Cutting performance of CBN and diamond tools in dry turning of cemented carbide

This research deals with the hard turning of cemented carbide with CBN and diamond tools, and focuses on the tool performance, mainly tool wear with respect to cutting force and cutting temperature. The internal turning tests without cutting fluid are executed with the vertical machining center. Seven types of tool materials: SC, CVD-SC, two PCDs, BL-NPD (Binderless nano-polycrystalline diamond) and CBN: are selected for cutting three grades of cemented carbides WC having the different Co binder content (12%, 20% and 25%). Attrition has been found to be the main tool wear mechanism for all tools with slight adhesion of the workpiece binder on the tool face. In cutting of softest carbide WC-m (25% Co), the polycrystalline CBN tool has the lowest tool wear than any other PCD tools. In turning of harder carbides WC-d (20% Co) and WC-t (12% Co), both polycrystalline CBN and PCD cannot be used continuously due to their low hardness, and BL-NPD, SC and CVD-SC tools are applicable. And the BL-NPD tool has the best cutting performance with less flank wear. As for WC-d, extremely stable cutting can be done with BL-NPD where the principal cutting force is kept almost constant at 40 N. Only BL-NPD tool can continue to turn the hardest WC-t. In spite of turning hard materials, the tool temperatures measured are relatively low below 450°C due to the high thermal conductivities of tool materials. However, cutting temperature is directly related to the tool wear and cutting force rather than thermal conductivity of tool in turning of WC-m and WC-t.