Design and mechanism research of online control and monitoring system for laser welding quality

• Developed the first closed-loop system integrating gas pre-filling and plasma diagnostics, enabling real-time control of oxidation and spectral monitoring during titanium alloy welding. • Established quantitative standards for oxidation-free welding: oxygen content <22 at% and Ti/O ratio >3.6 under complete protection conditions. • Defined benchmark parameters and control strategies that provide practical guidelines for high-reliability titanium alloy welding in aerospace applications. The utilization of appropriate protective gas is essential for achieving superior quality in the laser welding of titanium alloys. This research focuses on optimizing the protective environment of the welding zone by varying the precharge duration of the protective gas. A systematic investigation was conducted to assess the impact of these adjustments on the quality of weld formation. By employing a combination of multi-scale characterization techniques, including macro-morphological analysis of the weld, plasma spectroscopy assessments, and microstructural evaluations, the fundamental physical phenomena occurring during the welding process and the patterns of weld quality evolution were elucidated. Additionally, a real-time monitoring approach utilizing plasma spectroscopy diagnostics was developed. This method allows for the reverse inference of the welding process state through the interpretation of plasma spectral characteristics, thereby establishing connections with the oxidation behavior of titanium alloys and facilitating a comprehensive analysis of the factors contributing to disturbances in the molten pool fluid dynamics. Furthermore, a numerical model grounded in thermodynamic principles was created to simulate the dynamic evolution of the molten pool, offering a quantitative explanation of the mechanisms by which the state of the protective gas influences the fluid behavior and thermal stability of the molten pool.