Study On The Laser-Selective Melting Printing Quality Of Overhanging Structures And Their Cutting Properties

Selective Laser Melting(SLM)is a promising additive manufacturing technology that can form arbitrarily shaped parts based on 3D However,when forming complex parts,overhanging structures will inevitably appear,because the unique structural characteristics of overhanging structures lead to poor heat dissipation conditions and melt pool stability at the location of the overhanging surface,often warping and deformation,hanging slag and other defects,seriously affecting the overall forming quality of the part.Therefore,based on the SLM point-line-surface-body progressive accumulation forming principle,this paper investigates the influence of the tilt angle,forming height,forming plane size and other characteristics of the overhanging structure on the forming quality,and establishes an empirical model for predicting the deformation of the overhanging structure.Considering that the poor quality of the overhanging surface needs subsequent treatment,the influence of cutting processing on the forming quality of the overhanging structure is analyzed.The specific research contents and results are as follows.(1)The SLM forming process simulation model of the overhang structure was established,and the thermal-force indirect coupling numerical simulation of the SLM multi-layer multi-pass forming process of 316 L stainless steel was carried out using the thermoelastic-plastic finite element method,and the average strain value of the forming process was calculated and obtained after analyzing the simulation results of the temperature field and stress field,which was used as input to realize the simulation of the forming process of the overhang structure parts using the intrinsic strain method.(2)The influence of the tilt angle,forming height,forming surface length and width of the overhang structure on the deformation was analyzed.It was found that the deformation decreased with the increase of tilt angle,increased with the increase of forming surface length and width,and the effect of forming height on deformation was not significant.On this basis,Box-Behnken experiment was designed and regression fitted to establish an empirical model for predicting the deformation of the overhanging structure.(3)Based on the numerical simulation results,SLM forming experiments of the overhang structure were conducted to analyze the effects of the tilt angle and forming dimensions on the deformation and surface morphology of the overhang structure.It is found that the experimental measured deformation is basically consistent with the simulation results,and the maximum error is within 20%;the roughness of the overhang surface decreases with the increase of the tilt angle,and the forming size basically does not affect the roughness of the overhang surface.The deformation of the overhanging structure was corrected by the pre-compensation method,and the deformation was significantly reduced after the compensation.(4)The effect of milling on the forming quality of the overhang structure is studied,and the milling allowance of the overhang structure is determined according to the analysis and calculation,and the milling parameters of the SLM forming overhang structure are optimized with the target of the roughness of the overhang surface.Based on this,a prediction model of the milling force of the overhang structure is established and the deformation of the overhang structure milling process is calculated by combining with the theoretical analysis,and finally the accuracy of the reserved machining allowance and milling force model is verified by the overhang structure milling experiment.