A thermal model for hard precision turning

This work presents a developed thermal model of hard precision turning, in which the depth of the cut is made to be considerably smaller than the tool nose radius for final finishing. The required input data for this model was extracted from a previously published mechanistic model of precision turning. This mechanistic model is based on Merchant’s analysis of 3D cutting, which was modified to adopt the precision turning operation. Calculations were obtained of the shear plane temperature rise at the primary deformation zone and the temperature rise of the chip due to the work done in overcoming friction at the secondary deformation zone (frictional temperature rise). The thermophysical properties of the workpiece and cutting tool materials as well as their variation under different shear plane and frictional temperatures were considered. After performing the required calibrations, the cutting temperatures were measured with the tool-workpiece thermocouple technique during machining of hardened HSS and D2 tool steel by PCBN and mixed alumina ceramic tools. The occurrence of secondary hardening during HSS machining was found to be dependent on the thermal conductivity of the tool material. The estimated cutting temperatures were found to be reasonably close to the measured ones.