At present, there are three mainstream automotive power batteries, namely square lithium battery, cylindrical lithium battery and soft pack lithium battery.

The most commonly used is the square battery, and it is also the battery type with the most laser welding parts. The market share and laser welding demand of the other two types of batteries are relatively much less.

The main problems of the weld are insufficient strength, insufficient sealing and poor forming, which lead to these problems. Their commonness is due to the incorrect selection of welding process. In addition, there are welding difficulties caused by the structure of the parts to be welded and the requirements of the weld.

Let's take a look at the difficulties and solutions of laser welding of square aluminum shell lithium battery together with HGLASER editor.

There are many laser welding parts of square lithium battery, which are mainly made of aluminum alloy, a few parts are made of red copper, nickel and other materials, and very few parts are made of stainless steel as the battery shell.

Among these materials, the laser welding process of nickel and stainless steel is relatively simple and more mature, but there are still many difficulties in the laser welding of aluminum alloy and red copper. In addition to the influence of material characteristics, the state of welded joint will also have a great influence on the welding effect.
 

Welding difficulties and solutions in the types and states of materials to be welded

1. Type of material to be welded

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

1) Both belong to high reflection materials for fiber laser, and the absorption rate of fiber laser is not high, resulting in poor stability of welding process;

2) Both have good thermal conductivity, difficult weld forming and easy to produce pores;

At the same time, there are some 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 are the same and there are some differences:

aluminium alloy

1. Relatively small focusing spot (0.1mm ~ 0.3mm) is used for welding;

2. The welding speed shall not be too low and shall be controlled above 60mm / S;

3. Optical fiber semiconductor laser hybrid welding is adopted;

4. Swing welding is adopted.

Red copper

1. Use a small focus spot (0.02mm ~ 0.2mm) for welding;

2. The welding speed should be fast, and it is recommended to be more than 100mm / S;

3. Swing welding is adopted.

2. Status of materials to be welded

The state of materials to be welded in this paper refers to the surface cleanliness and pretreatment degree of materials, which will lead to poor weld quality. Specific results and solutions:

There are impurities on the material surface;

There are pores in the weld, the tightness is not enough, and the strength is not enough;

The weld has a burst point and the product is scrapped.

Solution:

Impurities such as oil stain and water stain shall be removed before welding the materials to be welded.

The oxide on the surface of aluminum alloy is not cleaned

Difficulties:

There are many pores in the weld, the tightness is not enough, and the strength is not enough;

The forming is unstable and the yield is reduced.

Solution:

The materials to be welded shall be treated with de oxide film before welding, and then welded as soon as possible.

3、 Rough processing of materials to be welded

Difficulties:

Uneven forming and poor appearance;

It is prone to welding leakage and has no sealing property.

Solution:

The materials shall be machined and leveled without deformation.

When the square battery is combined and welded, the pole column or connecting piece is polluted and thick. When the connecting piece is welded, the pollutants decompose, which is easy to form welding explosion points and cause holes; The battery with thin pole and plastic or ceramic structural parts under it is easy to be welded through. When the pole is small, it is easy to weld to the plastic burning loss and form explosion point. Do not use multi-layer connecting pieces. There are pores between layers and it is not easy to weld firmly.

The most important procedure in the welding process of square battery is the packaging of shell cover, which is divided into the welding of top cover and bottom cover according to different positions. Due to the small volume of batteries produced by some battery manufacturers, the "deep drawing" process is adopted to manufacture the battery shell, which only needs to weld the top cover. Therefore, when selecting laser welding equipment, it is necessary to select appropriate welding process and welding equipment according to different weldment requirements. HGLASER specialty provides overall solutions for laser welding, and can customize laser welding equipment according to requirements to realize semi-automatic and automatic production.