Study on EDM phenomena with in-process measurement of gap distance

In this paper, the machining phenomena in the electrical discharge machining (EDM) process are investigated through a new method of in-process measurement of gap distance. The aim of this study is to understand the cause of short-circuiting and to improve the machining rate. A pipe electrode is used and the working fluid is supplied to the gap space though a fixed restrictor and the pipe electrode. Since the pressure between the fixed restrictor and the tip of the pipe electrode (fluid pressure) depends on the gap distance, the absolute value of the gap distance can be determined in-process by measuring the fluid pressure. It is found that the gap distance at the moment when the short-circuiting occurs is more than several micrometers. This result indicates that the cause of the short-circuiting is the bridging of the gap space by collected debris. Based on these results, a new gap control method in which the gap distance is kept constant even when short-circuiting occurs is examined.