How to improve the qualification rate and stability of laser welding in the mass production stage of power battery?

Power batteries provide power for automobiles and determine the safety, reliability and durability of automobiles to a large extent. The special technology of laser welding has been widely used in the manufacturing of batteries and modules.

Taking the square shell core commonly used in power batteries as an example, the laser welding of the cover explosion-proof valve, the laser welding of the pole post, and the laser welding of the cover and shell are introduced.battery pilot line In the aluminum alloy laser welding process, it is easy to produce bursting point, porosity, welding cracks, penetration depth is too large, melt width is too large and other unqualified phenomena, so it is necessary to define the impact of unqualified items, analyze the impact (degree of harm), understand the mechanism of laser welding unqualified, so as to take effective measures to improve the quality and consistency of the laser welding of the high-volume production stage, improve the production line output, reduce the welding failure Qualified, reduce scrap costs.

Common laser welding faults.

1. Battery explosion-proof valve seal welding common faults.

The explosion-proof valve is a pure aluminum round sheet. With infrared fiber laser welding, due to the traditional solid aluminum on the infrared laser reflectivity, and the material is very thin, such as welding technology process is not handled properly, explosion-proof valve in the laser through the welding process is more likely to lead to the emergence of overcooking perforation problems or blow holes,laser welding machine for lithium ion batteries so that the development of the loss of pressure relief and explosion-proof function.

Potential Failure 1: Excessive burning / melting penetration

Cause:With infrared laser welding, due to the solid aluminum alloy surface of the infrared laser reflectivity is high, often use a higher laser power, 0.08 ~ 0.1 mm explosion-proof valve thickness is too small, easy to melt through.

Solution Suggestion: Choose the appropriate welding process parameters, realize the steep rise and fall of laser power, and control the heat input.ESS lithium battery machine Utilizing the pre-peak waveform can increase the laser absorption rate, and the subsequent exponential decay waveform can prevent perforation caused by high power density.

Potential Failure 2: Blowout

Cause: Caused by gas escaping from the molten pool during the laser welding process.

Source of gas: Power car battery covers and explosion-proof valves are thin-thick stamped parts that are prone to residual lubricants and cleaning fluids after processing. In the high power electron density of laser therapy, these are liquids are extremely easy to vaporize and float to the surface of the molten pool, bursting at the same time can produce the need for a large number of spatter and leave a crater on the surface of the actual weld, the formation of blowholes. Explosion-proof valve width-thickness ratio is generally up to about 30, welding due to heat and very easy to produce thermal deformation warping, resulting in explosion-proof valves and the top cover of the assembly of the working gap in the problem of a large amount of research air. Welding of these data residual analysis of air systems subjected to thermal expansion, sprayed out of the molten pool, the formation of blowholes.

Solution Suggestions: Thoroughly clean the cover and explosion-proof valve before welding; Optimize the welding process, the use of pre-welding + weld welding, fixed by spot welding to prevent warping and deformation, reduce blowhole defects.

2. Battery pole welding common faults.

When the power battery is grouped, the connection between positive and negative poles and transfer block is realized by laser welding.

Potential Failure 1: Blowout

Cause:The pole weld is the mating surface between the aluminum adapter and the pole, which is prone to leaving impurities such as lubricants and cleaning agents. The heat from the laser welding causes the impurities left on the pole to vaporize quickly, and gas escapes from the molten pool, resulting in a blown hole.

Solution suggestions: thorough cleaning before welding, remove gas impurities; optimize the design of welding technology process, by improving the power slow rise to reduce blowholes. Optimize the conventional one welding production process into two welding, low-power the first appearance of welding preheating activity material and discharge gas, high power the second welding to make the depth of the melt to meet the development requirements.

3. Battery shell and cover welding common faults

Power battery shell is mainly used Al3003 aluminum alloy, the thickness is generally between 0.6-0.8mm, generally using low power fiber continuous laser welding. The main quality problem of the laser weld here is porosity, which will reduce the sealing performance of the battery.

Potential Failure 1: Porosity

Solution Suggestion: Porosity is mainly a breakdown of metallurgical pores caused by oxide film or water vapor. By reducing the laser power and increasing the welding speed, porosity can be reduced by 1.1%. In order to further reduce the porosity, it is recommended to use galvanic laser instead of pulsed laser spot welding.

Power battery laser welding is a special process, all aspects of the loss of control may affect their own and the vehicle's safety, performance and life. Fully understanding and mastering the laser welding process of power battery and systematically introducing the best practice of laser welding process quality supervision are the basis for ensuring high qualification rate and consistency of laser welding in mass production stage.