Material behaviour in metal cutting: strains, strain rates and temperatures in chip formation

A major problem in finding the flow stress in metal cutting is the intense circumstances under which deformation takes place in the chip root. Large deformations are imposed on the workpiece material at high speed in a very small area. This results in mechanical material behaviour far removed from that encountered in conventional material tests. Therefore, to determine the flow stress in cutting it is necessary to determine the conditions under which the material is being deformed. This paper describes how the strains, strain rates and temperatures have been determined in orthogonal cutting tests of steel AISI 1045 and aluminium AA 6082-T6. It appears that in the region where the chip is separated from the workpiece (i.e. the primary shear zone) the workpiece material is sheared considerably to equivalent strains in the order of 1–2. Also, the strain rate in the primary shear zone is found to be very large: in the order of 2.0×104 s−1. To find the temperatures in metal cutting an IR camera is used. It appears that the feed rate and cutting speed hardly influence the shear plane temperature. The measured shear plane temperature is approximately 290 °C in the case of the steel and approximately 190 °C in the case of the aluminium alloy.