Observation of arc plasma expansion and delayed growth of discharge crater in EDM

In this research, the relationship between the expansion of arc plasma and increase of discharge crater diameter during electrical discharge machining was investigated. Expansion of the plasma generated by a single pulse discharge was observed using a high-speed video camera. In order to identify the arc column area, where discharge current flows, the radial temperature distribution in the plasma was measured using spectroscopy, and the area with high degree of ionization was identified. As a result, it was found that the expansion of the arc column completes within a few microseconds after dielectric breakdown, while the diameter of the crater grows gradually with a much lower speed than the arc column.