In new Corvette Stingray, another step forward for composites
21. January 2013
Chevrolet introduced the 2014 Corvette Stingray to much fanfare at the North American International Auto Show (NAIAS) in Detroit, Mich., on Jan. 14. The car represents the ongong evolution of the Corvette design brand and features a carbon fiber hood and carbon fiber roof, both molded by Plasan Carbon Composites (Bennington, Vt., USA).
Plasan molded these via its "pressure press," a high-speed thermoset molding process co-developed with Globe Machine Manufacturing (Tacoma, Wash., USA), at a new Plasan facility in Walker, Mich. Jim Staargaard, president of Plasan, and Gary Lownsdale, chief technology officer, told CompositesWorld that the pressure press features a 17-minute "button-to-button" cycle time and represents a major investment for the company as it positions itself for growth in the automotive industry.
Staargaard says the Stingray's carbon fiber composite roof is available in two versions molded by Plasan, one painted and the other with exposed weave. The roof is about six plies (1.2 mm) thick and uses the same resin chemistry and prepreg as Plasan employed in the manufacture of the roof for the Corvette ZR1. The hood, he says, is comprised of two 1.2-mm-thick carbon fiber shells that are hot-bonded together.
What's notable, however, is the information Lownsdale shared about the pressure press process, which he says is not a compression press and not an autoclave. In the pressure press, prepreg is laid up on a one-sided, hot oil-heated tool (made by Weber Manufacturing Technologies) that ramps up quickly to process temperature. The prepreg is covered by a reusable, 0.5-inch silicone canopy that is also molded and conforms to the shape of the part. The tool, with prepreg and silicone canopy, are loaded into Globe Machine's sealed pressure box, says Lownsdale. To consolidate the part, pressure is provided via an air chamber (<150 psi) that surrounds the tool and compacts the prepreg. The result, says Lownsdale, is a part with a high-quality A side molded in just minutes.
Staargaard says the Walker plant has five Globe machines for producing Stingray roofs and hoods; there is room at the facility, he says, for expansion, which is already being planned. Look for a longer report on the Plasan process and the Stingray parts in the March issue of High-Performance Composites magazine. In the meantime, you can add "pressure press" to your composites molding lexicon.