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Thermoplastic composites put a new spin on Chinese EV exterior

Thermoplastic composites put a new spin on Chinese EV exterior
The ES8 and ES6 all-electric SUVs from startup NIO feature carbon fiber-reinforced polycarbonate blade inserts in the aluminum wheel rims.

Thermoplastic composite materials are gaining traction in automotive as they offer many benefits. They have no shelf life issues; they are inherently recyclable; and they enable significant increases in production speed. And there’s one more characteristic that offers promise: aesthetics.

The thermoplastic carbon fiber-reinforced polycarbonate wheelblade insert can survive braking-induced temperatures of up to 150°C.

Thanks to their unidirectional carbon fiber optics and a high-quality surface offered by the polycarbonate matrix, Covestro’s Maezio continuous fiber-reinforced thermoplastic composites reportedly bring a new tool to automotive designers’ toolbox for designing unique appearances. One case in point: they have given the ES8 and ES6, the all-electric SUVs from Chinese electric vehicle startup NIO, a boost on the wheels.

The wheels feature aluminum rims with opt-in carbon fiber blade inserts, designed to lend the vehicle a high-end aesthetic appeal with a lightweight flavor and improved aerodynamics. What Maezio composites bring to the table is a combination of a unique appearance with unidirectional carbon fiber optics and a wide variety of finishing options.

“Maezio composites are a very unique material because they kind of redefine how beauty is associated with carbon fibers,” says Yanbing Wang, senior CMF (Color, Materials, Finishing) designer from NIO. “They have set a new aesthetic direction with the unidirectional strands of fibers that remind me of the flowing shapes of rocks within the Antelope Canyon. It feels dynamic and full of energy.”

To achieve a high level of aesthetics, the choice of the resin system is crucial. Polycarbonates boast high surface quality and optical performance. Furthermore, polycarbnate-based composites are compatible with a wide range of coatings and decoration processes for designing unique surfaces. This makes it possible to develop a matt-coating system for the wheelblade that not only retains the beauty of the unidirectional fibers but also provides the needed protection – wheels are every vehicle’s touchpoints with the road, and as such, must perform flawlessly.

Automotive exteriors exist in a harsh environment, and the requirements are demanding. Parts have to display high scratch, weather, ageing and chemical resistance properties. For wheelblades comes the additional requirement of high heat resistance during braking. Therefore, automotive exterior components not only have to look good after years of use but also perform on an everyday basis under tough conditions.

In combination with the coating system, the composite wheelblades have withstood rigorous safety and performance requirements, such as impact, chemical and weather resistance. The Makrolon polycarbonate on which Maezio is based displays high thermal stability qualities so the wheelblade insert can survive braking-induced temperatures of up to 150°C.

For composites to be widely adopted in automotive they also need to be easily integrated with other materials in a multi-material system. Because of their thermoplastic matrix system, Maezio composites can be easily joined with functional components during processing, e.g., through back injection molding. In the case of the wheelblade inserts, they are joined with the aluminum spokes of the wheel through back-molded screw bosses made of polycarbonate. The common resin material makes it easy and secure to bond the two parts.

Maezio composites can be cut and remelted for reuse at the end of life, or reground into short fiber compounds and used in an injection molding process.

“We have proved with this major breakthrough that Maezio composites are a technically and commercially viable material solution in automotive exterior applications,” says Lisa Ketelsen, head of the thermoplastic composite business of Covestro. “The end result is a newly-defined aesthetic direction and benchmark for thermoplastic composites in automotive.”

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