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 mec hanism during interrupted cutting, and in particular, to study the effect o f CBN content. Results show significantly different wear characteristics be tween 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 spe ed. In contrast, CBN-H shows a monotonic decrease of tool life with increas ing cutting speed. Moreover, CBN-H is less sensitive to interrupted cutting than CBN-L, which shows consistent decrease of tool life with increasing f requency of interruption. It is suggested that the higher hardness and frac ture toughness of CBN-H result in greater resistance to mechanical wear tha t becomes more dominant in interrupted cutting. However, the metallic binde r in CBN-H has high affinity with workpiece materials and, therefore, resul ts in rapid thermally activated wear at high cutting speeds. (C) 1999 Publi shed by Elsevier Science S.A. All rights reserved.