Study on the Effect of External Hydrostatic Pressure on Electrical Discharge Machining

This paper describes the influence of external hydrostatic pressure on material removal rate of electrical discharge machining (EDM). In EDM, because electrode materials and dielectric liquid are evaporated by arc plasma, gas bubbles are generated in the working gap. The machining gap is mostly occupied with gas bubbles during the machining process. In this study, machining was conducted under some external hydrostatic pressure from below to above atmospheric pressure in order to investigate the influence of gas bubbles on the material removal rate. EDM experiments were conducted on drilled holes. Machining results shows that the material removal per pulse in consecutive pulse discharges slightly decreased as the external pressure increased. This is probably because under the lower pressure, the boiling point of the electrode materials decreases. In addition, under optimal pressure, the feed of tool electrode was stable and the material removal rate was largest. This is because the sufficient large bubbles enhance the flushing of the dielectric liquid contaminated with debris particles and gas bubbles in the machining gap.