FACC: Aerospace infusion pioneer

Although it’s “new” to aerospace, liquid resin infusion has been the focus of R&D at FACC (Ried im Innkreis) since 2001. “The issue,” said FACC’s aerostructures product development director Hermann Filsegger, “is in getting 100 percent wetout with no voids in a large part with this much complexity.” That’s not, by any means, an easy task. The skins FACC developed for Moscow, Russia-based Irkut’s MS-21 wingbox, for example, are more than 1 inch/25.4 mm thick at the roots, with stringers on top. On such a critical component, Filsegger pointed out, “It is not acceptable to go back and do ‘emergency’ processes to remediate dry spots.” 

The difficulties encountered in the infusion of large parts prompted FACC to develop its patented process, called membrane-assisted resin infusion (MARI). Filsegger contends that it does not infringe on the Vacuum Assisted Process (VAP) patent because the membrane is not applied directly to the part surface.

“It is still in the breathing path but easier to apply and enables a very robust process that takes care of the consistency problems while delivering 100 percent impregnation.” When asked about the cost of producing primary structures in this way, Filsegger explained that the dry fiber lay down is much faster than hand layup and even automated prepreg layup, due to the lack of tack. “This integrated wing panel has just a slightly curved surface,” he noted. “So laying these fabrics is like rolling out carpet. The noncrimp fabric basically prefabricates your laminate, configuring five plies into one layer.” (See photo.) 

The company continues to refine its proprietary MARI process with an eye toward production of primary structures. Can OOA liquid infusion molding compete with ATL prepreg in production manufacturing? Filsegger said yes, assuming some necessary innovations in NDT. “But we still need to work on the right fiber materials for permeability and also better flow resins with a short cure time.”

He pointed out that the entire system must be developed together — fiber, resin, process and inspection — and much work remains in optimization. Well-developed processing technology notwithstanding, such work also demands a commitment in time and perseverance. “Our thermoplastic copolymer is woven into the fabric, making up 8 percent of the laminate without any clustering or filtering of the toughener,” he said, by way of example. “We did many tests, trying four to five resins and then 10 to 15 different combinations of parameters to see what worked and how to minimize variability, realizing that permeability is the largest cause of unreliability in infusion.”

“Only one resin worked,” he added, naming Cytec’s (Woodland Park, N.J.) 977-20 toughened epoxy resin system. 

This short article is a sidebar to a feature article titled "FACC AG: Aerocomposites Powerhouse." To read the main article, click on its title under "Editor's Picks," at top right.