There have been advances in fiber reinforcement as well. Aerospace designers have primarily used continuous fiber thermoplastics to achieve the strength and performance predictability required for aircraft parts. But continuous fiber materials have some drawbacks when it comes to fabricating complex parts. “You are generally forming these parts very quickly, and getting the fibers and plies to move around in an extremely short time – often a matter of seconds – is a challenge,” says Leach. “If you have a discontinuous form, you can actually make much more complex parts, because you’re allowing some movement to occur in the fiber direction.” But parts designers have had concerns about the performance of discontinuous fiber materials.
Now there’s another option. In conjunction with NASA, the University of Delaware’s Center for Composite Materials recently developed a form of discontinuous fiber material that has properties equivalent to continuous fiber thermoplastics. Using TuFF (tailored universal feedback for forming) materials, manufacturers could produce aerospace-quality parts at the same production rate as automotive parts, according to the center. (TuFF received an Excellence in Composites “Infinite Possibility for Growth” award at CAMX 2019.)
New resins are speeding up processing as well. Thermoplastic composite manufacturers have been incorporating resins in the polyaryletherketone (PAEK) family into their products since the 1980s. These high-performance polymers are challenging to work with, however, because of more demanding processing conditions, such as high temperature. A few years ago, Victrex introduced low melt PAEK (LMPAEK™) to speed things up.
“LMPAEK was developed to find the balance of these high-performance polymer composite materials with the processability and suitability for automated production systems. These materials require less overall energy to lay up, which can contribute to significantly faster processing speeds,” says James Myers, head of research and development for aerospace and composite applications at Victrex.
Low melt PAEK has similar properties for mechanical strength, chemical resistance and other characteristics as polymers in the PAEK family, but its melting point is about 40 degrees Celsius lower. Although that may not seem significant, it makes a huge difference in manufacturing processes like stamp forming, injection molding and automated fiber placement (AFP), says Gilles Larroque, Victrex’s global strategic marketing manager.
Victrex recently worked with aerospace tooling and automation manufacturer Electroimpact on a LMPAEK demonstrator project. “Using LMPAEK with an automated fiber placement process, we’ve been able to reach 100 meters per minute in lay-up speeds. That’s close to four times faster than a similar PAEK UDT,” says Larroque.