This paper describes some relations between electrical input power and demensions of EDM craters. To our authors' Knowledge, there were no reports taking into account expansion of arc column for metal heating by transient electrical input power. We have estimated expansion of virtual heat input radius in EDM energy range and proposed to use the time average of the thermal expansion as heat input radius for material heating. To determine crater profile, the dimensions of melting zone were calculated from the temperature distribution in the materials, estimated by using the equation of thermal conduction. Comparison between calculated EDM crater dimensions and experimentally obtained ones has shown reasonability of our proposal. Our study has made it possible to calculate time dependence of expansion of arc column for EDM region. It has become clear that the virtual heat input radius is larger than crater radius, and, in addition, that removal amount of work material with repetitional discharge can be estimated from the removal amount with impulse discharge.
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