FACTORS EFFECTING ELECTROMAGNETIC FLAT SHEET FORMING USING THE UNIFORM PRESSURE COIL A THESIS Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Graduate School of The Ohio State University By Kristin E. Banik, B.S. ***** The Ohio State University 2008 Master’s Examination Committee: Approved by Professor Glenn S. Daehn, Adviser Professor Kathy Flores _______________________________ Adviser Graduate Program in Materials Science and Engineering ABSTRACT Electromagnetic forming is a possible alternative to sheet metal stamping. There are multiple limitations to the incumbent stamping methods including: complex alignment, changes to component shapes, and ductility issues, which often limits available formed geometry. Electromagnetic forming allows for the avoidance of some of these issues, but introduces a few other issues. In this thesis, the issues with electromagnetic forming will be discussed in conjunction with the application of the uniform pressure coil. Also, the effects on properties of the electromagnetically formed samples in comparison to the traditional samples will be presented. These properties include hardness, formability and interface issues. Lastly, discussed in this paper is the implementation of the Photon Doppler Velocimetry (PDV) system, a velocity measurement system used to determine the velocity of the workpiece and compare it to physics-based models of the process. ii Dedicated to my parents. iii ACKNOWLEDGMENTS I want to thank my adviser, Dr. Glenn Daehn for his support and guidance throughout graduate school and in running experiments and writing my thesis. I would also like to thank John Bradley, Steve Hatkevich and Allen Jones for their support of the work in our group as well as electromagnetic forming. I thank all my group members, for their support and help and especially Geoff Taber for his aid in velocity measurement and experimental setup. Lastly, I want to thank my family for their support through all the years. I could not have made it this far without the support of my parents, my brother and my sisters. The research was supported in part by General Motors, American Trim and the Third Frontier Grant from the State of Ohio. iv VITA January 2, 1984……………………………Born--Milwaukee, Wisconsin 2006………………………………………..B.S. Materials Science and Engineering University of Kentucky 2006-present………………………………..Graduate Research Associate The Ohio State University FIELDS OF STUDY Major Field: Materials Science and Engineering v TABLE OF CONTENTS ACKNOWLEDGMENTS .......................................................................................... IV VITA............................................................................................................................ V LIST OF TABLES....................................................................................................... X LIST OF FIGURES ...................................................................................................XII CHAPTER 1 ................................................................................................................. 1 CHAPTER 2 ................................................................................................................. 5 2.1 Traditional Sheet Metal Forming............................................................................ 5 2.2 High Velocity Forming........................................................................................... 7 2.2.1 Explosive Forming........................................................................................... 9 2.2.2 Electromagnetic Forming............................................................................... 10 2.2.3 Electrohydraulic Forming .............................................................................. 14 2.3 Comparison of Traditional Stamping to EM forming........................................... 15 2.4 Coils...................................................................................................................... 18 2.4.1 Single Turn and Machined Coils ................................................................... 18 2.4.2 Multiturn Coils............................................................................................... 18 2.4.2.1 Uniform Pressure Coil ............................................................................ 19 2.5 Photon Doppler Velocimetry System ................................................................... 22 CHAPTER 3 ............................................................................................................... 25 3.1 Traditional Stamping Simulation Setup/Pressure-pad Setup................................ 25 3.1.1 Pressure-pad Comparison to Traditional Stamping ....................................... 27 vi 3.2 Electromagnetic Forming Experimental System .................................................. 28 3.2.1 Key Setup Components.................................................................................. 29 3.3.2 Instrumentation Components......................................................................... 33 3.3.2.1 Vacuum and Current Measurement ........................................................ 33 3.3.2.2 Velocity Measurement—Photon Doppler Velocimetry.......................... 34 3.3 Sample Analysis.................................................................................................... 37 3.3.1 Sample Preparation for Analysis ................................................................... 37 3.3.2 Hardness Measurements ................................................................................ 38 3.3.3 Forming Depth Measurements....................................................................... 38 3.4 Experimental Variables......................................................................................... 39 3.4.1 Discharge Energy........................................................................................... 39 3.4.2 Coil Geometry................................................................................................ 39 3.4.3 Vacuum.......................................................................................................... 40 3.4.4 Standoff.......................................................................................................... 42 3.4.5 Driver Material............................................................................................... 42 3.4.6 Workpiece Material ....................................................................................... 43 CHAPTER 4 ............................................................................................................... 44 4.1 Velocity Measurement......................................................................................... 44 4.1.1 Summary........................................................................................................ 52 4.2 Velocity Estimates ................................................................................................ 53 4.2.1 Summary....................................................................................................... 60 CHAPTER 5 ............................................................................................................... 61 5.1 Enclosure............................................................................................................... 62 5.1.1 Previous Generations ..................................................................................... 62 5.1.2 New Generation ............................................................................................. 63 5.2 Clamping Mechanism ........................................................................................... 63 5.2.1 Previous Generations ..................................................................................... 63 5.2.2 New Generation ............................................................................................. 63 5.3 Coil........................................................................................................................ 64 vii 5.3.1 Previous Generations ..................................................................................... 64 5.3.2 New Generation ............................................................................................. 66 5.3.3 Experimental and Theoretical Comparison ................................................... 69 5.3 Summary............................................................................................................... 72 CHAPTER 6 ............................................................................................................... 74 6.1 Hardness Effects .................................................................................................. 74 6.1.1 Discharge Energy.......................................................................................... 74 6.1.2 Standoff......................................................................................................... 77 6.1.3 Comparison of pressure-pad to electromagnetic forming............................. 79 6.1.4 Summary....................................................................................................... 82 6.2 Formability........................................................................................................... 83 6.2.1 Traditional versus Electromagnetically Formed..........................................