Measuring Residual Stress Caused by Wire EDM of Tool Steel

Abstract

EDM causes thermally induced residual tensile stress to form in the top layer of a machined surface. This paper deals with a mechanical method for measuring the residual stress profile in function of depth beneath the surface. Deformation due to stress relaxation is measured while removing influenced material containing residual stress. The measurement is done for samples of tool steel, machined with Wire EDM. Results show that the maximum tensile stress and the penetration depth of tensile stress decrease with increasing number of finishing steps. In some cases, after rough W -EDM, a relaxation of residual stress in time is observed. The harmful influence of residual stresses is clear after rough W-EDM of thin beams: the rough machining causes major deformation of the part, which makes further finishing impossible.