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.
The laser welding joints of power batteries are numerous, and the materials are mainly aluminum alloys, with a small number of parts using copper, nickel, and a very few 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

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 materials are considered high-reflective materials for fiber lasers, with low absorption rates for fiber lasers, leading to poor stability during the welding process;

② Both materials 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 of the two materials have similarities as well as certain differences:

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 oscillating welding. 

Copper

1. Use a small focused spot (0.02mm to 0.2mm) for welding;

2. The welding speed should be fast, recommended above 100mm/s;

3. Use oscillating welding.

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. The specific results and solutions are as follows:

Impurities on the surface of the material

Difficulties: The weld seam has porosity, insufficient sealing, and insufficient strength; the weld seam has blowholes, leading to product scrap.

Solution: Remove impurities such as oil stains and water stains from the materials to be welded before welding.

Oxides on the surface of aluminum alloy not cleaned

Difficulties: The weld seam has many pores, insufficient sealing, and insufficient strength; unstable forming, reduced yield.

Solution: Perform deoxidation treatment on the materials to be welded before welding, and then weld as soon as possible.

Rough processing at the welding area of the material

Difficulties: Uneven forming, poor appearance; prone to welding leaks, no sealing. Solution: The material should be machined to be flat and without deformation.

Type and Requirements of Components Associated with Weld Seams

Currently, there are three mainstream types of automotive power batteries: square batteries, cylindrical batteries, and pouch batteries. The most commonly used is the square battery, which is also the battery type with the most laser welding areas. The other two types of batteries have relatively smaller market shares and laser welding demands. The main problems with weld seams are insufficient strength, insufficient sealing, and poor forming. The common cause of these problems is the incorrect choice of welding process. Additionally, there are welding difficulties caused by the structure of the welding area and the requirements of the weld seams. The specific situations and solutions are as follows:

Pouch Battery Component Tabs/Busbars

Welding difficulties: Thin materials, multiple layers of overlapping welding are prone to weak welding, leading to insufficient strength and poor conductivity.

Solution: Control the flatness of incoming materials; design high-performance fixtures to control clamping gaps.

Cylindrical Battery Component 21700 Battery Cap

Welding difficulties: Thin materials, prone to burn-through, strength not met.

Solution: Control the consistency of incoming materials; design high-performance fixtures to control clamping gaps; use small core fiber lasers and weld with high speed (above 300mm/s).

Module

Welding difficulties: High penetration requirements, poor weld seam formation.

Solution: Select a laser core with a diameter of 50μm to 100μm, and utilize higher power for high-speed welding (exceeding 80mm/s).

Square Battery Component Injection Hole, Flip Plate, Pole, Explosion-proof Valve Welding Difficulties: Many pores, prone to blowholes, leading to insufficient sealing.

Solution: Enhance the cleanliness of the welding area; opt for a fiber laser with a 50μm core, which allows for an increase in welding speed.

Shell Sealing

Welding difficulties: Many pores, prone to blowholes, leading to insufficient sealing.

Solution: Enhance the cleanliness of the welding area; opt for a fiber laser with a 50μm core, which allows for an increase in welding speed; employ a small core fiber laser combined with a semiconductor laser for hybrid welding.

Welding difficulty: The four corners of the square weld are prone to burn-through, leading to insufficient sealing.

Solution: Choose a welding platform with better acceleration performance; use a higher welding speed to shorten the laser exposure time at the corners.

Welding difficulty: Uneven weld formation, insufficient processing efficiency.

Solution: Use a small core fiber laser + semiconductor laser for composite welding.

Busbar

Welding difficulties: Thin materials, multiple layers of overlapping welding are prone to weak welding, leading to insufficient strength and poor conductivity.

Solution: Control the flatness of incoming materials; design high-performance fixtures to control the clamping gap. Welding difficulty: Insufficient weld connection width leading to insufficient strength. Solution: Use a small core fiber laser and employ oscillation welding.

Side plate

Welding difficulty: Many welding points, high efficiency requirements.
Solution: Choose a high-power fiber laser for remote scanning welding.

Soft connection

Welding difficulties: Thin materials, multiple layers of overlapping welding are prone to weak welding, leading to insufficient strength and poor conductivity.

Solution: Control the flatness of incoming materials; design high-performance fixtures to control clamping gaps.

Welding difficulty: Insufficient weld connection width leading to insufficient strength.

Solution: Use a small core fiber laser and employ oscillation welding.