A study on transient molten pool dynamics in laser polishing of Ti6Al4V using numerical simulation

Laser polishing is a novel surface restructuring technique aimed at diminish the surface roughness. Nevertheless, the lack of research on laser polishing mechanisms limits its industrial application. In this paper, a two-dimensional axisymmetric model was developed which describes the evolution of polished surface morphology and transient molten pool dynamics in surface over-melt mechanism of laser polishing. The results illustrated that the melt flows are dominated by thermocapillary and capillary forces while the surface temperature is lower than the evaporating ones. On the other hand, the local evaporated material generated a recoil pressure that dominated the molten material is extruded to the periphery, resulting in surface morphology significant asperities. Additionally, a model based on moving heat source was performed so as to bring the simulation results closer to the experimental ones. The results demonstrated that obvious bulge and depression are formed at the initial and final positions of the polished surface respectively. Simultaneously, comparing the simulated remelting depth with the those obtained from the optical images of the continuous wave laser polished surface sample cross-sections, it was found that the errors are respectively controlled within 7.2 % and 19.6 %, which corresponded to the laser radiation duration of 1 ms and 5.6 ms. The aforementioned results indicated that the prediction of the numerical model agree reasonably well with the experimental data and micrographs.