To achieve carbon neutrality, lithium batteries, as a new generation of green energy products, are poised to enter the terawatt-hour (TW·h, equivalent to 1000 GW·h) era. Currently, mainstream manufacturers of state-of-the-art energy batteries have reached a production capacity of 200 pieces per minute (PPM), and there are plans to increase the production capacity of cylindrical batteries to 300 PPM. Consequently, extremely high-speed production lines present substantial challenges to the welding process. Therefore, the development of highly efficient and reliable battery-welding technologies and processes has become an urgent concern for the automobile manufacturing industry. Laser welding, with its small laser spot, high energy density, efficient welding, precise energy control, automation capabilities, and safety features, has been widely used in the field of new energy battery welding, including vehicle manufacturing. Recent research has primarily focused on enhancing the welding quality of aluminum alloys by optimizing laser welding process parameters and beam shaping. However, as the demand for higher welding efficiency in power battery welding increases, the scope for ensuring both welding quality and speed becomes constrained, making it increasingly challenging to identify suitable process parameters. Considering that lasers, as a new type of welding light source, exhibit characteristics distinct from those of the arc light sources generated by arc welding machines, research has primarily focused on laser power. The impact of laser light source characteristics on welding quality and efficiency, particularly the influence of laser beam quality, has received limited attention. To meet the demands of high-speed production lines for new energy power batteries, the effect of the beam quality from fiber lasers in aluminum alloy laser welding is systematically analyzed in this study based on the energy distribution characteristics within the laser welding process. The quantitative relationship between beam quality and welding stability, as well as welding efficiency, is also explored.
An industrial-grade 3-kW continuous fiber laser is used in the experiment. The laser employs a circular swing path for welding with a swing amplitude of 0.6 mm and spacing of 0.25 mm. The upper-layer material consists of a 1.5-mm-thick 3003 aluminum alloy plate, while the lower-layer material is a 3-mm-thick 3003 aluminum alloy plate.
With a decrease in the laser beam quality factor (M2), the welding speed increases, corresponding to the same weld penetration (2.7 mm), and the complex process capability index (CPK) value of weld penetration also increases. When the M2 is reduced from 11.6 to 1.25, the welding speed increases by 5.5 times, and the CPK value of the weld penetration increases by 2.3 times, corresponding to the same weld penetration (2.7 mm) (Fig. 4). Analyzing the energy distribution of postlaser welding oscillations on the YOZ surface reveals that, as the M2 improves, there is a consistent downward trend in the maximum value of the laser energy density. In addition, the area between the two maximum values decreases. For instance, the maximum energy density at M2=1.18 is 1.4 times higher than that at M2=11.6 (Fig. 5). To gauge the influence of the laser energy density on the welding efficiency, a factor derived from the product of the maximum laser energy density and the difference in the maximum value of the energy density is introduced. Calculations demonstrate that, at M2=1.18, this influence factor for laser energy density welding efficiency is 5.2 times higher compared with that at M2=11.6 (Fig. 6). To facilitate the assessment of the area disparities between the maximum peak and intermediate minimum at both ends of the weld, the region between these points on the energy distribution map is defined as the laser energy occupied space line density. Remarkably, when M2 is 1.18, the laser energy occupied space line density is 10.7 times greater than that when M2 is 11.6 (Fig. 6).
The influence of the beam quality from fiber lasers on aluminum alloy welding is systematically analyzed by considering the energy distribution characteristics during the welding process. A quantitative relationship between beam quality and welding stability, as well as welding efficiency, is established. The improvement mechanism for the laser beam quality effect is as follows. When the M2 decreases while retaining the same penetration depth, the maximum value of the energy density increases, and the energy density between the edge of the weld bead and the middle interval also increases. The higher the energy absorption efficiency of the workpiece material, the higher the welding efficiency of the laser. The product of the maximum value of the laser energy density and the difference in the maximum value of the energy density is used as a factor influencing the laser energy density welding efficiency. The theoretical calculations show that, when M2 is 1.18, the influence factor of the laser energy density welding efficiency is 5.2 times higher than that when M2 is 11.6, which is basically consistent with the experimental results.
