al. [16], without using

MRF, showed that the best results in terms of maximum and minimum hole diameter deviations and

surface roughness are obtained for the uncoated and coated tungsten carbide drills. The need for

25

coated drills, show the limitations in precision other than its limitations in non linear channel paths. A

different technology that is able to produce channels with any desirable path is EDM.

2.2.2 EDM

Drilling has its qualities, but when holes must be drilled in curved or angles surfaces, great

difficulties arise with conventional drilling techniques. A solution for these difficulties is: EDM drilling. In

EDM (Electrical Discharge Machining) drilling, the electrode never contacts the surface that is being

cut. This non-contact of the tool in the machining process eliminates the tool pressure when drilling on

curved or angled surfaces. The rotating electrode helps in producing concentricity, causing even wear,

and also helps in the flushing process. The high flushing pressure through the center of the electrode

tends to stiffen it. Also, the dielectric fluid being forced out of the hole produces a centering effect upon

the electrode. With the aid of the electrode guide and the flushing effects on the electrode, EDM hole

drilling can penetrate much deeper in higher rates than almost any other EDM drilling method [17].

The process consists of using a precision tubular electrode (generally brass or copper)

mounted into the drill chuck located on the "Z" axis and held in location on top of the workpiece by the

ceramic guide. The top of the workpiece is located and the drilling depth is set. The electrode rotation

is turned on and the deionized (pure) water solution, which is pressurized between 50 and 100 kg/cm2,

is sent through the tubular electrode as a flushing agent [18]. The power supply parameters are set-

which normally consist of on-time, off-time, peak current and amount of capacitance. At this point, the

discharge is turned on to begin the drilling cycle. At the end of the drilling cycle, the discharge is

turned off and the "Z" axis is retracted above the workpiece.

EDM hole drilling is a different variation of EDM processes, such as die sink EDM and wire

EDM. Although EDM fast hole drilling uses the same principles as other EDM methods (as shown in

Figure 2.15), a constantly rotated hollow electrode and pumping of dielectric fluid through the

electrode tube are the two distinct features [19].

Figure 2.15. – EDM hole drilling process schematic demonstration [19].

26

The main difference between fast hole drilling and other processes lies in the use of a high

pressure (70 – 100 bar) dielectric pump. The combination of [20] the high pressure dielectric fluid, the

rotation of the tubular electrode and the high electrode feed rate (controlled by a fast response servo)

make it possible to produce holes at a very fast rate.

The development of EDM hole drilling was eminent, and an example of that were the tests

performed by Yilmaz et al. [21], which involved drilling micro and macro-scale holes (0.4 to 3 mm

diameters) on Ti-6Al-4V and Inconel 718 alloys, which are commonly used in the aerospace industry

and the medical sector for manufacturing of highly critical components. An automated approach for

EDM hole drilling was suggested by the referred authors, which could be an intelligent industrial

application for repair and production of products for the aerospace and medical industry. Although

EDM hole drilling is a variation of an EDM process, it does not use oil-based dielectric and does not

leave toxins. Therefore, EDM hole drilling machines are environmentally-friendly machines, since the

dielectric is usually pure (deionized) water, which opened a lot of application possibilities in the

medical field. Moreover, the automation of EDM hole drilling saves time and material particularly. It

has been alternatively used for making holes in turbine blades, fuel injectors, medical equipments,

plastic mould vent holes and wire EDM starter holes. Consequently, EDM hole drilling demonstrates to

have great advantages in specialized sectors of the industry due to its high precision and flexibility.

The flexibility of EDM hole drilling has been reinforced by Production Machining. Since 2005,

there are 4-axis and 5-axis EDM hole drilling machines that are able to create angled holes for various

different industrial applications such as, cooling and/or exhaust gas holes in turbine rings and blades,

medical prosthetics and instruments, electronic housings and components, laboratory and analytical

equipment, optical instrumentation, and extrusion dies for glass and composite fibers. The rotary axis

is programmed and controlled using a standard CNC machine and can be easily installed on new

machines or easily retrofit to existing machines in the field [22]. The evolution of this technology and

its ability to work with highly resistant materials reinforces its great potential in various industries such

as: medical, aerospace and automotive.

Another aspect of EDM hole drilling is its durability, since it is a very “sensitive” technology due

to the high precision tools it uses. An interesting investigation was performed by Yilmaz et al. [23] to

understand the EDM hole drilling tool wears and its influence on the hole creation. In this study, a

comparative investigation of fast hole drilling of aerospace alloys was done, once again using Inconel

718 and Ti-6Al-4V. An EDM method was performed in order to explore the influence of electrode type

and material, i.e. single and multi-channel tubular electrodes. The comparisons were made from the

results of MRR, electrode wear (EW) and scanning electron microscope (SEM) images taken from the

machined hole surfaces. The experimental results revealed that the single-channel electrodes have

comparatively better MRR and lower EW. However, the SEM images showed that multi-channel

electrodes produce less damage on machined surfaces than single-channel electrodes for both

aerospace alloys. In conclusion, it is beneficial in all desirable circumstances a single-channel

electrode enabling the process to have a reduced tool wear and a larger produced channel.

Comment [U5]: SWOT analysis

Comment [U6]: SWOT analysis

Comment [U7]: SWOT analysis

Comment [U8]: SWOT analysis

27

2.2.3 Milling

Drilling has clearly demonstrated that it is not viable for certain materials, which EDM is able to

machine and possibly another technology: Milling. Sharman et al. [24] stated that when using

commercially available drills with Inconel 718 the resulting hole quality is not sufficient to meet the

requirements of the aerospace industry and therefore secondary processing is required. So, an

alternative other than EDM hole drilling or reaming after drilling, could be mill boring with a standard

milling tool, which appears to have significant potential for improving productivity and reducing costs.

In particular the mill bore technique gave very low surface roughness values down to 0.046 μm Ra

compared to 0.178 μm Ra for reaming. The milling tools used by Sharman et al. [24] were standard

commercially available solid carbide end mills and with the use of circular interploitation the same

milling tool can be used for many different hole sizes and shapes giving further cost savings and

productivity increases compared to reaming (reduced tool changes, less tooling inventory). Sharman

et al. also stated that future work will focus on improving the stability in mill boring as the tool enters to

cut and achieving the same dimensional tolerance that can be obtained with reaming. In this case,

milling is an intermediate technology between drilling and EDM due to the fact that its cost and hole

quality are approximately in between the two other technologies. Firstly, the technological cost of

milling is clearly more expensive than drilling, but not as expensive as EDM drilling. Second, the hole

quality can be determined according to its low surface roughness as well as the amount of damage

performed on the machined surface. Another aspect to take in consideration is that in certain

situations milling in comparison with drilling avoids one more machining process, which is in general

reaming after drilling a hole.

Milling can be beneficial for hole producing due to the low damage that is causes to the

machined surface. In accordance with this statement, Schulze et al. [25] assured that circular milling

and wobble milling are an alternative to drilling because they cause less damage on the machined

surface because they draw the process forces towards the centre of the workpiece. High feed rates

are the major cause of this surface damage, so milling has a setback owing to the low feed rates that

are needed for it to cause less damage. In this case, milling has demonstrated to be an alternative

technology to produce channels, while creating less damage to the manufactured part. Nonetheless, it

is a process that has a low productivity when compared to alternative technologies.

Another type of milling is the helical milling, which for Iyer et al. is an enabling process

technology for machining precision holes in fully hardened AISI D2 tool steel. Taking into

consideration that, conventional drilling of this material is shown to predominantly result in catastrophic

fracture of the cutting edge at the drill periphery due to insufficient wedge angle, which is a geometric

characteristic inherent to drills. Helical milling with negative rake tools corresponds to a robust process

with a significant improvement in tool life (an order of magnitude), and facilitates dry cutting that

represents considerable cost savings and a substantial benefit to the environment, as it was already

mentioned in the Drilling section. Further, helical milled holes are of H7 quality that eliminates the

need for an additional reaming process leading to an important improvement in process productivity

Comment [U9]: SWOT analysis

Comment [M10]: Determine roughness values for FS channels

Comment [U11]: SWOT analysis

Comment [U12]: SWOT analysis

Comment [U13]: SWOT analysis

Comment [M14]: Mais uma vez referencias à rugosidade da superfície, na qual ter valores para a rguosidade dos nossos canais acrescentaria valor ao estudo pois havia um termo de comparação.

28

[26]. The benefit of using milling as a hole producer is obvious if the hole surface quality is a priority,

as well as, if the material is of very high resistance. On the other hand, if productivity rates are a

priority milling is not the solution.

Last but not least, is laser milling, which offers a cost-effective and time-efficient solution for

two different applications. These applications were defined by Pham et al. as manufacturing of a micro

tool and machining of small ceramic components. The latest version of laser milling equipment has

made a leap in finding the solution to a drawback, usually associated with the laser ablation

processes, which now includes the ability to produce vertical walls. Producing vertical walls was until

recently an obstacle for laser milling; a draft angle was unavoidable on all laser-machined structures.

According to Pharm et al., laser milling is capable of processing a large range of materials, which are

not machinable with conventional manufacturing processes, such as normal drilling. Pharm et al. [27]

demonstrated that engineering ceramics can be machined without requiring expensive special tools

and without any limitations on the three-dimensional complexity of the component. Nevertheless, laser

milling is still in its infancy. Laser material interactions are not yet fully understood. Much effort in R&D

of the available laser sources is still needed. Ultrafast lasers are beginning to be applied; they can

offer more precise machining without the thermal damage that accompanies long pulse laser

manufacturing. Most certainly, the development of this innovative technology will continue, but its price

will always be quite elevated compared to other alternative technologies. The ultimate goal of the

various industries around the world is to find a compromise between all of the main variables:

productivity, cost, flexibility and precision.

This global compromise is always very hard to find, the industry makes the call. Therefore, an

important task at a first stage is to define the target industry. Each technology has their target

industries depending on the attributes and characteristics of that same technology they tend to satisfy

certain needs of specific industries. Accordingly, an important step to determine the industrial

applications of FSC is to define its target industries and establish which processes of those target

industries can be replaced or performed by FSC technology.

Comment [U15]: SWOT analysis

29

2.3 Industrial Applications

The development of a technology is always subject to the necessity of the industry. The

potential, or value, of a technology is related to the amount of solutions it can provide to the industry.

The industry is always searching for a better solution or an easier way to solve problems.

Consequently, if a new technology is being developed it is of major importance to analyze which are

its possible industrial applications. In this case, FSC has two main areas of interest in the world

industry: Moulds and Heat Exchangers.

2.3.1 Mould Production

Mould production is part of a major industry, the mould industry, which has massive mould

production all around the world. Two ways of producing moulds, which FSC can be an alternative to

are: Conformal Cooling and Rapid Prototyping.

2.3.1.1 Conformal Cooling

Conformal cooling is a new concept for the production of moulds. The mould production is

performed with a specific configuration of the cooling channels. The refrigerating channels follow the

configuration of the part (workpiece) shape, enhancing the cooling procedure. The influence on the

cooling time and workpiece surface quality is significant and this concept has been growing recently.

Conventional methods for mould cooling involves drilling holes as close to the moulding

geometry as possible. However, Goldsberry [28] stated in his article that this method does not and

cannot address the many complex part geometries that make up various moulds nowadays, making it

difficult - and often impossible - to drill the cooling lines close enough, to cool the mould cavity in a

uniform manner. Conformal cooling has been developed to help address this problem of cooling cavity

steel consistently and adequately and at the same time preserve mould integrity. For this reason,

companies have started since 2010 producing more and more moulds with conformal cooling

technology. According to Goldsberry, by definition, conformal cooling is conforming and contouring the

water channels to cool the cavity in a more effective and uniform manner, regardless of part geometry.

The specific configuration of the channels makes all the difference in the process efficiency. Luckily,

FSC is a technology that is able to produce conformal cooling channels.

Computer simulations have been performed to prove the benefits of this concept. An example

of these simulations is the analysis of virtual models done by Dimla et al. The referred authors [29]

demonstrated that moulds with conformal cooling channels predicted a considerably reduced cycle

time as well as a noticeable improvement in the general surface finishes quality of the part when

compared to a conventionally cooled mould.

30

Non-uniform cooling or long cooling cycle time would result if a poorly designed cooling

channel is adopted. Due to limitations of traditional machining processes, the cooling channel is

usually formed from straight-line drilled holes and only simple shapes are allowed, regardless of the

shape complexity of the part being moulded. According to a melt flow analysis executed by K. M. Au et

al. [30], the more complex shaped cooling channel does provide a more uniform cooling performance

when compared to the traditional method. In consequence, the appearance of injection moulding

defects can be reduced.

During the last few years, supporters of conformal cooling against traditional processes have

documented noteworthy reductions in two of the most important cost drivers of injection moulding:

cooling times and scrap rates. A striking example of success with conformal cooling comes from a

project undertaken by a major laser-sintering supplier in Germany. The supplier created a tool insert

that incorporated conformal channels to boost coolant flow at hot spots in a mould for manufacturing

low-volume plastic parts (40,000/year). Here are the results of that project [31]:

• The first savings was in the cost of the new insert: €3250 vs. €19,444 for a traditional insert.

• Then there was the cycle time cut of 55%, from 90 to 40 seconds.

• Finally, the two cost reductions together resulted in an amortization time for the insert of only two

months.

It is clear that conformal cooling channels can reduce significantly cycle times for injection moulding

processes. FSC is the adequate solution to produce conformal cooling channels due to its low cost,

high productivity and unique capability of producing channels with any desirable path.

A noteworthy reduction in production cycle time causes a significant reduction in production

costs. The industry is constantly searching for solutions to reduce production costs as much as

possible. FSC can be a solution to produce conformal cooling channels for moulds at a low cost.

However, the wide range of channel sizes and lengths that FSC can manufacture, it can also be a

threat to a technology that has been developing recently, which is Rapid Prototyping.

2.3.1.2 Rapid Prototyping

Rapid prototyping (RP) is a technology that manufactures conformal cooling channels.

However its main limitation is the type of materials that it is able to process. Since, it is a very

“sensitive” technology; it can only use materials that are not of great use to mould industries, for now.

However, in a futuristic perspective RP could be an alternative technology for FSC.

In fact, Gorni states that the time economy and costs savings obtained by applying the rapid

prototyping techniques in building models is about 70 to 90%. However RP is not perfect. The volume

of the prototype is generally limited to 0,125m3 or even less. It is still difficult to make prototypes made

31

of metal; however that will change in the near future with technological development. At the moment,

the conventional machining techniques are still more economic than RP in the case of models made of

metal. Summarizing, all processes of RP have five basic steps [32]:

Creation of a Computer-aided design (CAD) model of the workpiece that is being projected;

Conversion of the CAD archive into Standard Tessellation Language (STL) format, proper for

stereolithography;

Slicing of the STL archive in thin transversal layers;

Physical construction of the model, piling up slice by slice;

Washing and implementing surface finish to the prototype.

These 5 basic steps are important to acknowledge, understanding that RP is a specific and

expensive process, which can reach a great level of detail. In some cases, it is not used because of its

costs and level of expertise. For instance, FSC could be a cheaper alternative when the project budget

is not that high. Even though, FSC is not as precise as RP, it is always a manufacturing technology

that can produce very small conformal cooling channels with a considerable precision.

The mould industry would largely benefit from the usage of RP models. There are three simple

steps that can be implemented into the mouldmaking process, which will increase the mouldmaking

power of the business, avoiding the pains of making unnecessary mistakes. There are three powerful

steps to improve mouldmaking power and those who have implemented these steps are well on the

way to becoming the ultimate toolmakers in their industry. These steps are [33]:

1. STEP 1: Start at Zero - Have the engineer send a model made from a RP process that uses

stereolithography (SLA), selective laser sintering (SLS) or fused deposition modeling.

2. STEP 2: Buy the insurance – From the beginning have a RP model produced, so the tool

designer can understand the geometry of the part or its unique features. A RP model allows a

complete understanding of the part—by holding it in the hands. This provides the insurance

needed to keep the project on schedule and under budget by eliminating future problems.

3. STEP 3: Provide Clarity throughout the Process - A real RP model that travels with the project

through the program allows the mouldmaker to see what is expected and be able to provide

valuable feedback very early in the process.

The new rapid prototyping process proposed by Karunakaran et al. combines Layer

Manufacturing (LM) and conventional machining methods in order to exploit their benefits and avoid

their limitations. LM technologies are also often referred to as RP technologies. In manufacturing, one

uses a fast roughing process followed by one or more finishing processes that are slow but accurate.

The methodology adopted in the proposed RP process also uses this concept of two-level processing,

32

such as, near-net building of the layer and net-shaping it by high-speed machining. This will result in

producing parts and tools economically, accurately and rapidly. The process does not pose any

restriction or loss of accuracy on the prototype as its size grows. Since the size of the part is limited

only by the traverse available on any existing CNC machine, a larger CNC machine can be used to

produce larger prototypes [34]. The evolution of RP is obvious and this only occurs owing to the great

potential RP has to add value to the design of a mould. Hopefully, RP will be an example in the mould

industry for FSC to follow as a technology that adds value to the complexity of mouldmaking and

heating/cooling channels configurations.

It is always important to understand where the technology started and how it grew. "Time to

Market" was originally the strongest inspiration and economical driving force in RP. RP (or LM)

technologies shorten the product life cycle and build up interest. Virtual modeling largely fulfils these

needs and is in continuous rivalry with RP. On the other hand, this conflict increases the interest and

chances of RP processes as alternative or autonomous manufacturing processes and elevates the

interest. The production of long-term usable components and tooling increases the interest in LM [35].

RP has everything that is needed to keep evolving and “step up the game” to stop competing just with

virtual modeling but to produce actual components that will eventually be part of a manufacturing

process.

It is a fact that rapid prototyping has gained a very wide acceptance over the last decade, with

an estimated production of 3.55 million models and prototypes in 2001 and a steady growth of about

20% per year, sales of 1000-1500 machined a year over the last 5 years and about 400 RP service

bureaus worldwide offering RP services. The market of rapid tooling (i.e. the first application of rapid

manufacturing for direct and fast production of tools) is still limited, but has nevertheless found

numerous real applications for the production of soft tools (for limited series) and hard tools (e.g. SLS

tools for series up to 100.000 shots). As for real direct rapid manufacturing (RM) of products, its

application is still in its infancy, even though very promising. The real breakthrough of RM will mainly

depend on cost and productivity improvements, which have to be accompanied with further technical

progress in material properties and most of all in accuracy and reliability [35]. FSC is in a very similar

position in terms of technological development. The cost of FSC is substantially lower, but it is not as

precise as RP. As always, the question is: what are the industry needs? If the prototype does not have

to be that precise and production costs are limited, FSC would be the adequate solution. On the other

hand, if precision is a priority, RP would be the most appropriate technological solution.

Conformal Cooling and Rapid Prototyping are two techniques used nowadays in the process

of mould production that, in some particular cases, can be replaced by FSC. FSC has the capability of

creating conformal cooling channels for normal size moulds. Alternatively, FSC is also able to

manufacture conformal cooling channels for prototypes, which signifies the ability to substitute rapid

prototyping in the mould production procedure. Other than mould production, FSC has the potential to

produce channels for heat exchangers due to its competence in producing internal channels with

significantly reduced sizes.

33

2.3.2 Heat Exchanger Production

The generation of a continuous internal channel by FSC has the potential to open a wide

range of applications in the heat exchanger industry. Heat exchangers are devices that are used to

transfer thermal energy between two or more fluids, or between a solid surface and a fluid, at different

temperatures and in thermal contact. Typical applications of heat exchangers involve heating or

cooling of a fluid stream and evaporation or condensation of fluid streams, with an objective to reject

or recover heat. Heat exchangers are usually classified on the basis of the transfer process, as either

direct contact type or indirect contact type. The heat exchangers are also classified on the basis of the

number of process fluids, or on the basis of the construction or flow arrangements or the heat transfer

mechanisms. Another basis for classification of the heat exchangers is on the basis of surface

compactness. The main objectives of compact heat exchangers are to maximize the efficiency of a

heat exchanger and also to reduce the size of the heat exchanger for a given duty. Compact heat

exchangers are generally used in industry, especially in gas-to-gas or liquid-to-gas heat exchangers.

For example, vehicular heat exchangers, condensers and evaporators in air-condition and

refrigeration industry, aircraft oil-coolers, automotive radiators, and intercoolers or compressors [36].

FSC has the ability to produce the channels for any of these types of heat exchangers, which

demonstrates the elevated applicability it has in the various industries.

The industrial heat exchangers can be classified according to their channel sizes (hydraulic

diameters) and their heat transfer area density. In general, as the size of flow channels employed in

heat exchangers decreases, its heat transfer area per unit volume increases. According to Wadekar

[37], the channel size and the area density are two interrelated parameters, which reflect the

compactness of a heat exchanger and enable a classification of industrial heat exchangers as it is

illustrated in Figure 3.16.

Figure 2.16 – Broad classification of industrial heat exchangers based on heat transfer area

density and channel size [37].

34

The classification of heat exchangers is essential to differentiate the different types of heat

exchangers that are used in the industry. The same thing occurs with channels and consequently the

channel classification. Taking into account that mini-channels are defined as channels in the diameter

ranges of 200 µm–3 mm, most of the refrigeration heat exchangers can be classified as mini-channel

heat exchangers (MCHX). The surface area and heat transfer coefficient enhancements associated

with mini-channel flow can be exploited effectively to make the refrigeration equipment smaller in size.

Significant refrigerant charge reductions are also possible due to the higher surface area-to-volume

ratio for the mini-channels. This ratio comparing the surface area of a channel compared to its volume

is another aspect of FSC that boosts its potential in industrial applications. Since the shape of the FS

channels is a sort of a rhombus its surface area-to-volume ratio is greater than the traditional circle

shaped channels produced all around the world for heat exchangers. Additional advantages of MCHX

include capital cost reductions, reduced environmental impact due to lower refrigerant inventory, and

possible improvements in the Coefficient of Performance (COP) of the system. The MCHX currently

being considered for refrigeration applications are modeled after the existing heat exchangers in

automotive applications [38]. FSC has potential to produce MCHX and the transfer of this technology

to the automotive industry is one of the goals to achieve, where a great variety of MCHX is used at an

elevated cadency.

Mould and heat exchanger production are the two main production industries for FSC to

penetrate. Nonetheless, FSC supported by successful application in the previously mentioned

industrial applications, could in the future, acquire innovative industrial applications in many other

industries, such as the aerospace, defense (military) and biomedical, following the widely known

successful steps of the FSW technology.

2.3.3 Other Applications

During the last decade, the defense and aerospace sectors have taken the lead in

implementing FSW. Recent advances in probe-tool designs and optimized processing parameters

have enabled FSW and Friction Stir Spot Welding (FSSW) applications in the marine, ground

transportation, and automotive industries. Further innovations in low-cost equipment and the

development of industry standards, design guidelines, and a trained workforce will enable the

introduction of FSW and FSSW into the broader light manufacturing, heavy manufacturing, and

construction industries during the next decade [39]. Possibly the projection of Friction Stir Channeling

will be the same in the near future, however FSC is very recent and it is being developed on a daily

basis in Instituto Superior Técnico by Pedro Vilaça and Catarina Vidal. For now, it reveals a great

potentiality and flexibility to be introduced in various industrial applications. The present work

contributes to this goal by increasing the knowledge on the FSC process and technology as well as to

make the connection between the FSC concept and the actual industry along with its corresponding

35

needs. An important aspect for the evolution of FSC is to determine how it can be beneficial compared

to alternative technologies in the industry that already produce internal channels.

The aim of the present work is to demonstrate that Friction Stir Channeling has the capability

and potential of producing conformal cooling channels for different types of moulds by analyzing

opportunities and strengths FSC might have compared to the already referred, existing alternative

technologies. An interesting investigation that will be performed in this work is to develop a competitive

analysis with alternative technologies and afterwards demonstrate the unique advantages inherent to

FSC with a detailed description of the design process and technological implementation of actual

prototypes. The completion of these Case Studies is a material proof of the actual capabilities of the

FSC technology. In addition to that, the prototypes developed in the present work illustrate the

possible industrial applications of FSC, which provides it with a tremendous potential to be an

alternative for technologies such as drilling, EDM and milling.

36

3 Competitive Analysis with Alternative Technologies

Three different Strengths, Weaknesses, Opportunities and Threats (SWOT) analyses were

performed comparing Friction Stir Channeling with three alternative technologies to determine the

strengths and weaknesses of this emerging technology. The SWOT analyses also facilitate an easier

comprehension of the possible opportunities and threats FSC has in terms of external factors

compared to the existing technologies in the industry.

The three main existing technologies in the industry that produce internal channels, or holes,

in the various industries around the world are: Drilling, EDM and Milling. Therefore, a SWOT analysis

comparing FSC and each of the three referred technologies was elaborated to determine the precise

advantages FSC has in relation to each of these technologies as well as the disadvantages that it

presents. Some more relevant data that can be obtained from a SWOT analysis are the external

factors that involve the opportunities and threats FSC has compared to the other three alternative

technologies. These factors provide clues on the adequate path FSC technology should take to be a

successful internal channel producer in various industries.

The three SWOT analyses elaborated in the current work can be applied to any industry in

which FSC could add value to the state of art technology. Even if small adaptations are needed, it will

only aid in identifying specific strengths and weaknesses of FSC compared to presently used

technologies as well as the external opportunities and threats it will face if the industrial

implementation is taken forward.

A final discussion on the main conclusions obtained from the competitive analysis with

alternative technologies, was elaborated. The major aspects to take in consideration were discussed

to determine the key points to focus on, for a successful start in the process of finding adequate

industrial applications that supply added value to the industry compared to the already established

technologies.

37

3.1 FSC vs Drilling

Drilling is the number one hole making technology all over the world, due to its low cost high

productivity and simple process. However, when it comes to drill a hole, its path has to be straight.

The major difference between FSC and drilling lies on the path of the hole (channel). FS channels can

have any desirable path and still be a very low cost technology. Another relevant aspect that

differentiates both of these technologies is that with FSC, the size of the channel can vary along its

path. In the near future, with FSC tool evolution a variation in channel depth along its path will also be

possible and doable.

Opportunities:

Higher productivity

Conformal Cooling

Threats:

Low know how of FSC

Surface finish (Very rough) of the internal channel and of the processed surface

Strengths:

The channels can have any path

The dimension of the channel may vary along its path

Bigger S/V of the internal channel due to shape of the cross section. (square vs. circle) and its high roughness

FSC can produce better (higher

quality) components with higher productivity

Determine if variation of channel dimension along the path is beneficial for heating/cooling system

Faster production cycles due to elevated heat power transfer

Gain know-how Determine

importance/ make use of surface roughness and different cross section shape

Benefits support tests for better know how

Weaknesses:

FSC needs access from one surface

The channels cannot have start and end in the same position

Open hole at the end of the channel path

Range of materials used (only non ferrous) due to budget

Channels can´t reach lateral walls of the mould

Determine if technology

restrictions may affect the productivity (limitation to reach lateral walls, processing surface only contrary to moulding surface)

Drilling of lateral wall is needed and closing processing surface may keep good productivity

Conformal cooling may not be affected by different start/end position

Use the residual open hole at the end for “racord”

Appropriate materials for the tools may permit FSC to be done on other materials (≠AA)

Tested with other

materials but for now focus on aluminum

Determine if hole at the end of channel is a problem for mould

Determine if the channels can be made on the surface contrary to the moulding surface

Finishing of processed surface applied during FSC (in-process)

38

3.2 FSC vs EDM

The major difference between FSC and EDM is the production costs. Both FSC and EDM can

produce internal channels with any desirable path. Other than the difference in production costs, the

need to use a coolant of the EDM technology is a disadvantage compared to FSC. In the case of

industrial application such as mould or heat exchanger production, FSC can produce internal channels

in a solid block.

Opportunities:

Higher productivity

Conformal Cooling

Lower cost

Threats:

Low know how of FSC

Surface finish (Very rough) of internal channel and processing surface

Strengths:

The channels can have any path

The dimension of the channel may vary along its path

Bigger S/V of the internal channel due to shape of the cross section. (square vs. circle) and high roughness

Non consumable tool

No coolant needed

FSC can produce better

components (higher quality) with less cost and higher productivity

Faster production cycles due to higher heat power transfer

Higher tool life and environmentally friendly

Determine if variation of channel dimension along the path is beneficial for heating/cooling system

Benefits support

tests for better know-how

Determine importance/ make use of surface roughness and different cross section shape

Weaknesses:

FSC needs access from one surface (processing surface)

The channels cannott have start and end in the same position

Open hole at the end of the channel path

Small range of materials used due to budget

Channels can´t reach lateral walls of the mould

Determine if technology

restrictions may affect the productivity (limitation to reach lateral walls, processing surface only contrary to moulding surface)

Drilling of lateral wall and closing processing surface may keep good productivity

Conformal cooling may not be affected by different start/end position

Use the residual open hole at the end for “racord”

Appropriate materials for the tools may permit FSC to be done on other materials (≠AA)

Tested with other

materials but for now focus on aluminum

Determine if hole at the end of channel is a problem for mould

Determine if the channels can be made on the surface contrary to the moulding surface

Finishing of processing surface applied during FSC (in-process)

39

3.3 FSC vs Milling

The major difference between FSC and milling is that FSC can produce internal channels and

milling can only manufacture open channels. In the case of industrial applications such as mould or

heat exchanger production, FSC can produce internal channels in a solid block in one single run. On

the other hand, milling creates open channels and to produce internal channels for moulds and heat

exchangers it needs to produce the channels in two runs (steps) in two different workpieces and then

subsequently braze the two pieces.

Opportunities:

Higher productivity

Conformal Cooling

Lower cost

Threats:

Low know how of FSC

Surface finish (Very rough) of internal channel and processing surface

Strengths:

Bigger S/V of the internal channel due to shape of the cross section. (square vs. circle) and higher roughness

Only one component

Channels at different depths processed on same surface

FSC can produce components

with similar quality with less cost and higher productivity

Faster production cycles due to higher heat power transfer

Easier to make channels at different depths

No time loss in joining components and assures better mechanical properties of channel

Benefits support

tests for better know-how

Determine importance/make use of surface roughness and different cross section shape

Weaknesses:

FSC needs access from one surface (processing surface)

The channels cannot have start and end in the same position

Open hole at the end of the channel path

Small range of materials used due to budget

Channels can´t reach lateral walls of the mould

Determine if technology

restrictions may affect the productivity (limitation to reach lateral walls, processing surface only contrary to moulding surface)

Drilling of lateral wall is needed and closing processing surface may keep good productivity

Conformal cooling may not be affected by different start/end position

Use the residual open hole at the end for “racord”

Appropriate materials for the tools may permit FSC to be done on other materials (≠AA)

Tested with other

materials but for now focus on aluminum

Determine if hole at the end of channel is a problem for mould

Determine if the channels can be made on the surface contrary to the moulding surface

Finishing of processing surface applied during FSC (in-process)

40

3.4 Discussion

A final discussion was executed after analyzing the advantages and disadvantages of the three

different alternative technologies already referred as well as comparing them with FSC. The following

conclusions were determined in a follow-up brainstorm of the competitive analysis with alternative

technologies performed in the present work:

Drilling has less production costs and more productivity than FSC, but the capability of

manufacturing internal channels with any desirable path revokes those disadvantages.

EDM is a high precision technology.

Milling also has the capability of producing channels with any desirable path; however the

channels are not internal, in other words, are open to the processed surface, which

differentiates from the aptitude of FSC to manufacture internal channels with any desirable

path.

FSC manufactures internal channels with an inverted rhombus shaped cross section, which

grants a larger “wet surface” than internal channels with circular cross sections.

However, the lack of control on the surface roughness of some FS channel walls can cause

significant pressure and temperature drops along the channel flow.

All in all, FSC finds the compromise between the strengths and weaknesses of the various

technologies and offers solutions that no other technology in the industry provides, with a

slight exception on the channel surface roughness.

In the following chapters, modeling and experimental tests were performed as a preliminary study of

the potential of FSC to be industrially applied, with a specific focus on the mould industry.

41

4 FSC Applications

After analyzing and comparing the alternative technologies that already exist in the industry with

FSC and spotting the opportunities and strengths FSC has in relation to all of the other three, it is

mandatory to create real prototypes that prove the advantages as well as the potential of the FSC

technology. Two prototypes were developed in the present work: an injection mould prototype and a

curing process mould prototype. The industrial applications of FSC that were defined in the present

work are ambitious; however with the realization of these prototypes, it is obvious that they are

achievable.

At a preliminary stage, the materials, equipment, tool and fixturing system used in the present

work must be defined and demonstrated. A simple and direct explanation should be provided with

important details to permit a global comprehension of the precise procedures implemented to fabricate

the two different FSC applications elaborated in the present study.

The first one is an injection mould prototype involving the major needs of the injection moulding

industry and proves the capabilities of FSC to manufacture channels with complex paths and at

different depths. However, the channels need to be short due to the fast cooling processes involved in

production cycle.

The second FSC application was a curing process mould prototype, which relies on slower

heating/cooling processes with insignificant variations in temperature in comparison with time

variations. The long duration heating/cooling cycle allows the channels to have bigger lengths and

more complex paths. The ultimate aim is to obtain excellent workpiece surface quality due to uniform

heating/cooling processes provided by well distributed FS channels.

First of all, it is essential to determine the objectives of each FSC application, followed by a

computational development of the solution to test and compare different hypothesis and reach the final

configuration that best suits the objectives that were formulated. After that the actual hands-on,

involving the technological implementation of the solution that was developed with computational

simulations is produced. Challenges will certainly be encountered at this stage; the practical work

always meets obstacles that are not detected in the computational simulations. Following the

technological implementation is the analysis of the obtained results and how the different obstacles

were overcome. Finally, suggestions for future FSC applications were established to reinforce the vast

potential of FSC technology.

42

4.1 Experimental Set-up

4.1.1 Materials Characterization

In this investigation, a commercial AA5083 (AlMg 4.5 Mn 0.7) alloy was used as base material,

both cold hardened (H111), as well as annealed (O).

Table 4.1 - AA5083 aluminum alloy chemical composition [40].

Chemical composition (weight %)

Si Fe Cu Mn Mg Cr Zn Ti+Zr Al

Min 0.4 4 0.05

Max 0.4 0.4 0.1 1 4.9 0.025 0.25 0.15

Table 4.2 - AA5083 aluminum alloy physical properties [40].

Physical properties

Density 2.66 g/cm3

Modulus of Elasticity 71000 MPa

Linear thermal expansion coef. (20 – 100 ºC) 23.8 x 10-6

K-1

Thermal conductivity (20ºC) 105-120 W/mK

Electrical conductivity (20ºC) 15-17 mS/m

Specific Heat Capacity 900 J/kgK

Table 4.3 - AA5083-H111 aluminum alloy mechanical properties [40].

Mechanical Properties

Ultimate tensile strength, UTS (MPa)

UTS 0.2 (MPa)

Brinell Hardness

Min Max Min 73

275 285 125

Table 4.4 - AA5083-O aluminum alloy mechanical properties [41].

Mechanical Properties

Ultimate tensile strength, UTS (MPa)

UTS 0.2 (MPa)

Brinell Hardness

Min Max Min 72

230 290 120

43

4.1.2 Equipment

Friction Stir Channeling prototypes were produced using a ESAB LEGIOTM 3UL numeric

control friction stir welding machine available at IDMEC, Instituto Superior Técnico, Universidade

Técnica de Lisboa (UTL), for investigation and development purposes.

The machine comprises a fixed framework with worktable, built-in guides, and a travelling

welding head assembly with (X, Y, Z) axis movement, as depicted in Figure 4.1. The welding

movement is made by a slide that moves the welding head while the workpiece stands still. Both the

welding spindle shaft and tool are water cooled by an internal refrigeration system. The welding angle

can be manually set from 0 to 5º, by rotating the welding head vertically. A user friendly control panel

allows to set processing parameters. Plunging speed and dwell time can also be controlled. Tool

rotation direction used in FSC was counter clockwise, so that the left-hand threaded probe (pin) could

push material flow from the bottom of the probe to the shoulder, top of the workpiece, and then with

the scrolls on the shoulder the material would flow to the sides of the shoulder. The referred

equipment also permits the user to program the path the FSC tool will execute throughout the FSC

process; this attribute was widely used in the present work to manufacture FS channels with any

desirable path.

Figure 4.1 - ESAB LEGIOTM 3UL Friction Stir Welding machine. Degrees of freedom

representation [42].

N (RPM)

44

The equipment presented in Figure 4.1 allows to control the FSC cycle by tool vertical position

control or by tool force control:

Upper tool position control – tool vertical position remains approximately constant throughout

the cycle, given the tool penetration set in the welding parameters menu.

Upper tool force control – tool vertical position may vary as the tool force set in the welding

parameters remains constant.

To achieve the proper thermo-mechanical conditions for processing and tool penetration depth,

tool plunge and dwell time can be determined by position or tool force control. Since tool plunge

causes plate temperature to rise, the material becomes softer and a deeper penetration is needed to

reach the vertical force required to start the cycle. A tool position control dwell time is more suitable

because tool penetration matches the proper depth at processing start and plunge force will be closer

to the force applied during processing. After dwell time, it is more advantageous to use a tool force

control in order to assure process parameter consistency between all trials.

Process parameters such as force, torque, tool position (X,Y,Z) and velocity can be monitored

in real time and recorded thanks to a data acquisition system installed.

4.1.3 Tool Design

Tool geometry is a vital component for the FSC process. Although probe (pin) and shoulder

geometrical features define material flow, the tool body plays a very important role as this component

must bear the mechanical stress involved and dissipates heat generated during the process.

A third version of the modular FSW welding tool developed at IST-UTL [43], called

iSTIRtool_v3, was used in this work (Figure 4.2). In this case, it is known as FSC tool, this tool is a

patented modular concept of a FSW tool that enables internal forced refrigeration and it was utilized to

manufacture all internal channels of the present work.

45

Figure 4.2 - iSTIRtool_v3 model views, (a) Model views and (b) section view. 1 – Tool body; 2 –

Probe; 3 – Shoulder; 4 – Probe fixation screw; 5 – Shoulder fixation screw [44].

The probe and shoulder are fastened to the tool body, as depicted in Figure 4.2a. By

independently joining the shoulder and probe to the same tool body, this 3 module assembly design

allows to easily adjust probe length to the desired depth of the FS channel, quick part replacement

and several tool geometry combinations (Figure 4.3b-e). Probe and shoulder rotation is locked by a

set of screws.

Figure 4.3 - iSTIRtool_v3 tool version assembly. Probe and shoulder fastening (a) and several tool

geometry combinations (b-e): (b) & (c) cylindrical probes; (d) & (e) conical probes [44].

46

The protruding probe length can be adjusted without disassembling the tool from the FSW

machine clamping system, simply by screwing or unscrewing the shoulder in the body, between

several multiple coincident positions between the holes of the shoulder and the machined slots of the

body (Figure 4.4). A rotation between two consecutive positions leads to ±0.0833 mm increments of

probe length. Thus, it is possible to preserve the distance between the end of the probe and the

worktable.

Figure 4.4 - Cross section view of tool assembly with probe (pin) adjustment system [44].

As shown in Figure 4.2b, the body and probe are hollow so that the cooling fluid from the

equipment refrigeration system can more effectively dissipate heat, thus safeguarding its structural

integrity.

The tool body was machined from DIN Ck45 steel, while the shoulder and probe used an AISI

H13 tool steel appropriate for high temperature application [44].

4.1.4 Fixturing System

Since Friction Stir Channeling is essentially a mechanical process, the workpiece plate must

be strongly constricted to avoid plate warping. The fixturing system used allows the fabrication if FS

channels on plates with a maximum width of 200 mm and a 350 mm length. Two steel bars were

bolted to a machined base plate by 2 screws each. Constriction is given by 2 smaller screws that

press down a group of plates, granting an evenly distributed pressure along the workpiece. The base

plate is bolted to the worktable of the FSW equipment. Since there is no joint between plates, a

vertical fixture system is enough to constrict all degrees of freedom, producing quality processed

channels. All system elements were machined from DIN Ck45 steel.

47

Figure 4.5 – Two different configurations of fixturing system for FSC process.

Figure 4.5 shows two different configurations of the fixturing system used for the present

study. Several other configurations are possible depending on the size and path of the FS channel

being produced.

4.1.5 Testing Description

4.1.5.1 Injection Mould Prototype

First of all, the aluminum alloy AA5083-H111, which was obtained in IST, was used in this

FSC application. The nominal composition (by %weight) of AA5083-H111 is 94.57Al–4.39Mg–

0.51Mn–0.33Fe–0.12Si-0.08Cr. FS channels were produced on 15mm thick plates of this alloy, along

the rolling direction, using the ESAB Legio FSW 3UL numeric control equipment, which was already

referred. Plunge and dwell periods (v=0) were performed under vertical position control and

processing period (v>0) was carried out under vertical downward force control. It was selected, for all

trials, a conical probe with an 8mm bottom diameter and left-handed threads along its length and a

plane shoulder with two spirals striates scrolling an angle of 360º with outer and inner diameters of

20mm and 8mm, which is demonstrated in Figure 4.6 [45].

Figure 4.6 – Modular tool with internal refrigeration used in FSC trials of injection mould

prototype with conical probe and 2 striates shoulder [45].

48

The FSC parameters implemented, while producing the injection mould prototype, are shown

in Table 4.5. All channels were produced with a very small gap between the shoulder and the

workpiece.

Table 4.5 – FSC process parameters for injection mould prototype.

Channel depth

Vertical force

Tool travel speed

Tool rotation speed

Rotation direction

Plunge speed

Dwell time

FSC control

8mm 420kg 100mm/min 400rpm CCW 0.1mm/s 5s Vertical force

control

4.1.5.2 Curing Process Mould Prototype

The material used to manufacture the curing process mould prototype was the aluminum alloy

AA5083-O, which was delivered to IST by Gleich Aluminum. FS channels were produced on 30mm

thick plates of this alloy, along the rolling direction. Plunge and dwell periods (v=0) were performed

under vertical position control and processing period (v>0) was carried out under vertical downward

force control with a 0º rake angle. It was selected, for all the runs, a cylindrical probe with an 8mm

bottom diameter and left-handed threads along its length and a plane shoulder with one spiral striate

scrolling an angle of 360º with outer and inner diameters of 19mm and 8mm, which is demonstrated in

Figure 4.7.

Figure 4.7 – Modular tool with internal refrigeration and with special insert for surface finishing

“add-in” used in FSC trials of curing process mould prototype with cylindrical probe and 1

striate shoulder.

The FSC parameters implemented, while producing the curing process mould prototype, are

shown in Table 4.6. All channels were produced with a very small gap between the shoulder and the

workpiece.

Table 4.6 – FSC process parameters for curing process mould prototype.

Channel depth

Vertical force

Torque Tool travel

speed

Tool rotation speed

Rotation direction

Plunge speed

Dwell time

FSC control

8mm 500kg 42N.m 100mm/min 600rpm CCW 0.1mm/s 8s Vertical

force control

49

4.2 Injection Mould Prototype

First of all, a brief introduction of the company that participated in a partnership with IST to

perform this injection mould prototype. Iberomoldes is one of the largest mould engineering and

product development companies in the world with about 800 employees. At present, they supply the

following three distinct areas that can be commercialized jointly or separately:

Engineering and product development (including prototyping, quick tools & control gauges)

Moulds for injection of thermoplastics and metallic alloys

Production of plastic components for the automobile sector, electronics sector, etc.;

A great part of the moulds produced by Iberomoldes are used to produce plastic products.

Injection moulding has been the most popular method for making plastic products due to its high

efficiency and manufacturability. The injection moulding process includes three significant stages:

filling and packing stage, cooling stage, and ejection stage. Among these stages, the cooling stage is

considered by many to be the most important one because it mainly affects the productivity and

moulding quality. Normally, 70%~80% of the moulding cycle is taken up by the cooling stage. An

appropriate cooling channel configuration can considerably reduce the cooling time and increase the

productivity of the injection moulding process. On the other hand, an efficient cooling system which

achieves a uniform temperature distribution can minimize the undesired defects that influence the

quality of moulded part such as hot spots, sink marks, differential shrinkage, thermal residual stress,

and warpage [46] [47].

Taking into consideration the relevance of the cooling times in injection moulding, the task

suggested by Iberomoldes seemed very interesting. The challenging task to develop a prototype for

Iberomoldes, would clearly demonstrate the potential of FSC in producing a more effective cooling

channel configuration. The prototype was discussed with the company, to determine if it could be an

alternative to produce small dimension channels for moulds that produce thermoplastic parts by

injection moulding. The thermoplastic is heated up and injected in the mould filling up the cavities of

the mould that make up the part geometry, and then it is cooled down until the thermoplastic turns into

solid phase. The cooling part of the process is performed with the help of the mould cooling channels

that have water at room temperature passing through it. However, these moulds are supposed to have

cooling channels behind the moulding surface at an equivalent distance along all of the part geometry.

Owing to the complex geometries of certain parts, it is very challenging and sometimes impossible to

manufacture channels that are all of them at exactly the same distance from the moulding surface,

especially with conventional drilling techniques. FSC could be the solution for this challenge, because

it can manufacture these channels due to the flexibility of the FSC technology that permits the

channels to have any desired path with depth variations, as it was mentioned in the SWOT analysis in

the previous chapter.

50

The advantages and capabilities of FSC were exposed to Iberomoldes and it was agreed that

a first prototype should be produced with specific geometries. This first prototype included channels at

different depths with curved paths to produce a simple but geometrically challenging part. The final

shape of the injection mould prototype is presented in Figures 4.8 and 4.9.

Figure 4.8 – Solidworks design of injection mould prototype (cavity and male).

Figure 4.9 – Solidworks assembly of injection mould prototype: male assembled with cavity of

mould.

The final product, in other words, the part that the Iberomoldes mould prototype would

eventually produce would have the geometry presented in Figure 4.10.

Figure 4.10 – Part to be produced from injection mould prototype.

The final product of a mould is its final objective. The appropriate design of a mould is determined by

the quality of the part it produces. Therefore, it is always important to visualize the final product of the

moulds, since the ultimate goal of the moulds is to produce a zero-defect workpiece, which can only

be achieved with an efficient and uniform cooling from the channels to the moulding surface.

51

4.2.1 Formulation of Objectives

The objective of this FSC application with Iberomoldes is to analyze if the manufacturing of FS

channels is feasible to function as conformal cooling channels of injection moulds that produce parts

with complex geometries. A secondary, and inherent, objective is to demonstrate the flexibility of the

FS channels, showing how the channels can have any path that is necessary even the most

complicated ones and at any desirable depth. The compromise of these two scenarios is the goal of

this FSC application, demonstrating that the FS channels can cool down a complex shaped part and

simultaneously illustrate the potential of FSC to manufacture channels with any desirable path.

In the case of injection moulding, the channels not only need to be close to the moulding

surface but they also need to be considerably short in length. Owing to the fact that, the moulds are at

high temperatures because injection moulding is a production process with very short cycle times, so

the mould is constantly at high temperatures. Therefore, when the cooling fluid enters the mould, it

starts heating up very rapidly and if it stays inside the mould channels too long, it reaches the mould

temperature and loses its cooling effect. As a result, if the conformal cooling channels are too long the

cooling fluid loses its low temperature along the channels. Consequently, the mould channels need to

be close to the moulding surface but bearing in mind that they need to have limited length. This

change in the cooling fluid temperature needs to be taken into consideration when designing moulds

for injection moulding.

A second important aspect to take in consideration in the design phase of an injection mould is

that mould channels need to have their inlets and outlets on the lateral walls of the mould plates. The

channel “racords” of the mould channels lie on the sidewalls of the moulds to connect to the cooling

fluid circuit of the injection mould. The liquids normally used in cooling fluid circuits of the moulding

industry are water or oil. The difference between the cooling fluid temperature and the mould

temperature is considerable and it decreases as the cooling fluid passes through the mould, therefore

it needs to go back to the cooling fluid circuit to reduce its temperature once again, therefore the only

possible surface to enable the continuous circulation in the cooling fluid circuit, are the lateral walls of

the mould cavity and male.

The proper process to develop a solid prototype is to execute computational simulations to

develop a suitable solution. Subsequently, the technological implementation is performed with its

inherent obstacles and limitations that always occur with innovative technologies. A detailed

description of the design development and corresponding problems encountered was provided, as

well as the processes involved in overcoming those same problems. Finally, a result analysis was

elaborated to consolidate the final comments on the injection mould prototype, including the learned

lessons for future development of FSC technology.

52

4.2.2 Computational Development of Solution

The computational development of the adequate solution for the injection mould prototype was

performed in Solidworks software. A flow analysis was then performed in Solidworks Floxpress, by

performing a cooling fluid flow analysis to the Solidworks design of the injection mould prototype. The

analysis was made assuming an internal flow of a specific cooling fluid within the mould channels,

which would heat up considerably the cooling fluid. The cooling fluid used in this case was water,

which is used in many injection moulding processes. This analysis demonstrates the effect of the

mould temperature on the cooling fluid and how the channels need to have a limited length, if not they

lose their functionality and will not cool down the part. Some different channel configurations were

analyzed and an optimal configuration was obtained for Iberomoldes to analyze at a later stage. An

important aspect that was considered, while developing different channel configurations was that the

part being produced needs to be uniformly cooled down so the channels need to be at an equivalent

distance from the moulding surface, in this case the mould cavity and male. It is important to

acknowledge that the mould cavity has to be cooled down at a uniform temperature throughout the

whole cavity to assure that the part has a first-class surface quality; the same scenario is applied to

the mould male.

Figure 4.11 – Simulation of cooling fluid flowing through the injection mould prototype with

fluid progressing along one of the FS channels.

The temperature conditions to approximate the computational development to reality were

defined as 50ºC at the channel inlet and 80ºC at the outlet of the FS channel. It is clear in Figure 4.11

that the cooling fluid velocity increases in the more curved parts of the channel paths, consequently

increasing the temperature of the cooling fluid. This property of the cooling fluid should be taken into

consideration when designing the conformal cooling channels.

53

Figure 4.12 – Cross section view of the injection mould prototype with the part placed on top of

the cavity mould, this procedure was performed in Solidworks software.

Another important aspect taken in consideration in this injection mould prototype was the inlet

and outlet of each channel. In the injection moulding industry, cooling channels connect to the cooling

fluid circuit through the lateral walls of the mould cavity and male. Consequently, the FS channels

need to begin and end on the lateral walls (sidewalls) of the mould prototype and it was a design

limitation considered in the technological implementation of the Iberomoldes mould prototype. Figure

4.13 shows the inlets of the FS channels with small cylinders inserted in the corresponding inlets.

Figure 4.13 – Simulation of different velocities of cooling fluid flowing through one FS channel

of the injection mould prototype.

The computational development of the adequate solution for a prototype should predict and

alert the researcher on possible obstacles that will appear during the technological implementation.

The computational development also assures that the design of the FS channels is feasible according

to the known technological limitations of FSC.

4.2.3 Technological Implementation

The technological implementation consisted in producing a injection mould prototype for

Iberomoldes to demonstrate that FSC is capable of producing conformal cooling channels for the

mould industry, and in this case more specifically for injection moulds. It is relevant to take into

consideration that when it comes to state of art technology, the technological implementation is by far

the most challenging stage. The process of developing a technology, especially such at an initial

stage, which is the case of FSC, involves constantly facing new obstacles, one after the other.

54

At first, the channel in the center was intended to have a transversal direction, but as the

thickness of the aluminum plate was not enough to manufacture one channel from one side and

another from the opposite side, the center channel was also manufactured on the longitudinal side.

Another design problem was that the inlet and outlet of the channels had to be on the lateral walls of

the mould so the FS channels had to be longer than their final size, and then they were cut with a

mechanical saw. A design limitation encountered in the technological implementation is that, at

present, it is not possible to produce channels on top of each other. For instance, two channels with

exactly the same cross section size, length and path cannot be manufactured, from the same

processing surface at different depths on top of each other. A major obstacle encountered was probe

breakage due to length of the channels as well as the change in direction. The major problems

occurred with long distance channels and challenging channel paths, such as accentuated curves and

changes in direction. Nonetheless, the injection mould FSC application ended up being a successfully

completed mould prototype. Figure 4.14 includes some photographs of the actual prototype produced

with FS channels in IST and some of the intermediate phases throughout its manufacturing:

Figure 4.14 – FS channels of injection mould prototype top views right after being produced,

before the mould cavity was manufactured.

Figure 4.15 – Injection mould prototype top view.

A

A

55

Figure 4.16 – Injection mould prototype cross section view.

Figures 4.14, 4.15 and 4.16 show the evolution of the injection mould prototype production.

First, the two outer channels were produced on one side of the 15mm thick aluminum plate. Then the

center FS channel was manufactured. Figure 4.16 clearly demonstrates that the channel bottom

surface of the centre channel is different from the other two. In Figure 4.17 it is possible to visualize

the final injection mould prototype produced with FS channels, including at the left a compact solid

cavity mould and at the right a sectioned mould cavity showing the FS channels cross sections.

Figure 4.17 – Perspective view of injection mould prototype with corresponding FS channels as

well as 4 sections demonstrating the FS channel cross sections.

The injection mould prototype was a success due to the fact that it demonstrated in a very

simple way how FSC can manufacture conformal cooling channels for a complex shaped part. After

trying some different channel configurations, a most advantageous channel configuration was

reached. To determine the best channel configuration two aspects were considered: channel length

and channel path. The channel path is related to the uniform cooling of the part, which is reflected on

the surface quality of the final produced part. The channel length is related to the high temperature of

the mould when producing at a very fast rate, so the FS channels cannot be very long for the cooling

fluid not to lose its cooling purpose.

A A

56

4.2.4 Result Analysis

The results of this first Case Study were very encouraging. The three FS channels of the

injection mould prototype were manufactured in one single step without any probe breakage or any

kind of major upset. However, these three successful runs were only attained after meticulous

investigation of the correct process parameters to use with that specific FSC tool and base material as

well as channel depth, channel length and channel path. All of these channel characteristics have to

be taken into consideration when defining the adequate process parameters. For each specific

channel the process parameters vary slightly and that know-how has to be obtained through a

painstaking process of trial and error. The technological implementation in an innovative process, such

as FSC, is the most relevant part of its development since it will determine all of the potential FSC

technology has.

The injection mould prototype development and implementation showed some major

difficulties that the evolution of FSC technology will face. The results demonstrate that the FSC

technology is still at a very initial stage and that it needs a lot of development and follow up. The range

of tool materials available for FSC technology is still limited. Various problems such as: FSC tool heat

up, poor channel geometry in long, curved and sharp curved channel paths, base material sticking to

the FSC tool, restricted usage of different base materials. All of these obstacles were encountered

throughout the production of the injection mould prototype.

Future developments will be focused towards solving these initial difficulties, which are

perfectly normal to occur with a technology that was recently discovered. FSC is an innovative solid-

state manufacturing technology that still has a long way to go, although it certainly is on the right track.

A future suggestion to improve the potential of FSC, which was suggested and reinforced by

Iberomoldes, is to develop a FSC tool that enables a FS channel to vary its depth (distance between

processed surface and channel base) along its path on other words, while the channel is being

produced. Consequently, FS channels would vary their depths according to the depth variation of the

moulding surface, giving FSC even more flexibility by allowing it to perform an internal channel with

any desirable path at a three dimensional scale.

57

4.3 Curing Process Mould Prototype

Initially, the author acknowledges the support and availability of Optimal to participate in this

partnership with IST to execute the curing process mould prototype of the present work. Optimal

Structural Solutions is a Portuguese team focused on providing the optimal structural solutions for its

customers, which focuses on the engineering and manufacturing of composite components including

various successful projects with the automotive and aeronautical industry. These industries use high

quality composites that are produced with specific curing processes, which use open moulds to

“produce” their workpieces. The mould industry could also be an interesting possibility for Optimal to

intervene, with its advanced know-how in composite materials.

A prototype was developed to explore the potential of Friction Stir Channeling in the design

and conception of conformal cooling channels for its open moulds. The configuration of the prototype

was suggested by the company, and a prototype was developed to produce a small dimension piece

to test the efficiency of the FS channels in heating/cooling the workpiece in a uniform way along all of

its geometry. In this case, a film of a structural motorsport pre-preg would be placed on the mould and

the cooling conditions of the material would certainly be different with a conformal cooling

configuration of FS channels than with straight channels produced with conventional drilling

techniques. FSC allows serpentine and circle paths for the channels to have the most adequate

configuration for enhanced cooling conditions and a uniform temperature along the whole part surface.

First of all, the geometry of the curing process prototype, including the mould and the part, is

demonstrated in Figure 4.18.

Figure 4.18 – Solidworks design of curing process prototype (mould and workpiece).

58

4.3.1 Formulation of Objectives

The objective of this application is to analyze if the manufacturing of FS channels is feasible to

function as conformal cooling channels for parts with complex geometries. Another objective is to

demonstrate the flexibility of the FS channels, showing how the channels can have any path desired

even the most complicated ones.

Figure 4.19 – FS channels configuration of curing process mould prototype.

Optimal partnered with IST to develop a mould prototype that has conformal cooling channels

produced with the FSC process. The objective of this partnership is to demonstrate how the FSC

process is able to produce channels that enhance the heat transfer from the cooling channels to a

geometrically challenging moulding surface and also enable a uniform temperature distribution

throughout the whole complex moulding surface. A thermal analysis was performed to demonstrate

the positive impact of the channels produced with FSC compared to channels produced with

conventional drilling techniques.

The thermal analysis was performed in IST with the aid of a computational simulation and it

was based on a curing process suggested by Optimal. The curing process consists of an initial heating

phase from 20°C to 80°C at a rate of 2°C per minute. After that, there is a 10 minute period at a

constant temperature of 80°C. Then, the increase in temperature continues to 120°C, with the same

heating rate of 2°C per minute. Subsequently, the moulded part is kept at 120°C for 60 minutes and

then it is cooled down to 20°C at a cooling rate of 2°C per minute. The material of the moulded part

used in Optimal is a pre-impregnated fiber fabric (pre-preg) with a toughened epoxy resin developed

specifically for the manufacture of components. The pre-preg used is the MTM49-3 which belongs to

an ACG series of structural motorsport pre-pregs with moderate toughness and high glass transition

59

temperature (Tg). One of the main features of these pre-pregs is that it has a wide range of end use

temperatures, which depend on the application of post-cure methods. They also have versatile

processing techniques, which include autoclave, vacuum bag or press moulding. Other than that, they

have a good tack and drape as well as a good impact resistance. The specific pre-preg used in this

thermal analysis (MTM49-3) has 42% resin content with a 2 by 2 Twill fabric of T800 carbon fiber [48].

The pre-preg specifications were provided by Optimal to approximate the thermal analysis as much as

possible to reality conditions.

The objective of this analysis is to show that a channel configuration that is closer to the actual

surface of the part being moulded is more efficient than a typical channel configuration produced by

conventional drilling techniques. FSC is an economic way to produce these channels with conformal

cooling properties, which can improve significantly the heat transfer between the heating/cooling

channels and meet the challenging complexities of certain moulding surfaces. The geometry of the

mould and corresponding moulding surface was developed by Optimal and suggested to IST. The

dimensions and geometries of the curing process mould prototype and the corresponding workpiece

(part) are presented in Figure 4.20.

Figure 4.20 – 3D dimensions of curing process mould prototype and corresponding workpiece.

60

Figure 4.21 – 2D dimensions of curing process mould prototype and corresponding workpiece.

Consequently, IST determined the most adequate channel configuration and produced a small

dimension prototype of the mould. Thereafter, Optimal produced the corresponding part to prove the

capability of the FSC process to produce complex shaped parts such as the one proposed by Optimal.

A thermal analysis seemed to be an adequate solution to investigate and prove the

capabilities of the FSC process in creating conformal cooling channels. To enable a clear

understanding of the heat transfer between the channels and the moulding surface, the thermal

analysis was performed in various stages. First of all, a simple block with a channel going through it

was modeled and analyzed to obtain a perception of all the boundary conditions needed and

simulation procedures to approximate it as much as possible to reality. After that, the contact

simulation was optimized with the introduction of a third layer, between mould and part, to

approximate the computational simulation to real conditions. The following stage was to define the

different channel configurations that would be used in the thermal analysis. Two conventional

configurations with straight path channels were included, to demonstrate the great difference in the

cooling uniformity compared to a channel configuration with conformal cooling FS channels.

Consequently, the major difference between heat transfer, from channels to moulding surface,

between FS channels and channels produced with conventional drilling techniques shows the great

potential FSC has for a successful introduction in various industries, more specifically in the mould

industry. FSC is a very low cost technology compared to other technologies that produce conformal

cooling channels, such as rapid prototyping. FSC can have a reasonable productivity with the

appropriate tools as well as a considerable flexibility. It is possible to have variation in depth and

channel size along a channel, just with simple evolutions in the present day FSC tools. FSC can,

without a doubt, in some years of thorough investigation and sustainable development, be a serious

and established manufacturing process of conformal cooling channels in the mould industry.

61

4.3.2 Computational Development of Solution

The computational analysis was performed in Abaqus, by performing a thermal analysis to the

Solidworks part of the curing process prototype (mould, interface and workpiece). The analysis was

executed assuming an internal flow of a specific cooling fluid, so the simulation was simplified to the

implementation of a constant temperature being transmitted from the fluid in the channels to the part

surface of the prototype. The value assumed for the temperature of the cooling fluid was assumed to

have the values of the temperatures provided by Optimal that were part of their curing process. Taking

into consideration that the part has to have a good surface quality, it is essential that the part surface

has to be heated up and cooled down at a uniform temperature throughout its entire surface.

The thermal analysis performed for Optimal was done in various steps. First, it was simplified

to the simplest form: a small block (rectangular prism) with a small channel across it. The heat transfer

from the channel to the top surface of the small block was analyzed. Then a thin film with all of the

epoxy resin properties (mechanical and thermal) was placed on the top surface of the block to

simulate the heat absorption of the resin, heat transfer and liberation to the air in natural convection

conditions. However the contact simulation was very poor. So, an extremely thin layer of a material

with a very low thermal conductivity, low density and low specific heat capacity was positioned

between the block and the epoxy resin. After determining the contact conditions and boundary

conditions, the channel configuration was determined. The two configurations produced with

conventional drilling techniques were produced only with straight path channels in the transversal for

one configuration and in the longitudinal direction for the other configuration. Both configurations had

several parallel channels along the limits of the moulding surface, and all at the same depths, with no

intersections to correspond to the manufacturing limitations of the conventional drilling techniques.

The conformal cooling configuration was produced with channels that have different paths and at

different depths with any desirable intersections, enabling channels very close to the moulding surface

and all of them at an equivalent distance from the moulding surface to accomplish a uniform

temperature distribution along all of the workpiece geometry. These different configurations were

produced in Solidworks and then imported into Abaqus.

The thermal analysis was initiated with a small block (rectangular prism) with only one channel

across its longer side and crossing it at middle height, in other words, starting and finishing in the

middle of one of the smaller faces. This first stage was performed to understand the different

behaviors of the heat transfer in Abaqus. Initially the idea was to analyze the heat transfer from the

channel to the top surface of the block just to verify if the properties were consistent with the flow of

heat transfer. As well as, to understand which would be the necessary boundary conditions to analyze

the desired heat transfer. Including, the geometry sections that should be considered as insulated and

others that should have boundary conditions with natural convection conditions with different

convection constants (h) depending on the different type of material. To have a clear view of this first

step of the thermal analysis, the block that was used in this first step is presented in Figure 4.22, in

62

which a specific high temperature was imposed in the channel as well as a constant heat flux on the

entire channel surface to acknowledge the heat transfer behavior:

Figure 4.22 – Block model developed in Abaqus software.

However a lot of limitations and lack of robustness was detected on the first stage of the

thermal analysis. Consequently, it was decided that a thin layer of material of about 2-3mm thick,

which was the thickness indicated by Optimal for the epoxy resin (pre-preg). This thin squared layer

was introduced in the thermal analysis to simulate the epoxy resin (pre-preg) used in Optimal and its

effect on the heat transfer, entering the pre-preg and exiting it, as well as the quantity of heat that it

absorbed. At this stage, the block was analyzed only with a thin rectangular portion of material with

epoxy resin (pre-preg) properties on top of it. The 2nd

version of this initial block simulation is

demonstrated in Figure 4.23.

Figure 4.23 – Block model with workpiece square unit on top.

The 2nd

version of the initial block model had a contact simulation that was not very realistic

and to obtain an accurate simulation of the contact conditions, it would be necessary to determine

different values of thermal conductance depending on the amount of clearance present between the

two components (materials). It was a requirement of the Abaqus software, so a more simplified

version was elaborated. A simpler solution for this specific problem was determined and a very thin

film of a material which represented the interface between the pre-preg and the block was added to

the simulation. The interface had specific properties, such as, extremely low values of density and

thermal conductivity, as well as a reduced value for the specific heat capacity. These properties

simulated the behavior of the small spaces that in real conditions always exist between two materials

63

that are in contact. Especially, in this case that we are dealing with an open mould, so the pre-preg

does not have pressure being applied to it against the mould. Consequently, the 3rd

version of the

initial block simulation is presented in Figure 4.24.

Figure 4.24 – Block model with interface between block and workpiece square unit.

Finally, a thermal analysis was performed to this initial block. It was heated up to 80°C,

imposing a constant temperature of 80°C to the channel surface area. This condition assumes that the

liquid passing through the channel is always circulating and an average temperature of 80°C is being

transferred to the channel walls, and then through conduction it transfers along the block and to the

interface and eventually to the prepreg squared layer. Clearly, with visual aid it is easier to

comprehend the heat transfer from the channel to its adjacent surfaces and the differences of heat

transfer through the diverging materials. This initial thermal analysis, heating up to 80°C, is the first

step of the curing process suggested by Optimal and encouraging results were obtained. The model

was improved through an iterative process of trial and error, which aided in defining the appropriate

properties of the interface component as well as some of the unkown properties of the prepreg. The

temperature distribution of this simplified thermal analysis, simple block and channel, is shown in

Figure 4.25, with the corresponding temperature values of the different colors (in degrees Celsius).

Figure 4.25 – Temperature distribution of block model heated up to 80°C (perspective).

64

In this intial analysis, the bottom surface of the block and its side walls were all with insulated

conditions, or in Abaqus software, when no boundary conditions are applied, it considers as an

insulated frontier. The contact definitions between block, interface and workpiece squared layer were

identical considering 50% of heat trasnfer (conductivity and convection) and radiation emission

between touching surfaces. Another boundary condition is the top surface of the workpiece squared

layer, which has a natural convection condition with a fluid temperature outside the thermal layer of

20°C and natural convection constant of 5 W/mK. In Figure 4.26, is a more frontal perspective of the

initial block of the thermal analysis, which clearly shows that it is possible to obtain a uniform

temperature distribution of the epoxy resin if the the channel configuration is appropriate according to

the complexity of the part geometry. Once again this perspective emphaizes that the channel

configuration should be given major importance. Defining the correct channel configuration can be the

most critical part of creating a mould with FS channels to have a succesful implementation of the FSC

process.

Figure 4.26 – Temperature distribution of block model heated up to 80°C (front view).

After defining the boundary conditions and understanding the heat transfer complexity, the

next step was to apply the appropriate geometries of the mould, interface and workpiece in the

thermal analysis. However, before that, it was imperative to define the adequate channel

configurations of the three moulds that were going to be analyzed, two with channels produced by

conventional drilling techniques and one with FS channels. After investigating some options, three

final versions were accomplished. The final channel configurations of the three moulds (3 Case

Studies) are demonstrated in Figure 4.27.

Case Study 1 – Case Study 2 – Case Study 3

Figure 4.27 – Channel configurations of all 3 Case Studies.

65

The channel configurations were designed and finalized with the Solidworks software. The first two

Case Studies have channels with straight paths because channels produced with drilling techniques

can only have straight paths and cross sections that are circles. On the other hand, Case Study (CS) 3

has the cross section of the typical FS channels (inverted rhombus) and have paths that approximate

as much as possible the channels to the complex-shaped moulding surface, with the intent of assuring

that all of them are at an equivalent distance from it.

The process of determining the channel configuration that enhanced the FSC potential and was

viable to the purpose of the mould, in other words, optimizing the curing process heat transfer as well

as assuring uniform temperature along the workpiece geometry and designing a channel configuration

that is feasible to produce with FSC and economic in terms of time and different runs. Taking into

consideration that a curing process is not an injection moulding process, so the cooling process is not

a matter of seconds and the channels can be quite longer because the heating/cooling process occurs

during a long period of time, so the temperature has more time to stabilize along the whole channel.

Figure 4.28 presents FS channels configurations that were considered before attaining the final one:

Figure 4.28 – Different FS channels configurations for curing process mould prototype, tested

before using final FS channels configuration (Case Study 3).

66

Now that all of the ingredients needed: theory, boundary conditions, component geometries and

case studies, were already determined, the computational simulation could be implemented.

Obviously, this computational simulation was performed to simulate a curing process performed in

Optimal as mentioned before, so it was divided in 4 major steps:

1. STEP 1: Heating from 20°C to 80°C at a rate of 2°C/min during 30 minutes.

2. STEP 1A: Plateau at 80°C during 10 minutes.

3. STEP 2: Heating from 80°C to 120°C at a rate of 2°C/min during 20 minutes.

4. STEP 2A: Plateau at 120°C during 60 minutes.

These 4 steps were introduced in Abaqus and a mesh with a Heat Transfer element type, a tetahedral

element, was created with the same approximate global seed size for each component of 4 with a

curvature control maximum deviation factor of 0.1 and minimum size factor, as fraction of global seed

size of 0.1. Owing to the fact that, the components were imported from Solidworks, their shapes were

not defined in Abaqus, so the only possible element type in the “Heat Transfer” family is the tetahedral

(tet) type, the DC3D4: a 4-node linear heat transfer tetrahedron. This situation occurred due to

irregularities in the component geometries especially due to the complex-shaped moulding surface

and FS channels. The author determined that the step periods correspond to a time period of 1

minute: Therefore, STEP 1 has a time period of 30, STEP 1A has a time period of 10, STEP 2 has a

time period of 20 and STEP 2A has a time period of 60. The boundary conditions of the thermal

analysis were the 20°C to all components at the intial stage before STEP 1. The workpiece had a

natural convection with a constant of 5 W/mK and a surrounding temperature of 20°C and the mould

with a natural convection constant of 20 W/mK and the same surrounding temperature. The boundary

conditions applied in each step only considered the corresponding temperatures applied on the

channel surface areas. The contact simulation applied to the contacts between mould and interface as

well as interface and workpiece, were both considered to transfer 50%of the total heat transfer and

50% of the total emissivity.

These basic conditions were maintained for all three Case Studies. It is important to mention

that the cooling down part of the curing process was excluded from the computational simulation

because it was thought to be of minor importance. The focus of this thermal analysis was to assure

that the heat transfer of the FS channels to the moulding surface was more efficient than that of the

other channels. So, the critical part of the curing process for this thermal analysis was to determine if

the workpiece was uniformily heated at the end of the last high temperature (120°C) plateau. The

ultimate goal of this thermal analysis is assuring that the final surface quality of the workpiece is the

best possible. Since the section of the curing process that majorly affects the workpiece surface

quality is the section with highest temperatures, it was defined that the cooling down phase of the

curing process could be removed from the computational simulation due to its lack of relevance for the

research being performed.

67

The graph, presented in Figure 4.29, with a Temperature vs. Time curve, demonstrates the

conditions of the curing process used in the computational simulation:

Figure 4.29 – Temperatures versus time of Optimal curing process.

The computational simulation had three main components, each one with its corresponding properties

and attributes. Figure 4.30 clearly demonstrates the three main components associated with the

computational simulation of the curing process, which the mould prototype will encounter:

Figure 4.30 – Properties distribution of curing process prototype computational simulation.

Obviously, these three main components have different properties and behaviours. So, in the

computational simulation these different properties have to be introduced to simulate their different

characteristics throughout the simulation and to approximate as much as possible to the real

conditions of the curing process. The properties of each component that are listed below were

obtained from various literatures, which are also referenced. The material used for the mould

component was the AA 2024-T6, due to lack of information on thermal properties of AA 5083, with a

nominal composition in weight percent of 4.5Cu–1.5Mg–0.6Mn. The properties of the interface were

determined by the author and in the case of the workpiece, some properties were given by Optimal

while others were determined by the author from intensive research in various literatures.

0

50

100

150

0 20 40 60 80 100 120 140

T [°

C]

t [minutes]

Optimal Curing Process

68

The mould component had the thermal and mechanical properties of the aluminum alloy, AA

2024-T6, presented in Figure 4.31, including their variations with temperature, which were considered

in the computational simulation [49]:

Figure 4.31 – Properties distributions and values for mould component [49].

Table 4.7 - Properties values for the interface (defined by the author) and the workpiece

component [48] [50].

Component Thermal

Conductivity Density

Thermal Natural Convection

Specific Heat

Interface 0.05 W/mK 100 kg/m3 - 200 J/kgK

Workpiece 0.5 W/mK 1220 kg/m3 0.5 W/m

2K at 20ºC 794 J/kgK

Identical computational simulations were performed to the three Case Studies and it was clear

that the Case Study (CS) 3 with the FS channels had a more enhanced heat transfer between the

channels and the moulding surface as well as a more uniform distribution of the temperature along the

workpiece. The images below demonstrate a clear difference between the moulds that have channels

with channels produced with conventional drilling techniques and channels produced with FSC.

Figures 4.32 and 4.33 show two different cross sections, one of the largest side of the mould and the

second one of the smallest side of the mould. The differences between CS 3 and the other two Case

Studies are obvious:

69

Figure 4.32 – Cross sections of the longitudinal (longer) side of the 3 components at the end of

the curing process prototype computational simulation with the corresponding temperature

distribution for all of the 3 Case Studies.

Figure 4.33 – Cross sections of the transversal (short) side of the 3 components at the end of

the curing process prototype computational simulation with the corresponding temperature

distribution for all of the 3 Case Studies (Case Study = CS).

70

The red circles in Figures 4.32 and 4.33 highlight the major differences between the first two

Case Studies and the FSC mould (Case Study 3). The FSC mould demonstrates the impact the

proximity of the heating/cooling channels to the moulding surface can have on the heat transfer to the

workpiece. The poor heat transfer to the workpiece in complex-shaped moulding surfaces is a major

issue of the moulding industry and FSC is the “perfect” solution for that same issue. Consequently, a

very important factor when designing a mould is to assure that the FS channels are as close as

possible to the moulding surface and all of them are at an equivalent distance to assure a uniform heat

transfer along all of the workpiece geometry. It is essential to note that, as in Case Study (CS) 3, when

the channels are not close enough to the moulding surface, they will not have the desired effect on the

heat transfer form heating/cooling channels to the moulding surface. A good example in the FSC

mould is on the inclinated faces of the moulding surface, the heat tansfer of CS 3 is better than the

other two but it could be much better if a channel was manufactured right below it. As a result, this

reality always has to be present when producing FS channels for moulds. The FSC feature that

differentiates it from conventional drilling techniques has to be exploited as much as possible, to

enhance the heat transfer between channels and moulding surface. Therefore, the FS channels

should be produced as close as possible to the moulding surface in any mould. A precise

measurement should be made to enable the channels to be equidistant from the moulding surface so

the heating/cooling of the workpiece is uniform along its geometry.

4.3.3 Technological Implementation

As in the injection mould FSC application, the technological implementation faced obstacles

inherent to a technology that is in the initial stage of its development. The process parameters have

been optimized as well as the FSC tool material and base material, but any time there is a slight

change in any of these variables, all of this process has to be redone. Nonetheless, using the material

provided by Optimal, the curing process mould prototype was produced in IST with success. Figure

4.34 shows top views of FS channels produced along the manufacturing of the prototype:

Figure 4.34 - FS channels of curing process mould prototype with serpentine and contour

paths (top views) immediately after being produced and before the moulding surface was

manufactured.

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The prototype developed in this FSC application demonstrates once again the applicability of

FSC to the mould industry, and not only in the injection moulding industry (Figure 4.35). There are

many other processes that use moulds such as this prototype that undertake curing processes of fiber

carbon materials, which involve processes with bigger durations and slower variations in temperature

when compared to injection moulding cooling processes. The technological implementation of the

curing process mould prototype had three main challenges: the length of one FS channel, the

serpentine path of another FS channel and the depth for the third FS channel. All three challenges

were overcome, with a certainty that FSC process parameters need to be consolidated, so that slight

variations in the process parameters can be more controllable.

Figure 4.35 – Two FS channels of curing process mould prototype immediately after being

manufactured.

The discoveries made along the technological implementation of the curing process mould

prototype provided consistent evidence that FSC is a technology that has to be operated at “colder

conditions” than FSW and all of the other friction stir based technologies. This appreciation can be

proved with actual demonstrations of the FS channels cross sections, demonstrating a considerable

capacity of extracting material and at the same time to maintain the processed surface at the initial

level and with a considerable surface quality/roughness. Figure 4.36 demonstrates the processed

surface of two FS channels immediately after being manufactured with “colder conditions”. Apparently,

if these optimal process parameters are attained the processed surface is almost unaffected by the

FSC process. Once again, Figure 4.36 illustrates one more unique capability of FSC in comparison

with alternative technologies, which definitely increases its potential as an industrial application.

72

Figure 4.36 – FS channels immediately after being produced at “colder conditions” leaving

processed surface at same level as before being processed just with a slight roughness

variation, a) serpentine path and b) straight path.

Another important aspect of FS channels that were manufactured at “colder conditions” is the

quantity of material that the FSC tool is able to pull from the base material with the probe threads as

well as, which is a critical point of the FSC process, the capacity of the shoulder base to remove to its

sides all of the base material that the probe is able to pull upwards. This capacity of the shoulder to

evacuate the material that is pulled by the probe depends on the effectiveness of the shoulder scrolls

as well as the combination of the three main process parameters: tool travel speed, tool rotation speed

and vertical downward forging force. Figure 4.37 confirms the big sized channels that correspond to

“colder conditions”, with the appropriate process parameters and adequate FSC tools.

Figure 4.37 – Top view of initial FSC trials for curing process mould prototype and 2 cut pieces

demonstrating the corresponding FS channel cross sections.

As FSC develops, it discovers new attributes that improve its potential and increase its

credibility. Unaffected processed surface and larger channels are perfect examples of those emerging

improved characteristics that enhance the potential of FSC technology and its industrial applicability.

a)

b)

73

4.3.4 Result Analysis

FSC demonstrated in the present work that it can be a solution for complex shaped

workpieces due to the challenging conditions to maintain uniform temperature along all of the

moulding surface geometry. This situation is more evident in processes such as the Optimal curing

process, in which uniform temperature along the whole workpiece is the ultimate goal. In this case, the

thermal analysis performed in this study clearly showed the potential FSC has to maintain a uniform

temperature, while heating/cooling a complex shaped workpiece along all of its geometry.

The channel manufactured for this FSC application, a curing process mould prototype, with a

serpentine path along great part of the longitudinal side of the moulding surface indicates the

possibility of introducing FSC in the heat exchanger industry. Heat exchangers need channels with

identical paths in extremely reduced spaces. Therefore, a lot of investigation and hard work has to be

performed in IST to allow FSC to produce channels with smaller sizes, longer paths and with sharper

curves. The FS channel surface roughness also needs to be taken into consideration for the heat

exchanger industry due to the pressure and temperature drops. FSC technology still has this limitation

and a solution to control it needs to be discovered.

The results obtained show that the FSC technology is still at a very initial stage and it still

needs a lot of development and follow up. A major problem still to be solved in FSC technology is the

tool material. The major obstacle encountered while producing FS channels was probe breakage. The

FSC technology is not yet completely controlled, so the process parameters are not always adequate.

Even when, process parameters are adequate probe breakage can occur due to fatigue, which also

increases with the channel path complexity especially with change in channel direction. In the FSC

process, the tool material needs to be very resistant in terms of hardness as well as resistant to

flexion. Inherent related problem arise such as: tool heating, poor channel geometry in long, curved

and sharp curved channel paths. All of these obstacles were encountered in the development of FSC,

but with a continuous increase of know-how the corresponding solutions were rapidly discovered.

Nonetheless, encouraging results were obtained, assuring an enthusiastic future for the

evolution and consequent implementation of FSC in the mould industry and possibly in the heat

exchanger industry. However, a lot of investigation and technological development is still needed for

FSC to have a successful entrance in the “industries”. FSC has all of the necessary attributes to be a

competitive alternative to conformal cooling channel producers. The ease that FSC has to produce

channels with any path also enables it to be introduced in the heat exchanger industry, but that has

not been thoroughly investigated in this dissertation. On the other hand, it is important to acknowledge

that FSC is still at a very early stage of its maturity and it still needs a long way to grow and most of all

to gain robustness. The results show FSC has high potential and adequate features to develop into a

manufacturing technology of the mould industry and perhaps the heat exchanger industry.

74

5 Global Analysis of Performed Developments

The work developed consisted in producing two prototypes that assured the real needs of their

corresponding industries as well as to add value to the existing technological limitations. The

technological implementations of this innovative solid-state manufacturing technology named Friction

Stir Channeling demonstrate the possible breakthrough, this technology can be in various industries

such as the mould and heat exchanger industries, if it follows the right steps to evolve and consolidate

its attributes and specific characteristics.

The two prototypes produced in IST demonstrated that FSC has the adequate potential to be

introduced in the mould industry, which includes injection moulding as well as open moulding

techniques. Both technologies involve heating/cooling processes that are a major contribution to the

production cycle time and quality. Consequently, they constantly need to be optimized and improved.

Either, in terms of timing or performance, these moulds produce parts that depend on the uniformity of

the heating/cooling process. The surface quality of these parts is affected by a heating/cooling process

that is not uniform along all of its geometry or in a different perspective, if it takes too long or too short

in heating/cooling the actual workpiece. Therefore, all of these parameters need to be evaluated and

optimized. Taking into consideration an industry policy: “time is money”, if the heating/cooling

channels are closer to the moulding surface, the heating/cooling process will be faster. FSC is the

solution for this constant industry quest for faster cycle times and more uniform temperatures along

the geometry of the part, which will increase the profit and surface quality of the produced part.

The major obstacle encountered throughout the technological implementations of the present

work was the breakage of the FSC tool probe (probe breakage). Probe breakage occurred due to the

fact that inadequate FSC tool material was used throughout the production of the two mould

prototypes. The appropriate tool material for this innovative process still needs to be encountered,

since the FSC tool material used nowadays does not have the adequate mechanical and thermal

properties to avoid probe breakage after a few short distanced FSC trials. After discovering the

appropriate FSC tool material, a secondary FSC limitation should be addressed. Nowadays, another

aspect of the FSC process that needs to be explored in more detail is the application of FSC

technology to other base materials other than aluminum alloys. The base material used for the

prototype production in the present work was the same aluminum alloy (AA-5083). The next important

steps to be accomplished in FSC are: determine the adequate FSC tool material and apply FSC in

another base material such as steel. However, these breakthroughs will only be accomplished with

intensive research involving various technological implementations and intensive laboratory/practical

work.

The evolution of know-how during the technological implementation of the curing process

mould prototype was evident. The capability to produce FS channels at much lower heat indexes,

demonstrated significant progressions in the FSC potential. The greater size of the channels, the less

exigent conditions for the FSC tool material and the unchanged processed surfaces are excellent

75

evidences of a great leap in the development of FSC technology. This leap completely changed the

concept of this innovative technology making it a technology closer to a plastic deformation process

than to a viscous flow of material. Consequently, the productivity and flexibility of FSC can increase

providing it with more strengths and opportunities compared to alternative technologies already

established in the industry.

Obviously, technologies that manufacture internal conformal cooling channels for moulds already

exist. However, FSC is able to produce those channels at a lower cost and at an industry standard

productivity. Taking into consideration that the industry is always searching for lower production costs

while maintaining the same productivity, FSC can be the appropriate solution the industry is looking

for. FSC can easily follow the steps of FSW and be the most important achievement in the ‘welding

world’ of the present decade. Nonetheless, it still needs countless investigations, endless hours and a

lot of money invested in its development. The industrial applications of FSC are evident and it can be

an alternative technology to the already existent ones due to its different characteristics that satisfy the

industry requirements. Especially, when it comes to complex shaped parts, FSC can be a

breakthrough technology to produce at an average rate with low production costs conformal cooling

channels with paths that are complicated to manufacture with some alternative technologies already

existing in the industry as well as very expensive with other ones.

A tough reality about the industry is that it always wants numbers, which establish and compare

the precise capabilities of all the different manufacturing technologies that are capable of helping it.

The numbers that define FSC are: the ranges of channel depth, the maximum channel length, the

minimum and maximum channel sizes, the specific channel geometry, the surface wettability of the

channels, the channel productivity rates in comparison with changes in its different characteristics as

well as the channel surface roughness. All of these numbers that specify the physical limitations of

FSC need to be determined, in order to provide the industry with proofs of its real potential.

76

6 Conclusions

The following overall conclusions result from the present study:

The results of the present work show that FSC is capable of producing internal channels with

any desirable path.

The SWOT analysis undertaken in the present work shows that FSC finds the compromise

between advantages and disadvantages of the alternative technologies and has potential to

offer solutions that no other technology in the industry provides.

The thermal analysis performed in the present work clearly showed the potential FSC has to

produce channels that maintain a uniform temperature while heating/cooling a complex

shaped workpiece along all of its geometry.

The two prototypes developed in the current work demonstrated that FSC has the adequate

potential to be introduced in the mould industry, which includes injection moulding as well as

open moulding techniques.

The results show that FSC can reduce cycle times and obtain more uniform temperatures

along the geometry of the part, increasing the profit as well as surface quality of the produced

part.

The higher productivity of FSC compared to alternative technologies is a major opportunity for

it to be implemented in various industries that depend on high productivity rates.

The rough surface finish of the processed part and of the internal channel are possible threats

to the FSC technology, but they can easily be suppressed by an evolution (which is being

developed) to improve surface finish of processed surface. On the other hand, the rough

internal channel surface finish can even aid in enhancing the heat transfer from the channels

to the moulding surfaces due to an increased wet surface (surface “wetted” by heating/cooling

fluid). Nonetheless, the pressure and temperature drops due to high surface roughness of FS

channels are still a limitation, and a possible threat, for FSC.

FSC has potential to “penetrate” the mould industry, to optimize heating/cooling times and

enhance uniform heating/cooling performance in complex shaped moulding surfaces, which

implies having a complex shaped workpiece (part).

FSC has the possibility due to its inherent process demands to operate at a very low cost,

which gives FSC a distinct aptitude in comparison with alternative conventional drilling

techniques that are present in many industries throughout the world.

77

The approach undertaken in the present work that consisted in designing a computational

solution based on which the experiments were performed, allowed to reach a good result in a

productive and cost effective way. Industrial applications will benefit from similar applications.

The technological implementation of the proposed computational solutions allowed to identify

a range of problems, typical of preliminary studies in any innovative manufacturing technology

and to pin point corresponding solutions.

The production of the two prototypes allowed to identify the high sensitivity of FSC to minimal

material and procedure alterations, namely compared to FSW. Thus, procedure development

needs to be accurate.

FSC could develop the potential to be a producer of channels (mini channels) for the heat

exchanger industry.

FSC still needs a lot of research and sustainable development to reach enough maturity, and

to eventually be introduced in its potential industries, being until now the mould and the heat

exchanger industry.

Some future work proposals would be:

A preliminary step would be to define an adequate material for probes, to avoid the current

high rate of probe breakage.

First of all, to consolidate FSC process parameters and possible FSC tool materials it is

essential to determine a certain range of process parameters and corresponding materials

that need to be thoroughly evaluated and tested.

Second, determine durability of probes and shoulders with different sizes and features.

Determine their ranges and corresponding channel lengths and sizes. Consolidate all of the

possible sets into a reference table that could be used as a base template for all FSC process

parameters.

Determine relations between all of the possible process parameters with different base

materials, as well as different materials for the FSC tool (probe and shoulder), with an inherent

goal of defining limits for material, depth, length and path ranges, which means minimums and

maximums for all of these parameters.

After determining all possible process parameters and materials that can be used, compare in

qualitative and quantitative terms with alternative technologies that were introduced in the

present study.

An immediate evolution in the FSC tool would be to increase by more or less 50% the size of

shoulder striates and to use shoulders with only one striate on each side of the probe and with

78

the surface finishing “add-in” developed by C. Vidal and P. Vilaça in IST, which can be

incorporated in any FSC tool.

At last, design and produce a FSC tool that permits variation in the z direction as it produces

internal conformal channels enabling variation of channel depth along its path, which can also

vary in any direction. This means an even greater flexibility in internal conformal channel

manufacturing.

Share FSC know-how with other researchers to boost the technological development of FSC,

such as Balasubramanian and Mishra, which were referred in the present work.

Explore the heat exchanger industry in terms of possible applications for FSC. FSC has the

capability, in the near future, to produce low cost heat exchangers at a considerable rate

owing to its capability of producing small dimension internal channels in flat or curved

surfaces, with any possible path. In this case, it is essential to take in consideration the

capability of FSC to produce internal channels with serpentine paths.

Investigate other possible industrial applications such as: (i) solar panels could be fabricated

with channels that join three thin plates by its thickness side forming channels and at the same

time welding them together; (ii) produce heating/cooling channels of heat pump systems with

serpentine paths as for the heat exchanger industry.

79

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