Machining Phenomena in EDM of Insulating Ceramics with Powder Mixed Oil

In this paper we describe the machining characteristics of insulating Si3N4 ceramics by using several kinds of powder mixed oil. With powder mixed oil, the removal rate was improved due to discharge dispersion. However, contrary to expectations, the surface roughness was not sufficiently improved by using only the powder mixed oil, since a long pulse discharge that exceeded the settled pulse duration was generated. This phenomenon is often observed in the case of EDM of a high-resistivity material. In order to obtain a smooth surface, the machining was carried out under limited pulse duration with powder mixed oil so that the long pulse could not be generated. Tests revealed that the removal rate in drilling Si3N4 by EDM was almost the same as that by the grinding process and the surface roughness was reduced to 4μmRy.