General Motors will offer a carbon fiber hood on 2,000 to 3,000 special edition Corvettes for the 2004 model year.
Working with General Motors and Toray Composites, MacLean Vehicle Systems (MVS) has developed, qualified and produced of a lightweight, structurally stiff carbon fiber hood for GM’s 2004 Chevrolet Corvette Z06 Commemorative Edition. The hoods are supplied to GM’s Bowling Green, Kentucky assembly plant where they will be processed identically to current production fiberglass body panels. Between 2,000 and 3,000 Corvettes will be fitted with the carbon fiber hood for the 2004 model year. The hoods are produced in West Jordan, UT at MacLean Quality Composites, an operating unit of MVS.
“”This application of carbon fiber is a major innovation, marking a significant milestone in performance and value for the industry,”” says Dave Hill, Vehicle Line Executive and Chief Engineer for the Chevrolet Corvette. “”It helps further celebrate Corvette’s racing success, and is a very appropriate addition to the Z06, the Corvette for the extreme performance enthusiast.”” The carbon fiber hood is claimed to represent the first time the material has been used as original equipment for a painted exterior panel on a North American-produced vehicle.
Weighing only 20.5 lbs, the carbon fiber hood is 10.6 lbs. lighter than the standard fiberglass SMC hood. The painted, class-A outer skin is only 1.2 mm (0.048 inch) thick, whereas SMC typically runs 2.0 to 2.5 mm thick. The exterior skin panel is fabricated from 100 percent carbon fiber/epoxy prepreg, while the inner structure is a hybrid of carbon fiber SMC and low density fiberglass SMC. The finished assembly has passed all GM requirements for strength, stiffness and durability.
The MVS process relies on cellular manufacturing and a combination of automated and manual techniques. As in aerospace components, an autoclave is used, however, the unidirectional carbon/epoxy prepreg, supplied by TCA, is formulated to fully cure in only 10 minutes at 300ºF. This unidirectional epoxy prepreg is a proprietary formulation of G83C quick cure resin and Torayca T600SC standard modulus carbon fiber. The P3831C prepreg was specially developed for GM and meets the stringent structural design and class-A surface finish requirements of the Corvette hood. It also withstands the high temperatures of the prime and paint ovens.
The prepreg is automatically cut into patterns and oriented in multiple directions to achieve balanced strength and stiffness properties. A significant challenge for MVS was the development of a mold release compatible with existing GM power wash and approved paint systems without the need to scuff sand or solvent wipe the molded components. To achieve the 2004 model year volumes and provide tooling durable enough for years of aftermarket production, Invar, a nickel/iron alloy was selected for the molds. Following cure, the hood outer skins are removed from the mold, automatically routed, and urethane adhesive robotically applied. The outer skins are bonded to the compression molded inner panels and a primer applied prior to delivery to Bowling Green.
The hood is believed to be the highest production volume of a single carbon fiber component using aerospace autoclave technology and the first use of Invar tooling for serial automobile components. “We expect this project is the first of many automotive applications for our carbon fiber technology, from body panels to structural components,” emphasizes Jeff Keller, VP and General Manager, Plastics and Composites for MVS.
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