Asymmetric molten pool morphology in wire-arc directed energy deposition: Evolution mechanism and suppression strategy

Abstract

Symmetric molten pool morphology is essential and fundamental in manufacturing three-dimensional (3D) components by wire-arc directed energy deposition (DED) method. However, when the molten metal droplets are deposited on non-level surfaces, various inclined substrates lead to undesirable molten pool behaviors, asymmetrical weld bead morphologies, or even formation of defects, which are mainly triggered by the gravity. Therefore, the evolution mechanism and suppression strategy of the asymmetric molten pool morphology on the inclined surface are necessary for the fabrication of 3D components. Herein, experimental and simulation analysis was carried out to reveal the evolutionary mechanism of molten pool and forming characteristics of wire-arc DED on various inclined surfaces, and a printing strategy was proposed to suppress the asymmetric molten pool morphology. First, a series of deposition experiments based on variable tilted substrates was conducted to evaluate the influence mechanism of weld bead morphology, and a characteristic parameter was introduced to quantitatively analyze the influence of inclination angle on the forming morphologies of weld beads. Second, in order to better comprehend the evolution of the asymmetric molten pool morphology, 3D numerical simulation and high-speed photography test were conducted to investigate the evolution of temperature field, velocity field, and fluid dynamics during the deposition on variable substrates. Finally, based on the theory of equilibrium of forces, a strategy was proposed to suppress the undesirable fluid flow pattern and eliminate the asymmetric morphology of single bead. Besides, for the multi-bead deposition process, this paper proposed an alternate printing strategy to alleviate asymmetric molten morphology and improve the forming quality. The feasibility of the proposed methods were verified via comparative quantitative evaluation. • Evolution mechanism of molten pool in wire-arc DED is systematically investigated. • Adverse effect of gravity on the mass transfer behavior of molten pool is revealed. • The influencing mechanisms of asymmetric morphology of molten pool are explored. • Printing strategies are proposed to eliminate the asymmetric weld bead morphology.