Aircraft engineers looking for ways to simplify the joints in the parts they design could find an alternative in a new thermoplastic composite material from GE. The material is an ULTEM polyetherimide (PEI)-based composite that's thermoformable.
Rob Butterfield, director of design at Fitch, Inc., an industrial firm affiliated with GE, says that thermoforming offers deeper draws than compression molding-six inches for thermoforming vs three for compression molding. "The main benefit of the deep draw is that it allows us to create 3D curved shapes," he says. More importantly, from an assembly standpoint, he says the thermoforming process enables a form on in-mold assembly, and that reduces the need for secondary operations.
GE itself has experimented with heat-activated adhesives to join plastic subparts to the main composite component while both are inside matched-metal tooling. The company has been able to press metal attachment points into the composite surface during the thermoforming operations.
Says Butterfield, the ability to create complex curves and mold in attachment points could reduce the complexity of joints, particularly where metal meets plastic. "We can do away with features like returns and flanges," he asserts.
Additionally, in forming typical aircraft-interior parts, Butterfield has found that thermoforming's cycle time of three-to-five minutes offers a significant productivity gain over the 15-60-minute cycle time for compression molding comparable thermoset composite parts. Thermoforming pressures are a fraction of those needed for compression molding, and that low pressure translates into less expensive tooling and processing equipment.
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| Plastic sheet made from GE's ULTEM has been used in the aircraft industry for more than a decade. The fact that it is thermoformable means it could simplify joint design. |