Don’t write off glass thermoset composites as weight-saving automotive body panels.
A new version called TCA Ultra Lite from Continental Structural Plastics (CSP) is in production on the 2016 Chevrolet Corvette, resulting in a 20 lb (9 kg) weight savings on the Stingray Coupe model.
“Through a joint continuous improvement effort, Chevrolet and CSP have significantly reduced the density of the Corvette body panels – from 1.9 specific gravity for the 2013 model year, to 1.6 specific gravity for the 2014 model year to 1.2 for the 2016 model year,” says Christopher Basela, lead engineer for Corvette Body Composites.
The big breakthrough in the technology is the replacement of some calcium carbonate filler with a patented system that uses treated glass bubbles, a lighter density material. A total of 21 body panel assemblies, including doors, decklids, quarter panels and fenders, are molded from TCA Ultra Lite.
There is chemical bonding of the glass microspheres to the resin matrix due to a proprietary surface treatment on the microspheres. Mechanical properties are said to be improved due to the adhesion of the interface. Paint adhesion is also said to be better, particularly after water exposure.
According to the patent, which was issued in April, glass microspheres represents 2 to 12 percent of the total weight of the compound. Conventional fillers are squeezed into voids between the spheres, minimizing the amount of unsaturated polyester resin that is used as a matrix. The mean diameter of the spheres is 16 to 35 microns. Alkoxysilanes are used as surface-activating agent molecules.
CSP says that its patented vacuum and bonding manufacturing processes yield a premium Class A finish with paint and gloss qualities comparable to metals, including aluminum. The material is able to withstand the E-coat process, and passes all OEM paint tests. It also offers reduced costs at all volumes – and for production volumes under 150,000, tooling costs for composites can be as much as 50 to 70 percent less than those for stamping steel or aluminum.
The 2016 C7 Corvette is the first commercial use of TCA Ultra Lite. Tadge Juechter, Corvette Chief Engineer, says the product could be used on more models.
Previous efforts to use glass microspheres in sheet or bulk molding compounds have failed.
One problem was that the spheres tended to become displaced under molding pressure. Another problem has been the tendency of the bubbles to rupture when sanded, resulting in what is commonly referred to as a “paint pop”.