Numerical Simulation Study Of Forming Mechanism Of Selective Laser Melting TiC Ceramic

Selective laser melting(SLM),as a typical ceramic additive manufacturing technology,has the advantages of high forming efficiency,high precision,and freedom from mold limitations.However,SLM is a complex non-equilibrium thermophysical process,and it is difficult to visually characterize the microscopic phenomena involved by existing experimental means.Numerical simulation techniques can effectively reveal the forming mechanism of SLM and provide a basis for the efficient preparation of high-precision complex-shaped ceramic parts.In this paper,the SLM forming mechanism of TiC ceramics was investigated on a microscopic scale by establishing a microscopic dynamic threedimensional model of SLM and obtaining the preferred range of process parameters.The main research work and innovation points are as follows:(1)The SLM microdynamic simulation model of TiC ceramics was established to realize the simulation of the rapid melting and solidification process of ceramics under non-equilibrium thermophysical conditions.Based on the discrete unit method,a model of TiC ceramic powder bed with random filling of different thicknesses was established using EDEM software.Based on the finite volume method and the powder bed model,a3 D simulation model of the selective laser melting ceramic powder forming process was established using Flow 3D software,and the laser Gaussian heat source and thermal boundary conditions were loaded by writing the Flow 3D secondary development interface program.For the characteristics of SLM fast melting and fast solidification,the volume of fluid method was used to realize the dynamic tracking of the free liquid surface of the molten pool.The proposed model can effectively simulate the whole process of TiC ceramic materials forming by selective laser melting.(2)The evolution mechanism and solidification characteristics of the molten pool during selective laser melting of TiC ceramics were investigated,and the mechanism of melt track morphology and microstructure forming was identified.The evolution of the molten pool was mainly influenced by the surface tension and the sudden change of ceramic melt properties during SLM,and finally solidified into a concave geometry under the Marangoni effect.During the solidification process,the molten pool temperature gradient and cooling rate decreased with increasing laser power,and higher dense microstructure can be obtained at lower power.Controlled by the shape control factor G/R,the ceramic grains evolve from cytosolic crystals at the bottom to dendrites in the middle and to a mixture of granular and dendritic crystals at the top.The experimental results verified the correctness of the simulation model.(3)The influence of process parameters on the surface morphology of TiC ceramic melt track was studied,and the preferred process parameter intervals for selective laser melting of TiC ceramics were obtained.There is a corresponding relationship between the laser spot size and the powder coating thickness.When the spot radius is greater than the powder bed thickness,better forming quality and optimal process range can be obtained.The line energy density(LED)was introduced to investigate the combined effect of laser power and scanning speed on the forming morphology.In the preferred LED range,even if the same LED was applied,there was still a difference in the forming morphology obtained by different combinations of laser power and scanning speed.