Research On The Mass And Heat Transfer Characteristics Of Continuous Metal Droplet Deposition Based On Lattice Boltzmann Method

Additive manufacturing technology is a rapid prototyping technology based on the "discrete-stack" method.Due to the advantages of simple operation,low consumption and generalization ability on demand,it has valuable application in the fields of aerospace vehicles,automotive industry and medical auxiliary equipment.However,the rough surface quality and the worse internal bonding quality restrict the transformation from theory to application.In this thesis,the lattice Boltzmann method is used to study the interface evolutions,dynamical factors,heat transfer and phase change mechanisms during the deposition of the thermal droplets,which provides support for the further development of metal droplet deposition manufacturing technology.The specific research content includes:(1)Based on the single-component pseudo-potential model and the explicit enthalpy change model,the solid discriminant function in the immersed boundary method is modified to realize the simulation of the thermal droplet deposition process.The comparison with the deposition process of the room temperature droplets shows that cooling and solidification affect the interfacial movement and deposition morphology of single or multiple droplets.Since the surface wettability change of the droplet after solidification,the field potential energy of the solidified surface need to be reset to simulate the continuous deposition process.The infiltration of the deposited droplets and the solidified surface results in a deviation between the actual distance and the deposition distance,which can be optimizing to realise a uniform deposition morphology.(2)Establish a two-body continuous deposition model of heat source droplets to simulate the deviation in the inclined column deposition.According to the evolution of droplet's surface energy,the deposition process is divided into four stages: falling,rapid expansion,slow expansion and rebound.The pressure gradient force is the main driving force of the horizontal deviation,which makes the droplet sliding on the solidified surface and produce the main offset distance in the expansion stage.The axial distance,wettability and deposition height are the main process parameters that affect the degree of deviation,and affect the migration process through the competitive relationship between the duration of the acceleration section and the extreme value of the speed.The deposition distance is optimized according to the material parameters to achieve a uniform morphology of the oblique column deposition morphology.(3)Increase the deposition distance,adjust the wettability of the solidified surface and the substrate based on the two-body continuous deposition model to explore the attraction/repulsion characteristics in the horizontal deposition process.The horizontal continuous deposition process is affected by the capillary competition process between the substrate and the solidified surface,which results in the attraction/repulsion characteristics.The increase of the two kinds of wettability affects the deposition morphology and reduces the surface roughness.The change of the axial distance makes the deposition present two kinds of movement.The deviation degree of the attraction/repulsion is affected by the coupling of the two kinds of wettabilities.(4)The life and death element technology is introduced into the heat transfer phase change lattice Boltzmann equation to realize the simulation of the multi-scale multilayer deposition process.The initial temperature conditions,idle time and deposition size can be optimized according to the material parameters.The temperature environment,heat transfer capacity and heat transfer distance under different deposition locations,leading to the differences in temperature evolution trends and spatial distribution states.The metals are remelted by the deposited droplets under the influence of the deposition temperature difference and the deposition position,leads to the anisotropic of the metallurgical bonding quality.