Liquid bridge simulation of metal-wire laser additive manufacturing in microgravity environment

Unstable thermocapillary convection in metal liquid bridge is a typical phenomenon during the laser metal-wire additive manufacturing process in microgravity environment. The evolution and dynamic mechanism of the liquid bridge will influence the manufacturing process and quality for the forthcoming on-orbit space metal additive manufacturing. Therefore, it is very important to investigate the evolution and instability of thermocapillary convection in liquid bridges in microgravity. In present investigation, a numerical model is developed to reveal the characteristics of thermocapillary convection. The effects of aspect ratio and gravity on the critical Reynolds number for convection instability of thermocapillary convection in metal (Ti6Al4V) liquid bridge are investigated numerically. The results indicate that the critical Reynolds number for convection instability decreases with the increase of aspect ratio number at first, and then increases both in the gravity or microgravity environment. The numerical results also reveal that the critical Reynolds number for convection instability under gravity environment with natural convection in metal liquid bridge is larger than microgravity environment. The research shows that the influence of microgravity leads to a distinctly different behaviour of thermocapillary convection in metal liquid bridge compared to the gravity environment. A more comprehensive study will be conducted to cover the parameter space more systematically to identify the factors which significantly influence the stability of the thermocapillary convection in metal liquid bridge under microgravity environment, which is important for the on-orbit space metal additive manufacturing.