Numerical Simulation of Heat and Mass Transfer in CMT-based Additive Manufacturing

Abstract

Cold metal transfer (CMT)-based wire arc additive manufacturing(WAAM) technology has a broad application prospect in the direct forming of large-scale components due to the advantages of high melting efficiency, low heat input and stable forming shape. However, the physical field evolution mechanism of molten pool is not clear, and it is difficult to obtain by trial-and-error method. A two-dimensional heat transfer and fluid flow model of CMT-based WAAM is developed basing on dynamic meshing technical. The volume of fluid (VOF) method is used to track the metal-gas interface, the enthalpy-porosity method is employed to handle metal melting and solidification, and the periodic loading ellipsoid heat source is selected to describe the stage of arc combustion and extinguishing. By the developed model, the deposition process of aluminum alloy CMT-based WAAM is simulated, and the influence of various driving forces on the flow behavior of molten pool, the interaction between droplet and molten pool during CMT droplet transition and the influence of different substrate thermal conditions on the deposits shape are investigated. The results show that the Marangoni force is dominant to drive the fluid flow of molten pool, and followed by the arc pressure. When the droplet moves downward with the wire, liquid metal on the surface of droplet flows downward, while the metal inside flows upward to form a circulation. When the droplet enters the molten pool, the liquid metal on the free surface of molten pool flows to periphery of both sides, and two reverse vortexes are formed at the bottom of the molten pool. In addition, with the increase of substrate temperature, the deposition morphology changes from thin to flat.