Lithium-ion battery laser welding three major anti-spatter technology

The current welding methods for lithium-ion batteries mainly include resistance spot welding, ultrasonic welding and laser welding.

Lithium-ion battery shell is used to seal the battery and electrolyte. Currently commonly used shell material is generally aluminum alloy, in the manufacturing process will be separated from the shell and cover, and then through the welding process to weld the two together. Series-parallel connection between batteries is usually accomplished by welding connectors to individual cells.battery pilot line The connectors are usually made of copper or aluminum, the positive and negative materials are copper or aluminum, and the copper and copper, aluminum and aluminum are usually laser welded.

The safety of the battery pack is very important. Once the relevant failure occurs, it will lead to very serious consequences and threaten people's lives. Among them, the welding of key parts of the power battery pack is a decisive factor for the safety of electric vehicles, and the most important material for these parts is aluminum alloy, including explosion-proof valves, cell seals, pole lugs, and sink bars.laser welding machine for lithium ion batteries The second is copper material, such as pole post and pole ear. The welding quality of these positions will directly affect the quality and reliability of the battery pack.

Therefore, it is necessary to understand the generation of spatter so that we can seek ways to maximize the benefits and eliminate the effects of spatter.

How does spatter form?

What is spatter? Flying spatter is molten metal flying out of a molten cell. When the molten metal reaches its melting temperature, it changes from a solid to a liquid.

When the laser beam is continuously heated, the solid metal becomes liquid, forming a molten pool;ESS lithium battery machine then the liquid metal in the molten pool is heated again until it "boils"; finally, the material absorbs heat and vaporizes again, and the boiling changes the internal pressure, bringing out the liquid metal wrapped around it, and finally producing a "splash! Splash".

The laser continues to act on the material, causing it to vaporize and expand violently, creating a pressure that pushes the material towards the top of the keyhole and adheres to the surface to form a molten substance.

How to control splatter?

How to control splash has become a non-negligible part of laser processing technology. Domestic and foreign companies have started the research of low-splash laser processing technology since a long time ago. By comparing the low splash technology introduced by several mainstream laser manufacturers, you can understand and distinguish their principles.

1. Change the laser spot energy distribution to avoid boiling

Replacing a single Gaussian beam with a more complex ring and center beam reduces the thermal evaporation of the center material and the generation of metallic gases.

Small diameter of the center spot, high energy density, welding using deep penetration welding method, will produce small holes, forming a large depth to width ratio of the molten pool. However, it requires a high clearance, the use of deep penetration welding to form small holes will release a large number of high-pressure metal vapor, easy to cause spatter and explosion. High temperature of the molten pool, the internal flow is intense, the molten pool fluctuation is obvious.

Due to the large diameter of the round weld joints, energy density is small, the use of heat conduction welding, can form a wide molten pool, no spatter, weld seam smooth and beautiful. However, due to the dispersed energy density, it is impossible to obtain a large penetration depth.

Combining the two, by adjusting the appropriate energy ratio, the center spot ensures the depth of the molten pool, while the ring spot increases the width and existence time of the molten pool, which, on the one hand, improves the stability of the small holes and reduces spattering; on the other hand, the flow of the molten pool is more stable, and the bubbles overflow for a long time, and the probability of forming holes is reduced.

2. Change the scanning mode, swing welding

The laser head oscillation can improve the temperature uniformity of the weld and avoid localized boiling caused by high temperature. It only needs to control the x-axis and y-axis of the motion mechanism, it can complete a variety of trajectory swing.

The oscillation welding can only slightly reduce the welding spatter, because the larger the oscillation amplitude, the greater the temperature uniformity of the weld, but the energy density acting on the weld is reduced, the welding speed has to be slowed down. However, when the speed is reduced, the oscillating transverse feed is compressed and increasingly resembles a continuous non-oscillatory state. Material heating time becomes longer, boiling vaporization still exists, spatter and metal vapor can not be completely avoided.

3. Use short wavelengths, increase absorption, and reduce spattering with blue light

Blue light laser is able to realize welding, no porosity and defects which cannot be realized by infrared light. Advantage of blue light: can be in the case of equal heat absorption in the workpiece, by increasing the initial absorption rate, reduce the material breakthrough melting point after the difference in the absorption rate change to reduce the impulse temperature superheat, from the principle of change in the state of the material itself to achieve the avoidance of boiling, bring out the effect of spattering. At the same time can use lower power consumption to complete the dissimilarity welding between different metals, saving swing welding, pre-plating, filler brazing material and other complex processes, opening up a wider range of applicable technology window. Pendulum welding of the electrode section is an excellent welding method. By adding a blue laser to the pendulum welding head, it is possible to obtain a high-quality weld with less surface roughness, no porosity, and almost no spatter.