Research On Forming Mechanism Of Wire Arc Additive Manufacturing Based On Multiphysics Model

Wire arc additive manufacturing technology has great potential in large-scale and large-scale industrial manufacturing because of its advantages of low cost and high efficiency.However,there are some common problems in the current wire arc additive manufacturing process,such as difficult to control the geometry size and low mechanical properties of formed parts,which limit the application of this technology in the field of high-precision manufacturing.In the forming process of wire arc additive manufacturing,the wire is heated in the arc and then melts to form droplets,which fall,deform,collide with the substrate and solidify into form parts.The process involves the coupling among temperature field,flow field,electric field and magnetic field.Numerical simulation is a reliable method to deepen the understanding of the basic theory of heat and mass transfer in the process,and is of great significance to reveal the physical mechanism and forming law comprehensively and systematically.Plasma arc,as a heat source,is the basis of wire melting and droplet transition behavior.In this study,a three-dimensional multiphysics plasma arc model is established firstly.By solving the equations of mass conservation,energy conservation,momentum conservation and electromagnetic field,the multi physical field characteristics of plasma arc are analyzed in detail.Then the arc temperature and pressure measurement experiments are carried out to verify the arc model by comparing the simulation and experimental results.A three-dimensional arc-wire integrated model is established.The physical process of wire melting in arc is studied,the distribution law of wire heat flux and dynamic change of fusion line are summarized,the characteristics of multiple physical fields such as temperature field,flow field and electromagnetic field of the integration model are analyzed,and the physical mechanism of wire melting is revealed,which provides a foundation for better understanding the manufacturing process and optimizing process parameters.Based on the above wire-arc integrated model,the process parameters of additive manufacturing process are explored.The effects of wire feeding angle and wire material are studied through a series of numerical simulations.It is found that the increase of wire feeding angle is conducive to the faster melting of wire and farther of starting melting position from the bottom.Three wire materials,2219 aluminum alloy,Ti-6Al-4V and mild steel are explored.It is found that in the wire with the same diameter,the product of metal density and specific heat capacity is the key parameter to determine the wire melting speed.The larger the product of density and specific heat capacity,the slower the melting.Finally,the droplet transfer process is simulated.Firstly,the deformation and solidification of single droplet are analyzed.Then the forming process of multi droplets deposition is simulated,the surface morphology and temperature field characteristics of the parts are analyzed.Furthermore,the influence of droplet height on the forming process is explored.It is found that the lower drop height will significantly increase the height of the formed structure,but reduce the uniformity of the formed size.By the analysis of temperature field,it is found that the formed parts will experience periodic thermal cycle with the falling of droplets.