What does the future hold for additive manufacturing? Soon it could be leveraged to build stronger objects from materials impregnated with carbon nanofiber. It’s currently under testing for printing parts in space. Additive manufacturing of complete designs such as unmanned aerial vehicles and robotic arms is already on the verge of becoming a viable industry. In fact, additive manufacturing by many accounts will one day be used as a common approach to complement CNC manufacturing, shifting the methodologies of design to manufacture.
Additive for the space industry
According to Carol Tolbert, manager of the Manufacturing Innovation Project at NASA Glenn Research Center, Cleveland, a total of nine NASA centers use additive manufacturing. At her location, contractors working for NASA Glenn are using direct laser sintering to produce a subscale multielement injector for a rocket engine and reduce testing costs.
“We will be testing an injector this summer at NASA Glenn,” says Tolbert. “If the testing is successful, building injectors this way will significantly impact the rocket industry. Traditionally, full-size injectors take months to make because a lot of measuring must be done and it has to be exact.” Should someone make a mistake, everything must be machined all over again, which can take several months. If additive manufacturing proves successful, time between iterations will drop to weeks.
In this context, “subscale” refers to the model injector’s nozzle size, which is smaller than those used in a full-size rocket but bigger than a desktop model. “The subscale injector lets us learn about a lot of properties — for example, how hydrogen and oxygen mix in the rocket combustion chamber,” she says. “There are lots of nuances we must understand about the injector before we can take the next step and print a full-size unit.”
Current technology is capable of making an additively manufactured full-scale injector by printing two builds and then attaching them together. Even so, Eric Baumann, lead engineer of NASA Glenn’s Manufacturing Innovation Project, indicates that the printed injector needs more work before it can be called a space-rated part. Therefore, this is a field of innovation still undergoing technical development.
In another project, the agency is testing an approach it calls electron-beam free-form fabrication or EBF3. The technique uses an electron beam to weld together wire and build up parts. Ultimately, this could let astronauts make replacement parts while in space. Missions would, thus, avoid costly payloads just to carry spare parts.
They are currently exploring how the technique works with different materials — and NASA Langley personnel are testing EBF3 in a special aircraft that undergoes microgravity flights, which simulates the use of the process in space.
According to Tolbert, NASA will continue with 3D printing and additive manufacturing, which is what they see industry doing as well. “The administration got behind additive manufacturing some years ago and that push is continuing. We will all benefit from it in the end,” she says.
In another interesting application, Aurora Flight Sciences Corp. in Cambridge, Mass., uses fused-deposition modeling (FDM) to manufacture flying drones. Recall that in FDM, a polymer-based extruded bead accumulates to form the part.
“As with many companies, additive manufacturing is relatively new for us,” says Company Structures Research Engineer Daniel Campbell. “We became involved in additive manufacturing about two years ago for a joint project with the Air Force to develop new materials for FDM,” he says. “Then we got the idea that it would be possible to print the entire structure of unmanned aerial vehicles (UAVs) or small aircraft — those with about a 6-ft wingspan — using FDM,” he adds. About half the work is material development and the rest is the actual design and manufacturing of the drones.
Previously, the company made the drones using traditional methods involving composite layup. In this approach, a composite covers a core material — either foam or an aluminum honeycomb.
“We decided to check out additive manufacturing because there is a lot of buzz about it,” continues Campbell. Only recently has the approach been taken beyond prototyping for use on engineered parts. “Now, printing the UAV helps minimize logistics because it reduces the number of parts going into the plane and slashes material usage. The technique also helps keep inventories low because it is location agnostic.” For example, instead of shipping entire planes cross county, additive manufacturing could soon allow Aurora to digitally send over build-path files to equipped locations for creation.
FDM is a familiar additive-manufacturing process and, for aerospace applications, it has one of the highest strengths per material weight. “From a production perspective, our first use would be for tooling. But we are already discussing different parts on a plane that could benefit from the technology,” Campbell adds. Is FDM as strong as composite? “No, it falls a bit short on the modulus- to-weight ratio,” he says. “For small aircraft though, the benefit is having lots of design freedom. We find that the performance of the small printed aircraft comes pretty close to that of conventional composite craft.” For this reason, Aurora plans on continuing the use of additive manufacturing into the future.
New material options Carbon-fiber capabilities could soon address additivemanufactured component strength limitations. For example, parts produced with FDM are weak in the Z direction. Composites produced by traditional means consist of continuous or chopped fiber in ratios of 1,000 to 1 for applications demanding high material strength. Now, some new technologies produce nanofiber-impregnated materials, particularly for the tooling and aerospace industries. These leverage polyamide composites (largely still proprietary formulations) filled with carbon fibers and fused in preprogrammed patterns that boost mechanical rigidity and resistance to chemicals and vibration. Reconsider the Aurora UAV: Wing deflection in this additive design could soon be addressed with carbon fiber to allow wider wingspans.
Currently, few options exist for carbon-fiber parts made with additive manufacturing. One challenge is material cost and producing on a scale that enables commodity- priced carbon fiber polyamides. In contrast, other designs leveraging high-cost titanium are already in additive- manufacturing production, as the price differential here is less of a concern.
Additive for orthopedics
Building end-use orthopedic parts often involves machines that melt metal powder with an electron beam. According to Magnus René, CEO of Arcam, Mölndal, Sweden, which manufactures the machines, the electron beam is powerful enough to work on any common metal powder. “We only offer titanium and cobalt chrome, and often get asked why we sell so few materials,” he says. “We are in this for actual production, and to be successful in manufacturing, it is necessary to supply materials that are on par with conventional materials.” That said, the technology works for common materials like stainless as well.
Arcam works on orthopedic and aerospace designs. Orthopedics is characterized by volume manufacturing: Here, additive manufacturing is used to make hip, shoulder, dental, and spinal implants. “The components are well accepted on the market, and are manufactured in runs of 1,000s to 10,000s both in Europe and in the U.S.,” says René.
In contrast, aerospace lags a bit. Aerospace designs are fairly complex and often made of titanium. “Additive manufacturing in this segment is mainly for preproduction and R&D, and not volume production yet. We sell our machines to large aerospace OEMs in Europe and the U.S. Printed parts include brackets and components for the fuselage and engine,” says René. Production components are made in moderate volumes in the thousands. Even so, the moderate volumes, difficult materials, and complex parts of this market are a sweet spot for additive manufacturing.
Arcam sees no reason to branch out from orthopedics and aerospace because it foresees ample business for the next 10 to 20 years. “We have not even scratched the surface yet in terms of the technology’s uses,” René adds. “For example, there are no real commercial aerospace applications yet, offering a lot of possibilities in that area.”
Shared manufacturing facilities
The future of additive manufacturing will likely involve significant sharing of production facilities — a trend enabled by the inherently flexible nature of additive manufacturing that requires few customized machinery installations. That’s the business model of the National Additive Manufacturing Innovation Institute (NAMII), Youngstown, Ohio, which is supported by and entrusted with machinery from multiple private companies. The same approach at similar regional and national facilities is based on the concept that companies can leverage state-ofthe- art equipment, facilities, and dedicated staff to use the technology best suited for an application.
Case in point: Oak Ridge National Laboratory’s Manufacturing Demonstration Facility, Oak Ridge, Tenn., offers laser-powder, electron-beam powder bed, ultrasonic material-deposition, FDM, and polymer and polymerpowder technologies. “After a short proposal process consisting of a well-defined project of four to eight weeks, designers come in and work beside us at no cost,” explains Craig Blue, director of Oak Ridge’s Demonstration Facility. “We also work closely with equipment manufacturers to ensure that our innovations are applied. For example, we have an R&D agreement with Arcam that gives them access to our IT; they retain what they create, and can license what we develop.”
Every additive-manufacturing shared facility touts subspecialties. In the case of Oak Ridge, material science, computational modeling, and deep-material neutron testing are fields of expertise. For example, their FDM monitoring capabilities include visible and infrared mapping. Neutron testing, on the other hand, traces residual stresses in metal parts created by additive manufacturing and maps them in 3D. Designers then work to develop methods to control or eliminate these stresses. “Companies use our neutron-defraction facilities to help verify their models,” says Blue. “Stress throughout a component’s wall is nondestructively detected — or we heat treat components while doing residual stress measurement to map the treatment’s effects in real time.”
Part-count reduction in automotive
In the automotive industry, additive manufacturing could soon allow for component consolidation. “For example, a single-piece air scoop can be converted into a multifunctional air-distribution system,” says Blue. “The goal here isn’t to replace components with like components, as that makes for a tough business case for additive manufacturing. Instead, the aim is to reduce part counts and lightweighting by removing material.”
Converting what is essentially prototyping equipment into production equipment for the large-volume demands of the automotive industry will require tighter controls. Consider that most additive equipment today works open loop. In the future, closed-loop controls will become more common. Here, systems measure temperature, and CAD models are sectioned into say, 100-μm layers while the controls discern their integrity. If the temperature is too low, the system prompts an increase; if larger problems are detected, the machine control nixes the process before the component is built.