A contribution to a qualitative understanding of thermo-mechanical effects during chip formation in hard turning

This contribution deals with thermo-mechanical effects on chip morphology. Only the case of hard turning of AISI4340 steel (47 HRC) is treated. The study proves that serrated chip formation is the result of a softening phenomenon simulated by using Abaqus/Explicit software. The beginning of the saw-tooth chip initiation is due to an adiabatic shear at the tool tip with a propagation pathway towards the free surface. However, due to heat insulation accompanying a purely adiabatic calculation, it is impossible to simulate the evolution of the thermal field in the cutting tool. In order to stop heat dissipation affecting the model (to respect the adiabatic hypothesis), for the machined workpiece, a fully coupled thermal-stress analysis was adopted with a zero conductivity value of the machined material. Therefore, heat in the workpiece is generated only by material strain and friction. Moreover, a parametric study is proposed of thermal properties such as variations of contact conductance and the fraction of frictional work converted to heat at the tool/workpiece interface.