A Study to Use the Electrically Conductive CVD Diamond as Electrodes in Electrical Discharge Machining

摘要

In electrical discharge machining (EDM), the property of an electrode is one of the most important factors for improving the EDM performance, such as material removal efficiency, machining accuracy, quality of workpiece surface, and so on. In this paper, an electrically conductive CVD diamond thick film is adopted as an electrode in die sinking EDM for the first time. The electrically conductive CVD diamond thick film, with a thickness of 0.5mm and having recently become commercially available, has a low specific resistance, suitable for carrying out an EDM operation, and a very high coefficient of thermal diffusivity, desirable for high performance EDM. Experiments of the die sinking EDM on high speed steels, such as SKH51 and HRC63, using kerosene oil as the working fluid, show that the electrically conductive CVD diamond film electrode makes it possible to achieve significantly high stock removal rate along with virtually no wear of the electrode for various pulse durations at the reversed polarity, in which the workpiece is negative. Especially, EDM operation is possible at a high current density of 10A/mm~2, which is impossible with a conventional copper or graphite electrode. In addition, a significantly high stock removal rate of 0.11mm~3/min along with an insignificant amount of electrode wear is obtained. In the EDM experiments, in which the workpiece is also the electrically conductive CVD diamond film, the diamond electrode shows an excellent shape control along with insignificant amount of electrode wear, comparing with a copper electrode. The results suggest that the electrically conductive CVD diamond film as an electrode material in micro EDM has a great application potential in the future.