Numerical simulation of molten pool flow behavior and keyhole evolution behavior in dual-laser beam oscillating bilateral synchronous welding of T-joints

Abstract

In the context of global warming and energy shortage, the key means to increase product competitiveness is how to achieve lightweight manufacturing of large spacecraft skin-stringer structures by welding instead of riveting. In this work, we propose dual-laser beam oscillating bilateral synchronous welding (DLBOW) by combining dual-laser beam synchronous welding (DLBW) with the oscillating process to overcome the long-standing porosity problem in T-joint welds and investigate the effect of different laser incidence angles on the porosity of the weld during welding. At the same time, the corresponding numerical model was established by computational fluid dynamics to analyze the molten pool flow behavior and keyhole evolution under molten pool coupling. This is the first time that complete wire melting process has been achieved in the T-joint dual-laser beam synchronous welding numerical model, reproducing more realistically the influence of the wire fusion behavior on the molten pool flow. Both experimental and simulation results show that the porosity is significantly reduced under DLBOW compared to DLBW; in addition, the porosity is lower when the laser incidence angle is smaller. An in-depth analysis of the numerical model reveals the mechanism of this physical phenomenon: First, the oscillation process optimizes the laser energy density distribution and reduces the peak temperature of the T-joint molten pool. The impact of the metal flow on the keyhole is weakened, which reduces the probability of bubble formation and thus significantly decreases the porosity. Moreover, for the oscillation process, the keyhole effect is more obvious at large laser incidence angles, and the actual heat input to the molten pool is larger, which makes the slender keyhole more prone to collapse and more likely to generate pores. This work provides new insight into the interrelationship between keyhole and pore in T-joint dual-laser beam synchronous welding.