| The drop-on-demand(DOD)based 3D printing is a novel rapid prototyping technology,which has the advantages of short manufacturing cycle,low cost,high flexibility,wide application of materials and recycling.It can be used in the fields of biomedicine,microelectronics manufacturing,aerospace construction and so on.This technology has been received widely attentions among scientific researchers.However,the rough surface topography with low precision is the main factor that restricts the further popularization and application of this technology.The deposition of droplet on the wall,the vertical column formed by stacking perpendicularly to the wall,and the horizontal line formed by lapping parallelly to the wall are all the basic manufacturing elements of this technology.The deposition of droplet on the wall is influenced by many factors.Many unpredictable deformations such as splashing,bouncing and migration may occur.The fusion collapse and instability are easy to form in vertical stacking and horizontal lapping processes,respectively.All these greatly affect the precision of the morphology of the forming parts.Therefore,it is of great significance to conduct the influence study of the droplet deposition on the wall and optimize the morphology and structure of vertical column and horizontal line.The droplet deposition and deformation are the results of the coupling of flow and thermal field inside the droplet.In view of the complex multiphase flow and heat transfer mechanism,a numerical calculation model of droplet deposition based on FTM(Front Tracking Method)was developed in this paper.The projection iteration and discrete solution methods for FTM tracing the gas-liquid interface and governing equations(continuity equation,momentum equation and energy equation)are included.By improving the projection algorithm,the numerical calculation of the droplet solidification phase transition was realized.According to the characteristics of the multiphase interface expressed by FTM,the numerical characterization method of the wetting contact Angle under FTM was proposed.The numerical calculation model based on FTM can provide a numerical tool for the study of droplet depositionTo obtain the influence mechanism of droplet deposition on the wall,the dimensionless length of droplet in horizontal and vertical directions are used as the morphology evaluation index,and the two-dimensional axisymmetric FTM numerical model is applied to study the influence of Ohnesorge,Weber,Super Heat number and other thermal and kinetic parameters on the deposition process.In addition,the capillary number and center of mass position are used to measure migration velocity and track motion trajectory,respectively.The effects of physical parameters such as viscosity coefficient,characteristic Reynolds number and wall boundary conditions such as wetting gradient and roughness on droplet deposition and migration are studied by using three-dimensional FTM model.The obtained influence parameters of controllable deposition can provide support for following study of the morphology optimization of continuous droplet depositionBased on the mechanism of fusing collapse effect,the positive enthalpy value in the droplet is used to monitor the heat accumulation during the vertical stacking process,which provid a basis for the quantitative study of the vertical fusing collapse effect.According to the forming characteristics and morphology parameters of the vertical column,a set of criteria for judging the morphology structure type is established,and a numerical calculation process for the ideal vertical column morphology structure was developed.In the mean time,the influence of Superheat and Weber number on the ideal shape structure is analyzed respectively,which can provide a reference for the design of ideal vertical structure and the elimination of fusion collapse;A stability boundary condition with local wetting constraint was designed for continuous horizontal droplet deposition,and a theoretical calculation model was established to predict the optimal droplet deposition spacing.The three-dimensional FTM numerical model is used to simulate the forming process of liquid lines,and the influence law of deposition spacing on the stability of liquid lines is explored,which is a reference for improving the stability of liquid lines. |
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