ISSUE 115 MARCH 2025 LASER WELDING


THE LASER USER


NEW CHALLENGES IN LASER WELDING


TECHNOLOGY: A CASE STUDY AXEL LUFT & PRAVIN SIEVI The transformation of passenger car


technology is in full swing. Automotive manufacturers are working tirelessly to transition their product portfolios to e-mobility. In recent years, particularly the large, well-established companies in the industry have been undergoing a challenging transformation, as new players—particularly from China—are entering the market, with highly cost- competitive models. This has significant implications for traditional manufacturing technologies in the automotive industry. One of the major challenges lies in developing manufacturing technologies that enable cost-efficient mass production. In this context, three key parameters must be considered, which play a crucial role in the production of high-volume models: speed, quality, and cost.


This article describes a case study in which a request from a major automotive manufacturer led to the development of an innovative battery welding system.


The challenge: creating contacts between cells


Bergmann & Steffen GmbH, founded in 1970, specialises in welding and joining technology with 70 employees engaged in the development and production of laser welding systems. Most of their customers are in the automotive industry. As with other automotive suppliers, the changeover to e-mobility is playing an important role. Because the trend is moving toward high-voltage systems, an increasing number of battery cells have to be connected in series.


One large manufacturer uses about 4680 cells, with 960 cells per battery pack (Figure 1). This company is currently exploring future serial manufacturing using a pilot series system from Bergmann & Steffen. In these cells, the anodes and cathodes of neighboring cells are contacted by welding short aluminum bars, known as cell connectors, onto their respective upper surfaces. While the contact to the anode is made of aluminum, the cathode contact uses nickel-plated steel (Hilumin), making the welding process significantly more demanding.


An additional challenge is that individual battery cells and cell connectors have positional tolerances. The system must reliably identify the points where welding is to take


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Figure 1: Up to 960 round 4680 battery cells form the battery pack for an electric vehicle. Copyright: istock.com/SweetBunFactory.


place and must not weld in areas where a secure connection cannot be achieved. On top of this, the usual requirements must be met: process reliability and speed. A single faulty weld joint renders the entire battery pack unusable. High speed is essential to achieve the short cycle times that are always demanded in the automotive industry for high-volume models.


Combination of clamping technology and laser welding


To ensure reliable and rapid welding of contacts, Bergmann & Steffen developed a system that combines image processing, rapid clamping technology and laser welding (Figure 2). In this system, linear drives move a clamping device from cell to cell to attach the previously positioned cell connectors. The two clamping devices operate alternately and their motion resembles walking, and so the system was named Scanwalker. During the process, the laser


optic with its scanners is continuously moved across the welding field on an independent linear axis, which makes control very demanding. Scanwalker is patent pending.


During the development of the system, various laser beam sources, laser welding optics and process monitoring systems were tested. The developers chose the system technology from Scansonic for the optics. Depending on the application’s requirements, the laser optics can generate different laser spots and laser power levels. The magnification range varies from 2.9 times to 6 times. Single-mode lasers with fibre diameters of 10 µm or 14 µm can be used as laser sources. For multi-mode lasers, 50 µm and 100 µm fibres are employed, enabling laser powers of up to 6 kW.


To consistently focus the laser beam on the working plane, the optics use a directly driven collimation system. This system adjusts the focus


Figure 2: Thanks to the combination of two clamping devices and the Scansonic laser welding optic, the system achieves high production speeds. Coypright: Bergmann & Steffen GmbH.


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