FEATURE: Additive manufacturing goes large – Aerospace prints bigger and better parts

Alex Eliseev

An ambitious project is helping aerospace companies to print bigger and better parts
An ambitious project is helping aerospace companies to print bigger and better parts

Additive manufacturing creates objects in a painstaking, layer-by-layer process, building them up one micron at a time.

An ambitious new project has set its sights on making metal components that will be measured in metres rather than millimetres, but first it must navigate what researchers call ‘the valley of death’. The Open Architecture Additive Manufacturing (OAAM) project will build three powerful AM machines to help convince companies to invest in the technology, and to print larger metallic components ranging from plane landing gear to satellite fuel tanks.

“The scale of the machines that we are producing is far greater than what we have seen in the past,” says OAAM project manager Tom Pinto. “This is a very exciting project which will provide access to equipment that is at the forefront of what’s being developed. None of these machines exists. There are no blueprints for them.” The multi-million-pound project is being led by The Welding Institute (TWI) in partnership with several prominent universities and companies, including Airbus. What makes the OAAM project different is that it’s exploring new wire-based, ‘out of the box’ techniques of printing things in three dimensions, along with more established ‘in the box’ methods such as directed energy deposition (DED). 

The ultimate prize is for the UK to build world-first AM machines to inspire other nations, and to help build what Airbus describes as “a globally competitive DED AM supply chain in the UK”. Many other industries, from energy to marine, stand to benefit from the research. 

No longer boxed in

AM requires various feedstocks and melting instruments to build objects up from nothing, one layer at a time, according to a computer-generated design. This is the inversion of traditional manufacturing, which takes chunks of raw materials and cuts or mills them down to the required components. It’s not uncommon for 40kg of raw material to produce a part weighing only 1kg. In the aerospace sector, this is known as the buy-to-fly ratio. 

With additive manufacturing, companies are able to dramatically improve this ratio by using only the material required, which means less waste and huge savings. The bigger the component, the bigger the saving, explains Pinto. Although AM has long escaped the arena where it was used for prototypes or small hobby projects, its potential has, until now, been limited at a manufacturing level. 

Traditionally, AM components have been created inside printers or ‘inside the box’. This allows for strict control over the printing envelope, but restricts the 3D parts to the size of the printer. Things are changing, however. 

Cranfield University, an OAAM partner, has already 3D-printed a 6m aluminium spar using a robotic arm that moves along a track and deposits layers in a style not too different from spreading toothpaste onto a toothbrush. This means that, once AM is truly out of the box, there are no limits to how big a 3D-printed component can be. 

Cranfield University printed a 6m aluminium spar

Cranfield University printed a 6m aluminium spar, one of the biggest parts ever produced by AM

The internet is full of stories about the odd 3D-printed car, bridge or even house, all using this principle of large-scale deposition or DED. But the key difference with the OAAM project is that it aims to bring this technology to industries with the highest integrity standards, and to fuse it into the factories of the future. To achieve that takes research, regulation and investment from companies such as Airbus, Boeing and GKN. 

“Here, we are looking at a completely different beast,” explains Filomeno Martina, a lecturer in additive manufacture at Cranfield University. “These components will be highly mission-critical, structural, primary elements, which will be stressed severely and will be doing a lot of work while the aircraft is flying. We have had to take more time to achieve commercial readiness because lives are at stake. 

“But the business opportunity is huge because of substantial savings in lead times and costs. Aerospace is moving towards a more automotive way of production and that’s why we are doing this research.” 

Martina speaks of the “valley of death”, explaining that most products travel a similar path. This path is known as the Technology Readiness Level, or TRL. Generally, universities handle TRL 1 to 3. Companies invest once products are mature and reach TRL 7 to 9. The valley of death – where concepts can die – lies across TRL 4 to 6, and is where a research organisation such as TWI comes in and where projects like OAAM are crucial. 

“This is a perfect chance to explore the concepts that we see as key to moving the technology forward,” adds Martina. “A chance to try out ideas and to enable companies to try the technology, with a view to accelerating industrial implementation. We see this as a key element in retaining the UK’s leadership in large-scale 3D-printing capabilities.”   

The OAAM project aims to build components such as turbine blades using AM at large sizes

The OAAM project aims to build components such as turbine blades using AM at large sizes

The OAAM project moves away from the more traditional powder-bed techniques of AM and explores melting wires using lasers and electron beams or blowing powder into moving heat sources. Part of the project will see the creation of a hybrid system that combines more of these methods, for instance the use of wire arc AM (WAAM), which Cranfield University used to print its 6m aluminium part, with wire and laser AM. The digital technology and operating systems required to run these machines also form part of the research.   

These technologies have the potential to take AM parts from the small cameo roles they currently play on aeroplanes or spacecraft and help them become the superstars of the sky. Companies would be able to print landing gear parts, components that make up the wing ribs or important pieces of the engines. 

Lighter, faster, cheaper

At first, this would mean faster, lighter and cheaper parts, along with far more economically attractive buy-to-fly ratios. In September, GKN Aerospace announced that AM had allowed it to produce a “revolutionary” engine nozzle (the Ariane 6) using 90% fewer parts. The nozzle was 40% cheaper to make and was produced 30% faster. GKN’s new AM rocket engine turbines (which are part of the Prometheus project) are being built at a fraction of the cost and with a reduction of components from 100 to just two.  

Beyond that, once the techniques are refined, designers will be able to create entirely new concepts and reimagine what aeroplanes or spacecraft look like and how they perform. With new metals being created and fused, lighter aircraft could also help the fight against global warming. 

“The stuff that excites me is when you start to have a big performance impact on an aircraft,” says Russ Dunn, the chief technology officer of GKN Aerospace. “If you consider the total fuel burn over the life of an aircraft, you’re talking about millions of tonnes of fuel being saved by taking a few kilograms out of every aircraft. The environmental benefits of improving weight and performance are huge.” 

GKN has three AM technology centres and, as Dunn puts it, more PhDs working on additive manufacturing than on anything else. For him, the journey of AM runs from improving the buy-to-fly ratio (and all associated benefits), through the birth of new designs that were previously impossible to create, and then to the tuning of metallurgy to enhance performance. 

“You can tune the material properties much like the way a tree grows,” explains Dunn. “A tree grows material where it needs it, strengthened in the direction it needs it. With AM, you get that complexity for free. You can control it as you add it.” 

Research in all these fields is under way, while the breakthrough into the mass-production of large, mission-critical AM parts appears to be around the corner. “We are on the verge of much more significantly sized components being ready for production,” says Dunn. “There’s a lot happening and a lot still to be done. In the long term, there is huge opportunity.”

The OAAM project is moving away from more traditional powder-bed techniques to explore other methods

The OAAM project is moving away from more traditional powder-bed techniques to explore other methods

Airbus, meanwhile, hopes to use the OAAM project to help it push through what it calls “class 1/principal structure element” parts on a scale of a metre-plus. Such parts would include a 400kg main landing gear attachment rib for the wings of its large aircraft. David Steer, airframe research engineer at Airbus, says: “A wide range of large-scale AM applications are nearing exploitation: military aircraft applications of multi-metre scale are being developed, and delicate but dimensionally critical parts for satellites can be expected within a few years. It is widely expected that DED AM will enable integration of large, complex assemblies, permitting topologically optimised pylon structures in Airbus applications within the next five years.” 

Like GKN, Airbus believes the next frontier will require not only engineers, but also scientists. “Functional materials are likely to be the next near-term target,” says Steer. “Materials are already being developed for AM which have more favourable solidification dynamics and better resulting properties. Further scale-up and integration of parts will occur, probably only limited by practical considerations for managing residual stress.” 

On the software side, the OAAM project has attracted the likes of Autodesk, which believes the power of the collaboration is that it “can’t hide behind academic discussions, presumptions and laboratory-based solutions”. 

Jan Willem Gunnink, manager of collaborative innovation at Autodesk, says: “OAAM will deliver solutions that can, will and should be used by the high-end and advanced manufacturing industry. Companies will be able to use facilities developed in OAAM (hardware, software, process and procedures), lowering the entry level and enabling more of the industry to explore and benefit from the promises of DED technologies.”

Consultancy McKinsey has estimated that the overall economic impact of AM (including printers, printed products and supporting infrastructure) could reach $250bn by 2025 if industries continue to adopt the technology at today’s rate. One of the core industries to drive this, McKinsey believes, will be aerospace. 

Don’t wait

Jörg Bromberger, one of the authors of a report McKinsey released last year on the future of additive manufacturing, says the technology is taking “huge steps”. “We haven’t spoken to any aerospace players who are not exploring the possibilities of AM,” says Bromberger. 

“Our advice to companies is: keep the technology on your radar and start exploring what’s possible. I would not wait too long.” 

AM technologies, says the report, facilitate a shift from what is feasible to what is possible. With “freedom of design”, says Bromberger, new generations of engineers will break boundaries and create products that have not yet been imagined. They will work without the limitations of today’s manufacturing techniques and materials. 

This approach, of exploration and experimentation, is at the heart of the OAAM project, which was unveiled recently but began quietly at the start of the year. With £6.5m from Innovate UK, the government-funded initiative is now in its ‘specification’ phase. Patents have been filed, tenders for parts are out and the machines will be built in the coming months. The project partners include TWI, Airbus, Autodesk, Cranfield University, Glenalmond Group, and the universities of Bath, Manchester and Strathclyde. 

“The project is about getting the kit ready and taking away the risk,” concludes TWI’s Pinto. “We can provide access to the equipment, and the industry can see what the benefits are without having to buy the machines.” 

Although already capable of prints up to 10m, Cranfield University will focus its OAAM research on printing parts measuring about 2m. TWI is building a laser machine that will hold a printing envelope of 4m. In an industry where a typical AM component is the size of a school ruler, that’s a giant leap forward and worth a trip through the valley of death. 

Jargon buster

Cranfield University’s Filomeno Martina on what all those AM acronyms mean.

DED: Directed Energy Deposition

Additive manufacturing processes in which the raw material is fed directly into the melt pool created by a moving heat source, as opposed to being pre-placed and scanned selectively.

WAAM: Wire + Arc Additive Manufacturing

The raw material is in the form of wire, and the heat source is an electric arc.

WLAM: Wire + Laser Additive Manufacturing

The raw material is in the form of wire, and the heat source is a laser.

LMD: Laser Metal Deposition

The raw material is in the form of powder or wire, and the heat source is a laser.

W-EBAM: Wire + Electron Beam Additive Manufacturing

The raw material is in the form of wire, and the heat source is an electron beam.

Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.

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