A new IR-assisted advanced out-of-autoclave (OOA) process from Kubota Research Associates Inc. reportedly enhances adhesion properties and “significantly” accelerates the curing speed of thermoset resin systems for installing adhesive bonded fasteners (ABFs) such as Clickbond studs and standoffs from Click Bond Inc. onto composite fuselage and metal structures.
The P-Wave/PTIR process technology invented by Kubota Research—which was founded in 2000 and is headquartered in Hockessin, DE—is a core technology for the development of new continuous fiber-reinforced thermoset and thermoplastic composites that promise cost/performance benefits compared to conventionally manufactured composites, the company claims.
For the OOA manufacturing technology, PTIR prepreg films are laid up on a mold, and an IR transparent vacuum bag applies pressure on the prepreg. The P-Wave radiation system is scanned across the prepreg and emits a selected range of infrared radiation, which passes through the vacuum bagging material and is absorbed by and heats the PTIR prepreg under pressure for consolidation. The P-Wave system and PTIR method can be used in the tow and tape placement process.
Core technology of the P-Wave/PTIR out-of-autoclave process was developed through National Science Foundation grants, #0512869 in 2005 and #0711789 in 2007, according to CEO Mike Kubota, who shared the development timeline and other details with Aerospace Engineering. The company then applied this core technology to rapid-bond ABFs starting in September 2008 through the U.S. Navy Naval Air Systems Command (NAVAIR) SBIR N08-030. Phase II of that program, which ended in September 2012, saw the TRL 7 (technology readiness level) process jointly evaluated at Bell Helicopter and the University of Delaware Center for Composite Materials (UDel-CCM).
“The project had two subcontractors, Bell Helicopter and UDel-CCM, to validate performances including the cure speed of Bell and NAVAIR prequalified epoxy adhesives, the flatwise tension strength, bending strength, shear strength, and the hot and wet tests compared with baseline,” Kubota explained. Specific performance results could not be shared since the project was developed under the ITAR (International Traffic in Arms Regulations) NAVAIR program.
OEM-qualified room temperature cured structure-grade two-part epoxy adhesives such as Henkel Hysol EA9394 and Magnolia Plastics Magnobond 6398 are used to install Clickbond fasteners, for example, onto composite fuselages. These adhesives typically set in 24 hours and cure in 5 to 7 days at 25°C (77°F). Kubota Research claims that its P-Wave/PTIR process, used with the same qualified adhesives, can bond and cure the fasteners onto the substrate in less than 10 min. The process can be applied under a range of operating temperature conditions from -20 to +50°C (-4 to +122°F).
“The main challenges are heating the bond-line temperature higher than the first surface and not producing thermal degradation on both upper substrate (fastener) and bottom substrate (fuselage),” Kubota shared. “Another challenge was Bell and NAVAIR prequalified epoxy adhesives such as Hysol EA9394 and Magnobond 6398 had to be used without modifying the formulation.”
The process enhances wettability between the adhesive and substrates, resulting in increased fastener-to-substrate bonding strength. The P-Wave/PTIR ABF installation fixture also is reusable and replaces the disposable one-time-use pressure application fixture.
“Legacy technology is using a mechanical and disposable fixture,” Kubota noted, explaining how his company’s process is unique. “P-Wave/PTIR IR-assisted advanced OOA heats adhesive in the bond-line instead of the first surface and cured in less than 10 minutes. The rheology of the adhesive was optimized to enhance the wettability.”
Kubota Research is a member of the UDel-CCM University-Industry Consortium, a center of excellence for research and knowledge in the advanced composites industry. Kubota notes that his company and its global partner Bell Helicopter plan to continue collaborating with UDel-CCM to advance the development of P-Wave/PTIR technology “to bring a new generation of cost-effective composite parts manufacturing methods to the industry.”
The advanced OOA process is in the premarketing stage, according to Kubota, and is expected to be fully commercially available in January 2013. The rapid bonding technology can also be applied to boat and ship manufacturing.