Page 17 - 3D Metal Printing Spring 2016

Later this spring, a 3D-printed flight-critical part printed from a titanium alloy will be demonstrated on a V-22.A U.S. Marine Corps MV-22B Osprey, shown here. (Photo: Staff Sgt. Joseph Digirolamo)
3D
In mid-2014 Vice Adm. Dunaway, then commander of the Naval Air Systems Command (NAVAR), challenged the
AM/Digital Thread Integrated Product Team (IPT) to “operationalize” additive manufacturing (AM) across NAVAIR.
“Our original goal—and it was a stretch goal—was to demo a flight-critical part in three years,” says Liz McMichael, IPT team leader for NAVAIR. “We’re actually going to do it in 14 to 18 months.”
NAVAIR plans to fly its first additively manufactured metal part on a V-22 Osprey
tilt-rotor aircraft this spring. The part, made of the titanium-aluminum alloy Ti-6Al-4V, or Ti64, is considered flight-critical.
But it won’t be the first metal 3D-print- ed part to fly by a long shot.
After GE launched a full-scale produc- tion facility to make 3D-printed fuel noz- zles for its new LEAP commercial aircraft engine, the thrust to print metal parts for tooling, prototypes and production has spread quickly throughout the vast aero- space sector, including commercial and military aircraft as well as space and mis- sile systems.
While the first LEAP engines won’t enter service, on the Airbus A320neo jet- liner, until sometime later this year, GE’s first FAA-approved part—a small housing for the compressor inlet-temperature sen- sor inside its GE90 jet engine—was cleared for commercial flight in April 2015.
In the meantime, MTU Aero Engines has begun mass 3D printing of nickel-alloy borescope bosses for a new Pratt & Whit- ney engine, also to be used on the A320neo. Like the GE temperature sensor, the borescope boss was selected to mini- mize risk in flight, while establishing a business case to confirm the advantages of metal 3D printing.
Metal Technologies
These initial forays into metal 3D print- ing for aerospace have relied on powder- bed fusion technology, which uses high- powered lasers to trace a computer- generated 3D design on a thin layer of metal powder. The beam melts and fuses the powder into solid form. Another layer of powder is then spread over the piece and the steps are repeated hundreds or thousands of times. The machine slowly lowers the platform with each successive layer, so that the part (or parts) builds up inside the bed as it fills with powder. When
the part is complete, the excess powder is blown away.
Different manufacturers use slightly different variations of the technology. Examples include selective laser sintering (SLS), selective heat sintering (SHS) and selective laser melting (SLM). A trade- marked version, called direct metal laser sintering (DMLS), developed by EOS GmbH, of Germany, is the process used by NAVAIR to print its demo parts.
Another powder-bed fusion technolo- gy, called electron beam melting (EBM), was pioneered by Swedish company Arcam. EBM employs a high-temperature electronic beam, rather than a laser, to melt the metallic powder.
“The difference between the technolo- gies is that a laser machine can provide 200 to 1000 W of power, while EB machines provide as much as 3500 W,” says Don Godfrey, engineering fellow for additive manufacturing at Honeywell. The company employs Arcam EBM machines at its Additive Manufacturing Technology Center (AMTC) in Phoenix, AZ, one of four AMTCs operated by the company. According to a recent blog post by Godfrey, “Honeywell is developing this technology to reduce capital-tooling budgets and marching it into production to reduce component costs and to improve quality.
“After a part is built on a laser machine,” he says, “you can open the door and take it out, much like cooking something in your kitchen—it’s about 200 deg., but you can handle it right away. The electron- beam machine never gets below 1900 F. You have to let it cool down for about 8 hr. before you can take a part out of the machine—and that has to be calculated into your overall production time.”
Printing Larger Parts
Because metallic powders are expensive and heavy, powder-bed fusion technology is limited in the part volume it can print, though each new generation of printers seems to accommodate larger and larger builds. Currently, the largest powder-bed fusion machine available, the X line
Holly B. Martin is a freelance science and technical writer based in Winchester, VA (www.hollybmartin.com). She has a B.S. degree in engineering science from the University of Tennessee. In addition to more than 15 years of experience writing for numerous manufacturing trade publications, she has worked for Oak Ridge National Laboratory and The Aerospace Corp.
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