Machining simulation of Ti6Al4V using coupled Eulerian-Lagrangian approach and a constitutive model considering the state of stress

Abstract

The accuracy of a machining model depends on the capability of this model to describe the physical phenomena associated to the real machining system. This includes the material constitutive model and the approach used to describe the field flow of the material in cutting. In this paper, a model of high speed machining (HSM) of Ti6Al4V titanium alloy is developed. This cutting model includes the proposed constitutive model considering the influence of strain hardening, strain-rate, temperature, and state of stress (e.g., stress triaxiality and Lode parameter) in the material plasticity and damage. Finite Element Method (FEM) using Coupled Eulerian-Lagrangian (CEL) approach is used to simulate the cutting model. A sensitivity analysis of the influence of the mesh topography on the chip geometry and cutting force is performed resulting in the determination of the optimal element size and element orientation. Simulation results obtained using the CEL approach are compared with those obtained using the Lagrangian one. Moreover, simulated cutting force and chip geometry obtained using the proposed constitutive model are compared with those obtained using the Johnson-Cook (J-C) model, and experimental data. Both chip geometry and cutting force predicted by the proposed constitutive model is closer to the experimental one than the J-C constitutive model. The CEL approach combined with the proposed constitutive model can simulate material side flow, which results in a larger width of chip compared to the width of cut, and in the formation of lateral burr on the workpiece. It also permits simulating the cyclic variation of the plastic strain and topography of the machined surface along the cutting direction, observed experimentally.