Enhancing droplet transfer in laser-arc hybrid welding via oscillating laser-induced plasma interaction

Controlling droplet transfer is crucial for achieving high-quality laser-arc hybrid welding of aluminum alloys. This study systematically investigates the effects of oscillating laser beam modes (transverse, longitudinal, circular) on the welding process of 8 mm thick AA6082 aluminum alloy. High-speed imaging reveals that non-scanning mode leads to coarse projected transfer with significant spatter. While transverse and longitudinal scanning improve stability, they still involve medium projected and short-circuiting transfer. In contrast, circular scanning uniquely promotes stable fine projected transfer, reducing the average droplet diameter by 47% (to 0.9 mm) and transfer time by 44% (to 3.8 ms), while drastically suppressing spatter. Plasma spectroscopy analysis provides the underlying physical mechanism: circular scanning most effectively enhances laser-arc plasma interaction, increasing arc zone electron temperature by ∼8.5% and electron density by 43%. This reduces arc resistivity, promotes wire melting, refines the molten metal column necking diameter (D∼R∼ to 0.45 mm), and stabilizes the arc force direction. Consequently, the critical wavelength for liquid column instability decreases, facilitating droplet detachment. This work elucidates the mechanism of droplet regulation by oscillating lasers and identifies circular scanning as the optimal strategy for high-quality aluminum alloy hybrid welding.