Laser processing of material surface is a rapid and non-equilibrium process. Under the action of laser beam, the material surface melts and solidifies very quickly, and there exists very high thermal gradient. Accordingly, the topography, microstructure and performance of material surface will all change. To analyze these phenomena, the heat transfer and the fluid flow issues during laser surface processing need to be studied in-depth. In this paper, a hybrid analytical-numerical solution model is developed for the heat transfer and fluid flow during laser surface processing. Taking the laser texturing of GCr15 roll surface as example, the model is solved through the surface tension model developed for the melt formed in laser texturing and the numerical results from finite element analysis on the temperature field during laser texturing of roll surface. The laser textured roll surface roughness profile is then theoretically predicted using the solution to the hybrid model. The roll surface topography obtained experimentally agrees very well with the theoretical prediction, which proves the validity of the analytical-numerical solution model.
The morphologies of roll surfaces are modified with pulsed Nd:YAG laser and characterized by topography measuring instrument (WYKO-16 DRT2TC). Sombrero shaped bumps with diameters of 230-250 μm and heights of 2-4 μm are produced by out-of-focus laser beam. In laser surface heating, the cooling rate is high enough for all the material that undergoes austenitic transformation to be transformed into martensite. To explain the mechanism leading to the surface topography resulting from the Nd:YAG laser texturing of roll surface. A quantitative model is proposed to predict the bump formation during martensitic transformation. The results show: the bump height caused by martensitic transformation is very small. The key factor of macroscopic bump formation on roll surface during laser texturing is surface tension of molten metal.