Electromobility needs new ideas

Challenges

High-voltage battery storage units and the battery boxes that surround them form the heart of electric vehicles. The latter not only protect the sensitive cells from the consequences of crashes, but also from external influences such as humidity and temperature fluctuations, which can have a negative impact on the battery's performance. Until now, these battery boxes have mainly been made of aluminium alloys. They are lightweight and thus aim to maximise the vehicle's range. However, Christian Buse and his colleague Conrad Frischkorn, both development engineers in the Automotive Division at BENTELER, also see great potential in stainless steel as a material. Together they are developing a special design for a flexible and scalable battery box: the folding box concept. A high level of manufacturing process expertise is required, explains Buse: "We sought support from TRUMPF for the design of the overall manufacturing process. For the experts from the battery pack industry management team, the major challenge was to develop a fast and reproducible laser welding process for gas-tight welding of stainless steel.

Solutions

Together with technology and application experts, Mauritz Möller from the battery pack industry management team at TRUMPF is developing a fully automated process chain with punching, cutting and bending technologies for series production of the battery box with integrated cooling plate developed by BENTELER. The gas-tight and helium-tight welding of the parts by laser is possible thanks to existing TRUMPF Technologie BrightLine Weld. With the help of BrightLine Weld it is possible to weld stainless steel with low spatter even at the high speeds used in series production. This eliminates the need for post-processing of the component and protects the machine and the focusing optics. For BENTELER's concept, however, it is crucial that the technology can also be used to produce perfect gas-tight and helium-tight seams, as Möller explains, "The high process speed requires a tailored input of thermal energy - this is the only way to ensure a stable weld pool during welding. Pores can form. BrightLine Weld prevents exactly that." Spurred on by this success, the BENTELER development engineers and the experts at TRUMPF set themselves the goal of also welding aluminium battery boxes with the laser. Mauritz Möller and his team are developing the so-called Multifocus optics especially for BENTELER. In conjunction with BrightLine Weld this has achieved what was previously considered impossible: gas-tight welding of aluminium.

Implementation

BENTELER relies on strategic development partnerships in many areas, explains Christian Buse: "We choose our partners to complement our own strengths. Our customers benefit from this array of different experts in many ways, including faster development times." When working with TRUMPF's battery pack industry management team, he appreciates the communication on a level playing field. "Working with technology experts and being able to run trials with application experts helps us tremendously as a customer of TRUMPF." The foundation of a good working relationship like this is open communication and a lot of trust, he says. "When it fits", Buse says, "everyone involved benefits from the cooperation."

Forecast

BENTELER is always open to new solutions, even if the market is not yet asking for them. "We want to be prepared for everything and be open to anything", explains Conrad Frischkorn. In the electromobility sector, Buse and Frischkorn are certain that their developments are just beginning, particularly when it comes to battery modules and battery box design, as well as surrounding vehicle structures. The duo currently uses the solution developed by TRUMPF for the gas-tight and helium-tight laser welding of aluminium for demonstration purposes. But studies on how safe and reproducible the process is in series production are underway.