Although the technology is still in its early stages of development as something beyond its early years as a curiosity, it already is being used in aerospace and defense, primarily for prototyping under the term “additive manufacturing,” but also for the temporary replacement of non-critical parts as 3D printing. According to GE Additive in Auburn, Ga., those are two of the pioneering sectors for additive manufacturing.
“These sectors are characterized by small batch sizes and manufacturer-specific adaptations. At the same time, these products are renowned for having very longlife cycles, and extremely high safety requirements. High levels of thermal or mechanical loading, especially during take-off and landing or if there is air turbulence, are one of the special features of the requirements profiles for most components,” according to the company.
When it comes to product longevity, 3D printed components may be used in passenger aircraft for more than 30 years. In December 2019 the U.S. Air Force, within its Materiel Command’s Rapid Sustainment Office at Wright-Patterson Air Force Base, Ohio, set up the first program office for agile manufacturing. The goal was to think about the strategy and overall adaptation of agile manufacturing throughout the Air Force; what are the manufacturing materials, processes and technologies needed and how to deploy that across the service.
“The real need for us is 50 percent of the Air Force supply chain is provided by a single source or no source at all, so we’re looking at additive manufacturing as a way to provide a new source,” says Nathan Parker, Deputy Program Executive Officer in the Rapid Sustainment Office. “There are a lot of nodes in the value stream — from reverse engineering to material and machine quality to production and support, all of which we are involved in, to one extent or another.”
Use of 3D printed parts is growing, Parker points out. “Looking at how we are doing, two to three years ago there were around 100 printed parts, today there are almost 2,000. Obviously, we want to continue to grow that and apply what we have learned across the enterprise.”
Between metal and polymer, the Air Force has more than 130 machines, all in major fixed facilities in the U.S. The service has special needs, however. Some Air Force 3D printing needs only now are beginning to be addressed, some of which remain outside of today’s most advanced technologies.”
For the Air Force, production capability is the key. “It’s helpful to think of these as individual nodes that have to grow in unison from a technology perspective,” Parker says. “I can have a large quantity of qualified materials to print parts, but if I don’t have production capacity, it won’t really move the needle. So we’re looking at what machines are needed and where and what materials are available to pull all that together. We’ve had a great improvement over a short period of time, but how do we continue to grow it? We need testing to ensure these parts are safe to fly. There are a lot of things in the overall process we have to work through — it’s not just a matter of materials and machines.”
The U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., also is heavily involved in advancing and improving 3D printing.
“Open Manufacturing was a very elaborate program — how do you get first time quality when you print something. The big problem with printing now is the materials properties are quite different from what you find in bulk material and they change during the build of the part, primarily due to the thermal history,” says Jan Vandenbrande, program manager in the DARPA Defense Sciences Office (DSO).
“The consequence is your final parts will have different properties through the entire build, so how do you satisfy the original requirements of structural integrity; how much energy should you deposit; how fast should we traverse; how much material should you lay down? We put together a computational system to tell how to set the machine to get first-end quality,” Vandenbrande explains. “That means now we have shown you can actually use computational tools to figure out how to do something without having to do it many, many times to get a quality build.”
Vandenbrande was DARPA’s program manager for the now-completed Open Manufacturing program and heads the agency’s Transformative Design (TRADES) program.
“3D printing allows some control over material properties at pretty much every point and the creation of very fine micro structures,” Vandenbrande says. “If configured properly, you can create capabilities that don’t exist in nature; you can create a structure with built-in resonators. The problem is trying to design something of this complexity is beyond what current CAD/CAM can handle. TRADES is trying to come up different ways of representing shape, compute strength and how to meet design objectives.”
State of the art
The state-of-the art in 3D printing enables the creation of components for a wide range of applications that cannot be made with other manufacturing methods. An example is the General Dynamics leak fuel nozzle. They created a printed fuel nozzle as a monolithic part, which eliminated all the internal brazing that was causing failures. The result was an intricate fuel nozzle with a lot of internal structures to mix air and fuel that no conventional manufacturing method can accomplish.
However, it is still very hard to control material properties and defects that may appear. Another problem is the accuracy is still not quite as good as desired.
“It’s a rapidly changing field with a lot of innovation happening. Several of our sites have 3D printers for plastic prototypes and we’ve started using other materials, such as metals. On the metal side, there is a lot of effort going on, especially by platform manufacturers, who have the resources to tune their processes and do materials research,” says Ivan Straznicky, Chief Technology Officer for Advanced Packaging at the Curtiss-Wright Corp. Defense Solutions division in Ashburn, Va.
“The main metal formation methods include direct metal laser centering, which is a subset of powder bed fusion, and directed energy deposition, which is not quite as developed. One of the main materials is aluminum silicon magnesium, which has good properties for being made into powder and laser meltability.”
Curtiss-Wright is using 3D prototyping for fit checks. As for actual parts, that is still in the R&D stage, mostly on the research side. Even so, Straznicky agrees with Vandenbrande that, while not a high volume manufacturing process, 3D printing can create parts impossible with traditional manufacturing processes. That, he says, is one of the real advantages of metal 3D printing. Still, he admits, “not everything has worked as planned.”
Some companies are using 3D printing for operational parts, however.
“We do additive manufacturing, using Ultem 9085, a high temperature, high strength thermal plastic, to build the air distribution system for our next generation inertial navigation, which is called WSN-12, for the Navy, replacing the WSN-7,” Tom Disy, Manager for Strategy and Business Development at Northrop Grumman’s Maritime Systems & Integration unit, says.
“Within the system is a requirement to have fairly small and elaborate ducting for air to cool the system, a geometrically complex component where additive
Northrop Grumman also uses polymer based materials, such as nylon or plastics, to create custom tools or fixtures to improve the manufacturing process, and designing and printing needed tools rather than trying to use something not really designed for the task.
“It’s easier to produce the printed component than to design, train and manufacture using traditional methods. However, 3D printed materials sometimes are not suited to stress or heat levels required for DoD applications, so it is not a panacea,” Disy acknowledges. “It has a niche — and the one we have found is geometrically complex components. I think technology will naturally move toward better materials that will increase applications for DoD components. There are metallic additive manufacturing capabilities that someday could be of use, for example.
“The fact you don’t have to retool and repurpose your line means you can just write new software, making it easier to keep up with advances in the technology,” Disy continues. “Those are moving quickly and the workforce has to pay attention to make sure they are considering the latest technologies available.”
Read more about the Limitations on 3D printing, Complex Requirements and the possibilities On-demand printing.