Modeling periodic adiabatic shear band evolution during high speed machining Ti-6Al-4V alloy

Cutting experiments were performed on Ti-6Al-4V alloy over a wide range of cutting speeds. The transition of chip morphology from continuous to serrated is observed with increasing the cutting speeds, which is found to be ascribed to a periodic shear band formation that caused by thermo-plastic instability occurred within the primary shear zone (PSZ). Further microscopic observations reveal that the spacing of these periodic shear bands, i.e., the segment spacing, is significantly related to the evolution degree of shear band which increases with increasing the cutting speed. Since the segment spacing is the most important parameter to characterize the chip serration, to predict the segment spacing is fundamentally useful for the understating of serrated chip formation mechanism. However, the complicated conditions of high speed machining (HSM) give rise to greater difficulties for the prediction of segment spacing, and there is still no theoretical prediction has yet considered the effect of shear band evolution. In this work, by analyzing the plastic deformation within the PSZ, and taking into account the evolution of shear band as well as the material convection caused by chip flow, a new theoretical model is developed to predict the segment spacing, in which the momentum diffusion due to unloading within the shear band had been considered. The predictions of this model were compared with the experimental and simulated results, which clearly reveal that the proposed model can satisfactorily capture the process of chip segmentation over a wide range of cutting speeds.