Introduction of EV battery laser welding process

The reasonable selection of welding methods and processes in the EV battery manufacturing process will directly affect the cost, quality, safety and consistency of the battery.

As an advanced welding process, the battery laser welding system is widely used in the EV battery manufacturing process.

The principle of laser welding

Laser welding uses the excellent directivity and high-power density of the laser beam to work. The laser beam is focused in a small area through the optical system, so that the welded area forms a highly concentrated heat source zone in a very short time, so that the welded object melts and forms a firm solder joint and weld.

Types of laser welding

Heat conduction welding: The laser beam will melt on the surface of the workpiece along the joint, and the melt will flow together and solidify to form a weld. Mainly used for relatively thin materials, the maximum welding depth of the material is restricted by its thermal conductivity, and the width of the weld is always greater than the welding depth.

Deep penetration welding: When the high-power laser is concentrated on the surface of the metal, the heat will not be lost in time, and the welding depth will be sharply deepened. This welding technology is deep penetration welding. Because the deep penetration welding technology has a very fast processing speed, a small heat-affected area, and minimizes distortion, this technology can be used for deep welding or welding of several layers of materials.

The main difference between thermal conduction welding and deep penetration welding is the power density applied to the metal surface per unit time, and the lower critical value is different for different metals.

Through welding: the connecting piece does not need to be punched, and the processing is relatively simple. Penetration welding requires a laser welder with higher power. The penetration depth of penetration welding is lower than that of seam welding, and the reliability is relatively poor.

Seam welding: Compared with penetration welding, only a smaller power laser welder is required. The penetration depth of seam welding is higher than that of penetration welding, and the reliability is relatively good. However, the connecting piece needs to be punched, which is relatively difficult to process.

Pulse mode laser welding system for battery pack

When laser welding, the appropriate welding waveform should be selected. Commonly used pulse waveforms include square wave, peak wave, double peak wave, etc.

The aluminum alloy surface of the power battery has too high reflectivity to light. When a high-intensity laser beam hits the surface of the material, 60%-98% of the laser energy on the metal surface will be lost due to reflection, and the reflectivity varies with the surface temperature.

Generally, sharp wave and double peak wave are the best choice when welding aluminum alloy. The slow-down part behind this welding waveform has a longer pulse width, which can effectively reduce the generation of pores and cracks.

Due to the high reflectivity of aluminum alloy to the laser, in order to prevent the laser beam from being incident perpendicularly and causing vertical reflection and damaging the laser focusing lens, the welding head is usually deflected to a certain angle during the welding process.

The diameter of the solder joint and the effective joint surface increases with the increase of the laser tilt angle. When the laser tilt angle is 40°, the largest solder joint and effective joint surface are obtained. The welding point penetration and effective penetration decrease with the laser tilt angle. When it is greater than 60°, the effective welding penetration will drop to zero. Therefore, tilting the welding head to a certain angle can appropriately increase the weld penetration and width.

In addition, when welding, with the welding seam as the boundary, 65% of the laser welding spot must be welded to the cover plate and 35% of the shell, which can effectively reduce the explosion caused by the cover problem.

Continuous mode laser welding machine for battery pack

Because of the heating process of the battery continuous laser welding machine, unlike the pulse laser welding system, the crack tendency is not obvious during welding. In order to improve the quality of the weld, continuous laser welding is used. The surface of the weld is smooth and uniform, without spatter, and defect. No cracks are found in the weld.

In the welding of aluminum alloy case power batteries, the continuous laser has obvious advantages. Compared with traditional welding methods, it has high production efficiency and does not require wire filling; compared with pulse laser welding, it can solve its defects after welding. , Such as cracks, pores, splashes, etc., to ensure that the aluminum alloy has good mechanical properties after welding; it will not sag after welding, and the amount of polishing and grinding after welding is reduced, which saves production costs. However, because the spot of continuous laser is relatively small, it is correct the assembly accuracy of the workpiece is required to be high.

In EV power battery welding, it is necessary to select the appropriate laser and welding process parameters according to the battery material, shape, thickness, and tensile requirements, including welding speed, waveform, peak value, and welding head inclination angle to set reasonable welding process parameters. Ensure that the final welding effect meets the requirements of power battery manufacturers.