Observation and analysis of three-dimensional weld pool oscillation dynamic behaviours: A sensor was used to observed weld pool oscillation in three dimensions, and then the 3D data was used to analyze the oscillation behaviours

Pool oscillation frequency is thought to have a direct relationship with weld joint penetration, and appropriate oscillations help refine grains and reduce defect sensitivity. This paper uses a novel laser dot-matrix sensor to observe the pool oscillation three dimensionally (3D) and use the 3D data as an enhanced ability ot analyze oscillation behaviours. To this end pool oscillations were excited using pulse current, oscillation images were captured at 1000 frames per second by a high-speed camera, and the acquired high-speed images were processed and observed. The processed/observed images provide experimental data about oscillation amplitude and mode to study oscillation behaviours. It was found that three oscillation modes associated with partial, complete, and critical penetration exist during the base time period. From the observed 3D dynamic evolution process, the periodical contraction and expansion at its natural frequency as excited by the pulsing current were observed. The amplitude of the oscillation was found to gradually decrease as the oscillation process proceeded and the liquid metal solidified during the base current period. Furthermore, the amplitude was found to increase as the peak current increased. The experiments under constant current and high-frequency pulsing current provided supplemental data to understand the pool behaviours. Because of the enhanced ability of 3D observation of the oscillation, this study enhanced the understanding on the pool oscillation and experimentally verified certain theoretical derivations about oscillation that have not been verified previously.