New capability opens the way for high-volume production.
Facing higher Corporate Average Fuel Economy (CAFE) standards of 54.5 miles per gallon in the U.S. and 95g/km CO2 emissions limits in Europe, automotive OEMs are evaluating every option for lightweighting vehicles. The increasing stringency creates a need for new approaches.
Automotive OEMs and Tier 1 suppliers are well aware of the strong, lightweight properties offered by CFRP prepreg and are eyeing the development of fast-curing prepreg to replace metals for a range of structural and Class A surface automotive parts. The attraction is based on the capability for out-of-autoclave compression molding of CFRP prepreg to reduce cycle times for high-volume production.
Until recently, the potential for CFRP prepreg had a ceiling. Production volumes were inhibited by the time needed for thoroughly cross-linked curing during conventional autoclave processing. Significant manual labor for layup is a non-starter, and the steep cost of CFRP prepreg also creates a boundary.
“About 14,000 to 40,000 parts would be considered very high volume for CFRP prepreg, but for automotive applications this is considered low- to mid-volume,” says Adam Harms, marketing manager – automotive for Huntsman Advanced Materials. “Around 20,000 to 25,000 parts per year on a single production line such as the Corvette roof has been the sweet spot for prepreg, an application where it makes the most sense. In automotive, you haven’t reached high volume until about 100,000 parts.”
Several material suppliers have accepted the challenge from OEMs to develop rapidly curing prepregs that can achieve 2- to 3-minute cycle times through compression molding, qualifying prepreg for high-volume production in the area of 80,000 to 100,000 parts per year. The race between material suppliers, Tier 1 suppliers and automotive OEMs is on.
Speed + Quality Control
Compression molding of fast-cure prepregs is being evaluated alongside high-pressure resin transfer molding (HP-RTM) and wet compression molding. In HP-RTM and wet compression molding, the end user places dry carbon fiber into a press, wets it out with an appropriate resin system and applies pressure to form the component. There are disadvantages to these related approaches, says Will Ricci, technical services engineer for Gurit.
“When wetting out the carbon fiber, the fibers may move, compromising directional strength and aesthetic appeal,” he says. “Shifting fibers may cause distortion and negatively impact the distribution of forces within the part, reducing overall part stability, a critical concern especially for structural parts requiring impact resistance. In structural parts positioned where vehicles emit high heat loads, the maintenance of fiber orientation and the polymer’s thermal stability is critical.”