Particle migration mechanisms in in-situ laser shock assisted cored-wire WAAM

Abstract

In-situ laser shock (ILS) technology pioneers a novel strategy to combat particle inhomogeneity, specifically low-density particle floating-aggregation, in cored-wire arc additive manufacturing (CWAAM). However, a critical knowledge gap persists regarding the real-time particle migration, ILS-induced melt pool dynamics, and the fundamental mechanisms by which ILS suppresses flotation, hindering its advancement. To address this, we developed a sophisticated 3D transient multiphysics model integrating heat-mass transfer, fluid flow, and particle dynamics. This model uniquely elucidates the flotation-agglomeration mechanisms of low-density particles and reveals the underlying principles of ILS suppression. The results indicate that the Stokes number for most particles ranges between 0 and 0.1, signifying predominant entrainment by liquid flow. In the absence of ILS, the combined action of Marangoni convection and buoyancy forces drives particle migration towards the upper region, inducing agglomeration. Concurrently, high-speed flow entrains particles at the rear surface of melt pool. Furthermore, the drag force plays a critical role in particle motion, exhibiting dependence on the relative velocity between the fluid and particles. The application of ILS fundamentally alters the melt pool's flow field morphology. The formation of a multi-vortex flow field and the shift of high-velocity regions effectively suppress agglomeration, increasing the coefficient of variation for particle distribution by 23 %. Simultaneously, the reverse pressure (up to 11.57 kPa) generated by the pulsed laser effectively counteracts buoyancy-induced flotation, promoting downward particle movement. During this process, an equilibrium state occurs when the relative particle-fluid velocity is lower, whereby buoyancy, gravitational force, and drag force mutually counteract. At higher relative velocities, drag force predominance still facilitate particle ascent. This investigation into particle migration behaviour in CWAAM provides a significant theoretical foundation for the further development of WAAM technology.