Analysis Of EDM Parameters During The Micro Hole Machining Of Tungsten Carbide.
ABSTRACT
Electrical discharge machining (EDM) is a widespread process which works very
effectively in machining of micro holes and harder material with high dimension
accuracy. In this study, the objective is to optimize the machining parameter of the EDM
process including peck current, pulse duration, and with or without flushing process to
increase the material removal rate and reduce the electrode wear rate. EDM machine
model MITSUBISHI has been used in this project and the weight for the workpiece and
electrode has been measured using the digital weight machine. The material removal rate
and electrode wear rate were calculated using the formula. Copper has been used as
electrode to machine the tungsten carbide, which is widely used to make micro die for
plastic extrusion. Response surface methodology (RSM) method has been applied in this
project at two levels (high, +1 and low, -1) and there are 26 experiments have been done.
From the result, the lowest material removal rate is 4.55952E-006g/second while the
maximum material removal rate is 5.49336E-005g/second. The lowest electrode wear
rate is 1.91171E-006g/second while maximum electrode wear is 6.30569-005g/second.
The optimum machining parameter to increase material remove rate and reduce the
electrode wear rate are 14.67 A of peak current, 2.57 μs pulse on time and ON the
flushing process.
i
ABSTRAK
Electrical discharge machining (EDM) ialah proses yang digunakan untuk menjalankan
pemotongan lubang yang bersaiz mikro dan bahan yang keras dengan ukuran yang tepat.
Dalam projek ini, pembolehubah yang dikawal ialah peak current, pulse duration, dan
sistem flushing. Hasil yang telah diuji ialah kadar pemotongan bahan kerja dan kadar
kehausan bagi electrode. Mesin EDM model MITSUBISHI digunakan untuk memotong
benda kerja tungsten carbide dengan menggunakan electrode kuprum. Berat electrode
dan bahan kerja diukur dengan menggunakan mesin penimbang digital sebelum dan
selepas ujukaji. Masa untuk pemotongan bahan kerja dicatatkan dan kadar pemotongan
bahan kerja dan kadar kehausan electrod dikira dengan formula. Jumlah eksperimen
yang telah dijalankan ialah 26 kali dan response surface methodology (RSM) digunakan
dalam projek ini untuk menentukan pembolehubah yang paling sesuai untuk mencapai
kadar pemotongan bahan kerja yang maximum dan kadar kehausan electrod yang
minimum. Nilai untuk kadar pemotongan bahan kerja maksimum dalam projek ini ialah
5.49336E-005g/saat sementara minimum adalah 4.55952E-006g/saat. Nilai maksimum
untuk kadar kehausan electrod ialah 6.30569-005g/saat sementara minimum ialah
1.91171E-006g/saat. Pembolehubah yang paling sesuai untuk mencapai kadar
pemotongan bahan kerja yang maksimum dan kadar kehausan electrod yang minimum
ialah 14.67 A of peak current, 2.57 μs pulse on time dan flushing system ON.
ii
DEDICATION
This project is dedicated to my parent, without whose caring support it been possible to
done the project. Besides that, this project also dedicated to sister and brother, who
support me in knowledge and other.
iii
ACKNOWLEDGEMENT
I am heartily thankful to my supervisor, Miss Liew Pay Jun, whose encouragement,
guidance and support from the initial to the final level enabled me to develop an
understanding of the project. Lastly, I offer my regards and blessings to all of those who
supported me in any respect during the completion of the project. Besides that, I want to
thank my parent that always supports me in project.
iv
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of Content
v-vii
List of Table
viii-ix
List of Figure
x-xi
List Abbreviations
xii
1. INTRODUCTION
1
1.1
Introduction
1-2
1.2
Problem Statement
3
1.3
Objective
3
1.4
Scope
1.5
Important of Study
4
1.6
Expected Result
4
2. LITERATURE REVIEW
5
3-4
2.1
Principle of EDM
5-6
2.2
The Electrode
7-8
2.2.1
Copper Electrode
9
2.3
Tungsten Carbide
10
2.4
Dielectric Fluid
10-11
2.5
EDM Parameter
11
2.5.1
Flushing
2.5.2
Peak Current, IP
2.5.3
Pulse-on Time, On
2.5.4
Pulse-off Time, OFF
11-12
12
12-13
13
v
2.6
EDM Machining Characteristics
13
2.6.1
Electrode Wear Rate
2.6.2
Material Removal Rate
2.7
Design of Experiment (DOE)
14-15
2.7.1
Response Surface Methodology (RSM)
15-17
2.8
Summary Previous Journal
18-22
2.9
Summary
23
3. METHODOLOGY
24
3.1
Flow Chart of Study
25
3.2
Step 1: Define the Objective for the Project
26
3.3
Step 2: Identify the Machining Parameter and Response Variable
26
3.3.1
Variable Machining Parameter
26
3.3.2
Constant Machining Parameter
27
3.4
Step 3: Preparation of the Experiment
27
3.4.1
Workpiece
27-28
3.4.2
EDM Electrode
28-29
3.4.3
Digital Weight Machine
29
3.4.4
Design of Experiment Matrix
30
3.5
Step 4: Running the Experiments
31
3.5.1
Machining Flow Chart
32
3.5.2
Testing the Finish Produce
33
3.6
Step 5: Analysis Result
33
3.6.1
Material Removal Rate (MRR) Measurement
34
3.6.2
Electrode Wear Rate (EWR) Measurement
34
3.7
Step 6: Define the Optimal Setting of Experimental Parameters
35
3.8
Step 7: Confirmation Run
35
3.9
Step 8: Make Conclusion for Project
35
13-14
14
4. RESULTS AND DISCUSSION
4.1
36
Result
36-37
vi
4.2
Analysis of Material Removal Rate
37-38
4.2.1
Fit Summary
38-39
4.2.1.1 Lack of Fit
39
4.2.1.2 Model Summary Statistic
40-41
4.2.2
ANOVA
41-43
4.2.3
Model Graphs
43-47
4.3
Analysis of Electrode Wear Rate
4.3.1
Fit Summary
48
48-49
4.3.1.1 Lack of Fit
49
4.3.1.2 Model Summary Statistic
49-51
4.3.2
ANOVA
51-52
4.3.3
Model Graphs
53-57
4.4
Optimization
4.4.1
Numerical
4.5
Confirmation Run
59
4.5.1
Average Deviation Percentage Value
59
57
57-58
4.5.1.1 Material Removal Rate
60
4.5.1.2 Electrode Wear Rate
60-61
4.6
Discussion
61
4.6.1
Material Removal rate
61-62
4.6.2
Electrode Wear Rate
62-63
5. CONCLUSION AND RECOMMENDATIONS
64
5.1
Conclusion
64
5.2
Recommendation
65
REFERENCES
66-67
APPENDICES
A
Gantt chart PSM 1
B
Gantt chart PSM 2
vii
CHAPTER 1
INTRODUCTION
This chapter is introduces the micro EDM process and problem statement. Besides that,
this chapter also includes the objective, scope, importance of study and expected result
for the project.
1.1
Introduction
Rapid advances in technology require further development in the manufacturing of
micro parts and micro-electromechanical system components. Increasing demand for
micro-parts made micro-machining processes more focused and investigated among the
front end of the technology in recent years. Micro-machining is the basic manufacturing
technology of the miniaturized and smaller parts having size of millimeter down to
micrometer.
Electrical Discharge Machining (EDM) is one of the machining processes that may have
high potential to manufacture small size components. It is a thermal process that utilizes
spark discharges to erode a conductive material and electrode is almost unloaded. There
is no physical contact between the tool electrode and the work piece so the process
works efficiently and particularly in the machining of hardness material. When the same
process principles are applied to the micro machining, the process is called as microEDM.
1
The basic physical characteristics of the micro EDM process is essentially similar to that
of the conventional EDM process but the main difference is the size of the electrode that
used. Electrical discharge machining is widely used in machining of dies and for
produce of unusually shaped or size production work. Example for EDM products are
fuel injector valves, parts and components for medical devices, fiber optic connectors,
micro mold making, stamping tools and micro electronic parts.
There are many manufacturing techniques to drill micro holes and micro parts beside
micro-EDM. The recently developed methods are Wire Electric Discharge Grinding
(WEDG), Micro-Electrochemical Machining (MECM), Laser-Beam Machining (LBM),
Focused Ion Machining (FIM), Micro milling, Micro Ultrasonic Machining (MUSM),
Electrochemical Discharge Machining (ECDM) and Micro punching. Performances of
these methods are unique, because they have different machining mechanisms. For
example, LBM can be used to drill a hole under diameter of 4 μm, however, it causes
deterioration and micro cracks on the machined surface. Besides that, ECDM can
improve the material removal rate to 1.5 mm/min and surface roughness to 0.08 μm.
However, the walls of the micro-holes are over etched (Yan et al, 2002).
Micro EDM is suitable for these and similar applications because its low discharges
energy generate smooth surfaces and that have no physical contact between the tool
electrode and the work piece so the process works efficiently. However, micro EDM
face two significant challenges that is high electrode wear and low Material Removal
Rate (MRR). Electrode wear which results from each discharge removing some material
from the electrode, degrades the geometric accuracy of machined features.
This report was analysis the MRR and EWR for the process by using the different
machining parameter that are peak current, pulse on time and add the flushing process
when machining. The type of electrode is copper and the material is tungsten carbide. At
the end, this project were also determined the optimum machining parameter to get the
good result.
2
1.2
Problem Statement
In micro EDM process, the pulse on time, peak current and flushing are very important
machining parameter because it can control material remove rate and electrode wear rate.
However, there are difficulties to determine the optimum machining parameter to
increase the material remove rate and reduce the electrode wear rate. The unsuitable
pulse duration and peak current will increase the cost of production. Besides that, adding
the dielectric fluid flushing process will increase the material remove rate.
In this study, that were determined the optimum machining parameter to increase
material remove rate and reduce the electrode wear rate.
1.3
Objective
The objectives of this experiment are to:
1. Analysis the material remove rate and electrode wear rate for the process by
using the different machining parameter sure as peak current, pulse on time and
the flushing process.
2. Determine the optimum machining parameter to increase material remove rate
and reduce the electrode wear rate.
1.4
Scope
This project were analysis the material remove rate and electrode wear rate relate to the
EDM machining parameter such as peak current, pulse on time and the adding the
flushing process when machining. The type of electrode is copper and the material is
tungsten carbide. This study were not included the surface roughness for the work piece
and the other EDM machining parameter. Response surface methodology has been
applied in this project.
3
1.5
Important of Study
This project were defined the suitable EDM machining parameter such as peak current,
pulse on time and the flushing process to get more material remove rate and less of the
electrode wear rate. Besides that, this study was bringing benefit for industry to
minimize the costs when using the EDM machining to process the tungsten carbide.
1.6
Expected Result
At the end of this project, we were determined the optimum machining parameter to
increase material remove rate and reduce the electrode wear rate.
4
CHAPTER 2
LITERATURE REVIEW
This chapter discuss about the principle of EDM, electrode, material (tungsten carbide),
dielectric fluid, flushing process, machining parameter, and EDM machining
characteristics. Besides that, summary of the previous journal is included at the end of
this chapter.
2.1
Principle of EDM
Electrical discharge machine is a controlled metal remove technique whereby an electric
spark is used to cut (erode) the work piece, which takes a shape opposite to that of the
cutting tool or electrode. The electrode is made from electrically conductive material,
usually carbon. The die sinking electrode, made to the shape of the cavity required, and
the work piece are both submerged in dielectric fluid light lubricating oil). This
dielectric fluid should be a nonconductor (or poor conductor) of electricity. A servo
mechanism maintains a gap of about 0.0005 to 0.01 in. (0.01 to 0.02mm) between the
electrode and the work, preventing them from coming into contact with each other. A
direct current of low voltage and high amperage is delivered to the electrode at the rate
of approximately 20000 hertz (Hz). These electrical energy impulses vaporize the oil at
this point. This permits the spark to jump the gap between the electrode and the work
piece through the dielectric fluid. Intense heat is created in the localized area of the
spark impact; the metal is expelled from the surface of the work piece. The dielectric
fluid, which is constantly being circulated carries away the eroded particles of metal
5
during the off-cycle of the pulse and assists in dissipating the heat caused by the spark.
(Steve et al, 2005)
Servo
Electrode
Electrode
Work
piece
Material
Figure 2.1: a) A controlled spark remove metal during electrical discharge machining (EDM); b) basic
element of an electrical discharge system.
Figure 2.2: Stages of single spark
6
2.2
The Electrode
The electrode in die sinking EDM is formed to the shape of the cavity desired. As in
conventional machining, some materials have better cutting and wearing qualities than
others. Therefore, electrode must have the following characteristics:
Be good conductors of electricity and heat.
Be easily machined to shape at a reasonable cost
Produce efficient metal removal from the work piece
Resist deformation during the erosion process
Exhibit low electrode (tool) wear rates
The most common electrode materials are graphite, copper, copper graphite, copper
tungsten, brass, and steel. None of these electrode materials has general-purpose
application. Each machining operation dictates the selection of the electrode material.
Copper produces better results in the resistance capacitance circuits where higher
voltages are employed. It is commercially available in various shapes and side, is
relatively inexpensive, can be machined easily, and makes an excellent electrode. Its tool
wear rate is much less and its high metal removal ate is almost double that of nay other
electrode material (Steve et al, 2005).
7
Table 2.1: Selection of electrode material (Pandey et al, 2008)
Material
Wear ratio
Metal
Fabrication
Cost
Application
High on
Easy can be
High
On all metals
rough range
sprayed also
High only on
Easy
Low
On all metals
Difficult
High
Only where
removal rate
Copper
Brass
Low
High
finishing
ranges
Tungsten
Lowest
Low
small holes are
to be drilled
Tungsten
Low
Low
Difficult
High
copper
Used for higher
accuracy work
alloys
Cast iron
Low
Low
Easy
Low
Can be used
only on few
material
Steel
High
Low
Easy
Low
Can be used for
finishing only
Zinc based
High
alloys
Copper
High on
Easily die cast
Low
rough range
Low
Can be used in
all metals
High
Very delicate
graphite
and hence
difficult
8
High
Can be used on
all metals
Electrical discharge machining (EDM) is a widespread process which works very
effectively in machining of micro holes and harder material with high dimension
accuracy. In this study, the objective is to optimize the machining parameter of the EDM
process including peck current, pulse duration, and with or without flushing process to
increase the material removal rate and reduce the electrode wear rate. EDM machine
model MITSUBISHI has been used in this project and the weight for the workpiece and
electrode has been measured using the digital weight machine. The material removal rate
and electrode wear rate were calculated using the formula. Copper has been used as
electrode to machine the tungsten carbide, which is widely used to make micro die for
plastic extrusion. Response surface methodology (RSM) method has been applied in this
project at two levels (high, +1 and low, -1) and there are 26 experiments have been done.
From the result, the lowest material removal rate is 4.55952E-006g/second while the
maximum material removal rate is 5.49336E-005g/second. The lowest electrode wear
rate is 1.91171E-006g/second while maximum electrode wear is 6.30569-005g/second.
The optimum machining parameter to increase material remove rate and reduce the
electrode wear rate are 14.67 A of peak current, 2.57 μs pulse on time and ON the
flushing process.
i
ABSTRAK
Electrical discharge machining (EDM) ialah proses yang digunakan untuk menjalankan
pemotongan lubang yang bersaiz mikro dan bahan yang keras dengan ukuran yang tepat.
Dalam projek ini, pembolehubah yang dikawal ialah peak current, pulse duration, dan
sistem flushing. Hasil yang telah diuji ialah kadar pemotongan bahan kerja dan kadar
kehausan bagi electrode. Mesin EDM model MITSUBISHI digunakan untuk memotong
benda kerja tungsten carbide dengan menggunakan electrode kuprum. Berat electrode
dan bahan kerja diukur dengan menggunakan mesin penimbang digital sebelum dan
selepas ujukaji. Masa untuk pemotongan bahan kerja dicatatkan dan kadar pemotongan
bahan kerja dan kadar kehausan electrod dikira dengan formula. Jumlah eksperimen
yang telah dijalankan ialah 26 kali dan response surface methodology (RSM) digunakan
dalam projek ini untuk menentukan pembolehubah yang paling sesuai untuk mencapai
kadar pemotongan bahan kerja yang maximum dan kadar kehausan electrod yang
minimum. Nilai untuk kadar pemotongan bahan kerja maksimum dalam projek ini ialah
5.49336E-005g/saat sementara minimum adalah 4.55952E-006g/saat. Nilai maksimum
untuk kadar kehausan electrod ialah 6.30569-005g/saat sementara minimum ialah
1.91171E-006g/saat. Pembolehubah yang paling sesuai untuk mencapai kadar
pemotongan bahan kerja yang maksimum dan kadar kehausan electrod yang minimum
ialah 14.67 A of peak current, 2.57 μs pulse on time dan flushing system ON.
ii
DEDICATION
This project is dedicated to my parent, without whose caring support it been possible to
done the project. Besides that, this project also dedicated to sister and brother, who
support me in knowledge and other.
iii
ACKNOWLEDGEMENT
I am heartily thankful to my supervisor, Miss Liew Pay Jun, whose encouragement,
guidance and support from the initial to the final level enabled me to develop an
understanding of the project. Lastly, I offer my regards and blessings to all of those who
supported me in any respect during the completion of the project. Besides that, I want to
thank my parent that always supports me in project.
iv
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of Content
v-vii
List of Table
viii-ix
List of Figure
x-xi
List Abbreviations
xii
1. INTRODUCTION
1
1.1
Introduction
1-2
1.2
Problem Statement
3
1.3
Objective
3
1.4
Scope
1.5
Important of Study
4
1.6
Expected Result
4
2. LITERATURE REVIEW
5
3-4
2.1
Principle of EDM
5-6
2.2
The Electrode
7-8
2.2.1
Copper Electrode
9
2.3
Tungsten Carbide
10
2.4
Dielectric Fluid
10-11
2.5
EDM Parameter
11
2.5.1
Flushing
2.5.2
Peak Current, IP
2.5.3
Pulse-on Time, On
2.5.4
Pulse-off Time, OFF
11-12
12
12-13
13
v
2.6
EDM Machining Characteristics
13
2.6.1
Electrode Wear Rate
2.6.2
Material Removal Rate
2.7
Design of Experiment (DOE)
14-15
2.7.1
Response Surface Methodology (RSM)
15-17
2.8
Summary Previous Journal
18-22
2.9
Summary
23
3. METHODOLOGY
24
3.1
Flow Chart of Study
25
3.2
Step 1: Define the Objective for the Project
26
3.3
Step 2: Identify the Machining Parameter and Response Variable
26
3.3.1
Variable Machining Parameter
26
3.3.2
Constant Machining Parameter
27
3.4
Step 3: Preparation of the Experiment
27
3.4.1
Workpiece
27-28
3.4.2
EDM Electrode
28-29
3.4.3
Digital Weight Machine
29
3.4.4
Design of Experiment Matrix
30
3.5
Step 4: Running the Experiments
31
3.5.1
Machining Flow Chart
32
3.5.2
Testing the Finish Produce
33
3.6
Step 5: Analysis Result
33
3.6.1
Material Removal Rate (MRR) Measurement
34
3.6.2
Electrode Wear Rate (EWR) Measurement
34
3.7
Step 6: Define the Optimal Setting of Experimental Parameters
35
3.8
Step 7: Confirmation Run
35
3.9
Step 8: Make Conclusion for Project
35
13-14
14
4. RESULTS AND DISCUSSION
4.1
36
Result
36-37
vi
4.2
Analysis of Material Removal Rate
37-38
4.2.1
Fit Summary
38-39
4.2.1.1 Lack of Fit
39
4.2.1.2 Model Summary Statistic
40-41
4.2.2
ANOVA
41-43
4.2.3
Model Graphs
43-47
4.3
Analysis of Electrode Wear Rate
4.3.1
Fit Summary
48
48-49
4.3.1.1 Lack of Fit
49
4.3.1.2 Model Summary Statistic
49-51
4.3.2
ANOVA
51-52
4.3.3
Model Graphs
53-57
4.4
Optimization
4.4.1
Numerical
4.5
Confirmation Run
59
4.5.1
Average Deviation Percentage Value
59
57
57-58
4.5.1.1 Material Removal Rate
60
4.5.1.2 Electrode Wear Rate
60-61
4.6
Discussion
61
4.6.1
Material Removal rate
61-62
4.6.2
Electrode Wear Rate
62-63
5. CONCLUSION AND RECOMMENDATIONS
64
5.1
Conclusion
64
5.2
Recommendation
65
REFERENCES
66-67
APPENDICES
A
Gantt chart PSM 1
B
Gantt chart PSM 2
vii
CHAPTER 1
INTRODUCTION
This chapter is introduces the micro EDM process and problem statement. Besides that,
this chapter also includes the objective, scope, importance of study and expected result
for the project.
1.1
Introduction
Rapid advances in technology require further development in the manufacturing of
micro parts and micro-electromechanical system components. Increasing demand for
micro-parts made micro-machining processes more focused and investigated among the
front end of the technology in recent years. Micro-machining is the basic manufacturing
technology of the miniaturized and smaller parts having size of millimeter down to
micrometer.
Electrical Discharge Machining (EDM) is one of the machining processes that may have
high potential to manufacture small size components. It is a thermal process that utilizes
spark discharges to erode a conductive material and electrode is almost unloaded. There
is no physical contact between the tool electrode and the work piece so the process
works efficiently and particularly in the machining of hardness material. When the same
process principles are applied to the micro machining, the process is called as microEDM.
1
The basic physical characteristics of the micro EDM process is essentially similar to that
of the conventional EDM process but the main difference is the size of the electrode that
used. Electrical discharge machining is widely used in machining of dies and for
produce of unusually shaped or size production work. Example for EDM products are
fuel injector valves, parts and components for medical devices, fiber optic connectors,
micro mold making, stamping tools and micro electronic parts.
There are many manufacturing techniques to drill micro holes and micro parts beside
micro-EDM. The recently developed methods are Wire Electric Discharge Grinding
(WEDG), Micro-Electrochemical Machining (MECM), Laser-Beam Machining (LBM),
Focused Ion Machining (FIM), Micro milling, Micro Ultrasonic Machining (MUSM),
Electrochemical Discharge Machining (ECDM) and Micro punching. Performances of
these methods are unique, because they have different machining mechanisms. For
example, LBM can be used to drill a hole under diameter of 4 μm, however, it causes
deterioration and micro cracks on the machined surface. Besides that, ECDM can
improve the material removal rate to 1.5 mm/min and surface roughness to 0.08 μm.
However, the walls of the micro-holes are over etched (Yan et al, 2002).
Micro EDM is suitable for these and similar applications because its low discharges
energy generate smooth surfaces and that have no physical contact between the tool
electrode and the work piece so the process works efficiently. However, micro EDM
face two significant challenges that is high electrode wear and low Material Removal
Rate (MRR). Electrode wear which results from each discharge removing some material
from the electrode, degrades the geometric accuracy of machined features.
This report was analysis the MRR and EWR for the process by using the different
machining parameter that are peak current, pulse on time and add the flushing process
when machining. The type of electrode is copper and the material is tungsten carbide. At
the end, this project were also determined the optimum machining parameter to get the
good result.
2
1.2
Problem Statement
In micro EDM process, the pulse on time, peak current and flushing are very important
machining parameter because it can control material remove rate and electrode wear rate.
However, there are difficulties to determine the optimum machining parameter to
increase the material remove rate and reduce the electrode wear rate. The unsuitable
pulse duration and peak current will increase the cost of production. Besides that, adding
the dielectric fluid flushing process will increase the material remove rate.
In this study, that were determined the optimum machining parameter to increase
material remove rate and reduce the electrode wear rate.
1.3
Objective
The objectives of this experiment are to:
1. Analysis the material remove rate and electrode wear rate for the process by
using the different machining parameter sure as peak current, pulse on time and
the flushing process.
2. Determine the optimum machining parameter to increase material remove rate
and reduce the electrode wear rate.
1.4
Scope
This project were analysis the material remove rate and electrode wear rate relate to the
EDM machining parameter such as peak current, pulse on time and the adding the
flushing process when machining. The type of electrode is copper and the material is
tungsten carbide. This study were not included the surface roughness for the work piece
and the other EDM machining parameter. Response surface methodology has been
applied in this project.
3
1.5
Important of Study
This project were defined the suitable EDM machining parameter such as peak current,
pulse on time and the flushing process to get more material remove rate and less of the
electrode wear rate. Besides that, this study was bringing benefit for industry to
minimize the costs when using the EDM machining to process the tungsten carbide.
1.6
Expected Result
At the end of this project, we were determined the optimum machining parameter to
increase material remove rate and reduce the electrode wear rate.
4
CHAPTER 2
LITERATURE REVIEW
This chapter discuss about the principle of EDM, electrode, material (tungsten carbide),
dielectric fluid, flushing process, machining parameter, and EDM machining
characteristics. Besides that, summary of the previous journal is included at the end of
this chapter.
2.1
Principle of EDM
Electrical discharge machine is a controlled metal remove technique whereby an electric
spark is used to cut (erode) the work piece, which takes a shape opposite to that of the
cutting tool or electrode. The electrode is made from electrically conductive material,
usually carbon. The die sinking electrode, made to the shape of the cavity required, and
the work piece are both submerged in dielectric fluid light lubricating oil). This
dielectric fluid should be a nonconductor (or poor conductor) of electricity. A servo
mechanism maintains a gap of about 0.0005 to 0.01 in. (0.01 to 0.02mm) between the
electrode and the work, preventing them from coming into contact with each other. A
direct current of low voltage and high amperage is delivered to the electrode at the rate
of approximately 20000 hertz (Hz). These electrical energy impulses vaporize the oil at
this point. This permits the spark to jump the gap between the electrode and the work
piece through the dielectric fluid. Intense heat is created in the localized area of the
spark impact; the metal is expelled from the surface of the work piece. The dielectric
fluid, which is constantly being circulated carries away the eroded particles of metal
5
during the off-cycle of the pulse and assists in dissipating the heat caused by the spark.
(Steve et al, 2005)
Servo
Electrode
Electrode
Work
piece
Material
Figure 2.1: a) A controlled spark remove metal during electrical discharge machining (EDM); b) basic
element of an electrical discharge system.
Figure 2.2: Stages of single spark
6
2.2
The Electrode
The electrode in die sinking EDM is formed to the shape of the cavity desired. As in
conventional machining, some materials have better cutting and wearing qualities than
others. Therefore, electrode must have the following characteristics:
Be good conductors of electricity and heat.
Be easily machined to shape at a reasonable cost
Produce efficient metal removal from the work piece
Resist deformation during the erosion process
Exhibit low electrode (tool) wear rates
The most common electrode materials are graphite, copper, copper graphite, copper
tungsten, brass, and steel. None of these electrode materials has general-purpose
application. Each machining operation dictates the selection of the electrode material.
Copper produces better results in the resistance capacitance circuits where higher
voltages are employed. It is commercially available in various shapes and side, is
relatively inexpensive, can be machined easily, and makes an excellent electrode. Its tool
wear rate is much less and its high metal removal ate is almost double that of nay other
electrode material (Steve et al, 2005).
7
Table 2.1: Selection of electrode material (Pandey et al, 2008)
Material
Wear ratio
Metal
Fabrication
Cost
Application
High on
Easy can be
High
On all metals
rough range
sprayed also
High only on
Easy
Low
On all metals
Difficult
High
Only where
removal rate
Copper
Brass
Low
High
finishing
ranges
Tungsten
Lowest
Low
small holes are
to be drilled
Tungsten
Low
Low
Difficult
High
copper
Used for higher
accuracy work
alloys
Cast iron
Low
Low
Easy
Low
Can be used
only on few
material
Steel
High
Low
Easy
Low
Can be used for
finishing only
Zinc based
High
alloys
Copper
High on
Easily die cast
Low
rough range
Low
Can be used in
all metals
High
Very delicate
graphite
and hence
difficult
8
High
Can be used on
all metals