Observation of EDM gap phenomena of single pulse discharge under different environments

In electrical discharge machining (EDM) with a liquid dielectric, most of the interelectrode gap space during continuous discharge machining is occupied by bubbles. The bubbles would generate a lot of liquid bridges between the electrodes and the electrode surfaces above and under the bubbles are covered with liquid films. Therefore, the discharges are ignited in different environments during the machining. To clarify the influence of different discharge environments on the machining results, in this study, the gap phenomena of single pulse discharges under different environments were observed by a high-speed video camera. By virtue of a laser light source, the melt pool dynamics and the material removal could be directly observed, and the gap phenomena of discharge on dry surfaces, on wet surfaces and in liquid bridge were compared and analyzed. The results show that the existence of liquid films on the electrode surfaces would increase the velocity of radial flow and thus increase the material removal compared with the discharge on dry surfaces. On the other hand, when discharge was ignited in the liquid bridge, with the increase of bridge diameter, the material removal was decreased because of the decreased radial velocity.