Comparative Study of the Capabilities of Various Micromachining Processes

Comparative Study of the Capabilities of Various
Micromachining Processes

University of Illinois at Urbana-Champaign

Thesis

Submitted in partial fulfillment of the requirements
for the joint degree of Master of Mechanical Engineering and Business Administration
at the Technical University of Darmstadt, Germany

Urbana, Illinois

Acknowledgement

The author would like to thank all the following people for all their help with the completion of this thesis.

Professor R. DeVor and Professor S. Kapoor who provided important guidance, insight, and structure for this project. They have been always willing to help me and give me advise during the completion of these thesis. Their knowledge and experience were the biggest support I could wish to have for this project. Professor DeVor and Professor Kapoor have been always willing to take time out of their busy schedule and talk about any problems or questions I was having.

All the students in the research group who supported me with their advise and friendship. I especially want to thank Mike Vogler and Patrick Bless who always found the time to help me with my smaller and bigger problems.

Finally, I would like to thank my family who always believed in me, supported me, and loved me you all helped to make this possible.

Contents

1 Introduction ... 1
1.1 Background and Motivation ... 1
1.2 Research Objective, Scope, and Research Plan ... 4
1.3 Thesis Content ... 5

2 Laser Machining ... 7
2.1 Introduction ... 7
2.2 Laser Parameters ... 11
2.3 CO2 Lasers ... 14
2.3.1 Introduction ... 14
2.3.2 Capabilities ... 14
2.3.3 Industrial Applications ... 15
2.3.4 Costs ... 15
2.4 ND:YAG Lasers ... 17
2.4.1 Introduction ... 17
2.4.2 Capabilities ... 17
2.4.3 Industrial applications ... 22
2.4.4 Costs ... 22
2.5 Excimer Lasers ... 23
2.5.1 Introduction ... 23
2.5.2 Techniques ... 24
2.5.3 Capabilities ... 28
2.5.4 Industrial Applications ... 33
2.5.5 Costs ... 34
2.6 Femtosecond Lasers ... 36
2.6.1 Introduction ... 36
2.6.2 Ablation process ... 37
2.6.3 Techniques ... 43
2.6.4 Capabilities ... 47
2.6.5 Industrial Applications ... 51
2.6.6 Costs ... 52
2.7 Conclusion ... 53

3 Mechanical Machining ... 56
3.1 Introduction ... 56
3.2 Tool Materials ... 58
3.2.1 Diamond ... 58
3.2.2 Tool Steel and Tungsten Carbide ... 60
3.3 Microdrilling ... 61
3.3.1 Drilling Machines ... 61
3.3.2 Drills ... 63
3.3.3 Cutting Process ... 66
3.3.4 Capabilities ... 72
3.3.5 Industrial Applications ... 76
3.3.6 Costs ... 77
3.4 Micro-Turning ... 78
3.4.1 Turning Machines ... 78
3.4.2 Turning Tools ... 80
3.4.3 Difficulties of Microturning ... 81
3.4.4 Cutting Process ... 85
3.4.5 Development of a micro-lathe ... 92
3.4.6 Capabilities ... 94
3.4.7 Industrial Applications ... 99
3.4.8 Costs ... 99
3.5 Micromilling ... 101
3.5.1 Milling Machines ... 101
3.5.2 Milling Tools ... 102
3.5.3 Cutting Process ... 105
3.5.4 Development of a meso-scale milling machine ... 113
3.5.5 Capabilities ... 114
3.5.6 Industrial Applications ... 122
3.5.7 Costs ... 122
3.6 Conclusion ... 123

4 Microforming ... 125
4.1 Introduction ... 125
4.2 Microforming Techniques and Capabilities ... 126
4.2.1 Extrusion ... 126
4.2.2 Cold Forging ... 127
4.2.3 Deep Drawing ... 128
4.2.4 Embossing/Coining ... 130
4.2.5 Air Bending ... 132
4.2.6 Blanking and Punching ... 133
4.3 Forming Process ... 134
4.3.1 Material Behavior ... 135
4.3.2 Friction ... 136
4.4 Machines ... 139
4.5 Forming Tools ... 139
4.6 Costs ... 141
4.7 Conclusion ... 141

5 Micro Electro-Discharge Machining (Micro-EDM) ... 142
5.1 Introduction ... 142
5.2 Principles of Material Removal in EDM ... 144
5.3 Factors influencing the Micro-EDM Process ... 147
5.4 Micro-EDM Techniques ... 151
5.4.1 Micro Electro-Discharge Die-Sinking ... 151
5.4.2 Micro Electro-Discharge Drilling ... 153
5.4.3 Micro Wire Electro-Discharge Machining ... 153
5.4.4 Micro Wire Electro-Discharge Grinding ... 155
5.4.5 Micro Electro-Discharge Grinding ... 156
5.4.6 Micro Electro-Discharge Milling ... 157
5.4.7 Uniform Wear Method ... 158
5.4.8 Summary of the Machining Techniques ... 162
5.5 Capabilities ... 163
5.5.1 Micro Electro-Discharge Die-Sinking ... 163
5.5.2 Micro Electro-Discharge Drilling ... 166
5.5.3 Micro Wire Electro-Discharge Machining ... 167
5.5.4 Micro Wire Electro-Discharge Grinding ... 168
5.5.5 Micro Electro-Discharge Grinding ... 169
5.5.6 Micro Electro-Discharge Milling ... 170
5.5.7 Uniform Wear Method ... 171
5.6 Machines ... 171
5.7 Industrial Applications ... 172
5.8 Costs ... 173
5.9 Conclusion ... 175

6 Conclusion ... 176
6.1 Summary and Comparison ... 176
6.2 Process Selection ... 179
6.3 Research and Application Issues ... 182

List of References ... 187

A Surface Roughness Measures ... 205

B Machine Specifications ... 207
B.1 CO2 Laser ... 208
B.2 Nd:YAG Laser ... 209
B.3 Excimer Laser ... 210
B.4 Femtosecond Laser ... 211
B.5 Drilling Machine (Via Drilling) ... 212
B.6 Turning Machine ... 213
B.7 Milling Machine ... 214
B.8 Forming Machine ... 215
B.9 Micro Electro-Discharge Machine ... 216

List of Tables

1.1 Methods used for micromachining [1] ... 2
2.1 Comparison of direct writing method with mask projection method [2] ... 8
2.2 Excimer gas mixtures [3] ... 23
2.3 Energy per photon at different excimer wavelengths [4] ... 30
2.4 Ablation rate using a KrF excimer laser [5] ... 30
2.5 Comparison of different beam techniques [6] ... 45
3.1 Wear of Diamond by Sliding Metals at a sliding speed of 100-200 m/sec [7] ... 59
3.2 Materials that can be diamond machined [8] ... 59
3.3 Materials that can be diamond machined via ductile mode/Diamond grinding [8] ... 60
3.4 Typical Diamond Turning Parameters [8] ... 79
3.5 Recommended machining conditions depending on workpiece material [9] ... 81
3.6 Maximal feedrates for good surface qualities [8] ... 88
3.7 Microturning Parameters and Results ... 98
3.8 Parameter variation in micromilling using FIB-tools [10] ... 121
3.9 Comparison of different results of mechanical micromachining... 123
4.1 Deep drawing of 100 um thick sheets [11] ... 129
5.1 Summary of EDM techniques and machinable shapes [12] ... 163
5.2 Material removal rates in micro-EDM ... 164
5.3 Comparison of different micro-EDM techniques and their capabilities ... 175
6.1 Comparison of micromachining techniques ... 178
6.2 Advantages and disadvantages of laser micromachining processes ... 179
6.3 Advantages and disadvantages of mechanical micromachining processes ... 180
6.4 Advantages and disadvantages of microforming and micro-EDM processes ... 181

B.1 CO2 laser specifications ... 208
B.2 Nd:YAG laser specifications ... 209
B.3 Excimer laser specifications ... 210
B.4 Femtosecond laser specifications ... 211
B.5 Drilling machine specifications ... 212
B.6 Turning machine specifications ... 213
B.7 Milling machine specifications ... 214
B.8 Forming machine specifications ... 215
B.9 Micro electro-discharge drilling/milling machine specifications ... 216

List of Figures

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Chapter 1
Introduction
1.1 Background and Motivation

There has been a significant increase in the importance of miniature parts in recent years. The forerunner of this technology was mostly the electronics industry with their need of manufacturing processes for electronic components, like printed circuit boards and integrated circuits. The market of microsystem technologies is in general a very fast growing market. According to a study of the European NEXUS organization (Network of Excellence in Multifunctional Microsystems), the worldwide market for microsystem technologies is growing at an average rate of 18% a year to a total of $38 billion in 2002 [75] . However, the focus of the development is distributed different in certain countries. While the US has for example a focus on parts for micro-electro-mechanical systems (MEMS), equipment for information technology, biomedicine and genetic engineering, Germany dominates in sensor technology for the automotive industry. Japan has traditionally a strong position in fine mechanics and precision engineering as well as in equipment for information technology and consumer goods [77] .

Until recently, the production of miniature components was focused on technologies, traditionally used in the electronics and semiconductor industry, like etching and other photofabrication techniques. Using these technologies extremely small feature sizes can be produced. Optical lithography for example produces features as small as 0.18 um and X-ray lithography can be used to produce even smaller features [78] . Table 1.1 gives an overview of some of the methods which can be used for the production of miniature parts. An introduction to these techniques is given in some papers which brie y summarize different micromachining methods. A very good paper was published by Masuzawa [12] . The most complete description of different processes is included in the book "Fundamentals of microfabrication: the science of miniaturization" by Marc J. Madou [13] . Some other papers summarizing different micromachining methods are for example [69, 79,81] .

Because of the steadily increasing demand for 3-dimensional microparts, for example for the development of micromachines, techniques which are capable of creating these features have a growing importance. However, some of the micromachining technologies mentioned in Table 1.1 lack the capability to produce complex 3-dimensional parts with high aspect ratios. The processes, which are best suited to create these parts are for example laser micromachining, mechanical micromachining, microforming, electrochemical machining, and micro electro-discharge machining. Besides the creation of truly 3-dimensional miniature parts with a high aspect ratio, the achievable accuracy, respectively the relative accuracy is always a challenge in micromachining. While the absolute accuracy which can be reached in micromachining is excellent, the relative accuracy is rather bad. In traditional manufacturing of precision parts relative accuracies of 10 can be attained, but these relative accuracies cannot be reached in micromachining [13]. To clarify about which range of sizes, accuracies, and relative accuracies one talks in micromachining, some examples are shown in Figure 1.1. Micromachining means usually that the size of the parts is smaller than 1 mm, but even feature sizes of less than 1 um are created. As it is shown in Figure 1.1, 1 um is the hardly imaginable size of a bacterium. With some processes, surface finishes as good as 1 nm can be created, which is approximately ten times the size of an atom. If the relative accuracy of a house, which is not considered to be a precision part, is compared with the relative accuracy of a lithography based micromachine, it can be noticed that these are approximately the same. The optimum in relative accuracies is usually achieved at sizes, that are bigger than micromachined features. In general, it can be seen that the smaller the micromachined part is, the more difficult is it to achieve a good relative accuracy. Nevertheless, the absolute accuracy of micromachined features increases with a decreasing size of the machined feature. Other challenges which need to be considered in micromachining are the assembly and handling of the small parts and the stringent requirements for the alignment and positioning accuracy of the tools. However, many of the micromachining techniques mentioned cannot be accounted for specific industrial applications, because they are still in the research and not the industrial stage.

Even though these micromachining processes currently draw a lot of attention in research, there was only little effort put into summarizing and synthesizing the results of this research. Most of the information exists in form of very specific publications, examining only one factor of a certain process. This is unsatisfying if one wants to get information on the capabilities and state-of-the-art of a process or if several processes should be compared. Especially, as these processes are becoming more important in industrial applications, it is crucial for companies to have the possibility to judge the different manufacturing possibilities.

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