This paper investigates the coalescence of bubble and the ratio of pulse discharges generated in liquid, in bubble and around the bubble boundary in electrical discharge machining (EDM) process in order to discuss the effect of coalescence of bubble on material removal rate. The easiness of bubble coalescence was observed using a video camera. Then, continuous EDM process was carried out and pulse discharges were classified into above three categories by the rise time of discharge current. It is found that few pulse discharges are generated in bubble and the ratio of around the bubble boundary is large. It is also found that difficulty of bubble coalescence can prevent the scattered material from reattaching on workpiece surface.
