The Volvo Car Group has turned to CFRP construction for the first time with production of the Polestar 1 two-door coupe. Polestar, Volvo’s solo performance brand, has developed an energy-efficient hybrid electric vehicle that can travel up to 93 miles on electric power alone. (By comparison, the popular Chevrolet Volt maxes out at 53 pure electric miles.) Polestar 1 features a predominantly CFRP body to produce weight savings of 507 pounds and improve the car’s handling, according to the company.
Polestar and Volvo collaborated on the design, working closely with their material supplier and attracting a small team of experts in the CFRP field. CFRP is used extensively in the car’s exterior, including the hood, fenders, tailgate, trunk lid, side panels, doors and the entire roof structure. In the vehicle’s interior, the cowl (front part of the car frame), the parcel shelf located behind the back seats and the floor reinforcement are also manufactured with CFRP. The largest CFRP parts on the Polestar 1, a body side inner molding and body side outer molding, are 118.1 x 44.9 inches while the smallest is an A-pillar extension, measuring 15.2 x 12.5 inches.
The inclusion of CFRP parts offers many advantages, including weight reduction and higher specific stiffness compared to metallic materials. “Because CFRP is mainly used in the upper body, the lowering of the center of gravity resulted in better handling of the car,” says Zef van der Putten, Polestar’s team member responsible for carbon fiber development. “The Polestar 1 is an electric performance hybrid where performance and range are at the core of its design.”
While Polestar holds the details of its materials and production methods close to the vest, van der Putten says the CFRP parts are constructed from a high modulus carbon fiber prepreg in three different architectures, including two-dimensional woven prepregs and a biaxial non-crimp prepreg with unidirectional tapes, all relying on an epoxy matrix.
“All of the parts except the braided tube for the cant rail in the roof are made using prepreg material and by means of hand lay-up, putting the prepreg into the molds,” says van der Putten. “We use an automated plotter to cut our raw material to minimize waste.” For the exterior where finish is critical, the team produced many test panels to achieve Class A parts and opted to use a surface film rather than a gel coat.
Two of the vehicles’ CFRP parts, the cant rail and floor reinforcement, pushed the team to design unique solutions. Developed to meet crash and safety requirements, the cant rail uses a co-cured braided tube structure. The structural tube travels through the cant rail from the A-pillar all the way to the quarter glass over the B-pillar. The cross section of the tube changes along the length of the cant rail to maximize structural performance and packaging space.