Influence of sequential machining process on the surface topography of dies

Abstract

Near net-shape manufacturing of components is a trend that aims to significantly reduce machining times and material waste, trading the machining efficiency for smaller lead times. Cold forging of gear-shaped components is one such operation that generates a component with superior geometrical accuracy and precision, however, the machined cavity is often subject to high mechanical loads and fatigue failures. The usual manufacturing chain involves hard machining, die-sinking electro-discharge machining, and mechanical polishing with abrasive media. Without proper knowledge of the resulting surface roughness and morphology, the tribological aspects of the surface can be neglected. Therefore, this study aims to investigate the manufacturing chain of gear-shaped cavities in terms of surface roughness, surface morphology, and surface residual stresses generated after die-sinking electro-discharge machining (roughing and finishing regimes), as well as mechanical polishing. The surface of the gear tooth was evaluated in three distinct regions: flank, top, and bottom. The results showcased that, even though the surface roughness/texture of the different regions of interest illustrates similar magnitudes, the surface morphology presented completely adverse features, highlighting the importance of a thorough analysis of the machined surface. Residual stress analysis indicated that the mechanical polishing operation was not enough to remove the high-magnitude tensile residual stresses.