Advantages and difficulties of laser welding system for li ion battery pack

Advantages of using laser welding for lithium ion battery packs

The advantages of laser welding system for lithium ion battery pack welding are energy concentration, high welding efficiency, high processing accuracy, and large weld depth-to-width ratio.

The laser beam of the battery laser welding machine is easy to focus, align and be guided by optical instruments. It can be placed at an appropriate distance from the workpiece, and can be guided between fixtures or obstacles around the workpiece. Other welding rules are subject to the aforementioned space Restricted and unable to play.

The heat input of laser welding is small, the heat-affected zone is small, and the residual stress and deformation of the workpiece are small; the welding energy can be accurately controlled, the welding effect is stable, and the welding appearance is good.

Laser welding is non-contact welding, optical fiber transmission, good accessibility, and high degree of automation.

When using a laser welding system to weld thin materials or thin-diameter wires, it will not be as prone to remelting as arc welding.

In addition, since the battery cells used for power batteries follow the principle of "lightness", they usually use lighter aluminum materials, but also need to be made thinner. Generally, the shell, cover, and bottom are basically required to reach 1.0 Below mm, the current basic material thickness of mainstream manufacturers is about 0.8mm.

The laser welding machine of lithium-ion battery pack can provide high-strength welding for various material combinations, especially when welding between copper materials and aluminum materials is more effective. Laser welding is also the only technology that can weld electroplated nickel to copper materials.

Difficulties of laser welding for lithium-ion battery packs

At present, battery shells made of aluminum alloy materials account for more than 90% of the entire power battery. The difficulty of laser welding of aluminum alloy is that aluminum alloy has high reflectivity to laser, and high pore sensitivity during welding. Some problems and defects will inevitably appear during welding. The most important ones are pores, hot cracks and explosions.

Stomatal problem:

There are two main types of pores in the laser welding process of aluminum alloy: hydrogen pores and pores caused by bubble bursting. Because the cooling rate of laser welding is too fast, the hydrogen gas hole problem is more serious, and there are more holes caused by the collapse of small holes in laser welding.

Thermal crack problem:

Aluminum alloy is a typical eutectic alloy. Hot cracks are prone to occur during welding, including weld crystallization cracks and HAZ liquefaction cracks. Due to the segregation of components in the weld zone, eutectic segregation will occur and grain boundary melting will occur. Liquefaction cracks are formed at the grain boundaries, reducing the performance of welded joints.

Splash problem:

There are many factors that cause splashing, such as the cleanliness of the material, the purity of the material itself, and the characteristics of the material itself. The decisive factor is the stability of the laser.

The surface of the shell is raised, pores and internal bubbles. The main reason is that the fiber core diameter is too small or the laser energy is set too high.

The beam quality of laser welding machine is better, and its welding effect is not necessarily better. Good laser beam quality is suitable for superposition welding with larger penetration depth. Finding the right process parameters is the magic weapon to solve the problem.