Productionising 3D printing

Additive manufacturing is having a profound effect on the way some engineers produce plastic parts. Ben Hargreaves and Justin Cunningham look at some pioneering aerospace examples that could see the technology exploited more widely.

The potential of additive layer manufacturing to transform aerospace engineering applications has been recognised for many years – but its use to make aircraft components on a commercial scale has been slow to materialise.

As with 3D printing in general, there’s plenty of hype. BAE Systems, which has been working with the technology for some time, suggested that military drones produced entirely by additive manufacturing (AM) techniques could be a reality by 2040. Still, by all accounts, a long way off. However, perhaps this view is somewhat conservative, with drone manufacturers already taking advantage of the new found possibilities.

US based Leptron is a producer of remotely piloted helicopters that get put to use by law enforcement agencies, the military and hobbyists. It’s RDASS 4 weighs just over 2kg and can be in the air in less than five minutes. Its four battery powered electric motors enable it to hover at 30m (100ft), enabling a half-mile line of sight.

The fuselage of the RDASS 4 is constructed in a number of layers that fit together similar to that of a Russian doll. The company has developed multiple designs for each layer for specific civilian and military applications.
When designing the RDASS 4, Leptron engineers faced the challenge of developing eight variations of complex fuselage components in a short period of time to beat potential competitors to market. The plastic components that form the shell of each layer must withstand crash tests where the RDASS 4 is flown into the ground. The craft must then demonstrate the ability to be easily repaired and flown again after the crash.

3D printing an advantage
Injection moulding would have cost $250,000 and taken six months for the tooling needed to make the fuselage components. Another problem is that any design change after the tool was made would require expensive modifications. Major changes would have involved even greater costs and delays.

“We investigated various rapid prototyping technologies and discovered that the Fused Deposition Modeling (FDM) process could provide components that met the mechanical requirements for all of our plastic fuselage components,” says John Oakley, chief executive of Leptron.

Leptron used the Stratasys Dimension 3D Printer to quickly build end-use parts for the RDASS 4. The core components took 48 hours while smaller components averaging six hours to print. The printed parts are suitable for form and fit evaluation, functional testing and end-use. Using the same machine for making prototype and production parts reduces up-front investment and enables Leptron to build UAVs without a machine shop. The plastic parts needed for prototypes and eight production craft were built for $100,000 in eight months.

“We made approximately 200 design changes during the course of the project,” says Oakley. “They included everything from reinforcing the structure to shoring up weak areas to making aerodynamic improvements. Every single part has changed a minimum of four times. FDM gives us the flexibility to make these changes without incurring a significant time or cost penalty. It would not have been possible for a company of our size to design and build this product using conventional manufacturing methods.”

In fact, functional parts made using AM have been found onboard military aircraft for some time. For example, a number of flight-cleared plastic parts for fighter aircraft have been made out of materials such as ULTEM – an amorphous thermoplastic polyetherimide resin that gives elevated thermal resistance, high strength, and stiffness.

Replacement aircraft components have also been made using Polyamide12, a carbon fibre reinforced nylon with wear resistance so good that it’s thought it could replace metal parts for some applications.

For older aircraft that need upgrading with small runs of components and bespoke parts, AM saves time, and therefore money. For example, 3D printing technology is used to maintain the Tornado fighter jet.

At RAF Marham, where the Tornado 31 Squadron is based, engineers produce a 3D printed protective cover for cockpit radios. The parts are made from a plastic material and also include the support struts on the air intake door and protective guards for power take-off shafts. The covers are made in a day for less than £100 each. Using these parts cuts the cost of repair, maintenance and service to the Royal Air Force to the tune of £1.2 million over the next four years.

Mike Murray, head of airframe integration at Warton says: “You are suddenly not fixed in terms of where you have to manufacture these things. You can manufacture the products at whatever base you want, providing you can get a machine there, which means you can also start to support other platforms such as ships and aircraft carriers.

“And if it’s feasible to get machines out on the front line, it also gives improved capability where we wouldn’t traditionally have any manufacturing support.”

AM machines could also potentially be used in theatre to support military equipment in combat zones, eliminating the need to transport replacement parts for long distances. According to 3D printer maker Stratasys, engineering firms will double the use of parts made from 3D printing over the next three years, especially in consumer goods, automotive, medical – and aerospace.

Stratasys owns Makerbot, a leading desktop AM printing brand, and runs what it claims is the largest additive manufacturing parts making bureau in the world.

Danny Weber, vice president, strategy and strategic alliances at the company, says its parts making operation – Stratasys Direct Manufacturing – has “healthy demand” for parts.

He suggests a state-of-the-art passenger aircraft such as the Airbus A350 contains some 1,000 components that could potentially be replaced by parts made using existing Stratasys technology. But large scale adoption of AM-produced parts on passenger aircraft is still a long way away, he admits.

“It is very hard to predict when we will reach the tipping point for adoption,” he says. “But we see a lot of appetite from the leading aerospace companies in terms of research and development of AM parts for the aerospace industry.”


Unlocking potential
Just like a design that is engineered to exploit the properties of a certain material, engineering parts to be made on 3D printers needs some thought. It is rarely the case that parts can be made with exactly the same physical properties as those from an injection moulded process, for example.

However, for many designers, AM actually allows more design freedom and rather than acting as a constraint, it becomes an enabling process. And with the current climate dictating that parts need to have the least weight possible, AM is a technology that could lend itself to this trend, as optimised parts usually weigh less.

Author
Justin Cunningham

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