In less than a century — less time than this journal has been publishing — it’s gone from basic mechanical engineering closer to bicycle building than anything else, combined with classical woodworking skills and fabric work; to working and joining first steel and then aluminium plate; and now to using man-made composite materials; while engines have progressed from simple piston-based internal combustion models through several generations of jet, flirting relatively briefly with rocketry, culminating in today’s turbojets, with the whole system controlled by mechanical linkages pulled by wires, to electrical signals transmitted along wires, and now advanced electronics with digital signals sometimes sent without any wires at all.
But we’re now on the cusp of a manufacturing revolution which may affect aerospace considerably. The advent of new manufacturing techniques, advanced metallic and ceramic materials, and the increasing use of composites will mean that the aircraft factories of the coming decades will be very different from the ones we see today: and that’ll affect not only the way the aircraft they produce look and operate, but also the type of skills that people who work there will need. ‘
We don’t really know what the aircraft of the future will look like,’ said Marcus Bryson, chief executive of GKN Aerospace, at a recent briefing, ‘but we absolutely know that we won’t be building them the same way we do now.’
GKN, the manufacturing specialist which numbers most of the world’s major airframe and propulsion manufacturers among its customers, is working on a number of projects which exemplify the changes coming in aerospace. Some of these, of course, are in progress now.
Whereas aerospace facilities were previously dominated by metalworking machine tools and equipment to join together large expanses of metal, the rise of composites over the past decade has meant these are overshadowed by different machinery: the autoclave. These massive chambers are used to create the temperature and pressure conditions needed to cure the resin component of composite parts, setting the tough, durable carbon-fibre components within their plastic matrix; and, as the whole part — large sections of wing, for example – needs to be inside the pressure chamber, their dimensions can be literally cavernous.
Microwave curing is going to be a key technology for the future
Marcus Bryson, GKN Aerospace
It seems that the dominance of the autoclave might just be a passing phase, however. ‘We think that microwave curing is going to be a key technology for the future,’ said Bryson. ‘We can’t go on the way we have been; there won’t be enough room for anything among all the autoclaves.’
Technical director Richard Oldfield expanded on this point. ‘Autoclaves are a major bottleneck in composite manufacture; they’re very large, very expensive and rather slow,’ he said. ‘We’re looking for ways around that.’
Microwaves enable targeted heat-curing, which is already in use with electrically-heated tooling; using a microwave cavity — basically a scaled-up version of a domestic microwave oven (pictured above) — to heat the tooling is a more efficient version of this. ‘You get a huge cycle time benefit compared with autoclaves, and you use about 90 per cent less energy,’ said Oldfield.
The speed of microwave curing make it particularly suited to high-rate structures such as panels, which need to be made rapidly and in bulk. ‘Otherwise you need lots of autoclaves,’ Oldfield explained. ‘There is a slight loss in performance, because you’re working under vacuum with different grades of resin. If you’re making only a few components and you need that very high performance, you’d probably still cure under pressure in an autoclave, but for components where you make a lot, and for very large structures where you need enormous autoclaves which aren’t very efficient, being able to cure outside the autoclave is very important.’
Microwave curing will probably start with relatively simple components and gradually grow to include larger and more complex structures, Oldfield said. ‘One important advantage is that you can focus microwaves on one part of a structure and shield others, so you get partial curing; then you can join together components of larger structures by joining the uncured portions. That isn’t possible with autoclave curing,’ he added.
The other production revolution set to hit aerospace is additive manufacturing, but tempting though the thought of simply printing an aircraft might be, this isn’t going to happen. Instead, Oldfield indicated, we can expect to see two types of additive process in aerospace. ‘There’s a suite of techniques such as wire deposition that deposit material quickly to make near-net shapes which need further machining or processing and don’t have added functionality; and at the other end of the scale is creating final parts directly using powder-based processes to produce components with complex geometry and intricate features that can’t be made any other way.’
The first group are components which are identical to those being made today by conventional machining from solids, casting or forging. ‘These can be large airframe components; you aren’t constrained by size and could make parts like a wing rib, with dimensions up to 2m3.’ These needn’t be whole components; they could be parts, or extra features onto a forging, allowing you to reduce the complexity of the original forging.’
This is driven by cost, he said. ‘It might take more time to make the part, but your machining time is drastically reduced, and so is material and energy usage, and it’s all about efficient use of materials and energy.’
For these larger components, production philosophy will be to use a suite of techniques including additive and subtractive processes. ‘As today where we have families of components made by different processes, we’ll see some components transferred into an additive family and some made by combinations of processes; it’ll be driven by economics. The goal will be to make conventional parts in the most optimised way.’
The other family of components, grown from powder using electron beams or lasers, will completely change the design space for aerospace. ‘This isn’t a complementary technology like high deposition; this is disruptive,’ Oldfield said.
Perhaps more familiar to Engineer readers, powder-bed additive manufacturing allows manufacturers to optimise the shapes of their components, placing material preferentially into areas which will experience most stress during use, often producing components with complex, sweeping curved shapes reminiscent of birds’ skeletons. ‘This is principally an opportunity to enhance performance using advanced materials and creating advanced structural concepts,’ Oldfield said.
This is a process in its infancy, Oldfield conceded. ‘Powder bed manufacturing is constrained to chambers about half a metre to each side and it’s relatively slow. But we predict that the size of parts you can make will get bigger, speed will increase and the price of powder materials will reduce over time. As with all technologies, we’ll see a phased approach.’
Marcus Bryson believes such technology could drive the development of the next family of aero engines, enabling a step improvement in performance; meanwhile, he added, wire-deposition processes, originally developed for engine component making, are now being investigated for airframe structures.
Oldfield added that in the near future additive techniques could be used to make increasingly complex mechanical systems with, for example, fluid cooling channels built in to the parts from the start. Machining will still be needed, but waste would be dramatically reduced, and additive, joining and subtractive processes used increasingly in concert to create ever larger components and systems.
But their biggest influence could be to speed up the point where civil aircraft beak away from their current architecture and bring forward the introduction of new technologies. ‘For example, we’re using additive to make an optimised version of a Kruger rib, which is part of the leading edge of a laminar wing we’re working on with Airbus,’ Oldfield said. Laminar wings reduce the fuel consumption of aircraft by eliminating turbulent airflow; this project is part of Airbus’s CleanSkies project to improve the environmental profile of commercial flight.
New technologies will also change the skills profile of the aerospace industry. ‘The effect of all these technologies is to continue a trend that started with the adoption of composites; it makes a much closer link between design and manufacture,’ Oldfield said. ‘This is a big challenge, because you have to think about things in an entirely new way. We currently have the ‘black metal’ phenomenon, where people design who composite parts haven’t fully shifted away from metallic design principles and aren’t fully exploiting the potential of composite properties; that’s progressively changing, and additive will bring in a similar change, but the degrees of design freedom are an order of magnitude greater.’
Materials science in particular becomes much more important with new techniques, because the material is being synthesised at the same time as the part; engineers in both design and manufacturing will need a better understanding of how bulk properties are generated and affected by the way additive processes work. ‘It’s about investigating the art of the possible, in a much wider design space than we’ve had before.’ Oldfield said. ‘This is absolutely an argument for prospective and working engineering designers to have access to these techniques as early and as widely as possible, because it’s really by playing around with these suites of systems and toolkits that you create the correct mindset to design in this space and understand the potential of these new system.
The factory of now: additive techniques are already appearing on production aircraft
Although many speak of technologies such as additive manufacturing as things of the future, they are increasingly being trialled in current aircraft.
Airbus has been looking into the possibilities of additive manufacture for close to a decade, but such are the complexities of qualifying and certifying new processes in the aerospace industry that they are only just beginning to be seen on flying aircraft. The first ‘printed’ Airbus component for an aircraft in commercial operation — notably, neither structural nor mechanically relevant to the aircraft operation — flew in March of this year; it was a plastic crew seat panel on an A310.
We are on the cusp of a step-change in weight and efficiency, producing aircraft parts which weigh 30-55 per cent less
Peter Sander, Airbus
However, Airbus’s fleet of developmental aircraft features a raft of additively-manufactured components in plastic and metal, mainly brackets, used in systems such as undercarriages and control surfaces; these may well find their way onto the A350 XWB.
‘We are on the cusp of a step-change in weight and efficiency, producing aircraft parts which weigh 30-55 per cent less, while reducing raw material usage by 90 per cent,’ said Peter Sander of the Airbus Innovation Cell, which oversees rollout of new technologies across the company. ‘This game-changing technology also decreases total energy used in production by up to 90 per cent compared with traditional methods.’
The aircraft of the future will have a ‘bionic’ fuselage
Lead times for parts made using additive techniques are as little as one day for existing designs, said Sanders; redesigned parts can be produced in about a fortnight. ‘The aircraft of the future will have a ‘bionic’ fuselage, composed of complex parts printed using additive layer manufacturing,’ he claimed. ‘This dream will come true.’
Engines are also seeing this new technology making headway in their manufacturing systems. GE is using additive manufacturing to make fuel nozzles for its new-generation Leap high-bypass turbofan engines (pictured left: each engine has 19 nozzles, and the company has already sold more than 4000 engines), and has a full-scale additive manufacturing facility in Cincinatti. It uses a variety of materials in additive manufacturing, including ceramic matrix composites (CMCs)which incorporate ceramic-coated silicon carbide fibres in a silicon matrix. The company announced last year that it is spending $125million (£75million) on a 125,000ft2 plant to produce CMC engine components in North Carolina.
You can create any shape you like
Wenner Wapenhans, Rolls Royce
Rolls-Royce, meanwhile, says it is ‘a few years away’ from being able to incorporate additively-manufactured components into commercially-ready engines. ‘Through the 3D printing process, you’re not constrained by having to get a tool in to create a shape. You can create any shape you like,’ said head of technology strategy Wenner Wapenhans. The lack of tooling would significantly reduce lead times, he added; the need to make tooling means that it can currently take 18 months from designing a component to producing the first version.