As an efficient and precise connection method, laser welding has obvious advantages: high processing efficiency, high processing precision, 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.

Power batteries have many laser welding parts. The materials are mainly aluminum alloys. A small number of parts are made of copper, nickel and other materials, and a very few use stainless steel as the battery casing. Among these materials, the laser welding process of nickel and stainless steel is relatively simple. It is also more mature, but there are still many difficulties in laser welding of aluminum alloy and copper. In addition to the influence of material properties, the state of the welded joint will also have a greater impact on the welding effect.

Type and status of materials to be welded

Type of material to be welded 

When aluminum alloy and copper are used as materials to be welded, the main reasons for the poor results of conventional laser welding are:

① Both are highly reflective materials for fiber lasers, and their absorption rate for fiber lasers is not high, resulting in poor stability of the welding process;

②The thermal conductivity of the two is better, but the welding seam is difficult to form and pores are easy to occur.

At the same time, there are certain differences between the two materials. Relatively speaking, the absorption rate of aluminum alloy for fiber laser is higher than that of red copper, and the thermal conductivity of red copper is better than that of aluminum alloy. Therefore, the solutions to the difficulties of laser welding between the two are: In the same places, there are also certain differences:

Aluminum alloy

1. Use a relatively small focused spot (0.1mm~0.3mm) for welding;

2. The welding speed cannot be too low and should be controlled above 60mms;

3. Use fiber-semiconductor laser hybrid welding; 

4. Use swing welding.

Copper 

1. Use a smaller focused spot (0.02mm~0.2mm) for welding;

2. The welding speed should be fast, it is recommended to be above 100mms;

3. Use swing welding. 

Material status to be welded

The state of the material to be welded described in this article refers to the surface cleanliness and pretreatment degree of the material. These conditions will lead to poor weld quality. Specific results and solutions:

There are impurities on the surface of the material

Difficulties: there are pores in the welds, insufficient sealing, and insufficient strength; there are explosion points in the welds, and the product is scrapped.

Solution: Impurities such as oil stains and water stains need to be removed from the materials to be welded before welding. 

Aluminum alloy surface oxide is not cleaned

Difficulties: The weld seam has more pores, insufficient sealing, and insufficient strength; the molding is unstable and the yield rate is reduced.

Solution: Remove the oxide film from the materials to be welded before welding, and then weld as soon as possible.

The material to be welded is rough

Difficulties: uneven molding, poor appearance; prone to welding leaks, no sealing. Solution: The material must be machined and must be flat and without deformation.

Types and requirements of components to which welds belong

There are currently three mainstream automotive power batteries, namely prismatic batteries, cylindrical batteries and Pouch pack batteries. The prismatic battery is the most commonly used, and it is also the battery type with the most laser welding parts. The market share of the other two types of batteries and the demand for laser welding are relatively much less. The main problems of welds are insufficient strength, insufficient sealing and poor shaping, which lead to the occurrence of these problems. Their commonality is that the selection of the welding process is incorrect. In addition, there are welding difficulties caused by the structure of the part to be welded and its weld requirements. , specific situations and solutions:

Pouch pack battery component lug bus

Difficulties in welding: The material is thin, and multiple pieces are easily welded together, resulting in insufficient strength and poor conductivity.

Solution: Control the flatness of incoming materials; design clamps with excellent performance and control the clamping gap.