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Print me a plane

Lawrie Jones

Are 3D-printed parts ready for mission-critical applications? Few industries are as demanding as aerospace, so Lawrie Jones asks whether 3D printing is making the grade


Greg Morris builds planes. Or rather, he builds parts for aircraft engines, together with his team at the GE Additive Centre in Cincinnati, Ohio. They don’t have forges or lathes, though. As the head of GE’s additive manufacturing department, Morris and his colleagues use 3D printing, changing what’s possible in aerospace engineering – one component at a time. 

Last October, GE unveiled its ATP demonstrator powerplant, a propeller engine dubbed the Advanced Turboprop that uses more 3D-printed parts than any other engine in history. Working at the cutting edge of materials and design, 855 traditionally tooled parts will be replaced by just 12 printed ones. 

In the final specification, up to 35% of the engine will be 3D-printed, including high-performance components such as sumps, bearing housings, frames and heat exchangers. 

GE isn’t alone in this 3D printing business. Last June at the Berlin air show, Airbus unveiled Thor, or “Testing High-tech Objectives in Reality,” the world’s first fully 3D-printed aircraft. At only 4m long, it’s not big enough for paying passengers, but another example of pushing the boundaries of aircraft construction. And Rolls-Royce, with its Trent XWB-97 engine experimenting with 3D-printed parts, isn’t dragging its feet either.

3D printing “frees the engineer of the traditional limitations” of conventional manufacturing methods, says Morris – like milling, casting, forging, turning and welding solid blocks of material into the necessary shapes. These methods may be tried and tested, but they are also complicated and wasteful, with up 10kg of raw product needed for every kilogram of finished part. 

With new additive manufacturing technologies, a 3D printer builds up the part layer-on-layer – in powdered plastics, carbon, aluminium, titanium or stainless steel, slowly forming complex shapes that would be impossible to make with traditional methods. The machines use only the materials they need, cutting waste massively. The potential isn’t in recreating what we already have in new ways, it’s about rethinking everything from the ground up.

Shaving off weight

The technology to 3D print components has been around since the 1980s, but originally it was used mainly to rapidly create prototypes. When it came to the real thing, it was back to the traditional, reliable methods. In recent years, though, new technologies – and crucially new materials – have been changing what’s possible with 3D printing. 

Three years ago, a small, arm-length plastic panel that keeps the crew’s seatbelts in place became the first printed component to fly in an Airbus aircraft. Fast forward to today, and the company now has more than 2,700 3D-printed components in service. Inside the cabin of the plane, air ducts, armrests, wall panels and seat ends are all printed using a technique called fused deposit modelling. Using a flame-retardant resin called Ultem 9085, parts can be created quickly and to exact standards. 

And 3D-printed parts tend to be lighter, too – a big deal in the incredibly competitive and cost-sensitive world of commercial travel. Even a 1% cut in weight could translate into huge fuel cost savings across the aircraft’s lifetime, and a massive reduction in its carbon footprint. 

Take the A320neo, where Airbus has pledged to cut fuel consumption by 20% and hopes that additive manufacturing will help get it there. For example, the new plane sports the world’s largest 3D-printed cabin component – a partition wall between the seating area and the gallery. The part is created with a complex bionic structure that is meant to mimic organic cells and bones. At 35kg, the partition – which takes 900 hours to print – is much stronger and 45% lighter than previous versions. This weight reduction, says Airbus, will help its A320 fleet to cut 465,000 tonnes of CO2 emissions each year. 

For its part, aerospace giant Lockheed Martin estimates that using additive manufacturing to re-engineer solid components and replace them with stronger but less materially dense ones could reduce part weight by up to 40%.

The most complex part of an aeroplane, the engine, is also getting a 3D-printed upgrade. In the past, the aerodynamic shape of the turbine blade would have been formed by reducing down a solid material. With 3D printing, it can be built from the ground up. 

At UK start-up Betatype, materials scientist and designer Sarat Babu worked with the Manufacturing Technology Centre to do just that. “Using new techniques, we were able to replace the previously solid internals of the blade with our own proprietary ‘Core’ material,” he says. This new design, based on a complex internal lattice structure, can withstand incredible forces, but is also much lighter. 

The new LEAP engines, the product of a joint venture between GE and Safran Aircraft Engines, each have 19 3D-printed fuel nozzles. Made in one continuous motion, the nozzles replace a cast, tooled and brazed component made up of 20 individual parts. The material properties of each part are measured and managed, and the process is tightly monitored. 

“We are able to make parts lighter and far more durable,” says Morris, adding that the nozzles are also up to five times stronger than traditionally manufactured ones and are made much faster. “The response time with additive is quite amazing.”

The LEAP-1A engine is a massive step forward over current models, with GE claiming technological advances within the engine family – including its sister engines the LEAP-1B and LEAP-1C. The company says it will save 15% in fuel consumption and CO2 emissions. This development could have a huge impact, as LEAP is the world’s best-selling jet engine, with more than 11,500 on back order and a total order book worth in excess of $170 billion. 

A $14m LEAP-1A engine takes shape

Going mission-critical

The market for aircraft engines is hugely competitive and, in the race to stay ahead, Rolls-Royce is also in the game of trying the new technology. In 2015, its engineers tested a 3D-printed bearing housing in its Trent XWB-97 engine. Made of titanium, at 150cm in diameter and 50cm thick, it is the world’s largest 3D-printed part ever to fly in an aircraft engine. Created using electron beam melting technology from Swedish manufacturer Arcam, inside the bearing housing are 48 machine-printed aerofoils. Producing 97,000lb of thrust, the component was tested in the most powerful engine that Rolls-Royce has ever built. 

The design and build of the part was the result of a partnership between Rolls-Royce, the University of Sheffield’s Advanced Materials Research Centre (AMRC) and the Manufacturing Technology Centre. While the test was successful – reducing prototyping time by up to a third – Rolls-Royce has favoured a traditionally manufactured component in the finished design. Behind the scenes, the company is working on a new engine, dubbed the Ultrafan. It remains to be seen what – if any – parts of this engine will be 3D-printed.

The decision by Rolls-Royce to favour traditional components reflects the need for additive manufacturing to establish itself as a trusted technique, something traditional methods have done with years of datasheets and real-world testing. It can take a lot of time to establish new approaches in the aerospace industry, says Iain Todd, a materials expert at the AMRC. 

“If we invented casting today, we wouldn’t use it,” he says, pointing out that composite materials have been around for more than 30 years, but are only now being introduced into engines by companies such as Rolls-Royce and GE.

Todd and his colleagues work with firms such as Boeing and Rolls-Royce to design and test new materials and techniques – and were a key part of the team that launched the bearing housing used in the test flight. The reason casting is so widely trusted in the industry is that engineers understand the process, its capabilities and limitations, says Todd. Additive technology “has to prove itself,” he says, estimating that it could take decades.

One of the reasons 3D printing poses a challenge is that manufacturers need to pass stringent tests to prove that every component is fit to fly. In mission-critical applications, the demands of materials for aircraft manufacture – tolerances, tension, strength and performance – are tight. The margin for error is minuscule, and the reality is that failure means lives are on the line, so caution is understandable. 

Gaining ground

Morris at GE says that the key for widespread acceptance is in managing the properties of materials that are able to perform in the most demanding, mission-critical parts of a plane such as the engines. “We are getting smarter in terms of understanding material properties in the additive realm,” he adds. “It’s an ongoing process of learning, measuring and testing.”

At the British company GKN Aerospace, Robert Sharman, head of additive manufacturing, says that the current focus for the business isn’t on 3D-printed parts themselves but “on getting the materials properties right – without that, it’s useless”. And, he adds, there is another challenge to overcome to get 3D printing widely accepted – that around certification and qualification, which could “stagnate the adoption of the technology”. 

The aircraft industry moves in cycles, with lead times for airframes and engines measured in decades. The genuinely transformative opportunities of additive techniques will only be fully explored when suppliers are given what Sharman calls a “clean sheet,” and start actively designing with 3D printing in mind. “Too many people are trying to create parts that we already make today,” he says. “For me, it’s about doing what you can’t do today.” With its new Advanced Turboprop engine, GE is the first to the party, but it won’t be the last. 

In February, Siemens demonstrated its new range of 3D-printed gas-turbine blades, designed and manufactured by Worcester-based firm Materials Solutions. Printed in high-temperature-resistant, powdered polycrystalline nickel-based super-alloy, the blades operate in conditions far in excess of those experienced in the air, at temperatures exceeding 1,250°C and a speed of 1,600km/h – that’s twice that of a Boeing 737 in flight. 

The technology could soon be introduced into gas turbines that are in service, showing how quickly things can go from the drawing board to the real world. There are mission-critical 3D parts in the air right now. GKN, for instance, is printing fuel nozzles for the Ariane 5 rocket, and Lockheed Martin fitted the Juno satellite – currently orbiting the planet Jupiter – with eight titanium waveguide brackets, making it the first spacecraft ever to fly 3D-printed parts. In the secretive world of military aerospace, there’s widespread knowledge that additive manufacturing is already being used in core components. 

The need to advance the knowledge base is something that engineers are aware of. “Our experience in mass-producing the nozzle tip for the LEAP jet engine has been invaluable in learning how to certify the machines for mass-production of a highly-regulated product,” says Morris. This information isn’t being locked away within GE, it’s being shared across the company’s entire supply chain. Morris believes better materials and processes and time in the air will all help to convince the regulators that 3D-printed parts are a viable alternative.

While industry experts such as Morris, Todd and Sharman are positive and enthusiastic about 3D printing in the mid-term, they think it won’t completely replace traditional casting. “The technology must buy its way onto a sophisticated engine,” says Morris.

Todd sees the challenge in involving all levels – informing those in the boardroom, re-skilling those on the shop floor and inspiring the next generation who will enter the industry. The new industrial revolution is coming – and 3D printing could drastically change the way we build planes. For now, says Morris, “we have just scratched the surface”.

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