Numerical Simulation And Defect Mechanism Analysis Of Die Steel Laser Polishing Process

Laser polishing is a new type of polishing technology,with high efficiency,non-contact,automatic processing and other advantages,has been widely used in a variety of materials.At present,the research of laser polishing mainly focuses on the polishing process,but the mechanism of laser polishing has not been thoroughly studied.In this paper,a numerical model of laser polishing for die steel is established by combining numerical simulation with experiment.The surface flow process during laser polishing is simulated,and the influence of various parameters on polishing effect is obtained,which provides guidance for the selection of laser polishing parameters.(1)A two-dimensional transient model of laser polishing surface evolution was established.Based on the spectrum analysis of the die steel surface before polishing,the main frequency composite contour curve was used to construct the model surface.The model coupled the heat transfer field and the flow field,and used a moving laser source to simulate the temperature distribution and flow process of laser polishing by comprehensively considering the effects of capillary force and thermocapillary force in the molten pool.The simulation results show that during laser polishing,the rough surface flows under the action of capillary force and thermocapillary force,and the molten material at a high place flows to a lower position,which reduces the difference of surface height and obtains a smooth surface.(2)The influence of laser power and scanning speed on laser polishing process was simulated and analyzed.The depth of molten pool has a positive linear relation with laser power and a negative linear relation with scanning speed.The surface roughness after polishing and the laser power and scanning speed are U-shaped.(3)By comparing the experimental results of laser polishing with the simulation results,the error of the depth of molten pool is 7.5%,and the error of surface roughness is 7.0%.The solidification structure of the molten pool predicted by the model is in good agreement with the experimental observation,indicating that the model has high accuracy.(4)For the crater defects found during the laser polishing experiment,the crater was composed of aluminum and its oxides,and a formation mechanism of the crater was proposed.Under the action of buoyancy and thermocapillary forces,aluminum droplets in the molten pool float up,and break through the surface to form a crater after oxidative solidification.