The mechanism of dual-stagnation points flow phenomenon in keyhole plasma arc melt pool and corresponding control strategy

This study investigates the mechanism behind the dual-stagnation points flow phenomenon in the keyhole plasma arc welding (KPAW) melt pool and develops a corresponding control strategy. Positional information on flow stagnation points was obtained using the macroscopic morphology of the melt pool and liquid flow velocity measurements. The position of these stagnation points, determined by the directional flow of liquid metal, is crucial for characterizing the stability of the welding process. The study delves into the driving force mechanism that produces stable directional flow and a uniform temperature distribution within the melt pool. A significant discovery of this research is the identification of high-speed directional material transport channels within the melt pool. Furthermore, a correlation mechanism between the positions of stagnation points and the stable flow with temperature distribution has been constructed. To address the unstable and destabilization stages of the welding process, a dynamic material stability transfer control strategy was designed, based on liquid flow velocity and temperature distribution. This strategy ensures a smooth transition during the unstable stage and rapid self-healing of the melt pool during destabilization. This study provides a novel control strategy and a theoretical foundation for the automation and enhancement of the KPAW welding process, highlighting its necessity in advancing welding technology.