SHINHOP laser

The connection method of the power battery cell to module and to PACK not only affects the efficiency of power battery manufacturing, production mode, but also directly determines the performance of the power battery after installation in the vehicle. The welding types of power battery busbars have evolved over many years and can be summarized into the following methods. Below, we will analyze the characteristics of various welding methods.

1. Resistance welding.
Resistance welding is a type of welding method that uses resistance heat as energy. It utilizes the resistance heat generated when current flows through the contact surface of the workpiece and the adjacent area to heat it to a molten or plastic state, while applying pressure to form a metal bond. Resistance welding does not require filler metal during the welding process, has high productivity, minimal deformation of the welded parts, and is easy to automate.
To prevent arcing on the contact surface and to forge the welded metal, pressure must always be applied during the welding process. The contact surface of the workpieces being welded is crucial for achieving stable welding quality.
Therefore, before welding, the contact surfaces between the electrodes and the workpieces, as well as between the workpieces themselves, must be cleaned. In the grouping process of power batteries, resistance welding, as a relatively mature process, is applied to the welding of power battery cells to busbars, and the connection of power battery tabs to parallel conductive strips. Due to its simple equipment and low cost, it was widely used in the early development of the power battery industry, but in recent years, it has gradually been replaced by more advanced laser welding and ultrasonic welding.
2. Polymer diffusion welding.
Polymer diffusion welding is a welding method that involves bringing the welding surfaces of the materials to be welded into contact under certain temperature and pressure in a vacuum environment. This process expands the physical contact of the welding surfaces through microscopic plastic deformation or the generation of a small amount of liquid phase at the welding surface, bringing them within (1 to 5) × 10^-8 cm (only then can the atomic attraction take effect to form a metallic bond), followed by a prolonged period of continuous atomic diffusion and mutual penetration to achieve metallurgical bonding.
Polymer diffusion welding is a special welding process that can weld copper foils of different strengths together in specific areas. This welding process does not require any form of flux and can achieve perfect molecular connectivity, mainly used for soft connections in power batteries. The installed contact surfaces can withstand any form of compression, bending, or collision. Since the installed contact surfaces are customized, they can be installed in spaces as small as 2mm.
3. Ultrasonic welding.
Ultrasonic welding uses high-frequency vibration waves transmitted to the surfaces of two objects to be welded, causing them to rub against each other under pressure and form a fusion between molecular layers. The ultrasonic generator converts 50/60 Hz AC power into 15, 20, 30, or 40 kHz high-frequency electrical energy. The converted high-frequency electrical energy is then transformed into mechanical motion of the same frequency through a transducer, and this mechanical motion is transmitted to the welding head via an amplitude-changing device. The welding head transmits the received vibration energy to the joint of the workpieces to be welded, where the vibration energy is converted into heat through friction, melting the metal. The advantages of ultrasonic metal welding include:
1. Compared to resistance welding, ultrasonic welding has a longer mold life, less time for mold repair and replacement, and is easier to automate.
2. The welding materials do not melt, maintaining the integrity of the metal properties. The conductivity after welding is good, with a resistance coefficient that is extremely low or nearly zero.
3. Ultrasonic welding can be performed between the same type of metals and different types of metals, consuming much less energy compared to resistance welding. It has low requirements for the surface of the welded metals, allowing for welding of oxidized or electroplated surfaces.
4. Compared to other pressure welding methods, ultrasonic welding requires less pressure, with deformation below 10%, while cold pressure welding can cause deformation of 40% to 90%. The welding time is short, and no flux, gas, or filler is needed.
The disadvantages of ultrasonic metal welding are also evident:
1. The speed of batch welding is relatively slow, and the welding path is uncontrollable, making it impossible to achieve precision.
2. The uniformity of welding strength quality is poor.
3. Compared to laser welding, it has higher power consumption and production costs.
4. Laser welding machine.

Laser welding is highly efficient and easy to automate. With continuous improvements in welding technology and limitations on thermal effects during the forming process, its application in actual production is increasing. Laser welding combined with industrial robots is gradually becoming the main force in automated power battery module production lines.
Laser welding is an efficient and precise welding method that uses a high-energy density laser beam as a heat source. It is mainly used for welding thin-walled materials and low-speed welding. The laser welding process is thermal conduction type, where the laser radiation heats the surface of the workpiece, and the surface heat diffuses inward through thermal conduction. By controlling parameters such as the width, energy, peak power, and repetition frequency of the laser pulse, the workpiece is melted to form a specific molten pool. Laser welding can be achieved using continuous or pulsed laser beams, and the principles of laser welding can be divided into thermal conduction welding and laser deep penetration welding. When the power density is less than 10^4 to 10^5 W/cm2, it is thermal conduction welding, characterized by shallow melting depth and slow welding speed; when the power density exceeds 10^5 to 10^7 W/cm2, the metal surface is heated to form "pits," resulting in deep penetration welding, which features fast welding speed and a large depth-to-width ratio.

From the comparison of various welding methods for battery module busbars, it can be seen that laser welding is still the preferred technology for current battery welding. With the continuous development of automation and intelligent technology, the laser welding process for power batteries will become more refined and intelligent, including the entire production line of battery feeding, inspection, welding, quality monitoring, traceability, assembly, and discharging, becoming more diversified, and is an important component of dust-free workshops and smart factories!