With the exception of its 620hp LS9 engine, few features of the new ZR1 Corvette have been more thoroughly discussed than the car's lightweight carbon-fiber body panels. But what exactly is carbon fiber? How is it produced? How much stronger and lighter is it than fiberglass? And could it replace traditional body materials on all production cars in the future?
To answer these and other questions, we contacted Andrew Rich and Robert Murch, research-and-development engineers at Plasan (pronounced Plah-SAHN) Carbon Composites, the sole supplier of carbon-fiber body panels for the '09 ZR1 and Z06 Corvettes. Along with Anastasia Satterthwaite, the company's marketing manager, the pair told us everything we wanted to know about the automobile industry's most promising new material.
Vette Magazine: What is the most exciting aspect of working with GM on the Corvette ZR1 and Z06 body panels?
Robert Murch: The most exciting part is being a leader in taking what is typically a material used for aerospace and making it applicable to the automotive industry.
VM: What carbon-fiber body panels are utilized on the ZR1 and Z06?
Anastasia Satterthwaite: Plasan makes the ZR1 hood assembly with the exposed carbon-fiber inner, the exposed carbon-fiber roof, the roof bow, the rocker set, and the splitter. In addition, Plasan makes left and right fenders for both the Z06 and the ZR1 Corvettes.
VM: How light are the ZR1's carbon-fiber body panels?
AS: The Corvette ZR1 body panel weights are as follows: splitter, 1.3 pounds; fender, 4.5 pounds; rocker, 0.8 pound; roof, 14 pounds (with magnesium frame); roof bow, 4 pounds; and hood, 17 pounds (bonded with polycarbonate window and hardware).
VM: How is carbon fiber produced?
AS: Carbon fiber goes through the following manufacturing steps:
Kit CuttingThe fabrication of a composite part starts with cutting the material into precisely sized pieces that have the weave running in an appropriate direction. Carbon materials pre-impregnated with resin (these are sometimes called "pre-preg") are kept in a freezer until being thawed for cutting. Material is rolled onto a vacuum table and cut with a CNC machine. Once cut, materials are grouped so they can be mated with other plies to form the kits needed to create an individual part.
Lay UpThe materials are then laid into molds according to a detailed assembly plan. These plans determine specific placement and orientation of the material to achieve the desired physical characteristics of each part. After the composite material is "laid up" and vacuum valves are inserted, the vacuum is pulled to compress the composite material in preparation for autoclave processing.
Autoclave ProcessingThe uncured molded parts are then placed in an autoclave and maintained under vacuum. Heat and pressure are added to flow the resin and create strong, rigid, lightweight parts.
MachiningAfter autoclave processing, the parts move to machining on a five- or 6-axis router. The CNC robot then trims, cuts, and drills as necessary.
AssemblyParts that need to be bonded are brought to the bonding cell. Here, another CNC machine dispenses adhesive, and the marriage of the components is complete.
Finish, Prime, And PaintThe exposed-weave appearance of carbon-fiber composites-as seen on the Corvette ZR1 hood inner, roof, bow cover, splitter, and rocker panels-is often enhanced by a clearcoat. Other applications may require priming and painting, as seen on the ZR1 fenders and hood outer.
VM: What are the differences between carbon fiber and fiberglass?
Andrew Rich: Both fiberglass and carbon fiber can be produced in the same variety of methods. However, because of the cost of carbon fiber, there's usually more effort taken by the manufacturers to be efficient and effective. Most fiberglass for auto bodies is either hand-laid or SMC [sheet-molded compound]. In those methods, the fiber-to-resin ratio is usually pretty low, between 15 and 25 percent fiber, with the rest being resin and fillers. Most carbon fiber is made using a pre-preg or RTM [resin transfer molding] process, both of which are much higher in fiber content-65 percent for pre-pregs and 50 percent for RTM. The strength and stiffness of a composite is directly related to the fiber volume content, because the fibers are between 10 and 20 times stronger than the resin by itself.