ELECTRICAL DISCHARGE MACHINING OF SILICON CARBIDE USING

COPPER ELECTRODE

ARASH MAZAHERI SARABI

A project report submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Mechanical Engineering

(Advanced Manufacturing Technology)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

JANUARY 2013

iii

To my beloved Mother and Father

iv

ACKNOWLEDGEMENTS

Here, I would like to express my special thanks to my project supervisor,

Associate Professor Hamidon Bin Musa for his continuous and valuable advice and

guidance. He has given me inspiration and motivation to realize this project and

carry on facing new challenges in experiment.

Moreover I also would like to extend my deepest gratitude to all lecturers of

Faculty of Mechanical Engineering. I also wish to thank Mr. Aidid, Mr. Sazali and

Mr. Roslin and all the FKM technical staff for their help and guidance during the

implementation of the project.

Lastly, I would like to thank everyone who was involved directly or indirectly

in completing this project. May all your contribution, kindness and support receive

the full blessing from God.

v

ABSTRAK

Silikon karbida adalah bahan semikonduktor yang menjadi popular kerana

ciri-ciri yang istimewa. Tetapi, kegunnannya adalah terhad disebabkan kesukaran

pemprosesan. Proses pemesinan termaju didapati menjadi cara yang terbaik dan

ekonomi untuk memesin bahan ini. Walanbagaimanpun, parameter tertentu perlu

dikawal untuk memastikan ketepatan dan kecekapan proses. Kajian ini

membentangkan analisis beberapa parameter dalam pemesinan terhadap bahan ini.

Silikon karbida yang digunakan dalam kajian ini terhad kepada jenis Reaction

Bonded Silicon Carbide (SiSiC).

Kesan Beberapa parameter menetapkan seperti on-time (ON), discharge

current (I), off-time (OFF) dan Kekutuban (Pol) pada kadar pembuangan bahan

(MRR), surface roughness (Ra), nisbah kehausan alat (TWR), dan kekasaran

permukaan (Ra) dikaji. Analisis telah dilakukan menggunakan Pakar Rekabentuk

Perisian design expert dengan melaksanakan keadah reka bentuk eksperimen.

Daripada analisis ini, kesan yang signifikan ditentukan. Seterusnye, model

matematik yang mengambil kira kesan yang penting sahaja dibangunkan. Dalam

usaha untuk memastikan kesahihan model, Ujian pengesahan dilakukan dengan tiga

parameter persediaan yang berbeza. Akhirnya, tetapan optimum untuk mendapatkan

kadar pembuangan bahan maksimum, nisbah ke hausan alat minimum dan kekasaran

permukaan minimum ditentukan.

Secara keseluruhannya, hasil kajian menunjukkan bahawa kesan denyutan

pada masa dan Kekutuban adalah dominan bagi semua tindak balas yang terlibat.

vi

ABSTRACT

Silicon Carbide is the semiconductor material that becoming popular because

of its special characteristic. But, its application is limited due to processing difficulty.

Advance machining process is found to be the best and economic way to fabricate

this material. However, certain parameters need to be controlled for controlling the

accuracy and efficiency of the process. This study presents analysis of some

parameters in EDM machining of this material. The Silicon Carbide used for the

study is limited to Reaction Bonded Silicon Carbide (SiSiC).

Several effects of parameter setting such as on-time (ON), discharge current

(I), off-time (OFF) and polarity (Pol) on material removal rate (MRR), surface

roughness (Ra), tool wear ratio (TWR), and surface roughness (Ra) is studied. The

analysis was done using Design Expert Software by implementing design of

experiment method. From this analysis, the significant effect(s) is determined. From

that, the mathematical models that consist of only significant effect(s) are

established. In order to ensure validity of the model, conformation run is done with

three different parameters setup. Finally, the optimum setting to get maximum

material removal rate, minimum tool wear ratio and minimum surface roughness is

determined.

Overall, the results show that the effects of pulse on-time and Polarity are

dominant for all responses established.

vii

Table of contents

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRAK v

ABSTRACT vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xv

LIST OF APPENDIXES xvi

1 Introduction 1

1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objective of the Research 4

1.4 Scope of the Research 4

1.5 Research Question 5

1.6 Significance of the Study 5

2 Literature Review 6

2.1 Electric discharge machining (EDM) 6

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2.1.1 Mechanism of material removal 9

2.1.2 EDM electrodes 14

2.1.3 Dielectric fluid 15

2.2 Surface Roughness Parameter 18

2.2.1 Difference between Form, Waviness and

Surface Roughness 19

2.3 Material Removal Rate (MRR) 20

2.4 Tool Wear Ratio (TWR) 20

2.5 Tool Polarity 21

2.6 Ceramic Materials 22

2.6.1 Electrical Conductivity of Ceramic Materials 24

2.6.2 Silicon Carbide 25

2.7 Reaction Bonded Silicon Carbide 27

2.7.1 Application 28

2.7.2 Method of Fabrication 30

2.7.3 Machinability 30

2.8 Previous Research 31

3 Methodology 35

3.1 Introduction 35

3.2 Experimental Design 37

3.2.1 Dependant Variables 37

3.2.2 Independent Variables 39

3.2.3 Constant Parameters 40

3.3 Experiment Plan 41

3.4 Sampling Design 42

3.5 Research Equipment 44

3.6 Data Collection 45

3.7 Data Analysis 45

4 Results and Analysis 46

4.1 Introduction 46

4.2 Experimental Results and Analysis 47

4.2.1 Experimental Results 48

4.2.1.1 Material Removal Rate, MRR 48

ix

4.2.1.2 Tool Wear Ratio, TWR 50

4.2.1.3 Surface Roughness, Ra 51

4.2.2 Experimental Analysis 53

4.2.2.1 MRR Analysis 53

4.2.2.2 Tool Wear Ratio Analysis 63

4.2.2.3 Ra Analysis 72

4.3 Mathematical Model 80

4.3.1 Model for MRR 81

4.3.2 Model for TWR 82

4.3.3 Model for Ra 82

4.4 Optimum Condition 83

4.4.1 Maximum MRR 84

4.4.2 Minimum TWR 84

4.4.3 Minimum Ra 85

4.5 Confirmation Run 86

5 Discussion 91

5.1 Introduction 91

5.2 Selection of Parameters 92

5.3 Material Removal Rate (MRR) 93

5.4 Tool Wear Ratio (TWR) 95

5.5 Surface Roughness (Ra) 96

5.6 Satisfaction of All Machining Responses (Multi-Objective) 98

6 Conclusion and Recommendation 107

6.1 Introduction 107

6.2 Recommendation 110

Reference 111

Appendixes 114

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LIST OF TABLES

TABLE

NO. TITLE PAGE

2.1 Electrode Polarities For Different Workpiece Materials 22

2.2 Categories Of Engineering Ceramics 24

2.3 Previous Research Summary 32

3.1 Levels Of Running The Experiment 39

3.2 Constant Parameters 41

3.3 Physical And Mechanical Properties Of SiSiC 43

3.4 Machine And Equipment 44

4.1 Results for MRR 49

4.2 Results for TWR 50

4.3 Results for Ra 52

4.4 Suggested Setting for Maximum MRR 84

4.5 Suggested Setting for Maximum TWR 85

4.6 Suggested Setting for Maximum Ra 86

4.7 Optimum condition setting for parameters 87

4.8 Predicted and Actual Response 89

4.9 Residual and Response for Each Run 90

5.1 Suggested Solution for Optimum Condition That Satisfies All

Responses

99

xi

LIST OF FIGRES

FIGURE NO. TITLE PAGE

2.1 Principles of Electro discharge sinking 8

2.2 Typical EDM pulse current train for

controlled pulse generator

9

2.3 Variation of voltage with time using an RC

generator

10

2.4 Voltage and current waveforms during EDM 11

2.5 EDM spark description 11

2.6 Periodic discharges in RC-type generator 12

2.7 EDM schematic 14

2.8 Common dielectric flushing modes 16

2.9 Various methods for dielectric flushing 18

2.10 Comparison between Form, Waviness and

Roughness

19

2.11 Types of electrode wear in EDM 21

2.12 Specific Electrical Conductivities of Various

Materials

25

2.13 Microstructure of a SiSiC Material Made

from Sic Powder with a Mean Particle Size

23µm Without Doping; Light: Si, dark: SiC

28

2.14 Process Chain for Producing Laser Sintered

SiSiC

29

xii

2.15 Material Removal Rate versus Pulse Duration for

Die Sinking of Different Types of SiC

31

3.1 Operational Framework (Research Design) 36

3.2 Analysis Steps 38

3.3 Experiment Plan 43

3.4 Operational Framework (Sampling Design) 42

4.1 Half Normal Probability Plot for MRR 53

4.2 Normal Probability Plot for MRR 54

4.3 Revised ANOVA (MRR) 55

4.4 Revised ANOVA after the Augment Design

(MRR)

56

4.5 Determination of R-Square 57

4.6 Box Cox Plot (MRR) 57

4.7 Interaction Plot on same Time (MRR) 58

4.8 Three-Dimensional Surface Plot (MRR-with

Negative Polarity)

59

4.9 Three-Dimensional Surface Plot (MRR-with

Positive Polarity)

59

4.10 Contour Plot (MRR) 60

4.11 Interaction Plot (MRR) 61

4.12 Perturbation Plot (MRR) 61

4.13 Normal Plot of Residuals (MRR) 62

4.14 Residuals versus Predicted (MRR) 62

4.15 Half-Normal Probability Graph (TWR) 63

4.16 Revised ANOVA (TWR) 64

4.17 Determination of Prediction R-Square (TWR) 64

4.18 Box Cox Plot (TWR) 65

4.19 Factor A on a Time (TWR) 66

4.20 Factor B on a Time (TWR) 66

4.21 Factor C on a Time (TWR) 67

4.22 Factor D on a Time (TWR) 67

4.23 Three-Dimensional Surface Plot (TWR) 68

4.24 Contour Plot (TWR) 69

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4.25 Interaction Plot (TWR) 69

4.26 Perturbation Plot (TWR) 70

4.27 Normal Plot of Residuals (TWR) 71

4.28 Residuals versus Predicted (TWR) 71

4.29 Half-Normal Probability Graph (Ra) 72

4.30 Revised ANOVA (Ra) 73

4.31 Determination of Prediction R-Square (Ra) 74

4.32 Box Cox Plot (Ra) 74

4.33 Factor A on a Time (Ra) 75

4.34 Factor B on a Time (Ra) 76

4.35 Factor C on a Time (Ra) 76

4.36 Factor D on a Time (Ra) 77

4.37 Three-Dimensional Surface Plot (Ra) 77

4.38 Contour Plot (Ra) 78

4.39 Interaction Plot (Ra) 78

4.40 Perturbation Plot (Ra) 79

4.41 Normal Plot of Residuals for Response (Ra) 79

4.42 Residuals versus Predicted (Ra) 80

4.43 Predicted Response Value for the Predicted

Condition

87

4.44 Prediction Response for Condition Never Run

Before

88

4.45 Set 1 88

4.46 Set 2 89

4.47 Set 3 89

5.1 Surface Plot Graph for Optimum Condition

(MRR)

(Main effect D (Polarity) on the highest level)

101

5.2 Surface Plot Graph for Optimum Condition

(MRR)

(Main effect D (Polarity) on the lowest level)

102

5.3 Surface Plot Graph for Optimum Condition

(TWR)

103

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(Main effect D at high level)

5.4 Surface Plot Graph for Optimum Condition

(TWR)

(Main effect D at Low level)

104

5.5 Surface Plot Graph for Optimum Condition (Ra)

(Main effect D at low level)

105

5.6 Surface Plot Graph for Optimum Condition (Ra) 106

xv

LIST OF SYMBOLS

MRR Material Removal Rate

TWR Tool Wear Ratio

Ra Surface Roughness

SiC Silicon Carbide

SiSiC Siliconised Silicon Carbide

Adj R-Square Adjusted R-Square

Pred R-Square Predicted R-Sqaure

Std. Dev. Standard Deviation

EDM Electrical Discharge Machining

DOE Design of Experiment

ANOVA Analysis of Variance

xvi

LIST OF APPENDIXES

APPENDIX TITLE PAGE

A Surface Roughness Out put 100

B Run Order Generated by design

Expert

113

C Scanning Electron Microscopy

Result

115

D Equipment 118

CHAPTER 1

INTRODUCTION

1.1 Introduction

In this age of technology and development, humans try to solve a lot of

problems and at the same time bring in many new materials. Silicon carbide ceramic

is one of the materials that has been invented especially for the automotive and

aerospace industry. It is an unusual material that is widely used in structural

applications because of its properties of excellent oxidation resistance, high

mechanical strength at elevated temperature, high hardness, high corrosion

resistance, high thermal conductivity and high thermal shock resistance impact due

to strong covalent Si-C bonds. But, because of the properties of this material, it

makes SiC difficult to be machined by conventional method. [1]

2

With the invention of Silicon Carbide, Electro Discharge Machining (EDM)

is playing an important role because it can remove material through erosion

regardless of the material hardness. This is due to the fact that no cutting force will

be induced during machining. Other than silicon carbide, any material that is

electrically conductive can be machined through this process. [1, 2]

This research is conducted to mainly evaluate the machining performance of

Silicon carbide using copper electrode which is a highly conductive and easy to

machine material. The majority of silicon carbide material types are expensive.

Because of that, proper planning on manufacturing is critical. Improper planning and

lack of machining data or suitable parameter setting will increase the waste of

material, time and finally increase the manufacturing cost. By this statement, it

shows that research in this area is really important to be performed. [3]

1.2 Problem Statement

EDM is a non-conventional machining technology that focuses on machining

of super hard conductive material. Because of this potential, it is extensively used

specially in the automotive and aerospace industries. Like conventional machining

operation, some suitable parameter settings need to be determined before conducting

the machining operation. It is to ensure that the machining process will be done in an

efficient and accurate manner. Every material that has different material properties

will have different suitability of parameter setting. For EDM operation, the

conductivity and melting temperature of material will play an important role. Many

other machining parameters will also influence its processing. Hence the best

3

solution to get a high machining efficiency is by developing appropriate

mathematical models for the specific material in hand. [4]

Diverse researches have been done on this machining process including the

selection of machining parameter for different materials in order to get best results.

But, until now the study is far from extensive. Although there is up-to-date data base

that comes together with the machine, it only covers for certain parameters and for

some material. Furthermore, the manufacturer’s guidelines for the selection of

machining parameters are traditional in nature and do not ensure finest and

economically efficient use of the machines. [3]

In EDM, the major challenge is to minimize the overcut and also to get the

maximum material removal rate (MRR) in regard to the best surface roughness (of

course when doing finishing job). [5]

Previous researches have been carried out on the machining of various types

of ceramic materials using EDM. However studies involving die sinking EDM

Siliconised Silicon Carbide (SiSiC) are few. As mentioned earlier, only electrically

conductive materials can be machined using this method. Silicon carbide that has

electrical resistance of more than 100 Ω cm will affect the EDM machining

efficiency. This study will be carrying out to investigate the relationship between the

certain parameters of machining and quality parameters of EDM process involving

SiSiC. [4, 6, 7]

4

1.3 Objective of the Research

The objectives of this study are:

(i) To identify the significant machining parameters and their effect on material

removal rate (MRR), surface roughness (Ra) and overall tool wear ratio

(TWR).

(ii) To identify the optimum setting for maximum material removal rate (MRR),

minimum surface roughness (Ra), minimum tool wear ratio (TWR)

Overall, the main objective of the project is to analyze the parameter settings of

EDM on SiSiC.

1.4 Scope of the Research

The scopes of this research are:

(i) The material that will be used is limited to reaction bonded silicon carbide

(RBSiC).

(ii) Discharge On-Time, Discharge Current, Off-Time and Tool polarity will

be studied as machining parameters.

(iii) Material Removal Rate, Tool Wear Ratio and Surface Roughness will be

studied as Quality Parameters.

(iv) Copper electrode will be employed.

(v) DOE will be used in this study.

5

1.5 Research Question

The research questions for this study are:

(i) What are the parameter settings that significant on the material removal rate

(MRR), tool wear ratio (TWR), and surface roughness (Ra)?

(ii) What is the relationship of every significant parameter on material removal

rate (MRR), tool wear ratio (TWR), and surface roughness (Ra)?

(iii) How the material removal rate (MRR), tool wear ratio (TWR), and surface

roughness (Ra) will be varied with varying of significant parameter setting?

(iv) What is the optimum setting for material removal rate (MRR), tool wear ratio

(TWR) and surface roughness (Ra)?

1.6 Significance of the Study

The research finding will give information on the factors that will contribute

to the studied responses namely material removal rate (MRR), tool wear ratio

(TWR), and surface roughness (Ra). Since there is still a lack of information on

EDM of conductive ceramic until now, the information will be beneficial for

potential users including those in the aerospace and automotive industries. The

information on the machining parameters will provide useful reference for better

efficiency of silicon carbide machining process.

96

Reference

[1] El-Hofy, Hassan. Advanced Machining Processes. McGraw Hill, 2005.

[2] Jain, V.K. Advanced (Non-traditional) Machining Processes.

[3] (2012). Chapter 3 - The Current Situation in Ultra-Precision Technology –

Silicon Single Crystals as an Example. Advances in CMP Polishing

Technologies. D. Toshiro, D. M. Ioan, I. D. M. Syuhei KurokawaA2 -

Toshiro Doi and K. Syuhei. Oxford, William Andrew Publishing: 15-111.

[4] Jahan, M. P., M. Rahman, et al. (2011). "A review on the conventional and

micro-electrodischarge machining of tungsten carbide." International Journal

of Machine Tools and Manufacture 51(12): 837-858.

[5] König, W., D. F. Dauw, et al. (1988). "EDM-Future Steps towards the

Machining of Ceramics." CIRP Annals - Manufacturing Technology 37(2):

623-631.

[6] Ji, R., Y. Liu, et al. (2011). "Experimental research on machining

characteristics of SiC ceramic with end electric discharge milling." Journal of

Mechanical Science and Technology 25(6): 1535-1542.

[7] Liu, Y., R. Ji, et al. (2008). "Electric discharge milling of silicon carbide

ceramic with high electrical resistivity." International Journal of Machine

Tools and Manufacture 48(12–13): 1504-1508.

[8] Kiyak, M. and O. Çakır (2007). "Examination of machining parameters on

surface roughness in EDM of tool steel." Journal of Materials Processing

Technology 191(1–3): 141-144.

97

[9] Mahardika, M., T. Tsujimoto, et al. (2008). "A new approach on the

determination of ease of machining by EDM processes." International Journal

of Machine Tools and Manufacture 48(7–8): 746-760.

[10] Mohd Abbas, N., D. G. Solomon, et al. (2007). "A review on current research

trends in electrical discharge machining (EDM)." International Journal of

Machine Tools and Manufacture 47(7–8): 1214-1228.

[11] http://www.vulcanmold.com.

[12] Matoorian, P., S. Sulaiman, et al. (2008). "An experimental study for

optimization of electrical discharge turning (EDT) process." Journal of

Materials Processing Technology 204(1–3): 350-356.

[13] NorlianaMohdAbbas, D. S., Md.FuadBahari (2006). "A review on current

research trends in electrical discharge machining." Machine Tools and

manufacture.

[14] Schumacher, B. M. (2004). "After 60 years of EDM the discharge process

remains still disputed." Journal of Materials Processing Technology 149(1–

3): 376-381.

[15] R.Venkataraman. "Multi Objective Optimization of Electro Discharge

Machining of Resin Bonded Silicon Carbide." Applied Mechanics and

Materials, 2012: 1556-1560.

[16] Tani, T., Y. Fukuzawa, et al. (2004). "Machining phenomena in WEDM of

insulating ceramics." Journal of Materials Processing Technology 149(1–3):

124-128.

98

[17] Luis, C. J., I. Puertas, et al. (2005). "Material removal rate and electrode wear

study on the EDM of silicon carbide." Journal of Materials Processing

Technology 164–165(0): 889-896.

[18] Leão, F. N. and I. R. Pashby (2004). "A review on the use of

environmentally-friendly dielectric fluids in electrical discharge machining."

Journal of Materials Processing Technology 149(1–3): 341-346.

[19] Tsai, Y. Y., C. H. Tseng, et al. (2008). "Development of a combined

machining method using electrorheological fluids for EDM." Journal of

Materials Processing Technology 201(1–3): 565-569.

[20] Puertas, I., C. J. Luis, et al. (2005). "Spacing roughness parameters study on

the EDM of silicon carbide." Journal of Materials Processing Technology

164–165(0): 1590-1596.

[21] Yonghong, L., J. Zhixin, et al. (1997). "Study on hole machining of non-

conducting ceramics by gas-filled electrodischarge and electrochemical

compound machining." Journal of Materials Processing Technology 69(1–3):

198-202.

[22] Chen, P.-Y., J. McKittrick, et al. "Biological materials: Functional

adaptations and bioinspired designs." Progress in Materials Science (2000).

[23] Puertas, I. and C. J. Luis (2004). "A study on the electrical discharge

machining of conductive ceramics." Journal of Materials Processing

Technology 153–154(0): 1033-1038.

[24] Baker, A. R., D. J. Dawson, et al. (1987). "Ceramics and composite materials

for precision engine components." Materials & Design 8(6): 315-323.

99

[25] Orlova, T. S., V. V. Popov, et al. (2011). "Electrical properties of biomorphic

SiC ceramics and SiC/Si composites fabricated from medium density

fiberboard." Journal of the European Ceramic Society 31(7): 1317-1323.

[26] Lenk, Reinhard, Aniko Nagy, Hans-Jurgen Richter, and Anja Techel.

"Material development for laser sintering technique." 2006.

[27] Ji, Renjie, Yonghong Liu, Yanzhen Zhang, Baoping Cai, Jianmin Ma, and

Hang Li. "Optimizing machining parameters of silicon carbide ceramics with

ED milling and mechanical grinding combined process." Int J Adv Manuf

Technol, 2010: 195–204.

[28] Montgomery, D.C. Design and Analysis of Experiments. 7th edition. John

Wiley & Sons, Inc. New York.

[29] Antony, J. (2003). 8 - Some useful and practical tips for making your

industrial experiments successful. Design of Experiments for Engineers and

Scientists. Oxford, Butterworth-Heinemann: 93-104.