Page 20 - 3D Metal Printing Spring 2016

3D Aerospace Metal 3D Printing
must be submitted to the FAA.” Honeywell plans to use its cer-
tified engineering-design data
(EDD) lab in Bangalore, India,
to help test and develop new
powders, so that data can be
used in the engineering design
of a component. In addition to testingthepowder,gettingaprinted componentapprovedtakesmonthsand involves printing more than 1000 test bars that must undergo tensile and life-cycle testing, Godfrey adds. Then, several parts must be built and bolted to engines on test stands and flight test beds.
Processing and Heattreatment
Printing parts isn’t the end of the story—post-production processes also come into play.
“There’s still a lot of milling, lathe work and grinding to do on printed metal parts, depending on the part being made,” says Tim Simpson, professor of mechanical and industrial engineering and engineer- ing design at Pennsylvania State Univer- sity. Simpson also is co-director of the Penn State Center for Innovative Materials Processing through Direct Digital Depo- sition, which helped NAVAR print its first parts.
Though the high-temperature EBM process eliminates residual stresses, most metal 3D-printed parts will require heat- treatment in an oven to relieve stresses in the material, Simpson says.
“As you’re printing the part, it builds up stresses internally, and at a minimum you need to stress-relieve the part so that when you cut it off the build plate, it won’t warp or crack. And, often heattreatment is needed to obtain the required micro- structure,” Simpson says. “The cooling schedule may be critical, to achieve the correct microstructure and properties.”
Another post-processing step used par- ticularly for 3D-printed metal aerospace components is hot isostatic pressing (HIP). This process simultaneously applies heat and high isostatic gas pressure to printed parts to improve their mechanical qualities. Alcoa pioneered the use of HIP technology for aerospace applications in
Researchers at Northwestern University recently printed this copper lattice struc- ture using a new room-temperature metal-printing process that appears to provide the ability to produce complete- ly novel structures for aerospace appli- cations. (Photo: Dr. Adam Jakus, North- western University)
the 1970s, for use with cast parts. “During HIP,” explains Simpson, “the part is heated and essentially squeezed, which rearranges the material at the molecular level. The resulting phase trans- formations provide a different crystal growth structure that eliminates any voids or defects. The result is improved fatigue
strength and prolonged part life.”
Future of 3D Printing
It’s safe to say that metal 3D printing is revolutionizing the aerospace industry. All of the major players are printing, test- ing and beginning to fly 3D-printed parts. Meanwhile, new technologies and mate- rials for metal aerospace printing continue to advance, along with a better under- standing of how the printing process affects the mechanical properties of a part.
“Right now everybody in the industry is printing powders that have been around for 20 years, because it’s a new technology. When you change to a new powder you’re adding another unknown,” says Honey- well’s Godfrey. The company has some 40 new types of metal powders it hopes to test for 3D printing.
As new and different alloys and super- alloys become available, companies will have more options to create parts with unique material properties, even within
the same part. Before that can hap- pen, part designers must be able to understand exactly what occurs during a print, at the
micro or nano scale.
“We’ve got some unique
capabilities for modeling the actual printing process itself, and understanding how much a part is going to deflect as it’s built,” says Penn State’s Simpson. For example, a colleague of Simpson’s, engineering pro- fessor Pan Michaleris, is modeling a 10-ft. wing printed with a Sciaky EBAM system, funded by the Air Force Research lab. The goal is to learn how the wing dis- torts due to heating and cooling of the metal deposition, and how to mitigate the
distortion.
The future of 3D metal printing for
aerospace also may include new tech- nologies, like the room-temperature metal ink-extrusion process pioneered by Ramille Shah, assistant professor of mate- rials science and engineering, and her team at Northwestern University. Using a 3D bio-plotter system developed by EnvisionTec—the same type of extrusion printer used to build biological-tissue scaffolding—Shah and postdoctoral fellow Adam Jakus are printing with a liquid ink made of metal or mixed metal powders, combined with solvents and an elastomer binder. The printing takes place at room temperature, and afterward the structures are heated in a simple furnace where the powders fuse together and the binder melts away, leaving a solid metal part.
The exciting aspect of the new tech- nology is that after the object is printed, the structure remains flexible due to the elastic polymer binder. This allows it to be manipulated before being fired. According to Shah, the process potentially could be used to 3D-print full sheets that are meters wide, which then could be fold- ed into large structures, with the only lim- itation being the size of the furnace.
These and many other advances may someday result in cheaper, faster and more uniform processes and materials for 3D printing of metal parts in the aero- space sector. 3DMP
18 | 3D METAL PRINTING • SPRING 2016
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