Investigation of keyhole behaviour and its impact on the performance of laser beam oscillating welding through imaging and acoustic signal analysis

As an emerging laser welding optimisation technique, beam oscillation still lacks detailed investigation into its underlying process mechanisms. This study investigates the microstructure and mechanical properties of 316LN welded joints under four oscillation modes, the results demonstrate that beam oscillation can suppress columnar grain growth and reduce porosity defects, thereby enhancing weld formation and mechanical properties. Building upon these findings, visual and acoustic sensing techniques are employed to analyse dynamic features of keyholes and energy distribution. The correlation between keyhole geometric features and porosity propensity across different oscillation modes is elucidated through visual information. Additionally, the time and frequency domain features of the acoustic signals effectively characterise the stability of the welding process and laser energy absorption efficiency.