A significant move is afoot in the aerospace industry to find alternatives to effective yet expensive autoclaving for curing composite parts.
Quickstep Technologies from Australia has developed an out-of-autoclave (OOA) process built around a low-pressure curing chamber that resembles a stamping press. A flexible membrane separates the circulating heat-transfer fluid from the mold and composite component. The system employs optional vibration while applying balanced pressure, vacuum, and heat to compact the part and remove air during cure.
The company advertises cycle times between 40 to 120 min for many traditional autoclave-qualified materials. One comparison test using Hexcel 914C demonstrated a 110-min cure time using Quickstep vs. 300 min for a comparable autoclave cure.
“In general, any thermoset system that cures at 200°C or below can be cured in Quickstep. This includes all epoxy systems and most BMI resins, as well as polyester and vinyl ester,” explained Dale Brosius, Chief Operating Officer, Americas and Europe, Quickstep. It consolidates a limited number of thermoplastics as well. “We have processed polypropylene and several other low-temperature thermoplastics.”
Because it uses fluid circulating around a part, the Quickstep process is suited for parts of modest curvature, such as airfoils, helicopter blades, and spars, according to Brosius. And the process is scalable. “We designed a system that could cure a commercial aircraft wing skin, using larger tanks and multiple curing zones,” he said.
To date, Quickstep has processed certain carbon-fiber prepregs in fewer than 30 min total cycle time.
The company recently signed a memorandum of understanding with Lockheed Martin and Northrop Grumman for the companies to work toward finalizing a long-term agreement for Quickstep to supply 19,325 composite parts for the F-35 Joint Strike Fighter.
“The components covered by the MOU are currently qualified for autoclave production, and Quickstep in Australia will use the autoclave process to make these production parts,” said Brosius.
Quickstep’s U.S. subsidiary and Vector Composites, both located in Dayton, OH, recently teamed up to complete a Phase I Small Business Innovation Research project for the BMI resin used in the Joint Strike Fighter, supplying panels for testing. The companies are currently in discussions regarding a multiyear Phase II effort that would include manufacture of representative components.
“Out-of-autoclave technology is evolving,” said Gordon Emmerson, Product Development Manager in R&D for out-of-autoclave resin systems for Cytec Engineered Materials. “Current systems meet performance requirements for aircraft primary structure applications, but new generations will continue to strive for much higher toughness, compression, and impact resistance.”
Emmerson believes resins of the near future will have shorter curing and longer working times. He also points to development of bonding methodologies, such as “co-cure over core,” that would allow OOA technology to develop lighter, tougher structures using honeycomb panels.