Investigations of vibration cutting mechanisms of Ti6Al4V alloy

Abstract

This work involves systematical study of high-speed vibration cutting process of Ti6Al4V on numerical and theoretical aspects for the first time. In numerical simulations, the one-tool and double-tool cutting models are established based on the coupling Eulerian-Lagrangian (CEL) finite element (FE) method, to simulate forced vibration (FV) and self-excited vibration (SEV) cutting phenomena respectively. In theoretical analysis, linear perturbation method is used to analyze the critical condition of shear localized instability of chip material in the FV cutting process, and stability limits analysis is performed to study the tool vibration stability in the SEV cutting process, which consider coupled effects of wavy cutting thickness and periodic instability of shear bands. Different from vibration assisted machining in low-speed cutting, it is found FV with attainable frequency in industry promotes the evolution of shear bands, increase the cutting force and reduce the machined quality, whereas high-frequency FV can help improve the cutting process. On the other hand, SEV with smooth cutting thickness is found an effective strategy to weaken the evolution of shear bands and decrease cutting force in the high-speed cutting. The stability limit of SEV is related to the friction damping coefficient at the rack face, the penetration damping resistance, the ratio of the oscillation frequency of top wavy surface and the instability frequency of shear bands. These findings would help deepen the understanding towards the vibration effects in metal cutting and provide practical guidance to retrain and utilize vibration in the vibration assisted machining.