Study on the mechanism of surface topography evolution in melting and transition regimes of laser polishing.

• Simulation and modeling on laser polishing in melting and transition regimes. • Mechanism of surface topography evolution in laser polishing is revealed. • Contributions of surface forces and material removal in laser polishing are analyzed. • Thermocapillary force affected by surface-active component results in a bulge structure on the polished surface. • Surface roughness prediction is tried through the established model with a maximum error of 14.9%. Previous studies on the mechanism of laser polishing were limited to the melting regime, this paper proposed a numerical model for the melting and transition regimes of laser polishing, which coupled heat transfer, fluid flow, and material vaporization. Based on the model, the evolution of the temperature and velocity fields of the molten pool in laser polishing was presented. And the mechanism of surface topography evolution was revealed from the perspective of surface forces (capillary force, thermocapillary force, and recoil pressure), fluid velocity, and material removal. Furthermore, the corresponding relationships between surface forces, fluid velocity, and surface topography were determined. The contributions of surface forces and vaporization front velocity in laser polishing were investigated, and the reason for the formation of the bulge structure and the influence of laser power on it were analyzed. And the velocity direction change points which have a great influence on the surface evolution were found, and the method to determine the positions of these points was proposed. Besides, the surface roughness prediction after laser polishing was tried through the numerical model, and the maximum error between the predicted results and the experimental results is 14.9%. Therefore, this model can be used to optimize process parameters. [ABSTRACT FROM AUTHOR]