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PERFORMANCE EVALUATION OF COPPER AND

GRAPHITE ELECTRODE IN ELECTRICAL

DISCHARGE MACHINE (EDM) OF ALUMINIUM

ALLOY LM6

SURAYA BINTI LAILY

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

STATUS CONFIRMATION FOR MASTER’S PROJECT REPORT

THE STUDY OF PERFORMANCE DIFFERENT ELECTRODE

MATERIALS IN ELECTRICAL DISCHARGE MACHINE (EDM) OF

ALUMINIUM ALLOY LM6

ACADEMIC SESSION : 2014/2015

I, SURAYA BINTI LAILY agree to allow this Master Thesis to be kept at the Library under the

following terms:

1. This Master Thesis is the property of Universiti Tun Hussein Onn Malaysia.

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_________________________

Approved by,

__________________________

(SURAYA BINTI LAILY)

(DR. BUKHARI BIN MANSHOOR)

Permanent Address :

NO34, JALAN BELATUK MAS 2,

TAMAN BELATUK MAS,

76100 DURIAN TUNGGAL,

MELAKA.

Date: ___________________

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Universiti Tun Hussein Onn Malaysia

Panels:

PERFORMANCE EVALUATION OF COPPER AND GRAPHITE ELECTRODE

IN ELECTRICAL DISCHARGE MACHINING (EDM) OF ALUMINIUM ALLOY

LM6

SURAYA BINTI LAILY

A thesis submitted in

fulfillment of the requirement for the award of the

Degree of Master

Faculty of Mechanical and Manufacturing Engineering

Universiti Tun Hussein Onn Malaysia

January,2016

iii

I hereby declare that the work in this thesis is my own except for quotations and

summaries which have been duly acknowledged.

Student : ……………………………………………………

SURAYA BINTI LAILY

Date : …………………………………………………….

Supervisor : …………………………………………………….

DR. BUKHARI BIN MANSHOOR

Co Supervisor : …………………………………………………….

DR. MOHD AMRAN BIN MD. ALI

iv

For my beloved husband, son, parents, for their endless support.

v

ACKNOWLEDGEMENT

In the name of Allah, Praise is to Allah, the Most Gracious and Most Merciful. I

would like to thank Dr. Bukhari bin Manshoor, my supervisors for his support,

encouragement, motivation and help along my master study period. My special

thanks also to my co-supervisor, Dr Mohd Amran bin Md. Ali for his support and

guidance through my master education. Besides, thanks to research group under

MTUN vot C027 grant for their help and financial support.

My appreciation go to my beloved husband, Mohammad Ikmal bin

Mohamed and my son Ammar Hadif bin Mohammad Ikmal for their love and care

and also my dearest parents for their support.

Highly heartfelt thanks for the cooperation and guidance from technical

support and others lecturer for their brilliant idea given. It was a very interesting

team work environment along my journey to complete my master project with all

their kindness and helpful. Last but not least, I would like to thank for those who

directly and indirectly contributed to complete my master project.

vi

ABSTRACT

Electrical discharge machining (EDM) which is very famous among the non-

conventional machining methods is expected to be used quite extensively in

machining aluminium alloys due to the advantages that it can offer. This thesis is to

study on the influence of operating parameters of LM6 (Al-Sil2) on machining

characteristics such as material removal rate, electrode wear rate, surface roughness,

surface hardness thickness of recast layer. Copper and graphite were selected as

electrode with positive polarity. The experiment was done using SODICK AQ35L

EDM machine. Three level approach of Taguchi Method Design of Experiment

(DOE) was applied to design the experimental table of trials, analyze the significant

factors that affecting the machining characteristics for EDM process. Total of 27

experiments were conducted included 3 time repetition of every run. The weight of

electrode and workpiece were measured before and after machining using weight

scale and surface roughness tester was used to measure the Ra for each specimen.

Scanning Electron Microscope (SEM) has been used to measure the thickness of

recast layer while Vickers Hardness tester was used to measure surface hardness of

workpiece material. The experimental data was analysed by using ANOVA analysis

and the optimal combination of the process parameters can be predicted. From the

usage of copper electrode, it can be conclude that peak current was significantly

affect material removal rate (MRR), electrode wear rate (EWR) and surface

roughness (Ra) and surface hardness (Hv).While pulse on time mainly effected

thickness of recast layer by using copper and graphite electrode . Meanwhile, by

using graphite electrode, peak current also mainly affected material removal rate,

electrode wear rate, and surface roughness. Moreover, surface hardness was affected

by peak current while others parameters which are voltage, pulse on time and pulse

off time gave equally affect on surface hardness of the workpiece.

vii

ABSTRAK

Pelepasan mesin elektrik (EDM) yang sangat terkenal antara kaedah pemesinan

bukan konvensional dijangka akan digunakan agak meluas dalam pemesinan aloi

aluminium kerana kelebihan yang ia boleh tawarkan. Tesis ini adalah untuk

mengkaji pengaruh parameter operasi LM6 (Al-Sil2) ciri-ciri pemesinan seperti

kadar pembuangan bahan, elektrod kadar haus, kekasaran permukaan, ketebalan

kekerasan permukaan lapisan menyusun semula. Tembaga dan grafit telah dipilih

sebagai elektrod dengan kutub positif. Eksperimen telah dilakukan menggunakan

mesin SODICK AQ35L EDM. Tiga pendekatan tahap Taguchi Kaedah Rekabentuk

Eksperimen telah digunakan untuk mereka bentuk rangka eksperimen , menganalisis

faktor-faktor penting yang mempengaruhi ciri-ciri mesin untuk proses EDM.

Sebanyak 27 eksperimen telah dijalankan termasuk 3 kali pengulangan setiap jangka.

Berat elektrod dan benda kerja diukur sebelum dan selepas pemesinan menggunakan

skala berat badan dan penguji kekasaran permukaan telah digunakan untuk

mengukur Ra bagi setiap spesimen. Mikroskop Imbasan Elektron (SEM) telah

digunakan untuk mengukur ketebalan lapisan menyusun semula sementara Vickers

kekerasan ujikaji digunakan untuk mengukur kekerasan permukaan bahan bahan

kerja. Data eksperimen dianalisis dengan menggunakan analisis ANOVA dan

gabungan optimum parameter proses dapat diramalkan. Daripada penggunaan

elektrod tembaga, ia boleh membuat kesimpulan bahawa puncak semasa telah ketara

memberi kesan kepada kadar penyingkiran bahan (MRR), kadar haus elektrod

(EWR) dan kekasaran permukaan (Ra) dan kekerasan permukaan (Hv) .

viii

Semasa nadi pada masa ketebalan terutamanya dilaksanakan untuk menyusun

semula lapisan dengan menggunakan tembaga dan elektrod grafit. Sementara itu,

dengan menggunakan elektrod grafit, semasa puncak juga terutamanya dipengaruhi

kadar pembuangan bahan, elektrod kadar haus, dan kekasaran permukaan. Lebih-

lebih lagi, kekerasan permukaan dipengaruhi oleh arus puncak manakala parameter

yang lain seperti voltan, nadi pada masa dan nadi kira masa sama dia memberi kesan

kepada kekerasan permukaan bahan kerja.

ix

TABLE OF CONTENT

CHAPTER TITLE PAGE

TITLE i

DECLARATION iii

ACKNOWLEDGEMENT v

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENT viii

LIST OF TABLES xi

LIST OF FIGURES xiv

LIST OF ABBREVIATIONS AND SYMBOLS xvii

LIST OF APPENDICES xviii

CHAPTER 1 INTRODUCTION 1

1.1 Project Background 1

1.2 Problem Statement 2

1.3 Objective 3

1.4 Scope of Study 4

1.5 Outline of the report thesis 4

CHAPTER 2 LITERATURE RIVIEW 6

2.1 Introduction 6

2.2 Various electrical discharge machine 6

2.3 EDM die-sinking process 8

2.4 Types of materials 10

2.4.1Workpiece Materials Machined by EDM die sinking 10

x

2.4.2 Type of Electrode 13

2.4.2.1 Graphite Electrode 13

2.4.2.2 Copper Electrode 13

2.4.3 Die Electric Fluid 14

2.5 Material Aluminium Alloy LM6 (Al–Sil 12.30%) 17

2.6 Machining Parameters 18

2.6.1 Current (A) 19

2.6.2 Pulse Duration Time/Pulse ON time (μs) 20

2.6.3 Pulse Interval Time/Pulse OFF time (μs) 20

2.7 Summary 23

CHAPTER 3 METHODOLOGY 24

3.1 Introduction 24

3.2 Project Planning 25

3.2.1 Flowchart of Methodology Process 25

3.3 Design of Experiment (DOE) 27

3.3.1 Set Objectives 29

3.3.2 Select Process Variables 29

3.3.3 Identify Response Variables 29

3.3.4 Taguchi Method and ANOVA analysis 30

3.3.5 Material Aluminium Alloy LM6 32

3.3.6 Conduct Experiment 33

3.3.7 Analyze Result 34 28

3.4 Dielectric Fluid 34

3.5 EDM Die-Sinker Machine 35

3.6 Machine Responses Parameter 36

3.6.1 Electrode Wear Rate (EWR) 36

3.6.2 Metal Removal Rate (MRR) 36

3.6.3 Surface Roughness (Ra) 38

3.6.4 Surface integrity measurement (recast layer) 40

3.6.5 Surface Hardness 44

CHAPTER 4 RESULT AND DISCUSSION 50

4.1 Result of Experiment 50

4.2 Analysis of Result 54

xi

4.4 Analysis Result of MRR 54

4.4.1 Analysis Result MRR using Graphite electrode 54

4.4.2 Analysis Result MRR using Copper electrode 60

4.5 Analysis Result of EWR 64

4.5.1 Analysis result EWR using Graphite electrode 64

4.5.2 Analysis Result EWR using Copper electrode 70

4.6 Analysis Result of Ra 75

4.6.1 Analysis Result Ra using Graphite electrode 75

4.6.2 Analysis Result Ra using Copper electrode 80

4.7 Analysis of recast layer 84

4.7.1 Analysis result of recast layer by using copper

electrode

84

4.7.2 Analysis result of recast layer by using graphite

electrode

91

4.8 Surface hardness 97

CHAPTER 5 CONCLUSION AND RECOMMENDATION 102

5.1 Conclusion 102

5.2 Recommendation 104

REFERENCES 105

APPENDICES 112

xii

LIST OF TABLES

TABLE TITLE PAGE

2.1 The Physical Properties of Copper Electrode 9

2.2 Percentage of Composition LM6 (%) 13

2.3 Machining Parameter and Levels of Setting Conditions 16

2.4 Process parameters and their levels 17

2.5 Parameters and their levels 17

3.1 Factors and Levels Selected for the Experiment 23

3.2 Factorial Design Models 25

3.3 Mechanical,Physical, Electrical and Thermal properties of LM6 26

4.1 Results of experimental material MRR, EWR and Ra for

graphite electrode

52

4.2 Results of experimental material MRR, EWR and Ra for copper

electrode

53

4.3 Design of experiments and experimental results for MRR and

calculated S/N ratio

55

4.4 Average S/N Ratio and Main Effect of MRR 56

4.5 Optimum parameters combination for MRR 57

4.6 One-way ANOVA for MRR 58

4.7 The comparison between higher experimental MRR and

optimize MRR.

59

4.8 Design of experiments and experimental results for MRR and


60

4.9 Response Table for Signal to Noise Ratios of MRR 61

4.10 Optimum parameters combination for MRR 62

xiii

4.11 One-way ANOVA for MRR 63

4.12 The comparison between higher experimental MRR and

optimize MRR

64

4.13 Design of experiments and experimentalresults for EWR

and calculated S/N ratio

65

4.14 Average S/N Ratio and Main Effect of EWR 66

4.15 Optimum parametric combination for EWR 67

4.16 One-way ANOVA for EWR 68

4.17 The comparison between higher experimental EWR and

optimize EWR

69

4.18 Design of experiments and experimental results for EWR and


70

4.19 Average S/N Ratio and Main Effect of EWR 71

4.20 Optimum parameter combination for EWR 72

4.21 One-way ANOVA for EWR 73

4.22 The comparison between higher experimental EWR and

optimize EWR

74

4.23 Design of experiments and experimental results for Ra and

calculated S/N ratio using graphite electrode

76

4.24 Average S/N Ratio and main effect of surface roughness (Ra) 77

4.25 Optimum parameters combination for surface roughness (Ra) 78

4.26 One-way ANOVA for surface roughness (Ra) 79

4.27 The comparison between higher experimental Ra and optimize

Ra

79

4.28 Design of experiments and experimental results for EWR and

calculated S/N ratio using graphite electrode

80

4.29 Average S/N Ratio and main effect of surface roughness (Ra) 81

4.30 Optimum parameters combination for surface roughness (Ra) 82

4.31 One-way ANOVA for surface roughness (Ra) 83

4.32 The comparison between higher experimental Ra and optimize

Ra

83

xiv

4.33 Result of Recast Layer (RL) with different peak current, pulse

on time, pulse off time and voltage by using copper electrode

84

4.34 Result of Recast Layer (RL) with different peak current, pulse

on time, pulse off time and voltage by using graphite electrode

91

4.35 Result on hardness value by using copper electrode 98

4.36 Result on hardness value with process parameters for copper 98

4.37 Result on hardness value by using graphite electrode 100

4.38 Result on hardness value with process parameters for graphite 100

xv

LIST OF FIGURES

FIGURE TITLE PAGE

2.1 Wire EDM 6

2.2 Die Sinker EDM 6

2.3 Small Hole EDM Drilling 7

2.4 Ram-type EDMs plunge a tool 8

2.5 Powder Metallurgy Process of Composite Material 11

2.6 Classified Research Area in EDM Machining Process 16

3.1 Experimental Methodology 25

3.2 Design of Experiment Process Flow 27

3.3 Electrode and Work piece shape use 33

3.4 EDM die sinking Sodick AQ35L Series 35

3.5 Precise Digital Balance 37

3.6 Surface Roughness Equipment (Mitutoyo SJ- 301) 37

3.7 Scanning Electron Machine (SEM) 38

3.8 The heat-affected zone between white layer and

workpiece under Scanning Electron Microscopy (SEM)

38

3.9 Vickers Hardness test 39

3.10 Schematic view on Vickers Hardness Testing 40

4.1 Signal to noise graph for material removal rate ( MRR) 57

4.2 Main Effects Plot for Signal to Noise Ratios of MRR 62

4.3 Signal to noise graph for electrode wear rate ( EWR) 67

4.4 Signal to noise graph for electrode wear rate ( EWR) 72

xvi

4.5 Signal to noise graph for surface roughness (Ra) 78

4.6 Signal to noise graph for surface roughness (Ra) 82

4.7 Signal to noise graph for Recast Layer (RL) 85

4.8 SEM showing the cross-sectional view of the recast layer

of aluminium LM6 after EDM with [I=2A, V=21V,

Pon=1µs, Poff=1µs]

86




86




87




87




88




88




89




89




90

4.17 Signal to noise graph for Recast Layer (RL) 92

xvii




93




93




94




94




95




95




96




96




99

4.27 Signal to noise graph for hardness value by using copper

electrode

101

4.28 Signal to noise graph for hardness value by using

graphite electrode

101

xviii

LIST OF ABBREVIATIONS

DOE - Design Of Experiment

EDM - Electrical Discharge Machine

EWR - Electrode Ware Rate

MRR - Material Removal Rate

Ra - Surface Roughness

Hv - Surface hardness

RL - Recast layer

CCD - Charge Coupled Device

SEM - Scanning Electron Microscope

xix

LIST OF APPENDIX

Appendix A - List of published journal

1

CHAPTER 1

INTRODUCTION

1.1 Project Background

Aluminium-metal matrix composite (AMMC) such as Aluminium LM6 has been the

most exploited material for its low density and the ease of fabrication. AMMC

composes of a metallic base material called matrix, which is reinforced with

reinforcing agent such as ceramic, silicon and others (Mohan et al., 2004). Because

of this, AMMC has a high strength, hardness and stiffness that contributed more

application in aerospace, defence and automobile industries (Mohan et al., 2004).

However, in term of fabrication process, it faces difficulty during machining process

due to the presence of the abrasive reinforcing phase which cause severe tool wear.

Aluminium LM6 as an example, due to silicon content it is hard to machine by

conventional machine. The application of aluminium LM6 itself was make this

material more suitable to machine by advance machining. As an example making

microhole on shaft as one of automotive parts that need advance machining to make

precise hole. Besides, complex shape also can be done by advance machine since

most of the automotive and defence industry parts are .One of the fabrication process

that can be machined with either electroplated diamond-grinding wheel or with

carbide poly crystalline diamond cutting tools (Dhar et al., 2007). Thus, non-

conventional machining, that is electrical discharge machining (EDM) offered an

effective alternative way to cut the AMMC.

EDM Die-Sinking is controlled material removal technique where high

frequency electric spark are used to erode the workpiece which takes a shape

corresponding to that the electrode (Amri et al., 2009). The process was started when

2

electrode is moved down to workpiece until the gap is enough to ionize the dielectric

fluid. The erosion take effect when it is removed the material from workpiece and

electrode through dielectric fluid. The melted material get expelled from surface and

carried away by constantly circulated dielectric fluid.

EDM has proved in machining super tough alloy such as titanium alloy,

stainless steel and aluminium alloy. According to Lee and Li (2001), using

conventional method, these tough material is difficult to machine, even to make a

simple shape. EDM Die-Sinking offers many advantages such as non-contact with

the workpiece during the machining process Kumar et al., (2013), can cut deep slot

Hussein et al., (2008) and the ability to machine any conductive material especially

material with high hardness (Singh et al., 2004). Furthermore, EDM Die-Sinking is a

well established machining option for manufacturing geometrically complex or hard

material parts that are extremely difficult to machine by conventional machining

processes. Dhar et al., (2007) investigated the capability of EDM die-sinking process

of Al-4Cu-6Si alloy using brass electrode to see the effect of current, pulse on time,

and air gap voltage on material removal rate (MRR), tool wear rate (TWR), and

radial over cut (ROC). They found that MRR, TWR and ROC increase significantly

in non-linear fashion with increase current while MRR and ROC increase with

increase in puse duration.Besides that, Karthikeyan et al., (1999) was used copper

electrode on LM 25 Al alloy-SiC composites to see the effect of volume percent of

SiCp, current and pulse duration on MRR, TWR, and surface roughness.

1.2 Problem Statement

In this recently advance engineering area, advance machining was being the most

widely used to produce dies and mould. It is also being used by automotive and

aerospace industry in term of making small part with high precision. For example

shaft making in car’s part and small hole in bearing. These critical parts are need to

machine by advance machining like EDM Die-sinking due to avoid severe tool wear,

mechanical stress and vibration problem. The addition of hard reinforcement

materials into AMMC was categorized it as one of the most difficult materials to be

machined. Using conventional machining process significantly more difficult and

3

leads to severe tool wear and work piece damage. In many critical application and

shaped like pocket geometrical, deep slot shape and microhole, conventional

machining process method is difficult to achieve while machining AMMC.

Achieving the desired surface quality is of great importance for the effective use of

product (Lui et al., 2008). Besides, using conventional method, good surface finish is

difficult to achieve while machining AMMC due to the fracture and pull out the

reinforcing particles. Because of these, this research come out with the solution by

improving machinability of AMMC and developing machining data in order to

convince designers and manufacturers to use AMMC in their application. Non-

conventional machining such as EDM die-sinking is developed to perform

machining of AMMC in order to encounter difficulties during machining

conventional like high tool wear, and poor surface finish (Karthikeyan et al., 1999).

1.3 Objective

The main objective of the study are:

(a) To investigate the effect of various EDM parameters i.e. voltage, peak

current, pulse on time and pulse off time on the machining characteristics

of aluminium LM6 alloys which are MRR, EWR, surface roughness,

recast layer and surface hardness.

(b) To analyze the interaction between EDM parameters and machining

characteristics using two types of electrode.

(c) To identify the significance parameters using Taguchi method and

analyze its percentage contribution for each response investigated using

ANOVA.

4

1.4 Scope of the Study

Below shows the workpiece, electrode, machine parameters, EDM die-sinking

machine and equipments used for this project.

Copper and graphite with 12mm diameter are used as the main electrode

material for this research.

LM6 (Al–Si 12.30%) alloys with size 50mm (L) x 50mm (W) x 10mm (H) is

selected as workpiece.

Machining parameters of peak current,Ip (2A-30A), voltage,V(21V-30V),

pulse on time,ton(1µs-400µs) and pulse off time,toff(1µs-9µs) are selected as

the process input parameters.

Machining characteristic to be investigate are material removal rate (MRR),

electrode wear rate (EWR), surface roughness (Ra), recast layer and surface

hardness.

Kerosene oil is used as dielectric fluid.

Weighting Digital Scale is used to measure the weight of material and

electrode for before and after the process.

Surface Roughness tester will be use to measure surface roughness of

material after machining using EDM.

EDM die sinking Sodick AQ35L Series machine is the main equipment of

this project.

Minitab software with three levels of Taguchi method design and analysis of

variance (ANOVA) are employed to evaluate the data.

1.5 Outline of the Report Thesis

This report consists of five basic structures of chapters which are:

1. Introduction

This chapter describes the aim, objectives and scope of the research as

well as the structure of the thesis.

5

2. Literature Review

The literature review is written the published works by other research that

directly related to the thesis, providing information on theories and

technique.

3. Methodology

This important chapter explains the samples, instruments, materials,

procedures and data gathering methods used in the research.

4. Result and discussion

This chapter explains the data analysis technique and result through

written figures, text, tables and graph.

5. Conclusion and recommendation

Conclusion is drawn based on the research findings and their

implications. Future works are also discussed.

6

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This literature review explores the dominant themes includes study and research of

published materials like journals, thesis, case study, technical document, and online

library. Generally, the purpose of a review is to analyze critical segment of a

published body of knowledge through summary, classification and comparison of

previous research studies, reviews of literature, and theoretical articles. This chapter

will describe topics that related to EDM on LM6 which consist of their process,

parameter and material used and their application.

2.2 Various Electric Discharge Machine

There are three basic electric discharge machining method which are wire, die-

sinking and small hole EDM. All of these method based on principle of spark erosion

where spark generated between electrode and workpiece in a maintain gap to erode

the workpiece (Carl et al., 2011). Wire EDM is used to make through hole on the

workpiece. As shown in Figure 2.1, the spark jumps from wire electrode to the

workpiece and erode metal both from the wire electrode and the workpiece (Carl et

al., 2011).

7

Figure 2.1: Wire EDM (Carl et al., 2011)

EDM Die-Sinking usually to produce complex shape that removed the material from

workpiece and electrode through dielectric fluid. Figure 2.2 shows the schematic

view on how the EDM Die-Sinking process has done (Carl et al., 2011).

Figure 2.2 : Die Sinker EDM (Carl et al., 2011)

While the last common EDM process is small hole EDM drilling. The process was

done by drilled hole by eroding material from the workpiece. Usually material with

high hardness value like titanium alloy are to be machined by EDM Drilling where

there is a limitation to be machine by conventional machine (Hussein et al., 2011).

Figure 2.3 shows small hole EDM drilling schematic view.

8

Figure 2.3 : Small Hole EDM Drilling (Carl et al., 2011)

In this project, EDM process is used to machine aluminium alloy LM6. Next, detail

EDM Die-Sinking process is described.

2.3 EDM Die-Sinking Process

EDM is a non-traditional process that is used to remove metal through the action of

an electrical discharge of short duration and high current intensity between the

electrode and the work piece. There are no physical cutting forces between the tool

and the work piece. This process is finding an increasing demand owing to its ability

to produce geometrical complex shapes. EDM also have its ability to machine hard

materials that are extremely difficult to machine when using conventional process.

Mohan and Chandan, (2008) have stated that EDM has proved valuable especially in

the machining of super tough, hard and electrically conductive materials such as the

new space age alloys and have been agreed by (Lee and Li, 2001).

Other than that, since that the usage of hard, high strength, hardness and

toughness materials increasingly lately, EDM is one of the application machining

method that has getting important. It was proved by Amri et al., (2009), where

tungsten carbide have been machined using EDM Die-Sinking which has the highest

hardness in reinforcement. By using peak current, voltage, pulse duration and

interval time as the main parameters, they have found that peak current of EDM is

mainly effects the electrode wear rate (EWR) and surface roughness (Ra) while the

pulse duration was effected the material removal rate (MRR). Others present studies

also examine the effect of EDM parameters such as peak current, voltage, pulse on

9

time and pulse off time on EDM machining characteristic such as material removal

rate, electrode wear rate, surface roughness and surface integrity (Lonardo and

Bruzzone, 1999). EDM die-sinking also is one of the important process for

machining difficult to machine materials like metal matrix composite (MMC).As

such, Karthikeyan et al., (2009) had studied the effect of current, pulse duration and

percentage volume of SiC on MRR, EWR and Ra. It was found that MRR, EWR and

Ra were increased with increasing in current while EWR and Ra were perpendicular

with percentage volume of SiC. In addition, Singh et al., (2004) was agreed where

they found pulse duration was affected most of the responses by using MMC as the

main workpiece material.

Figure 2.4 : Ram-type EDMs plunge a tool (Bahari, 2007)

Figure 2.4 shows the process of EDM Die Sinking where the electrode is

moved towards the work piece until the gap is small enough, so that the impressed

voltage is great enough to ionize the dielectric fluid. A servomechanism is used to

maintain a gap between the electrode and the work piece. Hence, prevent them from

touching each other. The erosion take effect on part as it is removed the material

from work piece and electrode through dielectric fluid. The materials melts or

vaporizes and gets expelled from the surface of electrode and work piece, the eroded

particles are carried away by constantly circulated dielectric fluid.

10

In this research, peak current Ip, voltage V, pulse on time ton and pulse off

time toff are selected. It is due to several tipper utilized by others Karthikeyan et al.,

(2009)

2.4 Types of Materials

For this project, LM6 (Al–Sil 12.30%) alloys will be use as workpiece while copper

and graphite electrode will be use as the electrode material that need to differentiate

in term of machine characteristic.Further explaination on types of materials used and

their application will be explained .

2.4.1 Workpiece Materials Machined by EDM Die Sinking

There are a various type of material have been used for EDM Die Sinking machine.

Since this various of material have their various type of application, classification of

suitable material with their matched machining process are needed. Since that EDM

Die Sinking just allow conductive material to machine with, there are a huge

limitation to machine non-conductive materials. It is coincided with the EDM

process itself where electric spark were generated between electrode and workpiece

are used to erode the workpiece. These are caused the material of workpiece and

electrode must be conductive material. As such, Amri et al., (2009) used Tungsten

Carbide ceramic and graphite as the main workpiece and electrode material. While

Samsul, (2012) was used Copper Beryllium as the main workpiece, where it is

included in the copper alloy family.

Accordance with the development of processing method, material use is also

increasingly developing rapidly. Composite is one of them and there is some of

reseachers have been used these type of material to machine by EDM Die-Sinking.

Matrix composite material have been widely used in EDM. Properties on the based

material was to be integrated well enough with the properties on the ceramic to

improve the properties of new material. Due to the presence of hard and brittle

ceramic reinforcement, these type of materials are hard to machine by conventional

11

machine. Metal matrix composite as such, have been used by Kumar et al., (2013) as

the main workpiece material. In their present works LM6-5% SiCp composite, which

are fabricated by stir casting process were machine by EDM Die-Sinking. Dhar et al.,

(2007) used Al-4Cu-6Si alloy composite to machine by EDM with brass as an

electrode. Same technique fabricated with Kumar et al., (2013), they found that

Metal Matric Composite (MMC) are well know for their superior mechanical

properties and because of that, non-contact material removal process offer an

effective alternatives. Venkat, (2011) have stated that Aluminium–silicon alloys are

one of the most commonly Aluminium Metal Matrix Composite (AMMC) used

foundry alloys because they offer many advantages such as high strength to weight

ratio, good thermal conductivity, excellent castability, pressure tightness, wear and

corrosion resistance and good weldability. Because of these, they are well suited to

automotive cylinder heads, engine blocks, aircraft components, pipe fittings and

military applications.

Besides, Lau et al., (1990) have machine carbon fibre composite materials

where it is now widely used in aero-space, nuclear, shipping and chemical

industries.The process have been done with low current density since high current

density would cause the epoxy resin to smear over the surface leading to reduce

material removal rate.

Metal matrix composite is one of the matrix composite family where there are

four of them. Others are polymer matrix composite (PMC), ceramic matrix

composite (CMC) and the latest one is cement matrix composite (CeMC). According

to Kaczmar et al., (2000) metal matrix composite are produced by casting and

powder metallurgy methods. Casting is a process where molten alloy matrix was

reinforcing by dispersion particles and short fibre through blending them together.

There are direct squeeze casting and indirect squeeze casting where these two

processes have different usage of application. Direct squeeze casting is applied for

the production of composite elements characterised by relatively simple shape, and

the dies usually simple and reasonable price. The application of indirect squeeze

casting is more complex composite part and more expensive casting dies.

While powder metallurgy method, Kaczmar et al., (2000) also stated the

process are more classic where matrix powder and reinforcing elements was blending

together, continue with cold pressing and sintering followed by forging and extrusion.

Fligier et al., (2008) have stated that powder metallurgy method is mixing materials

12

with different properties in various proportions to make material properties easily to

control. Normally, this method is applied for production that uses magnesium alloy

matrix, aluminium alloy matrix and copper matrices.

Figure 2.5: Powder Metallurgy Process of Composite Material (The Metal

Casting.com)

Aluminium metal matrix composite (AMMC) have move to many

developments in term of characteristic material where in which mixed with hard and

brittle component such as ceramic. AMMC have good corrosion resistance, low

density, and high thermal stability and improved mechanical properties. AMMC that

reinforced with ceramic such as SiC, alumina and fly ash combine the high ductility

and toughness of aluminium with high hardness and tensile strength of ceramic

(Venkat et al., 2011). They studied the influence of peak current, flushing pressure

and pulse on time on MRR, EWR and Ra of AlSi10Mg alloy by means of Taguchi

method and design of experiment (DOE) technique. It was determined that peak

current was the most significant parameter influencing the responses, followed by the

pulse on time and flushing pressure. These result further strengthen the result of

machined aluminium LM6 by using copper and graphite where peak current mainly

dominant affected most of the responses. Karthikeyan et al., (1999) used ANOVA

analysis technique for optimization of EDM parameter such as current, pulse

duration and volume fraction of SiC with consideration of multiple responses like

MRR, EWR and Ra. The MRR was found to decrease with an increase in the present

13

volume of SiC while the EWR and the Ra increase with increase in the volume of

SiC in LM25 aluminium matrix. According to Dhar et al., (2007), MRR, EWR and

radial over cut (ROC) increase significantly in non-linear fashion with increase in

current by three factor, three level full factorial design and ANOVA analysis. It was

determined that peak current, pulse on time and voltage are the significant factor that

effect the response parameters by using Al-4Cu-6Si alloy as workpiece and brass as

electrode.

2.4.2 Type of Electrode

There are several types of electrode that can be used for EDM Die-sinking process

depending on the application. The selection of the most appropriate EDM Die

Sinkeing electrode material is a key decision in the process plan for any EDM Die

Sinking job. In this project, copper and graphite electrode is used as the main

electrode.

2.4.2.1 Graphite Electrode

Graphite has extremely high melting point. It does not melt at all, but sublimes

directly from a solid to a gad (just as the Carbon Dioxide in dry ice) at a temperature

thousands of degrees higher than the melting point of copper, this resistance to

temperature makes graphite an ideal electrode material. Besides, graphite is

significantly lower mechanical strength properties than metallic electrode material. It

is neither as hard, as strong, nor as stiff as metallic electrode materials.

2.4.2.2 Copper Electrode

In Europe and Asia, copper has been a popular electrode material, this is due to

several factors. First, the early EDM machines that were predominant in those areas

used R-C (Resistor Condenser) power supplies. Metallic electrodes, such as Copper,

Brass, Copper Tungsten, and others were the only electrode materials that would

perform effectively with an R-C EDM. When the next generation of machines was

developed, Copper was already firmly entrenched as the most popular electrode

14

material (McGeough and Regius, 1998) . Copper also has the qualities for high stock

metal removal. It is a stable material under sparking conditions. Its wear can be

comparable with graphite.

Indeed with some workpiece materials, it yields a finer surface finish. Copper

are easily obtainable, consistent in quality and low in cost. Copper has melting point

which is only about 1100°C. The temperature in the gap is in the range of a few

thousands of degree, hence there is rapid electrode wear (Bahari, 2007). Roger

(2008) have stated that Copper is compatible with the polishing circuits of certains

advanced power supplies. Most of the manufacturing industry in both Europe and

Japan still prefer to use Copper as the primary electrode material, due to their tool

making culture that is averse to the utidiness of working with graphite. Due to the

structural integrity, Copper can produce very fine surface finishes, even without

special polishing circuits. In addition to graphite, copper is used as an electrode to

machine aluminium LM6. Table 2.1 belows shows the physical properties of copper

electrode:

Table 2.1 : The Physical Properties of Copper Electrode (Bahari, 2007)

Physical Properties Value

Electrical resistivity (µΩ/cm) 1.96

Electrical conductivity compared with silver (%) 92

Thermal conductivity (W/mK) 268-389

Melting point (°C) 1083

Specific heta (cal/g°C) 0.092

Specific gravity at 20°C(g/cm3) 8.9

Coefficient of thermal expansion (x 10°C-1

) 6.6

2.4.3 Die Electric Fluid

There are many different types of fluid available. According to Krar, et al. (1998),

the workpiece and the electrode are submerged in the electric oil, an electrical

insulator that helps to control the arc discharge. The oil also acts as a coolant, and is

15

pumped through the arc gap to wash away the chips. A die electric fluid performs

three important functions:

i. Electrode /workpiece gap was insulated and prevents a spark from

forming until the gap and voltage are correct. When this happens,

the oil ionizes and allows the discharge to occur.

ii. Coolant act to cool the work, the electrode, and the molten metal

particles. Without coolant, the electrode and the workpiece would

become dangerously hot.

iii. Besides, coolant also flush the metal particles out of the gap. Poor

flushing will cause erratic metal removal, poor machining

conditions, and increase machining time and cost.

For most EDM operation, kerosene is the common dielectric used with

certain addictives that prevent gas bubble and deodorant. Silicon fluids and mixture

of these fluids with petroleum oils have excellent results. Other dielectric fluids such

as aqueous solution of ethylene glycol, water in emulsion and distilled water. All

dielectric oil will change in darken colour after use, but it seem only logical to start

with liquid that is as clear a possible to allow viewing of the submerged part

(McGeough and Regius 1998). In this project, kerosene is used as the dielectric fluid.

Figure 2.6 show the basic EDM research that most of the researchers have

done. This project is under improving the performance measurement where the

objectives and scope of the project are to study the interaction between EDM Die

Sinking parameters with the machine responses which are MRR, EWR, surface

roughness, recast layer and surface hardness.

16

Figure 2.6: EDM Research Area

PROJECT

AREA

17

2.5 Material Aluminium Alloy LM6 (Al–Sil 12.30%)

In the past, various studies have been carried out on metal matrix composites. SiC,

TiC and TaC are the most commonly used particulates to reinforce in the metal or in

the alloy matrix or in the matrices like aluminum or iron, while the study of silicon

dioxide reinforcement in LM6 alloy is still rare and scarce. This is due firstly to their

tendency to drag and secondly to the rapid tool wear caused by the high silicon

content. LM6 is based on British specifications that conform to BS 1490–1988 LM6.

LM6 alloy is actually an eutectic alloy having the lowest melting point that can be

seen from the Al–Si phase diagram. The main composition of LM6 is about 85.95%

of aluminium , 11% to 13% of silicon. It is widely used in many fabrication devices

due to its characteristics properties, such as the applications for motor housings,

manifolds, marine components and pumping cases. However, very limited studies

have been reported and so the information and the data available on the mechanical

properties

In term of strength at elevated temperatures, tensile strength and hardness of

LM6 decrease fairly regularly with increasing temperature and become relatively

poor at temperatures of the order of 250˚. LM6 exhibits excellent resistance to

corrosion under both ordinary atmosphere and marine conditions. LM6 can be

anodized by any of common processes, the resulting protective film ranging in colour

from grey to dark brown. The details of the LM6 alloy composition is shown in

Table 2.2.

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Table 2.2: Percentage of composition LM6 (%)

2.6 Machining Parameters

There are varieties of parameters that can be used as factor in order to operate EDM

machine. However, there are a few common parameters that researcher always used

which are peak current, voltage, pulse on time and pulse off time. It was observed

that surface roughness of workpiece and electrode were influenced by pulsed current

and pulse time, higher values of these parameters increased surface roughness.

Lower current, lower pulse time and relatively higher pulse off time have produced a

better surface finish (Kiyak and Akir, 2007).

The machining performances depend on various EDM parameters (variables).

Wang and Yan , (2000) categorized the parameters into two groups :

1. Electrical Parameters

I. Polarity

II. Peak current

III. Pulse duration

IV. Power supply voltage

Composition Percentage (%)

Al 85.95

Cu 0.1

Mg 0.1

Si 12

Fe 0.6

Mn 0.5

Ni 0.1

Zn 0.1

Lead 0.1

Tin 0.05

Titanium 0.2

Others 0.2

19

2. Non electrical parameters

I. Rotational of speed electrode

II. Injection flushing pressure

In the other hand, Van Tri (2002) categorized the parameters into five groups:

I. Dielectric fluid which is type of dielectric, temperature, pressure,

flushing system.

II. Machine characteristics; servo system and stability stiffness,

thermal stability and accuracy.

III. Tool, material, shape, accuracy

IV. Work piece

V. Adjustable parameters; discharge current, gap voltage, pulse

duration polarity, charge frequency, capacitance and tool materials.

There are varieties of parameters that can be used as factor in order to operate

EDM machine. It was observed that surface roughness of workpiece and electrode

were influenced by pulsed current and pulse time, higher values of these parameters

increased surface roughness. Lower current, lower pulse time and relatively higher

pulse off time have produced a better surface finish (Kiyak and Akir, 2007). In this

project, the parameters that have been concerned are current, pulse on time, pulse off

time and voltage.

2.6.1 Current (A)

Pulse current is the amount of power used in discharge machining, measured in units

of amperage. In both vertical and wire applications, the maximum amount of

amperage is governed by the surface area of the “cut” the greater the amount of

surface area, the more power or amperage that can be applied. Higher amperage is

used in roughing operations and in cavities or details with large surface areas (Bud ,

1997). During EDM process, the average current is the average of the amperage in

the spark gap measured over a complete cycle. This is read on the ammeter during

the process. The theoretical average current can be measured by multiplying the duty

20

cycle and the peak current (maximum current available for each pulse from the

power supply or generator). Average current is an indication of the machining

operation efficiency with respect to material removal rate. The concept of maximum

peak amperage that can be applied to the electrode is an important factor (Adnan,

2001). Plus, very high currents are not used as they often lead to heat damage of the

work surface, the depth of the recast layer might not entirely clean up, the intense

heat generated can sink deeply into the surrounding areas of the work piece which

might undergo an uncontrolled heat treating or annealing process. The overcut will

be determined by the amount of current and the on time, but usually when elevated

temperatures are applied, it is an under size electrode which will leave sufficient

material to be removed later in subsequent finishing modes using less power and

orbiting, or by changing to larger, finishing electrodes (Adnan, 2001).

2.6.2 Pulse Duration Time/Pulse ON time (μs)

All the work is done during on time. The spark gap is bridged, current is generated

and the work is accomplished. The longer the spark is sustained more is the material

removal. Consequently the resulting craters will be broader and deeper. Therefore,

the surface finish will be rougher. Obviously with shorter duration of sparks the

surface finish will be better. With a positively charged work piece the spark leaves

the tool and strikes the work piece resulting in the machining. More sparks produce

much more wear. Hence, this process behaves quite opposite to normal processes in

which the tool wears more during finishing than roughing (Adnan, 2001).

2.6.3 Pulse Interval Time/Pulse OFF time (μs)

While most of the machining takes place during on time of the pulse, the off time

during which the pulse rests and the deionization of the die-electric takes place, can

affect the speed of the operation in a large way. More is the off time greater will be

the machining time. But this is an integral part of the EDM process and must exist.

The Off time also governs the stability of the process. An insufficient off time can

lead to erratic cycling and retraction of the advancing servo, slowing down the

operation cycle (Adnan, 2001).

21

Hussien et. al. (2008) have stated that the main parameter of EDM machining

which are voltage, peak current, and pulse off time were the most dominant factors

that effecting the material removal rate (MRR). While they found that peak current

and pulse on time were clearly effected electrode wear rate (EWR). Table 2.3 below

showed the machining parameter and levels of setting condition while conducting

EDM machine.

Table 2.3: Machining Parameter and Levels of Setting Conditions (Hussien et.

al. 2008)

Machining Parameter Setting Conditions

Electrode Polarity Positive

Work piece Polarity Negative

Dielectric Fluid Kerosene

Level

Low(-1) High(+1)

Voltage (V) 70 100

Peak Current (A) 3 9

Pulse on Time (µsec) 30 50

Pulse off Time (µsec) 30 50

Other than that, Wang et. al., (2000) used experiment condition with

workpiece material 3.2mm thickness and the tool electrode material is a kind of

carbide. The machine holes diameter is 0.2mm and the machining voltage is 100V.

The current limiting resistor is 330Ω and the gap capacitance is about 5000pF.

Karthikeyan (1999) have used three levels full factorial design for

experimentation and mathematical models with linear, quadratic and interactive

effects of the parameters was developed. Table 2.4 shows the process parameters and

their level in order to get the interaction between parameters and response which are

MRR, EWR and Ra.

22

Table 2.4: Process parameters and their levels, (Karthikeyan, 1999)

Process parameters Level

0 (low) 1(intermediate) 2(high)

Volume of SiC (%) 6 13 20

Current (A) 2.5 7.5 12.5

Pulse Duration (µs) 200 600 1000

Besides, Venkat et. al., (2011) was studied about influence of EDM process

parameters which are peak current, flushing pressure, pulse on time on Ra, MRR and

EWR by using AlSi10Mg as material based on Taguchi method. It was determined

that peak current was the most significant parameter influencing the responses

followed by pulse on time and flushing pressure. Table 2.5 shows the parameters and

their levels.

Table 2.5: Parameters and their levels, (Venkat et. al., 2011)

Level Peak Current, I

(A)

Flushing Pressure, P

(kg/cm2)

Pulse on time, Ton

(µs)

1 10 0.5 80

2 20 1.0 280

3 30 1.5 480

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2.7 Summary

From all previous study and researched, found that in term of machining parameter,

some of the them said that there are four parameters that play important significant in

EDM machining process. They are voltage, peak current, pulse on duration and pulse

off time. These parameters give a huge effect on MRR, EWR, Ra, recast layer and

surface hardness which are the responses that need to measure. Based on the

objectives stated before, this research want to investigate the effect of voltage, peak

current, pulse on duration and pulse off time on the material removal rate

(MRR) ,electrode wear rate (EWR), surface roughness (Ra), recast layer and surface

hardness.

24

CHAPTER 3

METHODOLOGY

3.1 Introduction

In this chapter, the working procedure and method that have used were briefly

explained. There are some methodologies such as data collections, research study

and analysing the data to accomplish have describe the structure of the research

whereby it can be the guideline in managing. Besides that, the equipment, the

material and the machine involve in designing the experiment study had form and

state in this chapter. Start with project planning of this research, followed by design

of experiment (DOE), planning the matrix by using Taguchi method, discussed

about the material used and parameters setting. Besides, in this chapter, the

techniques and procedure of using the equipments have been discuss. All the steps

taken during the measuring data are recorded and analysed. Taguchi method with

design of experiment were the main technique to analyse the data with the clearly

graph plotted. Other than that, this chapter also briefly about the machine set up and

the measuring technique of every machine used. Lastly, end up with the EDM Die-

Sinking machine set up.

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