Relationship between Occurrence of Material Removal and Bubble Expansion in Electrical Discharge Machining

In this study, we observe the tracks of debris particles scattered from the discharge point and bubble expansion and contraction in a single pulse discharge ignited in the parallel flat gap space in order to discuss the mechanism of material removal in electr ical discharge machining (EDM). A metal rod and a transparent flat resin plate with metal wire inserts are used as electrodes, and a single pulse discharge was initiated in EDM oil. The tracks of the debris particles scattered from the discharge point and expansion and contraction of the generated bubble are observed using a high-speed video camera. The discharge duration was varied from 60 to 1000 s, where the latter condition is intended to maintain the discharge until after the generated bubble expanded and then contracted. By combining the observed results of the scattered debris particles and the generated bubble motion, it is found that material removal occurs while the bubble is expanding, that is, while the pressure at the discharge point is decreasing.