Tribological aspects of hard turning with ceramic tools

Abstract

Process parameters in hard turning are completely different from those in conventional turning. The tribological effects which occur in finishing hardened steels, using coolants and in dry cutting, were compared by means of turning tests with ceramic tools. Tool wear, surface integrity and chip formation, as influenced by different coolants in hard turning, are described. Cooling effect reduces the thermal load ot the cutting edge, and thus increases tool life as compared to dry cutting. In addition, surface roughness of the workpiece can be improved either by chemical interaction between workpiece surface and extreme-pressure additives of the coolant or by pure mineral oil application. On the workpiece surface, rehardened layers were found both in dry and wet cutting, a result of rapid self-cooling. However, rehardened zones at the bottom side of the chips appeared only when coolant was supplied because this operation exceeded the critical quench speed in the chip