Micro-hole machining of carbide by electric discharge machining

This paper describes the characteristics of the micro-hole of carbide by electric discharge machining with a copper tool electrode. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material, the tool electrode being almost non-unloaded, because there is no direct contact between the tool electrode and the workpiece. Therefore, the process works very efficiently, particularly in the machining of difficult-to-cut materials. This study takes advantage of these features to carry out the micro-hole machining of carbide with a copper tool electrode. To achieve minimal expansion of the machined micro-hole and minimal tool electrode wear rate to secure a high precision micro-hole in the carbide. the effects of changing the polarity, the tool electrode shape, and the rotational speed of the tool electrode are studied. The present experimental results show that positive polarity machining must be used. As for the rotational speed of the tool electrode, it is shown that a higher rotational speed electrode can minimize the expansion. In addition, it is demonstrated that the cross-sectional area of the tool electrode greatly affects the expansion and the tool electrode wear. Finally, removal of the debris discharge and reduction of expansion is shown to be improved remarkably by making a notch on the cylindrical cross-section. (C) 1999 Elsevier Science S.A. All rights reserved.