SHINHOP laser

Laser welding, as an efficient and precise connection method, has obvious advantages: high processing efficiency, high processing accuracy, small heat-affected zone, small deformation of welded parts, high degree of automation, etc. Applying laser welding to automotive power battery welding can greatly improve its safety, reliability, and service life.
There are many laser welding joints in power batteries, and the materials are mainly aluminum alloys, with a small number of parts using copper, nickel, etc., and a very small number using stainless steel as the battery shell. Among these materials, the laser welding process for nickel and stainless steel is relatively simple and more mature, but there are still many difficulties in laser welding of aluminum alloys and copper. In addition to the influence of material characteristics, the state of the welding joint also has a significant impact on the welding effect.
Types and states of materials to be welded
1. Types of materials to be welded
When aluminum alloys and copper are used as materials to be welded, the main reasons for poor laser welding effects in conventional methods are:
① Both are high-reflective materials for fiber lasers, with low absorption rates for fiber lasers, leading to poor stability during the welding process;
② Both have good thermal conductivity, making it difficult to form weld seams and prone to porosity.
At the same time, these two materials also have certain differences. Relatively speaking, aluminum alloys have a higher absorption rate for fiber lasers than copper, while copper has better thermal conductivity than aluminum alloys. Therefore, the solutions to the difficulties in laser welding for both have similarities, but also certain differences:
1. Aluminum alloy
1) Use a relatively small focused spot (0.1mm to 0.3mm) for welding;
2) The welding speed should not be too low, controlled above 60mm/s;
3) Use fiber-semiconductor laser hybrid welding;
4) Use oscillation welding.
2) Copper
1) Use a smaller focused spot (0.02mm to 0.2mm) for welding;
2) The welding speed should be fast, recommended above 100mm/s;
3. Use oscillation welding.
2. State of materials to be welded
The state of materials to be welded mentioned in this article refers to the surface cleanliness and pre-treatment level of the materials, which can lead to poor weld quality. Specific results and solutions:
1. Impurities on the surface of the material
Difficulties manifested:
Weld seams have porosity, insufficient sealing, and insufficient strength;
Weld seams have blowholes, leading to product scrap.
Solutions:
Impurities such as oil and water stains must be removed from the materials to be welded before welding.
2. Oxides on the surface of aluminum alloy not cleaned
Difficulties manifested:
Weld seams have many pores, insufficient sealing, and insufficient strength;
Unstable forming, reduced yield.
Solutions:
Deoxidation treatment should be performed on the materials to be welded before welding, and welding should be done as soon as possible.
3. Rough processing at the welding area of the material
Difficulties manifested:
Uneven forming, poor appearance;
Prone to welding leaks, no sealing.
Solutions:
Materials should be machined to be flat and without deformation.
Types and requirements of components for weld seams
Currently, there are three mainstream types of automotive power batteries: square batteries, cylindrical batteries, and soft pack batteries. The most commonly used is the square battery, which is also the type with the most laser welding joints. The other two types of batteries have relatively much smaller market shares and laser welding demands. The main problems with weld seams are insufficient strength, insufficient sealing, and poor forming, which arise mainly due to incorrect selection of welding processes, as well as welding difficulties caused by the structure of the welding area and the requirements of the weld seams. Specific situations and solutions:
1. Soft pack battery components
1. Tabs/Busbars

1) Welding difficulties:
Thin materials, multiple layers of welding are prone to weak welds, leading to insufficient strength and poor conductivity.
Solutions:
Control the flatness of incoming materials;
Design high-performance fixtures to control clamping gaps.
2) Welding difficulties:
Insufficient weld seam connection width leads to insufficient strength.
Solutions:
Select small core fiber lasers and use oscillation welding.
2. Cylindrical battery components

21700 battery cap
Welding difficulties:
Thin materials, prone to burn-through, strength not achieved.
Solutions:
Control the consistency of incoming materials;
Design high-performance fixtures to control clamping gaps.
Select a small core fiber laser and use a galvanometer for high-speed (above 300mm/s) welding.
3. Module

Welding difficulties:
The depth of fusion requirement is large, and the weld formation is poor.
Solutions:
Select a laser with a fiber core diameter of 50μm to 100μm, and utilize higher power for high-speed welding (above 80mm/s).
4. Square battery component

Liquid injection hole (top left), flip piece (top right), pole (bottom left), explosion-proof valve (bottom right)
Welding difficulties:
There are many air holes, which can easily lead to explosion points, resulting in insufficient sealing.
Solutions:
Improve the cleanliness of the area to be welded;
By selecting a fiber laser with a 50μm core, the welding speed can be increased appropriately.
5. Shell sealing

1) Welding difficulties:
There are many air holes, which can easily lead to explosion points, resulting in insufficient sealing.
Solutions:
Improve the cleanliness of the area to be welded;
By selecting a fiber laser with a 50μm core, the welding speed can be increased appropriately.
Select a small core fiber laser + semiconductor laser for composite welding.
2) Welding difficulties:
The four corners of the square weld are prone to burn through, leading to insufficient sealing.
Solutions:
Choose a welding platform with better acceleration performance;
Use a higher welding speed to shorten the laser exposure time at the corners.
3) Welding difficulties:
Weld formation is uneven, and processing efficiency is not high enough.
Solutions:
Select a small core fiber laser + semiconductor laser for composite welding.
6. Busbar

1) Welding difficulties:
Thin materials, multiple layers of welding are prone to weak welds, leading to insufficient strength and poor conductivity.
Solutions:
Control the flatness of incoming materials;
Design high-performance fixtures to control clamping gaps.
2) Welding difficulties:
Insufficient weld seam connection width leads to insufficient strength.
Solutions:
Select small core fiber lasers and use oscillation welding.
7. Side plate

Welding difficulties:
There are many welding areas, and efficiency requirements are high.
Solutions:
Choose a high-power fiber laser for remote scanning welding.
8. Soft connection
1) Welding difficulties:
Thin materials, multiple layers of welding are prone to weak welds, leading to insufficient strength and poor conductivity.
Solutions:
Control the flatness of incoming materials;
Design high-performance fixtures to control clamping gaps.
2) Welding difficulties:
Insufficient weld seam connection width leads to insufficient strength.
Solutions:
Select small core fiber lasers and use oscillation welding.