Influence of parameters on the overcut and surface roughness of deep cavity feature using edm die sinking.

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

INFLUENCE OF PARAMETERS ON THE OVERCUT AND

SURFACE ROUGHNESS OF DEEP CAVITY FEATURE USING

EDM DIE SINKING

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Process) (Hons.)

EILEEN CHIA MEI PING

B051010072

901030-13-6688

FACULTY OF MANUFACTURING ENGINEERING

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DECLARATION

I, hereby, declared this report entitled “Influence of Parameters on the Overcut and Surface Roughness of Deep Cavity Feature Using EDM Die Sinking” is the results of

my own research except as cited in references.

Signature : ...

Author’s Name : ... Date : ...

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APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfilment of the requirements for the degree of Bachelor of Manufacturing Engineering (Process) (Hons). The member of the supervisory committee is as follow:

...

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ABSTRAK

EDM telah digunakan dengan meluas dalam industri alat dan acuan kerana ia mampu menghasilkan bentuk yang kompleks tanpa mengira kekerasan bahan. Objektif utama kajian ini adalah untuk menentukan kesan current (Ip), pulse on-time (Ton), pulse

off-time (Toff), dan depth of cut (D) dalam overcut dan kekasaran permukaan menggunakan EDM. Ia juga untuk menghasilkan model matematik yang mentakrifkan hubungan antara input parameter dengan output responses. Elektrod yang digunakan dalam eksperimen ini adalah Grafit ISO 63, dan bahan kerja yang digunakan ialah AISI D2 keluli. SODICK NC EDM mesin telah digunakan untuk menjalankan eksperimen, Zeiss CMM Contura G2 mesin digunakan untuk mengukur diameter lubang, dan Mitutoyo SJ 301 Penguji Kekasaran Permukaan digunakan untuk mengukur kekasaran permukaan. Full Factorial Design of Experiment dengan dua replikasi telah digunakan untuk pendekatan eksperimen. Hasil dapatan telah dianalisi dengan menggunakan Analysis of Variance (ANOVA), Main Effect, dan

Interaction. Hasil dapatan yang diperolehi daripada ANOVA menunjukkan bahawa pulse on-time (Ton) dan depth of cut (D) adalah faktor yang paling penting dalam mempengaruhi overcut dan kekasaran pemukaan. Model matematik pun telah didapatkan daripada ANOVA.

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ABSTRACT

EDM is extensively used in the tool, mould, and dies industries as it is able to produce complex shapes regardless of the hardness of material. The objective of this study is to determine the effect of current (Ip), pulse on-time (Ton), pulse off-time (Toff), and depth of machining (D) on the overcut and surface roughness of deep cavity machining using EDM. It is also to develop mathematical modelling that defines the relationship between input parameters and output responses. The electrode used in this experiment was graphite ISO 63, and the workpiece used was AISI D2 steel. Experiments were conducted by SODICK NC Electrical Discharge Machine AQ35L, and the output response of diameter of cut was measured by using Zeiss coordinate measuring machine Contura G2 and calculated, whereas surface roughness was measured by using Mitutoyo SJ 301 portable surface roughness Tester. Full factorial Design of Experiment with two replications was used for experimental approach. The analyses carried out were the ANOVA, main effect, and interaction analysis. ANOVA results showed that pulse on-time (Ton) and depth of machining (D) were the most significant factors in affecting the overcut and surface roughness respectively. The mathematical modelling was also obtained from ANOVA.

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DEDICATION

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ACKNOWLEDGEMENT

I would like to express my highest appreciation to my research supervisor, Professor Madya Dr. Md Nizam Bin Abd Rahman for his patient guidance and valuable advice during the planning and development of this project. His willingness to spend his time so generously has been very much appreciated.

I would also like to thank the technicians of the laboratory of Faculty of Manufacturing Engineering at UTeM for their cooperation and helps in offering me the machines for running the experiment.

Last but not least, I would also to express my appreciation to my parents and fellow friends for their encouragement and support.

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TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables viii

List of Figures ix

List of Abbreviation, Symbols, & Specialized Nomenclature xi

CHAPTER 1: INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 3

1.3 Objectives 3

1.4 Scope 4

CHAPTER 2 : LITERATURE REVIEW 5

2.1 Electrical Discharge Machining 4

2.1.1 History of EDM 6

2.1.2 Principles of EDM 8

2.1.3 Process Mechanism 11

2.1.4 Typical EDM Die Sinking Machine 12

2.1.5 Dielectric Fluid 14

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2.2 Material Selection 20

2.2.1 Electrode 20

2.2.2 Workpiece 21

2.3 Current Research Trend on EDM Die Sinker 22

2.4 EDM Process Parameters 28

2.4.1 Peak Current (IP) 28

2.4.2 Pulse On-Time (Ton) 28

2.4.3 Pulse Off-Time (Toff) 29

2.5 EDM Performance Measures 29

2.5.1 Overcut 29

2.5.2 Surface Roughness (SR) 30

2.6 Design of Experiment (DOE) 31

2.6.1 Full Factorial Design 31

2.6.2 Analysis of Variance (ANOVA) 31

CHAPTER 3: METHODOLOGY 32

3.1 Experimental Planning 32

3.2 Full Factorial Design of Experiment 34

3.2.1 EDM Parameter 34

3.2.2 Experimental Matrix 34

3.3 Equipment 36

3.3.1 EDM Die-Sinking Machine 36

3.3.2 Coordinate Measuring Machine 37

3.3.3 Portable Surface Roughness Tester 38

3.4 Material Preparation 38

3.4.1 Workpiece 38

3.4.2 Electrode 39

3.5 Experimentation 40

3.5.1 EDM Setup 40

3.5.2 Overcut 41

3.5.3 Surface Roughness Measurement 42

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3.7 Report Writing 43

CHAPTER 4: RESULTS AND DISCUSSION 44

4.1 Data Analysis 44

4.2 Overcut 46

4.2.1 ANOVA 46

4.2.2 Main Effect Analysis 47

4.2.3 Interaction Plot 50

4.3 Surface Roughness 53

4.3.1 ANOVA 53

4.3.2 Main Effect Analysis 54

4.3.3 Interaction 57

CHAPTER 5: CONCLUSION 61

5.1 Conclusion 61

5.2 Recommendation 62

REFERENCES 63

APPENDICES 67

A- Results for Diameter of Cavity 67

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LIST OF TABLES

2.1 Physical Properties of Graphite Electrode 21

2.2 Chemical Composition of AISI D2 Steel 22

2.3 Mechanical Properties of AISI D2 Steel 22

2.4 Summary of the Research Papers 24

3.1 The Range of Parameter 34

3.2 Experimental Matrix 35

3.3 Specification of Sodick NC Electrical Discharge Machine AQ35L 37

4.1 Response Table 45

4.2 Analysis of Variance Table for Overcut 46

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LIST OF FIGURES

2.1 Examples of EDM Die-Sinking Finished Parts 6

2.2 Evolution of EDM Machines in 50 Years 7

2.3 Schematic Representation of the Basic Working Principle of EDM 8

2.4 Schematic Representation of the Charges of Electrode and Workpiece 9

2.5 Potential Difference Applied Thoughout the EDM Process 10

2.6 Power Supply Provides Current 11

2.7 The Material Melted and Vapourise Due To the Sparks 11

2.8 Debris Removed by the Flushing of Dielectric Fluid 12

2.9 A Typical EDM Die-Sinking Machine 12

2.10 Pressure Flushing Through The Electrode 15

2.11 Pressure Flushing Through The Workpiece 16

2.12 Suction Flushing Through The Electrode 16

2.13 Suction Flushing Through The Workpiece 17

2.14 Jet Flushing with Multiple Flushing Nozzles 18

2.15 Vertical Flushing 18

2.16 Rotary Flushing 19

2.17 Orbiting Flushing 19

3.1 Experimental Process Flow Chart 33

3.2 Sodick (NC Electrical Discharge Machine) Model AQ35L 36

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3.4 Portable Surface Roughness Tester (Mitutoyo SJ 301) 38

3.5 AISI D2 Steel 39

3.6 Graphite ISO 63 Electrode 39

3.7 EDM Process 40

3.8 Cavities Machined by EDM 41

3.9 Surface Roughness Measurement by Deep Cavity Detector 42

4.1 Model Graph for Overcut with Current 47

4.2 Model Graph for Overcut with Pulse On-Time 48

4.3 Model Graph for Overcut with Depth of Machining 49

4.4 The Interaction Graph of Current and Pulse On-Time on Overcut 50

4.5 The Interaction Graph of Current and Depth on Overcut 51

4.6 The Interaction Graph of Pulse On-Time and Depth on Overcut 52

4.7 Model Graph for Surface Roughness with Current 54

4.8 Model Graph for Surface Roughness with Pulse On-Time 55

4.9 Model Graph for Surface Roughness with Pulse Off-Time 56

4.10 Interaction Graph of Current and Pulse on-Time on Surface Roughness 57

4.11 Interaction Graph of Current and Pulse off-Time on Surface Roughness 58

4.12 Interaction Graph of Pulse On- and Off- Time on Surface Roughness 59

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LIST OF ABBREVIATIONS, SYMBOLS, SPECIALIZED

NOMENCLATURE

A Ampere

AISI American Iron and Steel Institute

ANOVA Analysis of Variance

C Carbon

CMM Coordinate Measuring Machine

Cr Chromium

D Depth of Machining

DC Direct Current

DOE Design of Experiment

EDM Electrical Discharge Machining

Fe Iron

HAZ Heat Affected Zone

IP Peak Current

mm millimeter

Mn Manganese

Mo ` Molybdenum

MRR Material Removal Rate

S Second

Si Silicon

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xv TWR Tool Wear Rate

Ton Pulse On-Time

Toff Pulse Off-Time

v Voltage

V Vanadium

Wt% Weight Percentage

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This chapter present the introduction of this project. The background of this project is on EDM die-sinking. Other than that, the problem statement, objectives, and scope which act as a framework for this project are also included in this chapter.

1.1 Background

Machining is a material removal process where a cutting tool is used to remove unwanted material from a workpiece to produce the desired shape. It can be divided into two categories, which are conventional and non-conventional machining. Conventional machining, also known as traditional machining, are those processes that mechanically remove small chips of material using sharp tool. It requires mainly mechanical energy to remove the material from a workpiece. Examples of conventional machining are milling, turning, drilling, boring and grinding.

In some industries, there are several hard and brittle materials such as high speed steels and tungsten carbide. These materials are difficult to be machined with conventional machining as the cutting tool will undergo extreme wear or it will damage the workpiece. Hence, non-conventional machining (or advance machining), is used to overcome these drawbacks. Non-conventional machining are those processes that remove material by the means of etching, evaporation, melting, chemical dissolution, and hydrodynamic action with the aid of fine abrasive particles, instead of producing chips as in conventional machining (Kalpakjian and Schmid,

INTRODUCTION

CHAPTER 1

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2010). An advantage of these processes is that the hardness of the material is not relevant. Examples of non-conventional machining include electrical discharge machining, abrasive jet machining, electrochemical machining, and chemical machining.

Among all the non-conventional machining methods, electrical discharge machining (EDM) is used extensively for high hardness materials (Iqbal and Khan, 2010). EDM is an important non-conventional machining method in the tool, mould, and dies industries as it is able to produce complex shapes. In EDM process, the tool does not contact with the workpiece, so the cutting forces are not generated. In addition, the workpiece can be of any materials with good electrical conductivity (Singh and Kumar, 2012). Therefore, it is applied widely for machining superior materials since it performs superior machining characteristics.

Since long, researchers have looked into a number of ways to enhance and optimize the EDM process. Most of the research work in this area shares the same objectives of achieving high material removal rate coupled with low tool wear rate and improved surface quality. It can be noticed that various machining parameters influenced the surface roughness significantly. However, there is a gap in the research work where not much interest is paid on the issue of overcut.

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1.2 Problem Statement

In manufacturing industries, it is important to get optimum machining process with high dimensional accuracy and good surface quality. Researchers had been looked into several ways to improve and optimize the EDM process by achieving high material removal rate, coupled with low tool wear rate and improved surface quality. However, there is a gap in the research area as the problem of overcut of EDM process has not been explored thoroughly. Thus, this project aimed to fill in the research gap by studying the effect of EDM parameters on the overcut and the surface roughness of deep cavity machining using EDM die sinking.

1.3 Objectives

The objectives of this project are:

i. To study the effect of process parameters on overcut and surface roughness of deep cavity machining using EDM.

ii. To develop mathematical modeling that defines the relationship between input parameters and output responses.

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1.4 Scope

In this project, Sodick (NC Electrical Discharge Machine) model AQ35L was used for the deep cavity EDM. The material of AISI D2 tool steel was used as the workpiece, and graphite was used as the electrode. For such a part, the overcut was selected to monitor the dimensional accuracy of the parts produced by EDM, and surface roughness was selected to monitor the performance of EDM. The four input parameters were current (IP), pulse on-time (Ton), pulse off-time (Toff), and depth of machining (D). The Full Factorial Design of Experiment was used to run and execute the experiment. A Coordinate Measuring Machine (CMM) and a Portable Surface Roughness Tester were used to measure the output responses, which were diameter of the cavity and surface roughness (SR). The results were then analyzed by using ANOVA, Main Effect Analysis, and Interaction. The expected outcome of this project is to determine the effects of four input parameters on the overcut and surface roughness of a typical component part produced by EDM.

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This section works as a reference, which give information and guidance for this project. This chapter gives a brief explanation on die-sinking electrical discharge machining (EDM). Research journals, books, and online conference article were the main source in the project guides. An overview of current research trends, the important parameters of EDM, and the performance measures of EDM are also included in this chapter.

2.1 Electrical Discharge Machining (EDM)

Electrical Discharge Machining (EDM) is a non-conventional machining technique that has been used extensively for more than fifty years. In EDM process, material is removed by a series of discontinuous electrical sparks between the workpiece and the electrode which are immersed in a dielectric fluid (Iqbal & Khan, 2010). This material removal process which is regardless of the hardness of the material has been its advantage to machine difficult-to-machines and high strength temperature resistant alloy. It is mainly used to produce complex shapes in the manufacture of moulds and dies component, automotive industry, watches, machines, surgical instrument, and electronic component (Schaller et al., 2006). Figure 2.1 shows some examples of EDM die-sinking finished parts.

LITERATURE REVIEW

CHAPTER 2

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Figure 2.1: Examples of EDM die-sinking finished parts: (a) High Speed Turbine; (b) Screw thread mold of the PET bottles. (Schaller et al., 2006)

EDM has multiple advantages as compared to conventional machining processes such as turning or milling. The main advantages of EDM is that it is able to machine any electrically conductive materials despite of its hardness such as tungsten carbide, hardened steel, and special alloys for aerospace application. Moreover, it can be used to produce parts with complex geometry, sharp corners and superior finishes. It does not produce mechanical stress on the workpiece as the tool does not contact with the workpiece, there is no cutting force has been generated, therefore allowing the machining of small and fragile pieces. However, it has relatively low metal removal rates than conventional machining processes, and undesirable erosion of material can occurs. Furthermore, as the geometry of mould cavities are exactly duplicated from the tool electrodes, lead time is needed to produce the specific corresponding electrode shapes (Schaller et al., 2006).

2.1.1 History of EDM

In 1770, Joseph Priestley – an English physicist, discovered that electrical discharges have erosive effect on various metals. However, it was not fully taken advantage of until the Soviet researchers B.R. and N.I Lazarenko learned how to control the destructive effects of an electrical discharge based on Priestley’s earlier research, and they developed a controlled process for metals machining.

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In 1943, a new machining method had been found, which is known as the spark machining process, where an outbreak of spark (electrical discharges) developed between two electrical conductive materials that are immersed in a dielectric fluid. They developed the “Lazarenko Circuit” which helped to maintain the gap width between the workpiece and the tool. It was used to erode hard materials, for example tungsten carbide, and the circuit maintained as the standard EDM generator for years.

In 1952, the first EDM machine was produced by the manufacturer Charmilles, but the machine performances were limited at that time due to the electronic components which have poor quality. In the 1970’s, they added feedback loops with ultra fast servos and numerical control, thus further improving the performance of EDM. Improvements were made continuously in the following decades and the world market of EDM started to expand greatly. Finally, in 1990’s, new EDM process control arose.

Figure 2.2: Evolution of EDM machines in 50 years: Eleroda D1 (1995) and Charmilles Robofil 2050 TW (2005).

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2.1.2 Principles of Electric Discharge Machining (EDM)

Figure 2.3: Schematic representation of the basic EDM working principle

Figure 2.3 shows that the principle of EDM is different from the conventional machining processes as physical contact between the electrode and the workpiece does not occur, hence chatter, mechanical stresses and vibration problems do not exist while machining (Ho and Newman, 2003). The electrode must always be placed away by the distance required for sparking from the workpiece, called as the spark gap. EDM is carried out in the presence of dielectric fluid which is generally kerosene or deionised water that creates path for discharge.

When a potential difference is applied to the electrode, rapidly recurring spark discharge took place, the material is then removed by the erosion effect of sparks (Singh and Kumar, 2012). Electrically conductive electrode and the workpiece are used so an electric field would be established. The volume of material removed by a single spark is in the range of 10-6 to 10-4 mm3, which is very small. However, this single spark occurs for typically 10,000 times per second (Schaller et al., 2006).

Generally, negative terminal of the generator is connected to the electrode to make it negative and the workpiece is made positive as shown in Figure 2.4.

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Figure 2.4: Schematic representation of the charges of electrode and workpiece of EDM process (Shailesh, 2010).

When an electric field is built up in the spark gap, electrostatic forces are subjected onto the free electrons on the electrode. The electrons are released from the electrode if the electron bonding energy is low. This type of electrons emission is known as “cold emission”.

The released electrons are then accelerated toward the workpiece through the dielectric fluid. When the electrons have gained enough energy and velocity, collisions would occur between the electrons and dielectric molecules, and dielectric molecule would ionize depending on the energy of an electron and the ionization energy of a dielectric molecule. The collision results in the generation of more positive ions and electrons. Thus, the concentration of electrons and ions between the electrode and workpiece would increase and creating a channel which is called as “plasma”.

When plasma is created, high amount of electrons will release from the electrode to the workpiece and ions will release from the workpiece to the electrode. This movement of electrons and ions is known as spark. Therefore, the electrical energy is converted into thermal energy of the spark.

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4 1.4 Scope

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