With the development of the new energy vehicle industry, laser welding has become increasingly popular in the manufacturing of power batteries because of its high welding speed, small heat-affected zones, and high degree of automation. However, as the laser involves high-energy beam, its interaction with materials is often intense. This can easily lead to defects, such as spatters and explosion points, thus compromising the quality of battery welding. In the field of power batteries, the adjustable ring-mode (ARM) laser has emerged as a high-speed low-spatter laser welding tool, gaining attention from both academia and industry. However, the spatter suppression mechanism of the ARM laser during high-speed welding remains unclear. This limitation hinders theoretical guidance and process optimization for industrial applications. Thus, in this study, the complete welding of an aluminum alloy roof is considered and how the core ring power ratio affects the penetration and width is analyzed. Moreover, how the ARM laser effectively curbs the metal spatter is elucidated by examining the dynamic behavior of the keyhole in the molten pool. Optical coherence tomography (OCT) measurement technology is used to monitor keyhole depth fluctuations in real time, providing a quantitative assessment of welding stability and identifying the optimal process window.

A synchronous-sensing monitoring platform (Fig. 1) is established by integrating high-speed visual shooting with penetration detection. For the visual sensing component, a high-speed camera is utilized to capture sharp keyhole images of the molten pool. For penetration detection, the platform is merged with an OCT-based monitoring module to acquire real-time keyhole depth information during the welding process. Initially, the process window of the ARM laser welding is determined by conducting an orthogonal experiment, as shown in Fig. 3. The keyhole images under different parameters are obtained, and the changes in the keyhole depth are recorded. Comparisons of the keyhole opening and depth reveal the mechanism behind the spatter suppression during ARM laser welding. To identify the best low-spatter process window, keyhole volatility is introduced as a variable. The variance in the keyhole depth, measured by applying OCT in real time, is calculated. This variance is used to assess the depth fluctuations of the keyhole and, consequently, the stability of the welding process. The relationship between the welding process stability and the power ratios of inner ring laser to outer ring laser is then established by using a contour map, resulting in the identification of optimal process window parameters (Fig. 10).

The spatter formation mechanism in the ARM laser high-speed (150 mm/s) welding is analyzed. The spatter formation process and suppression methods are elucidated, demonstrating that the ARM laser can indeed diminish the spatter occurrence rate by enlarging the keyhole opening. The effect of the power ratio of inner ring laser to outer ring laser on the keyhole stability is verified. First, a traditional orthogonal experiment is conducted to determine the process window for melting width when the inner ring laser power ranges from 600 W to 1300 W and the outer ring laser power ranges from 800 W to 1800 W. The process window for the penetration is determined for an inner ring laser power of 500?1150 W and outer ring laser power of 800?1800 W. Subsequently, the optical coherence scanning technology is employed to acquire the keyhole depth information. This information enables a qualitative evaluation of the welding process stability, facilitating the process optimization of the ARM laser welding. The findings suggest that a higher outer ring laser power is better for achieving a suitable penetration. A higher outer laser ring power stabilizes molten pool fluctuations and enlarges the keyhole opening.

This study presents a process optimization scheme combined with real-time monitoring of the laser welding depth. The theory that spatter is mainly caused by keyhole collapse is verified. The laser welding process is further optimized based on the standard deviation of keyhole depth fluctuations. The final process window that satisfies both the traditional process window and keyhole fluctuation stability analysis window is identified: the core laser power ranges from 800 W to 1000 W, ring laser power is between 1200 W and 1600 W, and welding speed is set at 150 mm/s. The optimal power ratio of inner ring laser to outer ring laser for welding aluminum alloys typically lies between 1∶2 and 1∶3. Within this range, the keyhole achieves maximum stability and the defect occurrence rate is the smallest.