From the manufacturing of energy storage battery cells to battery PACK into groups, welding is a very important manufacturing process, lithium battery conductivity, strength, airtightness, metal fatigue and corrosion resistance, is a typical battery welding quality evaluation criteria. The choice of welding method and welding process will directly affect the cost of the battery, quality, safety and consistency of the battery.
Among many welding methods, laser welding stands out with the following advantages: firstly, laser welding has high energy density, small welding deformation and small heat-affected zone, which can effectively improve the precision of the parts, and the weld seam is smooth, free of impurities, uniform and dense, without additional grinding work;
Secondly, laser welding can be accurately controlled, small focusing spot, high-precision positioning, with the robotic arm is easy to realize automation, improve welding efficiency, reduce man-hours, reduce costs; In addition, laser welding of thin plates or fine-diameter wires, will not be as easy as arc welding by the melting back trouble.
Energy storage battery welding methods mainly include wave soldering, ultrasonic welding, laser welding, dissimilar metal laser welding, of which laser welding is currently the most mainstream welding methods.
Energy storage battery
Energy storage battery welding methods:
- Wave welding: essentially a combination of ultrasonic welding and laser welding;
- Ultrasonic welding: the benefits of this program is simple welding, but need to take up more space, the volume of the module into the group efficiency will be lower;
- Laser welding: this program is currently the most widely used, but the structure is slightly different;
- Dissimilar metal laser welding: this welding method into a group is also very efficient, fast production speed.
What is laser welding?
Laser welding is through the optical system, the use of high energy density of the laser beam as a heat source, the laser beam will be focused on a very small area, in a very short period of time so that the welded place to form a highly concentrated energy heat source area, so that the welded material melting and the formation of a solid weld or weld seam.
Laser welding is a new type of welding method, currently in the high-speed development stage. When laser welding is used, the heat-affected zone of the workpiece is small; the weld joint is small, and the welding size precision is high; the welding method is non-contact welding, no external force is needed, the product deformation is small, the welding quality is high, the efficiency is high, and it's easy to realize the automated production.
Laser Welding Equipment for Energy Storage Battery
The structure of batteries usually contains a variety of materials such as steel, aluminum, copper, nickel, etc. These metals may be made into electrodes, wires, or shells, therefore, whether it is a material or a variety of materials between the welding, the welding process puts forward high requirements.
The advantage of the laser welding process lies in the wide range of materials that can be welded and the ability to weld between different materials.
Types of laser welding
Types of laser welding include laser heat conduction welding and laser deep melting welding. The main difference between heat conduction welding and deep melting welding is the power density applied to the metal surface per unit of time, which has different thresholds for different metals.
Three major lasers commonly used for laser welding of energy storage batteries
Energy storage battery is a whole composed of battery storage equipment (from single component → battery pack module → battery cabinet → battery storage unit → battery storage equipment), PCS and filtering links.
Energy storage battery laser welding field, the current use of the most pulse laser, continuous laser, quasi-continuous laser.
Pulsed laser: YAG laser, MOPA laser;
Continuous laser: continuous semiconductor laser, continuous fiber laser;
Quasi-continuous lasers: QCW laser series.
For these lasers, they can be understood in this way: using a hammer to smash the peg in one by one, which is pulsed; pressing the peg in directly by hand, which is continuous; when drilling a hole, the drill bit drills continuously for 10 seconds, rests for one second, and then drills continuously for 10 seconds again, rests for another second, which is called quasi-continuous.
Pulsed laser refers to the laser whose single laser pulse width is less than 0.25 seconds and works only once every certain interval of time, which has a large output power and is suitable for laser marking, cutting, ranging and so on.
Crylas-1064nm Pulsed Laser
Common pulsed lasers include yttrium aluminum garnet (YAG) lasers, ruby lasers, and neodymium glass lasers among solid-state lasers, as well as nitrogen molecule lasers and excimer lasers. Pulsed lasers are based on the YAG laser principle, with high single-pulse energy and high power consumption, requiring regular replacement of consumables such as xenon lamps, which must be equipped with a chiller.
1550nm Pulsed Laser
This type of laser is a very mature laser, the cost of a single machine is relatively low, is also currently the most widely used in metal welding a laser, because based on the principle of YAG laser, the overall industry is limited by the technical conditions of the limitations of the laser power can not be very large, the conventional general within 500W, the highest in the country on the 1,000W, electro-optical conversion efficiency is not high (at about 13%). The electro-optical conversion efficiency is not high (around 13%).
Pulsed laser
Continuous laser is a laser that produces light continuously, that is, it has a stable working state, that is, a steady state. The number of particles in each energy level and the radiation field in the cavity in a continuous laser have a stable distribution.
Its work is characterized by the excitation of the working material and the corresponding laser output, which can be carried out in a continuous manner over a long period of time. Solid-state lasers excited by a continuous light source and gas lasers and semiconductor lasers operated by continuous electrical excitation belong to this category.
Continuous Lasers
Since overheating of the device is often unavoidable during continuous operation, most of them require appropriate cooling measures.
Continuous lasers are based on the YLP fiber laser principle, because they can continuously emit light at a constant power (when the laser emits light fast enough and in sufficient numbers, it is connected to a line), the output laser energy is constant, the stability of the laser is very good, the spot pattern is also very good, and the efficiency of electro-optical conversion is also very high (around 30%).
Continuous Lasers
Quasi-continuous lasers (QCW), also called long-pulse lasers, produce pulses on the order of ms with a duty cycle of 10%. This gives pulsed light a peak power more than ten times higher than continuous light, which is very favorable for applications such as drilling. Depending on the pulse width the repetition frequency can be modulated up to 500 Hz. QCW lasers can be operated in both continuous and high peak power pulsed modes.
Quasi-Continuum Lasers
Unlike conventional continuous (CW) lasers, where the peak and average power are always the same in both CW and CW/modulated modes, QCW lasers deliver up to 10 times more peak power than average power in pulsed mode.
This enables, therefore, the generation of microsecond and millisecond pulses with high energies at repetition frequencies from tens of hertz to thousands of hertz, and average and peak powers of several kilowatts can be realized.
Quasi-continuum laser
Laser welding equipment in the energy storage battery welding advantages:
- The welding process is non-contact welding, the welding process on the welding bar internal stress is reduced to a minimum;
- Welding process does not produce other spills and other released substances, preventing secondary pollution;
- Welding of high strength and air tightness, can meet the functional needs;
- Laser welding can meet the welding between different substances, also can realize the membrane material, also can realize the connection technology between heterogeneous substances;
- Laser welding is convenient for automation integration, can also be done according to the capacity needs to synchronize the laser welding process program, high efficiency, welding internal stress is small;
- Laser welding involves a simple and convenient structure, reducing the mold structure difficulty factor;
- The welding process can achieve digital intelligent monitoring, to meet the welding process data visualization needs;
- The type of welding process solutions, can be effectively integrated with automated production lines, to meet the needs of the mass production program, to achieve efficient production, low consumption and other characteristics.
The key technology of laser welding in lithium battery PACK production line
Lithium battery laser welding machine battery module automation production line, generally including core loading, scanning, testing, cleaning, sorting, module stacking, stacking detection and module welding, welding detection, module discharging and other processes, the material transfer system, adaptive system, vision positioning system, MES manufacturing execution management, etc., is the key technology in the entire production line, but also an important production form to adapt to the small batch and multi-species Technical support.
Material transfer system
From core loading to final module unloading, the whole material transfer is completed through the material transfer system. The material transfer system can also flexibly expand the working stations according to the adjustment needs of the process, and the transfer between different working stations does not require human operation. The module positioning plate comes with a product size adjusting mechanism, which can be adapted to the clamping of modules of different sizes, and it is very suitable for the small-lot, multi-species production needs.
Adaptive system
In the production process of battery modules, the most common types of cells are soft pack, square and cylindrical. After stacking different sizes of cells into different sizes of modules, every process needs to be adapted with an adaptive system to ensure the linkage of the whole line, especially in the welding process, which can only be adapted to different sizes of modules to complete the module PACK process.
Adaptive system adopts multi-axis combination linkage to implement the positional positioning in the product processing area, and completes the welding work and transmits to the next process without any limitation of incoming materials.
Visual Positioning System
Welding surface cleaning of the battery cell, module marking, converging piece welding is usually completed by laser processing, battery module assembly, often with large dimensional tolerances, it is difficult to meet the requirements of laser processing on the gap position size, resulting in a rapid decline in processing quality.
The introduction of vision positioning system can meet the demand for accurate positioning, the accuracy can reach ±0.05mm, through the vision of the photo data acquisition, and feed back the incoming material deviation to the control system, so as to realize the processing position of high-precision positioning.
MES Manufacturing Execution Management System
MES Manufacturing Execution Management System has an open development platform, which can complete the implementation and development of the MES project according to the user's needs in a fast and agile way based on the underlying platform of the system, and the manpower only needs to guide the work in accordance with the parameter instructions of the MES, and improve the existing production setting information after comprehensive statistics and analysis in the form of charts and graphs.
From core loading to final module discharging, the parameters, data, and other incoming information of each process can be quickly queried and timely analyzed through the MES system, which really makes the process controllable and efficient.
The process data package in the laser welding process is directly integrated in the MES system to facilitate users to call and switch, the whole set of MES system can directly turn the production line into a quasi-unmanned production workshop, and manual workers only need to replenish the materials in the periphery, which improves the safety.
With the reserved industrial communication interface, users can not only realize remote monitoring and management, but also effectively docking with enterprise ERP, truly realizing intelligent and informative factory.
