Surface Morphology Control And Multi-field Coupling Simulation Of Stainless Steel Metal Powder SLM Forming Process

Selective laser melting(SLM),as the most promising technology in laser powder additive manufacturing,has been widely used in medical,aviation,aerospace and other fields.Despite progress in mechanical performance,the surface roughness of the formed test piece is still very large.Nowadays,post-treatment methods such as sand blasting are often used to reduce the roughness of the surface of the test piece,but it is very difficult to deliver the part with a complicated or micro-structured part.In order to make the SLM forming test piece reach the finishing level,reduce the forming period of the test piece,it is necessary to reduce the surface roughness of the test piece through parameter control.This article mainly used 316 L stainless steel metal powder to form a hexahedral specimen with an inclination angle of 60° through the SLM experiment to study the cause of the roughness of each surface.Used laser remelting technology to reduce the surface roughness of the specimen and observed the improvement effect.Used the numerical simulation of the formation process of the sub-melt channel and the forming rule of the sub-melt channel,the method of reducing the roughness by optimizing the parameters was explored.The research work in this article includes:(1)Used the SLM experiment to form specimens under different laser energy densities,and analyzed the effect of different energy densities on the micro-topography of the upper surface.(2)Laser remelting the top surface through three different filling patterns of grating type,stripe type and checkerboard type.By observing the surface morphology after surface remelting,the effect of remelting and the roughness after remelting are analyzed.Cause and establish a simplified model of the surface roughness.(3)By observing the micro-morphology of the vertical side,a simplified model of the vertical side roughness was established.And a plan to reduce the vertical side roughness was proposed.Observed the micro-morphology of the vertical side,down skin and up skin after contour remelting with different contour offsets.Then analyzed the effect of contour remelting to improve the side.(4)The discrete element method was used to consider the particle diameter distribution and collision to establish a 316 L metal powder bed.The fluid dynamics was used to consider the evaporation,infiltration,recoil pressure,Marangoni shear force,thermal radiation at the free interface,thermal convection,the physical phenomena of laser reflection and refraction in the powder bed.Then established a three-dimensional mesoscopic model of laser selection melting.(5)Used fluid dynamics simulation to analyze the laws of physical phenomena such as recoil pressure and Marangoni flow in the molten pool under different laser powers and velocities.Obtained the evolution of the molten pool to the single-layer single-channel melt channel.The influence law of morphology provided a reference for further optimizing the laser parameters and reducing the surface roughness of the specimen.