Gas bubble morphology in small working gaps at spark erosion [micromachining]

The morphology of the gas bubbles in the working gap determines the conditions for the electrical breakdown in spark erosion. Significant modification of the gas bubble structures can be proved by high speed recording if the pulses are changed only in a small parameter field. The investigations carried out are particularly important for the production of precise holes with the spark erosion process. In ED hole sinking, the work gap is smaller than 20 μm so that the size and number of gas bubbles are dominant criteria for decontamination of the discharge gap. The gap cleaning effect can be optimized by the specific choice of the pulse parameters, which leads to an essential reduction of the processing time. Comparative investigations with a high speed framing camera (HSFC) indicate that also for single discharges, the gas bubbles are considerably longer than the pulse periods usually used in spark erosion.