High-Performance Composites is read by qualified composites industry professionals in the fields of continuous carbon fiber and other high-performance composites as well as the associated end-markets of aerospace, military, and automotive.
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so urc e: V iste x WORK IN PROGRESS Press-molding method emulates autoclave By Sara Black rubber tool insert avoids consolidation pressure "dead zones" and slashs cost. A s the composites industry looks for ways to simplify and accelerate part processing, finding alternatives to autoclave cure has been a recurring theme. The Holy Grail? An alternative that offers the benefits of an autoclave without the high capital and energy costs. Vistex Composites (Howes Cave, N.Y.) may have found one in its (pat. pend.) Thermal Press Curing (TPC) technology. Marketed under the trade name Specialized Elastomeric Tooling, the method reportedly offers gamechanging reductions in processing cost, complexity and energy consumption, as well as short tooling lead times for thermoset and thermoplastic prepreg parts. Dr. Jaron Kuppers, chief technology officer at the startup company, a spinoff from the Rensselaer Polytechnic Institute's Center for Automation Technolo- 34 | gies and Systems (CATS, Troy, N.Y.), says that Vistek's focus was a method that could apply an autoclave's uniform temperature and consolidation pressure to parts both faster and cheaper. What the company ultimately developed is similar to the metal world's Guerin process, sometimes called rubber pad forming, in which sheet metal is pressed between a forming die and a block of rubber. In TPC a composite prepreg layup is placed on a heated and temperature-controlled metal "curing mold." A matching "base mold" is created and fitted with a thin, cast-in-place silicone rubber face, what Vistex calls a "mask," in the approximate shape of the part. The layup is processed by enclosing the two molds in a press and applying pressure roughly equal to that applied by the autoclave, which has a functional limit, according to Kuppers, high-performance composites of about 125 psi/8.62 bar. The rubber mask aids in consolidation and, most importantly, equalizes the applied pressure across the part surface while the tool mold heats and cures the part. "The uniform pressure across the part surface effectively reproduces the consolidation pressure provided by an autoclave," asserts Kuppers. "The key is designing the mask for uniform pressure." Although the pressure on the vacuum bag during autoclave curing is uniform, he explains, "this doesn't necessarily mean that the pressure on the part is uniform. In some situations, such as when a bag is trying to bridge a really sharp corner, the bagging material gets stuck, then external pressure is not transmitted to the part." In fact, a void results that is filled by excess resin. The rubber mask and base mold is designed, says Kuppers, to