| Additive manufacturing technology,a new manufacturing method,has attracted widespread attention from countries around the world.The high-energy beam additive manufacturing technology has produced great attraction to the industrial fields such as aerospace and medical equipment that need to manufacture complex product structures.However,high-energy beam additive manufacturing of metal parts can cause defects in molded parts due to unsuitable technology.Therefore,understanding and controlling the evolution law of the flow field and temperature field of the molten pool during the scanning of the high-energy beam,thereby further probing and predicting the microstructure formation process of the solidified and formed parts,and improving the metallurgical quality and mechanical properties of the formed parts are The primary task of rapid development of high energy beam additive manufacturing technology.In this paper,the method of numerical simulation is used to study the formation and evolution of the molten pool in the high energy beam additive manufacturing process,which provides theoretical guidance for understanding the additive manufacturing process and improving the manufacturing process.The main contents of this article are as follows:(1)The numerical simulation methods including lattice Boltzmann method and finite volume method are used to simulate the shape,temperature field,flow field and phase field of the molten pool in the electron beam selective melting additive manufacturing method.This part first establishes the physical model and mathematical model of electron beam selective melting,and then converts the mathematical model into a numerical model through numerical simulation to facilitate simulation.Then explore the changes of macroscopic characteristics such as temperature field,flow field and phase field of the molten pool under different process parameters(high electron beam power,diameter and scanning speed).Through the simulation of the macro temperature field,the cooling rate and temperature gradient that affect the growth of micro-scale dendrites are calculated,and the function law with the change of process parameters is studied.Finally,the effect of the Marangoni effect on the macroscopic characteristics of the molten pool is analyzed.It is found that the higher the electron beam power,the slower the scanning speed,and the smaller the electron beam diameter,the higher the maximum temperature of the molten pool and the larger the morphology of the molten pool,but it will appear when the diameter of the electron beam is smaller,and the width dimension is lower than the electron beam When the diameter is large.The cooling rate of the solid-liquid interface of the molten pool generally shows a trend that the greater the depth,the smaller the cooling rate,and the temperature gradient will increase with the angle of the selected point(the angle between the normal direction of the selected point of the solid-liquid interface and the scanning direction)There is an increasing trend.The stronger the Marangoni effect,the lower the maximum temperature of the molten pool,and the higher the maximum flow velocity of the flow field.(2)Based on the principle of cellular automata,the micro-dendrite growth at the solid-liquid interface of the molten pool made by high-energy beam additive was studied.In this part,the control equation for the growth of micro-dendrites is established,and then the cooling rate and temperature gradient of the selected point of the solid-liquid interface of the molten pool calculated by the macroscopic temperature field are discussed.The growth law mainly includes the change of solid phase fraction and solidification rate with time in the simulated area under different conditions.In addition,the influence of x-direction flow velocity on dendrite growth was analyzed.It is concluded that the cooling rate plays a decisive role in the speed of directional solidification,while the temperature gradient affects the solidification direction and grain morphology of the grains,and the flow velocity in the x direction promotes the speed of directional solidification.(3)Use the method of numerical simulation to simulate the macroscopic molten pool situation of laser selective melting and the directional solidification of the microsolid-liquid interface.This chapter mainly includes the establishment of macro and micro models of laser selective melting and the simulation of molten pool characteristics under different process parameters.In addition,the differences between laser additive manufacturing and electron beam additive manufacturing are analyzed.It is found that the effect of the laser process parameters on the temperature field,shape and size of the molten pool is basically the same as that of the electron beam selective melting,but the increase in the heat dissipation method of the laser selective melting makes the maximum temperature and size of the molten pool slightly lower than the electron beam method.Moreover,the cooling rate of the laser surface is faster than that of the electron beam method. |
