Micro EDM by Stray-Capacitance-Coupled Electric Feeding

Abstract

With the electrostatic induction feeding method which has been developed by the authors to decrease the minimum discharge energy in micro EDM, non-contact electric feeding to the tool electrode is possible, since a pulse power supply is coupled to the tool electrode by capacitance. In this study, the non-contact electric feeding was carried out with stray capacitance only, and hence machining could be carried out without an electric feeder or equipment for electric feeding to the tool electrode. With the stray-capacitance-coupled electric feeding method, since the stray capacitance was significantly small, a discharge current pulse peak of 200 mA and 3 ns in duration was obtained, realizing discharge craters of 0.8 μm in diameter. A micro-hole of 13.5 μm in diameter was drilled successfully in a stainless steel plate with a thickness of 30 μm. In order to change the discharge energy, a capacitor was connected between the pulse power supply and the work piece. Machining results showed that crater diameters can be decreased by decreasing its capacitance. It was also found that smaller crater diameter can be obtained with a lower pulse voltage. Moreover, in order to minimize the discharge energy, the tool electrode was insulated from the mandrel to decrease the stray capacitance. As a result, a discharge current pulse peak of 130 mA and 2 ns in duration was obtained, and the diameter of discharge craters could be decreased to 0.6 μm.