Machining phenomena in EDM of insulating ceramics: effect of condenser electrical discharge

摘要

Because of the high resistivity of insulating ceramics, there are some differences compared with theEDM of metallic materials. The secondary metal as an assisting electrode and a minus polarity of theelectrode overcame the difficulties of machining for insulating ceramics. And the insertion of acondenser between the electrode and the workpiece improves the removal rate and the stability inelectrical discharge machining for insulating ceramics. But there is no distinct explanation of themechanisms. In this paper, we certified the mechanism and the effects of the condenser EDM forinsulating ceramics as Si{sub}3N{sub}4, Sialon and SiC. There are two types of the electrical discharge waveforms in the condenser EDM of insulatingceramics. A high electrical resistance of the surface causes a discharge with longer pulse durationthan the settled value of discharge duration, which produces a lot of carbon from the working oil byheating. The low electrical resistance generates short discharge pulses which waste the carbongradually. These waveforms are affected by a discharge-detection voltage, an equivalent resistance ofceramics' surface, and electrical parameters of discharge circuits. An adequate balance of a long pulseand short pulses makes it possible to machine insulating ceramics with high removal rate and highstability.