currently supplies the Ford Shelby GT500KR, the Chevrolet Corvette Stingray, and the Chrysler SRT Viper. “I do not think anyone took carbon fiber seriously until we announced we were doing all of the exterior body panels [and closures] on the 2013 SRT Viper program,” said James Staargaard, CEO of the company. What is interesting for those monitoring CFRP are the Corvette Stingray volumes, expected to reach over 25,000 per year. Plasan is providing a base model hood, a premium exposed-weave roof and a painted roof in CFRP for the 2014 Chevrolet sports car. Te company invested heavily in developing a reasonably
fast process for large exterior body panels, such as doors, fend- ers, hoods, and roofs. Plasan uses this process for the Corvette program. Te core of this system is a specially designed pres- sure press that optimizes an autoclave process, curing parts in 17 minutes compared to the 90 minutes needed in an au- toclave. “Instead of using convection heat as in autoclave, we precisely heat the surface of a nickel-shell tool. Tis provides instantaneous heat transfer, to bring the resin to flow tempera- ture, then to cure temperature, then we cool it rapidly,” said Staargaard. Weber Manufacturing (Midland, ON) supplies the nickel-shell tool. In the Plasan process, unidirectional prepreg is cut and
layered in a kitting process, trimmed, and then laid on the nickel-shell tool. Tey use thermoset prepreg sheets provided by Toray Composites America Inc. said Staargaard. A flexible, elastomer, formed top tool is then placed over the CFRP. Te part plus tooling is placed inside the press chamber and a vacuum pulled while moderate pressure is applied to the flex- ible top during the heating and cooling cycle. Te part is then finished and primed before shipping to the assembly plant. “What our team, led by Gary Lownsdale our R&D direc-
tor, figured out is that curing an epoxy follows a nonlinear curve,” Staargaard said. Lownsdale used Design of Experi- ments in a years’ long quest to map out that curve to guide developing the process—an expensive, painstaking process according to Staargaard. Why thermosets? “One of the difficulties with thermoplas-
tics for body panels is heat resistance,” said Staargaard. “[Com- posite] body panels have to go through the existing assembly plants, especially the paint ovens. Tere is not a thermoplastic resin that I know of today that can be processed into these large Class-A body panels, that will survive the heat in those paint shops, exceeding 400°,” he said.
Faster Processing Requires Faster Cure Tree common thermoset resins are polyester, vinyl ester
and epoxy. Epoxy resins are the popular choice for automotive composite applications when structural performance is need- ed. Henkel (Düsseldorf, Germany) now offers a polyurethane, Loctite MAX 2, for automotive composite applications. “Our polyurethane matrix resin has unique properties for manufac-
turing fiber-reinforced plastics. Compared to standard epoxy resins, it combines very short cycle times for RTM-processing and superior toughness,” said Frank Deutschländer, Global Market Manager Automotive for the company. Henkel also states that its product endures high fatigue loadings, ideal in certain automotive applications. Deutschländer believes Henkel is the first to offer a poly-
urethane resin suitable for RTM mass production for auto applications. “Potential applications for Loctite MAX 2 are structural, complex parts, for example for body parts or roof systems,” he said. Demonstrating its potential speed, in late 2012, Henkel, working with machinery manufacturer Krauss- Maffei (Munich, Germany), announced reducing the cure time of Loctite MAX 2 to just one minute. Tis was in a resin transfer molding (RTM) process with a representative auto- motive part composed of four layers of carbon fiber, molded at 120°C. Loctite MAX 2 permits short cycle times (< 5 min) in composite component manufacture, according to the com- pany. Te first commercial application of Loctite MAX 2 is a glass fiber reinforced leaf spring, produced by Benteler-SGL.
Cutting Cost of Carbon Reducing the cost of carbon fiber is one of the main tasks
at Oak Ridge National Laboratory (ORNL, Oak Ridge, TN). “We are trying to create a more cost-effective carbon fiber with similar or acceptably reduced performance [to today’s carbon fiber],” said Cliff Eberle, composite materials technol- ogy development manager. While the aerospace industry can use carbon fiber at its present cost, it is more of a challenge for automotive, even as it is migrating onto premium platforms, he said. “As volumes go up, price is critical,” he remarked. Eberle noted ORNL believes $5–$7 per pound is a target price for carbon fiber that will bring about more widespread use in the auto industry. “About half the cost of carbon fiber is in the precursor
feedstock, and about half is in the energy-intensive processes used to convert it,” he said. Te cost-reducing efforts have been enhanced with a new
facility. In March 2013, ORNL announced the start-up of its Carbon Fiber Technology Facility, a demonstration scale plant for testing new recipes of materials and conversion technologies. A key price driver for carbon fiber is the quality. In most
cases, aerospace grade is not required to meet the needs of automotive applications, which helps with cost. For example, Zoltek advertises its Panex 35 as more of an industrial grade of carbon fiber. Zoltek’s Husman said that the company sells Panex 35 for $8–$9 per pound, sometimes less, depending on the size of the order to a particular customer. He also said Zoltek and Weyerhauser, with support from the US Department of Energy, are collaborating on a lignin/PAN mix precursor technology, aimed at reducing cost while delivering the needed structural performance appropriate for the auto industry.
Motorized Vehicle Manufacturing 13
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