Carbon fiber pickup box: A GM redux?

The 18^th Society of Plastics Engineers Automotive Composites Conference and Exhibition (SPE ACCE) was held in Novi, MI, US, in early September. This year’s event was a testament to the continued high level of interest in composites for automotive applications, drawing a record 1,100 registered attendees and nearly 100 technical papers over the three days. More than 75 of the industry’s leading companies had exhibits, and the show floor was populated with many innovative vehicle applications.

Among these included advances in structural thermoplastic overmolding, combining continuous tapes or fabric prepregs with short fiber-reinforced compounds to provide edge details and complex features. Also on display was a hybrid thermoplastic (long glass inner panel with low-CTE unreinforced outer panel) tailgate for the 2019 Jeep Cherokee, carbon fiber SMC wheels for urban mobility vehicles and a phenolic-based sheet molding compound (SMC) for a fire-resistant battery enclosure demonstrator. Ford and Warwick Manufacturing Group in the UK showed a front suspension component combining steel, carbon fiber/epoxy prepreg and carbon fiber/vinyl ester SMC molded in a single process.

One innovation that attracted considerable attention was the CarbonPro composite pickup box, slated for production starting in mid-2019 for the GMC 1500 Sierra Denali full-size truck. The display was augmented by a morning keynote speech from Mark Voss, engineering group manager of body structures, advanced composites and pickup boxes, at General Motors. I have known Mark since 2001, when he was new to composites at GM and I was serving as the project manager for the Tier 1 supplier of the 2004 Corvette Le Mans Commemorative Edition carbon fiber hood, GM’s first Class A carbon fiber panel on a production vehicle. This component led to deployment of carbon fiber on future generations of the Corvette platform. Mark and I co-authored a paper for the 2004 SPE ACCE on the design and manufacturing process for the hood.

Initially unveiled earlier in 2018, the CarbonPro box is GM’s first foray into using carbon fiber outside Corvette or high-performance versions of the Cadillac line. Up to this point, all previous carbon fiber components have been made from thermoset epoxy prepregs. The truck box changes that paradigm by being thermoplastic-intensive, employing a 35% chopped carbon fiber-filled, UV-resistant polyamide 6 resin for the box floor, sides and end panels. GM has worked closely with material supplier Teijin since 2011 to develop the Sereebo manufacturing technology used to make the structure, resulting in a box that is 28 kg lighter than the equivalent all-steel version. GM claims that testing shows it to be more durable than steel or aluminum, or any fiberglass composite box on the market. Molding of the thermoplastic composite mat is principally via compression, similar to SMC. The box is truly multi-material; in addition to the thermoplastic box interior, other supporting components have been produced from recycled in-plant offal (thermoplastic), thermoset SMC and steel. The outer panels of the box remain in steel and are painted the body color. Molding of the box components and assembly will occur at Teijin subsidiary Continental Structural Plastics’ facility in Huntington, IN, US, then shipped to GM’s nearby Fort Wayne, IN, assembly plant.

Wait. Why does this story have a familiar ring? Didn’t GM release a truck with a composite pickup box years ago? Indeed, it did. Called the Pro-Tec box and molded in the same Huntington factory as the new CarbonPro version, it was offered as a customer option on certain versions of the Chevrolet Silverado and GMC Sierra pickups starting in 2001. It was one of the largest parts produced using chopped fiberglass preforms and polyurethane resin, employing the structural reaction injection molding (SRIM) process. I visited the Huntington factory and wrote a feature story about the box in the April 2002 edition of Composites Technology. In production for only two years, only an estimated 10,000 boxes were produced, less than 10% of the anticipated volume. While a technical success, the box was considered a commercial failure, attributed partly to its only being available in short-bed version, and partly to a lack of promotion by GM to incentivize dealers to sell the $850 upgrade instead of a steel box with a thermoformed bedliner.

Is CarbonPro destined for the same fate? I hope not, and so should the composites industry. Slated for initial production of 15,000 per year and aimed at a specific high-end target market, GM is making sure to walk before it runs. Even at relatively low volumes, the application will consume sizable quantities of carbon fiber. Improvements in materials and manufacturing costs could see growth of this and other applications.