The application of precision laser welding machine in automotive air conditioning pipelines

Application of laser welding in the field of lithium batteries

Lithium-ion batteries are widely used in various electronic devices (such as mobile phones, laptops, PDAs, digital cameras and digital video cameras, etc.) and transportation tools (patrol cars, electric bicycles, electric vehicles, etc.) due to their high specific energy, long cycle life, low self-discharge, no memory effect and no pollution. They have become a high-tech industry that is supported by my country’s energy field.

Power batteries refer to batteries used in electric vehicles. They are relative to small-capacity batteries (such as mobile phones and laptop batteries). They have large capacity and output power and can be used as secondary batteries in the fields of electric vehicle driving power and large mobile power applications. There are many production processes for lithium-ion batteries or battery packs, and many of them, such as explosion-proof valve sealing welding, pole ear welding, soft connection welding, helmet spot welding, battery shell sealing welding, module and PACK welding, are all based on laser welding as the best process. The materials used for welding power batteries are mainly pure copper, aluminum and aluminum alloys, stainless steel, etc.

1. Battery explosion-proof valve welding

The battery explosion-proof valve is a thin-walled valve body on the battery sealing plate. When the internal pressure of the battery exceeds the specified value, the explosion-proof valve body ruptures to prevent the battery from bursting. The safety valve has an ingenious structure, and this process has extremely strict requirements on the laser welding process. Before the use of continuous laser welding, the welding of battery explosion-proof valves was all done by pulse laser welding, and continuous sealing welding was achieved by overlapping and covering the welding points, but the welding efficiency was low and the sealing was relatively poor. The use of continuous laser welding can achieve high-speed and high-quality welding, and the welding stability, welding efficiency and yield can be guaranteed.

2. Battery pole ear welding

The pole ear is usually divided into three materials. The positive electrode of the battery uses aluminum (Al) material, and the negative electrode uses nickel (Ni) material or copper-plated nickel (Ni-Cu) material. In the manufacturing process of power batteries, one of the links is to weld the battery pole ear to the pole. In the production of secondary batteries, it needs to be welded together with another aluminum safety valve. Welding must not only ensure reliable connection between the pole ear and the pole, but also require the weld to be smooth and beautiful.

3. Spot welding of battery pole strips

The materials used for battery pole strips include pure aluminum strips, nickel strips, aluminum-nickel composite strips, and a small amount of copper strips. The welding of battery pole strips generally uses a pulse welding machine. With the emergence of IPG’s QCW quasi-continuous laser, it has also been widely used in battery pole strip welding. At the same time, due to its good beam quality and small welding spot, it has unique advantages in dealing with high-reflectivity aluminum strips, copper strips, and narrow-band battery pole strips (pole strip width below 1.5mm).

4. Power battery shell and cover plate sealing welding

The shell materials of power batteries are aluminum alloy and stainless steel. Among them, aluminum alloy is the most commonly used, generally 3003 aluminum alloy, and a few use pure aluminum. Stainless steel is the material with the best laser weldability, especially 304 stainless steel. Whether it is pulse or continuous laser, it can obtain welds with good appearance and performance.

The laser welding performance of aluminum and aluminum alloys varies slightly depending on the welding method used. Except for pure aluminum and 3 series aluminum alloys, which can be welded with pulse welding and continuous welding without any problems, other series of aluminum alloys are best welded with continuous laser welding to reduce crack sensitivity. At the same time, select a laser with appropriate power according to the thickness of the power battery shell. Generally, when the shell thickness is less than 1mm, a single-mode laser within 1000W can be considered. When the thickness is above 1mm, a single-mode or multi-mode laser of more than 1000W is required.

Small-capacity lithium batteries often use relatively thin aluminum shells (thickness is about 0.25mm), and some 18650 and other batteries use steel shells. Due to the thickness of the shell, the welding of such batteries generally uses a lower-power laser. Using continuous lasers to weld thin-shell lithium batteries can increase efficiency by 5 to 10 times, and the appearance and sealing are better. Therefore, there is a trend of gradually replacing pulse lasers in this application field.

5. Power battery module and pack welding

The series and parallel connection between power batteries is generally completed by welding the connecting piece and the single battery. The positive and negative electrodes are made of different materials, generally copper and aluminum. Since copper and aluminum form brittle compounds after laser welding, they cannot meet the use requirements. In addition to ultrasonic welding, copper and copper, aluminum and aluminum are generally welded by laser. At the same time, since copper and aluminum have fast heat transfer and very high laser reflectivity, the thickness of the connecting piece is relatively large, so a higher power laser is required to achieve welding.