Numerical Simulation Of Internal Defect Formation Mechanism Of Inconel 718 Components Manufactured By Selective Laser Melting

In recent years,with the rapid development of additive manufacturing technology,selective laser melting(SLM)has been widely used in medical equipment,aerospace,power equipment,production and construction.The existence of internal defects in SLM forming parts affects the performance of forming parts and restricts the further application of this technology.Therefore,it is of great significance to study the formation mechanism of internal defects.Because the SLM forming process involves multi-physical field,multi-scale coupling and other transient processes,it is very difficult to study the formation mechanism of internal defects in SLM forming parts by experimental means.In this paper,the forming process of SLM has been simulated by numerical simulation method,the micro evolution process of molten pool in the single channel and double channel forming process of Inconel 718 alloy is studied,and the causes of defects in the selective laser melt ing process were analyzed,which provides support for the shape control strategy of SLM.The main work of this paper is as fo llows:1.The discrete powder layers with different filling densities were established by EDEM simulation software to deeply understand the movement,heat transfer and molten pool change of particles in SLM process,so that the model is close to the actual situation and the accuracy of numerical simulation is improved.2.The three-dimensional dynamic single-channel model of selective laser melting forming was established by discrete element method.The single-channel forming process of Inconel 718 SLM was simulated by FLOW-3D software,and the effects of different scanning speeds,laser power and filling density on the molten pool temperature,fluid flow rate and channel morphology were analyzed.It is found that with the increase of filling density,the heat transfer and flow stability in the molten pool are enhanced,which is conducive to the formation of good metallurgical effect.The optimal process parameters were determined as follows:laser power P=180W,scanning speed V=1000mm/s.3.The formula of linear energy density(L = P/V)is introduced to analyze the causes of spheroidization,porosity,unevenness of melting channel and edge erosion defects in SLM forming process,and the preventive measures and suggestions are given.It is found that the linear energy density affects the maximum temperature and fluid flow rate in the molten pool,thereby affecting the morphology of the molten channel and finally affecting the forming quality.4.A numerical model of two-channel molten pool flow was established to simulate the forming process of Inconel 718 SLM.The effects of different scanning methods and scanning spacing on the temperature of molten pool,fluid flow rate and morphology of molten channel were discussed.The defects of SLM two-channel forming were analyzed,and the preventive measures and suggestions were given.It is found that the unidirectional scanning mode or the decrease of scanning spacing will reduce the formation of SLM forming defects,thereby increasing the density and surface quality of the formed parts.