Mechanism of Rotational Adsorption Effect in Hollow Tungsten NPA Welding under Dual Magnetic-Gas Control

Aiming at the unresolved formation mechanism and the lack of quantitative control strategy for the negative-pressure arc in Supplying Gas Hollow Tungsten Negative-Pressure Arc (NPA-SHT) welding, this study develops a fully coupled multi-physics numerical model to systematically investigate the synergistic regulation mechanism of a longitudinal magnetic field and central gas flow on the arc's thermo-mechanical-flow behavior. The results reveal a fundamental competition-synergy relationship: high-speed gas flow cools and diffuses the arc, suppressing axial energy transport, while the magnetic field compresses and energizes the arc via the Lorentz force, promoting axial transport and inducing plasma backflow. Innovatively, the Magnetic-Gas Intensity Factor (MGF) is introduced as a unified dimensionless parameter to quantify this competition. The study further establishes dual design criteria for a stable negative-pressure arc with a rotational adsorption effect: (a) MGF ≥ 1, and (b) the formation of an enclosed counterclockwise backflow structure in the arc plasma. The M-framework not only characterizes the multiphysics coupling and the rotational adsorption effect but also establishes a quantitative relationship among welding current, gas flow rate, and magnetic field threshold. This work provides a theoretical foundation and practical design guidance for the emerging NPA-SHT technology, paving the way for its application in precision welding and additive manufacturing of thin-walled components. • Introduced the Magnetic-Gas Intensity Factor (MGF) for quantitative characterization of NPA physics and arc stability. • Revealed the competitive regulation between magnetic field and gas flow on arc thermal-force-flow behavior. • Proposed design criteria for a stable negative-pressure arc , including MGF≥1 and an enclosed backflow structure. • Establishes the physical foundation for NPA-SHT welding theory and its engineering application.