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Lasers wield the answers for the e-mobility society

Lasers are assisting in making electric vehicles a reality by successfully welding dissimilar materials and lowering the cost of battery manufacture.

The new area of electric- or e-mobility is persuading car makers to examine lasers for key production processes – and some of the research was presented at Laser World of Photonics.

With speakers from the BMW group, Reutlingen-based green power company Manz, Bavaria's Bayerisches Laserzentrum (BLZ) and the Institut für Werkzeugmaschinen und Betriebswissenschaften (IWB), an institute for industrial technology and management; plastics joining, carbon fibre reinforced plastics and battery electrode processing were all addressed.

With batteries being key part of the e-mobility drivetrain system, their cost is important and one way of reducing that cost is extending the life of the machine that is used to make it. Typically electrodes are cut into the desired length using punching machines. The punch cuts through the electrode material but it has a lifespan of only one million electrodes. Manz's researchers found that a laser could be used for 31 million electrodes.

Already providing laser system products that can do the job, Manz recommends an exhaust system to keep the electrode clean and moderate pulse energies from the laser. 'Products with low TACT times are already available,' Manz's laser application engineer Benjamin Schmieder said.

Another important part of the e-mobility drivetrain is copper. Used throughout the electric power system Copper is not easy to weld as it does not absorb infrared very well. This was the challenge outlined by BMW's Dr Rudiger Daub, from the company's electric energy storage prototype shop.

The existing state-of-the-art is ultrasonic welding. Compared to that technology the benefits of lasers are, no special tool is required, and it is easy to automate for high productivity. The car maker's research also found that green lasers, while their frequency is preferable for copper, are not powerful enough.

'Double today's power is needed for good results, about 1kW is what we need,' Daub said. Instead Daub recommended solid state fibre and disc lasers. Tests with copper also found that butt joints, where the ends of two pieces of copper are laid side by side, gives a better weld result than welding end to end.  

While battery power will deliver emission-free vehicles, the structure of the car has to be lighter than today's but still deliver the safety that is expected. The solution is to have a chassis made from different materials, not just the traditional steel. The materials to be joined with steel are lighter materials, perhaps aluminium, and plastics, both thermoplastics and plastics that reinforce carbon fibre (CFRP). 

'Laser cutting is very flexible for cutting CFRP,' IWB's Alexander Fuchs said. Using a gas-assisted laser process, CRFP can be cut in one pass. The optics are guided by a robot and the laser is reflected by mirrors; speeds of 12 metres per minute can be attained. The higher the power, the fewer the scan cycles/passes the laser needs to make to cut the composite.  However, despite its speed, Fuchs explained that there are still obstacles as carbon fibre suffers from heat-affected zones, and impurities in the CFRP can evaporate releasing a gas that needs to be dawn away. The fibres themselves can also swell from the heat. 

Joining CFRP and thermoplastics to metals does not have such obstacles. BLZ's Philipp Amend explained how it is done. Placing the metal at the bottom and the CFRP or thermoplastic on the top a glass plate is put on top and pressure is applied. Through the glass plate a laser than heats the CFRP or thermoplastic and the heat transfers to the bottom, where it meets the metal. There, the two are joined. 'We can produce strong joint cojnnections between dissimilar materials,' Amend said. For thermoplastics and aluminium, a grid structure is used. 

This year is the 40th anniversary for the Laser World of Photonics show. With the progress being made on laser processes for electric vehicles, it's unlikely to be another 40 years before the e-mobility society is with us.

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