Views: 10 Author: Danica Publish Time: 05-31-2021 Origin: Site
In the process of power battery production, the quality and stability of the battery shell welding will affect the consistency and safety of the battery assembly system. The inside of the power battery casing mainly contains organic electrolyte and a special diaphragm, and the cover plate mainly contains explosion-proof valves, poles, safety caps, liquid injection holes, etc. The sealing and welding requirements of the shell and the cover plate are very high, and the welding quality directly affects the sealing degree of the battery. Poor welding can cause problems such as battery leakage, lithium evolution, and battery appearance that does not meet the standard.
Hard shell square lithium battery welding
Common weld problems
1、Poor appearance: welding deviation, blisters, sample tilt;
2、Insufficient strength and sealing: Insufficient penetration, cracks, and pores roughly cause the battery to leak.
Process analysis of weld problems
According to FTA failure analysis, the problem of unqualified welding is mainly summarized as poor appearance and welding strength. Influencing factors of poor appearance: welding equipment CCD scanning accuracy, shielding gas type and flow rate, welding sample cleanliness, sample mechanical matching accuracy and method. Factors affecting welding strength and airtightness: the accuracy of raw material matching, aluminum composition, and process parameters.
The role of protective gas
The shielding gas can prevent the oxidation of the metal surface, protect the lens, and blow off the plasma during the laser welding process. It is necessary to control the airflow direction, pressure, and flow rate. The shielding gas forms a turbulent flow, and the welding seam will have problems such as pores and uneven welding seams.
Different gas characteristics
The types of shielding gas for laser welding include helium, argon and nitrogen.
Helium: High degree of ionization, the laser can pass through, and all beam energy reaches the surface of the workpiece, it is not easy to produce pores, but it is expensive;
Argon gas: The price is lower than helium gas, but it is susceptible to high-temperature plasma ionization. Although the protection effect is better, it will shield part of the laser energy processing, reduce the laser power, and use argon gas to weld the surface smoothly;
Nitrogen: low price, low ionization, and will react with some elements of aluminum alloy during welding to form unstable compounds, which will affect welding strength.
Effect analysis of different welding conditions
Nitrogen and argon are used as shielding gas for welding. When nitrogen is used as shielding gas, the weld width is poor; when argon is used as shielding gas, the weld is smooth, the scales are uniformly improved, and the appearance is better than that of nitrogen welding products.
Laser power affects welding. With the same welding speed and shielding gas, the greater the actual output power, the faster the welding material can melt and gasify, the liquidity of the molten pool increases, the fish-scale surface is more uniform, and the weld seam is flatter.
To sum up:
1、From the perspective of the on-site laser sealing equipment of the terminal, the CCD scanning positioning and welding parameters have an impact on the partial welding problem in the poor appearance.
2、Shielding gas types and parameter settings can improve the uniformity of the weld, ensure the cleanliness of the welding area, reduce the introduction of impurities and foreign bodies, and reduce the pores caused by welding slag.
3、Mechanical fit. The upper clearance fit is better than the interference fit. The method of spot welding and then continuous welding in the field welding process can largely solve the problem of welding stability during clearance fit.
Danica
danica@leapion.com
