Investigation The Effectiveness Of EDM Performance And Tool Roughness On Surface Finish Of Inconel 718.

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UNIVERSITI TEKNIKAL MALAYSIA MELAKA

INVESTIGATION THE EFFECTIVENESS OF EDM

PERFORMANCE AND TOOL ROUGHNESS ON SURFACE

FINISH OF INCONEL 718

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

(Process) (Hons.)

NOORHANANI BINTI MOHD NOR B051110221

910227-06-5056

FACULTY OF MANUFACTURING ENGINEERING 2015

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DECLARATION

I hereby, declare this report entitled “Investigation the effectiveness of the EDM performance and tool roughness on the surface finish of Inconel 718” is the results of my own research except as cited in references.

Signature : ……….

Author Name : ………

Date : ………

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APPROVAL

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

……… Dr. Mohd Shahir Bin Kasim Final Year Project Supervisor

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ABSTRACT

Inconel 718 is a high nickel content super alloy processing high strength at elevated temperature and resistance to oxidation and corrosion. Due to the abrasiveness, high hardness and low thermal conductivity, Inconel is known as difficult to be machine material. This alloy is widely used in widely uses in aerospace industry, automotive, nuclear power plant and medical purpose. Electrical Discharge Machining is one of the most popular advance machining processes. Thermal energy is used to generate heat that melts and vaporizes the workpiece by ionization within the dielectric medium. This research is focused on the ability of the EDM and the tool roughness in producing the good surface finish. Copper electrode with the diameter of 19mm has been selected as the working tool in this experiment. The roughness measures were arithmetic means roughness (Ra). Ra value is set as the input in this experiment due to the ability of EDM Sodick 3 axis Linear, Model AQ 35L to automatically display the parameter as to achieve the desired Ra. Historical data applied in this experiment. Response surface methodology (RSM) is used to formulate a mathematical model which correlates the parameter and EDM process parameters with the different machining criteria. The total experiment conducted is 13 where the smallest and highest surface roughness obtained in this experiment is 1.274µm and 5.778µm respectively. The factor involved in this experiment are current, pulse on-time, pulse off-time and tool roughness. ANOVA was used to identify the significant effect of the factors on the responses. Based on the analysis, pulse on-time was found to be the most significant factor in order to achieve minimum surface roughness. Mathematical model was generated by the ANOVA and average error resulted in 4.91%. The optimum parameter are current = 2.09A, pulse on-time = 5.178 µs and pulse off-time = 19.370 µs and the predicted surface roughness result is 1.158 µm.

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ABSTRAK

Inconel 718 adalah super pemprosesan aloi yang tinggi kandungan nikel, kekuatan yang tinggi pada suhu tinggi dan rintangan kepada pengoksidaan dan kakisan. Oleh kerana abrasiveness itu, kekerasan yang tinggi dan kekonduksian haba yang rendah, Inconel dikenali sebagai bahan yang sukar untuk dimesin. Aloi ini digunakan secara meluas dalam banyak digunakan dalam industri aeroangkasa, automotif, loji kuasa nuklear dan tujuan perubatan. EDM adalah salah satu proses pemesinan terlebih dahulu yang paling popular. Tenaga haba digunakan untuk menjana haba yang cair dan mengewap bahan kerja oleh pengionan dalam medium dielektrik. Kajian ini memberi tumpuan kepada keupayaan EDM dan kekasaran alat dalam menghasilkan kemasan permukaan yang baik. Elektrod kuprum dengan diameter 19mm telah dipilih sebagai alat kerja dalam eksperimen ini. Langkah-langkah kekasaran ialah aritmetik bermakna kekasaran (Ra). Nilai Ra ditetapkan sebagai input dalam eksperimen ini kerana keupayaan EDM Sodick 3 paksi linear, Model AQ 35L untuk memaparkan parameter untuk mencapai Ra diingini secara automatik. Data sejarah digunakan dalam eksperimen ini. Metodologi permukaan Response (RSM) digunakan untuk merumuskan model matematik yang ada hubung kait parameter dan proses EDM parameter dengan kriteria pemesinan yang berbeza. Jumlah percubaan yang dilakukan ialah 13 di mana kekasaran permukaan yang paling kecil dan paling tinggi yang diperolehi dalam eksperimen ini masing-masing adalah 1.274μm dan 5.778μm. Faktor yang terlibat dalam eksperimen ini adalah current, pulse on-time, pulse off-time dan alat kekasaran. ANOVA telah digunakan untuk mengenal pasti kesan yang signifikan ke atas faktor-faktor ke atas keputusan. Berdasarkan analisis, pulse on-time didapati faktor yang paling penting untuk mencapai kekasaran permukaan minimum. Model matematik telah dijana oleh ANOVA dan kesilapan purata mengakibatkan 4.91%. Parameter optimum adalah current = 2.09A, pulse on-time = 5.178 μs dan pulse off-on-time = 19.370 μs dan kekasaran permukaan yang diramalkan adalah 1.158 μm.

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DEDICATION

To everyone that contributes to this research, especially my family and my friends who always pray for the best and always help when in need.

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ACKNOWLEDGEMENT

In the name of Allah, the most Compassionate, the most Merciful.

In this opportunity, I would like to express the deepest appreciation to the respected supervisor, Dr. Mohd Shahir Bin Kasim who always helped us throughout this project with his invaluable advice and thought. His great knowledge is very resourceful and we are very impressed with his magnanimity.

My gratitude also goes to all staff of Manufacturing Engineering Faculty, especially to the Manufacturing Engineering lecturers for theirs generosity in giving advices and ideas. Not to be forgotten, Encik Mohd Taufik Bin Abd Aziz and Encik Mohd Hanafiah Bin Mohd for all the kindness in helping and allowing us to use the machine.

Last but not least, I would like to thanks to my family for their supports, my classmate and my housemate, Nurul Nadia Binti Muhammad Rafie Empari, Noraini Binti Ismail, Nurul Nabilah Binti Bazla and many more for their encouragement, supports and suggestions regarding to this study.

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TABLE OF CONTENT

Abstract i

Table of content iv

List of Figures x

List of Tables ix

List Abbreviations, Symbols and Nomenclatures vi

CHAPTER 1: INTRODUCTION

1.1 Project Background 1

1.2 Problem Statement 2

1.3 Objectives 3

1.4 Scope 4

1.5 Report Outline 4

CHAPTER 2: LITERATURE REVIEW

2.1 Introduction 5

2.2 Principle of Electrical Discharged Machine (EDM) 6

2.3 Dielectric Fluid 7

2.3.1 Flushing 8

2.4 Inconel 718 8

2.5 Copper Electrode 9

2.6 Surface Roughness Parameter 10

2.6.1 Peak Current and Pulse Duration against Ra 12

2.6.2 Pulse ON and Pulse OFF time 12

2.7 Measuring Surface Roughness 13

2.7.1 Duty Factor 14

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2.8 Difference between Ra and Rz 15

2.9 Response Surface Modelling 17

CHAPTER 3: RESEARCH METHODOLOGY

3.1 Introduction 21

3.2 Work Planning 21

3.2.1 Flow chart 24

3.3 Apparatus Equipment and Machine 25

3.4 Material Selection 27

3.4.1 Work Material 27

3.4.2 Machine Tool 28

3.4.3 Preparation of the working tool (Tool roughness) 29

3.5 Experiment set up 30

3.5.1 Operating Parameter 30

3.5.2 Historical Data 32

3.6 Data Collection 32

3.6.1 Measure of Surface Roughness (Ra) 32

3.6.2 Measuring Method 33

3.7 Data Analysis 33

3.7.1 Analysis of Variance (ANOVA) 34

3.7.2 Diagnostic 34

3.7.3 Model Graph 35

3.7.4 Optimization 35

3.7.5 Validate data

CHAPTER 4: RESULT AND DISCUSSION

4.1 Introduction 36

4.2 Data Collection 36

4.2.1 Experiment Results 38

4.2.2 Surface Profile for minimum and maximum surface roughness 38

4.2.3 Analysis of Variance (ANOVA) 39

4.2.4 Variance Analysis of surface roughness of Inconel 718 40

4.3 Mathematical Model 41

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vii

4.3.2 Excluding the outlier 45

4.4 Factor affecting surface roughness 46

4.4.1 Pulse ON time and Pulse OFF time 46

4.4.2 Discharge Current 48

4.5 Optimizing of Machining Parameters 49

4.5.1 Optimization Parameter of the surface roughness 40

4.5.2 Validation of the optimized parameter 52

4.5.3 Surface Profile for optimization and validation 52 4.6 Effect of tool roughness towards the surface finish 53 4.7 Comparison between the desired Ra the actual Ra 55

4.8 Sustainable Development 57

CHAPTER 5: CONCLUSION

5.1 Conclusion 58

5.2 Recommendation 59

REFERENCES 60

APPENDICES

A Calculation of the average surface roughness B Calculation Error for Mathematical Model C Optimization and Validation

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viii

LIST OF TABLES

2.1 Material properties of Inconel 718 8

2.2 Material properties of copper electrode 9

2.3 Comparison between Bottom and Side wall surface roughness 15

2.4 Type of Research in Journals 18

3.1 Work Planning for Final Project 1 22

3.2 Work Planning for Final Project 2 23

3.3 Chemical composition of Inconel 718 28

3.4 Design parameter of experiment 31

4.1 Surface Roughness Data Collection 37

4.2 Parameter obtained by the experiment conducted 38

4.3 Model in ANOVA 39

4.4 ANOVA for Response Surface Linear Model of surface roughness

4.5 Result of the surface roughness error 42

4.6 Optimized parameter range 50

4.6.1 Suggested parameter

4.62 Different value of Predicted Ra and Actual Ra

50 52

4.7 Results from the same desired Ra 54

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LIST OF FIGURES

2.1 Working Principle of EDM 7

2.2 Surface roughness influenced by the types of tool 10 2.3 Relationship between SR and Discharge current 11 2.4 Relationship between SR and Pulse-on-time 11 2.5 Relationship between SR and Shape Factor. 11 2.6 Relationship between the pulse current and pulse duration

with Ra.

2.7 Measuring surface roughness with stylus 13

2.8 Path of the stylus in measurements of surface roughness (broken line) compared with the actual roughness profile. The profile of stylus path is smoother than the actual surface profile

2.9a Example of determination of Ra 15

2.9b 3.1

Example of determination of Rz Flow Chart

16 24 3.2 Electrical Discharge Machine (EDM) Sodick 3 axis Linear,

Model AQ 35L

3.3 Mitutoyo Japan Portable Surface Roughness Machine 26 3.4 Diamond stylus of surface roughness tester 26

3.5 Desktop type grinding machine 27

3.6 Copper electrode with diameter of 19mm 28

3.7 Grinding process 29

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x 3.9 4.1a 4.1b 4.1c 4.1d

Approach in measuring EDM surface roughness Minimum Ra 1.274 µm (1 mm, 1x)

Minimum Ra 1.274 µm (1 mm, 4x) Maximum Ra 5.778 µm (1 mm, 1x) Maximum Ra 5.778 µm (1 mm, 4x)

33 40 40 41 41 4.2 Actual Values vs Predicted Values of surface roughness

Inconel 718

4.3a Normal plot of Residual 44

4.3b Diagnostic plot for the surface roughness 45

4.3c Outlier graph 45

4.3d Cook’s Distances before outlaying 45

4.4a Influence of Pulse on-time toward the surface roughness 47 4.4b Influence of Pulse off-time toward the surface roughness 48 4.4c Influence of Current toward the surface roughness 49 4.5

4.6a 4.6b 4.6c 4.6d

Parameter range to obtain minimum surface roughness Optimization Ra 1.232µm (1 mm, 1x)

Optimization Ra 1.232µm (1 mm, 4x) Validation Ra 1.014 µm (1 mm, 1x) Validation Ra 1.014 µm (1 mm, 4x)

51 52 52 52 52 4.7a Relationship between the tool roughness and the surface

roughness of workpiece 53

4.7b Tool roughness vs the surface roughness of the workpiece 54 4.7c Value of the flat surface tool vs the Actual Ra from the

experiment 55

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LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURE

ANOVA - Analysis of variance DOE - Design of Experiment

EDM - Electrical Discharge Machining WEDM - Wire Electric Discharge Machine RSM - Response Surface Methodology

Ra - Surface roughness

CCD - Central composite design

Cu - Copper

DOC - Design of Experiment

FCC - Faced-centered cubic

ISO - International Standard Organization

Mn - Manganese

Mo - Molybdenum

MRR - Material rate removal

Nb - Niobium

Ni - Nickel

Si - Silicone

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CHAPTER 1

INTRODUCTION

This chapter explains the background of the project in which the electrical discharge machining (EDM) is used in carrying out this experiment. The properties and applications of Inconel 718 are briefly described in this chapter, including the problem statement, objectives and scope covered in this project.

1.1 Project Background

Electrical discharged machining (EDM) is one of the prominent advance material removal processes. The different with this non-traditional and conventional process are the features that against normal rule for conventional machining that require contact between cutting tool and workpiece, large chip formation, the die must harder than workpiece and use mechanical energy (motion) (Kasim et al., 2013). Due to the demand in high precison engineering component from hard metal and alloy, some process using conventional machining is not be feasible, Therefore the application of EDM is widely accepted in the manufacturing of forming tools to produce molds and dies. EDM also has become a basic machining method for the manufacturing of microscopic, high precision, intricate part in critical industries such as aerospace, automotive, nuclear and medical (M. Kiyak, 2007).

The basic principle of EDM in removing material is by erosion process of workpiece by electrical spark (Dhirendra nath mishra et al., 2014). Tool and workpiece separated by a gap 10 to 200 µm (Manohar et al., 2014). This series of thermo electrical spark between workpiece and die which immersed in dielectric fluid melt and vaporize the work material. The residual of the process known as debris was ejected and flushed away by the electric (Rajaneesh N. Marigoudara, 2013).

This research involves the EDM process of Inconel 718. This nickel based super alloy is one of the hardest materials widely used in many industries such as

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2 aerospace, chemical and nuclear industries. The features of maintain strength, hardness , creep resistance, good ductility and anti-fatigue make this material to be selected in the rotating parts of gas turbine engine, blades, shaft and disks (F.Jafarian, 2014).

Surface roughness of the components or products is one of the important parameter in the engineering which is can represent the quality of the products. According to Rodriguez (2011), surface roughness has important role in the daily activities because the friction and wear in two solids sliding against each other are occurred frequently. Therefore, minimizing the surface roughness is very important in various industries such as automotive and aerospace. In EDM, many factors affecting the surface roughness such as, current, pulse on-time, pulse of-time and voltage. Surface roughness also affected by the type of working tool and workpiece used (S.Ahmad, 2013).

Working tool or electrode is one of the important components in EDM process. The selection of the best electrode in producing the good surface finish is very important. Good electrical conductivities, easy to be machined, high melting point, wear resistance and can produce fine surface finish are the main characteristic must be considered in selection of the working tool. Copper and graphite are commonly used as the working tool in EDM process. According to Ben Salem (2011), copper tool can produce better surface finish than graphite tool.

1.2 Problem statement

Inconel 718 is well known to be one of the most difficult materials to be machined. It is because of its high hardness, maintain the high strength at very high temperature and a low thermal conductivity (Ulutan et al., 2011). Due to its high strength and thermal resistance Nickel-based super alloy, Inconel 718 widely used and very important in the gas turbine industry, aircraft, nuclear and vehicles (Zhou et al., 2012).

These alloys also exhibit tensile resistance at temperatures below freezing point, causing widely used in the construction of aircraft components, power generators, medical equipment and components in nuclear reactors. High demand for the use of

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3 Nickel-based alloys is increased to 40% relative to the overall total weight of the engine, which is 10% more than the use of Titanium (Ezugwu et al., 2005).

Inconel was introduced in 1988 with the durability at a temperature of 600℃ in the aerospace industry. Heat treatment process causes the micro-structure matrix (SG) becomes finer, with increasing hardness to 455HV and yield strength of 740 MPa (Olovsjö et al., 2012). Due to that, more than 50% Inconel 718 material was used in jet aircraft components and aerospace transport (Kalluri et al., 1995).

Surface roughness is important to describe the quality and performance of the finished products. Therefore, minimizing the surface roughness in manufacturing sectors such as, automotive and aerospace is very important(Md. Anayet U. Patwari, 2012). The used of Inconel 718 on the component parts of the engine at temperatures above 1000℃ must meet several criteria, including (Klocke et al., 2012):

a) Surface roughness value (Ra) must not exceed 0.8 � b) No white layer

c) No foreign material, the depth must not exceed 0.01mm

This Bachelor Degree Project will attempt to identify the effectiveness of the EDM performance and tool surface roughness in producing surface finish.

1.3 Objectives

To meet ends, the following objective has been set:

a) To identify the effect of EDM performances and tool roughness on surface finishing.

b) To develop a mathematical model for surface roughness using response surface methodology (RSM)

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4 1.4 Scope

The scope of this Bachelor Degree Project is investigated on surface roughness during machining of electrical discharge machine (EDM). This study is to analyse the machining performance and the effect of tool roughness on the surface finish of Inconel 718. The comparison will be made between desired Ra, with the Ra value of Inconel 718 obtained from the experiment. The cutting parameter of servo Voltage, Current, and Time on that suggested by EDM machine at specific set Ra will be recorded. This data will be considered as input data include the surface roughness of electrode. As to study the variance effect of this parameter on Ra, ANOVA will be used based on observed data. The historical data of Response Surface Methodology will be used as a tool of design of experiment. The diameter of 19 mm copper electrode will be used as the working tool in this experiment.

1.5 Report Outline

Generally, Chapter 1 is describes about the research background and problem statement, objectives and scope that leads to this research. Chapter 2 consist a review from previous study on machining Inconel 718 and other research about EDM. Methods and technique in conducting the experiment is briefly described in Chapter 3. This chapter also mentioned about the material, equipment, and solution tool. Additionally, the method of measurement and analysis process covered in this chapter. Result and discussion of the effectiveness of EDM performance and tool roughness toward the surface finish of Inconel 718 discussed in chapter 4. Lastly, Chapter 5 is the conclusion about the key findings of this project.

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CHAPTER 2

LITERATURE REVIEW

The literature review works as a guide to run this analysis. From this chapter, the information about the EDM machining described and the idea for experimentation offered. Several of research studies have been carried out such as journals, books, and article. These review included the information about the EDM, machining method, parameter, data analysis, result and discussion.

2.1 Introduction

In year 1770, Joseph Priestly, an English Scientist has discovered the Electrical Discharged Machine techniques by noticing that electrical discharges had removal material of the electrodes during the experiments. Despite the fact that it was initially discovered by Priestly, EDM is inaccurate and filled with failure. The soviet scientist chose to damage the destructive effect of an electrical discharged and create a controlled strategy for metal machining. By the year of 1943, the construction of the first park erosion machining was announced. Lazarenko circuit, the spark generator used in 1943, has been utilized for a few years in power supplies for EDM machines and a progress structure is utilized as a part of numerous application. EDM technique was created commercially and transferred to a machine tool. This transforms made EDM more generally accessible and more preferred choice over conventional machining techniques (Sandeep, 2013).

For better performances of electrical discharge machining, lot of work has been carried out to improve the process and technique identified with discovering the attainability of harder material. The most important step to be considered is the correct selection of manufacturing conditions, especially the process that related to Electrical Discharged Machine (EDM). EDM is one the non-conventional machine that's able to machine the geometrically complex material, precise tool, composites, super alloys, tool steels, ceramics and carbides. The parameter that has been figured

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6 out in EDM such as discharges current, materials, possess greater strength and toughness (Ashok Kumar, 2010).

2.2 Principle of Electrical Discharged Machine (EDM)

Erosion begins by rapidly spark reduced occurred between the tool and workpiece in the EDM process, the metal is removed from the workpieces. A thin gap about 0.025mm is always ensured between the tool and workpiece by a servo system. For the further process, both tool and workpiece are submerged in a dielectric fluid. General types of dielectric medium used in EDM process are kerosene, hydrocarbon oil and deionized water (Sandeep, 2013).

The thermoelectric energy, energy that occurred between a workpiece and an working tool submerged in dielectric fluids with the present of electric current. Pulse arc in the small gap between the electrode and the workpiece filled with a dielectric medium like kerosene, hydrocarbon oil and deionized water. The spark gap is reduced when the electrode moved toward the workpiece and the dielectric fluid is ionized due to the high voltage applied. The working principle of EDM process is based on the thermoelectric energy. Spark gap is reduced when the electrode moves toward the workpiece and the applied voltage is sufficiently high to ionize the dielectric fluid. Short duration discharges are generated in a liquid dielectric gap between the electrode and workpiece. The erosive effect of the electrical discharges erodes the material from the tool and workpiece. The dielectric fluid cools the electrodes and flushes away the products of machine from the gap (Kuldeep, 2010).

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7 Figure 2.1: Working Principle of EDM (Kuldeep, 2010)

2.3 Dielectric Fluid

The dielectric fluid is a very important component in EDM process because it creates thespark gap and removes metal particles from the spark erosion area. The function of dielectric fluids mainly to cool the workpiece, electrode and the molten particle, solidify and flush the metal particles away from the gap (Mohammed B Ndaliman et al., 2013).

Dielectric is used to keep up the sparking gap between the electrode and the workpiece. EDM die sinking usually use the hydrocarbon oil as a dielectric, while wire-cut EDM use deionized water. The fundamental characteristics of dielectric fluid are electrical insulator. At the ionization point, the fluids changes into an electrical conductor and the spark occurs. At the point when the spark turned off, the fluids return to being an electrical insulator. This is happens for each spark. The function of dielectric fluids are: (Elman C, 2001).

1. Control the sparking-gap spacing between the tool and workpiece 2. Cools the hot material and form chip

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2.3.1 Flushing

In order to get the efficient cutting, flushing is the most important function in EDM because eroded particle must be removed from the gap. Flushing process, introducing fresh dielectric fluid into the gap and cools the electrode and workpiece. Improper applied flushing can cause erratic cutting and distract the EDMs performances. The metal removal becomes slower due to the high pressure of fluid. However, the chip's not completely removed with low pressure of the fluid. This will lead to the short circuit (Lei Li, 2011).

2.4 Inconel 718

Nickel-based super alloy, Inconel 718 widely use and very important in the gas turbine industry, aircraft, nuclear and vehicles. Due to the high temperature strength and high corrosion resistance, Inconel 718 merely used in the hot section gas turbine engine (N.G.Patil et al., 2014). The properties of Inconel 718 is shown in Table 2.1

Table 2.1: Material properties of Inconel 718 (Alloy Wire International Ltd., 2012)

Property Value

Melting point 1425℃

Heat expansion ₁₃_� _{/m.C (20-100℃)}

Conductivity (20℃) 0.15 W/cm.℃

Density 8.19 g/

Modulus of rigidity 77.2 kN/

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9 2.5 Copper Electrode

Copper with the present of power supply setting enables low wear burning. Copper turned into the metal anode due to the improvement of transistorized and pulse-type power supplies. Due to the structural integrity copper can create fine surface finish, even without special polishing circuits (S.Ahmad, 2013). In a poor flushing circumstance, the structural integrity makes copper electrode resistant to DC arcing. Copper is also commonly used for tubing for certain brands of High Speed Small Hole Machines. Copper electrodes are additionally the favoured material for all High Speed Small Hole applications including aerospace alloys as well as Carbide. (Kern, 2008).

Table 2.2: Material properties of copper electrode (Mohammadreza Shabgard, 2011)

Property Value

Melting point 1083℃

Boiling Temperature 2595℃

Thermal Conductivity 0.15 W/m.

Specific heat 0.092 cal/g. ℃

Specific gravity at 20℃ 8.9 g/

Coefficent of thermal expansion 17 x −6_(1/℃)

Before the experimentation, the surface of the working tool was polished by using the grinding machine in order to get the best value surface finish.(S.Ahmad, 2013) The experiment is carried out to investigate the best value of the surface roughness by using copper and brass as the tool. Copper with the density of 8.94x1000 kg/ and brass desity is 8.75x1000 kg/ . The melting point is 1085℃ and 930℃ respectively. From the result obtained, Copper give lower Ra value compare to the brass (M. Hafiz Helmi, 2009).

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10 The voltage was 60 V, the range of pulse interval from 12.8 to 200 µs and the peak current was from 3 to 25A. The tool materials are copper and graphite which are determined by the hardness of 100 HB and 10HB respectively. With the same discharged energy, copper tool produces a better surface finish than graphite tool (Ben Salem, 2011).

Figure 2.2: Surface roughness influenced by the types of tool (Ben Salem, 2011)

2.6 Surface Roughness Parameter

Several findings from previous work have been compiled. Based on the literature discharge current and pulse duration is the most influenced factor that affect the surface roughness. Surface roughness increases when discharged current and pulse duration increases. The circular tool electrode gives a better surface finish than the square one. Duty cycle and voltage does not significant to surface roughness. (Pushpendra S Bharti, 2010)

a) Copper electrode, Ra= 2.94� b) Graphite electrode, Ra= 3.55 �

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

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6 out in EDM such as discharges current, materials, possess greater strength and toughness (Ashok Kumar, 2010).

2.2 Principle of Electrical Discharged Machine (EDM)

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7 Figure 2.1: Working Principle of EDM (Kuldeep, 2010)

2.3 Dielectric Fluid

1. Control the sparking-gap spacing between the tool and workpiece 2. Cools the hot material and form chip

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2.3.1 Flushing

2.4 Inconel 718

Table 2.1: Material properties of Inconel 718 (Alloy Wire International Ltd., 2012)

Property Value

Melting point 1425℃

Heat expansion ₁₃_� _{/m.C (20-100}_℃₎

Conductivity (20℃ ) 0.15 W/cm. ℃

Density 8.19 g/

Modulus of rigidity 77.2 kN/

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9 2.5 Copper Electrode

Table 2.2: Material properties of copper electrode (Mohammadreza Shabgard, 2011)

Property Value

Melting point 1083℃

Boiling Temperature 2595℃

Thermal Conductivity 0.15 W/m.

Specific heat 0.092 cal/g. ℃

Specific gravity at 20℃ 8.9 g/

Coefficent of thermal expansion 17 x −6_(1/_℃₎

respectively. From the result obtained, Copper give lower Ra value compare to the brass (M. Hafiz Helmi, 2009).

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Figure 2.2: Surface roughness influenced by the types of tool (Ben Salem, 2011)

2.6 Surface Roughness Parameter

a) Copper electrode, Ra= 2.94� b) Graphite electrode, Ra= 3.55 �

Investigation The Effectiveness Of EDM Performance And Tool Roughness On Surface Finish Of Inconel 718.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA