Research on the formation mechanism of the surface structure in transition regime of laser polishing 304 stainless steel

Abstract

Laser polishing is an innovative surface finishing technology to reduce surface roughness through the interaction of laser and material. However, some new surface structures will be introduced into the polished surface, reducing the surface quality of the polished workpiece. This paper investigated the formation mechanism of a new type of surface structure that has not been studied before. The laser polishing experiments presented the complete evolution of the surface profile and size parameters of the surface structure with the laser power, and the reason for the formation of the surface structure was preliminary analyzed. Furthermore, a two-dimensional numerical model coupled with heat transfer, fluid flow, material vaporization, and volume expansion was established to further explore the formation mechanism of this type of surface structure. With the help of the established numerical model, the temperature field, flow field, material vaporization, and volume expansion were analyzed during the formation process of surface structure. The contribution of five factors (capillary force, thermocapillary force affected by surface-active elements, recoil pressure, material removal, and volume expansion) to the formation of the surface structure was investigated, illustrating that this type of surface structure is the result of the combined effects of these factors. In addition, the surface profile and size parameters of the surface structure were simulated, which were in good agreement with the experimental results. This work further improves the theory of laser polishing, which is of great significance to promote the application of laser polishing. Importantly, this paper demonstrates the potential of laser surface structuring under the combined action of the surface tension, recoil pressure, material removal, and volume expansion of the molten pool in laser processing.