Synchronized Observation of Machining Phenomena and Discharge Waveform in EDM of Transparent Insulator

(cid:3) The assisting electrode method has enabled the EDM of insulating materials. However, there is a need to change the machining conditions, otherwise the stability of EDM drops. To solve this problem, it is important to clarify the mechanism of EDM for insulating materials. We built a measurement system that enables the synchronized observation of machining phenomena and the discharge waveform. The observation clarified the two facts. The main role of a long pulse discharge is to form a conductive layer on the workpiece surface. Machining of the insulating material progresses with the concentration of normal discharge in the same area after a long pulse discharge. But, when the amount of pyrolytic carbon is large, the machining accuracy will deteriorate due to concentration of the discharge generated. Thus, the discharge conditions were changed according to the amount of pyrolytic carbon generated, resulting in the improvement of the machined shape accuracy.