INJECTION MOLDING OF MICRO-FEATURES

Clemson UniversityTigerPrints

All Theses Theses

8-2011

INJECTION MOLDING OF MICRO-FEATURESManjesh DubeyClemson University, [email protected]

Follow this and additional works at: https://tigerprints.clemson.edu/all_theses

Part of the Mechanical Engineering Commons

This Thesis is brought to you for free and open access by the Theses at TigerPrints. It has been accepted for inclusion in All Theses by an authorizedadministrator of TigerPrints. For more information, please contact [email protected].

Recommended CitationDubey, Manjesh, "INJECTION MOLDING OF MICRO-FEATURES" (2011). All Theses. 1184.https://tigerprints.clemson.edu/all_theses/1184

https://tigerprints.clemson.edu?utm_source=tigerprints.clemson.edu%2Fall_theses%2F1184&utm_medium=PDF&utm_campaign=PDFCoverPages

https://tigerprints.clemson.edu/all_theses?utm_source=tigerprints.clemson.edu%2Fall_theses%2F1184&utm_medium=PDF&utm_campaign=PDFCoverPages

https://tigerprints.clemson.edu/theses?utm_source=tigerprints.clemson.edu%2Fall_theses%2F1184&utm_medium=PDF&utm_campaign=PDFCoverPages

https://tigerprints.clemson.edu/all_theses?utm_source=tigerprints.clemson.edu%2Fall_theses%2F1184&utm_medium=PDF&utm_campaign=PDFCoverPages

http://network.bepress.com/hgg/discipline/293?utm_source=tigerprints.clemson.edu%2Fall_theses%2F1184&utm_medium=PDF&utm_campaign=PDFCoverPages

https://tigerprints.clemson.edu/all_theses/1184?utm_source=tigerprints.clemson.edu%2Fall_theses%2F1184&utm_medium=PDF&utm_campaign=PDFCoverPages

mailto:[email protected]

1

INJECTION MOLDING OF MICRO-FEATURES

A Thesis

Presented to

The Graduate School of

Clemson University

In Partial Fulfillment

Of the Requirements for the Degree

Master of Science

Mechanical Engineering

By

Manjesh Kumar Dubey

August 2011

Accepted by:

Dr. Laine Mears, Committee Chair

Dr. Joshua Summers

Dr. Yong Huang

ii

ABSTRACT

A method for creating regular arrays of surface features in the 10µm to 200µm range over

large areas in metallic materials enables the use of treated surfaces on injection molds.

This surface control is used for manufacturing products with controllable optical,

tribological, heat transfer, and surface tension properties. However, the flow, filling, and

solidification behavior of molten polymer at the micro scale is not well understood.

Therefore, the purpose of this study is to understand the formation of micro-structure on a

polymer surface and derive a range of robust solutions for injection molding of these

micro-featured surfaces. This study uses critical inputs of the molding process, mold

geometry, and working materials, and determines a range of feasible solutions to recreate

these micro structures without filling or de-molding defects. Five different molding

parameters hypothesized as most influential in molding microstructures were varied and

the resultant micro-features characterized using 3D surface profiling white light

interferometry and scanning electron microscopy. Regression responses were determined

and optimal value ranges for the key input parameters were identified and independent

tests run to verify the results. The five parameters tested are: injection pressure, injection

velocity, mold temperature, melt temperature and shape of micro structures. These tests

were carried out in both HDPE and EPDM/PP alloy materials using different mold insert

materials and coatings.

iii

The tests first conducted on a flat surface were repeated on a tube surface to identify if

change in geometry of component changes the formation of micro-structures.

The results obtained from these tests gave us a clear indication of how each of the above

parameters controls the formation of molded microfeatures, and how parameters interact.

In this case mold temperature was found to be the most critical factor, with a sensitivity

of only a few degrees greatly improving the micro feature formation. The biggest

concern was uniformity of micro features across the molded surface. Based on this

understanding we were also able to simulate macroscopic mold filling conditions and

verify homogeneous filling across the molded surface. These experimental results are

used to drive a predictive tool for process planning of complete undamaged feature

formation at the micro scale and uniformity at the macro scale.

It was also found that formation of structures at micro level is different from formation of

structures at macro level.

iv

DEDICATION

To my late father, for his love, support, and sacrifices made for me.

v

ACKNOWLEDGMENTS

I would like to express my gratitude to my advisor, Dr. Laine Mears, for his guidance and

support throughout my research efforts and mentoring through the Master’s program. I

would also like to thank Dr. Joshua Summers and Dr. Yong Huang for serving on my

research advisory committee.

I acknowledge the support and technical guidance of Hoowaki, LLC specially Ralph

Hulseman, Dr. Andrew Cannon, and Bradley Bailey which was of immense help during

this research. Special thanks to Dr. Thomas martens and Gary Lee Mathis of CU-ICAR

for their support and technical guidance in tooling and during tests. I would also like to

thank Kim Campbell-Djuric and Ed Martin of Autodesk for providing training and the

use of Moldflow software and AMRL, Clemson University staff for help in SEM use.

Finally, I would like to express my gratitude to my family and friends for their

continuous love and support. I will always be grateful to my father, Late Suresh Dubey

and mother Bindu Devi for their love, support and sacrifices they made for me.

vi

TABLE OF CONTENTS

ABSTRACT ............................................................................................................................ ii

DEDICATION ........................................................................................................................ iv

ACKNOWLEDGMENTS ....................................................................................................... v

TABLE OF CONTENTS ....................................................................................................... vi

LIST OF TABLES ................................................................................................................ viii

LIST OF FIGURES ................................................................................................................. x

CHAPTER 1 : INTRODUCTION ........................................................................................... 1

CHAPTER 2 : LITERATURE REVIEW ................................................................................ 5

2.1 Embossing Pillars ..................................................................................................... 5

2.2 Microinjection Molding ............................................................................................ 5

2.3 Factors affecting aspect ratios achievable in micro-injection

molding ...................................................................................................................... 6

2.4 Influence of temperature and mold surface interactions on

micro-feature replication ............................................................................................ 7

2.5 Runner size effects on micro injection molding ....................................................... 7

2.6 Effect of processing factors with one size factor on

replication capability .................................................................................................. 8

CHAPTER 3 : TOOLING AND INSTRUMENTS................................................................. 9

3.1 Design of injection molds ......................................................................................... 9

3.2 Introduction to instruments used ............................................................................. 14

CHAPTER 4 : IDENTIFICATION OF SUITABLE PATTERN

MATERIAL ...................................................................................................................... 18

CHAPTER 5 : TESTS WITH FLAT MOLD ....................................................................... 21

5.1 Tests with HDPE .................................................................................................... 22

5.2 Tests with EPDM/PP .............................................................................................. 33

vii

CHAPTER 6 : TESTS WITH TUBE MOLD ........................................................................ 44

6.1 Tests on outer surface of the tube ........................................................................... 44

6.1.1 Tests on outer surface of the tube with HDPE ............................................. 46

6.1.2 Tests on outer surface of the tube with EPDM/PP ...................................... 50

6.2 Tests on inner surface of the tube ........................................................................... 54

CHAPTER 7 : MEASUREMENT VALIDATION ............................................................... 58

7.1 Surface height geometry ......................................................................................... 58

7.2 Microscopic observations ....................................................................................... 60

CHAPTER 8 : MACROSCOPIC FLOW sIMULATION ..................................................... 65

CHAPTER 9 : THERMAL ANALYSIS ............................................................................... 68

CHAPTER 10 : CONCLUSION AND FUTURE WORK .................................................... 75

APPENDIX A ........................................................................................................................ 79

APPENDIX B ........................................................................................................................ 96

APPENDIX C ...................................................................................................................... 103

REFERENCES .................................................................................................................... 111

viii

LIST OF TABLES

Table Page

Table 3:1 Specification of injection molding machine used for

experiments .................................................................................................................. 14

Table 3:2 Specifications of interferometer used for micro-feature

measurement ................................................................................................................ 16

Table 4:1 Summery of pattern material characteristics .................................................... 18

Table 4:2 Brief description of the patterns used for experiments

with flat mold ............................................................................................................... 19

Table 5:1 Tests with pattern 1 (stainless steel insert, circular sharp

corner holes of depth 55 microns) on 1.5mm thick HDPE flat

surface. ......................................................................................................................... 23

Table 5:2 Regression results for 1.5mm thick flat HDPE

component .................................................................................................................... 29

Table 5:3 Regression results for 3.5mm thick HDPE component .................................... 29

Table 5:4 Tests results at optimum condition ................................................................... 32

Table 5:5 Tests with pattern 3 (nickel coated copper insert, oval

sharp corner holes of depth 65 microns) on 2.5mm thick

EPDM/PP flat surface .................................................................................................. 33

Table 5:6 Regression result for 2.5mm thick EPDM/PP component ............................... 40

Table 5:7 Regression result for 1.5mm thick EPDM/PP component ............................... 41

Table 6:1 Tests with Mylar film wrapped around in cavity, 1 mm

thick HDPE tube surface .............................................................................................. 47

Table 6:2 Tests with Mylar film wrapped around in cavity, 1 mm

thick EPDM/PP tube surface ........................................................................................ 51

Table 9:1 Constants used and their values ........................................................................ 69

Table B.1 Tests with pattern 1 (stainless steel insert, circular sharp


surface .......................................................................................................................... 97

ix



surface .......................................................................................................................... 98

Table B.3 Tests with pattern 3 (nickel coated copper insert, oval

sharp corner holes of depth 65 microns) on 2.5mm thick

EPDM/PP flat surface .................................................................................................. 99


corner holes of depth 55 microns) on 1.5mm thick EPDM/PP

flat surface .................................................................................................................. 100

Table B.5 Tests with Mylar film wrapped around in cavity, 1 mm

thick HDPE tube surface ............................................................................................ 101

Table B.6 Tests with Mylar film wrapped around in cavity, 1 mm

thick EPDM/PP tube surface ...................................................................................... 102

x

LIST OF FIGURES

Figure Page

Figure 1.1 Super hydro-phobicity on a micro-structured surface ........................................... 1

Figure 1.2 Flat mold component .............................................................................................. 2

Figure 1.3 Tube mold component ............................................................................................ 2

Figure 1.4 Thesis outline ......................................................................................................... 4

Figure 3.1 Core plate assembly showing type of gate and cooling in

Flat mold. .......................................................................................................................... 10

Figure 3.2 Partial cross-sectional view of the core and cavity side of

the Flat mold ..................................................................................................................... 11

Figure 3.3 HDPE component from Flat mold ....................................................................... 11

Figure 3.4 EPDM/PP component from Flat mold ................................................................. 11

Figure 3.5 Core plate assembly of Tube mold ....................................................................... 12

Figure 3.6 Partial cross-sectional view of core and cavity assembly of

the tube mold showing path of thermal fluid used for mold

temperature control ........................................................................................................... 13

Figure 3.7 HDPE Tube mold component from EDM cavity ................................................. 14

Figure 3.8 HDPE Tube mold component from Film cavity .................................................. 14

Figure 3.9 Injection molding machine and temperature control unit

used for experiments ......................................................................................................... 15

Figure 3.10 Interferometer used for micro-feature measurement

........................................................................................................................................... 16

Figure 3.11 S-3400 SEM used for measurement validation

........................................................................................................................................... 17

xi

Figure 4.1 SEM image of the Stainless Steel, circular, sharp cornered

holes .................................................................................................................................. 20

Figure 5.1 H1, H2, and H3 represent the sample feature height in area

1, 2 and 3 respectively; the arrow denotes the gate position ............................................ 22

Figure 5.2 Effect of injection pressure variation on micro-feature

height formed with pattern 1 on 1.5mm thick HDPE flat surface .................................... 24

Figure 5.3 Effect of injection velocity variation on micro-feature


Figure 5.4 Effect of melt temperature variation on micro-feature


Figure 5.5 Effect of mold temperature variation on micro-feature










Figure 5.10 Regression model prediction of micro-feature height in

plate center (Pattern 1, HDPE material, 1.5mm thick part) .............................................. 30


plate center (Pattern 1, HDPE material, 3.5mm thick part) .............................................. 31

Figure 5.12 SEM image of micro-featured flat surface molded with

pattern 3 at optimal conditions .......................................................................................... 32


height formed with pattern 3 on 2.5mm thick EPDM/PP flat

surface ............................................................................................................................... 35



surface ............................................................................................................................... 35

xii



surface ............................................................................................................................... 36



surface ............................................................................................................................... 36



surface ............................................................................................................................... 38



surface ............................................................................................................................... 38



surface ............................................................................................................................... 39



surface ............................................................................................................................... 39


plate center (Pattern 3, EPDM/PP material, 2.5mm thick

component ......................................................................................................................... 42


plate center (Pattern 3, EPDM/PP material, 1.5mm thick part) ........................................ 42

Figure 6.1 H1, H2, and H3 represent the sample feature height in area

(outer surface) 1, 2 and 3 respectively; the arrow denotes the gate

position. ............................................................................................................................. 45


height formed with Mylar film on 1 mm thick HDPE tube surface ................................. 48





xiii




height formed with Mylar film on 1 mm thick EPDM/PP tube

surface ............................................................................................................................... 52



surface ............................................................................................................................... 52



surface ............................................................................................................................... 53



surface ............................................................................................................................... 53

Figure 6.10 Colored patch (1cm2) represents the area in which micro-

features were replicated using EDM core ......................................................................... 55

Figure 6.11 Direction of ejection of the component using stripper

plate ejection ..................................................................................................................... 56

Figure 6.12 SEM Image of micro-features replicated through EDM

core on the inner surface of 1 mm thick HDPE tube ........................................................ 57

Figure 6.13 SEM Image of micro-features replicated through EDM

core on the inner surface of 1 mm thick EPDM/PP tube .................................................. 57

Figure 7.1 3D surface profile of micro-features formed with stainless

steel template showing spike like structure at the edges ................................................... 59

Figure 7.2 3D surface profile of micro-features formed with Nickel

coated Copper template showing reduced spike like structure at the

edges ................................................................................................................................. 59

Figure 7.3 SEM Image of Formed Structures. The structures filled

completely, some geometric inconsistencies were noted at the

outer edges but there was no evidence of spike-like structures ........................................ 60

Figure 7.4 SEM Images of injection molded micro-features at various

test conditions in case of tests conducted on flat surface with 55

µm holes ............................................................................................................................ 61

xiv

Figure 7.5 SEM image of formed micro-features at optimal condition.

The structures filled completely, but some geometric

inconsistencies were noted at the outer edges................................................................... 62

Figure 7.6 SEM Images of injection molded micro-features at various

test conditions in case of tests conducted on tube surface with 110

µm holes ............................................................................................................................ 64

Figure 8.1 Fill time simulation at macroscopic level on flat HDPE test

piece .................................................................................................................................. 66

Figure 8.2 Flow front temperature simulation at macroscopic level on

flat HDPE test piece .......................................................................................................... 66

Figure 8.3 Fill time simulation at macroscopic level on flat EPDM/PP

test piece............................................................................................................................ 67

Figure 8.4 Flow front temperature simulation at macroscopic level on

flat EPDM/PP test piece.................................................................................................... 67

Figure 9.1 Contour (surface) plot of steady state temperature

distribution in a 50 µm microstructure with mold temperature of

38º C and melt temperature of 250º C .............................................................................. 70

Figure 9.2 Line plot of temperature variation at the center of the 50

µm microstructure with mold temperature of 38º C and melt

temperature of 250º C ....................................................................................................... 70

Figure 9.3 Contour plot of steady state temperature distribution in 100



Figure 9.4 Line plot of temperature variation at the center of 100 µm

microstructure with mold temperature of 38º C and melt


Figure 9.5 Contour plot of steady state temperature distribution in 50



Figure 9.6 Line plot of temperature variation at center of 50 µm



xv

Figure 9.7 contour plot of steady state temperature distribution in 100



Figure 9.8 Line plot of temperature variation at the center of 100 µm



Figure A.1 Alloy steel cavity insert, flat mold, quantity - 2 .................................................. 80

Figure A.2 Alloy steel core insert, flat mold, quantity - 2 ..................................................... 81

Figure A.3 Mild steel cavity plate, flat mold, quantity - 1. ................................................... 82

Figure A.4 Mild steel core plate, flat mold, quantity - 1. ...................................................... 83

Figure A.5 Mild steel cavity back plate, tube mold, quantity - 1 .......................................... 84

Figure A.6 Mild steel cavity plate, tube mold, quantity - 1 ................................................... 85

Figure A.7 Alloy steel cavity insert, tube mold, quantity - 1 ................................................ 86

Figure A.8 Alloy steel cavity sleeve (Film), tube mold, quantity - 1 .................................... 87

Figure A.9 Alloy steel cavity sleeve (EDM), tube mold, quantity - 1 ................................... 88

Figure A.10 Mild steel core sleeve ring, tube mold, quantity - 1 .......................................... 89

Figure A.11 Alloy steel core sleeve (Film), tube mold, quantity - 1 ..................................... 90

Figure A.12 Alloy steel core sleeve (EDM), tube mold, quantity - 1.................................... 91

Figure A.13 Mild steel core cooling insert, tube mold, quantity - 1 ...................................... 92

Figure A.14 Alloy steel core insert, tube mold, quantity - 1 ................................................. 93

Figure A.15 Mild steel core insert holder, tube mold, quantity - 1 ....................................... 94

Figure A.16 Mild steel core plate, tube mold, quantity - 1 .................................................... 95

Figure C.1 SEM image of flat HDPE component molded at high

injection pressure ............................................................................................................ 104

Figure C.2 SEM image of flat HDPE component molded at low


xvi

Figure C.3 SEM image of flat HDPE component molded at high melt

temperature ..................................................................................................................... 105

Figure C.4 SEM image of flat HDPE component molded at low melt

temperature ..................................................................................................................... 105

Figure C.5 SEM image of flat HDPE component molded at high

injection velocity ............................................................................................................. 106

Figure C.6 SEM image of flat HDPE component molded at low


Figure C.7 SEM image of flat HDPE component molded at low mold

temperature ..................................................................................................................... 107

Figure C.8 SEM image of tube HDPE component molded at high


Figure C.9 SEM image of tube HDPE component molded at low



melt temperature ............................................................................................................. 108


melt temperature ............................................................................................................. 109






mold temperature ............................................................................................................ 110

11

CHAPTER 1 : INTRODUCTION

Regular and irregular arrays of surface features in the 10µm to 200µm range are being

used nowadays for manufacturing products with controllable optical, tribological, heat

transfer, and surface tension properties. However, the flow, filling, and solidification

behavior of molten polymer at the micro scale is not well understood.

This research is an attempt to derive a range of robust solutions for injection molding of

these micro-featured surfaces. The templates used for transferring micro-features to a

polymer surface were provided by Hoowaki, LLC [2], [5]-[7]. The micro-features used

for this research are used to make a surface super hydro phobic.

Figure 1.1 Super hydro-phobicity on a micro-structured surface [Ref.3: Cannon A.H. and

W.P. King, Hydrophobicity of curved microstructured surfaces Journal of Micromechanics

and Microengineering, 2010. 20(2): p. 025018.]

This study was designed to use critical inputs of the molding process, mold geometry,

and working materials, and determines a range of feasible solutions to recreate these

micro structures without filling or de-molding defects.

2

The first step in this research was to design and manufacture injection mold tools for

carrying out tests. Two different injection molds were designed and manufactured; the

idea behind doing so was to study the effect of change in component geometry on

formation of micro-structures. These molds would be called flat mold and tube mold

throughout this thesis.

Figure 1.2 Flat mold component

Figure 1.3 Tube mold component

Once the injection molds were ready several different mold materials and coatings were

tested and screened for measures of goodness related to uniformity of micro-features on

the pattern, transferability and de-molding. Based on the results of screening Stainless

steel and Ni-Cu inserts were selected for tests with flat mold and Mylar film was used for

tests with tube mold.

Five different molding parameters hypothesized as most influential in molding micro-

features: injection pressure, melt temperature, mold temperature, injection velocity, and

cavity thickness were varied during a fractional design of experiments study. In addition

to these, the effect of shape and size of micro-features was also tested. Two different

3

polymers, HDPE and EPDM/PP alloy were used for the tests to study the effect of

different molding material on micro-feature molding.

The quality of micro-feature formation / transferability was determined by analyzing the

injection molded surface under Zygo White-Light 3D Surface Profiler. This was done by

measuring the height of micro-features at 3 different locations over the molded surface to

test uniformity and to see whether or not the target height has been achieved. A multi-

variable regression analysis was done to identify most significant factors and to predict

the feature height.

Lastly, SEM (Scanning Electron Microscope) images of specimens were taken to validate

the findings. Also, an attempt to simulate the filling process for micro-features using

Moldflow [4] was made.

4

1.1 Thesis outline

Figure 1.4 Thesis outline

5

CHAPTER 2 : LITERATURE REVIEW

2.1 Embossing Pillars

In the past the impact of polymer film thickness and cavity size on polymer flow during

embossing of similar micro features has been studied for the nanoimprint lithography

process [8]. It was found that polymer deformation and fill time is governed by location

and rate of polymer shear during imprinting, exhibiting deformation predominantly close

to the vertical side wall that can result in either single peak or dual peak deformation

modes. There is no reference to observation of such modes in micro-injection molding.

2.2 Microinjection Molding

Chu et al. [9] investigated the effects of various injection molding process parameters on

the micro-molding process and part quality. They estimated the processing conditions

during the cavity filing stage in a plunger micro injection molding system by using short-

shot trials and by analyzing the data obtained from tracing the evolution of injection

pressure, runner pressure, and plunger position, at the millisecond time scale. They did

this study for three different polymers: POM, HDPE, and PC and through statistical

analysis found injection speed to be most significant factor while the effects of mold and

melt temperature varied from material to material.

In current study although Injection velocity appeared to be a significant factor, mold

temperature was found to be most significant factor for injection molding micro-features.

6

2.3 Factors affecting aspect ratios achievable in micro-injection molding

In a study conducted at Manufacturing Engineering Centre at Cardiff University, B.Sha et

al. [9] investigated the effect of five process factors and one size factor on the achievable

aspect ratios, and the role they play in producing micro components in different type of

polymer material. The factors considered for this study were: barrel temperature, mould

temperature, injection speed, holding pressure, the existence of air evacuation, and the

size of micro features. They found that for different material the key factors differed. In

case of PP and ABS the barrel temperature and the injection speed were found to be the

key factors affecting the aspect ratios of replicated micro features. In case of POM, in

addition to these two factors mold temperature was also found to be a key factor. It was

also noticed that an increase of feature sizes improves the melt flow in case of all three

material; however the increase in melt fill of the micro features did not increase linearly

with an increase of their sizes.

The finding of current research does not agree completely with the findings of the study

above. This may be because of the difference in sizes of micro features used for the

studies. The current research was done mostly on sub 100 µm micro features where as in

their experimental set up B.Sha et al. [9] used micro features in the form of “rectangular

legs” of width 250 or 500 µm and depth 70 or 100 µm. However the phenomenon of

“increase of feature sizes improves the melt flow” was observed in the current study too.

7

2.4 Influence of temperature and mold surface interactions on micro-feature

replication

In a thesis presented to the Graduate School of Clemson University, Varun Thakur [11]

assessed micro-feature replication at elevated mold temperature and ambient pressure

using a variety of polymers and commonly used mold surfaces. The study was conducted

on four different polymers; HDPE, PP, PMMA and PS. Factors affecting feature

replication were determined and it was found that through high mold temperatures it is

possible to achieve good feature replication.

Although the method used for replicating micro-features was different from the method

used in the current study, mold temperature was found to be a key factor for replicating

micro-features in both studies.

2.5 Runner size effects on micro injection molding

C.A. Griffiths, S.S. Dimov, and E.B. Brousseau conducted an experimental study at

Manufacturing Engineering Centre, Cardiff University [12] to investigate the flow

behavior of the polymer melts in micro cavities with a particular focus on the relationship

between the filling of micro parts and the size of the runner system. They studied the

filling performance of spiral like micro cavities as a function of runner size in

combination with melt temperature, mold temperature, injection speed and holding

pressure. DOE approach was followed and PP and ABS were used as test polymers. This

study showed that for both PP and ABS, 2mm size runner had optimum surface to

8

volume ratio and shear heating balance in regard to filling performance. It was observed

that an increase in runner dimension did not have a positive effect. This study also related

temperature and pressure to filling and with the help of simulation it was reported that

polymer properties play an important role in selecting runner design for micro cavities.

In current study the effect of runner system was not studied, mostly because the tests

were conducted with single and double cavities. Hence, the runner systems most suitable

to these cavities were chosen for the study.

2.6 Effect of processing factors with one size factor on replication capability

Yao D and Kim B. [13] investigated the effect of five processing factors together with

one size factor on replication capabilities of the microinjection molding process within

the conventional mold temperature scope. The tests were conducted with ABS, PP and

POM. They found that in case of PP and ABS, barrel temperature and the injection speed

were key factors while replicating micro features. In case of POM mold temperature

together with barrel temperature and injection speed was found to be most important.

They also found that use of air evacuation can increase the replication quality of micro

injection molding. Increase in depth and width of micro features helped in getting better

melt flow. Also significance of holding pressure was investigated.

9

CHAPTER 3 : TOOLING AND INSTRUMENTS

This chapter provides a brief description of the type of injection mold tools used for the

experiment. Injection molding machine used for this test and interferometer and SEM

used for measurement validation are also described briefly.

3.1 Design of injection molds

Two different injection molds were designed and manufactured for the experiments. The

idea behind doing so was to study the effect of change in component geometry on the

formation of micro-features on an injection molded surface. To save on cost and time the

basic structure of both the molds was kept same and minimum possible changes were

made.

Injection mold tool for flat component (44mm x 24mm) was designed as a two cavity

side gated mold. The cavity depth was kept constant at 5mm for both the cavities and the

variation in component thickness was achieved by varying the thickness of micro-

featured patterns placed inside the cavities. Pin ejection was used for ejecting out the

components as this is most preferred and economical way of ejecting out flat

components. For heating/cooling of the cavity and core side channel type of cooling was

used.

10

Figure 3.1 Core plate assembly showing type of gate and cooling in Flat mold.

The black arrow marks in Figure 3.1 show the inlet and outlet of cooling/heating fluid

flowing inside the cooling circuit.

A temperature control unit with microprocessor control of +/- 1º F over temperature of

thermal fluid was used to regulate the mold temperature.

11

Figure 3.2 Partial cross-sectional view of the core and cavity side of the Flat mold

Figure 3.3 HDPE component from Flat mold

Figure 3.4 EPDM/PP component from Flat

mold

Injection mold tool for tube component (flange dia. 44mm, body dia. 32mm with 2 º

draft, height 35mm and flange dia. 44mm, body dia. 26mm with 2 º draft, height 62mm)

12

was designed as a single cavity side gated mold. Ideally, unless it is a multi cavity mold,

these kind of tools are designed as top gated tools but since this mold was built as a

changeover tool on the flat mold base with minimum changes to facilitate both flat and

tube mold tests, it had to be designed as side gated tool.

Figure 3.5 Core plate assembly of Tube mold

Fan gate was used to facilitate the filling and stripper plate ejection was used to eject out

the component.

For temperature control of the mold, baffle type of cooling/heating channels were used in

the core side. This gave a better control over uniformity of temperature distribution over

the core surface.

13

Figure 3.6 Partial cross-sectional view of core and cavity assembly of the tube mold showing

path of thermal fluid used for mold temperature control

14

Figure 3.7 HDPE Tube mold component

from EDM cavity

Figure 3.8 HDPE Tube mold component

from Film cavity

3.2 Introduction to instruments used

FANUC MILACRON ROBOSHOT S2000i-B Injection molding machine was used for

the experiment. It uses precise all electric injection molding technology. Precise control

over injection pressure, barrel temperature and injection velocity can be achieved.

Table 3:1 Specification of injection molding machine used for experiments

ROBOSHOT

Injection

Size Range

(g)

Clamp

Stroke

(mm)

Max.

Daylight

(mm)

Min.

Mold

Thickness

(mm

Platen

Size (mm)

S2000i 17B 8.0-18.0 160 420 130 355 x 340

15

Wittmann TEMPRO plus temperature control unit was used for temerature control of

injection molding dies. The tempering medium is pumped in the die loop in a closed

cycle by the pump and returns to heat exchanger. The instrument precision is 1º F,

resulting in a constant temperature in the injection-molding tool within +/- 1º F.

Figure 3.9 Injection molding machine and temperature control unit used for experiments

Courtsey: CU-ICAR

Zygo NewView 7200 Interferometer was used for measuring the height and quality of

micro-features. Some important specifications of the interferometer are shown in Table

3:2.

16

Table 3:2 Specifications of interferometer used for micro-feature measurement

Measurement Technique Non-contact, three-dimensional, scanning white light

interferometry.

Scanner Closed-loop piezo-based, with high linear capacitive

sensors

Image zoom Single user-interchangeable zoom lenses (5x and 20x)

Field of view Objective and zoom dependent; from 0.03 to 14mm; large

area imaged with field stitching

Vertical Scan Range 150 µm; Extended scan range to 20 mm

Vertical Resolution < 0.1 n

Lateral Resolution 0.36 to 9.50 µm; objective dependent

Figure 3.10 Interferometer used for micro-feature measurement

Courtesy: CU-ICAR

17

S-3400N Scanning Electron Microscope (SEM) was used for measurement validation.

It is designed for conventional and variable pressure microscopy. It is equipped with an

Oxford INCA EDS, WDS, EBSD and built-in four quadrant solid-state backscatter

detector. Also has SEM imaging capability in variable pressure.

Figure 3.11 S-3400 SEM used for measurement validation

Courtesy: Clemson University

18

CHAPTER 4 : IDENTIFICATION OF SUITABLE PATTERN MATERIAL

Several materials and coatings were screened for measures of goodness related to

uniformity of micro features on the pattern, transferability and de-molding prior to actual

experiment. The summary of results is shown in Table 4:1

Table 4:1 Summery of pattern material characteristics

Material

Uniformity of

micro-features

on patterns

Transferability of

micro-features to

injection molded

surface

Remarks

Silicon rubber Good Average De-molding

issues

Epoxy Average Bad High de-molding

issues

Stainless steel Good Good No de-molding

issues

Ni coated copper Very good Very good Excellent de-

molding

Teflon coated stainless steel Good Very good No de-molding

issues

Based on these results, stainless steel and Ni coated copper were selected as pattern

material for the extended study in case of flat mold. In case of tube mold MYLER film

was used for extensive study for ease of operations. Use of MYLAR film gave flexibility

to wrap the film around cavity walls to replicate micro-features on the outer surface of

the tube. Stainless steel was used as template material for replicating micro-features on

the inner surface of the tube. Brief description of the patterns used for experiments with

flat mold is shown in Table 4:2.

19

Table 4:2 Brief description of the patterns used for experiments with flat mold

Pattern

number Material Shape Corner Depth (µm) Zygo 3D Profile

1 Stainless

steel Circular Sharp 55

2 Stainless

steel Circular Sharp 27

3

Nickel

coated

copper

Oval Sharp 65

4 Stainless

steel Circular Filleted 67

The depth of holes in MYLER film used for tube molding was found to be in the range of

102-114 µm.

20

The patterns selected for actual experiment were also analyzed and SEM images were

taken to identify any surface defects. SEM Image of one such pattern is shown in Figure

4.1

Figure 4.1 SEM image of the Stainless Steel, circular, sharp cornered holes

21

CHAPTER 5 : TESTS WITH FLAT MOLD

A fractional design of experiments (DOE) study was carried out to quantify the effect of

the following injection molding parameters on micro-feature formation: injection

pressure, melt temperature, mold temperature, injection velocity. In order to understand

the effect of component thickness on replication of micro-features, the same test was

carried out with two different component thicknesses. To test the effect of micro-feature

geometry and size the tests were carried out separately with all four pattern types

described in Table 4:2. Tests with holes of sharp and filleted corner conditions were done

to investigate the effect of corner geometry. Two different polymers, HDPE and

EPDM/PP alloy were used for the tests. In addition to this an optimality test was carried

out and with the help of regression analysis and trial runs optimal conditions to replicate

micro-features of a particular size range using HDPE were established. The tool and

apparatus used for these tests have already been described in chapter 3. The patterns used

for the tests have been described in Chapter 4.




test uniformity and to see whether or not the target height has been achieved. The areas in

which feature height H was recorded are marked as area 1, 2, and 3 in Figure 5.1.

22

Figure 5.1 H1, H2, and H3 represent the sample feature height in area 1, 2 and 3

respectively; the arrow denotes the gate position

5.1 Tests with HDPE

DOE study was conducted by varying four different parameters; injection pressure, melt

temperature, mold temperature and injection velocity. All other molding parameters

including cycle time were kept constant. Table 5:1 shows the intervals of variation. The

tests and the results shown in the table were carried out with pattern 1(stainless steel

insert, circular sharp corner holes of depth 55 microns). Similar tests were carried out

with all other patterns with component thickness of both 1.5 and 3.5mm. Since the tests

were conducted with stainless steel and nickel coated copper inserts, de-molding was not

an issue and hence chances of micro-feature deformation during de-molding got

minimized. To enhance the integrity of study, tests were carried out randomly and not in

the sequence shown in the Table 5:1.

23

Table 5:1 Tests with pattern 1 (stainless steel insert, circular sharp corner holes of depth 55

microns) on 1.5mm thick HDPE flat surface

Pattern

number

Molding parameters

Height of

micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

1

15 250 55 15 16 5 7

20 250 55 15 48 20 23

25 250 55 15 52 38 35

30 250 55 15 54 49 44

20 240 55 15 52 32 33

20 260 55 15 50 22 32

20 270 55 15 51 29 36

20 280 55 15 54 53 44

20 250 38 15 7 3 7

20 250 55 5 25 6 6

20 250 55 10 44 12 8

20 250 55 20 55 31 28

The height recorded in area 1, 2 and 3 has been represented as H1, H2 and H3

respectively in Table 5:1. The recorded heights were then plotted against injection

pressure, melt temperature, mold temperature, and injection velocity. Resulting graphs in

case of tests carried out with pattern 1 (stainless steel insert, circular sharp corner holes of

depth 55 microns) on 1.5mm thick HDPE flat surface have been discussed below.

24

Figure 5.2 Effect of injection pressure variation on micro-feature height formed with

pattern 1 on 1.5mm thick HDPE flat surface

Figure 5.3 Effect of injection velocity variation on micro-feature height formed with pattern

1 on 1.5mm thick HDPE flat surface

25

Figure 5.4 Effect of melt temperature variation on micro-feature height formed with


Figure 5.5 Effect of mold temperature variation on micro-feature height formed with


26

The sensitivity plots, Figure 5.2 to Figure 5.5 show the effect of injection pressure,

injection velocity, melt temperature, and mold temperature on replication of micro-

features. It is evident from these plots that each of these four parameters influences the

replication of microfeatures when stainless steel pattern with circular sharp corner holes

of depth 55 microns was used to produce 1.5mm thick HDPE part.

When the same insert was used to produce 3.5mm thick parts the results were similar but

the sensitivity changed. Figure 5.2 to Figure 5.5 show the effect of injection pressure,


features in case of 3.5 mm thick HDPE parts.



27

Figure 5.7 Effect of injection velocity variation on micro-feature height formed with pattern

1 on 3.5mm thick HDPE flat surface



28



When compared, the sensitivity plots for both 1.5 mm and 3.5 mm thick parts indicate

that all four parameters influence the replication of micro-features in case of HDPE.

However the degree of influence varies.

Multi-variable regression was performed by ANOVA for identification of significant

factors. The objective of doing so was to identify most critical parameter and to develop a

model for predicting the height of micro-features at a given setting. The resultant models

for prediction of feature height in the center of a test sample in HDPE with micro features

replicated using pattern 1 are shown below:

29

The regression equation to predict height of micro-feature in centre of flat part in case of

1.5 mm thick HDPE part is:

H1 = - 248 + 1.86 P + 0.277 Tm + 1.24 T0 + 1.64 V

Table 5:2 Regression results for 1.5mm thick flat HDPE component

Predictor Coefficient SE coefficient T P

Constant -247.72 79.84 -3.10 0.017

P 1.8611 0.8218 2.26 0.058

Tm 0.2772 0.2744 1.01 0.346

T0 1.2361 0.3419 3.62 0.009

V 1.6389 0.8218 1.99 0.086

S = 9.66962 R-Sq = 78.4% R-Sq (adj) = 66.1%


3.5 mm thick HDPE part is:

H1 = - 278 + 2.18 P + 0.322 Tm + 1.23 T0 + 2.22 V

Table 5:3 Regression results for 3.5mm thick HDPE component


Constant -277.83 87.87 -3.16 0.016

P 2.1833 0.9045 2.41 0.047

Tm 0.3217 0.3021 1.06 0.322

T0 1.2250 0.3763 3.26 0.014

V 2.2167 0.9045 2.45 0.044

S = 10.6429 R-Sq = 78.7% R-Sq (adj) = 66.5%

30

From the equations above it can be interpreted that all four parameters have a significant

role in replicating micro-features using HDPE. In case of 1.5 mm thick HDPE part the

most significant parameter was injection pressure (P) followed by injection velocity (V)

and mold temperature (T0). Melt temperature (Tm) was found to be least significant. In

case of 3.5 mm thick HDPE part the most significant parameter was injection velocity

(V) followed by injection pressure (P) and mold temperature (T0). Melt temperature

(Tm) was found to be least significant.

Regression models for both 1.5 mm and 3.5 mm part are shown in Figure 5.10 and Figure

5.11 respectively.

Figure 5.10 Regression model prediction of micro-feature height in plate center (Pattern 1,

HDPE material, 1.5mm thick part)

31


HDPE material, 3.5mm thick part)

On the basis of sensitivity plots, regression analysis and some trial run an optimum

condition was achieved to replicate micro-features of a particular range on HDPE flat

surface. Table 5:4 shows the results of tests done at: injection pressure 25 MPa, injection

velocity 20 mm/sec, melt temperature 280℃ and mold temperature 140℃.

The results obtained indicated that by adjusting the four significant factors (injection

pressure, injection velocity, melt temperature and mold temperature) it is possible to

achieve an optimum condition to replicate micro-features of a particular size range on flat

HDPE surface. Once the optimal conditions for replicating micro-features were achieved

using pattern 1, the same test was repeated with all other patterns. Irrespective of change

in pattern material, change in shape and corner conditions target height was achieved

across a size range of 27 to 67 micron.

32

Table 5:4 Tests results at optimum condition

Insert Material Shape Corner

Hole

depth

(µm)

Height of micro

features on

molded surface

(µm)

H1 H2 H3

1 SS circular Sharp 55 54 54 54

2 SS circular Sharp 27 27 27 26

3 Ni-Cu oval Sharp 65 62 65 65

4 SS Circular Filleted 67 67 67 67

Figure 5.12 is a SEM image of micro-features formed with pattern 3 at optimal

conditions. It can be noticed that micro-features appear to be fully formed. More about

SEM validation has been discussed in chapter 8.

Figure 5.12 SEM image of micro-featured flat surface molded with pattern 3 at optimal

conditions

33

5.2 Tests with EPDM/PP

The methodology of tests with EPDM/PP was similar to the tests with HDPE. However

certain material property based parameters had to be changed. DOE study was conducted

by varying four different parameters; injection pressure, melt temperature, mold

temperature and injection velocity. All other molding parameters including cycle time

were kept constant. Table 5:5 shows the intervals of variation.

Table 5:5 Tests with pattern 3 (nickel coated copper insert, oval sharp corner holes of depth

65 microns) on 2.5mm thick EPDM/PP flat surface

Pattern

number

Molding parameters

Height of

micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

3

15 220 55 15 41 54 61

20 220 55 15 57 62 62

25 220 55 15 58 62 62

30 220 55 15 58 63 63

20 200 55 15 44 54 60

20 210 55 15 46 58 60

20 230 55 15 52 62 65

20 240 55 15 56 62 62

20 220 38 15 15 25 41

20 220 55 5 51 63 63

20 220 55 10 55 61 64

20 220 55 20 61 62 62

34

The tests and the results shown in the table were carried out with pattern 3 (Nickel coated

copper, Oval sharp corner holes of depth 65 microns). Ni-Cu inserts were included in the

extensive experiments because EPDM/PP tends to stick to metal surfaces at higher

temperature. Ni-Cu patterns because of their excellent de-molding property hence were

the obvious choice. Similar tests were carried out with all other patterns with component

thickness of both 2.5 and 3.5mm. To enhance the integrity of study, tests were carried out

randomly and not in the sequence shown in the Table 5:5.

As in the case of HDPE, in the case of EPDM/PP too the recorded heights in the area1, 2

and 3 were plotted against injection pressure, melt temperature, mold temperature, and

injection velocity. Resulting graphs in case of tests carried out with pattern 3 (Nickel

coated copper, Oval sharp corner holes of depth 65 microns) on 2.5mm thick EPDM/PP

flat surface have been discussed below.

35


pattern 3 on 2.5mm thick EPDM/PP flat surface

Figure 5.14 Effect of injection velocity variation on micro-feature height formed with


36





37

The sensitivity plots, Figure 5.13 to Figure 5.16 show the effect of injection pressure,


features when Ni-Cu pattern with oval sharp corner holes of depth 65 microns was used

to produce a flat 2.5 EPDM/PP surface. Like in the case of HDPE in the case of

EPDM/PP too all these four parameters appear to influences the replication of

microfeatures. However the degree of influence was found to be different. More about

this has been discussed in regression analysis section of this chapter.

To produce 3.5mm thick parts Pattern 1 (stainless steel insert, circular sharp corner holes

of depth 55 microns) was used. The results were similar but the sensitivity changed,

indicating that component thickness too is an aspect which can influence the formation of

micro-features on a polymer surface. Figure 5.17 to Figure 5.20 show the effect of

injection pressure, injection velocity, melt temperature, and mold temperature on

replication of micro-features in case of 1.5 mm thick EPDM/PP parts.

38



Figure 5.18 Effect of injection velocity variation on micro-feature height formed with


39





40

Multi-variable regression was performed by ANOVA for identification of significant

factors. The objective of doing so was to identify most critical parameter and to develop a

model for predicting the height of micro-features at a given setting. The resultant models

for prediction of feature height in the center of a test sample in EPDM/PP are shown

below:


2.5 mm thick EPDM/PP part molded using pattern 3 is:

H1 = - 198 + 0.967 P + 0.300 Tm + 1.23 T0 + 0.267 V

Table 5:6 Regression result for 2.5mm thick EPDM/PP component


Constant -197.67 43.61 -4.53 0.003

P 0.9667 0.4330 2.23 0.061

Tm 0.3000 0.1622 1.85 0.107

T0 1.2333 0.1796 6.87 0.000

V 0.2667 0.4330 0.62 0.557

S = 5.12928 R-Sq = 89.3% R-Sq (adj) = 83.2%


1.5 mm thick EPDM/PP parts molded using pattern 1 is:

H1 = - 78.5 + 0.029 P + 0.130 Tm + 0.602 T0 + 1.20 V

41

Table 5:7 Regression result for 1.5mm thick EPDM/PP component


Constant -78.47 20.29 -3.87 0.006

P 0.0287 0.2015 0.14 0.891

Tm 0.13000 0.07549 1.72 0.129

T0 0.60230 0.08358 7.21 0.000

V 1.2046 0.2015 5.98 0.001

S = 2.38709 R-Sq = 92.4% R-Sq (adj) = 88.1%

From the equations above it can be interpreted that all four parameters have a significant

role in replicating micro-features using EPDM/PP. In case of 2.5 mm thick EPDM/PP

parts the most significant parameter was mold temperature (T0) followed by injection

pressure (P) and melt temperature (Tm). Injection velocity (V) was found to be least

significant. In case of 1.5 mm thick EPDM/PP parts the most significant parameter was

injection velocity (V) followed by mold temperature (T0) and melt temperature (Tm).

Injection pressure (P) was found to be least significant.

The differences in degree of significance of different factors when component thickness

and pattern material is changed indicate that both of these factors have a role in

replication of micro-features. Regression models for both 1.5 mm and 3.5 mm part are

shown in Figure 5.21 and Figure 5.22 respectively.

42


EPDM/PP material, 2.5mm thick component


EPDM/PP material, 1.5mm thick part)

43

On the basis of sensitivity plots, regression analysis and some trial run, an attempt was

made to find optimum condition to replicate micro-features of a particular range on

EPDM/PP flat surface. However, unlike in the case of HDPE, optimum conditions in the

case of EPDM/PP could not be found. The reason of this may have been inability to

conduct tests at higher mold temperature. EPDM/PP tends to stick to the mold surface at

higher mold temperatures and this caused sprue bush clogging when tests were conducted

at high mold temperatures. Hot runner system may provide an answer to this problem but

due to cost constraints, tests with hot runner system could not be done in the current

research.

44

CHAPTER 6 : TESTS WITH TUBE MOLD

A fractional design of experiments (DOE) study was carried out to quantify the effect of

the following injection molding parameters on micro-feature formation on a tube surface:

injection pressure, melt temperature, mold temperature, injection velocity. The main

objective of these tests was to compare the results obtained to results from flat surface in

order to study the effect of change in component geometry and feed system on replication

of micro-features.

Micro-features were replicated on both outer and inner surface of the tube using two

different techniques. Two different polymers, HDPE and EPDM/PP alloy were used for

the tests. The tool and apparatus used for these tests have already been described in

Chapter 3.

6.1 Tests on outer surface of the tube

Micro features were produced on the outer surface of the tube by placing a Mylar film

inside the cavity. The micro-features in the film were 110 microns in diameter and 102-

114 micron deep.

45




test uniformity and to see whether or not the target height has been achieved and since

unlike flat patterns the depth of the holes in the film was not constant, each reading was

repeated twice and a mean was used to plot graphs and interpreting results. The accuracy

of measurement in the case of tube surface might be less than the accuracy of

measurements on flat surface. The reason can be attributed to the complex geometry of

the tube surface.

Two different polymers, HDPE and EPDM/PP alloy were used for the tests. The feature

height H was recorded in area 1, 2, and 3 and denoted in Figure 6.1.

Figure 6.1 H1, H2, and H3 represent the sample feature height in area (outer surface) 1, 2

and 3 respectively; the arrow denotes the gate position.

46

The mold temperature values for these tests are the mean of mold temperatures recorded

at different sections of core and cavity.

6.1.1 Tests on outer surface of the tube with HDPE

The methodology of the tests was similar to tests conducted on flat surface. Table 6:1

shows the intervals of variation and the results of the interferometer analysis. Unlike in

the case of flat surface, the results of micro-feature height measurement have been

represented as a range in this case and not a single number. This was done because the

depth of the holes varied from 102 to 114 microns all across the film surface and hence

for a better representation multiple height readings were taken in a particular area. The

minimum and maximum heights from each area are shown in the Table 6:1. For sensitivity

plots mean of these heights were used.

The sensitivity plot shown in Figure 6.2 represents the response height variation with

injection pressure for HDPE material. In this plot, the dashed lines represents the mold

depth and since the depth of the holes varied from 102 to 114 microns all across the film

surface, the target height is represented by the interval between LSL and USL. The

47

effects of the other molding parameters on micro-feature formation have been represented

similarly in Figure 6.3 – Figure 6.5.

Like in the case of tests on flat surface in the case of tests on tube surface too tests were

carried out randomly and not in the sequence shown in the Table 6:1, to enhance the

integrity of the study.

Table 6:1 Tests with Mylar film wrapped around in cavity, 1 mm thick HDPE tube surface

Pattern

type

Molding parameters Height of micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

Mylar

film

15 250 54 15 104-

114

108-

112

102-

104

20 250 54 15 111-

119

104-

107 107-

114

25 250 54 15 104-

107

107-

111 109-

111

30 250 54 15 114-

116

104-

109 107-

116

20 240 54 15 104-

111

104-

111 107-

114

20 260 54 15 104-

107

107-

109 104-

107

20 270 54 15 102-

109

109-

114 102-

104

20 280 130 15 104-

107

109-

111 107-

114

20 250 38 15 109-

114

107-

114 109-

114

20 250 54 5 104-

107

107-

112 107-

111

20 250 54 10 109-

113

107-

109 99-

102

20 250 54 20 107-

116

114-

116 107-

109

48

Figure 6.2 Effect of injection pressure variation on micro-feature height formed with Mylar

film on 1 mm thick HDPE tube surface

Figure 6.3 Effect of injection velocity variation on micro-feature height formed with Mylar


49

Figure 6.4 Effect of melt temperature variation on micro-feature height formed with Mylar


Figure 6.5 Effect of mold temperature variation on micro-feature height formed with Mylar


50

The plots obtained above were different when compared to the HDPE plots in case of

tests done on flat mold surface. This difference was not expected. In case of tests with flat

mold the effect of various molding parameters could be seen clearly in the plots. In this

case no special trends or effects of molding parameters were noticed. After running some

more tests it was hypothesized that the difference in behavior of micro-feature replication

is because of the size of features in the templates used. After a certain size, features stop

behaving like micro-features and start to form like any other regular feature. To make

sure that difference in tool had no effect on the results obtained patterns having110µm

features were placed in flat mold cavity and tests were run. The results obtained were

similar to results obtained from tube mold. Features formed completely at even low mold

temperatures. This strengthened our hypothesis about micro-feature size.

6.1.2 Tests on outer surface of the tube with EPDM/PP

The methodology of tests with EPDM/PP was similar to the tests with HDPE. However

certain material property based parameters had to be changed. DOE study was conducted

by varying four different parameters; injection pressure, melt temperature, mold

temperature and injection velocity. Same Mylar film with features 110 microns in

diameter and 102-114 micron deep was used for tests with EPDM/PP too. All other

molding parameters including cycle time were kept constant. Table 6:2 shows the intervals

of variation.

51

Table 6:2 Tests with Mylar film wrapped around in cavity, 1 mm thick EPDM/PP tube

surface

Pattern

type


features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

Mylar

film

15 220 88 15 103-

108

110-

112

102-

112

20 220 88 15 111-

114

109-

114

108-

110

25 220 88 15 104-

108

109-

110

102-

103

30 220 88 15 114-

118

111-

115

114-

115

20 200 88 15 93-

97

97-

111

114-

115

20 210 88 15 112-

114

107-

112

104-

107

20 230 88 15 111-

113

109-

116

111-

112

20 240 88 15 109-

114

112-

114

95-

97

20 220 65 15 104-

114

107-

109

112-

114

20 220 88 5 109-

115

109-

112

100-

102

20 220 88 10 107-

109

116-

119

98-

102

20 220 88 20 105-

107

109-

112

107-

114

The sensitivity plot shown in Figure 6.6 – Figure 6.9 represent the response height

variation with various molding parameters for EPDM/PP material. Dashed lines represent

the mold depth. Since the depth of the holes varied from 102 to 114 microns all across

the film surface, the target height is represented by the interval between LSL and USL.

52

Figure 6.6 Effect of injection pressure variation on micro-feature height formed with Mylar

film on 1 mm thick EPDM/PP tube surface

Figure 6.7 Effect of injection velocity variation on micro-feature height formed with Mylar


53

Figure 6.8 Effect of melt temperature variation on micro-feature height formed with Mylar


Figure 6.9 Effect of mold temperature variation on micro-feature height formed with Mylar


54

The plots obtained above are very similar to the HDPE plots. This strengthens earlier

proposed hypothesis that the difference in behavior of micro-feature replication is

because of the size of features in the templates used. After a certain size, features stop

behaving like micro-features and start to form like any other regular feature.

Parameters like melt temperature, mold temperature, injection velocity, injection

pressure, and polymer material which were found to be significant while replicating

micro-features up to 67µm in size were found not so significant when the micro-feature

size was kept above 100µm.

6.2 Tests on inner surface of the tube

Tests on inner surface of the tube were conducted with an alloy steel core. The micro-

features were produced on the steel core by EDM (Electrical discharge machining) over

approximately 1 cm2 area. These micro-features were 66µm to 75µm deep with a

diameter of 70µm.

The objective of this testing was to investigate the effect of method of producing micro-

features on their transferability to a polymer surface. Tests were carried out by varying

different molding parameters and observing their effect. However a complete DOE study

55

was not carried out because the depth of micro features in the core template itself was not

constant. Figure 6.10 shows the area in which micro-features were replicated. Tests were

carried out with both HDPE and EPDM/PP.

Figure 6.10 Colored patch (1cm2) represents the area in which micro-features were

replicated using EDM core

During molding some deformation of micro-features was noticed. This deformation was

noticeable to naked eyes also. The deformation was more prominent in the case of HDPE

components. The reason for this deformation can be attributed to the mold tool itself.

Since solid alloy steel core pin was used for molding with stripper plate ejection

mechanism it caused micro-features to distort as the ejection mechanism was creating a

shear force as shown in the Figure 6.11. HDPE is stiffer than EPDM/PP; this caused

56

more distortion in HDPE micro-features. This type of deformation can be eliminated or

minimized by using split cores.

Figure 6.11 Direction of ejection of the component using stripper plate ejection

In addition to the above mentioned phenomenon, surface finish of the pattern may also

have contributed to deformation. The evidence of which can be seen in the SEM images,

Figure 6.12 and Figure 6.13.

Fixed

Steel core

Micro-featured

component

Ejection

force

57

Figure 6.12 SEM Image of micro-features replicated through EDM core on the inner

surface of 1 mm thick HDPE tube

Figure 6.13 SEM Image of micro-features replicated through EDM core on the inner

surface of 1 mm thick EPDM/PP tube

58

CHAPTER 7 : MEASUREMENT VALIDATION

This chapter deals with some irregularities during height measurement with the

interferometer and how they were overcome. SEM analysis of test pieces has also been

discussed. SEM images were taken to validate the findings and to make sure that the

results obtained from interferometer height measurement were reliable.

7.1 Surface height geometry

When the micro-features formed by injection molding were analyzed under Zygo White-

Light 3D Surface Profiler some spike like features were observed, mostly at the edges.

The amount of these spike like features decreased when Ni-Cu patterns were used for

molding. The surface finish of the Ni-Cu patterns used for the tests was lot better when

compared to stainless steel patterns also the geometry of the micro-features was different.

However when the same samples were observed under SEM no evidence of spikes was

found. A SWLI image of a part with numerous spike anomalies is shown in Figure 7.1,

and a part with few spikes is given in Figure 7.2.

59

Figure 7.1 3D surface profile of micro-features formed with stainless steel template showing

spike like structure at the edges

Figure 7.2 3D surface profile of micro-features formed with Nickel coated Copper template

showing reduced spike like structure at the edges

Initially it was hypothesized that the spike features were de-molding defects due to

adhesion at the feature wall, as some observation of tear away microfeatures that

remained in the mold had been observed in extreme cases. Investigation of these

60

anomalies was carried out using scanning electron microscopy but no evidence of such

spike like structures was found under SEM giving rise to a possibility that these

structures might just be measurement artifact resulting from software issue where the

sharp high aspect features were out of bounds for some light reflection data smoothing

algorithm used by the SWLI. An SEM image of a “spiky” part is given in Figure 7.3.

Figure 7.3 SEM Image of Formed Structures. The structures filled completely, some

geometric inconsistencies were noted at the outer edges but there was no evidence of spike-

like structures

7.2 Microscopic observations

SEM images validated the findings of this study about the effect of various injection

molding parameters such as injection pressure, melt temperature, mold temperature, and

injection velocity on formation/transferability of micro-features in case of tests done on

flat surface where the micro-feature size was between 27 and 67 microns. Figure 7.4

61

shows a representative comparison of HDPE samples for high and low values of the

levels tested.

HIGH LOW IN

JE

CT

ION

PR

ES

SU

RE

30 Mpa 15 Mpa

INJE

CT

ION

VE

LO

CIT

Y

20mm/sec. 5mm/sec.

ME

LT

TE

MP

ER

AT

UR

E

280ºC 240ºC

MO

LD

TE

MP

ER

AT

UR

E

55ºC 38ºC

Figure 7.4 SEM Images of injection molded micro-features at various test conditions in case

of tests conducted on flat surface with 55 µm holes

62

Injection pressure shows fully-formed structures at the higher level; melt temperature

variation had little effect, and mold temperature variation was significant. This is

consistent with the regression model results.

The Optimal values determined in the case of HDPE flat surface were run, with

geometric results shown in Figure 7.5. Structures are fully formed and geometrically

consistent. Some surface inconsistencies in the formed micro-features can be attributed to

the features present in the molding template itself.

Figure 7.5 SEM image of formed micro-features at optimal condition. The structures filled

completely, but some geometric inconsistencies were noted at the outer edges

63

In case of tests done on tube surface with 110 µm holes, the SEM images obtained

validated our findings about the effect of various injection molding parameters such as

injection pressure, melt temperature. Figure 7.6 shows a representative comparison of

HDPE samples for high and low values of the levels tested.

The above figure gives a clear indication that after a certain size micro-features start to

form like any other regular feature. Since both tests were conducted with different

tooling, to ensure that the difference in results are not just because of change of tooling,

tests were done on flat surface with 110 micron holes and similar results were obtained.

64

HIGH LOW

INJE

CT

ION

PR

ES

SU

RE

30 Mpa 15 Mpa

INJE

CT

ION

VE

LO

CIT

Y

20mm/sec. 5mm/sec.

ME

LT

TE

MP

ER

AT

UR

E

280ºC 240ºC

MO

LD

TE

MP

ER

AT

UR

E

55ºC 38ºC

Figure 7.6 SEM Images of injection molded micro-features at various test conditions in case

of tests conducted on tube surface with 110 µm holes

65

CHAPTER 8 : MACROSCOPIC FLOW SIMULATION

An attempt was made to simulate the filling process for micro-features using Autodesk

Moldflow and compare results with experimental data obtained. For this a Moldflow

environment very similar to actual experimental set up was prepared. The boundary

conditions for the Moldflow simulation were obtained from experimental runs but the

process could not be simulated at such micro level mainly due to meshing limitations.

Macroscopic simulation of the filling of the mold cavity was successfully done with both

HDPE and EPDM/PP in case of flat mold. For this micro-features were scaled 50 times

their actual size, the overall component size was kept same. This was done to predict

various factors like packing pressures, temperature and viscosity at filling for different

mold conditions. The fill time plots and temperature front plots were helpful in

understanding the process of polymer filling inside the cavities.

However the simulation results from macroscopic structures could not be related to

experimental results of microscopic structures. Some important macroscopic simulation

results are shown in Figure 8.1 to Figure 8.4.

66

Figure 8.1 Fill time simulation at macroscopic level on flat HDPE test piece

Figure 8.2 Flow front temperature simulation at macroscopic level on flat HDPE test piece

67

Figure 8.3 Fill time simulation at macroscopic level on flat EPDM/PP test piece

Figure 8.4 Flow front temperature simulation at macroscopic level on flat EPDM/PP test

piece

68

CHAPTER 9 : THERMAL ANALYSIS

This section is an attempt to explain the probable cause of difference between formations

of micro-features of different size. To explain the earlier proposed hypothesis that after a

certain size (in this case 100 µm) micro-features start to form like any other regular

feature, thermal analysis of two features of two different cross-sectional areas was carried

out. The first feature was 50 µm in diameter and the second 100 µm in diameter. The

height of both was kept same at 50 µm.

A simple heat conduction model was solved in steady state and the results and plots

obtained are shown below:

ambk T h T T Q

Q VCpT

Where, K is the thermal conductivity of HDPE, h is the heat transfer co-efficient between

HDPE and the mold surface, T is the melt temperature, ∇T is the temperature gradient,

Tamb is the mold temperature, Q is the heat content of the melt, ρ is the density of HDPE,

V is the volume and Cp is the specific heat of HDPE.

69

Following boundary conditions and assumptions were used;

At time t=0, the mold cavity is completely filled with the melt temperature being

250º C.

The thermal conductivity and the heat transfer coefficient are assumed to be

constant.

The heat possessed by the melt reduces continuously due to heat dissipation to the

mold.

Table 9:1 Constants used and their values

Constants Value Units

K 0.38 W/mK

h 200 W/m2K

ρ 930 kg/m3

Cp 1900 J/kgK

T 250 C

Tamb 38 and 55 C

70

Figure 9.1 Contour (surface) plot of steady state temperature distribution in a 50 µm

microstructure with mold temperature of 38º C and melt temperature of 250º C

Figure 9.2 Line plot of temperature variation at the center of the 50 µm microstructure with

mold temperature of 38º C and melt temperature of 250º C

71

Figure 9.3 Contour plot of steady state temperature distribution in 100 µm microstructure

with mold temperature of 38º C and melt temperature of 250º C

Figure 9.4 Line plot of temperature variation at the center of 100 µm microstructure with


72

From the above plots it is clear that as the cross-sectional area increases, there is a

decrease in rate of heat transfer. This means that in case of 100 µm microfeatures the

flow front inside the features remains at a higher temperature for longer time. Higher

temperature helps the liquid flow by keeping the viscosity low.

Viscosity and temperature relation is given by Andrade’s equation:

B TDe

Where D and B are constants and T is absolute temperature. In the above relation,

viscosity varies exponentially as temperature. So as the temperature value increases,

viscosity decreases.

When the same tests were repeated at elevated mold temperature (55ºC) similar results

were obtained but the temperature gradients observed were lesser. If we compare plots of

50 µm features at 38ºC and 55 ºC, the heat dissipation rate at 55 is lesser.

This again helps in keeping the flow front at higher temperatures for longer

time and thus aides in better formation of micro-features.

73

Figure 9.5 Contour plot of steady state temperature distribution in 50 µm microstructure


Figure 9.6 Line plot of temperature variation at center of 50 µm microstructure with mold

temperature of 55º C and melt temperature of 250º C

74

Figure 9.7 contour plot of steady state temperature distribution in 100 µm microstructure


Figure 9.8 Line plot of temperature variation at the center of 100 µm microstructure with


75

CHAPTER 10 : CONCLUSION AND FUTURE WORK

This study was used to derive a range of robust solutions for injection molding of micro-

featured surfaces with different polymers. Feasible conditions to form these micro-

features were obtained for two different polymers, HDPE and EPDM/PP alloy.

Several Mold material and coating were screened for measures of goodness related to

uniformity of micro features on the pattern, transferability and de-molding. Nickel coated

copper was found to be most suitable pattern material.

Effect of various injection molding parameters; injection pressure, melt temperature,

mold temperature, and injection velocity on replication of micro-features was studied

and their significance was determined. In addition to these factors effect of

component thickness and micro-feature size was also studied. It was noticed that

the factor of significance of these parameters vary with polymer material and

thickness of the component. For instance, In case of 1.5 mm thick HDPE part the

most significant parameter was injection pressure (P) followed by injection velocity (V)

and mold temperature (T0). Melt temperature (Tm) was found to be least significant. In

case of 3.5 mm thick HDPE part the most significant parameter was injection velocity

(V) followed by injection pressure (P) and mold temperature (T0). Melt temperature

(Tm) was found to be least significant. In case of 2.5 mm thick EPDM/PP parts the most

significant parameter was mold temperature (T0).

76

Using Design of Experiments technique, a regression model was derived for

predicting the height of surface microfeatures in an HDPE and EPDM/PP alloy

injection molding operation.

The study was conducted on two different component types with varying

geometry. Also the effect of micro-feature sizes on replication was studied. It was

noted that after a certain size micro-features start to form like any other regular

feature but as long as they are below that critical size (in our case 65 micron),

some molding parameters like injection pressure and mold temperature play a

greater role than others in micro-feature formation.

Thermal analysis was done to explain the difference between replication of 50 µm

features and 100 µm features and it was hypothesized that, as the micro-feature

size increases, the heat dissipation decreases. This keeps the flow front at higher

temperature and thus at lower viscosity which in turn helps the filling of cavities.

An attempt was made to simulate the flow at micro level in Moldflow.

Future work may include tests with other polymers. Future work in flow

simulation for microfeatures can be to isolate and scale the microfeatures for

77

accurate meshing, while maintaining constant non-dimensional flow properties

(e.g., Reynolds number) for accuracy. Also, the numerical simulation results could

be combined with the different regression analyses to improve the distribution of

height predictions and make a better feasible process plan.

Reasons for the surface residue or delamination appearance can be investigated.

78

APPENDICES

79

APPENDIX A

CAD DRAWINGS OF FLAT MOLD AND TUBE MOLD

This section contains Cad drawings used for manufacturing core and cavity parts of both

flat and tube mold.

80

Figure A.1 Alloy steel cavity insert, flat mold, quantity - 2

81

Figure A.2 Alloy steel core insert, flat mold, quantity - 2

82

Figure A.3 Mild steel cavity plate, flat mold, quantity - 1.

83

Figure A.4 Mild steel core plate, flat mold, quantity - 1.

84

Figure A.5 Mild steel cavity back plate, tube mold, quantity - 1

85

Figure A.6 Mild steel cavity plate, tube mold, quantity - 1

86

Figure A.7 Alloy steel cavity insert, tube mold, quantity - 1

87

Figure A.8 Alloy steel cavity sleeve (Film), tube mold, quantity - 1

88

Figure A.9 Alloy steel cavity sleeve (EDM), tube mold, quantity - 1

89

Figure A.10 Mild steel core sleeve ring, tube mold, quantity - 1

90

Figure A.11 Alloy steel core sleeve (Film), tube mold, quantity - 1

91

Figure A.12 Alloy steel core sleeve (EDM), tube mold, quantity - 1

92

Figure A.13 Mild steel core cooling insert, tube mold, quantity - 1

93

Figure A.14 Alloy steel core insert, tube mold, quantity - 1

94

Figure A.15 Mild steel core insert holder, tube mold, quantity - 1

95

Figure A.16 Mild steel core plate, tube mold, quantity - 1

96

APPENDIX B

DOE VALUES FOR FLAT AND TUBE COMPONENTS

This section contains experimental values of the micro-feature height at various test

conditions.

97

Table B.1 Tests with pattern 1 (stainless steel insert, circular sharp corner holes of depth 55


Pattern

number

Molding parameters

Height of

micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

1

15 250 55 15 16 5 7

20 250 55 15 48 20 23

25 250 55 15 52 38 35

30 250 55 15 54 49 44

20 240 55 15 52 32 33

20 260 55 15 50 22 32

20 270 55 15 51 29 36

20 280 55 15 54 53 44

20 250 38 15 7 3 7

20 250 55 5 25 6 6

20 250 55 10 44 12 8

20 250 55 20 55 31 28

98



Pattern

number

Molding parameters

Height of

micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

1

15 250 55 15 13 16 45

20 250 55 15 51 51 56

25 250 55 15 48 51 55

30 250 55 15 54 52 54

20 240 55 15 47 50 52

20 260 55 15 46 51 53

20 270 55 15 51 50 55

20 280 55 15 47 50 49

20 250 38 15 2 3 6

20 250 55 5 22 22 48

20 250 55 10 15 15 46

20 250 55 20 48 52 50

99

Table B.3 Tests with pattern 3 (nickel coated copper insert, oval sharp corner holes of depth

65 microns) on 2.5mm thick EPDM/PP flat surface

Pattern

number

Molding parameters Height of

micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

3

15 220 55 15 41 54 61

20 220 55 15 57 62 62

25 220 55 15 58 62 62

30 220 55 15 58 63 63

20 200 55 15 44 54 60

20 210 55 15 46 58 60

20 230 55 15 52 62 65

20 240 55 15 56 62 62

20 220 38 15 15 25 41

20 220 55 5 51 63 63

20 220 55 10 55 61 64

20 220 55 20 61 62 62

100


microns) on 1.5mm thick EPDM/PP flat surface

Pattern

number

Molding parameters

Height of

micro-

features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

3

15 220 55 15 47 47 53

20 220 55 15 46 53 51

25 220 55 15 50 51 51

30 220 55 15 46 48 57

20 200 55 15 43 52 46

20 210 55 15 50 51 52

20 230 55 15 49 49 52

20 240 55 15 50 49 52

20 220 38 15 29 33 49

20 220 55 5 35 25 37

20 220 55 10 39 36 47

20 220 55 20 51 52 56

101

Table B.5 Tests with Mylar film wrapped around in cavity, 1 mm thick HDPE tube surface

Pattern

type


features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

Mylar

film

15 250 54 15 104-

114

108-

112

102-

104

20 250 54 15 111-

119

104-

107 107-

114

25 250 54 15 104-

107

107-

111 109-

111

30 250 54 15 114-

116

104-

109 107-

116

20 240 54 15 104-

111

104-

111 107-

114

20 260 54 15 104-

107

107-

109 104-

107

20 270 54 15 102-

109

109-

114 102-

104

20 280 54 15 104-

107

109-

111 107-

114

20 250 38 15 109-

114

107-

114 109-

114

20 250 54 5 104-

107

107-

112 107-

111

20 250 54 10 109-

113

107-

109 99-

102

20 250 54 20 107-

116

114-

116 107-

109

102

Table B.6 Tests with Mylar film wrapped around in cavity, 1 mm thick EPDM/PP tube

surface

Pattern

type


features (µm)

Injection

pressure

(Mpa)

Melt

temperature

(ºC)

Mold

temperature

(ºC)

Injection

velocity

(mm/sec)

H1 H2 H3

Mylar

film

15 220 88 15 103-

108

110-

112

102-

112

20 220 88 15 111-

114

109-

114

108-

110

25 220 88 15 104-

108

109-

110

102-

103

30 220 88 15 114-

118

111-

115

114-

115

20 200 88 15 93-

97

97-

111

114-

115

20 210 88 15 112-

114

107-

112

104-

107

20 230 88 15 111-

113

109-

116

111-

112

20 240 88 15 109-

114

112-

114

95-

97

20 220 65 15 104-

114

107-

109

112-

114

20 220 88 5 109-

115

109-

112

100-

102

20 220 88 10 107-

109

116-

119

98-

102

20 220 88 20 105-

107

109-

112

107-

114

103

APPENDIX C

SEM IMAGES OF FLAT MOLD AND TUBE MOLD COMPONENTS

This section contains SEM images of samples molded at various test conditions.

104

Figure C.1 SEM image of flat HDPE component molded at high injection pressure

Figure C.2 SEM image of flat HDPE component molded at low injection pressure

105

Figure C.3 SEM image of flat HDPE component molded at high melt temperature

Figure C.4 SEM image of flat HDPE component molded at low melt temperature

106

Figure C.5 SEM image of flat HDPE component molded at high injection velocity

Figure C.6 SEM image of flat HDPE component molded at low injection velocity

107

Figure C.7 SEM image of flat HDPE component molded at low mold temperature

Figure C.8 SEM image of tube HDPE component molded at high injection pressure

108

Figure C.9 SEM image of tube HDPE component molded at low injection pressure

Figure C.10 SEM image of tube HDPE component molded at high melt temperature

109

Figure C.11 SEM image of tube HDPE component molded at low melt temperature

Figure C.12 SEM image of tube HDPE component molded at high injection velocity

110

Figure C.13 SEM image of tube HDPE component molded at low injection velocity

Figure C.12 SEM image of tube HDPE component molded at low mold temperature

111

REFERENCES

[1] Santoprene 121-M 50, Exxon-Mobil Corp.

[2] Hoowaki, LLC, Greenville, SC, USA

[3] Cannon A.H. and W.P. King, Hydrophobicity of curved microstructured surfaces

Journal of Micromechanics and Microengineering, 2010. 20(2): p. 025018

[4] Autodesk Moldflow 2011

[5] Cannon, A.H., et al., “Molding ceramic microstructures on flat and curved surfaces

with and without embedded carbon nanotubes.” Journal of Micromechanics and

Microengineering, 2006. 16(12): p. 2554-2563.

[6] Cannon, A.H. and W.P. King, “Casting metal microstructures from a flexible and

reusable mold.” Journal of Micromechanics and Microengineering, 2009. 19(9): p.

095016.

[7] Cannon, A.H. and W.P. King, “Microstructured Metal Molds Fabricated via

Investment Casting.” Journal of Micromechanics and Microengineering, 2010.

20(2): p. 025025.

[8] Rowland, H.D., et al., “Impact of polymer film thickness and cavity size on polymer

flow during embossing: toward process design rules for nanoimprint lithography.”

Journal of Micromechanics and Microengineering, 2005. 15(12): p. 2414-2425.

[9] Jingsong Chu, Musa R. Kamal, Salim Derdouri, Andy Hrymak, “Characterization of

the Microinjection Molding Process.” Polymer Engineering and Science, 2010

p.1214-1225.

[10] B.Sha, S.S. Dimov, D.T. Pham and C.A. Griffiths, “Study of Factors Affecting

Aspect Ratios Achievable in Micro-injection Moulding.” Manufacturing Engineering

Centre, Cardiff University, Cardiff CF24 3AA, UK.

[11] Varun Thakur, “Influence of temperature and polymer/mold surface interactions on

micro-feature replication at ambient pressure in micro injection molding”, A thesis

presented to Graduate School of Clemson University, 2006.

112

[12] C. A. Griffiths, S. S. Dimov, E. B. Brousseau, “Micro injection moulding: an

experimental study on the relationship between the filling of micro parts and runner

design.” Manufacturing Engineering Centre, Cardiff University, Cardiff CF24 3AA,

UK.

[13] Yao D and Kim B., Manufacturing Science and Engineering, Vol. 126 (2004) PP

733-739.

[14] Usama M. Attia, Silvia Marson and Jeffrey R. Alcock, “Micro-Injection Moulding of

Polymer Microfluidic Devices.” Microfluidics and Nanofluidics, Volume 7, Number

1, July 2009, Pages 1-28.

[15] Piotter V., Hanemann T., Ruprecht R., and Hausselt J., “Injection molding and

related techniques for fabrication of microstructures.” Microsystem Technologies,

1997. 3(3): p. 129-133.

[16] Heckele M., Schomburg W. K., “Review on micro molding of thermoplastic

polymers.” Journal of Micromechanics and Microengineering, 2004. 14(3).

[17] Donggang Y. and Byuang K. “Injection molding high aspect ratio microfeatures.”

Journal of injection molding technology, 2002. 6(1): p 11-17.

[18] Michaeli W. and Gartner R. “Injection Molding of Micro-Structured Surfaces.”

ANTEC-2004.

Documents

INJECTION MOLDING OF MICRO-FEATURES