Meaning
Concentrated beams of coherent light delivered through optical fibers provide the precision joining method necessary for thin busbar connections in high density battery modules. Fiber laser welding utilizes a solid state laser source where the light is generated in an active fiber doped with rare earth elements. This technology produces a high quality beam with a small spot size, allowing for deep penetration and a very narrow heat affected zone.
It is the preferred method for joining copper and aluminum terminals because the high power density overcomes the initial reflectivity of these metals. The application of this process stops when the gap between the two parts exceeds the diameter of the laser spot, as the beam will pass through without creating a weld.
Process Control
High speed galvanometers steer the laser beam in specific patterns to optimize the melt pool and reduce the formation of pores. Fiber laser welding requires real time monitoring of the back reflection to prevent damage to the laser source and to verify the depth of the weld. The power, speed and focus position are adjusted based on the thickness of the material and the required electrical conductivity of the joint.
If the speed is too low, the heat may damage the plastic housing of the battery cell.
Thermal Effect
Rapid cooling of the weld pool minimizes the time available for the growth of brittle intermetallic compounds at the interface of dissimilar metals. Fiber laser welding generates significantly less total heat than traditional arc welding, which protects the sensitive electrolyte inside the cell. The narrow beam ensures that the thermal distortion of the busbar is kept to a minimum.
This precision is essential for maintaining the tight tolerances required in automated battery assembly lines.
Join Quality
Mechanical strength and electrical resistance are the two primary metrics used to evaluate the success of the weld. Fiber laser welding produces joints with high consistency, which is verified through ultrasonic testing or visual inspection systems. The absence of spatter and smoke during the process keeps the production environment clean and reduces the need for post weld cleaning.
If the weld is too shallow, the electrical resistance will increase and cause local overheating during high current discharge. If the weld is too deep, it may puncture the cell lid and cause a leak.
