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.
In this paper, we propose laser-soldering method and use the process assisted with wire-mesh and soldering paste to weld the lateral electrode of piezoelectric ceramics transformer (PECT). The PECT were connected very well and were not affected much by heat. The process shows the good promise to the joint problems in multilayer heterogeneous lamination similarity to the PECT. Based on the above, our focus is on validating the finite element model, we build three-dimensional model of laser soldering temperature field in multilayer materials. Then, the reasonable simplification of heat source, materials parameters are put up in order to perform an efficient finite element analysis and the adaptive finite element technique is adopted. The temperature distribution characteristic in the laser soldering is acquired and verified by comparing experimental data. Although the finite element model contains numerous simplifications, the differences between experimental data and computed results are within 5%. The study shows that the adaptive finite element schemes give good agreement with the experimental data, which provides the theory reference for formulating correct process and optimizing joint properties. In addition, more exact material properties would improve the solution accuracy.
This paper presents a method of laser texturing, and a new type of regular surface roughness profile has been produced on the roll surface. A series of experiments have been developed to produce regular surface roughness profiles using a Nd:YAG laser. According to the analysis of the principle of laser texturing, the laser parameters are primely selected and matched. Consequently, the predesigned surface roughness profile and size have been successfully obtained. Furthermore, The measurement and analysis on the surface roughness hardness and abrasion resistance are carried on. The results show: the surface roughness has higher hardness rather than matrix, which adapted to the requirements of laser texturing. The surface roughness also has good abrasion resistance. In addition, the influence regulations between pulsed laser parameters and main profile parameters of roll surface have been investigated.
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