Influence of machining with defined cutting edge on the subsurface microstructure of WC–Co parts

Abstract To machine WC–Co cemented carbides, discontinuous cutting (milling, shaping, etc.) with diamond tools can be an economical alternative to grinding or electrical discharge machining operations for finishing mechanical parts after sintering. However, the machining with cutting depths within the range of sintering allowance (≈0.2 mm) leads to high cutting forces which may influence the quality of the workpiece. Single cuts of a shaping process of WC–Co with different rake angles and cutting depths were examined. SEM micrographs of the machined subsurface zone allow the measurement of microstructure parameters by an automated method programmed in MATLAB. The result is the determination of grain size, mean free path of the binder, contiguity and cobalt content of a selected region of interest within the subsurface compared to the according bulk properties. Regarding the influence of the cutting conditions, it can be assumed that the damage of the subsurface zone correlates with the acting forces. Larger cutting depths and an extremely-negative rake angle of the tool, which both lead to higher loads, generate larger and further reaching damage in the subsurface. Within deeper influenced subsurface zones, parameters vary depending on the distance to the surface. Close to the surface, small fragmented grains can be found while in the deeper regions of the damaged subsurface zone only few single larger cracks were observed.