The US Air Force’s 3-D printing experimentation becomes reality
The United States Air Force (USAF) certified the first 3-D printed nonstructural aircraft parts and developed a potentially high-strength, low-cost steel additive manufacturing powder
The United States Air Force (USAF) has been experimenting with 3-D printing (also referred to as “additive manufacturing”) since 2015, aiming to find ways of changing and improving and speeding up aircraft maintenance. But recently, this branch of the United States Armed Forces took such endeavor to the next level by certifying the first 3-D printed nonstructural aircraft parts and developing the AF-9628 powder.
Producing aircraft parts… super fast
USAF has used the Stratasys F900 3-D printer which is capable of printing plastic parts up to 36 x 24 x 36 inches. It uses a material called Ultem 9085 that is more flexible, dense and stronger than conventional plastic.
The printer, which is certified by the Federal Aviation Administration (FAA) and the Air Force Advanced Technology and Training Center, offers new opportunities to manufacture needed parts while saving time and money. “It brings us a capability that we’ve never had before,” stated Master Sgt. John Higgs, 60th MXS aircraft metals technology section chief. “There’s so many possibilities available to us right now. We’re just scratching the surface.”
Technicians are able to download blueprints from an online database that the University of Dayton Research Institute has approved. “The Joint Engineering Data Management Information Control System is where we go to download already approved blueprints,” Higgs explained. “Now, the University of Dayton Research Institute is working with the engineers to get those parts they developed into JEDMICS.”
The first approved project was printed on the Stratasys F900 on August 12 and will replace latrine covers on the C-5M Super Galaxy aircraft. Typically, parts that do not keep the aircraft from performing their mission don’t have as high as a priority for replacement. “The latrine covers we just printed usually take about a year from the time they’ve been ordered to the time they’ve been delivered. We printed two of the covers in 73 hours” Higgs added.
“The latrine covers we just (3-D) printed usually take about a year from the time they’ve been ordered to the time they’ve been delivered. We printed two of the covers in 73 hours” Master Sgt. John Higgs, 60th MXS aircraft metals technology section chief
AF-9628: a revolutionary additive manufacturing powder
The USAF is also involved in another promising study. Parts 3-D printed with “AF-9628”, an Air Force steel, are about 20 percent stronger than conventional 3-D printing alloys, in terms of ultimate tensile strength, according to research conducted by Capt. Erin Hager, an Air Force Research Laboratory employee and recent graduate of the Air Force Institute of Technology’s Aerospace Engineering Program.
AF-9628 was developed by AFRL’s own Dr. Rachel Abrahams; it offers high strength and durability. The formula, nicknamed “Rachel’s steel”, costs less than some other high performance steel alloys including Eglin Steel and HP-9–4–20; however, it is more expensive than common grades used in conventional munitions. AF-9628 is unique since it does not contain tungsten (a greyish-white lustrous metal), like Eglin Steel or cobalt, part of the formula for HP-9–4–20, which is in the Massive Ordnance Penetrator (a 30,000-pound bomb that destroys assets in well-protected facilities).
In working with Rachel’s Steel, Hager utilized powder bed fusion, a type of additive manufacturing in which a laser selectively melts powder in a pattern to create three-dimensional objects. As each layer is complete, the printer distributes more powder on the build area, and the process continues until the part is complete. “To determine if AF-9628 was printable, we characterized the shape and size of the powder and [identified] how it changed with melting and sieving,” Hager stated.
Hager gave the chemical composition of AF-9628 steel to Powder Alloy Corp., a manufacturer in Cincinnati, Ohio. After she received the powder and determined that it melted predictably in the machine, she moved on to creating actual test articles. After printing various parts, she analyzed the resulting porosity, strength and impact toughness.
She explained that many “alloys don’t take to [3-D printing] very well.” For instance, “certain alloys will not melt and they crack a lot once you actually try to make a part.” That being said, when Hager examined her parts, she noted that the mechanical properties were “quite good.” She found no evidence of cracking and described the output as “very similar to traditionally manufactured parts.” Following a more complete examination, she determined that the parts “matched the required 10 percent elongation indicating increased strength without becoming brittle.” Hager determined that the parts “met or exceeded [specifications] straight out of the machine.”
After she successfully created simple parts, Hager began printing more complex designs including several intricate projectiles. She printed about 130 articles including 30 small cylinders, 60 larger cylinders, 20 tensile bars and 20 impact specimens.
The parts she produced are suitable for weapons applications. When the Air Force initially developed AF-9628 for bunker-busting bomb applications, “the original idea was to make the penetrating weapon of the future with exactly the explosive profile desired.”
Currently, the AF-9628 powder is only available in tiny production quantities and companies can take months to formulate it but USAF is hoping that could change in the future.
The United States Air Force’s interest for 3-D printing and its potential applications is quite interesting; I’d even venture to say such partially validates this burgeoning industry.