Numerical simulation of surface structures in single and multi-track laser polishing of NiP alloy

Laser polishing represents an advanced surface treatment method that decreases surface roughness by utilizing the interaction between the laser beam and the material. Nevertheless, the laser polishing process often introduces new surface structures with certain fluctuations, which affect the final polishing outcome. In this paper, a two-dimensional cross-sectional numerical model integrating fluid flow, heat transfer, and material vaporization was developed to simulate the temperature field, momentum and surface morphologies of the polished sample. This model was used to investigate the generation mechanism of “M”-shaped surface structures induced by Gaussian continuous-wave (CW) laser scanning on NiP alloy. The surface structure was significantly influenced by the combined effects of material properties, laser energy distribution, and various surface forces. Comparison between simulated and experimental surface structures showed a deviation of 2.81 % in the distance between two bulges of the “M”-shaped surface structure ($d$) and a deviation of 6.24 % in the bulge height ($h$). The model was further employed to simulate the profiles of laser multi-track polishing at different track offsets. The research indicated that the optimal polishing occurs when the laser scanning track offset ($∆d$) equals $d/2$. Multi-track laser experiments confirmed the simulation predictions and revealed the potential of CW laser in surface configuration. This study successfully advances theoretical research on laser polishing and enhances the efficiency of selecting laser polishing process parameters.