the heat-affected zone, higher scanning speeds and larger scanning fields. “Even highly reflective materials such as welding of copper see clear improvements with the technology,” Franks adds. Independently of the welding techniques applied, welding machines are also getting smarter and more standardised, Hesse Mechatronics’ Holtkamper says, incorporating features drawn from mass-production technologies used in other industries. “For instance, pattern recognition can be freely programmed to find the right positions on batteries, BMSs or busbars in less than 10 ms,” he says. “Another improvement that comes with standardisation is the traceability and monitoring of quality in real time,” he adds. “That means the data created during the process can be sent to manufacturing execution systems to judge the quality of the welds.” He further explains that quality systems also operate in a decentralised manner, with sensors and algorithms on the machines, enabling them to react in real time to changing conditions. Hesse Mechatronics has launched a new laser welder designed to join thicker materials with larger contact areas, he adds. “Clamping and welding a contact in one shot will serve the high demand for flexibility without needing costly consumables or tooling,” he says. “This is especially true for cylindrical cells.” Architectural adaptation Welding technology also has to adapt to novel battery architectures such as cellto-pack and cell-to-chassis, particularly when it comes to automation. These architectures have been tending towards more conductive and thicker materials, especially in busbars, pushing solutions towards laser welding, Boyle comments. Franks adds, “In general, moving away from modules/packs means some reduction in the number of welds in a pack or an EV. But as we keep seeing new applications, this is having a negligible impact on the high demand we see for laser welding equipment.” Holtkamper focuses on the higher level of integration these architectures represent, noting that it means the products to be processed can be larger. Emerging processes Ultrasonic-assisted laser welding is a new process that is still at the r&d stage, Carr notes, and Carrs Welding is working with Brunel University to investigate the technology through the SoniLaser project. The idea is that the ultrasonic excitation will interact with the molten pool flow, the solidification mode, and the mixing of alloying elements and diffusion that happen during solidification. By breaking continuous flows such as Marangoni convection within the weld pool, the ultrasound will minimise the formation of intermetallic compounds and precipitates that can contaminate and weaken welds between dissimilar metals. Another process under investigation for future application to EV batteries is electron beam (EB) welding, which works by focusing and directing a stream of electrons generated by an electron gun using magnetic fields, much as cathode ray tube TVs did. The electrons’ kinetic energy is converted into heat by impact with the workpieces, causing localised melting and bonding. The technology is well-established in industry and is routinely used to join turbocharger wheels to shafts, for example. EB welding produces clean, high-quality welds with fine control of penetration depth and a very small heat-affected zone. It is also potentially 20 times faster than laser welding. However, it has to take place in a vacuum, because any gas between the electron source and the work will scatter the beam, which is a problem for batteries as exposure to vacuum can damage cells. Recently, a means of enclosing the electron gun in a vacuum box sealed to one side of the material to be welded has been invented, making it no longer necessary to put the whole battery module or pack in a vacuum chamber. The UK government’s UKRI is sponsoring a demonstration of the technology by a consortium of Aquasium Technology, Delta Cosworth and TWI. While there are no completely new techniques applied to batteries, adaptation, combination and increasingly advanced automation keep them relevant. Insight | Battery welding 56 September/October 2023 | E-Mobility Engineering FL-ARM technology delivers uniform laser power over a wide range of welding angles (Courtesy of Coherent)
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