Full analysis of square shell battery PACK production line: key processes, technical points and quality control

With the explosive growth of the new energy automobile industry, square shell power battery has become one of the mainstream technology routes in the current power battery market due to its advantages such as high energy density, strong structural stability and long cycle life. As the core link of connecting the battery cells to the end point application, the process level of square shell battery PACK production line directly determines the performance, safety and consistency of the battery pack. This paper will systematically share the expertise of square shell battery PACK production line from the four dimensions of the core process of the production line, key process details, technical difficulties and quality control system.

Square shell battery PACK refers to the combination of multiple square shell cells in series and parallel to form a module, and then integrate the thermal management system, battery management system (BMS), high and low voltage wiring harness and box to form a battery pack with complete power supply function. The core process of its production line can be divided into five links: cell pretreatment and sorting, module assembly, PACK final assembly, full inspection and testing, packaging and warehousing. Each link contains several high-precision process steps, and the details need to be strictly controlled to ensure product quality.

Cell pretreatment and sorting are the foundation of module assembly. Due to the small parameter differences (such as voltage, capacity, internal resistance, and self-discharge rate) in the production process of square shell cells, direct assembly will lead to uneven performance of the module. Therefore, the production line needs to be equipped with high-precision cell sorting equipment. The cells are tested in multiple dimensions through voltage internal resistance testers, capacity testers, etc., and the cells with consistent parameters are classified as the same batch to provide basic protection for subsequent module assembly. In addition, the surface cleaning of the cells is also a key step in pretreatment. Automated cleaning equipment is required to remove dust and oil on the surface of the cells to avoid affecting the welding quality.

The module assembly process is one of the core processes of the square shell battery PACK production line. This process mainly includes three steps: battery cell stacking, pole ear welding, and module packaging. The battery cell stacking is completed by automated robots. The sorted cells are stacked in a predetermined order, and thermal insulation spacers and buffer materials are placed between the cells to improve the safety of the module. Laser welding technology is usually used for pole ear welding. Due to its high welding accuracy and small heat-affected zone, it can effectively ensure the strength and conductivity of the pole ear connection. A real-time monitoring system is required during the welding process to determine whether there are defects such as virtual welding and missed welding in the weld through visual detection technology. Module packaging involves placing the stacked and welded battery cells into the aluminum alloy module frame, injecting heat-conducting glue and curing, and integrating module-level thermal management components (such as water cooling plates) to achieve the heat dissipation requirements of the module.

The PACK assembly process is the key step to convert the module into a complete battery pack. This process includes four core steps of module fixing, wiring harness connection, BMS integration, and box sealing. The module fixing adopts automatic tightening equipment, and multiple modules are fixed in the PACK box according to the design position to ensure that the spacing between the modules meets the design requirements. The wiring harness connection needs to complete the docking of high and low voltage wiring harnesses in strict accordance with the circuit diagram. The connection points need to be insulated and waterproof sealed. BMS integration is to communicate and connect the battery management system with the module to realize the condition monitoring, charge and discharge control and safety protection of the battery pack. The box sealing adopts laser welding or sealant process to ensure that the battery pack reaches the protection level above IP67 and prevents water and dust from entering the interior.

The full inspection and testing link is the last line of defense to ensure the quality of square shell battery PACK. This link covers three categories: electrical performance test, environmental adaptability test, and safety performance test. Electrical performance test includes capacity test, internal resistance test, charge and discharge cycle test, voltage balance test, etc., to verify the basic electrical performance of the battery pack. Environmental adaptability test includes high and low temperature cycle test, vibration test, salt spray test, etc., to simulate the extreme environmental conditions of the battery pack in actual use. Safety performance test includes overcharge and discharge test, short circuit test, extrusion test, puncture test, etc., to evaluate the safety performance of the battery pack under abnormal conditions. In addition, the production line needs to be equipped with an AOI visual inspection system to comprehensively inspect the appearance of PACK, wiring harness connections, and solder joints to ensure that the product appearance and structure meet standards.

The quality control system is an important support for the square shell battery PACK production line. The production line needs to establish a whole-process traceability system to record the production information of each cell, module and PACK through QR code or RFID technology, so as to realize the whole life cycle traceability from raw materials to finished products. At the same time, the production line needs to introduce intelligent manufacturing technology, which monitors and analyzes the parameters in the production process in real time through the MES system, and timely detects production abnormalities and adjusts process parameters. In addition, regular equipment calibration and personnel training are also the key to quality control, ensuring that the production line equipment is in the best condition and the operators have professional skills.

The technical difficulties of the square shell battery PACK production line mainly focus on the integration of thermal management and automated flexible production. In terms of thermal management integration, due to the large size of the square shell battery, the uniformity of heat dissipation is a key issue. The production line needs to precisely control the installation position of the thermal management components and the coating amount of thermal conductive materials to achieve efficient heat dissipation of the battery pack. In terms of automated flexible production, with the diversification of new energy vehicle models, the specifications of battery packs are also increasing. The production line needs to have the ability to quickly switch production specifications. Through modular design and intelligent scheduling system, the mixed-line production of multi-variety battery packs can be realized.

In the future, the square shell battery PACK production line will develop in the direction of intelligence, greening and efficiency. In terms of intelligence, digital twin technology will be introduced to simulate the actual production process through a virtual production line to optimize process parameters and production processes. In terms of greening, energy-saving equipment and environmentally friendly materials will be used to reduce energy consumption and waste emissions in the production process. In terms of efficiency, the automation of the production line will be further enhanced, the production cycle will be shortened, and production efficiency will be improved. These development trends will promote the technological upgrading of the square shell battery PACK production line, providing strong support for the development of the new energy automobile industry.