Numerical Research On Heat Transfer And Flow In Laser Selective Melting Process

Selective laser melting is an important branch of additive manufacturing.In recent years,many researchers have paid attention to it and rapid development has achieved.Many physical and chemical changes occur in the process of SLM,such as the movement of the laser heat source,the melting and solidification of the powder,the flow of fluid in the molten pool,and so on.These processes together determine the the quality and fatigue life of the manufactured parts,therefore it is of great significance for the study of the melting process of SLM.Among them,the temperature and velocity field of the molten pool during the melting process of the SLM are important to the melting and solidification of the material,so it can not be ignored.Therefore,the simulation research on the physical phenomena occurring inside the molten pool is of great importance for understanding the process of SLM more deeply.The main work and conclusions of this paper are as follows:In this paper,the Fluent software is used to study the physical phenomena occurring during the SLM process.The solid-liquid phase change is the basic phenomenon that occurs during the melting process of SLM.The classical melting experiment of helium is simulated in this paper.The results obtained are in good agreement with the experimental results,proving that the solidification and melting model used in this paper is correct and effective.The input of laser energy changes with time.Based on the solidification and melting model,the fixed and moving laser heat sources are added.The physical phenomena occurring in the process are studied and analyzed in detail,and the sign of the temperature gradient surface tension coefficients has an important influence on the velocity field and the shape of the molten pool.The molten pool is no longer symmetrical and the heat affected zone will change accordingly due to the movement of the laser heat source.It helps to understand the physical phenomena in the molten pool during the SLM process more deeply.Based on the study of moving heat source,the previous methods used in simulation to calculate the powder melting and collapse process were summarized and a modified VOF method for calculating the collapse process of powder after melting was proposed.A Gaussian distributed body heat source model was used to simulate the SLM process with the titanium alloy.The calculation results show that the change of the volume of the powder layer will affect the temperature and velocity field of the molten pool and its surrounding and the final shape of the workpiece.The calculated results are in good agreement with the experimental results.Therefore,this method can predict the influence of physical phenomena inside the molten pool on the formed parts to some extent.