Unveiling arc deflection instability in narrow gap laser-arc hybrid welding of thick Ti-6Al-4V plate

Unveiling the mechanism behind arc deflection under narrow gap laser arc hybrid welding (NGLAHW) is of paramount significance in mitigating laser-arc coupling failure and welding porosity for thick Ti-6Al-4V plate structure. This paper utilizes high-speed camera technology, data statistics and model prediction to comprehensively study the influence of constrained groove space and droplet transfer mode on arc deflection. The results demonstrate that narrowing groove gap exerts a substantial compressive effect on welding arc behavior, particularly rendering it more susceptible to arc deflection when the groove gap is smaller than the arc length. The small droplet transfer mode is characterized by stable arc behavior, whereas the large droplet transfer mode tends to be susceptible to arc instability due to the droplet deviation induced by turbulent metal vapor. Particularly noteworthy is the emergence of substantial arc deflection when the droplet deviation exceeds the critical threshold of 0.51 mm, which diminishes the driving force for droplet transfer and subsequently leading to potential short-circuiting explosions and unstable welding process. Moreover, the lateral force induced by arc deflection drives a deviation in arc heat source with accelerated solidification of molten pool, consequently resulting in an elevation in welding porosity. This paper has provided a comprehensive insight into the mechanism driving arc deflection in NGLAHW, which holds paramount importance in enabling effective strategies to regulate the arc behavior.