Research On Laser Polishing Mechanism And Process Of SLM Additive Manufacturing Surface

With the rapid development of laser additive manufacturing technology,especially the spread and application of selective laser melting(SLM)technology,higher demands are placed on the surface quality of additive manufacturing parts.At present,SLM forming parts mainly rely on manual grinding,sandblasting,electrolytic polishing and other methods to improve the surface quality.However,there are disadvantages such as low efficiency,difficult processing of complex inner surfaces,and environmental pollution.Laser polishing technology has become an effective method to improve the surface quality of additive manufacturing due to its many advantages such as non-contact,high efficiency and non-pollution.In order to make full use of this technology,it is necessary to scientifically characterize the surface morphology of SLM forming parts and research laser polishing process to establish the relationship between the forming surface and the polishing process.Further study of surface quality requires scientific characterization and description.The SLM forming part surface under different forming angles is observed and measured by laser scanning microscope.The surface characterization system for SLM forming surface that includes surface features,line features and point features was established.The influence of forming angle on the surface morphology of SLM forming parts was revealed,and the relationship between forming angle and performance was investigated.The results show that the side surface roughness decreases and then increases as the forming angle increases,while the horizontal surface roughness remains the same and the microhardness increases slightly and then remains the same.In order to meet the high-quality demand for SLM additive manufacturing surface in actual production,laser polishing technology is used to polish the SLM additive manufacturing surface.A single-factor experiment was designed to obtain the influence of laser polishing process parameters on polished surface morphology combined with the analysis of polished surface morphology characteristics,and the mapping relationship model between laser power,scanning speed,initial surface morphology and polished surface roughness was established.By studying the influence of laser polishing process strategy on the polished surface topography,it was found that multi-pass polishing strategies with appropriate process parameters could significantly reduce the surface roughness.During the laser polishing process,the material surface is re-melted and solidified,resulting in the revolution of the material organization.In order to study the influence of this process on the physical and mechanical properties of the polished surface,the microstructure of the polished surface was observed using optical microscope and Scanning Electron Microscope(SEM),and the evolution of the crystal structure of the polished surface was analyzed using Electron Backscattered Diffraction(EBSD).The results show that laser polishing can play a role in grain refinement,and the lower the laser power or the faster the scanning speed,the smaller the grain size of the polished layer.The effect of laser polishing on the surface microhardness was obtained.The surface microhardness of the polished layer increased due to grain refinement,and the lower the laser power or the faster the scanning speed,the higher the microhardness value.