TRIBOLOGICAL ASPECTS OF HARD TURNING WITH CERAMIC TOOLS

Process parameters in hard turning are completely different from those in conventional turning. The tribological effects which occur in fini shing hardened steels, using coolants and in dry cutting, were compare d by means of turning tests with ceramic tools. Tool wear, surface int egrity and chip formation, as influenced by different coolants in hard turning, are described. Cooling effect reduces the thermal load of th e cutting edge, and thus increases tool life as compared to dry cuttin g. In addition, surface roughness of the workpiece can be improved eit her by chemical interaction between workpiece surface and extreme-pres sure additives of the coolant or by pure mineral oil application. On t he 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.