Additive manufacturing, also called 3D printing, is an integral aspect of advanced manufacturing, and it keeps getting better with advanced materials. Advanced materials are like high-tech cloth, woven together with multiple chemicals and other properties, which are often stronger, lighter, more heat resistant, or in some other way better suited to certain jobs. One of the latest breakthroughs in this area is ESD PEKK with discontinuous carbon fibers, which is leading to exciting advancements in aircraft and spacecraft design.
What Makes It So Special
ESD PEKK stands for electrostatic dissipative (ESD) PolyEtherEtherKetone. That’s a long name that means it is a plastic with carbon fiber in it. But this isn’t just any composite material: It is a high-performance thermoplastic.
“It makes aircraft cheaper, lighter weight and faster to build,” said Eric Barnes, Northrop Grumman fellow in additive manufacturing and engineering.
Northrop Grumman developed ESD PEKK in partnership with NASA and the U.S. Air Force Research Laboratory.
The process works just like many other additive manufacturing processes. A powder material is put into a vat, and then a laser heats the material to melt it at precise locations. The process is repeated layer by layer to build the required part.
“One of the benefits as compared to other high-performance thermoplastic is it’s relatively easy to process,” said Barnes. “It brings a lot of really good performance properties to our applications.”
Unlike other 3D printing materials, ESD PEKK has properties that meet Federal Aviation Administration requirements for crewed aircraft. This means that more aircraft manufacturing can benefit from the perks of 3D printing, such as rapid prototyping, customization and portability. The performance properties of this material include:
- High thermal stability — the material will stay stable, with minimal change, up to high temperatures.
- Outstanding chemical resistance — the material won’t be affected by chemicals, solvents and liquids as some polymers are.
- Low fire and smoke toxicity
- Excellent mechanical properties over a wide range of temperatures
- Little susceptibility to gamma radiation and thermal cycling in space — the material is only slightly affected by radiation. (Most polymers can’t handle gamma radiation at all; they break down.)
- Doesn’t outgas in a vacuum space environment — outgassing is an issue that makes other materials unsuitable for space.
Regarding outgassing, Barnes explained, “When you put material in a vacuum in space, especially polymers, some of the molecules can come off and float around.” He added, “Eventually they attach to something and create a film.”
According to Barnes, in a recent experiment with America Makes and NASA, engineers saw that ESD PEKK lasted even under the most extreme radiation and temperature conditions.
“It survived unique space environments with gamma radiation, outgassing and thermal cycling [requirements] that most polymers do not meet,” Barnes said. “Most polymers are not able to be used in space because of those requirements, or those conditions.”
Previously, manufacturers could only use less capable polymers for additive manufacturing. Those materials don’t meet safety standards for crewed aircraft because they give off toxic chemicals when exposed to fire, and they don’t have ESD capability.
The new material incorporates carbon fiber into the powder. This helps prevent the static discharge buildup that can occur on an aircraft. Just like the little sparks that can happen when you shuffle your socks across a rug, you can get static buildup on an airplane. This is a common problem in the environmental control system ducting of an airplane, Barnes said. “You want it to go somewhere to prevent it, so we incorporate carbon fiber,” he explained.
ESD PEKK solves several problems in aerospace manufacturing. Because it’s approved for manned aircraft, it allows new types of aircraft to benefit from additive manufacturing. These benefits include the ability to make unique designs tailored to the requirements. For example, when an aircraft is in production and you need to make changes, it’s normally a huge disruption to the schedule. Additive manufacturing doesn’t require tooling, so the whole process is faster and easier.
This manufacturing process also saves weight, which is a huge benefit for aircraft and satellites. A component that used to be made of several parts can now be printed as one single unit.
It can also save volume, which is limited in places such as a fighter aircraft, where space is premium and electronics take up all the room.
“We have the potential to design all these subsystems, such as ducting and heat exchangers, to fit volumetrically, like a jigsaw puzzle,” Barnes said, “Because you can tailor all these shapes to fit like a jigsaw puzzle, you can fit more stuff in an airplane belly or fuselage.”
Rapid Prototyping for Aerospace Applications
This material will also give engineers more flexibility during the design process because they can iterate the best solutions.
“It gives us creative freedom without worrying about the cost or time penalties,” Barnes said.
He explained that ESD PEKK can be used in many aerospace applications; in addition to its potential use in ducting as mentioned above, it can also be used to manufacture access covers and brackets.
“Tooling is a huge driver in the schedule of aircraft fabrication,” said Barnes. “It typically takes at least six months to get most tools in place. We can often get them done in a week now.”
Additive manufacturing has already done so much to transform many industries. Now, materials engineers are continuing the evolution by developing new materials to expand 3D printing’s capabilities.