The effect of high speed machining on the crater wear behaviour of PCBN tools in hard turning

This study investigates the effect of high speed cutting on the crater wear behaviour of PCBN tools in continuous cutting. Turning tests were performed using two PCBN grades, one high CBN content (PCBNH) and one low CBN content (PCBN-L) at two cutting speeds (150 and 300 m/min). The tool life of each grade at both speeds was determined and the associated crater wear progression charts were generated. Examination of the wear surfaces in the SEM was used to study the wear mechanisms. In order to measure crater depth and evaluate the effect of wear on the tool geometry, the cross-section profile of each cutting edge was replicated. As expected, PCBN-L was found to be the most suitable grade for continuous cutting of hardened steel. While it was the most wear resistant grade, it is also the most sensitive to cutting speed. Flank and crater wear increase with increasing cutting speed. The wear behaviour of PCBN-H is very different; flank wear is significant but is not so sensitive to cutting speed. Crater wear decreases with increasing cutting speed. The results of the machining tests in conjunction with analysis of the wear scars suggest that the wear behaviour of PCBN-L is dominated by chemical wear and diffusion with adhesion and abrasion making a secondary contribution. This ranking is reversed for PCBN-H where abrasion and adhesion are the primary wear mechanisms but during high speed cutting, plastic deformation also contributes to the wear process.