A NEW LOOK AT CARBIDE TOOL LIFE

The mechanical behaviour of WC-Co composites can be divided into three temperature domains. WC-Co is brittle below 500-degrees-C, tough between 500 and 800-degrees-C and shows plastic deformation above 800-degrees-C. Once the tool temperature has been related to the cutting speed, the life of WC-Co cutting tools can be predicted based on the mechanical behaviour of WC-Co as a bulk material. As a result, the plot of the tool life as a function of speed also shows three domains of behaviour associated with the wear of the tool, due to brittle fracture, ductile fracture and plastic deformation. A model is presented to explain the observed behaviour of the tool life versus speed for continuous cutting (Taylor curve). This curve is generally non-linear on a log-log plot. The overall tool wear rate is generated by the superposition of a non-thermally activated process and two thermally activated ones. The interpretation of tool wear, based on three domains of temperature, also holds for interrupted cutting, such as milling. In this case, a qualitative model explains the brittle rupture observed below 500-degrees-C, and the occurrence of comb cracks above 500-degrees-C.