Study on Stress Distribution in Electric Discharge Machining. (6th Report). Change in Curvature of a Machined Thin Plate and Surface Structure by Tempering.

When a thin plate is machined by EDM on one side, a certain curvature results owing to tensile residual stress generated on the surface of the workpiece. If the machined plate is tempered, some change in curvature of the thin plate appears to occur due to reduction in residual stress and changes in the degenerated layers.This study was conducted to examine changes in curvature of a machined thin plate under various tempering conditions, in relation to those in the properties (phase changes) of the machined surface, using an X-ray diffractometerReduction in residual stress was concluded to occur due to stress relaxation, phase changes (transformation of γ Fe to α Fe) and the precipitation of carbides (Fe3C, M7C3). Change in curvature of thin plate was essentially the same as that noted by the X-ray stress measuring method. As a result, there occurs considerable plastic deformations (slip, twinning and lattice defects) of the EDM surface, owing to thermal effects.