Less is more in aerospace

Adoption of additive manufacturing is on the rise. Chris Jones outlines why it could find a natural home in the aerospace and defence sector, not just as it fits the low volume high value profile, but because it brings genuine engineering design advantages.

The core technology behind additive manufacturing, at a basic level, is not a new thing. However, despite initially being conceived in the 1980s, recent technological advances have brought this process from a novel and futuristic intrigue, to a present day reality.

The demand for additive manufacturing is growing: the global market is expected to increase from $3.07bn in revenue in 2013 to $12.8bn by 2018, exceeding $21bn by 2020. This is no more so apparent than in Aerospace and Defence (A&D) production and MRO applications, which currently account for around 15% of the global market. So, what impact is additive manufacturing having on A&D? Here, I look at some of the key benefits to the industry and how the technology is being applied to solve challenges today.

Streamlined for speed

3D printing is helping manufacturers address issues such as weight reduction and speed of production. The former of these is vital in Aerospace, as 1g on the ground is equivalent to around 40 to 50g in the air. With greater efficiency and reduction in fuel usage high on the agenda, every gram of weight saved counts. The latter has a greater role to play in MRO as the constant high pressure placed on parts results in some components needing to be regularly replaced. The faster this can be done, the less time aircraft fleets spend grounded – an issue that is costing the industry vast sums of money. Airbus China, for example, recently estimated the cost of a grounded A380 Airbus to be $1,250,000 every day.

In the Defence sector, reducing weight is also critical, with emphasis placed on achieving lighter loads and vehicles, as well as reduced inventory at military bases. There is also currently greater scope for the use of additive manufacturing in unmanned, rather than manned, vehicles due to the reduced required safety parameters when there is no human pilot present in the cockpit and the smaller capacity of the vehicle. This was exemplified by the recent 3D printed drone launch off the HMS Mersey, and the technology will certainly continue to play a role here in the production of faster and lighter drones.

Roadblocks to overcome

Despite the advantages of additive manufacturing in A&D, there are some challenges that need to be addressed before the technology can be adopted more widely across the industry. The nature of the inherent risks associated with aviation makes it a highly regulated sector and this impacts the speed at which 3D manufacturing processes are being adopted. The technology has drawn heavy scrutiny from regulators and manufacturers face a challenge in proving the safety of products produced by this new process and gaining accreditation. Some of the areas regulators are keen to focus their attention on over the next few years are how printed products will behave over time and based on the materials used, and it will be interesting to see how the industry adopts means to accelerate its adoption.

Nevertheless, A&D remains at the forefront of the take-off of additive manufacturing and despite the regulatory barriers, there are already innovative uses demonstrating significant results.

Hollow rotating blades

Rotating or runner blades are one of the most important components of rotary heat engines. It is in the moving stages that the thermal energy is converted into kinetic energy and thereby the motive power is generated. The Aerofoil or outer part of the blade must be finely tuned in design, with several aerodynamic considerations involving complex Computational Fluid Dynamics. All of this is geared towards providing maximum thermal efficiency by optimising aerodynamics, while still meeting safety requirements in strength and withstanding vibration.

There are however, two key challenges to address to ensure this can be achieved. Firstly, in conventional manufacturing, machining is subtractive: meaning the material is gradually removed in shaping the design. This imposes significant constraints on the design when trying to achieve optimum levels for these opposing variables of safety and aerodynamics because of the base process of production, the end-product is not optimised.

Secondly, blades’ aerodynamics must be optimised but, during operation, they are subjected to very high centrifugal and pressure forces that result in a high level of stress that the design must be able to withstand within the safety limits of the material. The stages of aerodynamic design and strength / vibrations tests are completely independent of each other and must be conducted one after the other. But each of these stages favours virtually opposite preferences: the light-weight design is more aerodynamic but more likely to fail under strength and vibration stresses.

Additive manufacturing addresses both these issues. Firstly, it is, by definition, a procedure where components are shaped by adding layers of material. This permits much greater complexity when shaping the aerodynamic design and makes it possible to manufacture components with blind cavities, in this case, hollow blades. This is impossible with traditional methods and unlocks new opportunities and benefits that could not previously be realised.

Looking at the second problem of stress pressures, the centrifugal forces produced by rotation have the greatest focus at the base and almost zero at the tip. The pressure loads are highest on the outer surfaces but almost non-existent in the centre. Thus there is plenty of scope to remove material from the inner regions and nearer the tip of the blade without compromising the blade’s safety or strength. This weight reduction actually further reduces the centrifugal force and therefore the stress acting on the blade.

But aerodynamics is paramount, and therefore the outer surfaces cannot be compromised to preserve the original design for high efficiency. Additive manufacturing makes this win-win scenario possible. In fact the lighter design aerofoil has resulted in nearly a 30% reduction in weight for a major aircraft manufacturer and around a 40% subsequent reduction in reaction force.

In recent years, there has been a rapid rise in the recent adoption of additive manufacturing, in no small part due to its uses in A&D. Despite regulatory hurdles to overcome, significant cost and efficiency benefits are being seen across the design and manufacturing lifecycle. Additive manufacturing is set to continue to have a transformational impact on the A&D industry and it will be fascinating to see where the next innovations come from.

Chris Jones is Global Aerospace and Defence Lead at Cyient