Micro-hole machining of carbide by electric discharge machining

This paper describes the characteristics of the micro-hole of carbide by el ectric discharge machining with a copper tool electrode. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to me lt a conductive material, the tool electrode being almost non-unloaded, bec ause there is no direct contact between the tool electrode and the workpiec e. Therefore, the process works very efficiently, particularly in the machi ning of difficult-to-cut materials. This study takes advantage of these fea tures to carry out the micro-hole machining of carbide with a copper tool e lectrode. To achieve minimal expansion of the machined micro-hole and minim al tool electrode wear rate to secure a high precision micro-hole in the ca rbide. the effects of changing the polarity, the tool electrode shape, and the rotational speed of the tool electrode are studied. The present experim ental results show that positive polarity machining must be used. As for th e rotational speed of the tool electrode, it is shown that a higher rotatio nal speed electrode can minimize the expansion. In addition, it is demonstr ated that the cross-sectional area of the tool electrode greatly affects th e expansion and the tool electrode wear. Finally, removal of the debris dis charge and reduction of expansion is shown to be improved remarkably by mak ing a notch on the cylindrical cross-section. (C) 1999 Elsevier Science S.A . All rights reserved.