Northrop Grumman bets on PBF 3D printed ESD PEKK for space
In a recent publication on the company’s official website, Northrop Grumman engineers focused on the benefits of PBF 3D printed ESD PEKK materials for aerospace applications. The evolution of additive manufacturing has opened a new door for advanced materials. One such additive advantage comes from electrostatic dissipative PolyEtherKetoneKetone (ESD PEKK), which according to Northrop Grumman fellow Eric Barnes, “makes aircraft cheaper, lighter-weight and faster to build.”
But how does this high-performance thermoplastic work? What benefits does it offer? And what does it mean for the future of aerospace manufacturing frameworks? One of the benefits as compared to other high-performance thermoplastic is it’s relatively easy to process. It brings a lot of really good performance properties to our applications.
The static quo
Static is a serious problem for aircraft. Just as static electricity can build up when you rub a balloon on your hair or scuff your socks along a rug, so too can static charge quickly accumulate in critical craft controls. Without an easy discharge path, it can cause significant damage or even systems failure.
Northrop Grumman engineers use ESD PEKK to help solve this problem through the use of discontinuous carbon fibers. This means adding carbon fiber to additive manufacturing material powder. This creates a natural outlet for static discharge in environmental and other aerospace systems.
“You want it to go somewhere to prevent it,” said Barnes, “so we incorporate carbon fiber.” What’s more, the distribution of carbon throughout the material means that no matter the system and no matter its location, it’s protected by a discontinuous defense.”
While shaking off shocks significantly benefits this advanced aerospace manufacturing material, that’s not its only advantage.
“One of the benefits, as compared to other high-performance thermoplastic, is it’s relatively easy to process,” noted Barnes. “It brings a lot of really good performance properties to our applications.” In addition, ESD PEKK meets key requirements set out by the Federal Aviation Administration (FAA) for building crewed aircraft, including improved thermal stability, enhanced chemical resistance, reduced radiation damage, absent outgassing.
As Barnes noted, outgassing is a significant problem in space. “When you put material in a vacuum in space, especially polymers, some of the molecules can come off and float around. Eventually, they attach to something and create a film,” he says. Over time, this film poses both functional issues for the craft and survivability problems for the crew, especially in confined spaces. However, this advanced thermoplastic produces no outgassing in a vacuum environment, making it safe for spacecraft manufacturing.
Barnes makes the benefits of ESD PEKK clear: “It survived unique space environments with gamma radiation, outgassing and thermal cycling requirements that most polymers do not meet.”
ESD PEKK options
It is not fully clear if Northrop Grumman engineers developed the ESD PEKK material for internal use or are resorting to external services. Today there is only one company offering ESD PEKK PBF 3D printing services. It is Hexcel, which established its HexAM division after acquiring the aerospace division of Oxford Performance Materials, the first company to develop the laser PBF process to enable EOS machines to process PEKK and PEKK composite powders.
Hexcel’s flagship additive material, HexPEKK-100, includes carbon in its formulation specifically to provide electrostatic discharge (ESD) requirements. In addition, Hexcel’s latest material offering, HexPEKK EM, goes even further with a resistivity that is more than three orders of magnitude lower than HexPEKK-100. HexPEKK EM maintains all the advantages of high-performance 3D-printed PEKK thermoplastic making it suitable for many components on aerospace systems.
Other possibilities for ESD PEKK materials in AM are provided via thermoplastic extrusion processes. Filament extrusion market leader Stratasys recently introduced the Antero 840CN03 — a high-performance, PEKK-based electrostatic discharge (ESD) thermoplastic. Advanced filaments manufacturer 3DXTECH also offers ESD PEKK filaments made using Arkema Kepstan PEKK (PolyEtherKetoneKetone) and state-of-the-art conductive additives, for one of the highest-performance polymers in world and ideal for demanding applications. Both filament materials are targeted for use in the highest-spec situations where tightly controlled static dissipation, thermal properties, and mechanical performance properties are required.
Space-bound
For Northrop Grumman, inherent material benefits are only half the battle — ESD PEKK also delivers when it comes to the speed, safety and scalability of aerospace manufacturing. By printing approved aircraft parts as single units rather than multiple pieces, manufacturers can reduce total weight and improve flying time. This advanced thermoplastic also offers increased flexibility in design and deployment because it can be used to create many things, including ductwork, access covers, brackets and craft-specific tools.
“It gives us creative freedom without worrying about the cost or time penalties,” said Barnes.
Also critical? Volume. In small-space applications, such as fighter craft or space shuttle cockpits, ESD PEKK makes it possible to print parts that fit as part of a larger plan rather than individual items. We have the potential to design all these subsystems, such as ducting and heat exchangers, to fit volumetrically, like a jigsaw puzzle,” said Barnes. “Because you can tailor all these shapes to fit like a jigsaw puzzle, you can fit more stuff in an airplane belly or fuselage.”
When it comes to aerospace manufacturing, advanced thermoplastics such as ESD PEKK pave the way for faster builds that meet higher performance thresholds and help to further the future of human innovation.
