Finite Element Analysis For Temperature And Stresses In The Alloy Steel Laser Melting Deposition Process

Laser additive manufacturing technology i5 an advaneed manufacturing technology that integrates digital technology,manufacturing technology,laser technology and new material technology.Compared with traditional manufacturing technologies such as cutting,casting and forging,it has the advantages of fast,high flexibility,no mold and automation,etc.It has been widely used in aerospace,medical,military and other fields.The laser melting deposition technology characterized by synchronous powder feeding is developed by the combination of rapid prototyping technology and laser cladding technology.The powders of the same kind or different kinds are melted by high-power laser,and stacked layer by layer.Although many researches have been carried out,macroscopic defects such as warpage,poor fusion and dimensional cracking are still exist in the forming process.What's more,many microscopic defects such as pores and inclusions are easily generated inside,especially for steel materials.In order to overcome the defects in the forming process,the key basic problems of non-equilibrium cyclic solid phase transition,temperature and stress evolution in the process of laser melting deposition of alloy steel were studied.Drawing on the experience of welding and metallurgy,X20Crl3 martensitic stainless steel and 316L austenitic stainless steel are selected as the representative alloy steels which are commonly used for laser melting deposition.Based on numerical heat transfer,thermodynamics,elastoplastic mechanics and continuous cooling phase change kinetics and other related theories,using SYS WELD finite element software to numerically analyze the temperature field and stress field of single-pass,track-by-track and layer-by-layer processes during laser melting deposition.The main tasks completed are as follows:Firstly,based on the three-dimensional transient Fourier law and laser melting mechanism,establish a laser heat source model;use variable density partitioning technology to construct the finite element mesh of the substrate and the melt track;use the live and death unit method to activate the unit layer by layer to simulate the temperature evolution of X20Crl3 and 316L alloy steel during laser melting deposition.The results show that:(1)under the same process parameters,the temperature evolution of the two alloy steels in the single-pass laser melting deposition process is basically the same;(2)revealing the influential mechanism of temperature distribution of X20Crl3 on different laser power,scanning speed,scanning mode,and lap ratio;(3)the temperature field distribution of X20Crl3 multi-layer laser melting process has a"three-dimensional effect".Secondly,based on the continuous cooling martensitic transformation K-M formula,establish a phase transformation model;considering the phase change volume effect and phase change plastic effect,based on the Mises yield criterion,the normal flow criterion and the isotropic strengthening model,the heat-phasee-stress coupling numerical simulation method is used to solve the stress field of laser melting deposition of X20Crl3 and 316L alloy steel.The results show that:(1)under the sane process parameters,the stress evolution of the two alloy steels in the single-pass and single-layer process is completely different,and the martensitic transformation has an important influence on the stress evolution of X20Crl3,and the influence of phase transformation stress is opposite to thermal stress;(2)revealing the stress revolution law of X20Crl3 on the variations of laser power,scanning speed,scanning path,lap ratio and preheating,then obtaining the best combination to get lowest residual stress;3)The residual stress distribution characteristics of X20Crl3 multi-layer melt deposition were found.The temperature field of X20Crl3 during the melting deposition process was numerically simulated.The morphology of the molten pool was obtained according to the melting point of the material.The displacement field was further analyzed and compared with the experiment.The rationality of the process simulation was verified qualitatively.