Multi-Scale Simulation And Process Optimization Of Selective Laser Melting Of Thin-Walled Parts

Thin-walled parts have the advantages of compact structure,light weight and strong functionality,and are usually used in the fields of machinery manufacturing,aerospace and system heat dissipation.When using traditional cutting,casting or welding processes to form complex thin-walled structures,there are problems such as difficulty,easy deformation and low precision.Selective Laser Melting(SLM)can theoretically realize direct and rapid prototyping of any complex three-dimensional model,and is a new method for thin-walled parts forming.However,the complex physical changes in the SLM molding process are prone to problems such as spheroidization,poor metallurgical bonding,and large residual stress and deformation,resulting in defects such as pores and cracks.Since it is difficult to capture its transient changes in experiments,it is necessary to use numerical simulation to study the defect formation mechanism and suppression methods of SLM forming of thin-walled parts.However,SLM numerical simulation generally only studies the physical changes at a single scale,and the models are independent of each other and lack consistency.The numerical simulation at multiple scales still needs further research.The main research contents are as follows:First,a multi-scale simulation framework including temperature field model,mesoscopic melt pool dynamics model and macroscopic thermomechanical coupling model is established.The model is preliminarily verified by the simulation results of single-track scanning,and the size error of single-track molten pool obtained is less than5%.Secondly,the change rule of the molten pool during single-pass forming and double-pass lapping of SLM was studied by mesoscopic scale simulation,aiming at improving the stability of single-pass molten pool and the effect of molten pool lap jointing,and obtained the optimal combination of process parameters.Based on the combination of process parameters,a multi-layer and multi-pass forming simulation at the macro scale was carried out,and the effects of different forming scanning strategies and laser remelting processes on the residual stress and deformation of thin-walled parts were studied.According to the residual stress and deformation mechanism of thin-walled parts,the laser in-situ annealing process was redesigned to reduce the residual stress and deformation,and the effects of rescanning laser power and scanning speed on the in-situ annealing effect were studied.Finally,based on the simulation results,SLM molding experiments of thin-walled parts are carried out to verify the reliability of the model.The results of metallographic experiments show that when the laser power is 150 W,the scanning speed is 500mm/s,and the scanning distance is 0.08 mm,the lap joint effect of the molten pool is good,there are no irregular pores and pores,and the error between the size of the molten pool and the simulation results is less than 5%.The length deformation and relative deformation of thin-walled parts before and after removing the base are used to characterize the deformation and residual stress,and the experimental results are consistent with the simulation results.The laser remelting process cannot reduce the residual stress and deformation,and the laser in-situ annealing process can reduce the maximum relative deformation and deformation of thin-walled parts by more than 55%.In addition,reducing the annealing frequency to once every three layers can obtain the same annealing effect,and can also reduce the total annealing time by more than 60%.