Preparation of Coated Microtools for Electrochemical Machining Applications

PREPARATION OF COATED MICROTOOLS FOR ELECTROCHEMICAL MACHINING APPLICATIONS Ajaya K. Swain, M.S. University of Nebraska, 2010 Advisor: K.P. Rajurkar Coated tools have improved the performance of both traditional and nontraditional machining processes and have resulted in higher material removal, better surface finish, and increased wear resistance. However, a study on the performance of coated tools in micromachining has not yet been adequately conducted. One possible reason is the difficulties associated with the preparation of coated microtools. Besides the technical requirement, economic and environmental aspects of the material and the coating technique used also play a significant role in coating microtools. This, in fact, restricts the range of coating materials and the type of coating process. Handling is another major issue in case of microtools purely because of their miniature size. This research focuses on the preparation of coated microtools for pulse electrochemical machining by electrodeposition. The motivation of this research is derived from the fact that although there were reports of improved machining by using insulating coatings on ECM tools, particularly in ECM drilling operations, not much literature was found relating to use of metallic coating materials in other ECM process types. An ideal ECM tool should be good thermal and electrical conductor, corrosion resistant, electrochemically stable, and stiff enough to withstand electrolyte pressure. Tungsten has almost all the properties desired in an ECM tool material except being electrochemically unstable. Tungsten can be oxidized during machining resulting in poor machining quality. Electrochemical stability of a tungsten ECM tool can be improved by electroplating it with nickel which has superior electrochemical resistance. Moreover, a tungsten tool can be coated in situ reducing the tool handling and breakage frequency. The tungsten microtool was electroplated with nickel with direct and pulse current. The effect of the various input parameters on the coating characteristics was studied and performance of the coated microtool was evaluated in pulse ECM. The coated tool removed more material (about 28%) than the uncoated tool under similar conditions and was more electrochemical stable. It was concluded that nickel coated tungsten microtool can improve the pulse ECM performance.