Advances Beyond Prepreg
Hexcel uses the broader definition of OOA in describing its technology. “OOA is what we call a ‘direct process,’ where the resin and reinforcement are combined and cured in the same molding operation,” says Girardy. Hexcel developed HiTape® for use in the manufacture of dry preform for aerospace applications.
HiTape is a dry carbon fiber reinforcement combined with a thermoplastic veil. It enables manufacturers to use an automated lay-up machine to make the dry preform, with laser heat or infrared heat directed at the location where the tape is laid down. The automated lay-up permits faster production.
With the high-performance liquid epoxy resins system Hexcel developed for HiTape, the tape can meet the performance levels required for primary aircraft structures, including impact resistance, Girardy said. The standard curing process for HiTape is low pressure or vacuum infusion at relatively low temperature, followed by an increase in mold temperature to cure the thermoset resin.
NONA Composites (short for No Oven, No Autoclave) is testing OOA vacuum infusion technologies with an eye to reducing costs. “It’s not as far along as the OOA prepregs and RTM and similar types of processes, but it is coming along,” says Ben Dietsch, company president.
One area they’re investigating is non-prepregs. “There’s definitely significant cost savings that can be had, more than 50 percent on materials in some cases,” Dietsch says. But with so many different OOA technologies available, including curing with radiation or microwaves, RTM and infusion molding, comparing the cost of processes can be difficult. “It’s hard to say if you do microwave curing you will save 20 percent over autoclave prepreg,” Dietsch adds.
Dietsch believes manufacturers could improve the quality of OOA parts with better control over curing processes. Technologies like directed hot air impingement or induction heating can provide that improved control, but they can also be expensive due to equipment costs. NONA, which currently uses a well-defined exothermic cure for its vacuum infusion OOA processing, is investigating some of these other options as well.
New curing methods could enable faster OOA production, making it more competitive in the automotive parts industry. “The material vendors are working in this world, too. How do they develop materials that cure very quickly but don’t have the same problems that traditional materials would have if you tried to cure them very quickly?” says Dietsch.