Abstract
In this paper, a new electrical discharge machining (EDM) of insulating ceramics with an assisting electrode and its machining mechanism are described. The proposed method is available for machining a complex shape on insulating ceramics. In experiments, insulating Si3N4 ceramics is machined with an electrical conductive plate as the assisting electrode in working oil. The machining starts on the assisting electrode. When the tool electrode reaches at the interface between the assisting electrode and the insulating ceramics, the machining does not proceed for several minutes. In this period, discharge concentration or short circuit state occurs frequently, and an electrical conductive black layer generates on the ceramics surface. After complete formation of the black layer at the interface, machining of insulating ceramics progresses in stable; meanwhile, the black layer is continuously generated on the ceramics surface. This black layer consists of turbostratic carbon and α-SiC. The equilibrium phase diagram of carbon and silicon explains the formation of the black layer. Fundamental technology of machining insulating ceramics into complex shape by EDM has been established through the above consideration.
