Electric Discharge Machining of Small Holes Through Polycrystalline Diamond Wire Drawing Blanks

Polycrystalline diamond (PCD) wire drawing die blanks with nominal grain sizes of 3 µm and 25 µm have been pierced with 1 mm diameter holes by electric discharge machining (EDM). The arrangement employed a 1 mm diameter brass tube electrode held in a rotating chuck fed with high pressure deionised water dielectric. Pulse generator settings were varied from 1 to 5 A using a fixed on time, off time and capacitance. The effect of peak current on surface roughness (Ra), material removal rate (MRR), electrode wear and surface integrity was investigated.In contrast wite conventional workpiece materials it was found that (Ra) improved with increasing current possibly as a result of graphitisation of the diamond crystals. Electrode wear for the 25 µm grain size material was double that for the 3 µm material and increased with increasing current density, however, MRR, was substantially higher with the 3 µm grain size material at all current densities.