Study Of Surface Topography When Machining SKD 11 Tool Steel By EDM

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

STUDY OF THE SURFACE TOPOGRAPHY WHEN MACHINING

SKD 11 TOOL STEEL BY EDM

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

(Manufacturing Process) with Honours.

by

SOH PIH LIN

UTeM Library (Pind.l/2ffi7)

UNIVERIITI TEKNIKAL IYIALAYSIA'UIELAKA

TAJUK: Studv of the Surface Topoeraohv

When llachinine SKD 11 Tool Steel bv

EDAI

5E5l PENGA.JIAN:

2fi18/2fl)9 Semester 2

Saya SOHPIII LIN

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Universiti

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lilataysia

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dengan

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seperti berikut:

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3. Perpustakaan

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SULIT

TERHAD

TIDAK

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(TANDATANGAN

PENULIS)

Atamat

Tetap:

54. Jatan

Bistari

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Secamat.

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Tarikh: 10th

Aprit 2009

(Mengandungi maktumat _{)rang berdarjah kesetamatan} atau kepentingan llataysia yarg termaKub di datam AKIA RAHSIA RASril 1972)

(ilengardrmgi maklumat TERHAD yang telah ditentukan oteh organisasi/badan di mana panyetidikan dljalankan)

(TANDATANGAN

PENYELIA)

Cop Rasmi:

Ftkulti l(cjuruterrsn Pembuatan Unlvcoiti Teknik.l Malayslr Mclrkr

Tarikh: P l4wo1

DECLARATION

I hereby declare that this report entitled "Study of The Surface Topography When

Machining SKD11 Tool Steel by EDM" is the result of my own research except as cited

in the references.

Signature :

N*i6

Author's Name : SOH PIH LIN

/Aia.*,'l';rli"$e -*

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 (Manufacturing Process) with honours. The mernbers of the supervisory

committee are as follow:

LttriAv.tr t

ABSTRACT

Electrical discharge machining (EDM) is a thermoelectric process that believed the

EDM process will open up an opportunity for the machining of SKD 11 tool steel. This

paper represented a comprehensive study which investigated the influence of the

machining parameters in EDM to the surface topography, composition of the machined

surface and surface roughness of SKD 11 tool steel. The selected EDM parameters were

peak current (4, 6, 8 and 16A) and pulse on-time (6, 9, 12 and 15µs). EDM tests on SKD

11 tool steel were conducted on a Sodick 3 axis linear AQ35L EDM die sinking machine,

with peak current and pulse on-time varied. The electrode used is copper and produced

by lathe machining. The EDMed surface topography and composition of the machined

surface was examined with a Scanning Electron Microscope (SEM) Evo 50 and Energy

Dispersive X-Ray Spectrometer (EDX). Surface roughness was determined with a

Portable Surface Roughness Tester. It is observed from the SEM micrographs that the

surfaces generally have a matt appearance formed on the EDMed surface. These various

factors increased with the increasing of peak current and pulse on-time. There are no

cracks being observed on the EDMed surface since the setting of parameters are

considered in a small range and the high carbon and chromium contain of SKD 11 tool

steel. There are no significant different in composition of the EDMed surface been

observed under different EDM condition compared with non-EDM specimen. It was

also found that higher values of peak current and pulse on-time increased the surface

roughness. Lower peak current and lower pulse on-time produced a better surface finish.

Peak current has a major influence in defining the EDM surface topography and

composition of the machined surface. Meanwhile, surface roughness greatly affected by

ABSTRAK

EDM ialah proses termoelektrik yang dipercayai dapat memberi satu dimensi baru untuk

proses pemesinan keluli alat SKD 11. Kertas kerja ini menerangkan satu kajian yang

menyeluruh tentang kesan parameter pemesinan untuk permukaan topografi, komposisi

pada permukaan yang telah dimesin dan kekasaran permukaan keluli alat SKD 11.

Parameter pemesinan yang digunakan adalah ‘peak current’ (4, 6, 8 and 16A) dan ‘pulse

on-time’ (6, 9, 12 and 15µs). Ujian telah dijalankan dengan menggunakan mesin ‘Sodick

3 axis linear AQ35L die sinking’ dengan menggunakan ‘peak current’ dan ‘pulse on

time’ yang pelbagai. Electrod yang digunakan dalam kajian adalah daripada bahan

tembaga yang dihasilkan dengan menggunakan mesin larik. Permukaan topografi dan

komposisi pada permukaan yang dimesin telah dikaji dengan menggunakan mesin

‘Scanning Electron Machining’ (SEM) dan mesin ‘Energy Dispersive X-Ray

Spectrometer’ (EDX). Kekasaran permukaan telah dikaji dengan menggunakan

‘Portable Surface Roughness Tester’. Daripada pemerhatian melalui SEM micrographs

secara umumnya permukaan bahan ujian mempunyai kesan-kesan daripada proses

termoelektrik. Pelbagai faktor ini bertambah dengan bertambahnya ‘peak current’ dan

‘pulse on-time’. Tidak ada retak dapat dikesan pada permukaan EDMed kerana nilai

parameter yang digunakan adalah kecil dan disebabkan oleh kandungan karbon dan

kromium yang tinggi dalam keluli alat SKD 11. Kandungan komposisi pada permukaan

dikesan tidak banyak berbeza di bawah keadaan EDM yang berlainan banding dengan

Non-EDM. Ia juga didapati bahawa nilai ‘peak current’ dan ‘pulse on-time’ yang tinggi

akan menyebabkan pertambahan kekasaran permukaan. ‘Peak current’ didapati paling

mempengaruhi permukaan topografi EDM dan komposisi pada permukaan. Manakala,

kekasaran permukaan paling dipengaruhi oleh ‘pulse on-time’ berbanding dengan ‘peak

DEDICATION

ACKNOWLEDGEMENTS

This report inevitably involves many helping hands. First of all, I am extremely grateful

and thanks to my supervisor, Ms. Liew Pay Jun, for all the guidance and critics given to

me directly or indirectly, and also appreciate her for spending time to teach and explain

to me. She gave me the guideline and useful information to do the preparation for the

presentation and also the thesis report so that I could score well in this final project.

Opinions and advices given really help me solute many problems faced.

Thank and deeply indebted to En. Azahar, En. Khairul, En. Jaafar, Puan Intan and others

FKP technicians who had help for guidance and share their ideas in help to test the EDM

machined surface for the project.

I would like to thanks to my lovely family and sincere friends for sharing their ideas and

supports. Their constant support keeps me going even when things look bleak. I count

myself very lucky of having these people around me. Thank you so much for given me

TABLE OF CONTENTS

Abstract ………... i

Abstrak ……… ii

Dedication ………... iii

Acknowledgement ……….. iv

Table of Contents……… v

List of Figures………. ix

List of Tables……….. xii

List of Abbreviations……….. xiii

1. INTRODUCTION……….... 1

1.1 Introduction………... 1

1.2 Background of Problems ……...……….……. 2

1.3 Statement of Problems……….….……… 2

1.4 Objective……….……. 3

1.5 Scope……….……... 3

1.6 Importance of The Study………..………… 3

1.7 Expected Result……… 4

2. LITERATURES REVIEW_{………. 5}

2.1 EDM……… 5

2.2 Die-Sinking EDM………….………... 7

2.2.1 Principle of Sinker EDM……….……….. 8

2.2.2 Mechanisms of Sinker EDM……….………….... 13

2.2.3 Advantages of EDM………..………...…. 13

2.2.4 Disavantages of EDM ……….. 14

2.2.5 EDM Application………. 14

2.3.1 Copper ……….………..…… 15

2.4 Dielectric Fluid……….……….………... 16

2.4.1 Hydrocarbon Fluids ………...……... 17

2.4.2 Flushing………..……….... 18

2.5 Tool Steel……….……… 19

2.5.1 SKD 11 Tool Steel.……….……….………..……….... 21

2.6Machining Parameters……….. 23

2.6.1Peak Current (Ip)……… 23

2.6.2 Pulse On-Time (ti) ………. 23

2.6.3 Others Parameter of machining Terminology……… 23

2.7 Surface Integrity ……….……… 24

2.7.1 Surface Topography……….. 26

2.8 Design of Experiment (DOE)……….. 28

2.8.1 Full Factorial Design……….. 29

2.9 Summarize of journal …..……… 32

3. METHODOLOGY_……….. 3.1 The Methodology for DOE …………..……….. 37

3.2 Planning Phase………. 37

3.2.1 Recognize the objective of experiment………. 38

3.2.2 Identify the process variables……… 38

3.2.3 Determining the parameters and levels……….. 38

3.3 Designing Phase………... 38

3.3.1 Classify the appropriate orthogonal array………. 39

3.4 Conducting Phase………. 39

3.4.1 Preparation of the Experiment……… 40

3.4.1.1Preparation of Workpiece ………... 40

3.4.1.2Preparation of Electrode ………..…. 41

3.4.1.3 EDM……… 42

3.4.2 Performing the Experiment (Procedures)……….. 43

3.5 Analyzing Phase……….. 43

3.5.1 Analysis of the result and data collected……….……… 45

3.5.2 Discussion and Determine the Result………. 45

3.5.3 Conclusion and Recommendation ……….. 45

4. RESULTS AND DISCUSSION _………. 4.1 Surface Topography …………..………...……….…….. 46

4.1.1Specimen 1 ………..……….………. 47

4.1.2 Specimen 4 ……….………...…… 49

4.1.3 Specimen 13 ……….. 50

4.1.4 Specimen 16 ……….. 52

4.1.5 Discussion ……...……….. 55

4.1.5.1Peak Current ………..…..………... 55

4.1.5.2Pulse On-Time ………..………..…. 56

4.1.5.3 Which One has Bigger Effect to the Surface Topography …….…… 56

4.1.5.4 Comparison the Result with Past Journal ……… 57

4.2 Composition of Machined Surface …………..……….……….…….. 58

4.2.1Specimen 1 ………..……….………. 58

4.2.2 Specimen 4 ……….………...…… 60

4.2.3 Specimen 13 ……….. 61

4.2.4 Specimen 16 ……….. 62

4.2.5 Non-EDM Specimen ………...……….. 63

4.2.6 Comparison of Compositions for Specimens ……… 65

4.2.7 Discussion ……...……….. 66

4.2.7.1Peak Current ………..…..………... 66

4.2.7.2Pulse On-Time ………..………..…. 66

4.2.7.3 Which has Bigger Effect to the Compositions of Machined Surface.. 67

4.2.7.4 Comparison the Result with Past Journal ……… 67

4.3 Surface Roughness ………..……….……….…….. 67

4.3.1.1 Main Effect Plot (data means) for Surface Roughness, Ra …………. 69

4.3.1.2 Interaction Plot (data means) for Surface Roughness, Ra ……..……. 71

4.3.2 Data Compare between the Lowest and Highest Value of Factors ……... 74

4.3.2.1 Cube Plot ………. 74

4.3.2.2 Surface Plot ……..………..…. 75

4.3.2.3 Normal Probability Plot of the Residuals ……….…..…. 76

4.3.2.4 Normal Probability Plot of Effects for Surface Roughness, Ra …….. 77

4.3.2.5 Pareto Chart of the Effects for Surface Roughness, Ra ……….. 78

5. CONCLUSION ………..………. 80

6. RECOMMENDATION FOR FURTHER STUDY_{………….………. 82}

REFERENCES_{……….. 84}

BIBLIOGRAPHY_{………... 87}

APPENDICES_………. A Flow Chart of the Study…………..………. 91

B Gantt Chart of Entire Project of PSM 1 and PSM 2………..…..………. 92

C Gantt Chart of PSM 1………...……… 93

D Gantt Chart of PSM 2………...………… 94

LIST OF FIGURES

2.1 Electro-discharge erosion 6

2.2 Basic EDM System. 7

2.3 The presence of graphite and metallic particles in the fluid. 8

2.4 Increasing of the number of ionic particles 9

2.5 Collision happened 9

2.6 Heat generated and discharge channel form 10

2.7 inward expansion of vapor bubble 10

2.8 Molten state of discharge channel 11

2.9 Vapor bubble collapse 11

2.10 Recast layer formed 12

2.11 Solidification of expelled metal 12

2.12 Industries using EDM machines 14

2.13 EDM hydrocarbon dielectric fluid 18

2.14 A. Pressure flush through electrode. B. Suction flush through

electrode 19

2.15 C. External flush. D. Combination pressure and suction flush 19

2.16 Common applications of SKD 11 tool steel 22

2.17 Surface topography of sample machined with EDM condition for

several electrode area 26

2.18 Pictorial display of surface characteristics 27

2.19 Roughness sample length (l) is the sampling length to determined

Ra 27

2.20 Simulated section of the surface layers of a manufactured workpiece 28

2.21 A 23 two-level, full factorial design; factors X1, X2, X3 30

3.1 Flow chart of DOE’s phases. 38

3.3 Minitab 14 (software) 41

3.4 Conventional Vertical Milling Machine 42

3.5 Mitsubishi RA90A1 Wire-cut EDM Machine 43

3.6 Conventional Lathe Machine 43

3.7 AQ35L Sinker EDM Machine 44

3.8 Flow chart of the experiment using SKD 11 tool steel 45

4.1 Scanning Electron Micrograph (SEM) Showing EDMed Surface of

Specimen 1(Scale 20µm)

47

4.2 SEM Micrograph Showing the Surface Topography under EDM

Conditions: Peak Current, Ip = 16A and Pulse On-Time, Ti = 15µs

(Scale 10µm)

48

4.3 Scanning Electron Micrograph (SEM) Showing EDMed Surface Of

Specimen 4(Scale 20µm)

49

4.4 SEM Micrograph Showing the Surface Topography under EDM

Conditions: Peak Current, Ip = 16A and Pulse On-Time, Ti = 6µs

(Scale 10µm)

49

4.5 Scanning Electron Micrograph (SEM) Showing EDMed Surface Of

Specimen 13(Scale 20µm)

50

4.6 SEM Micrograph Showing the Surface Topography under EDM

Conditions: Peak Current, Ip = 4A and Pulse On-Time, Ti = 15µs

(Scale 10µm)

51

4.7 Scanning Electron Micrograph (SEM) Showing EDMed Surface Of

Specimen 16 (Scale 20µm)

52

4.8 SEM Micrograph Showing the Surface Topography under EDM

Conditions: Peak Current, Ip = 4A and Pulse On-Time, Ti = 6µs

(Scale 10µm)

53

4.9 EDX on Spectrum 1 Of SKD 11 Tool Steel under EDM Conditions:

Peak Current, Ip = 16A and Pulse On Time, Ti = 15µS

59

4.10 EDX Analysis Result for EDMed Surface, Taken on Spectrum 1

under Ip = 16A and Ti = 15µS

4.11 EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:

Peak Current, Ip = 16A and Pulse On-Time, Ti = 6µS

60

4.12 EDX Analysis Result for EDMed Surface, Taken on Spectrum 1

Under Ip = 16A and Ti = 6µS

61

4.13 EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:

Peak Current, Ip = 4A and Pulse On-Time, Ti = 15µS

61

4.14 EDX Analysis Result for EDMed Surface, Taken on Spectrum 1

under Ip = 4A and Ti = 15µS

62

4.15 EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:

Peak Current, Ip = 4A and Pulse On-Time, Ti = 6µS

63

4.16 EDX Analysis Result for EDMed Surface, Taken on Spectrum 1

under Ip = 4A And Ti = 6µS

63

4.17 EDX on Spectrum 1 of SKD 11 Tool Steel under Non-EDM

Condition

64

4.18 EDX Analysis Result for EDMed Surface, Taken on Spectrum 1

under Non-EDM Condition

64

4.19 Main Effects Plot (Data Means) for Surface Roughness, Ra 69

4.20 Interaction Plot (Data Means) for Surface Roughness, Ra 71

4.21 Cube Plot for Surface Roughness, Ra 74

4.22 Surface Plot of Surface Roughness, Ra versus Peak Current and

Pulse On-Time

75

4.23 Normal Probability Plot of Residuals 76

4.24 Normal Probability Plot of Standardized Effects 77

LIST OF TABLES

2.1 Standard AISI-SAE Tool Steel Grades 20

2.2 _{Properties of SKD 11 Tool Steel} 21

2.3 A 2

3

two-level, full factorial design table showing runs in “Standard

Order” 30

2.4 Sunmarize of journals 32

3.1 Constant variable of the study 39

3.2 Levels for parameter 40

3.3 Experimental input of parameters 40

4.1 Chemical Elements of Specimen 1 Contain in Spectrum 1 59

4.2 Chemical Elements of Specimen 4 Contain in Spectrum 1 60

4.3 Chemical Elements of Specimen 13 Contain in Spectrum 1 62

4.4 Chemical Elements of Specimen 16 Contain in Spectrum 1 63

4.5 Chemical Elements of Non-EDM Specimen Contain in Spectrum 1 65

4.6 Comparison of Chemical Elements of Specimens 65

4.7 Summarized of Chemical Elements of Specimens 66

4.8 Result of Surface Roughness for SKD 11 Tool Steel 68

4.9 Mean of Responses Data Based on Levels of Peak Current 70

LIST OF ABBREVIATIONS

UTeM - University Teknikal Malaysia Melaka

EDM - Electrical Discharge Machining

DC - Direct Current

DOE - Design of Experiments

SEM - Scanning Electron Machining

EDX - Energy Dispersive X-Ray Spectrometer

PSM 1 - Projek Sarjana Muda Satu

PSM 2 - Projek Sarjana Muda Dua

ti - Pulse On-time

Ip - Peak Current

CHAPTER 1

INTRODUCTION

In this chapter, the introduction, background of problems, statement of problems,

objective, scope, importance of the study and the expected result in the study were

discussed.

1.1

Introduction

Electrical discharge machining (EDM) or it is also called as spark-erosion machining, is

a process that is used to removes material with repetitive spark discharges from a

pulsating DC power supply, with a dielectric fluid flowing between the tool and the

workpiece [1].

The EDM process of erosion using the electrical discharge was developed in 1770 by an

English scientist. The Russian scientists B. and N. Lazerenko adopted the principle and

developed a process to control the material removal of conductive materials. In 1952,

Charmilles Technology Corporation of Geneva, Switzerland was worked together with

Mr. Lazarenko to develop the first industrial economical die-sinking EDM machine. The

machine has been introduced in Milan, Italy in 1955. Shortly after, the team was

developed a surface finish scale that can be achieved on an EDM machine. The

development was also adopted by an organization of engineers in German [2].

The EDM process has become popular and widely used in production technologies in

plastic technology due to growing application of EDM process and the demand of the

human toward the advance technology era. The EDM can perform better than the other

machining method since the application of EDM had increased. The new materials

which are hard and difficult to machine but widely used in the modern manufacturing

industries such as hastalloy, hardened tool-steel, titanium, carbide and etc can easily

been carry out in the EDM [3].

In the review research work, various aspects of EDM on different types of workpieces

have been done. In this work, a study focused on the surface topography when

machining SKD 11 tool steel by die-sinking EDM was carried. The work also examined

the influence of the machining peak current and pulse-on time to the surface roughness,

surface topography and composition of the machined surface.

1.2

Background of Problems

EDM technology is one of the most advanced technologies since it has many advantages

over conventional machining processes. For the conventional machining, the processes

run manually by the operators. Sometimes, this affects the quality problem, waste of

time, extra manpower, uneconomic and etc. Moreover, the materials that were

electrically conductive cannot be cut, even though of its hardness due to rapid the tool

wears, cutting speed, current and so on. The surface finish formed was not good enough

and it is inability in generating complex shape. Meanwhile, the development of EDM

process had solved the criteria problem that occurred. In this work, an investigation of

the machining parameters (peak current and pulse-on time) to the surface roughness,

surface topography and the composition of the machine surface was carried out.

1.3

Statement of Problem

(a) What is the most consequence of machining parameters (peak current and pulse-on

time) that influence the surface roughness, surface topography and composition of

the machined workpiece surface?

1.4

Objective

The objective of the project was to analyze the influence of peak current and pulse-on

time to the surface roughness, surface topography and composition of the SKD 11 tool

steel by using copper electrode.

1.5

Scope

This research focused primarily on the surface roughness, surface topography and the

composition of the machined surface in the die-sinking EDM by using SKD 11 tool steel.

The machining parameters are peak current and pulse-on time. Other responses such as

the microstructure, white layer thickness and surface crack density were not covered in

this project.

1.6

Important of the Study

Through this study, it helped in investigated the influence of the machining parameters

(peak current or pulse-on time) to the surface roughness, surface topography and

composition of the machined workpiece (SKD 11) surface. Further, this project helped

1.7

Expected Result

The result had shown the effect of operating parameters of EDM on the machined

workpiece surface indicated that the peak current and pulse on time had a direct

relationship with surface roughness, surface topography and composition of the SKD 11

tool steel by using copper electrode. By applied DOE method on this experiment; the

influence of peak current and pulse-on time to the surface roughness; surface topography

CHAPTER 2

LITERATURE REVIEW

In this chapter, the theory related to the study was discussed in detail. Moreover, the

previous research and study were also summarized.

2.1

EDM

The acronym EDM is derived from Electrical Discharge Machining. EDM is among the

earliest non-traditional manufacturing process, having an inception 50 years ago in a

simple die-sinking application. Anyone who has ever seen what happens when a bolt of

lightening strikes the ground will have a fair idea of the process of EDM. The EDM

process we know today started with the observations of Joseph Preistly in 1770. He

noticed that electrical discharges had removed material from the electrodes in his

experiments. This is also known as electro-discharge erosion (Figure 2.1). In the 1940's,

Soviet researchers had developed a machining process, which was formed the foundation

for modern EDM [4].

EDM is a non-conventional metal removal machining method that utilizes the use of an

electrode to machine the desired shape into a workpiece under carefully controlled

conditions. It is a machining method primarily used for hard metals or those that would

be impossible to machine with traditional techniques [5]. However, EDM only works

with materials that are electrically conductive. Generally, those materials used are ferrous

pre-hardened steel without the heat treatment to soften and re-harden them as well as exotic

metals such as titanium, hastelloy, kovar, and inconel [6].

Figure 2.1: Electro-discharge erosion [6].

The EDM system consists of a shape tool or wire electrode, and the part. The part is

connected to a power supply. The basic concept of EDM is the machine uses an electrode

to erode a workpiece using electrical sparks (Figure 2.1). The electricity flows through

the electrode in the form of a square wave attacking the points of least resistance on the

workpiece. This "Zap" happens every time the current is switched on the square wave.

Then, the current is switched off to allow the debris to be flushed away. This process

happens over and over many times a second as the electrode is slowly advanced deeper

and deeper into the cut. Actually, the electrode never touches the workpiece because the

actual cutting is being done by the spark gap between the electrode and the workpiece.

Sometimes, to create a potential difference between the workpiece and tool, the workpece

is immersed in a dielectric (electrically non-conducting) fluid which is circulated to flush

away debris. However, the cutting pattern is usually controlled by using the CNC

machining. Many EDM machine electrodes can rotate about two to three axis allowing

for cutting of internal cavities. This has makes the EDM a highly capable in

manufacturing process [7].

Electrode

Workpiece Electrical

2.2

Die-Sinking EDM

It is also known as Sinker EDM, Ram EDM, Vertical EDM and Plunge EDM. The

die-sinking process was refined as early as the 1940 with the advent of the pulse generators,

planetary and orbital motion techniques, CNC and the adaptive control mechanism. From

the vacuum tubes to the transistors and then until the present day solid state circuits, it

was not only possible to control the pulse on time but also the pause time or the off time.

This made the EDM circuit better, accurate, and dependable, and therefore the EDM

industry began to grow [7]. Through sinker EDM, parts can be formed out of even the

most rigid materials and formed into very complex shapes.

Sinker EDM is used when parts need tight tolerances or when a tight corner is required. It

is a versatile process, allowing for a variety of sized parts from those that can fit in the

palm of a hand to parts that weight over 1,000 pounds, and everything in between.

Production dies and molds are often made through the sinker EDM process for these

reasons as well. Sinker EDM is generally used to produce the blind cavities such as

Mobile phone cavities, Speaker grills cavities etc [6].