CompositesWorld
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CompositesWorld.com 27 ABOUT THE AUTHOR Michael R. LeGault is a freelance writer located in Ann Arbor, Mich., and the former editor of Cana- dian Plastics magazine (Toronto, Ontario, Canada). mlegault@compositesworld.com supplied by US-based Airtech International (Huntington Beach, CA, US). Te material has a T g of 250°C, low water absorption and very low volumetric shrinkage on cure. Rod Brown, composites manager at LEA, says the resin, as supplied in pails, is highly viscous, and required pre-heating to enable transfer into a feed tank equipped with a thermocouple- controlled tempera- ture controller and lines for infusion and. Tere, the resin was stirred and grad- ually ramped up to the infusion temper- ature of 110°C. As the resin neared the infusion tempera- ture, the tank was ftted with a lid and a vacuum was applied to de-gas the resin. In-oven infusion When the resin was fully de-gassed, the tank was placed in the oven, in which the master had been pre-heated to the resin temperature. Resin feed lines were run from the tank to ports in the bagged layup. Opera- tors then had a pot-life window of about an hour in which to infuse the layup. After infusion was complete, the oven temperature was ramped up to the cure temperature of 185°C and held for 4 hours. After cure, an egg crate-type backup structure was attached and the mold was removed from the master. Ten the mold and backup structure, together, were postcured at 218°C for about 8 hours. "Te biggest challenge, working with this resin, is how to manage the material, lines and mold at the various temperatures," says Brown, noting that at 110°C, "you can still walk in the oven, briefy." Tat's not possible at the cure and postcure temperatures. "So everything has to be staged and ready to go," he cautions. After postcure, the mold was CNC-machined with a 5-axis unit supplied by Anderson America Corp. (Pineville, NC, US) and then sanded, operations that were followed by application of fller and releases supplied by Chem-Trend (Howell, MI, US). Te fnished tool, approximately 76.2 cm by 76.2 cm, was actually a reproduction of a corner section of a tool for a much larger production part. Te benzoxazine-infused mold was used to make test parts, each comprising 30 plies of Cytec 934 carbon/epoxy prepreg supplied by Cytec Aerospace Materials (Woodland Park, NJ, US). Te parts were autoclave-cured at 177°C and 6.21 bar. "Te tool performed great and maintained vacuum integrity through 15 test cycles," reports Brown. He adds that the decision to use benzoxazine rather than BMI to infuse the tool wasn't a strategic decision. "Both materials are very similar in terms of performance and cost," he notes. "We just tested benzoxazine because that's what Airtech ofers. Our ultimate objective was to fnd some alternatives to prepreg and the autoclave." Large aerocomposites? Tat said, Brown sees the results of the project as promising. Although LEA and its aerospace partner have no plans, currently, to fund additional testing, he sees benzoxazine as an OOA tooling alternative for aircraft stifeners, stringers and wing spars. "Te real need for something like this is large tooling because that's where you enter into problems with an autoclave," he contends. But he believes that eventual commercialization of OOA tech- nology involving benzoxazine will hinge, in part, on how benefts and costs weigh out: Te upside of using benzoxazine rather than epoxy to infuse tooling is that it produces fnished tools that are more durable and can operate at higher temperatures. Te downside is that it costs more and is trickier to infuse and cure at the necessarily higher temperatures required to ensure that it will have a viscosity low enough to fully wet out the reinforcement. Although the upside might have enough appeal among aerospace manufacturers to encourage its adoption, more trials and testing will be necessary to pave the path if it is to progress to commercial reality. Read this article online: short.compositesworld.com/BzOOAtool Read more about oven-curable epoxy and BMI prepregs online in "Out-of-autoclave prepregs: Hype or revolution?": short.compositesworld.com/OOAprepreg The performance of epoxies, BMIs and benzoxazines in tooling is compared and contrasted online in "BMI and benzoxazine battle for future OOA aerocomposites": short.compositesworld.com/BMIvsBenz Read more about Textron Airland's independently developed Scorpion warplane online: "New Scorpion twin-jet to debut at Farnborough Air Show": short.compositesworld.com/ScorpionFB "Resin infusion produces autoclave-capable tools for Scorpion jet": short.compositesworld.com/LEAjettool Infused Tooling Trial Pulled from the graphite master, this vacuum-infused male tool comprises 12 layers of woven (2x2 twill) 12K carbon fber fabric in a benzoxazine matrix. It was used to make about 15 test parts. Each part featured 30 plies of carbon/epoxy prepreg, and all were autoclave cured. Source / Leading Edge Aerospace NEWS N E W S N S N E W S E N W S W Benzoxazines for OOA Tooling