i

DEVELOPMENT OF ELECTRICAL DISCHARGE MACHINING POWER

GENERATOR

MUHD ABU BAKAR BIN MUHD RADZI

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical - Power)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2015

iii

This project report is dedicated to my family for their endless support and

encouragement.

iv

ACKNOWLEDGEMENT

First and foremost, I would like to express heartfelt gratitude to my

supervisor Dr. Azli Bin Yahya for his constant support during my study at UTM. He

inspired me greatly to work in this project. His willingness to motivate me

contributed tremendously to our project. I have learned a lot from him and I am

fortunate to have him as my mentor and supervisor

Besides, I would like to thank the authority of Universiti Teknologi Malaysia

(UTM) for providing me with a good environment and facilities such as to Faculty of

Biosciences Medical Engineering (FBME) to complete this project which I need

during process. Especially, to Mr Ade Erawan Minhad, Mr Trias Andromeda and Mr

Kartiko Nugroho who have offered a lot of helps in various ways throughout the

experimental work in the laboratory of FBME. Thanks also to staff from FBME and

Faculty of Electrical Engineering (FKE) for their kind help and support.

Last but not least, I would like to thank my family and my friend. They give

me a lot of moral supports and encouragement to accomplish this project. Without

them, I would not be able to accomplish this project.

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ABSTRACT

Electrical Discharge Machining process has been widely used for

manufacturing micro components due to its contactless process. The power generator

design and configuration requirements for producing the desired spark have always

been a challenge to the researchers. The aim of this project is to design and

implement the power generator using Switch Mode Power Supply (SMPS) with

100W output power for the EDM system. The power generator is designed based on

the SMPS push-pull topology. The hardware of the push-pull converter has been

successful built its characteristic almost similar to the designed specification. The

SMPS power generator for EDM machine is working properly according to the

supply current needed by the load. The SMPS is based on the push-pull topology that

utilize IGBT transistor. The project describes both simulation and experimental work

carried out on the developed circuit. Simulation results show that this push-pull

converter capable to produce DC voltage up to 100V. The experimental results show

that the 100W EDM power generator with up to 1A gap currant is stable and reliable.

vi

ABSTRAK

Proses ‘Electrical Discharge Machining’ (EDM) telah digunakan secara

meluas untuk pembuatan komponen mikro kerana kebaikan kaedah tanpa sentuhnya.

Reka bentuk dan konfigurasi keperluan penjana kuasa untuk menghasilkan bunga api

yang dikehendaki sememangnya merupakan cabaran kepada penyelidik. Tujuan

projek ini adalah untuk mereka bentuk dan melaksanakan penjana kuasa

menggunakan Switch Mode Power Supply (SMPS) dengan 100W kuasa output

untuk sistem EDM ini. Penjana kuasa direka berdasarkan konfigurasi SMPS push-

pull. Perkakasan penukar push-pull telah berjaya dibina dan sifatnya hampir sama

dengan spesifikasi yang direka. Penjana kuasa SMPS untuk mesin EDM berfungsi

dengan betul mengikut arus bekalan yang diperlukan oleh beban. Penjana kuasa ini

direka adalah berdasarkan topologi tolak-tarik yang menggunakan IGBT transistor.

Projek ini menggambarkan kedua-dua simulasi dan ujikaji dijalankan ke atas litar

maju. Keputusan simulasi menunjukkan bahawa ini penjana kuasa mampu

menghasilkan DC voltan sehingga 100V. Keputusan eksperimen menunjukkan

bahawa penjana kuasa 100W EDM dengan arus sehingga 1A adalah stabil dan boleh

dipercayai.

vii

TABLE OF CONTENTS

CHAPTER TITLE

PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xii

LIST OF ABBREVIATIONS xiv

LIST OF APPENDIXES xv

1 INTRODUCTION

1.1 Introduction 1

1.2 Problem Statement 4

1.3 Project Objectives 4

1.4 Project Scope 4

1.5 Report Organization 5

2 LITERATURE REVIEW

2.1 Introduction 7

2.2 EDM system and definition 8

2.3 Linear Power Supply (LPS) 11

2.4 Switch Mode Power Supply (SMPS) 12

viii

2.4.1 Comparison of LPS with SMPS 16

2.5 Transistor Switching Circuit Power Supply 17

2.5.1 Switching Circuit 17

2.6 Isolated DC-DC Converter 20

2.7 Topology of Push-Pull Converter 21

2.7.1 Analysis when S1 is on and S2 is off 22

2.7.2 Analysis when S1 is off and S2 is on 24

2.7.3 Analysis when both S1 and S2 are off 25

2.8 Transformer Review 26

2.9 Previous studies on EDM power generator 28

2.10 Summary 36

3 RESEARCH METHODOLOGY

3.1 Introduction 34

3.2 Parameter Calculation 35

3.2.1 Low Pass Filter 36

3.2.2 Pulse Width Modulator (PWM) 37

3.2.3 Drive Circuit 39

3.2.4 Source Rectification 41

3.2.5 Power Switch 41

3.2.6 Switching Circuit 42

3.2.7 Voltage Regulator 45

3.3 Transformer Winding 45

3.4 Summary 50

4 RESULT AND DISCUSSION

4.1 Introduction 51

4.2 Simulation Result 51

4.3 Experimental Result 56

4.3.1 RC Generator 56

ix

4.3.2 SMPS Pulse Generator 60

4.3.2.1 PWM Output 61

4.3.2.2 Driver Output 62

4.3.2.3 Transformer Winding 63

4.3.2.4 Parameter Test 64

4.3.2.5 Output Voltage 65

4.3.2.6 Switching Circuit 65

5 CONCLUSIONS AND FUTURE WORK

5.1 Conclusion 69

5.2 Future Works 71

5.3 Summary 71

REFERENCES 72-76

Appendices A − H 77-87

x

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Comparison of SMPS technology 15

2.2 Comparison of LPS and SMPS technology 16

2.3 Comparison of power supply technology 21

2.4 Novel Power Supply Topology for Large Working gap

dry EDM 28

2.5 Power Supply Unit for an Electric Discharge Machine 29

2.6 Design and Experimental Study of a High-Frequency

Fine Finish Power Supply for Wire-EDM 30

2.7 A Zero Current Switching Half-Bridge Power Supply

for High Speed Drilling Electrical Discharge Machining 31

2.8 A New Bipolar Power Supply for Spark Erosion

Based On Series-Parallel Resonant Inverter 32

2.9 Analysis, Design and Experimental Results of A

High-Frequency Power Supply For Spark Erosion 33

2.10 Development in Electric Power Supply Configuration

for Electrical Discharge Machining 34

2.11 Electrical Discharge Machining Experiences with

a Resonant Power Supply 35

3.1 List of Component Connected to SG3526 39

3.2 List of Component Connected to HCPL-3180 40

3.3 ETD44 Properties 46

3.4 Transformer Calculated Parameter 47

3.5 Winding Process of the ETD44 Transformer 49

4.1 Components Parameter 52

4.2 Summary of Simulation Result 54

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4.3 Line Current Harmonics 55

4.4 Limits for Class D Requirement 56

4.5 List of Component for RC generator 57

4.6 The Result of the PWM Output 61

4.7 Result of the Winding Test 63

4.8 Parameter of Transformer 64

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 EDM resistor-capacitor (R-C) circuit 3

2.1 Schematic layout of basic EDM components 8

2.2 Example of EDM machine 9

2.3 The basic relaxation circuit 10

2.4 The linear regulator schematic diagram 11

2.5 Basic switching regulator functions 13

2.6 Various topologies of SMPS in the market 14

2.7 Typical transistor switching circuit power supply 17

2.8 Block Diagram of Astable Multivibrator 18

2.9 Astable multivibrator using 555 timer 18

2.10 Waveform of Vc1 and Vout for astable

multivibrator

19

2.11 Basic circuit of Push-Pull Converter 21

2.12 Equivalent circuit when S1 is on, S2 is off 23

2.13 Equivalent circuit when S1 is off, S2 is on 24

2.14 Equivalent circuit when both S1 and S2 is off 25

3.1 Flow chart of the project methodology 35

3.2 PWM generator SG3526 top view 38

3.3 PWM generator schematic diagram 38

3.4 HCPL-3180 (Gate Drive) Connection to SG3526

(PWM) 40

3.5 Schematic Diagram of Switching Circuit 44

3.6 Schematic Diagram of Voltage Regulator 45

3.7 Cross Section of the Transformer Winding 48

3.8 Transformer Pin Connection 49

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4.1 Simulation circuit in PSpice software 52

4.2 Simulation Output Voltage 53

4.3 Output current and power 54

4.4 RC EDM schematic diagram 57

4.5 Waveform at point A (red) and point B (yellow) 58

4.6 Waveform of Output voltage (at Point C) 58

4.7 Photograph RC EDM prototype 59

4.8 Schematic diagram of SMPS pulse generator 60

4.9 Waveform of Output A and Output B of SG3526 61

4.10 Output Voltage of Drive Circuit 62

4.11 Output Voltage of the EDM power generator 65

4.12 Power switch and MOSFET Driver 66

4.13 Switching Circuit Using IC 555 Timer 67

4.14 Pulse timer signal 68

xiv

LIST OF ABBREVIATIONS

AC - Alternating Current

C - Capacitor

DC - Direct Current

F - Farad

f - Frequency

GND - Ground

H - Henry

Hz - Hertz

I - Current

kΩ - Kilo Ohm

L - Inductor

m - Mili

P - Power

Q - MOSFET

R - Resistor

V - Voltage

Ω - Ohm

xv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A PWM CONTROL CIRCUIT SG3526 77

B OPTOCOUPLER HCPL-3080 78

C IGBT FGA20S120M 79

D TRANSFORMER ETD 44 80

E ULTRAFAST DIODE MUR8100EG 82

F DC-DC CONVERTER NML1215S 83

G MURATA POWER INDUCTOR 85

H RECTIFIER BRIDGE KBPC608 86

CHAPTER 1

INTRODUCTION

1.1 Introduction

Electrical Discharge Machining (EDM) is the process of machining electrically

conductive materials by using precisely controlled sparks that occur between an

electrode and a workpiece in the presence of a dielectric fluid. Electrical Discharge

Machining process has been widely used for manufacturing micro components due to its

contactless process.

In EDM system, there are several subsystems, i.e. generator, (also known as

power supply), electrode, dielectric and servo mechanism. Generator provides a series of

DC current discharges between the electrode and the workpiece. Dielectric is electrically

non-conducting liquid which is used to fill the gap between electrode and workpiece. It

is used for removing EDM’s debris in the sparking gap. Electrode is usually made of

high strength material with high melting point and easy to machine such as Brass,

Copper and Graphite. Servo system feeds the electrode into the work piece maintaining

a constant gap as well as cooling system.

2

The first development of EDM machine was investigated by Dr. Boris

Lazarenko, Moscow University Professors and Dr. Natalya Lazarenko in 1943 at the All

Union Electro Technical Institute. The Lazarenkos developed a spark-machining process

with an electrical circuit that used many of the same components as the automobile

ignition system. This process became one of the standard EDM systems in use

throughout the world.

One of the key elements of EDM is a power generator unit that controls the

amount of energy consumed. This power generator helps to maintain the machining gap

(known as spark gap) in order to generate succession of uniform electrical discharge in

the form of sparks. It has a time-control function, which called on time that control the

length of time that current flows each pulse. It also controls the amount of current

allowed to flow during each pulse. In conventional EDM, the voltage and current level

are high, thus the electrode gets locally melted and welded work-piece and electrode.

Moreover, a present of stray arching should be minimized or eliminated. Until now, a

number of power supply units have been developed ranging from basic resistance-

capacitance (RC) power supply to the complex resonant power supply unit.

A Relaxation-type RC pulse power supply is the earliest pulse power for EDM,

with simple structure and reliable capability, is able to generate a small pulse width of

narrow pulse. However, the pulse in the discharge process is uncontrollable. The

machined parts would suffer from micro crack; melted electrode and left over debris.

Furthermore, some energy-saving EDM pulse power supplies have replaced the existing

linear power supplies. Thus, in this project pulse power generator will be designed by

implementing Switch Mode Power Supplies which is push-pull converter.

Figure 1.1 illustrates the application of the power generator in EDM system. The

RC power generator will be applied between the electrode and workpiece.

3

Figure 1.1 EDM resistor-capacitor (R-C) circuit [1]

Two basic types of EDM generator are RC and pulse. Both types are requiring

DC supply as a source. The power supply is a very unique role in this system. In many

respects, it is the mother of the system. It gives the system life by providing consistent

and repeatable power to its circuits. The two major DC source technologies are linear

power supply (LPS) and Switched Mode Power Supply (SMPS).

1.2 Problem Statement

Most conventional EDM power generator uses linear power supply as their main

topology. Main issue of linear power supply is a raw DC input voltage is usually derived

from the rectified secondary of a 50Hz transformer whose weight and volume was often

a serious system constrain. Besides, the Linear Power Supply is constrained to produce

only a lower regulated voltage from a higher non-regulated input. The regulation

efficiency is low, resulting in a considerable power loss needing large heat sinks in

relatively large and heavy power units.

4

1.2 Project Objectives

The objectives of the project are;

To design a 100W EDM power generator system with maximum 1A gap current.

To develop EDM power generator according to push-pull topology.

To experiment and analyze EDM power generator.

1.4 Project Scope

In order to achieve the objective of this project, there are some guidelines need to

be refered in this project. The theory involved in constructing the device is investigated

before constructing the device. First of all, the operation of EDM power generator has

been study. The behavior of the power generator is analyzed and it is consist of power

supply module and switching module. Push pull converter was chosen as the DC to DC

converter because the core size of the transformer is small due to the excitation of

transformer in both directions.

Push pull converter is the main focused of the circuit because of the complexity

of the circuit. The control circuit of the push pull converter is design using integrated

circuit to minimize the number of component. The design of the circuit is simulated

using PSpice. The hardware is built on breadboard first before it is printed on the circuit

board permanently.

Besides, the operation and topology of the MOSFET, transformer and PWM

circuit need to be study too. Their behaviour need to be analyzed so that any problems

can be avoided when it is being used in the circuit. The transformer is used to step down

5

or step up the voltage and at the same time it is also used to isolate the input voltage

from the output voltage. In the same time, it will transfer the energy from primary

winding to the secondary winding. Therefore, any considerations regarding on the

transformer must be acknowledged.

Next, after studying and reviewing all the information, the transformer and the

Push-Pull Converter need to be designed. All the parameters will be calculated by using

the related formulas in the analysis. The data is collected from the hardware and it is

compared to the theoretical and simulation data.

1.5 Report Organization

This project is organized in five chapters. Their contents are summarized as

follows:

(i) An overview of the project, problem statements, project objectives,

project scopes and project significance are all arranged under Chapter 1.

(ii) While in Chapter 2, the literature review of EDM system and push-pull

topology has been discussed in detail where the push-pull converter and

the basic operation of push-pull converter are being discussed as well.

(iii) As in Chapter 3, the overall discussion of research methodology is

detailed out in flow chart that will give a clear view of the project flow. It

discusses the designed circuit of push-pull converter circuit, the process

to build the hardware of designed circuit and the steps to produce the

printed circuit board. Apart from that, all the activities and deliverables

that need to be done are also listed in this chapter.

6

(iv) Chapter 4 presents an experimental works and discussion of the project.

Experimental results also being presented in this chapter. The push-pull

converter circuit has been tested in order to determine the characteristic

and the reliability of isolation power supply.

(v) Chapter 5 accomplishes the work undertaken and will conclude the

overall study on this project. Several recommendations are given for

future research possibility.

72

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