On repeated adiabatic shear band formation during high-speed machining

We compare the repeated adiabatic shear band formation that takes place at sufficiently large cutting speeds in a number of materials during high-speed machining operations with the more well-known formation of a single shear band that often takes place at sufficiently large strain rates in dynamic torsion tests on these materials. We show that there are several major differences in the physics of the two deformation processes. In particular, the shear stress in machining over the tool-material contact length is not even approximately homogeneous. Additionally, in high-speed machining, the material flow can become convection-dominated, so that the tool can “outrun” the thermal front generated in the workpiece material by the high-strain-rate cutting process. We demonstrate by means of a one-dimensional continuum model that these differences can lead to repeated oscillations in the plastic flow of the workpiece material during high-speed machining, leading to the repeated formation of adiabatic shear bands.