On Depth of Heat Effected Layer under Surface of Workpiece in EDM

Heat generated by the repeating pulse discharge in EDM affects the surface of workpiece. This heat effect depends on the wave form of the pulse discharge in EDM, for example, peak value of pulse discharge current, pulse duration, duty factor, and so on.This paper describes the relation between the electrical condition of wave form and the depth of heat effected layer of workpiece. We present fundamental data for determination of the optimum electrical condition in EDM.We think of the radius of virtual thermal source on producing micro craters by pulse discharge. The radius is derived with due regard to the expansion of arc channel. The depth of transformed layer is calculated from the radius, and is about the same value obtained from the microvickers hardness of workpiece. And we show that the radius can be calculated from the peak value of pulse discharge current and pulse duration, so the depth of heat effected layer can be estimated.