Laser Welding Is Used in Energy Storage Battery And PACK Production Lines

From the manufacture of energy storage battery cells to the assembly of battery PACKs, welding is a very important manufacturing process. The conductivity, strength, air tightness, metal fatigue and corrosion resistance of lithium batteries are typical battery welding quality evaluation standards. The selection of welding methods and welding processes will directly affect the cost, quality, safety and consistency of the battery. 

Among many welding methods, laser welding stands out with the following advantages: First,laser welding has high energy density, small welding deformation, and small heat-affected zone, which can effectively improve the precision of parts, and the weld is smooth, free of impurities, uniform and dense, and no additional grinding work is required;

Secondly, laser welding can be precisely controlled, with a small focused spot and high-precision positioning. It is easy to realize automation with a robotic arm, improve welding efficiency, reduce working hours and reduce costs; in addition, when laser welding thin plates or thin-diameter wires, it will not be as easily troubled by remelting as arc welding.

The main welding methods for energy storage batteries include wave welding, ultrasonic welding, laser welding, and dissimilar metal laser welding, among which laser welding is currently the most mainstream welding method.

Energy storage battery welding methods:

① Wave welding: It is essentially a combination of ultrasonic welding and laser welding;

② Ultrasonic welding: The advantage of this solution is that welding is simple, but it takes up more space and the volume grouping efficiency of the module will be lower;

③ Laser welding: This solution is currently the most widely used, but the structure is slightly different;

④ Dissimilar metal laser welding: This welding method also has high grouping efficiency and fast production speed.

What is laser welding?

Laser welding is to use an optical system to use a high-energy-density laser beam as a heat source, focus the laser beam in a very small area, and form a heat source area with highly concentrated energy at the weld in a very short time, so that the welded material melts and forms a firm weld or weld.

Laser welding is a new type of welding method, which is currently in a stage of rapid development. When laser welding is used, the heat-affected zone of the workpiece is small; the weld point is small, and the welding size accuracy is high; its welding method is non-contact welding, no external force is required, the product deformation is small, the welding quality is high, the efficiency is high, and it is easy to realize automated production.

Energy storage battery laser welding equipment

The structure of a battery usually includes a variety of materials such as steel, aluminum, copper, and nickel. These metals may be made into electrodes, wires, or shells. Therefore, whether it is welding between one material or between multiple materials, high requirements are placed on the welding process.

The technological advantage of laser welding lies in the wide variety of materials that can be welded, and the ability to weld different materials.

Types of laser welding

Types of laser welding include laser heat conduction welding and laser deep penetration welding. The main difference between heat conduction welding and deep penetration welding is the power density applied to the metal surface per unit time, and the critical value of different metals is different.

Three common lasers for energy storage battery laser welding

Energy storage batteries are composed of battery energy storage equipment (single element → battery pack module → battery cabinet → battery energy storage unit → battery energy storage equipment), PCS and filtering links.

In the field of energy storage battery laser welding, pulse lasers, continuous lasers, and quasi-continuous lasers are currently the most commonly used.

Pulsed lasers: YAG lasers, MOPA lasers;

Continuous lasers: continuous semiconductor lasers, continuous fiber lasers;

Quasi-continuous lasers: QCW laser series.

These lasers can be understood as follows: hammering a thumbtack in with a hammer is pulsed; pressing a thumbtack in directly with your hand is continuous; when drilling, the drill drills for 10 seconds, rests for one second, drills for another 10 seconds, and rests for one second, which is called quasi-continuous.

A pulsed laser is a laser with a single laser pulse width of less than 0.25 seconds and works only once at a certain interval. It has a large output power and is suitable for laser marking, cutting, ranging, etc.

Crylas-1064nm pulsed laser

Common pulse lasers include yttrium aluminum garnet (YAG) lasers, ruby lasers, neodymium glass lasers, etc. in solid-state lasers, as well as nitrogen molecule lasers, excimer lasers, etc. Pulse lasers are based on the principle of YAG lasers, with high single pulse energy and high power consumption. Consumables such as xenon lamps need to be replaced regularly, and chillers must be equipped.

1550nm pulsed laser

This type of laser is a very mature laser with relatively low unit cost. It is also the most widely used laser for metal welding. Because it is based on the principle of YAG laser, the entire industry is restricted by technical conditions. At present, it is impossible to make the laser power very large. The conventional one is generally within 500W, and the highest in China is only 1000W. The electro-optical conversion efficiency is not high (about 13%).

Pulse laser

A continuous laser is a laser that emits light continuously, which means it has a stable working state, i.e., a steady state. The number of particles at each energy level in a continuous laser and the radiation field in the cavity have a stable distribution.

Its working characteristic is that the excitation of the working material and the corresponding laser output can be carried out continuously over a long period of time. Solid lasers excited by continuous light sources and gas lasers and semiconductor lasers working in a continuous electrical excitation mode all belong to this category.

Continuous laser

Since the overheating effect of the device is often inevitable during continuous operation, appropriate cooling measures are required in most cases.

Continuous lasers are based on the principle of YLP fiber lasers. Because they can continuously emit constant power (when the laser emits light fast enough and in large quantities, it forms a line), the energy of the output laser is constant, the laser has very good stability, the spot pattern is also very good, and the electro-optical conversion efficiency is also very high (about 30%).

Continuous laser

Quasi-continuous lasers (QCW), also called long pulse lasers, produce pulses in the millisecond range with a duty cycle of 10%. This makes the pulsed light have a peak power more than ten times higher than that of continuous light, which is very beneficial for applications such as drilling. The repetition frequency can be modulated up to 500Hz depending on the pulse width. QCW lasers can operate in both continuous and high peak power pulse modes.

Quasi-continuous laser

Unlike conventional continuous wave (CW) lasers, where the peak and average powers are always the same in CW and CW/modulated mode, the peak power of a QCW laser in pulsed mode is 10 times higher than the average power.

As a result, it is possible to generate microsecond and millisecond pulses with high energy at repetition rates from tens of Hz to several kilowatts, and to achieve average and peak powers of several kilowatts.

Quasi-continuous laser

 

Laser welding equipment has advantages in energy storage battery welding:

1. The welding process is non-contact welding, which reduces the stress in the welding ribs to a minimum;

2. The welding process does not produce other overflows and other released substances, preventing secondary pollution;

3. The welding strength and air tightness are high, which can meet functional requirements;

4. Laser welding can meet the welding needs between different materials, and can also realize the connection technology between membrane materials and dissimilar materials;

5. Laser welding is convenient for automated integration, and can also achieve synchronous laser welding process solutions according to production capacity requirements, with high efficiency and low welding internal stress;

6. The structure involved in laser welding is simple and convenient, and the difficulty coefficient of mold structure is reduced;

7. The welding process can be digitally and intelligently monitored, meeting the need for digital visualization of the welding process;

8. This type of welding process solution can be effectively integrated with the automated production line, meeting the needs of mass production solutions, achieving efficient production and low consumption.

Key technologies of laser welding in lithium battery PACK production line

The automated production line of battery modules of lithium battery laser welding machines generally includes processes such as cell loading, code scanning, testing, cleaning, sorting, module stacking, stacking detection, module welding, welding detection, module unloading, etc. The material transmission system, adaptive system, visual positioning system, MES manufacturing execution management, etc. are the key technologies in the entire production line and are also important technical supports for adapting to small batch and multi-variety production forms.

01 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 workstations according to the process adjustment requirements. The transfer between different workstations does not require manual operation. The module positioning plate has a product size adjustment mechanism that can adapt to the clamping of modules of different sizes, which is very suitable for the production needs of small batches and multiple varieties.

02 Adaptive system

In the production process of battery modules, the most common types of battery cells are soft packs, squares and cylinders. After battery cells of different types and sizes are stacked into modules of different sizes, each process needs to be adapted to the adaptive system to ensure the linkage of the entire line, especially the welding process. Only by adapting to modules of different sizes can the module PACK process be completed.

The adaptive system adopts multi-axis combined linkage to implement product positioning within the processing area, is not restricted by any form of incoming materials, completes the welding work and transmits it to the next process.

03 Visual positioning system

Cleaning the welding surface of the battery cell, marking the module, and welding the busbar are usually completed by laser processing. After the battery module is assembled, the dimensional tolerance is often large, and it is difficult to meet the gap position dimensional requirements of laser processing, resulting in a rapid decline in processing quality.

The introduction of the visual positioning system can meet the needs of precise positioning, with an accuracy of ±0.05mm. Through visual photography data collection, the deviation of the incoming material is fed back to the control system, thereby achieving high-precision positioning of the processing position.

04 MES Manufacturing Execution Management System

MES Manufacturing Execution Management System has an open development platform, which can quickly and agilely complete the implementation and development of MES projects according to user needs based on the underlying platform of the system. Manual work only needs to follow the parameter instructions of MES, and improve the existing production setting information after comprehensive statistics and analysis in the form of charts.

From battery cell loading to final module unloading, the parameters, data, and other incoming material information of each process can be quickly queried and analyzed and processed in time through the MES system, truly achieving process controllability and efficient production capacity.

The process data package in the laser welding process is directly integrated into the MES system to facilitate user call and switch. The entire MES system can directly turn the production line into a quasi-unmanned production workshop. Human labor only needs to replenish materials outside, which improves safety.

The reserved industrial communication interface allows users to not only achieve remote monitoring and management, but also effectively connect with the enterprise ERP to truly realize an intelligent and information-based factory.