An A380

3D printing in the aviation industry

Image credit: Airbus

Aero engineers are turning to additive manufacturing for fast production and better product design. What will this mean for traditional aircraft?

At the 2016 Berlin air show in June, Airbus unveiled the first ever aircraft to be made using 3D printing. With a name derived from the phrase ‘Testing High-tech Objectives in Reality’, Thor weighs in at just 21kg and measures less than four metres in length. To observers, it resembles a large model aeroplane and was easily dwarfed by the other aircraft on show. But Airbus sees it as a testbed for a radical change in the way aircraft are built. Whereas traditional production methods such as milling involve manipulating a solid block of material, additive manufacturing, or 3D printing, ‘grows’ products by building up materials layer by layer. Taking this incremental approach, rather than using a solid block of material, allows for the creation of products with incredibly complex structures that would be very difficult to achieve, or in some cases impossible, using traditional methods.

Thor is not the only example of Airbus’s recent 3D-printed innovations - the company has also used 3D printing to attempt to replicate structures found in nature, and so create parts that are stronger yet lighter than is possible with traditional machining and assembly. “Nature has developed a lot of different design methods,” says Peter Sander, head of emerging technologies and concepts at Airbus.

For one concept part, an air spoiler, Airbus has turned to the giant water lily (Victoria amazonica) - a plant that sports leaves able to support the weight of a small child. A look at the underside of the leaves reveals a structure of various triangles and rectangles with the same skin size all over the surface to reduce weight. The Airbus team analysed the lily’s lightweight structure and the way in which it transfers loads.

Such designs can be applied across industries, but are particularly beneficial within aerospace, where reducing weight while maintaining strength are high on the list of priorities. It is an industry that constantly has to worry about fuel costs and will come under increasing pressure to reduce carbon dioxide emissions. Each kilogram shaved off the total weight pays for itself time and again in terms of fuel savings over the aircraft’s service life.

Tom Edwards, North American president of engineering design business Cyient, says: “Weight reduction is vital in aerospace. With greater efficiency and reduction in fuel usage high on the agenda, every gram of weight saved counts.”

In recent years, the market for additive manufacturing has expanded, with many industries, including aerospace, adopting additive methods for creative product design and prototyping. As Edwards points out, additive manufacturing is now one of the fastest-growing production markets. “The global market is expected to increase from a 2013 revenue figure of $3.07bn to $12.8bn by 2018, and exceeding $21bn by 2020,” he says. The flight business is already a significant user: “Aerospace and defence production and maintenance, repair and overhaul applications currently account for around 15 per cent of the additive manufacturing global market,” he adds.

Aerospace companies have a number of 3D-printing techniques they can employ. One of the better known methods is the fused deposition modelling employed by home 3D printers. This creates plastic products by building up layers from liquefied material. But manufacturers have other options, such as laser and electron-beam manufacturing, which produce metal parts by fusing particles of metal powder in layers.

Honeywell Aerospace was one of the industry’s first big players to adopt additive manufacturing techniques and has so far invested in 3D printing labs in China, India, Europe and the US. 

“Our developments in this field have already helped save time and deliver better solutions for our customers,” says Donald Godfrey, engineering fellow at Honeywell Aerospace. “As the aviation industry continues to grow, there’s an increasing need for more efficient and high-volume production processes to meet manufacturing deadlines and customer expectations.”

In the short term, additive manufacturing has proved successful at supporting the need for rapid prototyping during the design process. This allows engineers to check the physical behaviour of a design before production takes place, using specialised software to create a 3D model of the product and then print it.

“These new manufacturing techniques help streamline production lifecycles because they allow us to print components inhouse in a fraction of the time it takes today,” says Godfrey, pointing to Honeywell’s use of additive techniques to manufacture metal turbine blades quickly for use in prototype or test rigs. “These blades can be produced in just a few days, compared to between one and three years if cast,” he says.

Faster turnaround times for prototyping are supported by software. Examples of such products include the Functional Generative Design application offered by mechanical design tool supplier Dassault Systèmes. The application allows an engineer to develop components based on product-specific requirements and constraints, strength, load-bearing and space requirements, for a range of different materials.

Michel Teller, vice president of aerospace and defence at Dassault, says designing the product in such a way “means that a range of potential designs, from tens to hundreds, can be studied and compared that best meet business objectives”.

As well as reducing the weight of the parts themselves, 3D printing can cut waste by placing material only where it is required instead of having to machine it away from a solid block.

“Additive manufacturing processes are much more efficient in the consumption of raw materials,” says Teller. “The ‘buy-to-fly’ ratio, or the ratio of the amount of raw material to the amount of material contained in the delivered part, can vary by ten times or more when comparing a machined component with an optimised equivalent produced through additive manufacturing.”

“Further cost can be reduced due to the fact that the weight of an optimised additive manufactured part can be in the range of 50 to 80 per cent lighter than the equivalent machined component it replaces.”

While there are many obvious benefits to adopting 3D printing techniques within aerospace, the process is subject to strict regulatory constraints - regulators need assurance that the printed parts are as safe as those made by conventional means. “Organisations need to work closely with industry bodies to ensure they are up to speed with the regulatory environment, and are developing testing standards that will enable wider use of the technology,” says Maysoun Wahbeh, engineering and aerospace specialist at supply chain firm Vendigital.

For Honeywell, the first step towards getting 3D-printed products onto an aircraft is getting regulatory bodies, the industry and customers comfortable with the process. “In the aviation industry, technology has to earn its way onto an aircraft,” says Godfrey. “Every piece of technology Honeywell manufactures is subject to rigorous testing, and 3D-printed parts are no exception. For the foreseeable future, our focus is on using 3D technology to produce non-life-critical, non‑rotating components.”

Even for parts produced by more established methods, the technology is already contributing to reduced lead times. Godfrey says 3D technology can be used to build the ceramic casting cores needed to construct engine turbine blades for volume manufacture but without incurring the long lead times that it takes to build the moulds using wax tooling and other traditional techniques, which can be as much as three years.

Although the industry still has to demonstrate inflight safety for a wide range of components, progress is evident. This year, GE Aviation became the first aerospace manufacturer to gain approval from the US Federal Aviation Administration (FAA) for a 3D-printed part in a commercial jet engine - a metal housing for the T25 temperature sensor located in the compressor inlet. The device will be retrofitted to over 400 GE90-94B jet engines on Boeing 777 aircraft.

Indeed, additive manufacturing is particularly attractive when it comes to maintenance and repair of aircraft, especially within older models where stock may be difficult to obtain from traditional manufacturers even while commercial aircraft remain in operation - which may be much longer than you think. The two most common passenger jets, which make up around 65 per cent of all commercial aircraft currently in deployment, are the Boeing 737 and the Airbus A320, which were designed in the 1960s and 1980s respectively.

Although the overall designs of commercial aircraft have improved over time many of the components remain the same, with repairs carried out based on the original design. This is both costly and requires significant stock supplies. New repair techniques therefore come high on the list of priorities for aerospace manufacturers.

In response to this the European RepAIR project, a group of 12 partners including Boeing and Lufthansa Technik, was founded in 2013 to look into the potential for 3D printing to drive down costs in maintenance, repair and operations, and reduce overall aircraft downtime. The three-year project highlighted the potential for additive manufacturing processes to enable flexible on-time maintenance to take place, which could potentially go as far as fixing aircraft at the gate.

In the years since the consortium was established the use of additive manufacturing techniques in maintenance and repair operations has become increasingly attractive among some of the main aircraft manufacturers, while not yet being seen in the airport itself. Although Boeing became the first company to achieve FAA accreditation for a 3D-printed engine component to be used in its aircraft, other suppliers have begun sporting additional additive manufactured accessories.

For Airbus, 3D printing offered the ideal solution to supplying spare parts for some of its older aircraft that do not have the stringent structural requirements of airframe or engine components. In 2014, the company unveiled its first 3D-printed plastic spare part - a crew seat panel - for its old A310 aircraft.

“It’s a 30-year-old design, and we only need around 40 of these parts a year,” says Sander. The problem with small stock requirements such as this is that traditional manufacturers often have minimum purchase amounts, especially if the parts need to be specially manufactured. In this case, Sander points out, a minimum quantity of a thousand parts would last well over ten years, and take up significant warehouse space.

“For spare parts, additive manufacturing really makes sense,” says Sander. “Do a redesign, make it printable, qualify it and then you have a digital model which can be printed on demand without any need for inventory.”

According to RepAIR, on-demand printing of spare parts could have significant benefits for the aerospace sector, both in terms of dramatically improving turnaround time for the maintenance of aircraft and by reducing the money spent on shipment costs and storage space. The idea is that with an inhouse machine and the required materials, many parts could be manufactured in an airport hangar rather than relying on local stockholding or shipping parts out from a wholesaler.

Airbus is currently working on making on-demand printing a reality, by introducing qualified spare-part printing cells into its local storage areas across the globe, each of which currently stores a few thousand parts for maintenance purposes. Parts that are needed less frequently for repairs can be made on-site using 3D printing.

The limit to how many parts are made on demand is largely a factor of the amount of time it currently takes to produce 3D-printed components.

Sander points out that as additive manufacturing processes develop, production times will decrease and real-time on-demand printing for many more parts will become feasible.

In the medium-term the most attractive market for 3D printing in aerospace is within maintenance repair and operations procedures. In the future with developments in materials and production techniques, it may not be considered viable to keep old, heavy machines flying and we could see more additive manufactured products fitting into initial aircraft design.

Although the prospect of a 3D-printed commercial jet may seem far-fetched, the sector is developing, and quickly. Airbus’s 3D-printed mini aircraft could well offer a glimpse into the future of aircraft design.

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