Experimental investigation on the problems in the achievement of super-smooth surface of cemented carbide WC-Co through diamond turning

Abstract

The processing of cemented carbide (WC-Co) with mechanical methods has become problematic in the production of functional parts and molds due to the great brittleness and hardness. The application of ductile-regime machining to process the WC-Co has been attempted, but the outcomes are not satisfactory. To better understand the processing of WC-Co, the Vickers indentation, nanoindentation, single point diamond turning, and taper cutting experiments are carried out by referring to the empirical parameters, instrument options, and published works. Firstly, the effectiveness of the reported models in predicting the critical uncut chip thickness of brittle-ductile transition of WC-Co are verified and discussed in terms of the experimental observations. Then the impact of diamond turning on the morphologies and mechanical properties of the machined surface are examined. After that, the defects that affect the surface quality of WC-Co are analyzed. The results indicate that the deterioration of surface quality is dominantly decided by the breakage of WC grain. The grain breakage induced defects and further observations of taper cutting on the WC-Co reveal that the critical uncut chip thickness (40–50 nm) required to produce a super-smooth surface is much smaller than the depths predicted by the reported models of brittle-ductile transition (0.674–1.008 μm). Such difference may be derived from the improper use of fracture toughness and application of models that treat the workpiece material as a continuous and evenly distributed medium. Finally, a modified diamond turning process is conducted to verify the effectiveness of the analysis.