Steel truck beds. Aluminum truck beds. The battle to create the lightest, strongest pickup cargo bed intensifies yet again, as carbon fiber debuts as the bed material for the 2019 GMC Sierra Denali.
“This is a revolutionary application on the next-generation Sierra,” said Mark Voss, General Motors’ engineering group manager for pickup boxes. Voss and others involved with the industry-first carbon fiber truck box spoke with Automotive Engineering at the new Sierra Denali’s recent global debut in Detroit.
The carbon-fiber composite material, developed by GM and Continental Structural Plastics, offers superior dent, scratch and corrosion resistance, according to Tim Herrick, the 2019 Sierra’s chief engineer. Compared to the Sierra’s standard steel truck bed, the carbon fiber bed is 62 lb (28 kg) lighter. Because of the material’s formability, the sides of the carbon fiber box are pushed further outward--increasing the bed’s total volume by a cubic foot.
The carbon-fiber bed will be available for the GMC Sierra Denali in short-bed configuration. This 5-ft 9-in short box is 1 in (25 mm) longer and 2 in (50 mm) taller than that of the previous generation Sierra.
“We didn’t start out saying, ‘Let’s create a carbon-fiber truck box’,” Herrick said, pointing out that other carbon fiber applications, including some under the body, were considered before the cargo-bed program got the green light.
Making a carbon-fiber truck bed a production reality began with creating the material chemistry. “The decision to go with a carbon-fiber thermoplastic (nylon 6) allows for reusing and recycling the material,” noted Voss. “There are actually two parts on this cargo bed that are made from 100% of the recycled material that’s created during the production process,” he said, referencing the right- and left-side front stake pocket reinforcements.
Rather than opting for woven carbon fiber, the material is in a “chopped” form. “We really want to use every ounce of fiber—and with the chopped fiber we’re able to do that,” Voss explained.
The production process requires the joining of two layers, according to Herrick. “With sheetmetal, you’d spot-weld the layers together. But with this, we’re using a structural adhesive and a mechanical fastener at the beginning of the bond to prevent the susceptibility of peeling,” he said.
Akio Nakaishi, general manager of the composites business unit for the Teijin Group, parent company of Continental Structural Plastics, said the molding of parts has a one-minute takt time. “That is very innovative and it makes us able to produce this part on a large scale,” Nakaishi noted.
To confirm the cargo bed’s durability, the GM team loaded and unloaded objects that included snowmobiles with carbide-steel runners. They also flagrantly dumped in bricks, rocks, firewood and other materiel. Said Voss, “We tested many, many different scenarios of how the truck bed could be used and abused.”
Production versions of the carbon fiber truck bed will differ in one significant fashion from the prototype version shown to media at the vehicle’s debut. “A special production tool will be used that will make the top of the corrugations have a sandpaper-like grip,” said Voss. “The lower portion of the corrugation is made from a smoother grain, making it easy to wash out sand, dirt and mud.”
Workers at Continental Structural Plastics plant in Huntington, IN, will mold and form the carbon-fiber bed, which will then be trimmed out at GM’s Fort Wayne, assembly plant.
The 2019 GMC Sierra Denali goes on sale this fall.Continue reading »