FOCUS ON LASER WELDING
already working on a system that should reach 200,000Hz in the near future.
“ The investigation of complex material combinations, such as copper-aluminium joints, is extremely important for electromobility, where they are used in high-performance batteries and other critical components,” explained Dr. Alexander Olowinsky, head of the Joining and Cutting Department at Fraunhofer ILT.
“ Thanks to the data obtained at DESY, joints [ like this ] can be manufactured with greater strength and reliability. For lightweight construction, we are also investigating other structuring processes and the results flow directly into the development of new technologies,” he added.
Laser micro-welding of copper materials.
Image: © Chair for Laser Technology, RWTH Aachen University.
Laser welding for EV batteries
An electric vehicle uses a lot of batteries, which need joining to attain the desired capacity without compromising on safety. The joints need to be reliable, offer acceptable strength and electrical resistance, and be free from defects. An Innovate UK-funded project at the AMRC( Advanced Manufacturing Research Centre-Sheffield) focuses on the welding of tab-to-busbar materials in battery pack modules. The challenge was to develop laser-welding process development and parameters optimisation for attaching busbars to cells for the assembly of 22 prototype electric vehicle battery modules.
Helical Technology chose to work with the AMRC because it has the capabilities and previous experience of welding such cell terminals to the busbars using an 8kW laser welder at its AMRC North West facility in Lancashire( UK). Helical Technology works predominantly in the automotive sector with automotive manufacturers and motorsport teams, and as a component supplier for vehicle, powertrain and, increasingly, emissions testing. It has test facilities for vehicles, engines and components, including low and ultra-low-emission vehicle technologies such as hybrid and electric.
The welding of dissimilar materials presents various challenges mainly due to variations in melting point, chemistry and thermophysical / thermomechanical properties. The tab and bus bar materials used in this project were aluminium, copper and nickel-plated copper, owing to their light weight, good electrical properties and corrosion resistance.
“ Fusion welding these materials, using a laser, results in the formation of intermetallic, a hard and brittle phase with reduced electrical properties which causes premature failure of the joints. The laser welding of these
Laser-welded battery module.
The challenge was to develop laser welding process development and parameters optimisation for attaching busbars to cells for the assembly of 22 prototype electric vehicle battery modules
materials also produces porosities, blowholes and cracking. To overcome this, laser welding process development and parameters optimisation is needed to produce joints with acceptable strength and low electrical resistance,” explained the AMRC.
A methodology was developed using a knife, applied by a cobot, to secure the cell tabs on the busbars. This ensured uniform contact between the metals that needed to be welded. The laser welding was done as a series of‘ spots’ to build a seam to prevent any blowholes from propagating through the thin material. Welding parameters were also developed and optimised for both types of joints: aluminium to copper and copper to copper.
The weld pool formation, cooling rate, weld chemistry and heat input alter the solidification of the weld. By using a series of spot welds, rather than a linear line, it produced joints with good quality as the technique helps in creating and solidifying welds without any cracks. The produced joints had low electrical resistance and high strength, reported the AMRC.
“ Joints with acceptable strength and low electrical resistance are much desired in electric vehicle assembly. This project demonstrated the laser welding capability to rapidly produce dissimilar joints with prolonged life and desired properties. Moreover, this process can be automated and monitored for the production of battery packs. This has the potential to save time and reduce waste, creating more costeffective battery packs to support the net-zero agenda,” concluded the AMRC.
Beam shaping developments
The WMG / University of Warwick in the UK conducts laser welding research that focuses on improved understanding of laser-to-material interaction as well as strategies to weld similar and dissimilar materials. Other research aims to integrate Industry-4.0 tools for autonomous laser beam welding, as well as develop process monitoring and control systems.
In collaboration with Lumentum, a San-
Image: Helical Technology.
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