Heat transfer, fluid flow and electromagnetic model of droplets generation and melt pool behaviour for wire arc additive manufacturing

•A comprehensive model is proposed to investigate the heat and mass transfer mechanisms in WAAM process.•The main phenomena in the arc plasma are modelled including the droplet creation, its detachment and fly to the melt pool, as well as the deposition build-up during a multi-layered process.•The major role played by the droplet falling onto the melt pool and its behavior is discussed.•The model shows that the action of the droplets strongly influences the melt pool size, the fluid flow, and the temperature field in the deposit and so cannot be neglected in the model. In this study, a numerical model of Wire Arc Additive Manufacturing has been developed to obtain the geometry of the part as well as its temperature field from the operating parameters. This predictive model takes into account electromagnetism, fluid flow and heat transfer in the arc and the melt pool. The Lorentz forces, shear stress, arc pressure, and Joule effect are calculated. This model is developed using the COMSOL Multiphysics® software. In order to simulate the addition of layer-by-layer material and the strong topological changes, the level set interface tracking method is used. This model aims to simulate the build-up of a 304 stainless steel rod starting from the operating parameters in the case of a pulsed currents. The detachment of droplets of the deposited metal and their fall along the vertical axis are modelled to predict the geometry and the thermal history of the workpiece. The "material supply / cooling" cycles between each layer are simulated. To validate this model, the geometry and the temperature field are analysed and compared to experimental data.