GAZIANTEP UNIVERSITY

ENGINEERING FACULTY

EXPERIMENTAL INVESTIGATION OF

ABRASIVE FLOW MACHINING OF TI6Al4V

SUPERVISIOR

Prof. Dr. ÖMER EYERCİOĞLU

GRADUATION PROJECT

MECHANICAL ENGINEERING

BY

ERDİ KARAÇAL

JANUARY 2014

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Abrasive Flow Machining of TI6AL4V

Abstract

Abrasive flow machining (AFM) is a non-conventional finishing process by means of whıch a wide range of applications, from die-mould industry to medical, aircraft and aerospace components in which critical components must be finished to within precise or especially demanding tolerances. Ti6Al4V displays high strength, corrosion and heat resistant properties and are commonly used in high temperature applications such as turbine blades and rocket engines. It is considered more difficult to finish using conventional techniques (grinding, lapping, etc.) than other metallic materials.This paper conducted on the finishing of these difficult to machine materials. The influence of the AFM processon Ti6Al4V workpieces were investigated. The results show that the white layer formed during WEDM is successfully removed by AFM in a few cycles for each workpiece.

Key words: Abrasive Flow Machining, Surface Roughness, EDM, Ti6Al4V

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Acknowledgements

I would like to thank to my teachers Kürşat Gov and Ömer Eyercioğlu.I have been

with them for two years and these two years have added me so many things.I have

been almost every steps of the experiments thanks to them to give me this chance.

I have gained lots of experience.This experience will be very useful to me in my

business life.Again thanks to them.

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CONTENT

Abrasive Flow Machining of TI6AL4V ................................................................................. 1

Abstract ................................................................................................................................. 1

Acknowledgements ................................................................................................................ 2

1. Introduction.................................................................................................................... 4

2. Experimental works ....................................................................................................... 5

2.1 The workpiece material .............................................................................5

2.2 The abrasive flow machine ........................................................................6

2.3 The abrasive media ....................................................................................7

2.4 Experimental procedure .............................................................................9

3. Results and discussion .................................................................................................. 10

3.1 Measurements of surface roughness ......................................................... 10

3.2 Material removal ..................................................................................... 11

3.3 SEM Images ............................................................................................ 12

3.4 White layer .............................................................................................. 14

4. Conclusions.................................................................................................................. 15

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1. Introduction

AFM process has a greater potential of being used to deburr, radius, polish and

remove recast layer of component. Basically there are three types of AFM processes.

One way,Two way and Orbital AFM. Commonly we use two way AFM. In two way

AFM process consist of two cylinder stocks, one from the lower cylinder pumping an

Abrasive laden medium throughout and one from the upper cylinder makes up one

process. The polymer abrasive medium which is used in this process possesses

trouble-free flow ability, better nature deformability and excellent abrading capacity.

For the finishing of the components which have complex unsymmetrical

shape/profile, holes and undercut, a need is being felt to expand finishing operations

which can produce parts with superior quality performance and higher productivity.

Especially the internal passages which are difficult to polish by other techniques, are

finished by AFM process successfully, workpiece holder is used to restrict the media

flow over the appropriate surfaces for external passages.

The AFM process can be successfully applied to the aerospace, aircraft, medical,

and other precision manufacturing areas.

The AFM process is an effective finishing process for difficult to machine

materials, aerospace and aircraft components. This paper is focused on the effect of

AFM process on difficult to finish material Ti6Al4V.Specimens were cut by wire

electrical discharge machine (WEDM). The surface roughness (Ra) values were

measured through and perpendicular to the abrasive media flow lines, material

removal (MR) was calculated and scanning electron microscopy (SEM) images were

taken from the surfaces before and after AFM for various processing cycles. The

improvement of the surfaces quality according to the workpiece materials were

observed and compared.

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2. Experimental works

2.1 The workpiece material

The experiments were performed on Ti6Al4V. The specimens were cut from the slabs by using wire electro discharge machine (WEDM) to 5x10x20 mm as shown in Fig.1. The WEDM parameters kept constant for all specimens to ensure the pre-surface characteristics of the specimens. The surface roughness values of the specimens before AFM are given in Table1 (Ra), the physical and chemical properties of Ti6Al4V is given in Table2

.

Fig.1.Workpiece geometry

Table1 Surface roughness values of the specimens before AFM

Ti6AL4V Specimen Ra

No (µm) Ti-01 2,78 Ti-02 2,44 Ti-03 2,22 Ti-04 2,13 Ti-05 2,66 Ti-06 2,49

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Table2 Physical, mechanical and thermal properties of some materials

Material Hardness (HRC)

Ultimate Tensile Strength (MPA)

Yield Strentgh (MPA)

Thermal Conductivity (W/m-K)

Melting Point (Degree Celcius)

Ti6Al4V 30 1170 1100 6,7 -

2.2 The abrasive flow machine

In this study a two-way AFM machine that has two vertically opposed chambers

was used (shown in Fig.2). The machine contains of a main frame, hydraulic unit,

electronic control unit and heating-cooling unit.The specifications of the machine are

given in Table3.The hydraulic unit ensures adequate movement and media pressure

that can be automatically configured. The control system is designed to control the

volume of abrasive media and the number of cycles. One cycle in two-way AFM is

composed of reciprocating motion of forward and backward of the piston ram in the

media cylinder. Thus cycle time depends on the piston speed and one cycle in the

experimental study takes 2 minutes.

Table3 Abrasive flow machine

Machine specification

Hydraulic pressure 10–400 bar

Media capacity 6litres

Stroke 400 mm

Bore diameter 140 mm

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Fig.2.Two-way abrasive flow machine

2.3 The abrasive media

The abrasive media that were prepared for the present study is a mixture of

polymeric carrier, silicon carbide (SiC) abrasive particles, and 10% of hydraulic oil.

The polymeric carrier has specific gravity of 1.0 (at 25 oC) and viscosity about 60

Pas. 180 mesh size silicon carbide (SiC) abrasives of 70% ratio by weight were used.

However, the common definition of the percentage abrasive concentration is given

by: weight of abrasive particles x 100/ (weight of abrasive media). Before

performing the experiments, the abrasive media is run for 3–5 cycles with a trial

workpiece, so as to get uniform mixing. The specifications of the abrasive media are

summarized in Table4.Also preparing the abrasive media shown in Fig.3a and Fig.3b

Table4 Abrasive media

Parameters

Viscosity 60 Pas at 25 oC

Abrasive type SiC

Mesh size 180

Abrasive concentration 70 % wt.

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Preparing the abrasive media was the hardest process for us.Our teacher

Kürşat Gov and I was working on this process very much.We have used Garnet,SiC,

B4C and Al2O3 as a raw material of abrasive media.This material was taken from

water jet cutting machines.They were washed by me as shown in Fig3a. and after

that they were sieved by me to get optimum mesh size of this material.

Fig.3a.Preparing Abrasive Media

Fig.3b.Preparing Abrasive Media

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2.4 Experimental procedure

The experiments were performed on the Ti6Al4V. The workpiece holder

(seeFig.4) was used to hold the specimens allowing the flow of abrasive media

through the WEDMed surfaces with an opening of 10x20 mm. 12 litres of abrasive

media was flown through in each cycle. The experiments were carried out for

1,3,5,10,20, 50 and 100 cycles. The AFM pressure was 10 MPa and flow rate was 3

l/min. The experiments were repeated for three specimens in each condition and the

averages of the 5 surface roughness measurements were taken by using Mitutoyo SJ

401 surface measuring machine, with the cut off length 0.8 mm. The specimens were

cleaned by ethyl alcohol and weighed before and after the experiment by using

SHIMADZU AUX220 balance.

Fig.4. Workpiece holder

This workpiece holder shown in Fig.4 is machined by wire electrical discharge machine.

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3. Results and discussion

3.1 Measurements of surface roughness

From the Fig.5 the surface roughness value decreased with increase in number of

cycles for each specimens. The surface roughness (Ra)decreased significantly in the

third cycle for Ti6Al4V specimens, the surface roughness after 20 cycles for

Ti6Al4V are decreased slightly.

Fig. 5.Surface roughness values

0

0,5

1

1,5

2

2,5

3

3,5

4

0 20 40 60 80 100

Ra

µm

Number of Cycles

SURFACE ROUGHNESS

T6Al4V

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3.2 Material removal

The Fig.6 shows that the material removal (MR) increases nonlinearly with the

increase in the number of cycles. And the rate of MR decreasing with number of

cycles. The reason for this slight decrease in material removal rate can be explained

as the result of asperities on the workpiece surface before AFM. When the abrasive

particles within the media machine the peaks, they become flatter than before and in

the following cycles, the material removal is decreased.In the case of the Ti6Al4V

workpiece total material removal is low.

Fig. 6. Change in material removal with respect to AFM cycles

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100

mg

Number of Cycle

MR

T6Al4V

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3.3 SEM Images

The EDMed surface is unlike that produced by any traditional machining

process; it is characterized by globules and random debris of re-deposited and recast

material. The high temperature changes the metallurgy of the material. The region

affected by these thermal changes is referred to as the heat-affected zone (HAZ). The

HAZ is included of a recast layer (white layer) of material that has been melted and

re-solidified at the surface, white layer that is harder than the original material;

contains micro cracks.

For B4C and SiC based media. In the case of, five and twenty cycles were

required to fully remove the globules and debris.

Microscopic photographs of the white layers for four groups of specimens are

given inthe first cycles of the AFM process, the white layer is removed for specimens

which were finished by B4C and SiC based media. From Fig.5 the improvement in

the surface roughness values are similar and best improvement was occurred in

specimens which were finished by B4C and SiC based media these results are well

agreement to each other.

After removal of the white layer, abrasion behaviours of the four groups were

changed. In the specimens (finished by B4C and SiC based media) has less smearing

and ploughing. And no indentation of the abrasive particles to the surfaces was

observed and the final surface roughness is better.

For Al2O3 based media finished specimen, the globules were fully removed from

the surface in the fifth cycle but the lay of craters were fully removed after twentieth

cycle and also have less ploughing. For specimen that were finished by Garnet based

media, the globules were fully removed in the fifth cycle, but the debris was fully

removed after fiftieth cycle.

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Fig.7.SEM images of specimens

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3.4 White layer

Fig. 8 illustrates the removal of white layer with respect to the number of AFM

cycles for DIN 1.2379 55 HRC specimens. The results of SEM images and the

sectional microscopic views are in well agreement. The white layers were fully

removed in the first cycle of B4C and SiC based media. In the case of Al2O3 and

Garnet based media, five and twenty cycles were required to fully remove the white

layers.

Fig. 3. WLT views of specimens

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4. Conclusions

I have worked almost every steps of this experiments for two years.I helped my

teacher Kürşat Gov and Ömer Eyercioğlu when productions of workpiece holder.

I have been in a part of preparing the specimens.I took away them to Organized

Industry for cutting with wire electrical discharge machine.

I have also worked when preparing the abrasive media.I sieved them for the

optimum mesh sizes.This process took our days.

We worked on parameter which is mesh size, flow rate, to understand how will

change roughness of workpiece. We worked on titanium specimen. The surface

titanium of surface roughness is tired to desired measurement by AFM.

The effect of abrasive types (SiC, Al2O3, B4C and Garnet) of WEDMed DIN

1.2379 cold-work tool steel on abrasive flow machining was investigated. From the

experimental results, the following conclusions have been derived:

The white layer formed during WEDM is successfully removed by using all

types of abrasives.

The results of SEM images and the sectional microscopic views are in well

agreement. The white layers were fully removed in the first cycle of B4C and SiC

based media. In the case of Al2O3 and Garnet based media, five and twenty cycles

were required to fully remove the white layers.

Although the trends of surface roughness measurements are similar for all media

groups, the results show that the media prepared by B4C and SiC has more surface

improvement than Al2O3 and Garnet.

The surface improvement nearly the same for B4C and SiC therefore, SiC can be

preferred due to its lower cost and better performance.

According to the desired finishing condition the Garnet can be used for its better

cost.

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REFERENCES

Gov K, Eyercioglu O, Cakir MV. Hardness Effects on Abrasive Flow Machining.

Journal of Mechanical Engineering. 2013; 59: 626-31.

Eyercioglu O, CAKIR MV, GOV K. Influence of machining parameters on the

surface integrity in small-hole electrical discharge machining. Proceedings of the

Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture.

2013.