Cubic boron nitride tool wear in interrupted hard cutting

Cubic boron nitride (CBN) tool wear in interrupted turning of hardened M50 steel has been investigated. The goal was to identify the dominant wear mechanism during interrupted cutting, and in particular, to study the effect of CBN content. Results show significantly different wear characteristics between high (CBN-H) and low (CBN-L) CBN content tools. Contrary to Taylor's tool life equation, tool life of CBN-L is optimized at a medium cutting speed. In contrast, CBN-H shows a monotonic decrease of tool life with increasing cutting speed. Moreover, CBN-H is less sensitive to interrupted cutting than CBN-L, which shows consistent decrease of tool life with increasing frequency of interruption. It is suggested that the higher hardness and fracture toughness of CBN-H result in greater resistance to mechanical wear that becomes more dominant in interrupted cutting. However, the metallic binder in CBN-H has high affinity with workpiece materials and, therefore, results in rapid thermally activated wear at high cutting speeds. (C) 1999 Published by Elsevier Science S.A. All rights reserved.