Surface Integrity Evolution of Powder Metallurgical Tool Steel by Main Cut and Finishing Trim Cuts in Wire-EDM

Compared to mechanical machining, EDM can achieve high dimensional accuracy. But its thermal nature causes great concerns regarding surface integrity. With the newest generators, thermal damage could be minimized through main and trim cut strategies in wire-EDM. However, the evolution of surface integrity is not clear yet. In this study, tool steel ASP2023 was machined and surface integrity including surface finish, microstructure, microhardness, residual stress and element distribution was comprehensively compared. Average surface finish Ra of 0.1 μm and 0.2 μm for CH- and water-based dielectrics is achieved. White layer, characterized by the top porous structure and bottom solid recast, was minimized. Visibly clean cut surfaces with less than 0.3 μm rim zone were observed under high resolution SEM. CH-based EDM produced much lower tensile residual stress than water-based EDM.