Deepening the understanding of arc characteristics and metal properties in GMAW-based WAAM with wire retraction via a multi-physics model

Abstract

Wire retraction is used in the short-circuit droplet transfer mode of gas metal arc welding (GMAW) to improve the stability of transfer, reduce heat input and decrease spatter. The significant effects of wire retraction on the arc plasma characteristics and the thermal properties of the metal are not well understood. In this paper, we develop a three-dimensional, transient, multi-physics coupled GMAW model with wire retraction and apply it to wire arc additive manufacturing (WAAM) of an aluminum alloy. The model takes into account the wire's downward and upward motion, droplet growth and detachment, arc plasma heating, metal vaporization, melting and solidification of the molten pool, and the relative motion of the wire and substrate. The model is used to simulate the deposition of a single layer, and the evolution of the arc characteristics and the metal thermal and flow behavior are analyzed. The results demonstrate that during a wire motion period, the arc characteristics are determined by both the transient welding current and the distance between the welding wire and the molten pool. The arc plasma has a significant influence on the temperature and flow of the droplet and the molten pool metal when the wire is well separated from the melt pool and the welding current is in its peak phase. The energy and momentum of the metal in the molten pool are primarily influenced by the metal transfer, and the maximum flow velocity and maximum temperature occur at the time of the short-circuit contact. The results demonstrate the advantages of using a low welding current during droplet transfer, which is made possible by wire retraction. The model is validated by comparing the predicted morphology of the deposited layer and the shape of the arc during a wire motion period with experimental results, with reasonable agreement found.