Electrical discharge machining properties of noble crystals

As previously reported, several insulating ceramics such as Si3N4, SiC and ZrO2 have successfully been machined by sinking electrical discharge machining using the surface discharge modification phenomenon. As unstable discharges occur during the machining of Al2O3 ceramics, inferior machining properties have been obtained as compared to other ceramics. It seems that the formation process of the electrically conductive layer on the workpiece during discharge is much different compared with that of other dissociated ceramics at high temperature. In this study new methods are devised and the electrical discharge machining mechanism of insulating Al2O3 ceramics is researched using high purity alumina and single crystal Al2O3 of sapphire. Machining properties are dependent on the purity and structure of the workpiece, and correlated to its thermal properties.