Aviation is a necessarily cautious industry, where new technologies are adopted only after exhaustive testing and certification processes. As such, additive manufacturing, or 3D printing, is still in its infancy across the airframe and engine supply chains.
South Carolina-based 3D Systems, which produces additive manufacturing (AM) machines, manufactures only 12 such parts in current-production engines, and fewer than 1,000 on Boeing and Airbus aircraft. In comparison, the company prints more than 500,000 metal parts for other industries each year.
“In the commercial airline industry right now, most additive manufacturing is still in the prototyping and testing phases of commercial aviation and just now becoming applicable and certified for flight,” says Bryan Hodgson, aerospace applications leader at 3D Systems.
Nonetheless, in an industry where manufacturers are increasingly pushing sales of spare parts and support services, the ability to fabricate one’s own components has obvious appeal for airlines and MRO providers. They are now latching on to the potential of additive manufacturing and are laying the foundations to apply the disruptive technology more widely in the aftermarket.
Emirates Engineering is one organization at the beginning of its additive-manufacturing, 3D-printing journey. The Dubai-based technical arm of Emirates Airline has partnered with 3D Systems to produce a video monitor shroud and air vent for use in cabins.
Non-load-bearing interior parts have been a common starting point for additive manufacturing uses in aviation, since BAE Systems certified a 3D-printed window-breather pipe for the BAe 146 in 2013. Emirates’ first additively manufactured parts also are fairly basic but were carefully chosen to evaluate some of the fundamental variables that will influence a more sophisticated AM operation. These include scanning and printing times, weight savings, printing costs, certification and durability.
“We chose a high-volume part, a monitor shroud, which was relatively complex with a large surface area, and a low-volume small part, an air vent grill, so that we could test out different assumptions,” says Ahmed Safa, Emirates senior vice president for support services.
Certain other MRO providers developed 3D-printing capabilities earlier than Emirates Engineering. Lufthansa Technik, for instance, printed its own air vent in mid-2016, but Safa says the timing of Emirates’ entry into additive manufacturing reflects the maturation of other technologies, notably 3D scanning, new thermoplastics for selective laser sintering (SLS), the digital warehouse and nesting optimization (to reduce waste).
“We know that additive manufacturing has been around for a while, and we have been watching this space since early 2010, but [we] consciously decided to take the plunge only when we thought that all these various avenues were coalescing into a holistic platform pipeline that could offer considerable reward,” he adds.
HOW IT WORKS
A confusing array of acronyms—SLS, EBM, SLM and DMLS, among others—describe the various 3D-printing technologies, but those often used in aviation are:
- Fused deposition modeling (FDM). Working from a CAD file, parts are built from the ground up, layer by layer, in a machine that extrudes a plastic filament that is melted by the printing nozzle and then hardens after deposition.
- Stereolithography (SLA). The original 3D-printing technology. Often employed for prototyping plastic parts, SLA machines use lasers or light to cure a liquid plastic resin. The part is usually built from the top down, layer by layer.
- Selective laser sintering (SLS). This works in a way similar to stereolithography, but instead of a liquid resin, powdered material is fused together with high-powered lasers. As a result, many different materials can be used, including metals, glass and ceramics. Another advantage of SLS is that it negates the need for support structures, since the object is formed within a powder bed that provides stability.
- Selective laser melting (SLM). SLM lasers fully melt the metal powder rather than just fusing it together, as occurs with SLS. This technology creates dense components but is currently restricted to certain metals. Electron-beam melting (EBM) works in a similar way.
- Laser metal deposition (LMD). Often used in engine repairs and also known as laser cladding, this process uses a laser to generate a weld pool on the component surface. Material is then added to the melt pool as a powder or wire. The melted particles fuse and solidify, while the nozzle is manipulated to add the desired structure to the component.
For MRO companies, the choice of manufacturing technique is important, and determined by the complexity of the part to be produced, the materials used and the time to print and process the finished product.
“When you look at smaller parts like the air vent, it is possible to print more than one part [at a time] using FDM or SLS, but when it comes to large parts like the video monitor shroud, the game becomes more complex,” says Safa.
“FDM needs support structure to be printed along with the main part, and since the plastic is a liquid for a little while before it solidifies, we cannot have parts being printed at awkward angles,” he adds.
Safa also points out that SLS can be used to print several parts at once, unlike FDM, which, due to its need for support structures, is limited to one piece at a time when parts exceed a certain size.
“With SLS, we could nest three or even four video monitor shrouds to be printed at the same time by the same machine using the same powder bed,” he says.
Due to aviation regulatory requirements, Safa says that Emirates is limited to two thermoplastics for its additive manufacturing processes: ULTEM for fused deposition projects and FR1200 for laser sintering. However, other options may be explored by using additive manufacturing to print a mold of a scanned part by inverting the scanned image. Sheet plastic is then heated and formed around the mold in a process known as vacuum thermoforming.
While OEMs are exploring AM to cut weight and cost from production parts, the technology offers additional benefits for those further down the supply chain. As Safa notes, “3D printing helps manage inventory costs at many levels.”
An obvious advantage is lower lead times, which could be cut from 90 to just two days for certain cabin items, according to Safa. Self-build capabilities also allow a company to stock fewer spares, thereby reducing storage costs, while in-service feedback allows continuous improvement to the durability and performance of additively manufactured parts, which can be re-engineered at each new printing.
Lufthansa Technik has manufactured more than 1,000 such parts, and while not all make it into serial production, each failure is only a minor setback due to the rapid prototyping capability. Furthermore, an MRO can leverage its experience of common part defects and damage to produce optimized, 3D-printed versions. In 2016, for example, Lufthansa Technik consolidated six parts into one for an additively manufactured air grill that proved much more reliable than the original.
“Using additive manufacturing to enhance standard parts is another technological option for us, since it only needs digital models as a basis for production, so no tools, no fixtures and no expensive manufacturing lines,” comments Christian Carjell, project manager for additive manufacturing at Lufthansa Technik.
Carjell adds that 3D printing offers a competitive advantage for MROs over OEMs, because MROs can use their life-cycle knowledge of parts to produce their own, superior versions.
Air France Industries-KLM Engineering & Maintenance (AFI-KLM E&M) has 3D-printed more than 200 parts in service on different aircraft types. Fredric Becel, an innovation leader at the company, says that in addition to cabin parts fabrication and prototyping, AM is being explored for more complex applications such as engine maintenance.
“In the mid-to-long-term, we are seeking to increase our capability to repair engine parts in connection with work already done on laser cladding in Amsterdam, and by CRMA [AFI’s engine repair subsidiary] to rebuild specific areas of engine parts by metallic wire deposition,” he says.
Both AFI-KLM E&M and Lufthansa Technik also use additive manufacturing for rapid tooling. Becel says that while a standard metal tool might take 10 weeks to arrive in the shop, it can take less than a week to have one printed.
Other benefits of additive manufacturing include the replacement of out-of-production parts and the development of lighter and more functional parts tailor-made for a specific customer’s needs.
“Traditional production methods cannot produce some complex forms or highly integrated functions that the new technology can achieve. This will allow more new designs for our customers in the cabin area of aircraft,” says Becel.
Hodgson agrees, predicting that strong demand for customization will drive a surge in 3D-printed plastic cabin parts over the next five years. He also points out some of the inherent problems of traditional injection molding such as tooling costs, inventory and design limitations.
“Major airlines and OEMs are now getting into the position to be able to develop industry-wide practices to enable the adoption of plastic AM,” he says.
MOVING TO METAL
Additive manufacturing applications are increasing across all layers of the supply chain. GE Aviation has said the technology could cut costs by one-fifth and development time by half for its new Advanced Turboprop Program (ATP). The manufacturer plans to build one-third of the new engine’s parts via 3D printing. Using a 1-m (3.3-ft.) powder bed, GE is also seeking to further incorporate additive manufacturing into the in-production Leap engine, which already features 3D-printed fuel nozzles.
Rolls-Royce is also pushing considerable resources into the technology. It passed a major milestone in 2015 when it printed a 1.5-m-wide front bearing housing for the Trent XWB engine. Printed from titanium, the housing incorporated 48 vanes that were printed separately using EBM machines. To establish a business case for future applications, one of the goals of the project was to maximize the amount of titanium powder that could be reused.
However, these additive manufacturing applications require considerable investment and testing, which may put the production of more advanced components outside the reach of airlines and MRO providers.
Metal parts, for instance, can be produced by SLS, SLM or electron-beam melting in which metal powders are fused or melted together to create complex geometric shapes, or even hollow parts that traditional manufacturing techniques cannot replicate.
In principle, the process is very similar to that used by MROs to produce plastic cabin parts, but metallic additive manufacturing components can exhibit lower static and fatigue strengths than rolled billets of metal. This is partly due to the granular surface of the finished AM part. Maintenance-focused organizations may decide that overcoming such engineering challenges is best left to the OEMs, while they focus their AM efforts on parts that are simpler to prototype, produce and certify.
“Small, medium and large non-stress-bearing cabin plastic parts are what we are looking at currently,” says Safa at Emirates Engineering.
At 3D Systems, Hodgson also sees the immediate future of additive manufacturing in non-structural plastic parts, at least outside the OEMs. “As airlines are able to identify more and more parts for AM, they can convert their traditional tooling requirements to digital CAD files, and their physical inventory of multiple spares of hundreds of components can be converted to on-site manufacturing nearly on demand with just the raw plastic as inventory,” he says.
Widespread AM adoption for metal parts will follow, Hodgson believes, as the technology is perfected within aviation and with input from other industries.
“Over the last three years, the space industry has been critically pushing qualification of structural metal components, such as satellite brackets that deliver 25% lighter weight, increased tensile strength and significantly reduced production times. This same thing will happen in commercial aviation, but due to higher volumes and more stringent qualification requirements, this will take some time to develop,” he adds.
Eventually, Hodgson thinks that increasing take-up of additive manufacturing by airlines and MRO providers will drive interior manufacturers to design parts with the technology in mind, creating a feedback loop that “requires AM as a core competency, not just a niche application.”