Coupled effects of tool flank wear and shear localization on the formation of machined surface residual stress

During the machining of high-performance metal alloys, such as titanium- or nickel-based alloys, tool wear is inevitable and shear localization commonly occurs, both of which modify the thermal and mechanical loads imposed by a cutting tool and ultimately alter residual stresses on machined surfaces. Through a fully-coupled numerical modeling framework using finite element methods, we investigate formation mechanisms of residual stresses during machining of Inconel 718 with flank-worn tools when serrated chips are generated. The developed framework is also utilized to quantitatively determine variations in residual stresses on machined surfaces, caused by combined interactions between chip segmentation and tool flank wear. The obtained results suggest that introduction of tool flank wear has a negligible effect on serrated chip morphologies. However, both cutting forces and surface residual stress periodically vary for all flank wear lengths. Meanwhile, due to more uniform thermal-mechanical loading associated with the expanded tool-workpiece contact area, the amplitude of machined surface residual stress variation is reduced by 82.7% as flank wear lengths increase from 0 mm to 0.30 mm. Besides, compared with fresh inserts, flank-worn tools generate more tensile residual stresses on machined surfaces. As the increase in flank wear lengths, machined surfaces present reduced tensile residual stress. Conversely, both the maximum depth of compressive residual stresses and penetration depth of residual stresses increase. Those findings provide guidance for customizing tool geometries to engineer residual stress distributions on machined surfaces.