Numerical Simulation Of Single Track Formation And Defects Analysis In Selective Laser Melting

Selective Laser Melting(SLM),as one of additive manufacturing technologies,has been developed and applied widely in aerospace,biomedical and other fields in recent years because it can form complex metal parts with high precision.However,it has become more difficult for SLM to form accurately due to the less understanding of the defect formation mechanism.Numerical simulation,which is direct,effective and low-priced,has gradually become a valid method for selective laser melting research gradually.In this paper,after constructing the models of multi-physics and 316 L stainless powder bed,the single-track forming process was simulated by "3D Flow" software,the process parameters were selected to gain high quality single track in the simulation and the actual forming was done to certify them.Furthermore,some defects appeared in this project were analyzed,and the suggestions have been proposed to improve them.The main works and conclusions are as follows:1.After the physical phenomenon of the single-track forming process being analyzed,a multi-physics model of heat transfer and driving force of the molten pool was built,and a 316L-stainless-powder bed model was constructed.2.Taking laser power and scanning speed as the research emphasis,the change regulation of the temperature and size of the molten pool has been simulated.With the laser power increasing,the temperature of the molten pool rises and its size increases.With the laser scanning speed increasing,the temperature of the molten pool drops,and its size reduces.3.Taking the shape of the melt channel,the field of temperature and the size of the molten pool as the research objects,the single-track forming has been simulated.And the result is that when the spot size was set as 30 μm and the powder particle size in the range of 10 to 60 μm,laser power P = 250 W and scanning speed v = 1.0 m/s,the process parameters are the best.After the actual single-track forming experiments being performed with different laser power and scanning speed,the accuracy of the simulation model and process selection were verified.4.Balling defect phenomenon is caused by the substrate which is not melted,it has nothing to do with the arrangement of the powder particles.This phenomenon will disappears when the laser heat input is increased appropriately.5.The distortion phenomenon of single-track is caused by disturbing the flow direction of the melt pool,which is on account of the large size powder particles at the edge of the melt channel.This phenomenon will be improved when the laser heat input is increased and the powder particle size is reduced appropriately.6.The spatter defect phenomenon is caused by the molten pool liquid surface disturbed under the recoil pressure of evaporation and molten metal liquid thrown out of the molten pool due to the laser heat input is being set too high.It has nothing to do with the arrangement and the size of the powder particles.This phenomenon will be improved when the laser heat input is reduced appropriately.The research work has practical significance for suppling a method to reduce the defects of single track forming and improve the forming accuracy of metal parts in SLM technology.