edm ecm report whole 0307 tech distilled[1]

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A REPORT ON TECHNOLOGY ASSESSMENT OF ELECTRICAL DISCHARGE AND

ELECTRO-CHEMICAL MACHINE TOOLS

Prepared for

Association for Manufacturing Technology (AMT)

by

K. P. Rajurkar, Distinguished Professor of EngineeringJayakumar Narasimhan, Graduate Student

Center for Nontraditional Manufacturing Research University of Nebraska - Lincoln,

Lincoln, NE - 68588, U.S.A.

July 2003

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ACKNOWLEDGEMENTS

The invaluable assistance provided by a large number of graduate students of the Center for Nontraditional Manufacturing Research is gratefully acknowledged. We are especially thankful to Paul Warndorf for his advice throughout this study.

Published by:

AMT – The Association for Manufacturing Technology 7901 Westpark Drive, McLean, VA 22102

Printed in the United States of America

Copyright © 2004 AMT – The Association for Manufacturing Technology all rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher.

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Summary

This report is a state-of-the-art technology assessment of Electrical Discharge and Electro-chemical machine tools and accessories for the Association for Manufacturing Technology (AMT). The Center for Nontraditional Manufacturing Research (CNMR) at the University of Nebraska-Lincoln has conducted this technology assessment. The study was focused on the following aspects:

1. Die-sinking Electrical Discharge Machines (EDM), Wire EDM, Electrical Discharge Grinding (EDG) and Micro-EDM (MEDM).

2. Electrochemical Machining (ECM), Pulse Electrochemical Machining (PECM), and Electrochemical Micro Machining (ECMM)

Existing EDM and ECM literature available in the national and international journals, technical conference proceedings and technical reports has been thoroughly reviewed for preparing this technology assessment. The main objective of the report is to identify the latest and new developments in the field of EDM and ECM machine tool technology and the state-of-the-art research related to EDM and ECM processes.

Chapter 1 of this report provides a brief introduction to the nontraditional manufacturing processes. Chapter 2 introduces EDM process followed by the brief summaries of publications related to various aspects of EDM machine tool and process. Chapter 3 describes the ECM process and reports the summaries of the state-of-the-art literature on the research and development of the ECM machine tool and process. A complete list of references is included at the end of the report.

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Table of Contents

Title Page No.CHAPTER 1 1-1

1. Introduction to Nontraditional manufacturing processes ------------------- 1

CHAPTER 2 2-59

2. Electrical Discharge Machining ------------------------------------------------ 2

2.1 Macro EDM --------------------------------------------------------------- 4

2.1.1 Equipment --------------------------------------------------------- 6

2.1.2 Tool ----------------------------------------------------------------- 9

2.1.3 Process and Process Characteristics ---------------------------- 15

2.1.4 Monitoring and Control ------------------------------------------ 21

2.1.5 Surface Integrity -------------------------------------------------- 22

2.2 Wire EDM ----------------------------------------------------------------- 26

2.2.1 Equipment --------------------------------------------------------- 26

2.2.2 Tool ----------------------------------------------------------------- 30



2.2.5 Applications ------------------------------------------------------- 40

2.3 Micro EDM ---------------------------------------------------------------- 40

2.3.1 Equipment --------------------------------------------------------- 41


2.3.3 Applications ------------------------------------------------------- 51

CHAPTER 3 60-87

3. Electrochemical Machining ----------------------------------------------------- 60

3.1 Macro ECM ---------------------------------------------------------------- 62



3.1.3 Applications -------------------------------------------------------- 71

3.2 Micro ECM ----------------------------------------------------------------- 80

3.2.1 Equipment ---------------------------------------------------------- 81

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Title Page No. 3.2.2 Process and Process Characteristics ---------------------------- 82

3.2.3 Mask ECMM process --------------------------------------------- 84

3.2.4 Applications -------------------------------------------------------- 87

4. References ------------------------------------------------------------------------- 88

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List of Figures

Fig. No. Title Page No. 2-1 Sequence of events occurring during one pulse of and EDM cycle 3

2-2 A schematic diagram of an EDM relaxation power ------------- 3

2.1-1 Schematic of die-sinking EDM system ---------------------------- 5

2.1-2 Schematic of EDM milling system -------------------------------- 5

2.1.1.1-1 On-the-machine 3D measurement system ------------------------ 6

2.1.1.2-1 Linear Motor Head --------------------------------------------------- 7

2.1.1.2-2 Block diagrams of two servo system ------------------------------ 7

2.1.1.3-1 Relationship between tool wear rate and ratio M using AC

combined pulse line -------------------------------------------------- 8

2.1.1.3-2 Relationship between machining rate and ratio M using AC

combined pulse line -------------------------------------------------- 8

2.1.1.4-1 Sectional view of the mechanism ---------------------------------- 9

2.1.1.4-2 Principle of the electrode direct drive device --------------------- 9

2.1.2.1-1 Simulation Algorithm ------------------------------------------------ 10

2.1.2.1-2 Principle of reverse simulation ------------------------------------- 10

2.1.2.2-1 Shape changes of edge portion of cylindrical copper electrode 11

2.1.2.2-2 Relation between pulse duration and radius of attached area and of

single discharge crater ----------------------------------------------- 11

2.1.2.3-1 Tool Wear Compensation ------------------------------------------- 12

2.1.2.3-2 Schematic overview of combined wear compensation ---------- 12

2.1.2.4-1 Structure of CVD-carbon -------------------------------------------- 13

2.1.2.5-1 Grooving with a spinning electrode -------------------------------- 14

2.1.3.2-1 Principle of Multi-spark EDM -------------------------------------- 15

2.1.3.3-1 Principle of EDM in gas --------------------------------------------- 17

2.1.3.5-1 Experimental Set-up ------------------------------------------------- 18

2.1.3.6-1 Example of coolant tunnel with straight holes ------------------- 19

2.1.3.6-2 Example of curved tunnel ------------------------------------------- 19

2.1.3.7-1 Energy distribution in EDM process ------------------------------- 20

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Fig. No. Title Page No. 2.1.3.7-2 Flowchart for determining energy distribution ------------------- 20

2.1.4.3-1 Structure of the adaptive fuzzy logic controller ------------------ 22

2.1.5.1-1 Principle of Laser Surface modification --------------------------- 23

2.1.5.1-2 SEM of EDMed surface --------------------------------------------- 23

2.1.5.1-3 SEM of Laser irradiated surface ------------------------------------ 23

2.1.5.3-1 Variation of removal rate and surface roughness with NP

concentration ---------------------------------------------------------- 24

2.1.5.3-2 Relationship between nickel content in resolidified layer and NP

concentration ---------------------------------------------------------- 25

2.1.5.3-3 Vickers hardness of surface layers --------------------------------- 25

2.1.5.3-4 Results of sand abrasion test ---------------------------------------- 25

2.2-1 A schematic view of a WEDM system ---------------------------- 26

2.2.1.1-1 Principle of double-wire system and wire positions in various

cutting situations ------------------------------------------------------ 27

2.2.1.1-2 Wire lag for cut length of 7mm ------------------------------------- 27

2.2.1.2-1 Self-spinning Wire EDM -------------------------------------------- 28

2.2.1.3-1 Twin-Wire EDM developed by Charmillies Technologies ----- 28

2.2.1.3-2 Pocketing using Single wire and Twin Wire EDM -------------- 28

2.2.1.4-1 KE 500 Series Wire-EDM ONA America ------------------------ 29

2.2.1.5-1 Wire-cut micro parts for a medical application; material: TiAl6V4 30

2.2.2.1-1 Schematic diagram of detecting circuits -------------------------- 30

2.2.2.1-2 Variation of discharge position just before the wire breakage - 31

2.2.2.2-1 Shape of the workpiece finished with wire resonance frequency 31

2.2.2.3-1 Selected geometries and the main test conditions ---------------- 32

2.2.3.1-1 Relationship between electrical conductivity and machining rate,

surface roughness ----------------------------------------------------- 33

2.2.3.2-1 Cutting rate and surface finish as a function of pulse frequency for

various PCD grades and WC --------------------------------------- 34

2.2.3.2-2 Cutting rate and surface quality depending on the dielectric fluid 34

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Fig. No. Title Page No. 2.2.3.3-1 Geometry of WEDMed surfaces measured parallel to wire

electrode --------------------------------------------------------------- 35

2.2.3.3-2 Results of surface roughness ---------------------------------------- 35

2.2.3.4-1 Pressure distribution in case of front discharge ------------------ 36

2.2.3.4-2 Pressure distribution in case of side discharge ------------------- 36

2.2.4.1-1 A voltage waveform of the wire rupture process ----------------- 36

2.2.4.1-2 Block Diagram of the Sparking frequency monitor ------------- 37

2.2.4.2-1 On-line recorded identification data ------------------------------- 37

2.2.4.3-1 Sparking frequency monitoring and fuzzy control system ------ 38

2.2.4.4-1 On-line identified workpiece height ------------------------------- 39

2.2.4.6-1 HS-WEDM pulse state monitor system --------------------------- 40

2.2.5.1-1 Wire cut Titanium template ----------------------------------------- 40

2.3-1 Schematic of Micro EDM system ---------------------------------- 41

2.3.1.1-1 Scheme of micro-EDM system for mass production of microholes 41

2.3.1.1-2 Setup of micro-EDM system ---------------------------------------- 42

2.3.1.2-1 Entire process to produce a coaxial cavity with an over hang -- 43

2.3.1.2-2 Advantage of EDG with disc electrode ---------------------------- 43

2.3.1.2-3 Possible applications ------------------------------------------------- 43

2.3.1.3-1 Structure of the system ---------------------------------------------- 44

2.3.1.4-1 Sectional view of electrode feeding device with Impact Drive

Mechanism ------------------------------------------------------------ 45

2.3.1.4-2 Mechanism of IDM movement ------------------------------------- 46

2.3.1.4-3 Examples of electrode feeding with IDM ------------------------- 46

2.3.1.4-4 Structure of electrode feeding device utilizing impulsive force 47

2.3.1.4-5 Structure of electrode feeding device utilizing elliptical movement 47

2.3.2.1-1 Experimental configuration ----------------------------------------- 49

2.3.2.2-1 Internal surface of a micro-hole ------------------------------------ 50

2.3.2.2-2 Defects inside micro-hole bore ------------------------------------- 50

2.3.2.3-1 Wire Electro-Discharge Grinding ---------------------------------- 50

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Fig. No. Title Page No. 2.3.2.3-2 Traveling Wire in WEDG ------------------------------------------- 51

2.3.3.1-1 Layer by layer machining ------------------------------------------- 52

2.3.3.1-2 To-and-fro tool path -------------------------------------------------- 52

2.3.3.1-3 Machining cross cavity with inclined surface -------------------- 52

2.3.3.1-4 Machined spherical cavity and the electrode --------------------- 522.3.3.3-

1Basic set-up for machining silicon by EDM ---------------------- 54

2.3.3.3-

2Micro mirror --------------------------------------------------------

--

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2.3.3.3-

3Top view and assembled bevel gear ( 4.3 mm) --------

--------

55

2.3.3.3-

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Finished spring (7mm long, 4mm wide) against the

backdrop of Belgian coin --------------------------------------

--------------------- 55

2.3.3.4-1 Scanning tool path ---------------------------------------------------- 55

2.3.3.4-2 Experimental setup for circular holes ------------------------------ 56

2.3.3.4-3 Micro hole through 2.5mm plate ----------------------------------- 56

2.3.3.4-4 Triangular and square blind hole machined with planetary

movement ------------------------------------------------------------- 57

2.3.3.4-5 Comparison of Material Removal Rate (MRR) and Relative

Electrode Wear (REW) when drilling square blind micro hole 57

2.3.3.5-1 Fabrication process of a pin-plate module ------------------------ 58

2.3.3.5-2 MMA unit ------------------------------------------------------------- 58

2.3.3.5-3 Micro pipe and macro cylinder combination --------------------- 59

2.3.3.5-4 Machining process of Micro pipe and macro cylinder combination 59

3-1 Schematics of electrochemical machining operations ----------- 60

3-2 Electrochemical machining equipment schematic --------------- 61

3.1-1 Principle of Electrochemical Machining -------------------------- 62

3.1.1.2-1 PECM with group pulses -------------------------------------------- 64

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3.1.1.2-2 Interelectrode gap ---------------------------------------------------- 64

3.1.1.2-3 Experimental setup --------------------------------------------------- 64

3.1.1.2-4 Comparison of experimental and theoretical current pulses ---- 64

3.1.1.2-5 Comparison of peak current profiles ------------------------------- 64

Fig. No. Title Page No. 3.1.1.3-2 Computer prediction of erosion with moving tool and initial gap

of 0.05 mm ------------------------------------------------------------ 65

3.1.1.3-3 Computer prediction of erosion with moving tool and initial gap of

0.08 mm --------------------------------------------------------------- 66

3.1.1.3-4 Example of 2-D Erosion showing the effect of a stepped tool - 66

3.1.1.4-1 Typical workpiece surface profile ---------------------------------- 67

3.1.1.4-2 Computer Simulation of a Homogeneous material -------------- 67

3.1.1.4-3 Computer Simulation of a Heterogeneous material ------------- 67

3.1.1.5-1 Scheme of shaped-surface electrochemical machining with a

nonprofiled electrode ------------------------------------------------ 68

3.1.1.5-2 Profilograms representing a cross section of the machined material

used for calculating a, and Vw values -------------------------- 68

3.1.2.1-1 Simulated time response of the current to a ramp input --------- 69

3.1.2.1-2 Simulated time response of the ram position to a ramp input -- 69

3.1.2.1-3 ECM sparkout --------------------------------------------------------- 69

3.1.2.2-1 PECM data acquisition system ------------------------------------- 70

3.1.2.2-2 Correlation between damping ratio and gap size ----------------- 70

3.1.2.2-3 Correlation between variance of J and gap size ------------------ 70

3.1.3.1-1 Schematic of an idealized charge modulated electric field ----- 71

3.1.3.1-2 A 3-axis batch mode ECM positioning system designed and built

by Faraday Tech Inc ------------------------------------------------- 71

3.1.3.1-3 A 3-axis batch mode ECM surface finishing set-up designed and

built by Faraday Tech Inc ------------------------------------------- 71

3.1.3.1-4 Before and after polishing of Inconnel 718 part ------------------ 72

3.1.3.1-5 Before and after deburring of casting aluminum wheel --------- 72

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3.1.3.2-1 Current waveforms for ECM finishing ---------------------------- 73

3.1.3.2-2 Experimental Setup -------------------------------------------------- 73

3.1.3.2-3 Finished surfaces with graphite electrode ------------------------- 74

3.1.3.3-1 Factors influencing the ECM Process ----------------------------- 75

Fig. No. Title Page No. 3.1.3.3-2 ECM Electrolytic System ------------------------------------------- 75

3.1.3.3-4 Cone with electrolytic formed edges ------------------------------ 76

3.1.3.3-5 Electrolytically formed rifling --------------------------------- 76

3.1.3.3-6 10 Diesel Injector Fuel Chamber ----------------------------------- 76

3.1.3.3-7 Turbine blade with tip machined electrolytically ---------------- 76

3.1.3.4-1 Electrochemical Deburring ------------------------------------------ 77

3.1.3.4-2 Cut Away View of EC Deburred Valve --------------------------- 77

3.1.3.4-3 Electrochemical radiusing of blade dovetail ---------------------- 78

3.1.3.4-4 Ratchet contour ------------------------------------------------------- 78

3.1.3.4-5 Eight component tool with manual loading carrier -------------- 78

3.1.3.5-1 EDM damaged layers ------------------------------------------------ 79

3.1.3.5-2 S-N diagram showing EDM vs. PECM fatigue life ------------- 79

3.1.3.6-1 Schematic view of PECM copying process with a stepped tool 80

3.2-1 Scheme of an Electrochemical Cell -------------------------------- 80

3.2-2 Cu Microstructures using ECMM ---------------------------------- 80

3.2.1.1-1 Block diagram of the various System Components of the ECMM

setup -------------------------------------------------------------------- 82

3.2.2.2-1 ECM modeling by characteristic relations ------------------------ 82

3.2.2.2-2 Efficiency vs. current density for various pulse-on times using

250g/l NaNO3 electrolyte ------------------------------------------- 83

3.2.2.2-3 Efficiency vs. current density for various for various NaNO3

electrolyte concentrations, pulse-on times 10ms ----------------- 83

3.2.2.3-1 Schematic Diagram for ECMM Process -------------------------- 83

3.2.2.3-2 Effect of feed rate on side and frontal gap ------------------------ 84

3.2.2.3-3 Effect of voltage on side and frontal gap -------------------------- 84

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3.2.2.3-4 Comparison of theoretical and experimental values ------------- 84

3.2.3.1-1 Shape evolution during through mask ECMM ------------------- 85

3.2.3.2-1 Incorporation of a dummy photoresist to avoid island formation 86

3.2.3.3-1 Relationship between ECMM performance and parameters --- 86

Fig. No. Title Page No. 3.2.3.3-2 Schematic diagram of an experimental tool for one sided ECMM 86

3.2.4.1-1 Schematic representation of electrochemical actuator ---------- 87

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List of Tables

Table No. Title Page No. 2-1 Process characteristics of different EDM processes ---------- 4

2.1.2.4-1 Physical properties of CVD-carbon and graphite ------------- 13

2.1.3.2-1 Comparison of machining characteristics --------------------- 16

2.3.1.4-1 Comparison between electrode feeding devices -------------- 48

2.3.3.2-1 Micromachining technology comparison ---------------------- 53

2.3.3.2-2 Compatibility of machining technologies with different

materials ------------------------------------------------------------ 53

2.3.3.2-3 Adjustment of polarity according to the doping type of silicon 53

3.1.3.2-1 Surface Quality with bipolar pulses ---------------------------- 74

3.1.3.2-2 Surface Quality with combination pulses ---------------------- 74

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CHAPTER 1

1. Introduction to Nontraditional manufacturing processes

Nontraditional machining processes, such as Electrical Discharge Machining (EDM), Electrochemical Machining (ECM), Laser Beam Machining (LBM), Abrasive Water Jet Machining (AWJM), Abrasive Flow Machining (AFM), and hybrid machining processes provide one of the best alternatives, and sometimes the only alternative for machining a growing number of high-strength, corrosion resistant, and wear resistant materials. Many advanced materials such as superalloys, engineering ceramics and metal matrix composites cannot be machined by traditional methods, or at best they are machined with excessive tool wear and at high cost. The complexity and required surface quality of machined parts, tools and geometries, such as deep internal cavities, may only be produced by these advanced or nontraditional manufacturing processes. These processes are rapidly gaining importance in producing complex parts from a variety of material such as superalloys, ceramics, plastics, fiber reinforced composites, wood and textiles in diverse applications throughout the aerospace, automotive, electronic and medical industries, i.e. essentially all competitive manufacturers of durable goods.

This technology assessment report deals mainly with Electrical Discharge Machining (EDM) and Electro-chemical Machining (ECM) processes and related machine tools. A brief introduction of each process is followed by the summary of recent research and development reported worldwide.

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CHAPTER 2

2. Electrical Discharge Machining (EDM)

Electrical discharge machining (EDM) is a thermoelectric process that removes material from the workpiece by a series of discrete sparks between a work and tool electrode immersed in a liquiddielectric medium. The method of material removal from the workpiece is by melting and vaporizing. The molten material is ejected and flushed away by the dielectric leaving a very small crater on the electrode surface. The electro-erosion process is used to produce complex twoand three dimensional shapes, even in harder materials. According to the most agreed-on processmechanism, when a voltage is applied through a dielectric medium across the gap between thetool and the workpiece, an electric field builds along the path of least resistance. This causes a breakdown of the dielectric and initiates the flow of current. In the second stage, electrons and ions migrate towards the anode and cathode respectively at high current density, forming acolumn of plasma and initiating the melting of the workpiece. When the application of voltage is stopped, the plasma column collapses, a portion of the molten metal is ejected from the workpiece, and a very small crater is formed. The debris remaining on the workpiece is flushedaway by the dielectric*. The sequence of event during an EDM cycle is shown in the Fig. 2-1.

In EDM the erosion rate and tool wear, and the resulting surface integrity and geometry dependon many factors including current, voltage, on-time, off-time, polarity, pulse shape, work and tool material properties, dielectric flushing conditions, dielectric properties, electrode geometry,and machine characteristics.

2a. EDM Equipment:All EDM systems include the machine (including the frame, ram, worktable, tool and workpieceholders, and clamping devices), pulse power supply, tool electrode, dielectric system, and servo control system. Various types of power supply systems exist today among those that are suitable for EDM are the relaxation power system, which consists of a charge loop and a discharge loop, and independent power system, which consists of a dc power source, pulse controller and apower controller (Fig. 2-2). The pulse controller in this of power supply sets a time basis and controls the “on” and “off” states of the power controller. The power controller delivers the pulseto the gap with the required power. Some EDM machines are equipped with power supplies that combine the relaxation and independent power supplies in order to improve surface roughness.

Tool Material. The basic requirements for a tool material are high electrical conductivity, high melting point, and high thermal conductivity. The tool materials should be easy to machine and inexpensive. Some of the most frequently used tool materials include graphite and bronze for machining steels and copper-tungsten for machining carbides. Bronze and copper-tungsten areoften used for producing smooth surfaces and for high-precision EDM.

Dielectric Fluid. The main functions of the dielectric fluid are to insulate the gap between thetool and the workpiece before high energy is accumulated, to concentrate the discharge energy to a very small area, to recover the gap conditions after the discharge, and to flush away the discharge products. The two most commonly used dielectric fluids are petroleum-based

* Rajurkar, K.P., Kozak, J., Chatterjee, A., “Nonabrasive Finishing Methods,” ASM Handbook, Surface Engineering, Vol. 5, 1994.

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hydrocarbon mineral oils and deionized water. Dielectric flushing is very important in EDM operations, the commonly used flushing methods are immersion, spray, or jet.

Fig. 2-1 Sequence of events occurring during one pulse of an EDM cycle*

Fig. 2-2 A schematic diagram of an EDM relaxation power**

* “Technological aspects of spark erosion,” Agietron Corporation, Addison III, 1983. ** Rajurkar, K.P., “Nontraditional Manufacturing Processes,” Handbook of Manufacturing and Automation, Chapter. 13, 1994, pp. 211-242.

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Controls. A servo control is used to keep the inter-electrode gap within a small range of variations around a desired setting during machining. Depending on the voltage, current, dielectric media, surface finish requirements, the gaps can be as small as a few microns to as large as several hundreds microns. In order to maintain a constant gap size, the tool feed rate should equal the material removal rate in the feed direction. However, because the removal rate is often not constant, a servo control is used that takes the gap signals as the measure of the gap size and compares them with the servo reference voltage. Accordingly, either the tool is retracted or moved faster towards the workpiece to maintain the stability of the erosion process.

2b. EDM classification: EDM process is classified mainly into two groups: Die-sinking and Wire EDM. The Electrical Discharge Grinding (EDG) process uses a wheel electrode but its principle is similar to the die-sinking operation. EDM process can also be classified as Macro EDM and Micro EDM depending on the scale of the part or the feature on the part. The details of each of these types of processes are presented before.

2c. Process characteristics: In the case of EDM, the metal removal rate and the surface roughness depend on the peak current, pulse, on-time, peak voltage, frequency of pulses, and the flow rate of the dielectric. The process characteristics of the different EDM processes are summarized in the Table 2-1.

Table. 2-1 Process characteristics of different EDM processes EDM process Voltage Current / MRR Ra

CapacitanceI. Macro EDM (i) Die-sinking EDM 30 - 300V 20 - 400A 0.002 - 0.8mm3/sec 2.5 - 30 m (ii) EDM Milling 20 - 200V 20 - 300A 0.02 - 0.5mm3/sec 3 - 25 mII. Wire EDM 30 - 120V 0.5 - 128A 5 - 15mm3/sec 0.127 - 0.254 mIII. Micro EDM 60 - 100V 100 - 3300pF 200 - 1000 m3/sec 0.2 - 0.6 m

2d. Applications, Process Capabilities, and Limitations: EDM is capable of machining difficult-to-cut materials such as hardened steels carbides, high –strength alloys, and even ultra hard conductive material such as polycrystalline diamond and some ceramics. The process is particularly well suited to sinking cavities and drilling irregularly shaped holes. The only limit in machinability is the electrical conductivity of the workpiece material. The other problems in EDM include tool wear and the irregularity of the tool wear, and limitations of EDM to machine very sharp corners because of the existence of the gap between the tool and the workpiece. The recent development of micro-EDM expands the capabilities of EDM with respect to fine part fabrication.

The recent advances in the EDM process are discussed in the following sections.

2.1 Macro EDM

Diesinking EDM is traditionally performed vertically, but it may also be conducted horizontally. The tool takes the mirror image of the shape that needs to be produced. Because of the tool wear

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multiple tools are required in machining 3D complex shapes. The schematic of the diesinkingEDM system is shown in the Fig. 2.1-1. The EDM power system transforms the utility ac powerinto pulsed dc power with 30 - 300 V and from several milliamperes to 100 A of peak current.

Fig. 2.1-1 Schematic of die-sinking EDM system*

In EDM milling the simple shaped tool is strategically moved along a predetermined tool path to machine or finish a 3D cavity. The shape of the tool can be square or cylindrical depending on the shape requirement. EDM milling system eliminates the tool design and fabricationcomplexities. Fig. 2.1-2 shows the EDM milling schematic. The power supply and dielectric flow mechanism are same as diesinking EDM.

Fig. 2.1-2 Schematic of EDM milling system

* Benedict, G.E., “Nontraditional Manufacturing Process,” Marcel Dekker, 1987.

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The following are brief summaries of recently published papers/reports that focus on die-sinkingEDM and EDM milling machine tools and processes.

2.1.1 Equipment

2.1.1.1 Mohri, N., Takezawa, H., Satio, N., “On-the-Machine Measurement in EDM Process bya calibration System with Polyhedra,” Annals of the CIRP, Vol. 43, No. 1, 1994, pp. 203-206.

This paper deals with on-the-machine measurement of an electrode and a workpiece shapeand accuracy during electrical discharge machining. It describes the principle of calibrationmethod and the change of complex shape of an electrode and a workpiece measured in the process.

Fig. 2.1.1.1-1 On-the-machine 3D measurement system

Fig.2.1.1.1-1 illustrates the overview of the developed system. The system consists of numerically controlled electrical discharge machine, position detecting probes, and polyhedra for calibration. The signal from demodulation circuit for the transducer is sent to microcomputer when stylus touches the surface being measured. The coordinates of the target position are measured by reading NC data, which are transferred to microcomputer.The measurement process consists of three stages: 1. Location of stylus normal to surface being measured.2. Calibration of edge position of stylus. 3. Detection of surface coordinates of the workpiece. The following conclusions are obtained by using the above measurement system:1. High accuracy less than several micrometers have been achieved.2. It is confirmed through the measurement under a high wear rate condition that the wear

rate of the electrode depends on the location and the shape of the electrode3. The shape changes of an electrode and a workpiece with gap distance between them can

be observed against machining time by means of the proposed measurement system.

2.1.1.2 Kaneko, Y., Yamada, H., Toyonaga, T., “Performance of Linear Motor Equipped Die-Sinking EDM”, International Journal of Electrical Machining No. 5, 2000, pp. 59-64.

This paper reports on the improvement in the machining performance of quick response andhigher speed in the linear motor servo-equipped Die-Sinking EDM.

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Fig. 2.1.1.2-1 Linear Motor Head

Fig.2.1.1.2-1 shows the structure of the linear motor head. Armature coil units and magnetsare installed on both sides of the ceramic column; a magnetic force countervailing structure is incorporated to prevent the axis distortion. The column is made of self-developed ceramics to restrict its gravity weight. Coolant fluid is supplied to offer a satisfactory cooling performance against heat emitted by the two armature coils.Fig.2.1.1.2-2 shows the block diagram of linear motor servo system. This system allows the motor itself to move, so the travel distance measured by the linear scale is directly sent back to the motor, this provides a simpler control mechanism without the effect of backlash.As the electrode is directly installed at the motor itself, the movement of both the electrode and the motor can be regarded as a one-piece body’s movement. Due to this characteristic, even in machining systems based on the voltage feedback of the electrical discharge gaps, an excellent follow-up and a quick response are possible.

Fig. 2.1.1.2-2 Block diagrams of two servo system

Quick response servo technology enables stable and consistent machining at higher speed. The good follow-up performance at high speed and high acceleration jump movement makesshort-circuit between electrode and workpiece to be prevented.High-speed jump operation improves machining efficiency and also improves the debris disposal function and makes the efficient flushing possible even in deep machining.

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2.1.1.3 Fuzhu, H., Kunieda, M., Hashimoto, H., “EDM Using Combined Pulse Lines,”International Journal of Electrical Machining, No. 6, 2001, pp. 47-52.

This paper describes the dramatic improvement in the processing capabilities of EDM by the introduction of combined pulse lines, which is a combination of main-pulses, and sub-pulsesin which sub-pulses are inserted periodically in main-pulse lines.The main pulse is characterized by its short duration and high peak current. With these pulses the machining rate is high although tool wear is considerable.The sub-pulse is characterized by its long duration, low peak current, and negative workpiecepolarity. These pulses form carbon layers on tool surface thereby prevent tool wear. With conventional pulse lines, which are the succession of only one kind of wave form, it is impossible to satisfy the three requirements of high machining rate, small tool wear and fine surface roughness simultaneously.

Fig. 2.1.1.3-1 Relationship between tool wear rate and ratio M using AC combined

pulse line

Fig. 2.1.1.3-2 Relationship between machining rate and ratio M using AC

combined pulse line

In the machining using combined pulse lines, the effects of two kinds of pulses interact with each other. When long duration pulses are mixed into short duration pulses, lower tool wearmachining can be performed, because of carbon adhesion caused by the long duration pulses. The three important requirements in performance, machining rate, tool wear, and surface roughness, can be satisfied simultaneously using the combined pulse lines. Normally the DC combined pulse line is effective. But it is considered that when the main-pulse is extremely short, the AC combined pulse-line is more effective than the DC combined pulse-line.

2.1.1.4 Zhao, W., Liu, W., Di, S., “Research on Miniaturized Direct Drive Mechanism of EDMElectrode Using Linear Ultrasonic Motors,” International Journal of ElectricalMachining, No. 4, 1999, pp. 29-31.

This paper deals with an electrode direct drive device for EDM utilizing dual stator linearultrasonic motor.Fig.2.1.1.4-1 shows the structure of the new electrode driving mechanism that basically is a dual stator linear ultrasonic motor. The electrode corresponds to the moving object and being pressed by two stators with pre-pressing force of 1-3N. The stators have a number of teeth on the top of it and several piezoelectric elements are adhered at the bottom.

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Fig. 2.1.1.4-1 Sectional view of the mechanism

Fig.2.1.1.4-2 illustrates the principle of electrode direct drive device. When an ultrasonic signal is applied to the piezoelectric elements, according to certain phase relation, the elastic stator vibrates in a standing wave pattern, thus the tooth on the stator vibrate obliquely. As the electrode is pressed on the tooth of the stator, the frictional force generated by the horizontal element of the oblique vibration drives the electrode moving along its longitudinal direction in small step quickly. Since two stators are arranged to drive the electrode movingforward and backward respectively, controlling two stators alternately can easily generatecoaxial vibration of the electrode.

Fig. 2.1.1.4-2 Principle of the electrode direct drive device

Coaxial vibration of electrode applied by controlling the stators, improves the machiningstability and efficiency due to better evacuation of the debris.Machining test verifies that the device is suitable for small hole EDM drilling and the machining speed increases with the driving frequency for dielectric fluids, distilled water andkerosene.

2.1.2 Tool

2.1.2.1 Kunieda, M., Wataru, K., Takita, T., “Reverse Simulation of Die-Sinking EDM,” Annals of the CIRP, Vol. 48, No. 1, 1999, pp. 115-118.

This paper aims to develop a simulation method for die-sinking EDM to solve the inverse problem of obtaining the appropriate tool electrode shape for achieving the desired finalworkpiece shape.Fig.2.1.2.1-1 shows the simulation algorithm. In reverse simulation method developed, the same algorithm as that used in forward simulation is adopted. Fig.2.1.2.1-2 shows the principle of reverse simulation. The initial state of reverse simulation is considered to be the final state of the forward simulation. The workpiece is fed in thereverse direction towards the tool electrode taking the workpiece to be the tool electrode. Thevalue for the depth of the layers removed from the tool electrode and workpiece surface per pulse discharge is reversed.

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Fig. 2.1.2.1-1 Simulation Algorithm

Fig. 2.1.2.1-2 Principle of reverse simulation

The simulation takes into account a variety of influencing factors such as tool electrode wear, gap width distribution, curvature of the tool electrode surface, and debris particleconcentration, all of which affect each other in a complex manner.The suitability of the proposed algorithm was proved by demonstrating, through reverse simulation, that the shapes of the tool electrode and workpiece are restored to their initialshapes in forward simulation.

2.1.2.2 Mohri, N., Suzuki, M., Furuya, M., Saito, N., “Electrode Wear Process in ElectricalDischarge Machining,” Annals of the CIRP, Vol. 44, No. 1, 1995, pp. 165-168.

This paper deals with a systematic consideration of electrode wear phenomena in EDM. The whole process of electrode wear is evaluated in two stages in order to consider themechanism of electrode wear. The first stage is the transition state at the beginning of machining and the second is the stationary state. The shape of the electrode is measured by on-the-machine measurement system, which uses a polyhedron. Some of the measured samples are shown in Fig.2.1.2.2-1.

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Fig. 2.1.2.2-1 Shape changes of edge portion of cylindrical copper electrode

The observation of electrode shape, revealed significant wear at the edge portion of theelectrode at the beginning of machining.Fig.2.1.2.2-2 shows the relation between pulse duration and radius of the attached carbon. The electro-erosion of carbon steel results in the molten material being ejected out of the workpiece surface. The carbon precipitates as turbo-static carbon on the electrode surface.Thus, a low wear of electrode is realized.

Fig. 2.1.2.2-2 Relation between pulse duration and radius of attached area and of single discharge crater

Zero wear of electrode can be realized with a very long pulse duration taking into account of equilibrium of the removal rate with precipitation and deposited substance on the electrode. Powder suspended oil for working fluid is remarkably effective for getting the stability ofmachining even under the long pulse duration.

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2.1.2.3 Bleys, P., Kruth, J., Lauwers, B., Zryd, A., Delpretti, R., Tricarico, C., “Real Time Tool Wear Compensation in Milling EDM,” Annals of the CIRP, Vol. 51, No. 1, 2002, pp. 157-160.

This paper presents a new method of wear compensation. On-line estimation of tool wear is used for combining anticipated compensation with real-time compensation.

Fig. 2.1.2.3-1 Tool Wear Compensation

The anticipated wear compensation (Fig.2.1.2.3) is based on off-line tool wear simulation prior to machining. However, this method requires a solid model of the blank geometry as input for the wear simulation module as it needs to know where the material is to be removed.As an alternative to anticipated wear compensation, real-time wear compensation is based on the actual tool wear as it is evaluated on-line, without wear simulation before machining, thus a model of the blank is not required. However, in this method a small over-estimation in on-line wear sensing results in a continuously increasing machining depth and therefore, rapidly yields a very large geometrical error.

Fig. 2.1.2.3-2 Schematic overview of combined wear compensation

A new method of tool wear compensation for milling EDM is presented, which is called the combined wear compensation (Fig.2.1.2.3-2), which combines the existing anticipated wear compensation with real-time compensation based on on-line tool wear sensing. This enables milling EDM process without the need to provide an accurate model of the blank geometry.

2.1.2.4 Uno, Y., Okada, A., Nakanishi, H., Gua, C., Okamota, Y., Takagi, T., “EDM Characteristics of CVD-Carbon Electrode,” International Journal of Electrical Machining, No. 3, 1998, pp. 19-24.

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In EDM process, the reduction of electrode wear is very important to attain high accuracy machining. This paper investigates the EDM characteristics of CVD (Chemical Vapor Deposition) -carbon electrode with turbostratic structure to attain higher performance.Turbostratic carbon has a chemical structure in which hexagonal lattice plane are laminatedirregularly, different from graphite structure. EDM with low electrode wear rate can be accomplished by adhesion of carbon to the electrode and the workpiece, because of the protection effect of the carbon, which has a largeheat resistivity. As this phenomenon is observed only under the long pulse duration, EDM with low electrode wear rate under finishing condition is not possible.

Fig. 2.1.2.4-1 Structure of CVD-carbon

As proposed in this paper, EDM with low electrode wear rate is possible by using CVD-carbon electrode (Fig. 2.1.2.4-1) under finishing conditions, since the heat resolved carbonadhered to the end surface of CVD-carbon electrode has a stronger adhering ability than that of graphite one.Table 2.1.2.4-1 shows the physical properties of CVD-carbon.

Table. 2.1.2.4-1 Physical properties of CVD-carbon and graphite

EDM without electrode wear is possible using finishing conditions with CVD-carbon electrode. This is due to the high impact resistance as CVD-carbon has denser structure and high heat conduction in layer direction. The surface roughness increases with an increase in pulse duration. Under short pulse duration, the surface roughness in case of CVD-carbon electrode is smaller than that of graphite.The CVD-carbon electrode was found to be slightly fractured. This is due to the frequent impact generated during electrical discharges and the weak bond resulting from Van DerWaal’s force in the deposition direction of CVD-carbon.

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2.1.2.5 Sato, T., Imai, Y., Goto, A., Magara, T., “A New Grooving Method based on Steady Wear Model in EDM,” International Journal of Electrical Machining, No. 5, 2000, pp. 41-49.

In this paper, a new grooving method using steady state in proposed. First, the electrode wear model at the steady state is described. Based on this model, an approach to determine the machining conditions for grooves of any cross-sectional shape is described. EDM with an electrode being moved along a preprogrammed path is called EDM contouring. EDM contouring has advantages of lower machining cost and higher flexibility as complexgeometries can be produced using simple and inexpensive electrodes. EDM contouring can achieve high accuracy by using the steady state of the electrode wear. Using the steady wear model, different types of grooves can be machined with a non-spinning electrode, such as: 1. Trapezoidal grooving with trapezoid electrode 2. Isogonal Trapezoid grooving with square electrode 3. Semi-ellipse grooving with cylindrical electrode 4. Deep trapezoid grooving 5. Deep grooving with complex electrode

Fig. 2.1.2.5-1 Grooving with a spinning electrode

Grooving can be done with a spinning electrode (Fig. 2.1.2.5-1). Since the electrode spinning promotes the flow of the dielectric fluid in the working gap, a larger working current can be employed and, as a result, the machining becomes faster.

2.1.2.6 Enache, S., Opran, C., Stocia, G., Strajescu, E., “The Study of EDM with Forced Vibration of Tool-Electrode,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 167-170.

The paper describes a study of EDM with forced vibration of the tool electrode, coupled with the technological vibration of the technological machining system.The technological force is obtained by quantifying the effect given by the pressure waves occurring and developing in the working gap, due to the gas and vapor bubbles produced by microdischarges. The effect of the technological vibration consists in increasing themachining efficiency, improving the removal of erosion products, decreasing the roughness of the machined surface, and enhancing the stability of the machining process.The technological force is a disturbing force of the technological machining system,depending on the pulse duration, working intensity and working surface of the tool electrode.The vibratory motion of the tool electrode is yielded by adding the vibrations of thetechnological machining system to the vibrations of the imposed vibratory system.

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Electrodischarge machining with forced vibration of the tool electrode (EDM-FV) provides significant technical and economic advantages.

2.1.3 Process and Process Characteristics

2.1.3.1 Lonardo, P., Bruzzone, A., “Effect of Flushing and Electrode Material on Die-Sinking EDM,” Annals of the CIRP Vol. 48, No. 1, 1999, pp. 123-126.

The important performance measures of EDM are removal rate, electrode wear, accuracy andsurface texture. This paper discusses the influence of electrode material, flushing, electrode dimension, depth of cut and planetary motion on EDM performance.The analysis of the influence of qualitative factors (electrode material and flushing) and quantitative factors (depth of cut and electrode size), with two levels each, was carried out by adopting a full factorial experimental design.Productivity and electrode wear were measured differently for roughing and finishing operations. Surface quality was measured only for finishing, by adopting three height parameters and three form parameters.The experiment yielded the following conclusions: 1. The electrode material has significant influence in finishing operations on wear and height

roughness parameters. When copper electrodes are used, wear is larger and surface height is smaller.

2. Flushing in roughing operations increases both MRR and electrode wear. In finishing operations flushing influences the form parameters, increasing Rdq (RMS slope of the profile within the sample length), Rsk (Skewness), and Rku (Kurtosis).

3. In all the experiments, the electrode size was found to have a significant effect on the productivity and the electrode wear.

2.1.3.2 Kunieda, M., Muto, H., “Development of Multi-Spark EDM,” Annals of the CIRP, Vol. 49, No. 1, 2000, pp. 119-122.

This paper describes the Multi-spark EDM method to obtain higher removal rates and lower energy consumption compared with conventional EDM.

Fig. 2.1.3.2-1 Principle of Multi-spark EDM

Fig.2.1.3.2-1 shows the principle of Multi-spark EDM. The basic circuit of Multi-spark EDM comprises of a conventional pulse generator, a workpiece, and two electrodes, both of which

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are fixed onto the quill of the same EDM machine and connected serially. For each generator pulse, one discharge occurs in the gap between one tool electrode and the workpiece, and another discharge occurs at the same time in gap between the other tool electrode and workpiece. The removal rates are different for the two gaps due to reverse polarity of workpiece and the two gaps. To balance the removal rates in both gaps, the polarity of the pulse generator is changed adaptively to equalize the gap voltages measured at both gaps.

Table. 2.1.3.2-1 Comparison of machining characteristics

Advantages of Multi-spark EDM are follows (Table 2.1.3.2-1):1. The removal rate is higher than those of conventional EDM as the total voltage drop

through the two discharge gaps is two times larger than in conventional EDM.2. The power efficiency of Multi-spark EDM is two times higher than that of conventional

EDM.3. The tool wear ratio of Multi-spark EDM is higher than that of the single positive tool

electrode type in conventional EDM. 4. There is no significant difference in surface roughness between Multi-spark EDM and

conventional EDM 5. Multi-spark EDM of high-electric-resistivity materials is advantageous because placing

both the electrodes as close as possible to each other can minimize the voltage drop insidethe materials.

2.1.3.3 Kunieda, M., Yoshida, M., “Electrical Discharge Machining in Gas,” Annals of the CIRP, Vol. 46, No. 1, 1997, pp. 143-146.

This paper shows that EDM can be achieved in gas. An appropriate tool path to erode 3D curved surface is proposed and thus an improved machining rate is achieved by supplyingoxygen gas into the gap.

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Fig. 2.1.3.3-1 Principle of EDM in gas

Fig. 2.1.3.3-1 shows the principle of EDM in gas. A high velocity gas jet from a pipe tool electrode enhances the removal of molten and evaporated workpiece material. The gas jetcools and solidifies the removed material and prevents them from adhering onto the surfaceof tool electrode and the workpiece. During the pulse interval, the gas jet blows off the plasma formed by the previous discharge, thus guaranteeing the recovery of the dielectricstrength of the gap. Comparison of the characteristics of EDM in air with those of conventional EDM in dielectric liquid shows that, 1. The removed material driven by the high velocity air flow do not attach to the electrode

surface and is flushed out of the gap. 2. Using a thin-walled pipe as the tool electrode, reattachment of the removed material to the

electrode surfaces can be prevented.3. The material removal rate is improved as the concentration of oxygen in air is increased

due to heat generation caused by oxidation of the electrode materials.4. A uniform high-velocity air flow over the working gap is enabled by using an NC tool

path, thus making 3D machining possible. The machined shape obtained is very precise as the tool wear is negligible.

2.1.3.4 Kunieda, M., Nakashima, T., “Factors determining Discharge Location in EDM,”International Journal of Electrical Machining, No. 3, 1998, pp. 53-58.

This paper describes the factors, which affect the determination of the discharge location in EDM. The main factors investigated are the working gap width, the debris particle concentration, the surface area, and the degree of plasma deionization. It is observed that when the dielectric fluid is not contaminated, the probability of occurrenceof discharge at the narrow gap is high. In terms of surface area, however, the discharge does not always occur at the point where the gap is narrowest. Debris particles move between the anode and cathode in a direction perpendicular to the electrode surfaces due to electrophoresis, and some particles are linked in series to form chains parallel to electric field. Therefore in the gap, there are numerous chains of particles which almost bridge the gaps and that discharge occurs where the end of a chain is closest tothe opposite electrode surface.The debris particle generated and distributed around the first discharge crater in a clean dielectric fluid does not affect the next discharge location because of the surface area.

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However, in a series of pulse discharges in which numerous chains of debris particles growover the working surface, the influence of the debris particle concentration becomes moredominant than that of the gap width distribution. This seems to be the main reason for the occurrence of the discharge localization. From two consecutive pulse discharges, the first discharge does not affect the discharge location of the second one as long as the plasma formed by the first discharge is deionized during the discharge interval. The minimum discharge interval necessary for the plasma to be deionized is around 6 s under the pulse conditions used in the study.

2.1.3.5 Yoshida, M., Kunieda, M., “Study on the Distribution of Scattered Debris Generated by aSingle Pulse Discharge in EDM Process,” International Journal of Electrical Machining,No. 3, 1998, pp. 39-46.

This paper investigates the relationship between the bubbles and the distribution of scattered debris after a single pulse discharge in the dielectric liquid between plane parallel electrodes. In addition, the possibility of conduction during EDM process with air as dielectric mediumis investigated by studying at the effect of the bubble in material removal in comparison to the distribution of scattered debris after a single pulse discharge in air.

Fig. 2.1.3.5-1 Experimental Set-up

Fig. 2.1.3.5-1 shows the experimental setup. The discharge gap, on which a discharge is produced between electrodes, is distinguished from the gap between the glass disk and the workpiece. The workpiece is made of steel, and lapped to facilitate the observation of the distribution of the scattered debris. The wire is held above the workpiece at a set distance by a micrometer head. The polarity of the copper wire is positive and it is lapped. From the experiments it was concluded that, in liquid, the generated debris were mainlydistributed at the boundary of the bubble formed due to evaporation and dissociation of gelatin.In air, the generated debris was distributed over a wide range in the radial direction and debris density is lower as the radial distance from the center of the discharge crater increases. In air, the removal mechanism is mainly evaporation when the pulse duration is short, but the mechanism becomes removal of molten material as the pulse duration becomes longer. The material removal rate during a single pulse discharge reaches a peak in both air and liquid at 90 s after the pulse discharge begins and after it decreases.

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In air almost all the debris is scattered on the workpiece surface, and gets attached.Therefore, EDM may be performed with air as a dielectric medium provided the debris generated in the process is flushed out of the EDM gap before it solidifies on the workpiecesurface.

2.1.3.6 Goto, A., Watanabe, K., Takeuchi, A., “A Method to Machine a Curved Tunnel with EDM,” International Journal of Electrical Machining, No. 7, 2002, pp. 43-46.

In this paper, a system to machine a curved tunnel into a workpiece is proposed. With this technology, temperature control will be precise and quality of injection products will be improved.

Fig. 2.1.3.6-1 Example of coolant tunnel with straight holes

Fig. 2.1.3.6-2 is an example of a traditional coolant tunnel of an injection mold. The combination of straight holes is likely to make defects to an injection product. A new coolant tunnel which is proposed is shown in Fig. 2.1.3.6-2.

Fig. 2.1.3.6-2 Example of curved tunnel

This system is composed of a curved electrode-drive part that has an electrode at the end of it and a guide to straighten the electrode-drive part.The following conclusions are made by conducting machining test: 1. The system proposed is simple and easy to control. 2. Machining stability is good even when the curved area is machined.3. A smooth curved tunnel can be machined into the workpiece.

2.1.3.7 Hayakawa, S., Yuzawa, M., Kunieda, M., Nishiwaki, N., “Time Variation and Mechanism of Determining Power Distribution in Electrodes during EDM Process,” International Journal of Electrical Machining, No. 6, 2001, pp. 19-25.

This paper determines the mechanism of the power distribution in electrodes during EDMprocess.

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In order to obtain the time variation of the power distribution, the increase in the energy distributed in the electrodes by a single-pulse discharge is measured with increasingdischarge duration. Fig.2.1.3.7-1 shows the energy distribution in the electrode.

Fig. 2.1.3.7-1 Energy distribution in EDM process

Fig.2.1.3.7-2 shows a flowchart for determining the energy distribution in an electrode.

Fig. 2.1.3.7-2 Flowchart for determining energy distribution

The time variation of the power distribution is first measured by comparing the measured temperatures of the electrodes with the calculated results. In earlier stages of each pulse discharge, the measured power distribution in electrodes is about two thirds of the total discharge power. With the increase in the discharge duration, the power distribution in the electrodes approaches the total discharge power.The power distribution in the dielectric fluid during the time practically used in the EDMprocess is much more than for the steady state, which results in the gap condition not in equilibrium and a large fraction of the discharge power is consumed in transient phenomenasuch as evaporating, dissociating and ionizing of the dielectric fluid.

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2.1.4 Monitoring and Control

2.1.4.1 Kunieda, M., Kojima, H., “On-Line Detection of EDM Spark Locations by Multiple Connection of Branched Electric Wires,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 171-174.

This paper describes the on-line detection of spark locations in EDM processes. Supplying a discharge current through branched wires, and measuring the ratio of current allotted to each wire, helps in detecting a spark location.Under stable machining conditions it is important for the spark location to be distributed uniformly and not be localized. Localization of the spark contaminates the sludge and the dielectric strength decreases. Therefore an adequate method for on-line detection of spark location is necessary so that a better adaptive control of EDM processes can be achieved. The uneven distribution of spark locations is initiated when the flushing of the discharge gap becomes insufficient, and the reduction of the distribution area is a preliminary signal of an arc.An adaptive control of EDM process can be affected by means of monitoring the variance of the spark location. For this it is necessary to seek a value of variance such that the gap situation cannot be improved no matter how the discharge conditions are altered. Then the obtained value is considered to be a threshold of the occurrence of an arc.

2.1.4.2 Rajurkar, K. P., Wang, W. M., “Real-Time Stochastic Model and Control of EDM,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 187-190.

This paper proposes a new EDM servo control system in which a high-speed computer directly regulates the servo feed rate instead of servo reference voltage and takes the parameters of discharge time ratios from an EDM gap monitor as the feed back signal. The on-line control strategy is developed according to the real-time achieved stochastic model to minimize the variance of the controlled process and increase the machining speed with the control interval time of 2 milliseconds and thus, increasing the productivity. The self-tuning regulator for EDM servo adaptive control proposed in this paper can identify on-line the mathematical model which represents the relationship between the servo driving signal and the output value of EDM process formed by discharge parameters. The process stability significantly increases with this control system. The variance of the process output data is at least 10% lower than that achieved by many other control methods. The new EDM servo adaptive controller improves the process stability to have more normal sparking and less gap-open and gap-short pulses than many other control systems. This system increases the machining productivity by 15% when machining small holes and medium sized cavities.

2.1.4.3 Boccadoro, M., Dauw, D. F., “About the Application of Fuzzy Controllers in High-Performance Die-Sinking EDM Machines,” Annals of the CIRP, Vol. 44, No. 1, 1995, pp. 147-150.

This paper deals with the die-sinking EDM optimization and control systems. A description of fuzzy controllers, its principles and experimental results using a commercial EDM AGIE die sinker are presented.

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The optimal working conditions in EDM change continuously and drift away from theworking point may cause process degeneration and damage to the electrodes. The above problem is distinguished in two parts: 1. Adaptive Control Constraint (ACC) - Their main function is to avoid damage to electrodes

by avoiding arcing and other process degeneration. 2. Adaptive Control Optimization (ACO) – The main function is to optimize the spark

parameters as a function of active surface, and the flushing conditions to maximize the machining speed.

In EDM, machining at the optimal work point changes continuously, therefore it is necessary to add intelligence to the controller to make it capable to adapt automatically to the newmachining situations. This is adaptive fuzzy logic.

Fig. 2.1.4.3-1 Structure of the adaptive fuzzy logic controller

Fig. 2.1.4.3-1 shows the adaptive fuzzy logic controller. The controller is implemented using C programming language. The software runs on a single chip 16 bits high performancecontroller, featuring a 100 nanoseconds instruction cycle time, allowing the fuzzy controllerimplementation to be executed in less than 1 millisecond.The results obtained from experiments show that the stock removal increases in the range of 20% and 300% depending upon the machining task complexity. The electrode wear remainssame or decreases. The surface quality is slightly better.

2.1.5 Surface Integrity

2.1.5.1 Tamura, T., “Surface Modification of Electrical Discharge Machined Surface by C02Laser,” International Journal of Electrical Machining, No. 3, 1998, pp. 47-52.

This paper presents a new surface modification method, which applies laser beam to the surface of cemented carbide having cracks and micro craters. Fig. 2.1.5.1-1 shows the principle of laser surface modification. The heat-affected zones of cracks and micro craters generated by EDM disappear due to isolation of tungsten carbide (WC) based on melting Co acting as a binder. The new method modifies the laser-irradiated surface including the heat-affected zone to the same sintering state as before machining by EDM.

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SEM observations of EDMed surface and laser irradiated surface are shown in Fig. 2.1.5.1-2& 3. The abnormal structures consisting of face-centered-cubic and close-packed hexagonal structures of the surface machined by EDM were transformed to a hexagonal lattice in stablestate by the laser irradiation.

Fig. 2.1.5.1-1 Principle of Laser Surface modification

Fig. 2.1.5.1-2 SEM of EDMed surface Fig. 2.1.5.1-3 SEM of Laser irradiated surface

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2.1.5.2 Kruth, J. P., Stevens, L., Froyen, L., Lauwers, B., “Study of the White Layer of a Surface Machined by Die-Sinking Electro-Discharge Machining,” Annals of the CIRP, Vol. 44, 1995, pp. 169-172.

EDM generates a white layer at the surface of a workpiece. This paper discusses theinfluence of workpiece material, electrode material and type of dielectric on the compositionand metallographic phases of the white layer. Tests have been performed on the materials Impax, C35 and Armco, machined in oil or water dielectric. The tests yield the following conclusions: 1. The white layer of samples machined in oil contains about four times more carbon than

the base material.2. The carbon in the white layer of a sample machined in oil comes from the dielectric.3. The white layer machined in an oil dielectric, consists of dendritic structures, formed by

rapid solidification of the molten pool. 4. The use of copper, aluminium or graphite electrodes has almost no influence on the

structure of the white layer, as only small amounts of electrode material migrate fromelectrode to the white layer.

2.1.5.3 Uno, Y., Okada, A., Hayashi, Y., Tabuchi, Y., “Surface Modification by EDM with Nickel Powder Mixed Fluid,” International Journal of Electrical Machining, No. 4, 1999, pp. 47-52.

This paper proposes a new method of surface modification of aluminum bronze (AlBC3) with nickel powder mixed fluid, in order to form nickel layer on the EDM generated surface for higher wear resistance to shell sand abrasion. AlBC3 is characterized by high removal rate as that of steel, and low electrode wear.

Fig. 2.1.5.3-1 Variation of removal rate and surface roughness with NP concentration

Fig. 2.1.5.3-1 shows variations of removal rate and surface roughness with nickel powderconcentration. Increase in the nickel powder concentration does not affect the removal rateand it is almost constant. However the EDM generated surface with nickel powder mixedfluid has a smaller surface roughness than that in conventional EDM with kerosene typefluid.

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Fig. 2.1.5.3-2 Relationship between nickel content in resolidified layer and NP concentration

The resolidified layer containing nickel can be generated on EDM generated surface and the thickness of the layer becomes larger and uniform with an increase of nickel powder concentration in the machining fluid (Fig. 2.1.5.3-2).

Fig. 2.1.5.3-3 Vickers hardness of surface layers Fig. 2.1.5.3-4 Results of sand abrasion test

The EDM generated surface with nickel powder mixed fluid becomes harder than that withkerosene and it has higher resistance to sand abrasion (Fig. 2.1.5.3-3&4).

2.1.5.4 Dauw, D. F., Brown, C. A., Griethuysen, J. P., “Surface Topography Investigations by Fractal Analysis of Spark-Eroded Electrically Conductive Ceramics,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 161-165.

This paper discusses the relations between EDM conditions, workpiece material, microscopicanalysis, and fractal and conventional analysis of the machined surface. These machined surfaces are studied using scanning electron microscopy (SEM) and profilometry.The study suggests that the EDM theories which are reliable and applicable to metals cannot be confirmed when EDM is applied to electrically conductive ceramics. The materialremoval rates and machined surface roughness are not only dependent on the machiningparameters but also on the work material.It is possible to associate noticeable features on micrographs with parameters derived from fractal and conventional analysis of profilometry data. The fractal analysis results in parameters which appear to contain different information about the profile than the conventional parameters.

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2.2 Wire EDM

Wire EDM (WEDM) uses the same material removal principle as die-sinking EDM. WEDMuses a metal wire as the tool electrode; it can generate two or three dimensional shapes on the workpiece for making punch dies and other mechanical parts.

In a WEDM machine, the wire electrode is held vertically by two wire guides located separatelyabove and beneath the workpiece, with the wire traveling longitudinally during machining. Theworkpiece is usually mounted on an x-y table*. A schematic view of a WEDM system is shownin the Fig. 2.2-1. The trajectory of the relative movement between wire and workpiece in the x-y coordinate space is controlled by a CNC servo system according to a preprogrammed cutting passage. The CNC servo system also adjusts the machining gap size in real time, similar to thediesinking EDM operation. The dielectric fluid is sprayed from above and beneath the workpiece into the machining gap with two nozzles.

Fig. 2.2-1 A schematic view of a WEDM system**

The power generations in WED machines usually are transistor-controlled RC or RLC systemsthat provide higher machining rate and a larger gap size to reduce wire rupture risk. In someWED machines the machining gap is submerged into the dielectric fluid to avoid wire vibration and, therefore, to obtain a better accuracy. The upper wire guide is also controlled by the CNC system in many WED machines. During machining, the upper wire guide and the x-y table simultaneously move along their own preprogrammed trajectories to produce a taper and/or twist surface on the workpiece.

2.2.1 Equipment

2.2.1.1 Masuzawa, T., Wada, Y., “A double-wire system for accuracy improvement in WEDM,”International Symposium for Electromachining XI, 1995, pp. 201-208.

This paper proposes that eliminating wire lag and drum shape caused by bending and vibration of the wire electrode will improve the precision of WEDM.

* Rajurkar, K.P., Wang, W.M., “Nontraditional Machining,” The CRC Handbook of Mechanical Engineering, Chapter 13, CRC press, 1998, pp. 29-34.** Rajurkar, K.P., “Nontraditional Manufacturing Processes,” Handbook of Manufacturing and Automation, Chapter. 13, 1994, pp. 211-242..

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Fig. 2.2.1.1-1 Principle of double-wire system and wire positions in various cutting situations

The bending can be reduced by adopting a double-wire system where two wire are bonded together as shown in the Fig. 2.2.1.1-1. The figure also displays the wire position that can be used of various cutting scenarios.

Fig. 2.2.1.1-2 Wire lag for cut length of 7mm

Experiments show that double-wire system produces lesser wire lag. In Fig. 2.2.1.1-2 sample‘a’ that used single-wire has the maximum lag compare to samples ‘b’ and ‘c’ which used double-wire system.

2.2.1.2 Fengguo, C., Xiaoguang, F., “The Development Status and Analysis of Wire EDM in China,” International Journal of Electrical Machining, No. 6, 2001, pp. 1-5.

This paper summarizes China’s breakthrough progress in Wire EDM machines with respect to the structure, technology and technique effectiveness. Miniature Wire EDM machine tool (minicut-110) used for desktop manufacturing was successfully developed by Beijing Institute of Electro-Machining, which can meet the need of making the general miniature and precision parts and dies, and the specification of which is 100mm X 100mm X 120mm.Fig. 2.2.1.2-1 shows process mechanism of the self-spinning Wire EDM machine, a machinetool that is very innovative and has broken some of the technological indexes. The wire electrode spins by itself at a high speed while it is in a rectilinear motion, this changes thechip removal process by removing the chip to the rear of the machined surface instead of

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being removed to one end of the work-piece machined. Additionally, this process extendsthe range of the work thickness to be machined.

Fig. 2.2.1.2-1 Self-spinning Wire EDM

2.2.1.3 Gisbert Ledvon - Charmilles Technologies, “Twin-Wire EDM,” Fabricating & Metalworking Magazine, March 2003, pp.24-27. & http://www.charmillesus.com/products/wire/tw/tw.html

A Twin-Wire EDM is being developed to reduce the machining time up to 50% by eliminating the manual wire changing process.

Fig. 2.2.1.3-1 Twin-Wire EDM developed by Charmillies Technologies

Fig. 2.2.1.3-1 shows the Twin-Wire EDM equipment that uses an automatic wire EDM toolchanger that switches between larger and smaller wires for rough and finish machiningrespectively.

Fig. 2.2.1.3-2 Pocketing using Single wire and Twin Wire EDM

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Fig. 2.2.1.3-2 illustrates the reduction in total machining time by using Twin Wire EDM instead of single wire EDM. Moreover, usage of larger diameter wire for rough machiningeliminates the recast layer and slug formation.

2.2.1.4 “New Wire-EDM-Machine Series,” Metal Forming Magazine, March 2003, pp. 140. & http://www.ona-electroerosion.com/eng/productos/hilo/ke.htm

The ONA KE 500 is the first wire EDM unit allowing the operator to cut, in submergedmode, up to a height of 400 mm, at an inclination of ± 28º, the whole way along the X-axis or Y-axis.

Fig. 2.2.1.4-1 KE 500 Series Wire-EDM ONA America

Fig. 2.2.1.4-1 shows the ONA KE 500 Series machine that has a work table capacity of 1200 X 950 X 400 mm.The system controls the cutting process to ensure optimal machine performance at eachstage. All of this ensures long machining times without operator intervention. Features include a user-friendly CNC to enhance operator-machine interface; an Ethernet connection allowing the programmed machine to send messages to the user’s e-mail address at any location by PC or cell phone and a new patented built-in automatic threading system to handle a variety of wire types and diameters.

2.2.1.5 http://www.wzl.rwth-aachen.de/en/0_start/schneiderosion/, “Micro-machining by Wire-EDM”.

This web site reports an extensive research work concerning technology development for Micro-Wire-EDM. The targets are minimization of surface roughness and thermal damage ofthe rim zone, reduction in the producible geometric dimensions and improvement of the machining accuracy. The investigations are accompanied by the production of specific partsin order to rapidly transfer the results to practice and to create a wide application spectrum.Micro-Wire EDM tests and production are carried out on a AGIECUT 270 SF+F HSS Wire-EDM machine.

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Fig. 2.2.1.5-1 Wire-cut micro parts for a medical application; material: TiAl6V4

The Fig. 2.2.1.5-1 shows two ultra-precision machined and subsequently fine wire-cut (d =50 µm) parts for a foreseen application in surgery. A main difficulty in Wire-EDM of these partsis the clamping because possible clamping area is extremely small and three different contours have to be cut in different clamping positions. Adapted clamping devices based on different clamping mechanisms had to be implemented in order to solve these problems.

2.2.2 TOOL

2.2.2.1 Obara, H., Abe, M., Ohsumi, “Control of Wire Breakage during Wire EDM,” International Journal of Electrical Machining, No. 4, 1999, pp. 53-58.

A new method that divides the three gap monitoring signals (ignition delay time, discharge voltage and radio frequency signal) into groups depending on discharge position to pre-monitor wire breakage during wire EDM is proposed.

Fig. 2.2.2.1-1 Schematic diagram of detecting circuits

Fig. 2.2.2.1-1 shows a schematic diagram of the detecting circuits. The discharge voltage Vg,the ignition delay time d, the radio frequency signal RF, the total discharge current IT=IU+ID

and the difference of discharge current I=IU-TD are detected, where IU and ID are the upper and lower discharge currents supplied to the wire respectively.

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Fig. 2.2.2.1-2 Variation of discharge position just before the wire breakage

The - I/IT value is concentrated in the middle of the wire just before breakage so the location wire break position is determined to be the middle discharge portion (Fig. 2.2.2.1-2). The method also reveals that discharge voltage is the best signal to use for pre-monitoring the wire breakage. This signal identifies the increase in the short circuit pulses.

2.2.2.2 Han, F., Kunieda, M., Sendai, T., Imai, Y., “Simulation on Influence of Electrostatic Force on Machining Characteristics in WEDM,” International Journal of Electrical Machining, No. 7, 2002, pp. 31-36.

This paper describes a simulation method to determine the effect of electrostatic force on the wire vibration. It also confirms that the wire electrode can be resonated by the electrostatic force, when the discharge frequency is the same as the characteristic frequency of the wire electrode.

Fig. 2.2.2.2-1 Shape of the workpiece finished with wire resonance frequency

When the wire was vibrated at resonance frequency the vibration patterns were copied to theworkpiece surface in both the experiment and simulation, indicating that the resonance of the wire can decrease machining accuracy. This can be visualized from the Fig. 2.2.2.2-1.The study also found that if the voltage of the open circuit is set high, the wire collides with the workpiece at a high frequency due to the electrostatic force, causing the wire to break.This method assumes a perfect-elastic collision and ignores the explosive forces due to discharge.

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2.2.2.3 Klocke, F., Lung, D., Nöthe, T., “Micro Contouring by EDM with Fine Wires”,International Symposium for Electromachining XIII, Vol. II, May 2001, pp.767-779.

This paper studies WEDM micro contouring of tool steel and cemented carbide using a wire diameter of 50µm. By means of cutting typical contours like small teeth, sharp corners and small radii, the specific process behavior and the resulting contour deviations are discussed. The main process parameter to be varied was the discharge energy. The pulse frequency has been set at a low value to avoid any undesired impacts. Fig. 2.2.2.3-1 shows the selected geometries and the main test conditions.

Fig. 2.2.2.3-1 Selected geometries and the main test conditions

The minimum producible tooth width is limited by residual stresses caused by thermal action at the rim zone. Depending on the discharge energy, the desired tooth width, the materialproperties and its heat treatment, this stress formation can cause deformation or even break the tooth. With low discharge energy, a tooth width of 20µm can be produced by a main cut. In sharp corner cutting operation, the precision is affected by different mechanisms. Whilefor bigger corner angles the wire lag has a high share of the total measure deviation, for smaller corner angles, enhanced electric field strength and an uneven discharge distribution which cause an excessive removal at the tip are the dominant factors. When cutting small radii, the uneven discharge distribution is responsible for a too smallremoval at inner radii and a too high removal at outer radii. A variation for the open circuit ratio during the main cut can partly yield an improvement of accuracy. By adapting thistechnology the deviation can be reduced down to approx. 3 µm. By means of a trim cut with very low discharge energy carefully adapted machiningparameters it is possible to produce microstructures with a width of less than 10 µm and accuracy within ± 2 µm.

2.2.2.4 http://www.intech-edm.com/pdf/wirebook.pdfThis article is published by the Intech EDM company as a reference for selecting Wire forWEDM. It reports the developments in the wire material.

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Copper was the original material first used in wire EDM. Although its conductivity rating is excellent, its low tensile strength, high melting point and low vapor pressure rating severelylimited its potential. Today its practical use is confined to earlier machines with power supplies designed for copper wire. Brass was the first logical alternative to copper when early EDM users were looking for better performance. Brass EDM wire is a combination of copper and zinc, typically alloyed in the range of 63–65% Cu and 35–37% Zn. Higher Zinc content increases the tensile strength of the wire. But, brass wires cannot be efficiently fabricated using high concentrations. So coated wire were fabricated, which typically have a core of brass or copper, for conductivity and tensile strength, and areelectroplated with a coating of pure or diffused zinc for enhanced spark formation and flush characteristics.High precision work on wire EDM machines, requiring small inside radii, calls for wire diameters in the range of .001–.004" (Fine wires). Since brass and coated wires are not practical, due to their low load carrying capacity in these sizes, molybdenum and tungsten wires are used.Fines wires have limited conductivity so cannot be used to machine thick workpieces. So, a composite wire called MolyCarb was created that does offer significant advantages for smalldiameter work, since it coats molybdenum wire with a mixture of graphite and molybdenumoxide to improve its flushing characteristics.


2.2.3.1 Matsuo, T., Oshima, E., “Investigation on the Optimum Carbide Content and Machining Condition for Wire EDM of Zirconia Ceramics,” Annals of CIRP, Vol. 41, 1992, pp. 231-234.

This paper reports the experimental results of Wire EDM of Zirconia ceramics including NbC or TiC. The machining rate and surface roughness were measured for various operatingconditions.

Fig. 2.2.3.1-1 Relationship between electrical conductivity and machining rate, surface roughness

As the carbide content rises, the electrical conductivity increases leading to higher machiningrate. The machining rate reaches a peak at about 200 S/cm and then drops. The optimum

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carbide contents which give the maximum machining rates are by volume 28% with NbC and 30% with TiC. This is evident from the Fig. 2.2.3.1-1. It is also seen that as the carbide content increases after the optimal point, surface roughness decreases. The study also shows that there exists optimum pulse duration, and the critical pulse duration which gives maximum machining rate with increase in duty factor. The surface roughness increase with duty factor. A second cut with the same offset is recommended to obtain a better surface finish.

2.2.3.2 Spur, G., Appel, S., “Wire EDM cutting of PCD,” Industrial Diamond Review, April, 1997, pp. 124-130.

Polycrystalline diamond (PCD) is synthetic composite cutting tool material produced by sintering together carefully selected diamond particles under conditions of high temperatureand pressure. PCD can be machined reproducibly to a high surface quality using the wire EDM. However, less electrical conductivity of PCD leads to lesser productivity of EDM process.Fig. 2.2.3.2-1 illustrates that surface finish achieved on the fine-grained grades is superior tothat achieved on the coarser grades, but no such trend is evident with regard to cutting rates. This study determined that the type of wire material and the dielectric fluid influence the outcome of machining.Deionized water as dielectric fluid produced a higher cutting rate than oil, but the highercutting rate resulted in poor surface finish (Fig. 2.2.3.2-2).Productivity is higher with water; however errors of geometry, such as subsurface undercut,are substantial. This can be prevented by skilful position of the workpiece.

Fig. 2.2.3.2-1 Cutting rate and surface finish as a function of pulse frequency for various PCD grades and WC

Fig. 2.2.3.2-2 Cutting rate and surface quality depending on the dielectric fluid

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2.2.3.3 Wang, T., Kunieda, M., “Study On Dry WEDMed Surface,” International Symposium forElectromachining XIII, 2001, pp. 505-512.

Experiments were conducted to study the influence of various type of dielectric on output parameters like actual cutting depth, straightness, surface roughness and material removalrate.Dielectric media used in the study are water, atmosphere, compressed air and compressedoxygen.The discharge gap was found to be 3, 7, and 14 m for compressed gases, atmosphere and water respectively. It was found that the actual cutting depth in compressed gas is the smallest, because high pressure gas flow moves the debris immediately from the gap. Dry-WEDM produces excellent straightness of the machined surface because the amplitudeof the wire electrode vibration is small due to small process reaction forces like electrostaticforce and force due to bubble collapsing. This is evident from the Fig. 2.2.3.3-1. Fig. 2.2.3.3-2 shows that the surface roughness of the water and compressed air nearly equal and slightly lower that that in compressed oxygen. The size of craters on the WEDMgenerated surface in compressed oxygen is considered slightly larger due to higher heat generated by oxidation. Water has the highest material removal rate and the other dielectric media have equal butsmaller removal rates.

Fig. 2.2.3.3-1 Geometry of WEDMed surfaces measured parallel to wire electrode

Fig. 2.2.3.3-2 Results of surface roughness

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2.2.3.4 Obara, H., Nakase, M., Ohsumi, T., Hatano, M., “Analysis of Explosive Load on WireSurface Generated by Discharge of Wire EDM,” International Journal of Electrical Machining, No. 7, 2002, pp. 37-42.

In this paper, the explosive load acting on a wire surface generated by discharges at the roughcut and the finish cut of wire EDM is investigated. The hydrodynamic explosion process in the water-filled gap from each discharge is numerically analyzed using the adiabatic bubble expansion mode, and the impulsive load acting in the wire surface is calculated.

Fig. 2.2.3.4-1 Pressure distribution in case of front discharge

Fig. 2.2.3.4-2 Pressure distribution in case of side discharge

The Fig. 2.2.3.4-1 & 2 illustrate the pressure distribution caused by a discharge in the front and the side of the wire respectively. Pressure distribution and the force are obtained by theintegration of pressure distribution after 0.3 ms from the start of a discharge. It can be seen that the discharge force is not always constant and it is not perpendicular to the wire surface.This paper concludes that the influence of the skimmed depth on the wire deflection at thefinish cut is explained by the numerically analyzed results.


2.2.4.1 Wang, W.M., Rajurkar, K.P., Huang H., “Monitoring and Control Strategy for wire breakage in WEDM,” Transactions of NAMRI/SME, Vol. XIX, 1991, pp. 148-153.

Fig. 2.2.4.1-1 A voltage waveform of the wire rupture process

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A data acquisition system was developed to study the gap voltage wave forms. It was determined that a rapid voltage drop, from the level higher than 35V to that lower than 10V, can be accounted as a spark pulse. If the lasting time of a low voltage, less than 35V, is longer than an off-time period, it can be accounted for a short circuit pulse (Fig. 2.2.4.1-1).After the breakage the free end of the wire contacts the workpiece to generate more short circuits leading to damaged surface. To prevent this scenario a monitoring and control strategy was developed.

Fig. 2.2.4.1-2 Block Diagram of the Sparking frequency monitor

It was also found the wire always breaks when the sparking frequency is higher than 9.5 KHz. The wire breakage risk can be reduced by selecting longer pulse off-time. Fig. 2.2.4.1-2 shows the proposed sparking frequency monitor to record the sparking frequencies. Finally a control strategy was proposed that increases the pulse off-time whenever the sparking frequency exceeds the critical value.

2.2.4.2 Rajurkar, K.P., Wang, W.M., McGeough, J.A., “WEDM Identification and Adaptive Control for Variable-Height Components,” Annals of CIRP, Vol. 43, 1994, pp. 199-202.

To avoid the wire rupture due to change in height of the workpiece, a height identificationmodel was proposed. The workpiece height in WEDM was estimated on-line by modeling the transfer gain from the spark frequency to feed rate.

Fig. 2.2.4.2-1 On-line recorded identification data

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The nonlinear prediction model provided smoother identification data and was simpler thanlinear model (Fig. 2.2.4.2-1). With this control system, the sparking frequency is controlled according to an on-lineidentified workpiece height at the optimal value without the risk of wire rupture when cutting a workpiece with variable height. The error of the workpiece height identification with the proposed system is 1mm, and the response time is 1 second when workpiece height reduces in large steps.

2.2.4.3 Yan, M.T., Liao, Y.S., “Adaptive Control of WEDM process using the FUZZY ControlStrategy,” International Symposium for Electromachining XI, 1995, pp. 343-352.

An adaptive control optimization system for the WEDM process based on the multi-variableand 3-region fuzzy control strategy is introduced. The sparking frequency data is collected by a monitoring system which is fed into the fuzzycontroller to make decisions according to the situation.The schematic of the fuzzy control system is shown in the Fig. 2.2.4.3-1. The pulse-off timeand the wire feed rate are controlled using the following rules.1. When the sparking frequency is in the safe region the parameters are set at optimal level.2. When the sparking frequency is in the critical region the feed rate should be adjusted and

pulse off-time needs to be increased. 3. When the sparking frequency is in the dangerous region the pulse off-time is largely

increased and feed rate is decreased to prevent the wire breakage.

Fig. 2.2.4.3-1 Sparking frequency monitoring and fuzzy control system

Experiments were conducted using roughing and finishing conditions and the systemdemonstrated stable machining.

2.2.4.4 Rajurkar, K.P., Wang, W., Zhao, W.S., “WEDM-Adaptive Control with a Multiple Input Model for Identification of Workpiece Height,” Annals of the CIRP, Vol. 46, 1997, pp. 147-150.

The model proposed in this paper includes multiple inputs to estimate the height of the workpiece compared to a previously existing single input model (Rajurkar, Annals of CIRP, 1994).The multiple inputs model is the relationship between the output value of average gap voltage and input values of sparking frequency and cutting feed.

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This multiple inputs model avoids the disturbance caused by the instability of table feedduring workpiece height identification while single input model accounts only the relationship between the spark frequency and machine table feed.

Fig. 2.2.4.4-1 On-line identified workpiece height

This new model improves the stability and accuracy of workpiece height identification. Theidentification error with the multiple inputs model is 56% lower than that with the single input model when workpiece height changes in a large step (Fig. 2.2.4.4-1).

2.2.4.5 Hsue, W.J., Liao, Y.S., Lu, S.S., “A Study of Corner Control Strategy of Wire-EDMbased on Quantitative MRR analysis,” International Journal of Electrical Machining, No. 4, 1999, pp. 33-39.

In this paper a corner control strategy using material removal rate (MRR) analysis wasdeveloped to maintain the accuracy and straightness of the machined corner. The wire deflection and vibration are caused by machining load that is resulted fromdischarge power. So this strategy maintains the wire straightness by reducing power beforewire arriving at the apex, this also preserves the kerf width after the wire passes the corner apex.During the power suppression stage, the reference discharge power is reduced to a specific value which is equal to the ratio of MRR at the corner apex to MRR in straight path cutting multiplied by a corrected power.

2.2.4.6 Wu, J., Li, M.H., “The Identification of the Servo Control State in Wire Electrical Discharge Machining Process,” International Symposium for Electromachining XIII,2001, pp. 423-433.

This paper reports a new digital monitor system developed to identify the pulse state in HighSpeed-WEDM. The time ratios of normal discharge, short circuit and open circuit in sampling intervals are calculated and recorded by the monitoring system.The special feature of the monitor system shown in the Fig. 2.2.4.6-1 is that the gap voltage threshold can be adjusted online by the software to adapt the different power settings. This function is realized by a digital resistor in the monitor.Experimental analysis shows that the normal discharge sequence composed of the time ratio of normal discharge is a low order auto-regression model. When the gap size becomes small,the order of the model becomes large. It means that the normal discharge pulses will have stronger correlation when the gap size becomes smaller.

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Fig. 2.2.4.6-1 HS-WEDM pulse state monitor system

2.2.5 Applications

2.2.5.1 “EDM for the Dental Profession,” EDM Today, March/April, 1999. Wire EDM is used to generate sub structures that can be further machined to final shape using other machining techniques.Fig. 2.2.5.1-1 shows a wire cut Titanium sub structure blank (Tooth template) that is finished by die sinking EDM using a graphite electrode that carries the replica of the natural tooth.

Fig. 2.2.5.1-1 Wire cut Titanium template

2.3 Micro EDM

Miniature parts require a machining process that can remove material at micro level. Micro EDM can provide the machining needs for the micro parts. The material removal process is similar toMacro and Wire EDM, the only difference is the power involved. The voltage and current used in this process are several times lesser and because of that material removed per spark is in theorder of nanometer. The schematic of a micro EDM system is shown in the Fig 2.3-1.

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Fig. 2.3-1 Schematic of Micro EDM system

2.3.1 Equipment

2.3.1.1 Sheu, D., Masuzawa, T., “Development of Large-Scale Production of Microholes by EDM,” International Symposium for Electromachining XIII, Vol. II, 2001, pp. 747-758.

New machining method with Twin-WEDG system and Tandem Micro-EDM system is proposed (Fig. 2.3.1.1-1). Higher machining speeds of microelectrodes and microholes can be realized with this system because rough machining, finishing of electrodes and microholemachining are carried out simultaneously.

Fig. 2.3.1.1-1 Scheme of micro-EDM system for mass production of microholes

The mechanism of mechanical pencil was adopted to supply electrodes automatically. Newmandrel is designed to supple electrode material by knocking the knock–lever driven by a cam (Fig. 2.3.1.1-1). A prototype setup is shown in Fig. 2.3.1.1-2. The system combines Twin-WEDG, Tandemmicro-EDM and the electrode-material feed system. The main spindle is set horizontally. It

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includes a V-shaped bearing, a mandrel that holds the electrode and a DC motor. The rotation eccentricity of the spindle mechanism is smaller than 0.5µm.

Fig. 2.3.1.1-2 Setup of micro-EDM system

The system includes 3 detecting circuits for 3 pulse generators of Twin-WEDG and microhole machining. If any one of discharge conditions becomes unusual, the main spindle will be set back by the command from a computer.Experimental results show that Twin-WEDG reduces the total machining time for a 40µmmicroelectrode about half of that in a conventional system.Furthermore, after machining a through microhole, the worn length of the electrode will be recovered by Twin-WEDG system instead of machining with a completely new electrode. At the beginning of machining the next hole, only hole-making takes place because the part of the electrode for this machining has already been fabricated.Automatic mass-production of high-quality microholes has been proved to be able to achieve with this system. 400 microholes with a diameter of 50µm were successfully machinedautomatically in a 50µm thick stainless steel plate. The difference between diameters at the entrance and the exit was about 1-2 µm.

2.3.1.2 Masuzawa, T., Okajimam K., Taguchim T., Fujino, M., “EDM-lathe forMicromachining,” Annals of the CIRP, Vol. 51, No. 1, 2002, pp. 355-358.

A new type of micro-EDM machine operating similar to a turning lathe is proposed in this paper to machine coaxial micro products (Fig. 2.3.1.2-1).EDG system is installed to fabricate on-the-machine complex microelectrode with sharpedges and corners (Fig. 2.3.1.2-2). The disc electrode can have a large diameter and can be fabricated precisely by WEDG. The EDM lathe is constructed with a WEDG head, a X-Y table, for the ME head and three rotating spindles which are guided by V blocks and driven by DC motors.The possible applications of this machine are shown in Fig. 2.3.1.2-3.

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Fig. 2.3.1.2-1 Entire process to produce a coaxial cavity with an over hang

Fig. 2.3.1.2-2 Advantage of EDG with disc electrode

Fig. 2.3.1.2-3 Possible applications

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2.3.1.3 Fujino, M., Okamoto, N., Masuzawa, T., “Development of Multi-purpose Microprocessing Machine,” International Symposium for Electromachining XI, 1995, pp. 613-620.

This paper reports the development of a multipurpose processing machine, which enables micro EDM, WEDG, micro drilling and micro-endmilling on a single machine. Fig. 2.3.1.3-1 shows the structure of the system. Four driving axes, X, Y, Z, and c, are numerically controlled.

Fig. 2.3.1.3-1 Structure of the system

The wire feed system of the wire used for WEDG is arranged outside the working tank. The wire is steadily supplied to the wire guide inside the working tank. The travel speed of the wire is set at 50mm/min and wire tensile is about 300gf. An R-C generator is adopted for the discharge circuit in order to obtain micro discharge. The detection of mean current charged in a capacitor of the RC-generator is adopted as the method to detect discharge conditions.Experimental machining proved the possibility of EDM, WEDG, drilling and end milling onthis system. Moreover, with this system, processing using micro drills and end millsmanufactured by means of WEDG can be automatically performed on the same machine of tool making.

2.3.1.4 Furutani, K., Mohri, N., Higuchi, T., “Miniaturized Electrode Feed Devices Using Piezoelectric Elements”, International Symposium for Electromachining XI, 1995, pp. 621-628.

The requirements for the electrode feeding devices for machining micro holes are: 1) quick response to pull back an electrode when a short circuit happens, 2) repeatable fine resolution to adjust the gap length between and electrode and a workpiece, 3) ability to travel a longdistance, 4) small size, 5) applicability to an EDM system with multiple electrodes.

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To increase the machining speed of micro-EDM, one approach is to miniaturize electrode feeding devices so that a number of electrode feeding devices can be arranged closely to machine simultaneously. This paper introduces several types of miniaturized electrode feeding devices by using piezoelectric elements (peizo).An electrode feeding device using Impact Drive Mechanism (IDM) is first introduced (Fig. 2.3.1.4-1). This device measures 48 × 70 × 86 mm and weighs 1 kg. The electrode is held with a chuck. The peizo A is used for IDM. The piezo B is used for adjust gap length or forced vibration of the electrode.

Fig. 2.3.1.4-1 Sectional view of electrode feeding device with Impact Drive Mechanism

IDM utilizes friction and inertial force caused by rapid deformations of peizos. It consists ofa moved object, a weight, a peizo which connects the weight with one end of the movedobject. The moved object is pressed against the base to obtain friction. Downward movementis illustrated in Fig 2.3.1.4-2. At the first step the piezo is extended. 2) While the piezo is contracted with certain acceleration, the weight moves down while the friction between the moved object and the base keeps the moved object still. 3) When the deformation of peizo stops, the moved object gets momentum by stopping the weight. The IDM starts to movedownward. 4) After step 3) is completed, applied voltage to the piezo rises steeply so that it extend rapidly. The weight moves upward and the moves objects moves downward by thereactionary force, which is adjusted to be bigger than the friction. The IDM movesdownwards. 5) After step 4) is completed, a voltage of the piezo is fixed to the voltage for a pause. The IDM runs against dynamic friction until it lose its kinetic energy. Repeating thestep 1) to 5), the IDM can move for an infinite distance. Upward movement is also obtained by exchanging contraction and extension of the piezo.

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Fig. 2.3.1.4-2 Mechanism of IDM movement

Step like movement can be obtained with the IDM (Fig. 2.3.1.4-3).The feeding step can beadjusted from several nanometers to several micrometers by controlling the voltage amplitude.

Fig. 2.3.1.4-3 Examples of electrode feeding with IDM

Experimental study proved that the machining time with IDM is shorter than that withconventional electrode feeding device.Other structures of the electrode feeding device introduced in the paper utilizes impulsiveforce or elliptical movement (Fig. 2.3.1.4-4, Fig. 2.3.1.4-5). The first one measures 8 X 9 X 28 mm and weighs 7.1 g, 1/10000 times as small as conventional one in volume. The second measures 60 X 20 X 76 mm.

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Fig. 2.3.1.4-4 Structure of electrode feeding device utilizing impulsive force

Fig. 2.3.1.4-5 Structure of electrode feeding device utilizing elliptical movement

Direct drive devices using piezo are compared with conventional chucking methods (Table 2.3.1.4-1). A moving coil is small in scale and has high resolution. It is difficult to use because it doesn’t have enough stroke. A chuck has larger holding force and is adjustable forthe diameter of the electrode. In the direct drive method, the wear length of the electrode can be compensated by feeding the electrode. Therefore, the direct drive method is available for thin wire electrode.

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Table. 2.3.1.4-1 Comparison between electrode feeding devices

2.3.2 Process and Process characteristics

2.3.2.1 Tsai, Y.Y., Masuzawa, T., Fujino, M., “Investigations on Electrode Wear in Micro-EDM,” International Symposium for Electromachining XIII, Vol. II, 2001, pp. 719-726.

Although Micro EDM can achieve excellent machined surface quality, the accuracy of machining is affected by the electrode wear. The wear of electrode becomes large for thin electrode or in the location of small curvature. This phenomenon is called “area effect”.In this paper, volumetric wear is divided into two portions: changes of the electrode length and corner rounding. The relationships between volumetric wear ratio and materialcharacteristics, electrode diameter and circuit parameters such as capacitance, open circuitvoltage, resistance and inductance are investigated.Experiments were performed on a micro EDM including WEDG unit. Fig. 2.3.2.1-1 showsthe configuration of the equipment.It is concluded that materials with high melting point, boiling point and high thermalconductivity are beneficial for electrode in micro EDM as an extension of conventional EDM. Electrode wear increases when the diameter of the electrode is small. The main reason is due to poor heat conduction and difficulty in maintaining good gap control. Volumetric wear ratio decreases with the decrease of discharge energy. Using low open circuit voltage is not always effective because continuous arcs happen easily. It is recommended to use small capacitance in micro EDM for micro hole machining to obtain small discharge energy.

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Fig. 2.3.2.1-1 Experimental configuration

There are different inductances that minimize the volumetric wear ratio when different capacitances are used. Larger inductances correspond to the minimum wear ratio at larger capacitances. There is also a minimum volumetric wear ratio for different charge resistances.With appropriate choice of the charging resistance and the inductance in discharge loop, the tool wear can actually be reduced to 1% or less for machining stainless steel SUS304 when a

50µm tungsten tool-electrode was used.

2.3.2.2 Allen, D. M., Almond, H. J. A., Bhogal, J. S., Green, A. E., Logan, P. M., Huang, X. X., “Typical Metrology of Micro-Hole Arrays Made in Stainless Steel Foils by Two-stage Micro-EDM,” Annals of the CIRP, Vol. 48, 1999, pp. 127-130.

This paper investigates the fabrication of micro-holes with micro-EDM for ink jet printing nozzles where hole diameters are smaller than 50µm. The smoothness of the bore, high positioning accuracy and repeatability are the main parameters of interest.Two-stage micro-EDM, which involves two separate micro-EDM processes, is used tofabricate electrodes and to manufacture the holes. Optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and coordinate measuring machine(CMM) were used for measurements.Tungsten electrodes were machined with WEDG to under 50µm in diameter. It is shown that electrodes with better roundness and smaller taper could be obtained when machining with low speed and in several smaller steps. The microelectrode tip appeared to be more prone to the disturbance such as vibrations caused by dielectric flow than in proximity to the mandreldue to the cantilever type arrangement.The surface quality of microelectrodes has been investigated with AFM. It reveals smallparticles with diameters between 80-150nm on the machined surface and cracks with maximum depth of 1.3µm and width of 1.5µm. The typical Ra for an electrode was 180 – 300 nm.The positional accuracy of the micro-EDM machine was assessed while simulating themachining of an array of holes.

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Stainless steel foils from 100 –200µm have been used as workpiece. Aspect ratios of the micro holes are 2 – 4 with 50µm in diameter. The edge profile obtained is excellent withminimum corner radiusing estimated at 1- 2µm with pulse energies of approximately 10-8 J. To obtain the cross-section of such a small hole, micro holes were drilled into the joint line oftwo edge-polished foils butted together with conductive cement. After dissolving the cement,the machined surfaces were examined by SEM and AFM. The recorded Ra values of theinternal bores of the micro hole were 200 – 400nm. Metallurgical defects of the foil such as inclusion and cracks longer than the hole diameterwere also reveled which were suspected to be an integral part caused by the rolling process of the foil (Fig. 2.3.2.2-1 & 2).

Fig. 2.3.2.2-1 Internal surface of a micro-hole Fig. 2.3.2.2-2 Defects inside micro-hole bore

2.3.2.3 Morgan, C., Shreve, S., Vallance, R.R., “Precision of Micro Shafts Machined with WireElectro-Discharge Grinding”, Proceedings of the 2003 ASPE Topical Meeting on Machines and Processes for Micro-Scale and Meso0Scale Fabrication, Metrology and Assembly, University of Florida, 2003.

This paper presents an experimental study of the straightness error and surface roughness developed during wire electro-discharge grinding (WEDG) (Fig. 2.3.2.3-1 and Fig. 2.3.2.3-2) of a micro shaft.

Fig. 2.3.2.3-1 Wire Electro-Discharge Grinding

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µ

µ

Fig. 2.3.2.3-2 Traveling Wire in WEDG

81 micro shafts with a nominal diameter of 50µm and length of 500, 1000, 1500µm werefabricated with various machining conditions.Edges profiles of the shafts were measured with a 3D surface profilometer of sub-nanometerresolution and analyzed numerically to determining straightness and Ra values. A statistical analysis reveals that surface roughness is independent of feed rate and aspect ratio but is dependent on voltage and capacitance (i.e. discharge energy). Ra value down to 67 nm was achieved.Straightness ranged between 3.05 and 12.04µm. The statistical tests show that thestraightness is independent of voltage, capacitance, and feed rate. But as the aspect ratioincreases, straightness errors increase. An error model suggests the dependence of straightness on machine/ process errors rather than process conditions during WEDG.

2.3.3 Applications

2.3.3.1 Yu, Z., Masuzawa, T., Fujino, M., “Micro-EDM for Three Dimensional Cavities – Development of Uniform Wear Method,” Annals of the CIRP, Vol. 47, 1998, pp. 169-172.

In micro EDM, it is not practical to use a complex shape electrode to machine 3D cavitiesbecause the electrode loses its geometric features due to large wear. In this paper, a new method called Uniform Wear Method (UWM) is presented for 3D micro EDM using simple-shaped electrodes. During a layer-by-layer machining (Fig. 2.3.3.1-1), when the electrode feed for each machining layer and the section area of the electrode are small, the majority of machiningcan be done by the bottom of the electrode.To implement the uniform wear, a to-and-fro scanning tool path must be used to machine the inner part and the outline of the targeted area alternatively (Fig. 2.3.3.1-2). When the outline is being machined, the electrode tip becomes rounded due to wear. This deformation can becompletely removed when machining the inner part of the layer because of the discharges occur only on the bottom of the electrode. This restores the original end shape of the electrode and a sharp corner reappears before the start of the next outline path.

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Electrode

Fig. 2.3.3.1-1 Layer by layer machining Fig. 2.3.3.1-2 To-and-fro tool path

When machining a 3D cavity, a simple electrode is controlled to move along the tool paths according to the principle of UWM. With compensation of electrode wear, 3D micromolds ofdifferent shapes can be machined (Fig. 2.3.3.1-3). This method has also been approved to be applicable for normal size molds EDM (Fig. 2.3.3.1-4).

Fig. 2.3.3.1-3 Machining cross cavity Fig. 2.3.3.1-4 Machined spherical cavity with inclined surface and the electrode

2.3.3.2 Reynaerts, D., Heeren, P.H., Brussel, H.V., “Microstructuring of Silicon by Micro Electro-Discharge Machining (EDM) – Part I: Theory,” Sensors and Actuators A (Physical), Vol. A60, 1997, pp. 212-218.

This paper first presents an overview of EDM technology, the current state-of-art of microEDM, and a comparison of EDM with other micromachining technologies. The mainadvantages of micro EDM over other micromachining technologies are its flexibility and ability to machine complex 3D shapes (Table 2.3.3.2-1 and 2.3.3.2-2).

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Table. 2.3.3.2-1 Micromachining technology comparison

Table. 2.3.3.2-2 Compatibility of machining technologies with different materials

Silicon has a very low erosion resistance (0.0075 compared with steel 0.23x1012J2M-1kg-1).The machining speed of silicon is almost double that of stainless steel and the electrode wear was lower. Machining a hole with aspect ratio of 10 posed no problem. EDM of silicon in deionized water yields better results than in oil-based dielectric in terms of machining speed, accuracy and roughness.When machining monocrystalline silicon the polarity needs to be adjusted according to thedoping type of the silicon (Table 2.3.3.2-3). n-type silicon is slightly easier to machine than p-type.

Table. 2.3.3.2-3 Adjustment of polarity according to the doping type of silicon Silicon type Polarityp Electrode -, silicon + n Electrode +, silicon -

When machining with silicon wafers with a resistance of up to 50 , measurement to overcome the peripheral resistance, such as plating silicon with a conductor, is not necessary when using a modern generator capable of reaching high open circuit voltage higher than 200V. The main influence of the resistance of silicon wafer is on the machining speed, not on the attainable accuracy. The roughness after machining is proportional to the machining speed. The effects of EDMon the silicon are limited to a depth of 10 to 35µm. No inclusion of material from either dielectric or electrode was found in electrical discharge machined silicon.

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2.3.3.3 Heeren. P.H., Reynaerts, D., Brussel, H.V., Beuret, C., Larsson, O., Berthoulds, A., “Microstructuring of Silicon by Micro Electro-Discharge Machining (EDM) – Part II:Applications,” Sensors and Actuators A (Physical), Vol. A61, 1997, pp. 379-386.

In this paper, several examples are given of the possibilities of micro-EDM to machinecomplex three-dimensional shapes of silicon.AGIE compact 1 die-sinking EDM machine was used to machine all microstructures.Following modifications were made to the machine to enable the micro EDM of silicon including installation of a micro generator, replacement of the oil-based dielectric circuitwith a separate dielectric circuit using deionized water, installation of a rotating clampingdevice for small electrode improve flushing and stiffness of the electrode. Also, the electrode was made to pass through a ceramic wire guide just above the workpiece to increase the electrode stiffness and reduce vibration of the wire (Fig. 2.3.3.3-1).

Fig. 2.3.3.3-1 Basic set-up for machining silicon by EDM

An on-the-machine electrode machining process with EDM was adopted to avoid the loss of accuracy introduced by electrode transportation. Another tungsten wire was used as sacrificial workpiece. The wear of the sacrificial wire was compensated by adjusting the penetration of the electrode into the sacrificial wire. To test the attainable surface quality using EDM micro milling, a micro mirror was made(Fig. 2.3.3.3-2). The best strategy yielded a roughness of the mirror surfaces of 0.014µm Rain the direction of the electrode movement and 0.127µm Ra in the direction perpendicular to the electrode movement.

Fig. 2.3.3.3-2 Micro mirror

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Micro spur gear and bevel gear (Fig. 2.3.3.3-3) with involve-shaped teeth were successfully machined with 350µm thick wafer.

Fig. 2.3.3.3-3 Top view and assembled bevel gear ( 4.3 mm)

Detail analysis was carried out to determine the influence of the EDM process on the properties of the silicon material when machining an acceleration sensor. No heat-affected zone or change in the surface structure was found. No recrystallization was found. And the micro hardness was unchanged. Another application is a silicon microspring used to perform one-dimensional measurement(Fig. 2.3.3.3-4). The spring was designed in AutoCAD and then exported as a DXF-file (neutral format). The DXF-file was then imported into a postprocessor that translates theDXF-file into an appropriate NC-file for the spark erosion machine. The leading timebetween design and production can be kept to less than one hour.

Fig. 2.3.3.3-4 Finished spring (7mm long, 4mm wide) against the backdrop of Belgian coin

2.3.3.4 Yu, Z.Y., Rajurkar, K.P., Shen, H., “High Aspect Ratio and Complex Shaped Blind Micro Holes by Micro EDM,” Annals of the CIRP, Vol. 51, No.1, 2002, pp. 359-362.

This paper presents a new approach for effective self-flushing in Micro EDM using planetary movement (Fig. 2.3.3.4-1).

Fig. 2.3.3.4-1 Scanning tool path

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To reduce the influence of gravity on debris removal, deep hole machining was carried out horizontally. Planetary movement of workpiece along a circular path was realized by using two micro stages placed on Y-Z plane. Deionized water was used as dielectric (Fig. 2.3.3.4-2).

Fig. 2.3.3.4-2 Experimental setup for circular holes

Through micro holes with aspect ratio of 18 have been successfully drilled with theapplication of planetary movement (Fig. 2.3.3.4-3).

Fig. 2.3.3.4-3 Micro hole through 2.5mm plate

The advantage of planetary movement was also demonstrated by drilling blind micro holes with noncircular cross sections (Fig. 2.3.3.4-4).

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Fig. 2.3.3.4-4 Triangular and square blind hole machined with planetary movement

The process characteristics such as discharge gap, geometric characteristics of the hole, machining speed and electrode wear ratio were analyzed under different machiningconditions. It is proved that planetary movement efficiently reduces tool wear and increases machining speed by reducing debris concentration (Fig. 2.3.3.4-5).

Fig. 2.3.3.4-5 Comparison of Material Removal Rate (MRR) and Relative Electrode Wear (REW) when drilling square blind micro hole

2.3.3.5 Langen, H.H., Masuzawa, T., Fujino, M., “Modular Method for Microparts Machining and Assembly with Self Alignment,” Annals of CIRP, Vol. 44, 1995, pp. 173-176.

In this paper, modular machining and assembly of 3D microparts with self-alignment is developed.WEDG generated microparts and/or tools are temporarily fixed into a mini-worktable of aModular Machining Assembly (MMA) unit with high location accuracy for further assemblyand/or machining.A pin-plate module was fabricated with this method (Fig. 2.3.3.5-1). The outline of the pin isfirst machined with WEDG. The taper of the lower part is to improve self-aligned insertion.The pin is inserted into the hole machined with micro-EDM by applying ultrasonic vibration to the mini-worktable. Then the pin is twisted to break the neck and upper part can be further machined with micro-EDM/WEDG into desired shape.

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Fig. 2.3.3.5-1 Fabrication process of a pin-plate module

This module can be used as a workpiece, tool or assembly setup (Fig. 2.3.3.5-2).

Fig. 2.3.3.5-2 MMA unit

To realize the self-alignment of the upper part of the assembly, Reverse Micro EDM (RMEDM) is used to machine an appropriate cavity into a workpiece from its bottom with a pin-plate module fixed into the MMA unit as tool electrode. To achieve sufficient removal of debris and gas while still maintaining the desirable accuracy of the cavity, a small and a largecapacitor were switched alternately over the gap. Self-adjusted vibrojumping feed modewhich includes two backward jumps after every 25µm electrode feed was also adopted to improve flushing. After the cavity is generated by RMEDM into a particular micropart, it can be assembled on top of another part already fixed in the MMA unit by using ultrasonic vibration. A study on assembling characteristics of the pin-plate module concluded that breaking strength of the module depends on insertion force, amplitude of vibration and Young’s modulus of the materials. The finding can be used to choose different ultrasonic parameter

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and materials of pin and plate to realize good “bond” of assemblies or temporary storage of microparts in the MMA unit. A micropipe and macrocylinder combination was machined to demonstrate the possibility ofcontrol breaking strength for assembling and temporary storage. (Fig. 2.3.3.5-3 and Fig. 2.3.3.5-4).

Fig. 2.3.3.5-3 Micro pipe and macro cylinder combination

RMEDM process

Fig. 2.3.3.5-4 Machining process of Micro pipe and macro cylinder combination

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CHAPTER 3

3. Electrochemical Machining (ECM)

ECM consists basically of the electrochemical dissolution of the surface metal of a workpiece byconversion of metal to its ions by means of an electric current. The whole process isaccomplished in an electrolytic cell by applying a positive (anodic) potential to the workpiece and a negative (cathodic) potential to the tool used to shape the workpiece. ECM can be used forshaping, finishing for improving the quality of the surface, deburring, radiusing and polishing.Fig. 3-1 shows the various schematics for machining different geometries using ECM*.

Fig. 3-1 Schematics of electrochemical machining operations. (a) Die sinking, (b) Shaping of blades, (c) Drilling, (d) Milling, (e) Turning, (f) Wire ECM, (g) Drilling of curvilinear holes,

(h) Deburring and radiusing, (i) Electropolishing

The rate of material removal in ECM is governed by Faraday’s law, since it is a function of current, the primary variables that affect the current density and the material removal rate are: Voltage, Feed rate, Electrolyte conductivity, Electrolyte composition, Electrolyte flow and Workpiece material.

* Rajurkar, K.P., Kozak, J., Chatterjee, A., “Nonabrasive Finishing Method,” ASM Handbook, Surface Engineering, Vol. 5, 1994.

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3a. ECM equipment:Fig. 3-2 shows a schematic representation of the ECM system for finishing of a die or other complex shapes. The major components include the workpiece, cathode tool, electrolyte, power supply, and electrolyte circulating and purification system. A low voltage (8 to 30 V) is normallyapplied across the electrodes. A small gap (0.2 to 1mm) is maintained between them, producing a current density of the order of 10 to 100 A/cm2. The electrolyte is forced through the small gap between the cathode tool and the anodic workpiece with velocities of 5 to 30 m/s. The electrolyte movement flushes away the debris removed from the workpiece.

Fig. 3-2 Electrochemical machining equipment schematic. 1. tool electrode, 2. finishing workpiece, 3. tank of electrolyte, 4. clamping system, 5. electrolyte supply system, 6. power

supplyA typical ECM machine consists of a table for mounting the workpiece and a platen mounted on a ram or quill for mounting the tool. The workpiece is mounted on the table connected to the positive side of the power supply. The tool is mounted on the platen with electrical connection tothe negative side of the power supply. The part to be machined is held on a fixed table and the tool is head on a ram that moves either horizontally or vertically onto the workpiece. During the finishing operations while ECM sinking, the tool is either stationary or is fed in the direction of the workpiece. During deburring and machining of contours, however, the tool usually does not move relative to the workpiece.

The corrosive nature of the electrolyte requires that any portion of the machine or tooling thatcomes in contact with it must be made of a corrosion-resistant material. Workholding fixtures forECM are usually made from stainless steel, copper, or copper alloys.

Water-cooled power supplies are used on ECM equipment to convert alternating current electrical power to the direct current voltages required. ECM machines are available that can deliver currents from 50 to 10,000 amperes, with a voltage range of 4 to 30 V. Sufficient current must be available to maintain a current density of 10 to 500 A/cm2 at the workpiece.

3b. Process capabilities There are numerous parameters that influence the ECM process in terms of machining rate,surface finish, and other end product physical characteristics. In particular, the metal removal

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rate and the surface finish depend on current density, machining gap, feed rate, electrolyte composition, temperature, and flow rate or pressure of the electrolyte. The design of an ECMsystem for a specific application should take into account the range of values for these parameters.

The only requirement of the workpiece material for ECM is that it should be electricallyconductive. Because the physical properties of the material of the material determine themachining rate, alloys that contain more than one phase of the some material usually present noproblem for ECM. However, alloys with inclusions of different materials may be difficult to machine by ECM, or the surface may be unacceptable because of the preferential erosion of oneof the materials. One of the benefits of ECM is the higher machining rates for difficult-to-machine materials such as heat-resistant alloys and titanium alloys.

3c. Limitations:One of the major limitations of the ECM is its inability to machine electrically nonconductivematerials. Usually, sharp corners or clear cuts cannot be obtained by ECM. The complexity of the shape to be machined, the workpiece material, and the electrolyte limit the dimensionalaccuracy and the surface finish that can be achieved by ECM. Etching of the constituents, grain-boundary attack, and pitting due to electrochemical action may have drastic effects on the mechanical properties of the material, particularly the fatigue strength.

The ECM process can be classified as macro and micro ECM according to the equipment usedand the applications. The following section discusses these topics individually in details.

3.1 Macro ECM

Electrochemical machining (ECM) is based on a controlled anodic electrochemical dissolution process of the workpiece (anode) with the tool (cathode) in an electrolytic cell, during an electrolysis process as shown in Fig 3.1-1.

Fig. 3.1-1 Principle of Electrochemical Machining*

* Benedict, G.E., “Nontraditional Manufacturing Processes,” Marcel Dekker, 1987.

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During the anodic dissolution process a direct current with high density and low voltage is passed between a workpiece and a preshaped tool (the cathode). At the anodic workpiece surface, metal is dissolved into metallic ions by the deplating reaction, and thus the tool shape is copied into the workpiece. The electrolyte is forced to flow through the interelectrode gap with high velocity, usually more than 5 m/s, to intensify the mass/charge transfer through the sub layer near anode and to remove the sludge (dissolution products e.g. hydroxide of metal), heat and gas bubbles generated in the gap. In typical manufacturing operations, the tool is fed toward the workpiece while maintaining a small gap.

3.1.1 Process and Process characteristics

3.1.1.1 Rajurkar, K.P., Kozak, J., Wei, B., “Modeling and Analysis of Pulse Electrochemical Machining (PECM),” Transactions of ASME, Vol. 116, 1994, pp. 316-323.

This paper presents mathematical models for the PECM process which take into consideration the non-steady physical phenomena in the gap between the electrodes, including the conjugate fields of electrolyte flow velocities, pressure, temperature, gas concentrations, current densities and anodic material removal rates. The principles underlying higher dimensional accuracy and simpler tool design attainable with optimum pulse parameters are modeled into a theoretical mathematical model. Description of the quasi-steady state, interelectrode gap size estimation with and without tool feeding during pulse on time, distributions of the electrolyte conductivity and current density and distributions of the volumetric gas concentration and temperature were discussed in this paper.The validity of the proposed model was verified by comparing it with the experimental results.

3.1.1.2 Rajurkar, K.P., Kozak, J., Wei B., “Study of Pulse Electrochemical Machining Characteristics,” Annals of the CIRP, Vol. 42, No. 1, 1993, pp. 231-234.

A detailed PECM gap process model considering inhomogeneity of the electrolyte flow has been developed and experimental work related to the effect of pulsed current on anodic electrochemical behavior has been studied. A system of models describing the PECM process during a single pulse has been developed based on Lagrange’s co-ordinate system, which has been further simplified by Euler’s co-ordinate system. A special PECM cell along with a transistorized generator (Rapid Power Tech Inc. USA) and a computer-based data acquisition system (ISC-16 card with EGAA software, RC Electronics, USA) was used to obtain the effective volumetric equivalent (Kv) and to acquire the true data for the model verification. Experiments were conducted for a group of pulses instead of a single pulse to obtain significant amount of anodic metal removal. The experimental results on current changes during a pulse on time and the peak current profiles during a group of pulses were compared with the proposed model. A fair agreement between the experimental results and the results from the proposed model was found.

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Fig. 3.1.1.2-1 PECM with group pulses (a) voltage pulses (b) tool and workpiece

positions, t1 - machining time t2 – tool feed time

Fig. 3.1.1.2-2 Interelectrode gap

Fig. 3.1.1.2-3 Experimental setup

Fig. 3.1.1.2-4 Comparison of experimental and theoretical current pulses

Fig. 3.1.1.2-5 Comparison of peak current profiles

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3.1.1.3 Hardisty, H., Mileham, A.R., Shirvani, H., “A Finite Element Simulation of the Electrochemical Machining Process,” Annals of the CIRP, Vol. 42, No. 1, 1993, pp. 201-204.

This paper describes a computer package based on the Finite Element Method (FEM), which simulates the Electrochemical Machining process. The FEM is used to determine the two-dimensional potential and flux distributions in the electrolyte, in order to estimate surface erosions for a finite time-setup. Algorithms have been developed which automatically change the FE mesh, to simulate moving boundaries for tool movement and workpiece erosion. The complex flux distributions produced in the electrolyte have yielded considerable insight intothe erosion process for too shapes used in practice.The continuous erosion process has been simulated as a series of time-steps at each of whichthe complete potential and flux distribution in the electrolyte is calculated. Algorithms,external to the FE package, have been developed which determine those elements, if any, which must be eroded during a time-step.The computer model was validated by comparing predictions with predictions from one-dimensional ECM theory. Three characteristic cases were analyzed: (a) Tool stationary (Fig3.1.1.3-1). (b) Tool moving-small initial gap (Fig 3.1.1-10) (c) Tool moving- large initial gap (Fig 3.1.1.3-2). In all cases, the agreement between theory and computer predictions wereobserved.

Fig. 3.1.1.3-1 Computer prediction of erosion with stationary tool

Fig. 3.1.1.3-2 Computer prediction of erosion with moving tool and initial gap of

0.05 mm

In addition to the one-dimensional validation tests described here, further research was carried out in which industrial ECM processes have been simulated with a realistic model.Fig. 3.1.1.3-4 shows the final screen of a simulation in which a surface was eroded by a stepped tool until equilibrium was attained. The workpiece profile developed compares well with the shape produced by an actual ECM operation in which similar conditions were used.

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Fig. 3.1.1.3-3 Computer prediction of erosion with moving tool and initial gap of 0.08 mm

Fig. 3.1.1.3-4 Example of 2-D Erosion showing the effect of a stepped tool

3.1.1.4 Rajurkar, K.P., Wei B., Chatterjee, A., “Simulation and Experimental Investigation of Smoothing by Electrochemical Machining,” Transactions of the NAMRI/SME, Vol. XXIII, 1995, pp. 175-180.

A computer-based approach was developed to model and analyze the smoothing process during ECM. A program was developed to simulate the generation of surface profiles withtime during ECM. Experimental verification of this computer model was performed.Experimental results of the effect of voltage, interelectrode gap, electrolyte pressure and initial surface roughness on the final workpiece surface quality were studied. A mathematical model was developed for the smoothing process of the heterogeneous structure of alloys with a random surface profile. Analysis of voltage, feed rate, initial

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surface roughness, and structure of workpiece material and evolution of surface roughnesswas also performed. A 2-D model as shown in Fig. 3.1.1.4-1 was considered.

Fig. 3.1.1.4-1 Typical workpiece surface profile

A computer simulation model was built for the electrochemical surface smoothing of a heterogeneous material and compared with results from machining a homogeneous material.The simulations are shown in Fig. 3.1.1.4-2 & 3.

Fig. 3.1.1.4-2 Computer Simulation of a Homogeneous material

Fig. 3.1.1.4-3 Computer Simulation of a Heterogeneous material

Experiments were conducted to verify the computer model and the influence of various parameters on final surface roughness were studied. The computer model and the experimental results followed the same trend but there were some differences in the actual values. This difference could be attributed to the effect of secondary and tertiary current distributions.

3.1.1.5 Ruszaj, A., Zybura-Skrabalak, M., Chuchro, M., Novak, A., “The influence of process parameters on technological indicators of the electrochemical machining process with non-profiled electrode,” Proceedings of the 1993 ASME Winter Annual Meeting, Vol. 64, 1993, pp. 713-718.

This paper deals with the applications and advantages of using a non-profiled electrode with a working surface greater than the machined surface. Best results were obtained when a non-profiled electrode shaped like a spherical cup (Fig 3.1.1.5-1) is displaced over the machinedsurface along a properly designed track. The technological indicators that have been studiedin this paper are metal removal rate ‘Vw’, thickness of material excess removed ‘a’, surface

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roughness parameter ‘Ra’ and shape error on the border line between successive electrode passes ‘ ’.

Fig. 3.1.1.5-1 Scheme of shaped-surface electrochemical machining with a nonprofiled electrode

A theoretical model has been developed for all the indicators and experiments were conducted on a machine tool type EDCA 25. Results were obtained for 3 different interelectrode gap thicknesses. The non-profiled electrode was made of Copper M1 and the workpiece was made of hardened steel NC6. Water solution of NaNO3, concentration 1.135 g/cm3 was used. Cross feed per electrode pass was equal to 5 mm. In order to calculate a, and Vw values profilograms representing a cross section of the machined material in adirection perpendicular to the electrode displacement were made as shown in Fig. 3.1.1.5-2.

Fig. 3.1.1.5-2 Profilograms representing a cross section of the machined material used for calculating a, and Vw values

From the experimental and theoretical results, the spherical cup electrode was found to be auniversal electrode capable of machining flat and shaped workpieces. It was possible toremove excess material thickness a = 0.1 – 2.0 mm at metal removal rate Vw,max = 27 – 45 mm3/min. Because of the low metal removal rates, it was concluded that electrochemicalmachining using non-profiled universal electrode should be used only for finishing operations.


3.1.2.1 Rajurkar, K.P., Wei, B., Schnacker, C.L., “Monitoring and Control of Electrochemical Machining,” Transactions of the ASME, Vol. 115, 1993, pp. 216-223.

This paper presents a preliminary research on dimensional control and process stability control in ECM. An ECM dimensional control model has been proposed using the state space approach that accounts for the dynamic nature of the ECM inter-electrode gap process. A

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Stochastic methodology of Data Dependent Systems (DDS) was applied to ECM electric signal analysis for developing an indicator, which predicts the onset of random sparks or short-circuits.A review of the ECM process control and stability control was performed and future research was proposed. Modeling of ECM dynamics for the process control was performed and a suitable feedback method namely the state feedback was chosen to achieve the closed loop pole locations. Feed rate and voltage have been chosen as the input parameters for the control system. Time response curves for unit step input were studied as shown in Fig 3.1.2.1-1 & 2.

Fig. 3.1.2.1-1 Simulated time response of the current to a ramp input

Fig. 3.1.2.1-2 Simulated time response of the ram position to a ramp input

In conclusion, the modeled ECM system was found to be a fairly accurate model of the actual process and will serve as a good simulation model to try various control strategies.Analysis of the sparkout situation in ECM was studied. To study this, an artificial arc wassimulated. A typical current spike associated with a spark is shown in Fig. 3.1.2.1-3. It was found that there is a frequency shift and change in bandwidth with the changes in feed rate and applied voltage. This information is used as an indicator for the onset of sparking in ECM.

Fig. 3.1.2.1-3 ECM sparkout

3.1.2.2 Rajurkar, K.P., Kozak, J., Wei, B., McGeough, J.A., “Modeling and Monitoring Interelectrode gap in Pulse Electrochemical Machining,” Annals of the CIRP, Vol. 44, No.1, 1995, pp. 177-180.

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This paper presents with an interelectrode gap model for estimating machining parametersfor the minimum gap size under the limit of electrolyte boiling. An on-line monitoringstrategy based on a linear correlation found experimentally between pulse current signal variance and gap was also proposed. The PECM process is encountered with Joule Heating when rectangular voltage pulses are applied across a small interelectrode gap with a short pulse on time and a pulse off time long enough to ensure flushing of the electrolyte. Using balance energy equations, a model has been developed to determine the minimum gap size considering electrolyte boiling as the limit. This mathematical model eliminated the expensive “trial and error” methods.The on-line monitoring strategy was designed based on the dispersion of high frequencyvoltage surge to estimate the gap size. The pulse voltage and current signals are used as indicators of real-time gap changes at the gap. The acquired current signals have been modeled and analyzed using the Data Dependent System (DDS) methodology and variance analysis.

Fig. 3.1.2.2-1 PECM data acquisition system

DDS modeling procedure consists of fitting autoregressive moving average (ARMA) modelsof increasing order until there is no further significant reduction in the residual sum of squares as indicated by F-test. The DDS autospectrum analysis reveals that both frequency(damping ratio) and magnitude (filtered current J) change with gap size as shown in Fig. 3.1.2.2-2 & 3.

Fig. 3.1.2.2-2 Correlation between damping ratio and gap size

Fig. 3.1.2.2-3 Correlation between variance of J and gap size

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3.1.3 Applications

3.1.3.1 Zhou, C.D., Taylor, E.J., Sun, J.J., Gebhart, L.E., Stortz, E.C., Renz, R.P., “Electrochemical Machining of Hard Passive Alloys with pulse reverse current,” Transactions of NAMRI/ISME, Vol. XXV, 1997, pp. 147-152. &Taylor, E.J., Sun, J.J., Gebhart, L.E., Inman, M.E., Renz, R.P., “The Applications of CM-ECM technology to Metal Surface Finishing,” Transactions of NAMRI/ISME, Vol. XXVIII, 2000, pp. 245-250.

One of the recent developments in ECM polishing is the Charge Modulated ECM process. It is an effective surface finishing process for hard, passive materials such as nickel-base alloys,titanium and aluminum casting alloys.

ta

tc

tr

Fig. 3.1.3.1-1 Schematic of an idealized charge modulated electric field

The charge-modulated electric field consists of an anodic period, a cathodic period (reverse current) and a relaxation period that can be randomly combined during the ECM processwhere the period of modulation (T) is the sum of ta+tc+tr. The parameters such as frequency of modulated waveform, duty cycle and peak voltage or current are additional parametersavailable to control the CM-ECM process. The combinations of these parameters strongly influence the mass transport rates, current distribution, hydrodynamic condition, etc. in the interelectrode gap.

Fig. 3.1.3.1-2 A 3-axis batch mode ECM positioning system designed and built by

Faraday Tech Inc

Fig. 3.1.3.1-3 A 3-axis batch mode ECM surface finishing set-up designed and built by

Faraday Tech Inc

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CM-ECM was performed on Inconnel 718 production parts to perform polishing operation and casting aluminum wheels to perform deburring operation. A solution of 340g/L NaNO3

was used under a constant flow rate of 3 L/min at 22 psi maintained at 95 F. A Mitutoyosurface profilometer, Model MST-212 was used to measure surface roughness.

Fig. 3.1.3.1-4 Before (left) and after (right) polishing of Inconnel 718 part

Fig. 3.1.3.1-5 Before (left) and after (right) deburring of casting aluminum wheel

In conclusion, CM-ECM process for polishing operations improves surface finishing quality and material removal efficiency. provides a stable ECM polishing process to control surface roughness below 0.25 mm. further reduces the surface roughness and micro pits by using a reverse period instead of an “off” time in the case of pulse ECM.

CM-ECM process for deburring operations improves deburred surface finishing quality and burr removal efficiency.provides a focused current distribution to remove burrs without machining the adjacent areas around the burrs. reduces electrolyte flow rate for removing sludge’s.

3.1.3.2 Masuzawa, T., Kimura, M., “Electrochemical Surface Finishing of Tungsten Carbide Alloy,” Annals of the CIRP, Vol. 40, No. 1, 1991, pp. 199-202.

This paper deals with an experimental study on finishing the surface of tungsten carbide alloy. A special design of the pulse train for alternate polarity was suggested for realizing a uniform distribution of Tungsten Carbide and for suppressing the dissolution of the tool electrode. The effectiveness was confirmed by applying the pulse on an EDM generated surface.In the application for finishing with high precision, the duty cycle of the pulse train must be very small, typically less than 0.1. The special designs of current pulse trains used are shown in Fig. 3.1.3.2-1. Selection of electrode material is also important in the case of bipolar and

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combination pulses as the electrode becomes positive to the electrolyte during the negativecycles of the pulse. Hence the reaction at the electrode surface depends on the type of electrode material.

Fig. 3.1.3.2-1 Current waveforms for ECM finishing

The equipment used for the study was made of an acrylic dissolution cell as shown in Fig.3.1.3.2-2. The workpiece and electrode are fixed in the cell, facing the surfaces, which theelectrolyte flows. A NaNO3 solution with concentration 40% by weight was used. A solenoid valve inserted between the cell and the pump controlled the flow.

Fig. 3.1.3.2-2 Experimental Setup

The effects of the pulse designs were compared and it was found that a reduced negative pulse duration in combination pulses provides better surface quality and reduced tool electrode wear. Table 3.1.3.2-1 & 2 show the several pulse duration combinations for bipolar and combination pulses.

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Table. 3.1.3.2-1 Surface Quality with bipolar pulses

Table. 3.1.3.2-2 Surface Quality withcombination pulses

Comparison of the various electrode materials used concluded that graphite proved to be the best electrode with zero electrode wear when using bipolar and combination pulses. Fig.3.1.3.2-3 shows the SEM pictures of a graphite electrode using bipolar pulses and combination pulses.

(a) with bipolar pulse (b) with combination pulseFig. 3.1.3.2-3 Finished surfaces with graphite electrode

3.1.3.3 Risko, D.G., Extrude Hone ECM Group, “Electrochemical Machining- Innovative Solutions for Higher Productivity,” Advanced Machining Technology III Conference,Society of Manufacturing Engineers, Paper No. MR90-244, 1990. & Risko, D.G., Extrude Hone ECM Group with contributions from ECX, Surftran, Cation and Chemtool, “Chemtool Deburring and Surface Finishing with the electrolytic process,”.

Electrochemical Deburring (ECD) is the selective removal of burrs from the workpiece material by electrochemical dissolution. Fig. 3.1.3.3-1 shows the factors influencing the ECM process.

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Fig. 3.1.3.3-1 Factors influencing the ECM Process

Different factors including the electrochemical properties of the workpiece and the tool influence the machining process, accuracy and surface finish of the final product. The ECM has a CNC control and the power supply ranges from 200 to 40,000 amperes. Thevoltage varies between 7 and 25V DC. The other units in the ECM system are ‘Machine Supply Circuit’ (for pumping electrolyte), ‘Parameters regulating Unit’ (keeps electrolyte machining characteristics constant), ‘Metal Hydroxide Removal’ (removes dissolved precipitate), ‘Sludge Reduction Unit’ (reduces the volume of metal hydroxide). Fig. 3.1.3.3-2 illustrates the schematic of ECM electrolytic system.

Fig. 3.1.3.3-2 ECM Electrolytic System

The cycle time for the ECD process is very small and can process typically 12,000 parts per day. At a voltage of 18V, current of 150A, NaNo3 at 25 C, 8.0pH and 1.5bar, the average thickness of burr and deburring cycle time can be plotted as shown in Fig. 3.1.3.3-3.

Fig. 3.1.3.3-3 Relation between time and material removal for typical edge finishing application

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Some of the applications of the ECD process are:120mm projectile cones made from H-13 steel are produced electrochemically. The exterior requirements are achieved in a 2.5min cycle with the cathode advancing towardsthe workpiece parallel to the axis of the cone. The interior intersections are deburred and radiused in 1.5mins with fixed position cathode.

Fig. 3.1.3.3-4 Cone with electrolytic formed edges

Gun barrels rifling can be produced electrochemically with a stationary electrode spanning the length or a small cathode moving the length of the barrel at a fast rate. Both constant twist and gain twist rifling can be formed with no tool wear.

Fig. 3.1.3.3-5 Electrolytically formed rifling Fig. 3.1.3.3-6 10 Diesel Injector Fuel Chamber

Volume Machining: Electrolytic volumetric machining is a precise process of materialremoval by controlling the process parameters to predetermined values. A cathode ismade to a required shape based on the geometry to be machined and the precise volumerequirement is programmed into the machine control as process parameters.Jet-engine blades designed to self-seat are manufactured with abrasive particles bonded to the blade tip. The excellent repeatability and fast metal removal rate results in a high quality, productive operation. This operation uses low electrolyte flow and a large gap.

Fig. 3.1.3.3-7 Turbine blade with tip machined electrolytically

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3.1.3.4 Risko, D.G., Extrude Hone ECM Group, “Electrolytic Deburring: Deburring and radiusing in Seconds,” Select Automatic Deburring, Society of Manufacturing Engineers, Paper No. MR93-131, 1993. & Risko, D.G., Extrude Hone ECM Group, “High-reliability Deburring with ECD,” International Manufacturing Technology Conference, Society of Manufacturing Engineers, Paper No. MR90-409, 1990.

Fig. 3.1.3.4-1 Electrochemical Deburring

Electrochemical Deburring process has a very fast cycle time (typically 20 sec) and is widelyused for deburring the radii on the leading edge of turbine blades, intersecting holes on the stainless steel valves and critical areas on the engine crank shafts.Typical deburring applications include intersecting holes radiused for the valve body. Thedeburring process forms a minimum 0.005inch radius and blend cross holes intersecting with the upper counter bore.

Fig. 3.1.3.4-2 Cut Away View of EC Deburred Valve

In special machining application of the ECM deburring process, the complex radius formingis electrochemically machining blended radii on the dovetail attachment feature of the jet engine blade.

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Fig. 3.1.3.4-3 Electrochemical radiusing of blade dovetail

Profiles of irregular shape on a small component can be manufactured in high volumes using the electrolytic process. Eight workpieces of ratchet can be manufactured simultaneously. A multi part carrier is used for loading and unloading purpose per three minute cycle. The ratchet is shown in the Fig. 3.1.3.4-4 and the loading carrier is shown in the Fig. 3.1.3.4-5.

Fig. 3.1.3.4-4 Ratchet contour Fig. 3.1.3.4-5 Eight component tool with manual loading carrier

3.1.3.5 Lilly, B., Brevick, J., Chen, C., “The Effect of Pulsed Electrochemical Machining on the Fatigue Life of H-13 Steel,” Transactions of NAMRI/SME, Vol. XXV, 1997, pp. 153-158.

Pulse Electrochemical Machining (PECM) has been proposed as a viable method for removing EDM recast layers, which are caused due to the thermal nature of the EDM process. This layer can cause reduced thermal and mechanical fatigue life and reduction in impact strength, leading to premature die failure. This paper reports on experiments thatdetermined the effect of PECM in improving the fatigue life of H-13 tool steel by removingthe EDM generated surface damage.Crucible NuDie XL premium quality AISI H13 tool steel was used in this project. 32 specimens were subjected to EDM treatment but only 16 were subjected to the PECMprocess to analyze the difference between the specimens. The specimens that were processedby PECM showed better fatigue life as shown in Fig. 3.1.3.5-2. Examination of the fracture surfaces of the specimens following failure was conducted and in each case the crack initiation began on either of the shorter edges of the specimen, with the crack growing across the section.

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Fig. 3.1.3.5-1 EDM damaged layers

Fig. 3.1.3.5-2 S-N diagram showing EDM vs. PECM fatigue life

3.1.3.6 Rajurkar, K.P., Kozak, J., Wei, B., “Pulse Electrochemical Machining (PECM) of Ti-6Al-4V Alloy,” Transactions of NAMRI/SME, Vol. XXII, 1994, pp. 141-147.

Titanium alloys are generally regarded as mechanically difficult-to-machine materials. The main problems with machining titanium alloys are short too lives and low attainable materialremoval rates. PECM is capable of machining any electrically-conductive material with high stock removal rates regardless of their mechanical and thermal properties, such as hardness, elasticity and thermal conductivity. PECM eliminates pitting and surface roughness caused while using ECM to machine Titanium alloys. This paper studies pulsed current effects on the dimensional accuracy, surface quality andmetal removal rates in titanium alloy dissolution process. The correlations between thepitting and current waveforms and effects of the pulse parameters on the pitting generationare also studied.The experimental results were studied for the effect of pulse parameters on surface quality and it was found that the dissolution process reflected by the current variation can be divided into 3 stages - passivating dominant stage, activating dominant stage and quasi-stable stage.This led to the study of surface quality at different pulse on times and it was found out thatbetter surface quality is achieved at short pulse on times.The effect of pulse parameters on shaping accuracy was analyzed from the experimentalresults and it was found that there was no significant effect on the machinability index, Kv,when the pulse parameters were altered. However short pulse increases the Vav/ S which leads to an improved dimensional accuracy.

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Fig. 3.1.3.6-1 Schematic view of PECM copying process with a stepped tool

A mathematical model describing the copying process was developed to gain better insight. In conclusion, PECM performed at short pulse on times improves surface finish anddimensional accuracy in titanium alloys.

3.2 Micro ECM

When ECM is applied on the micro-machining range, it is called electrochemical micromachining (ECMM). Different process variables have to be optimally controlled to achieve high precision machining.

Fig. 3.2-1 Scheme of an Electrochemical Cell

Attempts are being made to achieve a satisfactory control of ECMM to achieve a high anodic dissolution with high precision machining. ECMM refers to the applications of ECM in theprocessing of thin films and in the fabrication of microstructures (Fig. 3.2-2).

Fig. 3.2-2 Cu Microstructures using ECMM

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1. In ECMM, the performance criteria depend on the ability of the system to provide desired mass transport effect, and the knowledge of this effect is a prerequisite for the development of EMM processes. A simple description of mass transport in anodic dissolution process is described in this paper.

2. ECMM similar to ECM process removes material based on controlled anodic dissolution process of the workpiece (anode), with the tool as the cathode in an electrolyte cell.

3. Slots, micro holes and complex shapes are needed to be machined, especially in the electronic and computer industries. ECMM is one of the precision machining techniques, which provides superior properties in some applications.

4. Comparable to the predominantly used chemical etching, the ECMM process offers better control and flexibility, requires very little monitoring and control and has minimum safety and environmental concerns.

5. The waste treatment and disposal costs often surpass actual etching processing costs. The ever-increasing cost of incineration and the imposition of land filling restrictions are the main reasons behind the need for developing alternative processes. The electrochemical metal removal is an alternative to wet etching processes

3.2.1 Equipment

3.2.1.1 Bhattacharyya, B., Doloi, B., Sridhar, P.S., “Electrochemical micro-machining: new possibilities for micro-manufacturing,” Journal of Materials Processing Technology, Vol. 113, 2001, pp. 301-305.

This paper highlights different activities to develop the ECMM system set-up including a set-up for the process containing mechanical and electrical components possible to machine micro holes. Power supply voltage in the order of 4-10V is needed in ECMM. The most common electrolytes used in ECMM are NaClO3, NaNO3 and NaCl with different concentrations. To reduce concentration of dissolved particles, the additive chemicals such as NaHSO4 can be used, which doesn’t affect the process adversely. Electrode material: Mostly platinum, tungsten, titanium and copper alloys are used as electrode material. Electrode material should have good thermal and electrical conductivity, corrosion resistance and stiff to withstand electrolyte pressure without vibration. The mechanical system consists of main machine body, tool-feeding device, work holding platform, machining chamber and table on which machining chamber rests. Tool feeding System: A stepper motor may be used where tool movement per pulse should be as small as 5-20 um. The precision movement can be achieved by precision screw, which is coupled with the motor. Also tool vibration is advantageous for better micro machining, so the tool be can moved back and forward by providing appropriate command signal to stepper motor with the help of a microprocessor unit. 220 V single phase AC power supply is converted to a low voltage pulse AC power supply by a step down transformer and a silicon controlled rectifier unit and a pulse generating modules is utilized to provide the required pulse nature of the power supply.

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Fig. 3.2.1.1-1 Block diagram of the various System Components of the ECMM set up


3.2.2.1 Schuster, R., Kirchner, V., Allongue, P., Ertl, G., “Electrochemical Micromachining,”Science Magazine, Vol. 289, July 2000, pp. 98-101.

The application of ultrasonic pulse is based on the finite time constant for double layer charging which varies linearly with the local separation between the electrodes. The nanosecond pulse confines the electrochemical reaction to the proximity of the toolelectrode thus making possible to machine three dimensional cavities of conducting materialwith sub micrometer precision.During the pulse ECMM process the dissolution rate of the material far exceeds the re-deposition rate of the material during the pause of the pulse. The experimental study reveals that there is a linear correlation between time constant, specific electrolyte resistance and spatial resolution.It was found that lowering the electrolyte concentration and shortening the pulse duration increases the precision of the machined cavity.

3.2.2.2 DeSilva, A.K.M., Altena, H.S.J., McGeough, J.A., “Precision ECM by Process Characteristic Modeling,” Annals of the CIRP, Vol. 49, No. 1, 2000, pp. 151-155.

The precision in the ECMM process can be achieved by having a gap size as small as possible, factors like stiffness of the machines, electrolyte boiling, process instability and tool positioning errors limit the minimum gap size. The mathematical modeling has been done by using the characteristic relations.

Fig. 3.2.2.2-1 ECM modeling by characteristic relations

The efficiency for different pulse duration time has been found to increase with the increase in the current density.

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The efficiency for different electrolyte concentration has also been found to increase with the increase in the current density.

Fig. 3.2.2.2-2 Efficiency vs. current densityfor various pulse-on times using 250g/l

NaNO3 electrolyte

Fig. 3.2.2.2-3 Efficiency vs. current densityfor various for various NaNO3 electrolyte

concentrations, pulse-on times 10ms

It has been found that the final surface finish is determined by the efficiency and an increase in the efficiency leads to a better surface finish.

3.2.2.3 Kozak, J., Rajurkar, K.P., Makkar, Y., “Study of Pulse Electrochemical Micro Machining”, Transactions of NAMRI/SME, Vol. XXXI, 2003, pp. 363-370.

A new ECMM system was designed to realize the micro machining using electrochemicalprocess (Fig. 3.2.2.3-1). This set up uses a 3-axis drive table with a travel resolution of 6 m.Small power (4 watt) magnetic drive pump, with the nylon casing is used for supplying the electrolyte during machining.Oscilloscope was used to record, measure and verify the accuracy of input power signals. Electrode: Tungsten cylindrical tool electrode.

Fig. 3.2.2.3-1 Schematic Diagram for ECMM Process

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The investigation used a frequency of 1MHz, pulse on time of 0.2 sec, the machining of the material with the above parameters has limited the machining resolution to 20 m range.The investigation has shown that the as the voltage increases the side gap and the frontal gapincreases, which are the measure of the accuracy of the machined slot.As the feed rate of the tool is increased from 21mm/min to 63mm/min, the accuracy of the machined slot has been found to improve.

0102030405060

0 50 100

Vf mm/min

gap

in m

mX1

000

Side gap Frontal gap

0

0.05

0.1

0.15

0.2

0 5 10Voltage (V)

Gap

in m

m

15

Side Gap Front al gap

Fig. 3.2.2.3-2 Effect of feed rate on side and frontal gap

Fig. 3.2.2.3-3 Effect of voltage on side and frontal gap

It has been found that the value of the ratio of the side gap to the base level for the experimental and theoretical value has been same for the voltage of less than 1.5V and is different for a voltage of more than 1.5V, therefore a more accurate model needs to be developed for the higher voltage to predict the accuracy.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.50 1.00 1.50 2.00 2.50 Voltage ratio to the base level

Side

gap

ratio

to th

e ba

se le

vel

Theoratical Experimental

Fig. 3.2.2.3-4 Comparison of theoretical and experimental values

3.2.3 Mask ECMM

3.2.3.1 Datta, M., Shenoy, R.V., Romankiw, L.T., “Recent Advances in the Study of Electrochemical micromachining,” Journal of Manufacturing and Engineering, ASME, Vol. 64, 1993, pp. 675-692.

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Through-mask electrochemical micromachining process involves careful implementation of a procedure, which includes production of a master art work, surface preparation, choice of proper photoresist and imaging.Rate of the anodic reaction, which depends on the ability of the system to remove thereaction products as they are formed and to supply fresh electrolyte for the anode surface and operating conditions determine the machining performance, which is measured in terms ofdissolution rate, shape control and surface finish of the workpiece. The limiting current density has been found to increase with an increase in the electrolyteflow in the channel. The limiting current density is, therefore, controlled by the convective mass transport. It has been found that for an aspect ratio of greater than 0.5, the maximum vertical displacement of the metal surface is at the center and the shape of the evolving cavity can be fit by an ellipse. The etch factor is independent of the spacing to the opening ratio and decrease as the cavity evolves.

Fig. 3.2.3.1-1 Shape evolution during through mask ECMM

3.2.3.2 Shenoy, R.V., Datta, M., Romankiw, L.T., “Investigation of Island Formation during Through-Mask Electrochemical Micromachining,” Journal of Electrochemical Society, Vol. 143, No. 7, July 1996, pp. 2305-2309.

In applications involving ECMM of metal films covered with a insulating substrate, non-uniformities in the current distribution may lead to non-uniform metal removal rate and maysubsequently cause loss of electrical contact. The results indicate that the problem of island formation is likely for a combination of smallaspect ratio and small metal thickness ratio. For a given combination of photoresist parameters, a critical ratio can be defined, which is the thickness ratio required for the maximum vertical displacement to move to the center of the feature and avoid the formationof island of unetched metal film.During the dissolution of large surfaces in through-mask ECMM process non-uniformcurrent distribution may cause island formation. Due to a faster rate of dissolution at the edges, an island of unetched material may be formed which looses contact with rest of the metallic surface. The formation of the islands can be avoided by using dummy photoresistartwork (Fig. 3.2.3.2-1). It has been successfully demonstrated that during the incorporation of the dummy photoresist artwork, the size of the dummy should match the undercut so that the dummy artwork can be removed upon the completion of the metal removal process.

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Fig. 3.2.3.2-1 Incorporation of a dummy photoresist to avoid island formation

3.2.3.3 Datta, M., “Microfabrication by electrochemical metal removal,” Journal of Research and Development, Vol. 42, No. 5, Sep. 1998, pp. 655-669.

Maskless material removal involves highly localized material removal induced by impingement of a fine electrolytic jet. In ECMM, the performance criteria are dependent on the ability of the system to provide desired mass-transport rates, current distribution and surface film properties at the activesurface.

Fig. 3.2.3.3-1 Relationship between ECMM performance and processing parameters

The basic set up for one sided ECMM involves a driving mechanism in three directions, an electrolyte delivery system in form of multi nozzle assembly, which also acts as cathode, an electrolyte reservoir and electrolyte pumping and filtration system.

Fig. 3.2.3.3-2 Schematic diagram of an experimental tool for one sided ECMM

Design of ECMM tools requires careful attention of desired current distribution and masstransport conditions. Care should also be taken about electrolyte delivery system. Someapplicable systems include channel flow, electrolyte jet, slotted jet and multi-nozzle systems.

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The fabrication of V-shaped nozzle using through mask EMM involves a metallic foil laminated on both sides by a photoresist. The photoresist on one side is then exposed and developed to define initial pattern, consisting an array of circular openings. This manufactures flat-bottomed, V- shaped nozzle on the sample. The photoresist is then stripped and the sample is inspected for entry and exit holes. The final nozzle shape is determined by factors like, dissolution time, undercutting, etch factor and dissolution conditions.

3.2.4 Applications

3.2.4.1 Neagu, C.R., Gardeniers, J.G.E., Elwenspoek, M., Kelly, J.J., “An ElectrochemicalMicroactuator: Principle and First Results,” Journal of MicroElectroMechanical Systems,Vol. 5, No. 1, March 1996, pp. 2-9.

The gas that is generated during the electrolysis of an electrolyte solution is used to deflectthe membrane of the actuator. It has three stages:

The electrolysis stage: O2 is generated and the pressure builds up in the actuator deflecting the membrane.The passive stage: the circuit is open and the pressure is maintainedThe pressure reduction stage: electrodes are short circuited in and the electrolysis reactionis reversed.

Fig. 3.2.4.1-1 Schematic representation of electrochemical actuator

The advantage of this actuator is that it can maintain relatively high pressure with low energy consumption. Power is required only for the pressure build up and only for changing thestates.It has been seen that for small deflections, the relationship between pressure and deflection is linear. The tensile stress caused by stretching of the membrane in large deflections is thecause of non linearity. It has been concluded from the investigation that a pressure of 20mbar can be maintained by supplying a power of 7 W for a duration of 100 seconds, this causes a deflection of flatmembrane over 1.25 m.The study of the electrochemical micro actuator acknowledges that the main issue in the performance of the actuator is to prevent the loss of gas, when the membrane has been deflected and the pressure is being maintained.

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4. References

2.1.1.1 Mohri, N., Takezawa, H., Satio, N., “On-the-Machine Measurement in EDM Process by a calibration System with Polyhedra,” Annals of the CIRP, Vol. 43, No. 1, 1994, pp. 203-206.

2.1.1.2 Kaneko, Y., Yamada, H., Toyonaga, T., “Performance of Linear Motor Equipped Die-Sinking EDM”, International Journal of Electrical Machining No. 5, 2000, pp. 59-64.

2.1.1.3 Fuzhu, H., Kunieda, M., Hashimoto, H., “EDM Using Combined Pulse Lines,” International Journal of Electrical Machining, No. 6, 2001, pp. 47-52.

2.1.1.4 Zhao, W., Liu, W., Di, S., “Research on Miniaturized Direct Drive Mechanism of EDM Electrode Using Linear Ultrasonic Motors,” International Journal of Electrical Machining, No. 4, 1999, pp. 29-31.

2.1.2.1 Kunieda, M., Wataru, K., Takita, T., “Reverse Simulation of Die-Sinking EDM,” Annals of the CIRP, Vol. 48, No. 1, 1999, pp. 115-118.

2.1.2.2 Mohri, N., Suzuki, M., Furuya, M., Saito, N., “Electrode Wear Process in Electrical Discharge Machining,” Annals of the CIRP, Vol. 44, No. 1, 1995, pp. 165-168.

2.1.2.3 Bleys, P., Kruth, J., Lauwers, B., Zryd, A., Delpretti, R., Tricarico, C., “Real Time Tool Wear Compensation in Milling EDM,” Annals of the CIRP, Vol. 51, No. 1, 2002, pp. 157-160.

2.1.2.4 Uno, Y., Okada, A., Nakanishi, H., Gua, C., Okamota, Y., Takagi, T., “EDM Characteristics of CVD-Carbon Electrode,” International Journal of Electrical Machining, No. 3, 1998, pp. 19-24.

2.1.2.5 Sato, T., Imai, Y., Goto, A., Magara, T., “A New Grooving Method based on Steady Wear Model in EDM,” International Journal of Electrical Machining, No. 5, 2000, pp. 41-49.

2.1.2.6 Enache, S., Opran, C., Stocia, G., Strajescu, E., “The Study of EDM with Forced Vibration of Tool-Electrode,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 167-170.

2.1.3.1 Lonardo, P., Bruzzone, A., “Effect of Flushing and Electrode Material on Die-Sinking EDM,” Annals of the CIRP Vol. 48, No. 1, 1999, pp. 123-126.

2.1.3.2 Kunieda, M., Muto, H., “Development of Multi-Spark EDM,” Annals of the CIRP, Vol. 49, No. 1, 2000, pp. 119-122.

2.1.3.3 Kunieda, M., Yoshida, M., “Electrical Discharge Machining in Gas,” Annals of the CIRP, Vol. 46, No. 1, 1997, pp. 143-146.

2.1.3.4 Kunieda, M., Nakashima, T., “Factors determining Discharge Location in EDM,” International Journal of Electrical Machining, No. 3, 1998, pp. 53-58.

2.1.3.5 Yoshida, M., Kunieda, M., “Study on the Distribution of Scattered Debris Generated by a Single Pulse Discharge in EDM Process,” International Journal of Electrical Machining, No. 3, 1998, pp. 39-46.

2.1.3.6 Goto, A., Watanabe, K., Takeuchi, A., “A Method to Machine a Curved Tunnel with EDM,” International Journal of Electrical Machining, No. 7, 2002, pp. 43-46.

2.1.3.7 Hayakawa, S., Yuzawa, M., Kunieda, M., Nishiwaki, N., “Time Variation and Mechanism of Determining Power Distribution in Electrodes during EDM Process,” International Journal of Electrical Machining, No. 6, 2001, pp. 19-25.

2.1.4.1 Kunieda, M., Kojima, H., “On-Line Detection of EDM Spark Locations by Multiple Connection of Branched Electric Wires,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 171-174.

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2.1.4.2 Rajurkar, K. P., Wang, W. M., “Real-Time Stochastic Model and Control of EDM,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 187-190.

2.1.4.3 Boccadoro, M., Dauw, D. F., “About the Application of Fuzzy Controllers in High-Performance Die-Sinking EDM Machines,” Annals of the CIRP, Vol. 44, No. 1, 1995, pp. 147-150.

2.1.5.1 Tamura, T., “Surface Modification of Electrical Discharge Machined Surface by C02Laser,” International Journal of Electrical Machining, No. 3, 1998, pp. 47-52.

2.1.5.2 Kruth, J. P., Stevens, L., Froyen, L., Lauwers, B., “Study of the White Layer of a Surface Machined by Die-Sinking Electro-Discharge Machining,” Annals of the CIRP, Vol. 44, 1995, pp. 169-172.

2.1.5.3 Uno, Y., Okada, A., Hayashi, Y., Tabuchi, Y., “Surface Modification by EDM with Nickel Powder Mixed Fluid,” International Journal of Electrical Machining, No. 4, 1999, pp. 47-52.

2.1.5.4 Dauw, D. F., Brown, C. A., Griethuysen, J. P., “Surface Topography Investigations by Fractal Analysis of Spark-Eroded Electrically Conductive Ceramics,” Annals of the CIRP, Vol. 39, No. 1, 1990, pp. 161-165.

2.2.1.1 Masuzawa, T., Wada, Y., “A double-wire system for accuracy improvement in WEDM,” International Symposium for Electromachining XI, 1995, pp. 201-208.

2.2.1.2 Fengguo, C., Xiaoguang, F., “The Development Status and Analysis of Wire EDM in China,” International Journal of Electrical Machining, No. 6, 2001, pp. 1-5.

2.2.1.3 Gisbert Ledvon - Charmilles Technologies, “Twin-Wire EDM,” Fabricating & Metalworking Magazine, March 2003, pp.24-27. & http://www.charmillesus.com/products/wire/tw/tw.html

2.2.1.4 “New Wire-EDM-Machine Series,” Metal Forming Magazine, March 2003, pp. 140. & http://www.ona-electroerosion.com/eng/productos/hilo/ke.htm

2.2.1.5 http://www.wzl.rwth-aachen.de/en/0_start/schneiderosion/, “Micro-machining by Wire-EDM”.

2.2.2.1 Obara, H., Abe, M., Ohsumi, “Control of Wire Breakage during Wire EDM,” International Journal of Electrical Machining, No. 4, 1999, pp. 53-58.

2.2.2.2 Han, F., Kunieda, M., Sendai, T., Imai, Y., “Simulation on Influence of Electrostatic Force on Machining Characteristics in WEDM,” International Journal of Electrical Machining, No. 7, 2002, pp. 31-36.

2.2.2.3 Klocke, F., Lung, D., Nöthe, T., “Micro Contouring by EDM with Fine Wires”, International Symposium for Electromachining XIII, Vol. II, May 2001, pp.767-779.

2.2.2.4 http://www.intech-edm.com/pdf/wirebook.pdf2.2.3.1 Matsuo, T., Oshima, E., “Investigation on the Optimum Carbide Content and Machining

Condition for Wire EDM of Zirconia Ceramics,” Annals of CIRP, Vol. 41, 1992, pp. 231-234.

2.2.3.2 Spur, G., Appel, S., “Wire EDM cutting of PCD,” Industrial Diamond Review, April, 1997, pp. 124-130.

2.2.3.3 Wang, T., Kunieda, M., “Study On Dry WEDMed Surface,” International Symposium for Electromachining XIII, 2001, pp. 505-512.

2.2.3.4 Obara, H., Nakase, M., Ohsumi, T., Hatano, M., “Analysis of Explosive Load on Wire Surface Generated by Discharge of Wire EDM,” International Journal of Electrical Machining, No. 7, 2002, pp. 37-42.

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2.2.4.1 Wang, W.M., Rajurkar, K.P., Huang H., “Monitoring and Control Strategy for wire breakage in WEDM,” Transactions of NAMRI/SME, Vol. XIX, 1991, pp. 148-153.

2.2.4.2 Rajurkar, K.P., Wang, W.M., McGeough, J.A., “WEDM Identification and Adaptive Control for Variable-Height Components,” Annals of CIRP, Vol. 43, 1994, pp. 199-202.

2.2.4.3 Yan, M.T., Liao, Y.S., “Adaptive Control of WEDM process using the FUZZY Control Strategy,” International Symposium for Electromachining XI, 1995, pp. 343-352.

2.2.4.4 Rajurkar, K.P., Wang, W., Zhao, W.S., “WEDM-Adaptive Control with a Multiple Input Model for Identification of Workpiece Height,” Annals of the CIRP, Vol. 46, 1997, pp. 147-150.

2.2.4.5 Hsue, W.J., Liao, Y.S., Lu, S.S., “A Study of Corner Control Strategy of Wire-EDM based on Quantitative MRR analysis,” International Journal of Electrical Machining, No. 4, 1999, pp. 33-39.

2.2.4.6 Wu, J., Li, M.H., “The Identification of the Servo Control State in Wire Electrical Discharge Machining Process,” International Symposium for Electromachining XIII, 2001, pp. 423-433.

2.2.5.1 “EDM for the Dental Profession,” EDM Today, March/April, 1999. 2.3.1.1 Sheu, D., Masuzawa, T., “Development of Large-Scale Production of Microholes by

EDM,” International Symposium for Electromachining XIII, Vol. II, 2001, pp. 747-758. 2.3.1.2 Masuzawa, T., Okajimam K., Taguchim T., Fujino, M., “EDM-lathe for

Micromachining,” Annals of the CIRP, Vol. 51, No. 1, 2002, pp. 355-358. 2.3.1.3 Fujino, M., Okamoto, N., Masuzawa, T., “Development of Multi-purpose

Microprocessing Machine,” International Symposium for Electromachining XI, 1995, pp. 613-620.

2.3.1.4 Furutani, K., Mohri, N., Higuchi, T., “Miniaturized Electrode Feed Devices Using Piezoelectric Elements”, International Symposium for Electromachining XI, 1995, pp. 621-628.

2.3.2.1 Tsai, Y.Y., Masuzawa, T., Fujino, M., “Investigations on Electrode Wear in Micro-EDM,” International Symposium for Electromachining XIII, Vol. II, 2001, pp. 719-726.

2.3.2.2 Allen, D. M., Almond, H. J. A., Bhogal, J. S., Green, A. E., Logan, P. M., Huang, X. X., “Typical Metrology of Micro-Hole Arrays Made in Stainless Steel Foils by Two-stage Micro-EDM,” Annals of the CIRP, Vol. 48, 1999, pp. 127-130.

2.3.2.3 Morgan, C., Shreve, S., Vallance, R.R., “Precision of Micro Shafts Machined with Wire Electro-Discharge Grinding”, Proceedings of the 2003 ASPE Topical Meeting on Machines and Processes for Micro-Scale and Meso0Scale Fabrication, Metrology and Assembly, University of Florida, 2003.

2.3.3.1 Yu, Z., Masuzawa, T., Fujino, M., “Micro-EDM for Three Dimensional Cavities – Development of Uniform Wear Method,” Annals of the CIRP, Vol. 47, 1998, pp. 169-172.

2.3.3.2 Reynaerts, D., Heeren, P.H., Brussel, H.V., “Microstructuring of Silicon by Micro Electro-Discharge Machining (EDM) – Part I: Theory,” Sensors and Actuators A (Physical), Vol. A60, 1997, pp. 212-218.

2.3.3.3 Heeren. P.H., Reynaerts, D., Brussel, H.V., Beuret, C., Larsson, O., Berthoulds, A., “Microstructuring of Silicon by Micro Electro-Discharge Machining (EDM) – Part II: Applications,” Sensors and Actuators A (Physical), Vol. A61, 1997, pp. 379-386.

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2.3.3.4 Yu, Z.Y., Rajurkar, K.P., Shen, H., “High Aspect Ratio and Complex Shaped Blind Micro Holes by Micro EDM,” Annals of the CIRP, Vol. 51, No.1, 2002, pp. 359-362.

2.3.3.5 Langen, H.H., Masuzawa, T., Fujino, M., “Modular Method for Microparts Machining and Assembly with Self Alignment,” Annals of CIRP, Vol. 44, 1995, pp. 173-176.

3.1.1.1 Rajurkar, K.P., Kozak, J., Wei, B., “Modeling and Analysis of Pulse Electrochemical Machining (PECM),” Transactions of ASME, Vol. 116, 1994, pp. 316-323.

3.1.1.2 Rajurkar, K.P., Kozak, J., Wei B., “Study of Pulse Electrochemical Machining Characteristics,” Annals of the CIRP, Vol. 42, No. 1, 1993, pp. 231-234.

3.1.1.3 Hardisty, H., Mileham, A.R., Shirvani, H., “A Finite Element Simulation of the Electrochemical Machining Process,” Annals of the CIRP, Vol. 42, No. 1, 1993, pp. 201-204.

3.1.1.4 Rajurkar, K.P., Wei B., Chatterjee, A., “Simulation and Experimental Investigation of Smoothing by Electrochemical Machining,” Transactions of the NAMRI/SME, Vol. XXIII, 1995, pp. 175-180.

3.1.1.5 Ruszaj, A., Zybura-Skrabalak, M., Chuchro, M., Novak, A., “The influence of process parameters on technological indicators of the electrochemical machining process with non-profiled electrode,” Proceedings of the 1993 ASME Winter Annual Meeting, Vol. 64, 1993, pp. 713-718.

3.1.2.1 Rajurkar, K.P., Wei, B., Schnacker, C.L., “Monitoring and Control of Electrochemical Machining,” Transactions of the ASME, Vol. 115, 1993, pp. 216-223.

3.1.2.2 Rajurkar, K.P., Kozak, J., Wei, B., McGeough, J.A., “Modeling and Monitoring Interelectrode gap in Pulse Electrochemical Machining,” Annals of the CIRP, Vol. 44, No. 1, 1995, pp. 177-180.

3.1.3.1 Zhou, C.D., Taylor, E.J., Sun, J.J., Gebhart, L.E., Stortz, E.C., Renz, R.P., “Electrochemical Machining of Hard Passive Alloys with pulse reverse current,” Transactions of NAMRI/ISME, Vol. XXV, 1997, pp. 147-152. &

Taylor, E.J., Sun, J.J., Gebhart, L.E., Inman, M.E., Renz, R.P., “The Applications of CM-ECM technology to Metal Surface Finishing,” Transactions of NAMRI/ISME, Vol. XXVIII, 2000, pp. 245-250.

3.1.3.2 Masuzawa, T., Kimura, M., “Electrochemical Surface Finishing of Tungsten Carbide Alloy,” Annals of the CIRP, Vol. 40, No. 1, 1991, pp. 199-202.

3.1.3.3 Risko, D.G., Extrude Hone ECM Group, “Electrochemical Machining- Innovative Solutions for Higher Productivity,” Advanced Machining Technology III Conference, Society of Manufacturing Engineers, Paper No. MR90-244, 1990. & Risko, D.G., Extrude Hone ECM Group with contributions from ECX, “Chemtool Deburring and Surface Finishing with the electrolytic process,” Surftran, Cation.

3.1.3.4 Risko, D.G., Extrude Hone ECM Group, “Electrolytic Deburring: Deburring and radiusing in Seconds,” Select Automatic Deburring, Society of Manufacturing Engineers, Paper No. MR93-131, 1993. &

Risko, D.G., Extrude Hone ECM Group, “High-reliability Deburring with ECD,” International Manufacturing Technology Conference, Society of Manufacturing Engineers, Paper No. MR90-409, 1990.

3.1.3.5 Lilly, B., Brevick, J., Chen, C., “The Effect of Pulsed Electrochemical Machining on the Fatigue Life of H-13 Steel,” Transactions of NAMRI/SME, Vol. XXV, 1997, pp. 153-158.

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3.1.3.6 Rajurkar, K.P., Kozak, J., Wei, B., “Pulse Electrochemical Machining (PECM) of Ti-6Al-4V Alloy,” Transactions of NAMRI/SME, Vol. XXII, 1994, pp. 141-147.

3.2.1.1 Bhattacharyya, B., Doloi, B., Sridhar, P.S., “Electrochemical micro-machining: new possibilities for micro-manufacturing,” Journal of Materials Processing Technology, Vol. 113, 2001, pp. 301-305.

3.2.2.1 Schuster, R., Kirchner, V., Allongue, P., Ertl, G., “Electrochemical Micromachining,” Science Magazine, Vol. 289, July 2000, pp. 98-101.

3.2.2.2 DeSilva, A.K.M., Altena, H.S.J., McGeough, J.A., “Precision ECM by Process Characteristic Modeling,” Annals of the CIRP, Vol. 49, No. 1, 2000, pp. 151-155.

3.2.2.3 Kozak, J., Rajurkar, K.P., Makkar, Y., “Study of Pulse Electrochemical Micro Machining”, Transactions of NAMRI/SME, Vol. XXXI, 2003, pp. 363-370.

3.2.3.1 Datta, M., Shenoy, R.V., Romankiw, L.T., “Recent Advances in the Study of Electrochemical micromachining,” Journal of Manufacturing and Engineering, ASME, Vol. 64, 1993, pp. 675-692.

3.2.3.2 Shenoy, R.V., Datta, M., Romankiw, L.T., “Investigation of Island Formation during Through-Mask Electrochemical Micromachining,” Journal of Electrochemical Society, Vol. 143, No. 7, July 1996, pp. 2305-2309.

3.2.3.3 Datta, M., “Microfabrication by electrochemical metal removal,” Journal of Research and Development, Vol. 42, No. 5, Sep. 1998, pp. 655-669.

3.2.4.1 Neagu, C.R., Gardeniers, J.G.E., Elwenspoek, M., Kelly, J.J., “An Electrochemical Microactuator: Principle and First Results,” Journal of MicroElectroMechanical Systems, Vol. 5, No. 1, March 1996, pp. 2-9.

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