The research of single point diamond turning of tungsten carbides

Ultraprecision turning of different cobalt contents tungsten carbides by different rake angle diamond tools under dry cutting and minimum quantity lubrication (MQL) with various liquid and gaseous fluids were studied. Tool wear, machined surface roughness and morphology were taken for comparison. It is found that tool wear increases with the increase of cobalt content and grain size of the tungsten carbide. Turning tool with -20°rake angle performs better than that of -25°rake angle tool. There is apparent tool wear in the application of oil mist. This is due to permeation of the cutting fluid into the cutting region aided by the compressed air. Oil films are formed on the tool and workpiece surfaces, and cause the chips to adhere on the machined surface as a result. The film in turns abrades the tool and accelerates the wear rate. The application of soluble fluid improves chip disposal, but micro-chipping of the cutting edge is observed. Comparatively, there is less tool wear under dry cutting condition than MQL with liquid fluids. However, the machined surface is deteriorated due to uneven wear of the cutting edge. With the use of pressurized air only, effect of air penetration and flushing of chips are promoted. It is noted that tool life is increased and surface roughness is decreased by 14% and 57%, respectively. Moreover, the use of cold air of about zero Celsius degree can effectively slow down the catalytic reaction due to cobalt and avoid graphitization of the diamond tool. No tool wear is detected. The surface roughness of 2 nm Ra in cutting WC-1%Co and 4 nm Ra in cutting WC-13%Co are successfully achieved.