A Deep Dive into Factors Affecting Battery Pack Airtightness

Carbon steel sheet metal box?

Typically, the carbon steel sheet metal box is directly spliced and then spot welded after it has been stamped into parts using sheet metal. Controlling the welding current is the first step in preventing welding penetration or leakage.

Second, the box needs to be shaped after it has been welded and formed, paying particular attention to making sure the sealing surface is smooth and free of burrs. Thirdly, the paint film's surface roughness on the plug-in installation surface must be preserved.?

Aluminum alloy profile box?

Currently, it is fairly common practice to combine "aluminum profile extrusion molding + stirring friction welding + cold metal transition (CMT) welding". The following are the precise control points:

Priority one should be given to preventing partial seams, welding penetration, and CMT leakage.

Second, the friction welding and stirring processes will cause the box body to deform due to the high heat generated by the contact between the tool and the bottom plate of the box. This will result in the box cover being pressed tightly during assembly, and the uneven local pressure of the gasket will form a different compression deformation rate. Air leakage will happen when there is a pressure differential between the battery pack's interior and exterior. Stirring friction welding is advised with a speed of 800–1000 mm/min and recommended parameters of 1600–1800 rpm to minimize deformation and welding defects.

CMT repair welding comes in second. Generally speaking, manual welding must be used when stirring friction welding is offline. This welding must be done correctly in areas where air leaks or subpar welding may occur, particularly in the binding portion of the box sealing surface frame, which has a thickness of 2 mm. Owing to the properties of the aluminum alloy material itself, virtual welding is easily produced when the welding current is too small and the welding depth is insufficient; thread welding and plate cracking are also easily produced when the welding current is too large.

It is frequently necessary to ser facing at the seams to ensure the welding strength, and the height is typically ≤2.5mm. But the high weld will result in uneven angles and spaces between the weld and the surface of the flange. The gasket will be subjected to various extrusion stresses during the assembly process when the box cover compresses it, and the weld must be polished to create the ideal arc transition shape. Force is applied to the gasket during assembly, filling the space around the weld and providing a good seal.

To minimize welding deformation and the likelihood of welding defects, it is essential not only to modify the stirring friction welding process parameters but also to construct a sturdy welding fixture.?

Aluminum die-casting box?

One mold for the aluminum die-casting box is possible. The primary goal of the improvement points is to prevent manufacturing defects like "trachoma" and slag in alloy materials. Furthermore, the sealing strip installation surface flatness and accuracy on the aluminum die casting box body must meet strict specifications, and the installation plane must be fine-tuned. The die-cast aluminum box works well with small battery packs in general. The welding process can be added to make up for the larger battery box size. Large battery packs require careful consideration from the standpoints of process realization and lightweight.?

Gasket?

The airtightness of the entire package is largely dependent on the gasket. While preventing permanent deformation, the material should have flame-retardant qualities and adhere to the industry's standard requirements for substances that are prohibited in the automobile industry. The material for the gasket can be silicone foam.

The same test environment and test conditions were used for the entire test. The test data results demonstrate that the permanent deformation force of the gasket varies significantly depending on the compression rate. On the other hand, the greater the compression rate, the less leakage there is and the better the air tightness. It is necessary to take into account in the design the relationship between the compression rate and the permanent deformation rate. The gasket's width should, to the greatest extent feasible, cover the entire box's sealing surface when choosing the proper compression rate.?

Battery case cover?

Battery lid products vary widely in terms of toughness and strength due to various molding and manufacturing processes. The installation of the battery bag cover can lead to uneven force and cracking, thereby compromising the battery pack's airtightness. When making design improvements, consideration must be given to the use environment and the particular needs of the battery pack. To lower the chance of cracking, the SMC battery cover, for instance, can optimize the location of the fiber distribution and increase the radius of the flange edge and the facade of the box cover.?

Electrical connector?

The airtightness of the battery pack has the strongest correlation with the electrical connector's quality. The electrical plug-in's primary areas for improvement are its sealing, particularly the way the pin position is sealed, the plug-in's installation surface's flatness, the O-shaped sealing ring's permanent deformation, etc. all of which have an impact on how airtight the battery pack is.?

Explosion-proof and breathable valve?

The breathable, explosion-proof valve serves as both an external sealant and an internal exhaust system, adding safety to the battery pack. Its air tightness specifications are comparable to those of electrical connectors, but the explosion proof and breathable valve's service life must last the duration of the battery pack. As a result, in addition to carefully taking into account its sealing, the design improvement also has higher service life requirements.?

In conclusion, ensuring a well-sealed battery pack requires a multi-faceted approach. Precise welding techniques, meticulous gasket selection, and robust designs for components like the cover and valves are all crucial. By prioritizing these factors throughout the manufacturing process, we can guarantee optimal battery performance and safety. This not only extends battery life but also minimizes potential safety hazards, making electric vehicles and energy storage systems more reliable and dependable.

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About Semco?- Established in 2006, Semco Infratech has secured itself as the number 1 lithium-ion battery assembling and testing solutions provider in the country. Settled in New Delhi, Semco provides turnkey solutions for lithium-ion battery assembling and precision testing with an emphasis on Research and Development to foster imaginative, future-proof products for end users.

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