Micromachining using electrochemical discharge phenomenon : fundamentals and application of spark assisted chemical engraving

This book explains the fundamentals of SACE, promotes the technology, and encourages researchers and engineers from industry to use it for their specific applications. Therefore, the book, after presenting in details the fundaments of SACE (in particular the Electrochemical Discharges), deals mainly with practical aspects of implementing the machining technology. The book is written so that researchers from fields other than micro-technology (e.g., from life science) will be able to build a simple machining set-up, together with his mechanical work-shop, for individual needs.

Author Notes

Rolf Wuumlet;thrich is an Assistant Professor in the Department of Mechanical and Industrial Engineering at Concordia University, Montreal. His research includes: micromachining of glass and ceramics by non-traditional processes (fundamental aspects, modeling and simulation); development of microdevices for microfluidic, Lab on a Chip, microfuel cells and biosensors; and fabrication of nano-particles using electrochemical discharges. Dr. Wuumlet;thrich has published over 50 peer-reviewed journal and conference papers in his research field of micromachining of glass using electrochemical discharges, and has been invited to give keynotes in international conferences.

Series Editor's Preface	p. xi
Preface	p. xiii
1 Machining with Electrochemical Discharges-An Overview	p. 1
1.1 Spark-Assisted Chemical Engraving	p. 2
1.1.1 What is Sace?	p. 2
1.1.2 Machining Examples	p. 3
1.1.3 A Short Historical Overview	p. 5
1.2 Sace as a Micromachining Technology	p. 6
1.2.1 Mechanical Machining	p. 7
1.2.2 Chemical Machining	p. 7
1.2.3 Thermal Machining	p. 8
1.3 Scope of the Book	p. 8
Part 1 Electrochemical Discharges	p. 11
2 Historical Overview of Electrochemical Discharges	p. 13
2.1 Discovery and Early Applications	p. 13
2.2 The Wehnelt Interrupter	p. 15
2.3 Spectrum of the Electrochemical Discharges	p. 21
2.4 Nature of the Electrochemical Discharges	p. 22
2.4.1 Townsend Discharges	p. 23
2.4.2 Arc Discharges	p. 27
2.4.3 Electrochemical Discharges	p. 29
2.5 Contact Glow Discharge Electrolysis	p. 29
2.5.1 Glow Discharge Electrolysis	p. 30
2.5.2 Anodic Contact Glow Discharge Electrolysis	p. 32
2.5.3 Cathodic Contact Glow Discharge Electrolysis	p. 33
3 Gas Evolving Electrodes	p. 35
3.1 Introduction to Electrochemistry	p. 35
3.1.1 The Nernst Equation	p. 35
3.1.2 Electrochemical Cell Out of Thermodynamic Equilibrium	p. 37
3.1.3 The Charge Transfer Current Characteristics	p. 40
3.1.4 Hydrogen and Oxygen Evolution	p. 41
3.1.5 Electrical Conductivity in Electrolytes	p. 43
3.2 Bubble Formation during Electrolysis	p. 44
3.3 Bubble Layer	p. 47
3.4 The Bubble Diffusion Region	p. 49
3.5 The Bubble Adherence Region	p. 51
3.5.1 Clusters and Bubbles	p. 52
3.5.2 Percolation Theory	p. 52
3.5.3 The Infinite Cluster and Percolation Threshold	p. 55
3.5.4 Model of the Bubble Adherence Region	p. 57
3.6 Bubble Evolution on a Gas Evolving Electrode	p. 59
3.7 Mean Stationary Current - Voltage Characteristics	p. 61
3.7.1 Experimental Description	p. 62
3.7.2 Theoretical Description	p. 63
4 The Gas Film-A Key Element	p. 69
4.1 Formation of the Gas Film	p. 69
4.1.1 Gas Film Formation by Local Electrolyte Evaporation	p. 70
4.1.2 Gas Film Formation by Electrochemical Gas Evolution	p. 74
4.1.2.1 Critical Voltage as a Random Variable	p. 75
4.1.2.2 Influence of the Electrode Geometry	p. 75
4.1.2.3 Influence of the Electrolyte Concentration	p. 76
4.1.2.4 Gas Film Formation Time	p. 77
4.1.3 Hybrid Mechanisms	p. 80
4.2 Shape of the Gas Film	p. 81
4.3 Discharge Activity Inside the Gas Film	p. 83
4.3.1 Definition of the Model	p. 84
4.3.2 Probability Distribution of Electrochemical Discharges	p. 84
4.3.3 Probability of Discharge as a Function of the Terminal Voltage	p. 86
4.3.4 Current Evolution Equation	p. 89
4.3.5 Mean Current and Fluctuations in the Current	p. 90
4.4 Controlling the Gas Film	p. 92
4.4.1 Reducing the Critical Voltage	p. 92
4.4.2 Controlling the Gas Film Stability	p. 93
4.4.3 Controlling the Gas Film Shape	p. 94
Part 2 Micromachining with Electrochemical Discharges	p. 95
5 Material Removal Mechanism	p. 97
5.1 General Considerations	p. 97
5.2 Machining at Low Depths	p. 100
5.2.1 Thermal Model	p. 100
5.2.2 Material Removal Rate	p. 103
5.2.3 Application to Glass Micromachining	p. 105
5.2.4 Application to Ceramic Micromachining	p. 107
5.3 Machining at High Depths	p. 107
5.4 Chemical Contributions	p. 110
5.5 Summary	p. 112
6 Common Machining Strategies	p. 115
6.1 General Overview	p. 115
6.2 Gravity-Feed Drilling	p. 116
6.2.1 Discharge Regime	p. 118
6.2.2 Hydrodynamic Regime	p. 119
6.2.3 Repeatability of Drilling	p. 120
6.2.4 Drilling Time	p. 120
6.2.5 Influence of the Inter-electrode Resistance	p. 121
6.2.6 Microhole Dimensions	p. 122
6.2.7 Machining Quality	p. 125
6.3 Constant Velocity Feed Drilling	p. 127
6.4 2D and 3D Machining	p. 128
6.4.1 Quality of Machined Microchannels	p. 129
6.4.2 Maximal Allowed Tool Travel Speed	p. 132
6.4.3 Depth of Machined Microchannels	p. 133
6.4.4 Influence of Tool Distance from Workpiece	p. 134
6.5 Wire Electrochemical Discharge Machining	p. 135
7 Controlling the Machining Process	p. 137
7.1 Process Analysis	p. 137
7.2 Promoting Chemical Etching	p. 138
7.2.1 Effect of Tool-Electrode Shape	p. 139
7.2.2 Effect of Tool-Electrode Vibration	p. 140
7.2.3 Effect of Tool-Electrode Rotation	p. 143
7.2.4 Adding Abrasive to the Electrolyte	p. 144
7.3 Controlling the Heat Generated	p. 144
7.3.1 Influencing the Heat Transfer	p. 145
7.3.1.1 Heat Transfer through the Electrolyte	p. 145
7.3.1.2 Heat Transfer through the Tool-Electrode	p. 146
7.3.2 Reducing the Critical Voltage	p. 147
7.3.3 Pulsed Voltage Machining	p. 148
7.3.3.1 Microhole Drilling	p. 148
7.3.3.2 2D and 3D Machining	p. 149
7.3.3.3 Travelling Wire Electrochemical Discharge Machining	p. 152
7.4 Controlling the Tool-Workpiece Gap	p. 152
7.5 Searching for Process Control Signals	p. 153
7.6 Summary	p. 155
8 Designing a Sace Micromachining Set-up	p. 157
8.1 General Design Rules	p. 157
8.1.1 Electrodes	p. 157
8.1.2 Processing Cell	p. 159
8.1.3 Electrolyte	p. 159
8.1.4 Power Supply	p. 159
8.2 Drilling Set-ups	p. 160
8.2.1 Manual Drilling	p. 160
8.2.2 Constant Feed Drilling	p. 160
8.2.3 Gravity-Feed Drilling	p. 161
8.3 2D Machining Set-ups	p. 162
9 Outlook	p. 165
References	p. 167
Index	p. 173

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