Numerical Simulation And Experimental Research On Stress Field Of 316L Stainless Steel In Selective Laser Melting

Selective laser melting(SLM)is a kind of additive manufacturing(AM)characterized by laying powder on the substrate.This emerging rapid prototyping technology is now widely used in aerospace,automobile manufacturing,biomedical and other fields.However,in the SLM forming process,the metal powder can only be partially melted by the laser beam and gradually formed the part.The violent reaction process is accompanied with a wide range of temperature fluctuations,which tends to produce a large temperature gradient in the part.And the thermal stress caused by the temperature gradient may cause defects such as deformation,warping and even cracks in the parts,which will seriously affect the forming quality and dimensional accuracy of the parts.In order to predict and reduce the residual stress of SLM parts,the temperature field and stress field in SLM forming process are simulated and analyzed by ANSYS finite element simulation software.At the same time,the variation rules of temperature field and stress field of SLM parts under different process parameters are also studied.The main contents of this paper are shown as follows:(1)Finite element model establishment,calibration and temperature field simulation.According to the actual working conditions of SLM forming,the corresponding simulation model is established,and the single melting point,single track and multi-layer block simulation and forming experiments are carried out.By comparing the temperature field and the experimental geometric characteristic parameters of the molten pool,the error of the adjusted simulation model can be controlled at about 5%.At the same time,a rapid optimization model of process parameters based on the geometry of the molten pool section is established.Then,the simulation of temperature field explored the maximum temperature of the molten pool and the geometry size of the molten pool under different process parameters,and then analyzed the variation of temperature field with time and path.(2)Stress field simulation and analysis.The formation of stress is mainly due to the fact that in the process of powder melting,the molten pool is subjected to compressive stress due to the thermal expansion,and tensile stress due to the cooling of the molten pool.The stress value increases with the increase of laser power and scanning speed,and the influence of laser power on the residual stress is larger than that of scanning speed.The residual stress after cooling of the molten pool is mainly tensile stress,which shows that the stress in the part is smaller at the edge and larger at the center.(3)SLM forming experiment and residual stress detection.In order to ensure the forming quality of the parts,the multi-layer block forming experiments with power of 100W-400 W and scanning speed of 0.2m/s-1m/s were carried out,and the density,microstructure,typical defects,tensile mechanical properties and tensile fracture were tested and analyzed.By comparing the experiment and simulation results of the residual stress,it is found that the simulation results show the same trend with the residual stress which measured by experiment,and the error value can be controlled at about 10%.