IKV, Kautex Textron cooperation on all-plastic battery housings

Kautex Textron GmbH & Co. KG and researchers from the Aachen, Germany-based IKV Institute for Plastics Processing have developed a 1,600-by-1,300-by-200-millimeter "first full-scale thermoplastics battery housing for electric vehicles."

Kautex Textron showed the final prototype, called Pentatonic, at its September 2022 IKV International Colloquium Plastics Technology booth. IKV researcher Frederik Block described development and testing in Aachen during a presentation on integration of endless fiber reinforcement into the long-fiber reinforced thermoplastic (LFT) compression molding process.

Block; Roman Bouffier, Kautex Textron director of research; and Nicolay Bergmann, senior development engineer, said high-impact strength is important to withstand damage to battery modules from front, rear, underbody (bollard puncture) and vehicle touchdown impact.

Block described component level tests on glass-filled-nylon 6/glass-fiber long-fiber thermoplastic ribbed beams, reinforced by organic sheet produced at Pfinztal, Germany-based Fraunhofer Institute for Chemical Technology (ICT) in a direct LFT process. As all initially failed the 100 kN limit, Block arranged several rib structures next to each other for improved load bearing distribution.

Bouffier pointed to challenges with current metal-design housings. They use deep-drawn sheet steel or aluminum housing structures and interior diecast and extruded and welded aluminum profile reinforcement, with holes laboriously cut and milled in the extruded profiles.

The Pentatonic housing weighs 55 kilograms compared with 61 kg and 89 kg for equivalent housings in aluminum and steel, respectively. It offers key plastic design benefits of 15 percent weight saving, 20 percent cost saving and a 45 percent lower CO2 footprint than metal housings [93 kg less than aluminum, 556 kg less than steel, over 200,000 km], Bouffier stated.

The housing has a high degree of functional component integration and is molded in a one-shot process, with seamless flanges, vertical UD profiles instead of metal profiles, screw thread integration and "safe coolant routing," Bouffier stressed.

Kautex Textron Engineering Manager Havya Premkumar said earlier in the year: "What is unique about our Pentatonic battery system is that it doesn't require any metallic reinforcements. Unlike inflexible steel and aluminum battery housings, Pentatonic offers a customizable, lightweight solution benefiting feature integration and thermal management."

Bouffier referred to internal and external fire resistance. In view of use of the B24CMH 2.0 grade of GF-nylon 6 and compression molded Dynalite 102-RGUD600 Tepex composite sheet from Cologne, Germany-based Lanxess Germany GmbH (Hall 6, Booth C76-C78), Bouffier was asked whether UL94 V-O flame retardant material is needed. He replied, "We don't necessarily need V-0, but smart design with just as much flame retardancy as needed determines whether fire tests are passed."

Kautex Textron's commitment to thermoplastic battery housings has been confirmed by its August 2021 announcement of production expansion at the Pinghu, China, plant, with installation of a D-LFT line based on a 5,500-tonne press, specifically for Pentatonic battery housings and aimed at serving more than five local customers.

Bouffier admitted evaluation of polypropylene-based material, but it was rejected due to 10°C lower heat resistance than nylon. Rudolf Stauber of Stauber-Engineering, an earlier BMW manager, said vehicle transport by rail, road or ships causes damage through repetitive impact. So some cushioning should be used. Another former BMW manger, Hans Schwager of Consulting4Carbon, who previous led development of the BMW i3 carbon-fiber passenger cell structure, asked about temperature variations, whereupon Bouffier replied this hadn't been tested.

Bouffier suggested carmakers can better speak to recycling but suggested nylon in end-of-life battery housings could, in theory, be solution dissolved and residual glass fibers ground and used for other purposes, due to fiber length shortening during grinding, "if we ideally have a closed loop." Stauber was skeptical, saying, "Many cars are owned by private persons, whose vehicles have various parts demounted, while the rest goes into one of 66 shredders in Germany. They won't come back to Kautex; this industry is market driven and regulated by politicians."

Bouffier explained that compression molding was chosen as a "versatile and mature manufacturing process, excellent when applied with long continuous fiber reinforcement," equally for D-LFT, GMT or fiber-reinforced sheet molding compound (SMC) base on polyester or vinyl ester resin. He admitted there is room for improvement in fiber orientation simulation. And although electromagnetic shielding hadn't been "intrinsically solved, there are solutions in place."

IKV also investigates SMC battery housings. This was clear from a presentation by IKV researcher Vera Austermann and parts displayed in the IKV composites laboratory in Aachen-Melaten. Austermann described modeling and validation of local continuous external and/or internal local carbon-fiber resin impregnated towpreg tape reinforcement of SMC for battery housings. This relates to enhancing mechanical properties of "comparably low-cost SMC material."

This "hybridSMC" approach, based on CF towpregs from Wiesbaden, Germany-based SGL Carbon SE and 40 percent glass-fiber-reinforced unsaturated polyester SMC compound from Scanzorosciate, Italy-based Polynt SpA, could form the basis for hybrid SMC battery housings reinforced internally by a combination of SMC sinusoidal ribs and carbon-fiber-reinforced pultruded profiles, Austermann suggested.

Austermann said pre-cured towpregs with "45-gram CF" accounts for 3 percent of part weight, yet results in 20 percent less z-axis deformation. A hybridSMC demonstrator combining local 4 percent CF content towpreg reinforcement with an internal sinusoidal rib crash structure showed ductile instead of brittle fracture behavior. It withstood 57 percent higher force and showed a 317 percent increase in energy absorption.

Ongoing work at IKV includes "in-depth evaluation of recycling procedures, CO2 saving potential and cycle time reduction," Austermann said. Interestingly, Kautex Textron was a partner in the hybridSMC project, which was completed at the end of 2021.

IKV used equipment from Lotte, Germany-based Frimo Group GmbH (Hall 13, Booth C60) installed in the IKV composites laboratory and in the nearby AZL Aachen GmbH lightweight engineering solutions center on the same RWTH university campus as IKV. Simulation was done with software from Aachen-based SimpaTec Simulation & Technology Consulting GmbH (Hall 13, Booth A94).

Kautex Textron GmbH & Co. KG

Hall 14, Booth C16