Over the years of evolution in the lithium battery industry, spot welding equipment has undergone continuous advancements, progressing from the initial AC pulse spot welder to the energy storage spot welder, intermediate frequency spot welder, transistor spot welder, and eventually to the laser spot welder. This ongoing development has led to a consistent enhancement in the quality of spot welding equipment.
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New design lithium battery laser welding machine
The AC pulse spot welder operates by having the thyristor controlled by a single-chip microcomputer intercept the AC pulse voltage to the primary coil of the welding transformer. The transformer then converts the high-voltage pulse into a low-voltage large current, which is outputted to the spot welding needle for discharge spot welding.
The advantages of the AC pulse spot welding machine include its low cost and low failure rate. However, a notable disadvantage is that once the thyristor is triggered and turned on, it must wait until the AC zero-crossing point before turning off. This results in prolonged welding time, which is detrimental to the welding effect. Prolonged welding time increases the temperature of the solder joints, leading to reduced power, virtual welding, frying welding, tin melting, and other issues. This phenomenon is commonly observed in the spot welding of nickel sheets on protective plates, particularly due to the high spot welding temperature of the AC pulse. When spot welding the negative electrode of the aluminum shell or the positive electrode of the steel shell, the small area of the rivets makes heat dissipation challenging, often resulting in the melting of the sealing ring.
The energy storage spot welding machine delivers concentrated discharge energy, resulting in a short welding time and relatively low costs, making it highly suitable for battery spot welding applications. However, it is associated with large welding sparks and a higher failure rate. The performance of the welding machine can decline due to the capacity attenuation of the energy storage capacitor. In recent years, with the increasing trend of welding automation, the charging time of the energy storage capacitor has posed limitations, preventing the quick and stable output of welding energy. Consequently, it is best suited for manual spot welding applications.
The frequency and control method of an inverter welding machine serve as crucial indicators for assessing its performance. Generally, an inverter frequency ranging from 1-10KHz is collectively referred to as intermediate frequency, while frequencies above 10KHz are termed high frequency. In terms of control mode, the primary side constant current is considered an ideal control method. The primary side constant current involves closed-loop control, allowing for the adjustment of high-frequency pulse width based on the actual output current. In less optimal cases, fixed pulse width modulation is adopted, falling under open-loop control.
During spot welding, the spot welding needle and the weldment itself significantly influence the welding process, resulting in relatively poor stability. The preferred frequency for an intermediate frequency welding power supply typically falls within the range of 4-5KHz. This frequency range ensures the attainment of a stable welding waveform at the output end and facilitates effective feedback and control of a large discharge current. It's noteworthy that transformers have a specific response time, and excessively high frequencies may not contribute significantly to the current.
The most optimal resistance welding power source eliminates the need for a welding transformer, enabling rapid current rise and direct high-frequency output of the current waveform. It offers flexibility in selecting control modes, including constant current, constant voltage, or a combination of constant current and constant voltage. However, it comes with the drawback of being relatively expensive.
The laser spot welding machine comprises components such as a crystal, xenon lamp, condensing cavity, optical resonant cavity, cooling filter, and laser power supply. Widely utilized in the battery industry, it finds application in the welding of steel shells and aluminum shell cover plates, with recent advancements extending to the spot welding of polymer PACK protective plates. In comparison to resistance welding, the laser welding machine offers several advantages, including the elimination of the need for spot welding needle grinding, firm and uniform welding, and a reduced likelihood of false welding.
From the production of lithium-ion battery cells to battery pack assembly, welding stands as a critical manufacturing process. The conductivity, strength, airtightness, metal fatigue, and corrosion resistance of lithium-ion batteries serve as crucial quality evaluation standards for battery welding. The choice of welding methods and processes directly impacts the cost, quality, safety, and consistency of lithium-ion batteries.
Among various welding methods, laser welding stands out for lithium-ion battery processing due to the following advantages: Firstly, laser welding offers high energy density, resulting in minimal welding deformation and a small heat-affected zone. This effectively enhances part accuracy, providing smooth, impurity-free, uniform, and dense weld seams without the need for additional grinding work. Secondly, laser welding allows for precise control, featuring a small focus spot and high-precision positioning. It is easily automated with a mechanical arm, leading to improved welding efficiency, reduced man-hours, and cost savings. Additionally, when laser welding thin plates or small diameter wires, it is less susceptible to meltback compared to arc welding.
As a high-precision and high-efficiency welding technology, battery laser welding plays an important role in the manufacture of lithium battery packs. This article will introduce the application of battery laser welding technology in lithium battery packs, and discuss its advantages and future development prospects.
The application of battery laser welding technology in lithium battery pack including ternary lithium battery and lifepo4 battery has the following advantages:
High-precision welding: Battery laser welding can achieve micron-level weld seam control, making the welding connection more uniform and reliable.
Small heat-affected zone: Battery laser welding has the characteristics of high energy density and rapid heating, which makes the heat-affected zone extremely small and reduces thermal damage to surrounding materials.
High efficiency and automation: Laser welding has the ability of high-speed welding and automatic operation, which can greatly improve production efficiency and quality stability.
No need for welding materials: Battery laser welding is a non-contact welding technology that does not require additional welding materials, reducing material costs and pollution.
Lithium battery laser welding machine battery module automatic production line, generally including battery loading, scanning code, testing, cleaning, sorting, module stacking, stacking inspection, module welding, welding inspection, module unloading and other processes .
Material transfer system, self-adaptive system, visual positioning system, MES manufacturing execution management, etc. are the key technologies in battery laser welding, and also important technical support for adapting to small-batch and multi-variety production forms.
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Material transfer system
From cell loading to final module unloading, the entire material transfer is completed through the material transfer system. The material transfer system can also flexibly expand the station according to the adjustment requirements of the process. The transfer between different stations does not require manual operation.
The module positioning plate has a product size adjustment mechanism, which can adapt to the clamping of modules of different sizes, and is very suitable for the production needs of small batches and multiple varieties.
Self-adaptive system
In the production process of battery packs, pouch, prismatic, and cylinders are the most common types of incoming battery packs. After batteries of different types and sizes are stacked into battery packs of different sizes, they need to be adapted after each process. Adaptive system to ensure the linkage of the whole line beat. Especially in the welding process, the packing process can only be completed if modules of different sizes are adapted.
The self-adaptive system adopts multi-axis combined linkage to implement position positioning in the product processing area, and is not restricted by any form of incoming materials, completes the welding work and transmits it to the next process.
Visual positioning system
Cell welding surface cleaning, module marking, and busbar welding are usually done by laser processing. After the battery module is assembled, the dimensional tolerance is often large, and it is difficult to meet the gap position size requirements for laser processing, resulting in a rapid decline in processing quality.
The introduction of the visual positioning system can meet the needs of precise positioning, and the accuracy can reach ± 0.05mm. Through visual camera data collection, and feed back the deviation of incoming materials to the control system, high-precision positioning of the processing position is realized.
MES manufacturing execution management system
From cell loading to final module unloading, the parameters, data, and other incoming material information of each process can be quickly queried and analyzed in a timely manner through the MES system, truly achieving process controllability and high productivity.
The process data package in the battery laser welding process is directly integrated in the MES system. In order to facilitate users to call and switch, the whole set of MES system can directly build the production line into a quasi-unmanned production workshop, and manual labor only needs to replenish materials at the periphery, which improves safety.
The application of battery laser welding technology in lithium battery pack mainly includes the following aspects:
Battery cell connection: Battery laser welding can realize the connection between battery cells to ensure the reliability and stability of the connection. Through laser welding, high-strength welds can be achieved, improving the overall performance of the battery pack.
Battery pack connection: Battery laser welding can be used to different battery hookup, ensuring electrical and mechanical connection between modules. The high precision and high efficiency of laser welding make the module connection more firm and reliable.
Conductive sheet connection: Laser welding can be used to connect conductive sheets and battery cells to realize current transmission. The high energy density of battery laser welding can quickly complete the welding process and ensure the stability and conductivity of the connection.
The energy storage battery is a whole composed of battery energy storage equipment, PCS and filtering links. In the field of laser welding of energy storage batteries, pulsed lasers, continuous lasers, and quasi-continuous lasers are currently the most used.
The welding advantages of laser welding equipment in terms of energy storage batteries include the following aspects:
The welding process is non-contact welding, and the internal stress of the welding rib is reduced to the minimum during the welding process;
The welding process does not produce other flashes and other released substances to prevent secondary pollution;
The strength and airtightness of the welding are high, which can meet the functional requirements;
Battery laser welding can meet the welding between different substances, and can also realize the connection technology between membrane materials and heterogeneous substances;
Battery laser welding is convenient for automatic integration, and can also achieve synchronous laser welding process schemes according to production capacity needs, with high efficiency and small welding internal stress;
The structure involved in battery laser welding is simple and convenient, and the difficulty factor of the mold structure is reduced;
The welding process can realize digital intelligent monitoring, which meets the needs of data visualization in the welding process;
This type of welding process scheme can be effectively integrated with automated production lines, meeting the needs of mass production schemes, achieving high-efficiency production, and low consumption.
The application of laser welding technology in lithium battery packs is still developing and has broad prospects:
Further improve efficiency: With the continuous innovation and improvement of laser welding technology, its welding speed and quality will be further improved, further improving production efficiency and reducing costs.
Adapt to a variety of materials: Battery laser welding technology can be applied to different types of materials, including different battery cells and conductive sheet materials, which improves applicability and flexibility.
Develop intelligent production: The combination of laser welding technology and intelligent production can realize automatic operation and real-time monitoring, and improve production efficiency and quality control.
The application of battery laser welding technology in lithium battery packs has a wide range of advantages, including high-precision welding, small heat-affected zone, high efficiency and automation.
With the continuous development and innovation of technology, the application prospect of battery laser welding in the manufacture of lithium battery energy storage pack is very broad. It will continue to promote the development of lithium battery energy storage technology for top 10 energy storage lithium battery companies and provide reliable support for the promotion and application of clean energy.
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