Measurement of impulsive forces and crater formation in impulse discharge

Electrical discharge machining (EDM) is widely used for manufacturing various kinds of dies and molds. However, EDM has numerous problems such as low material removal rate and generation of heat-affected zones, in which there are numerous cracks and microcraters. Recently, many new machining technologies utilizing EDM have been developed. However, the mechanism of material removal in EDM has not yet been sufficiently explained. In this study, to clarify the mechanism of material removal, first, the impulsive force transitions in an impulse discharge were measured. Second, how the mechanism by which the impulsive forces affect the crater formation by impulse discharge was examined. The following results were obtained: (1) a typical waveform obtained from an impulse discharge in kerosene consists of primary, secondary, tertiary and quaternary waves, and the intervals between the peaks of the waves gradually become smaller; (2) because the shape of the crater is strongly dependent on the polarities under the same conditions in EDM, the effect of the impulsive force acting between the workpiece and the electrode on the crater formation by impulse discharge may be insignificant.