On the instability of chip flow in high-speed machining

High cutting speed usually gives rise to a breakdown of steady chip flow and results in a serrated flow pattern, which is one of the most fundamental and challenging problems in metal cutting. Here, we systematically analysed the experimental results of high-speed cutting on various typical metallic materials over wide ranges of cutting speeds. With considering the coupling effects of inertial, tool-chip compression and material convection, the critical condition for the onset of serrated chip flow is determined based on a stability analysis of the deformation inside primary shear zone. It is found that the emergence of the serrated chip flow is dominated by a dimensionless number which characterized the competition among the effects of inertia, thermal softening, strain hardening, elastic unloading, viscous diffusion and thermal diffusion. More interestingly, a power law between the serration frequency and the Reynolds thermal number Pe is clearly revealed.