Research on Electrode Erosion of EDM

The present paper deals with a research on the electrode erosion of the electric discharge machining (EDM), which is caused by repeating of the pulse discharge in a kerosene dielectric. The effect of pulse shape on electrode wear was investigated for understanding the physical aspect of EDM.In the experiment, copper was used as the tool electrode E, hardned steel was used as the workpiece W and the tool electrode was always held to positive polarity. The electric circuitry of EDM is illustrated in Fig. 1, Which is composed of two different pulse generators.As for pulse shape, positive pulses with short duration were superimposed on long square pulses in previous report. So, in this study, negative pulses with short duration are superimposed on long square pulses as shown in Fig. 2 (a) and Fig. 3. Then, short negative pulses are added in the intervals of long square pulses as shown in Fig. 2 (b) and Fig. 5, and also short positive pulses are added as shown in Fig. 2 (c) and Fig. 7. The phase τd of short pulse can be shifted at each pulse train.In above mentioned pulse trains of three kind, the electrode wear rate Ma, the workpiece removal rate Mc and the relative electrode wear γ were measured against the phase τd of short pulse.It became clear from Fig. 4, 6 and 8 that the erosion characteristics of electrodes are essentially influenced by both phase and polarity of short pulse. When phase of positive pulse with short duration reaches in front of long square pulse, the relative electrode wear is found to be remarkably reduced as given in Fig. 8.