Offset impacting of a liquid aluminum droplet train on a molten pool on a horizontally moving substrate during TIG-assisted droplet deposition manufacturing

Abstract

Internal metallurgical defects and poor mechanical properties and surface quality of the formed parts are the most important challenges of metal micro-droplets deposition manufacturing technology. Lack of strong coalescence between neighboring droplets and the blocking effects of periodic ripples on the fusion process are major sources of abovementioned problems. To address this issue, a tungsten inert gas (TIG) welding arc was introduced to pre-melt the material below the droplet impacting location, thus, one droplet train will be deposited on a curved molten pool surface to fabricate deposited layers in an additive approach. In the present work, a numerical model based on the computational fluid dynamics (CFD) method was developed to investigate the dynamic behaviors of successive droplets’ impact and coalescence on the molten pool created by a tilted TIG welding arc, and focuses on the effect of the offset distance between the impacting point of droplet and the longitudinal plane of molten pool on the deposition morphology and the impact-induced molten pool behaviors. The simulated tracks exhibit regular scaly shapes at different offset distances, which is validated against the corresponding experiments. The results indicated that as the lateral offset distance increases, the symmetric spreading and recoiling of the subsequent droplets on the pre-existing bead will be broken due to the inclined and curved solidification front morphologies, the inclined front morphologies are caused by the increased growth rate of the solidification front at the impact zone. With an increased lateral offset distance, the volume of the molten pool decreases, the width of the rear molten pool increases slightly. The calculated solidification parameters are found to be dependent of the offset distance, and vary significantly at the onset of solidification at different portions of the molten pool. The scientific findings provide useful insights for further researches of TIG-assisted DDM.