Paul Roehm, product development engineer for advanced product development at Shape Corp., says the composite engineering company was already exploring advanced development efforts into pultrusion when approached by GM. The OEM was interested in using a composite solution to reduce the weight of the Stingray while meeting tough performance requirements.
The team ultimately chose a blend of carbon fiber and Scott Bader’s Crestapol® urethane acrylate resins to achieve the right balance of strength and lightweight properties for the bumper beam. In collaboration with Germany-based fiber composite pultrusion company Thomas Technik + Innovation, Shape engineers began prototyping pultruded profiles. The engineers started with straight profiles to develop an initial understanding of the manufacturing process and resulting product attributes before pushing for the industry’s first curved pultruded profile.
“In addition to the required quality and complexity of the targeted profile, with its multi-hollow design and thin walls, we also needed to be able to make the pultruded profile with curvature for our targeted application, something not done in the industry today,” explains Joe Matecki, Shape advanced product development product manager.
To create the curved profile, the engineering team had to rethink the standard pultrusion process. “In typical straight pultrusion, the grippers move to constantly pull the part,” explains Roehm. “To add curvature in thermosets, the part needs to be cured in a curved state.” The bumper beam production cell developed by Thomas Technik uses a curved, moving die to pull the part and a stationary gripper.
Photo Credit: EconCore
The finished bumper beam was to be bonded to the steel structure at the rear of the car, yet this presented another challenge. Several structural adhesives were tested to find the best combination of strength and toughness to meet the crash, impact and durability requirements necessary to achieve Chevrolet’s standards, as well as the high temperatures of the electrophoretic coating process, the finishing process used for steel components. To assemble the bumper beam on the manufacturing line, it had to withstand this tough primary finishing process. The team selected Crestabond® M7-05 in part due to its ability to bond under the high-temperature test protocol. Not only was the finished part able to achieve stringent Class A surfacing requirements, but it was able to do so on the primary manufacturing line.