Study Of Surface Topography When Machining SKD 11 Tool Steel By EDM.
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UNIVERIITITEKNIKALIYIALAYSIA'UIELAKA
TAJUK:Studvof the SurfaceTopoeraohvWhenllachinine SKD11 Tool Steel bv
EDAI
2fi18/2fl)9 Semester2
5E5lPENGA.JIAN:
Saya SOHPIII LIN
Universiti
laporanPSitini disimpandi Perpustakaan
mengakumembenarkan
Teknikatlilataysiafitelaka(UTetrf)dengansyarat-syaratkegunaansepertiberikut:
1. LaporanPSMadatahhak mitik UniversitiTeknikatMataysiaMetaka'danpenutis.
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Tarikh: 10thAprit2009
(TANDATANGAN
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DECLARATION
I herebydeclarethat this reportentitled"Study of The SurfaceTopographyWhen
MachiningSKD11 Tool Steelby EDM" is the resultof my own researchexceptas cited
in the references.
Signature
:
N*i6
Author's Name
:
SOH PIH LIN
Date
:
10frApril2009
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APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM,as a
partial fulfillment'of the requirementsfor the degree of Bachelor of Manufacturing
Engineering (Manufacturing Process)with honours. The mernbers of the supervisory
committeeare as follow:
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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 15+s). 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
the pulse on'time rather than peak current.
i
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 15+s). 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
current’.
ii
iii
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
yours endless supports.
iv
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
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
…………………………………………………….
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 Electrode…………………………………………………………………….
15
v
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
2.6 Machining Parameters………………………………………………………..
23
2.6.1 Peak 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
……………………………………………………………..
3.1 The Methodology for DOE …………..……………………………………..
37
3.2 Planning Phase……………………………………………………………….
3.2.1 Recognize the objective of experiment………………………………….
37
3.2.2 Identify the process variables……………………………………………
38
3.2.3 Determining the parameters and levels…………………………………..
38
3.3 Designing Phase……………………………………………………………...
3.3.1 Classify the appropriate orthogonal array……………………………….
38
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
3.4.2.1 Flow chart of the experiment…………………………..…………….
43
vi
38
39
3.5 Analyzing Phase……………………………………………………………..
3.5.1 Analysis of the result and data collected……………………….………
43
45
3.5.2 Discussion and Determine the Result…………………………….
45
3.5.3 Conclusion and Recommendation ……………………………………..
45
……………………………………………….
4.1 Surface Topography …………..……………………………...……….……..
46
4.1.1 Specimen 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
4.2.1 Specimen 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 Data Compare between the 16 Specimens …..………………….……….
68
vii
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
………………………………………..……………………….
80
………….……………….
82
……………………………………………………………………..
84
…………………………………………………………………...
87
……………………………………………………………………….
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
E
SEM micrographs on surface SKD 11 Tool Steel under different EDM
95
conditions ………………………..…………………………….…………….
F
EDX on spectrum of SKD 11 tool steel under different EDM conditions……
viii
107
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 ( ) is the sampling length to determined
Ra
2.20
27
Simulated section of the surface layers of a manufactured workpiece
3
28
2.21
A 2 two'level, full factorial design; factors X1, X2, X3
30
3.1
Flow chart of DOE’s phases.
38
3.2
SKD 11 tool steel (workpiece)
41
ix
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
47
Specimen 1(Scale 20+m)
4.2
SEM Micrograph Showing the Surface Topography under EDM
48
Conditions: Peak Current, Ip = 16A and Pulse On'Time, Ti = 15+s
(Scale 10+m)
4.3
Scanning Electron Micrograph (SEM) Showing EDMed Surface Of
49
Specimen 4(Scale 20+m)
4.4
SEM Micrograph Showing the Surface Topography under EDM
49
Conditions: Peak Current, Ip = 16A and Pulse On'Time, Ti = 6+s
(Scale 10+m)
4.5
Scanning Electron Micrograph (SEM) Showing EDMed Surface Of
50
Specimen 13(Scale 20+m)
4.6
SEM Micrograph Showing the Surface Topography under EDM
51
Conditions: Peak Current, Ip = 4A and Pulse On'Time, Ti = 15+s
(Scale 10+m)
4.7
Scanning Electron Micrograph (SEM) Showing EDMed Surface Of
52
Specimen 16 (Scale 20+m)
4.8
SEM Micrograph Showing the Surface Topography under EDM
53
Conditions: Peak Current, Ip = 4A and Pulse On'Time, Ti = 6+s
(Scale 10+m)
4.9
EDX on Spectrum 1 Of SKD 11 Tool Steel under EDM Conditions:
59
Peak Current, Ip = 16A and Pulse On Time, Ti = 15+S
4.10
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
under Ip = 16A and Ti = 15+S
x
59
4.11
EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:
60
Peak Current, Ip = 16A and Pulse On'Time, Ti = 6+S
4.12
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
61
Under Ip = 16A and Ti = 6+S
4.13
EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:
61
Peak Current, Ip = 4A and Pulse On'Time, Ti = 15+S
4.14
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
62
under Ip = 4A and Ti = 15+S
4.15
EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:
63
Peak Current, Ip = 4A and Pulse On'Time, Ti = 6+S
4.16
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
63
under Ip = 4A And Ti = 6+S
4.17
EDX on Spectrum 1 of SKD 11 Tool Steel under Non'EDM
64
Condition
4.18
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
64
under Non'EDM Condition
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
75
Pulse On'Time
4.23
Normal Probability Plot of Residuals
76
4.24
Normal Probability Plot of Standardized Effects
77
4.25
Pareto Chart of Standardized Effects
78
xi
2.1
Standard AISI'SAE Tool Steel Grades
20
2.2
Properties of SKD 11 Tool Steel
A 23 two'level, full factorial design table showing runs in “Standard
21
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
4.10
Mean of Responses Data Based on Levels of Pulse On'Time
70
2.3
xii
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
Ra
'
Central Line Average of Surface Roughness
xiii
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
manufacturing field. The recent development of EDM has progressed in the industries of
1
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
This research study focused on the following question:
2
(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
to minimize various criteria of machined surface integrity for EDM industry.
3
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
and composition of the SKD 11 tool steel were investigated.
4
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
alloys. EDM can cut into small or odd#shaped angles, intricate contours or cavities in pre#
5
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].
Electrical
Sparks
Electrode
Workpiece
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].
6
2.2
Die5Sinking 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].
Figure 2.2: Basic EDM System [7].
7
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UNIVERIITITEKNIKALIYIALAYSIA'UIELAKA
TAJUK:Studvof the SurfaceTopoeraohvWhenllachinine SKD11 Tool Steel bv
EDAI
2fi18/2fl)9 Semester2
5E5lPENGA.JIAN:
Saya SOHPIII LIN
Universiti
laporanPSitini disimpandi Perpustakaan
mengakumembenarkan
Teknikatlilataysiafitelaka(UTetrf)dengansyarat-syaratkegunaansepertiberikut:
1. LaporanPSMadatahhak mitik UniversitiTeknikatMataysiaMetaka'danpenutis.
UniversitiTeknikati{ata}aiaMetakadibenarkanmembuatsalinan
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q. Sita tandakan(0)
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AtamatTetap:
54. JatanBistari4/18
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Tarikh: 10thAprit2009
(TANDATANGAN
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sekatisebabdantempohtesisini pertudiketaskan
derganmen)ratakan
DECLARATION
I herebydeclarethat this reportentitled"Study of The SurfaceTopographyWhen
MachiningSKD11 Tool Steelby EDM" is the resultof my own researchexceptas cited
in the references.
Signature
:
N*i6
Author's Name
:
SOH PIH LIN
Date
:
10frApril2009
/Aia.*,'l';rli"$e
-*
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM,as a
partial fulfillment'of the requirementsfor the degree of Bachelor of Manufacturing
Engineering (Manufacturing Process)with honours. The mernbers of the supervisory
committeeare as follow:
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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 15+s). 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
the pulse on'time rather than peak current.
i
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 15+s). 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
current’.
ii
iii
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
yours endless supports.
iv
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
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
…………………………………………………….
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 Electrode…………………………………………………………………….
15
v
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
2.6 Machining Parameters………………………………………………………..
23
2.6.1 Peak 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
……………………………………………………………..
3.1 The Methodology for DOE …………..……………………………………..
37
3.2 Planning Phase……………………………………………………………….
3.2.1 Recognize the objective of experiment………………………………….
37
3.2.2 Identify the process variables……………………………………………
38
3.2.3 Determining the parameters and levels…………………………………..
38
3.3 Designing Phase……………………………………………………………...
3.3.1 Classify the appropriate orthogonal array……………………………….
38
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
3.4.2.1 Flow chart of the experiment…………………………..…………….
43
vi
38
39
3.5 Analyzing Phase……………………………………………………………..
3.5.1 Analysis of the result and data collected……………………….………
43
45
3.5.2 Discussion and Determine the Result…………………………….
45
3.5.3 Conclusion and Recommendation ……………………………………..
45
……………………………………………….
4.1 Surface Topography …………..……………………………...……….……..
46
4.1.1 Specimen 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
4.2.1 Specimen 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 Data Compare between the 16 Specimens …..………………….……….
68
vii
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
………………………………………..……………………….
80
………….……………….
82
……………………………………………………………………..
84
…………………………………………………………………...
87
……………………………………………………………………….
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
E
SEM micrographs on surface SKD 11 Tool Steel under different EDM
95
conditions ………………………..…………………………….…………….
F
EDX on spectrum of SKD 11 tool steel under different EDM conditions……
viii
107
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 ( ) is the sampling length to determined
Ra
2.20
27
Simulated section of the surface layers of a manufactured workpiece
3
28
2.21
A 2 two'level, full factorial design; factors X1, X2, X3
30
3.1
Flow chart of DOE’s phases.
38
3.2
SKD 11 tool steel (workpiece)
41
ix
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
47
Specimen 1(Scale 20+m)
4.2
SEM Micrograph Showing the Surface Topography under EDM
48
Conditions: Peak Current, Ip = 16A and Pulse On'Time, Ti = 15+s
(Scale 10+m)
4.3
Scanning Electron Micrograph (SEM) Showing EDMed Surface Of
49
Specimen 4(Scale 20+m)
4.4
SEM Micrograph Showing the Surface Topography under EDM
49
Conditions: Peak Current, Ip = 16A and Pulse On'Time, Ti = 6+s
(Scale 10+m)
4.5
Scanning Electron Micrograph (SEM) Showing EDMed Surface Of
50
Specimen 13(Scale 20+m)
4.6
SEM Micrograph Showing the Surface Topography under EDM
51
Conditions: Peak Current, Ip = 4A and Pulse On'Time, Ti = 15+s
(Scale 10+m)
4.7
Scanning Electron Micrograph (SEM) Showing EDMed Surface Of
52
Specimen 16 (Scale 20+m)
4.8
SEM Micrograph Showing the Surface Topography under EDM
53
Conditions: Peak Current, Ip = 4A and Pulse On'Time, Ti = 6+s
(Scale 10+m)
4.9
EDX on Spectrum 1 Of SKD 11 Tool Steel under EDM Conditions:
59
Peak Current, Ip = 16A and Pulse On Time, Ti = 15+S
4.10
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
under Ip = 16A and Ti = 15+S
x
59
4.11
EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:
60
Peak Current, Ip = 16A and Pulse On'Time, Ti = 6+S
4.12
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
61
Under Ip = 16A and Ti = 6+S
4.13
EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:
61
Peak Current, Ip = 4A and Pulse On'Time, Ti = 15+S
4.14
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
62
under Ip = 4A and Ti = 15+S
4.15
EDX on Spectrum 1 of SKD 11 Tool Steel under EDM Conditions:
63
Peak Current, Ip = 4A and Pulse On'Time, Ti = 6+S
4.16
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
63
under Ip = 4A And Ti = 6+S
4.17
EDX on Spectrum 1 of SKD 11 Tool Steel under Non'EDM
64
Condition
4.18
EDX Analysis Result for EDMed Surface, Taken on Spectrum 1
64
under Non'EDM Condition
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
75
Pulse On'Time
4.23
Normal Probability Plot of Residuals
76
4.24
Normal Probability Plot of Standardized Effects
77
4.25
Pareto Chart of Standardized Effects
78
xi
2.1
Standard AISI'SAE Tool Steel Grades
20
2.2
Properties of SKD 11 Tool Steel
A 23 two'level, full factorial design table showing runs in “Standard
21
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
4.10
Mean of Responses Data Based on Levels of Pulse On'Time
70
2.3
xii
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
Ra
'
Central Line Average of Surface Roughness
xiii
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
manufacturing field. The recent development of EDM has progressed in the industries of
1
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
This research study focused on the following question:
2
(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
to minimize various criteria of machined surface integrity for EDM industry.
3
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
and composition of the SKD 11 tool steel were investigated.
4
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
alloys. EDM can cut into small or odd#shaped angles, intricate contours or cavities in pre#
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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].
Electrical
Sparks
Electrode
Workpiece
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].
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2.2
Die5Sinking 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].
Figure 2.2: Basic EDM System [7].
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