A fully-coupled FEM-based 2D metallo-thermo-mechanical model of laser-assisted machining of Ti-6Al-4V - a focus on residual stresses

Abstract

The complex interaction between the laser beam, the workpiece, and the cutting tool during laser-assisted machining (LAM) can result in considerable thermal gradients, variational strains and microstructural phase transformations, ultimately leading to residual stresses. This study presents a finite element-based model for the LAM of Ti-6Al-4V alloy, integrating the material’s metallurgical transformations and thermo-mechanical behaviour to predict residual stresses. The thermal, mechanical, and metallurgical aspects of the LAM process are fully-coupled in the model, accurately capturing chip formation and serration, while also accommodating strains induced by metallurgical transformations. Implemented within the finite element software, ABAQUS, the model’s predictions for surface residual stresses align closely (¿90%) with experimental data from literature. Notably, the model elucidates the transition of surface residual stresses towards tensile nature due to laser heating in LAM. The results reveal that the metallurgical transformation exerts a more pronounced influence at lower cutting speeds. Moreover, surface residual stresses tend towards tensile nature with increased laser power but shift towards compressive nature with higher laser-tool gap, cutting speed, and feed. Depth-wise residual stress distributions underscore the significant impact of laser power, speed, and feed compared to laser-tool gap. The proposed model can be used to optimise the LAM process and improve the quality and reliability of the finished products.