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Thinking out of the box, with Clean Sky’s AMATHO

Thinking out of the box, with Clean Sky’s AMATHO

The gearbox housing of Leonardo’s Next Generation Civil Tilt-Rotor is benefitting from an innovative use of Additive Manufacturing technology to reduce weight, use higher performing materials, and push Europe’s aero-industrial capabilities further, thanks to Clean Sky’s AMATHO project.

Additive Manufacturing (AM), and particularly the ever-increasing size of what can be produced using AM techniques, opens up new opportunities in aeronautical design and manufacturing. Clean Sky’s AMATHO (Additive MAnufacturing Tilt-rotor HOusing) project, which started at the end of 2016 and runs for five years, is leveraging AM to bring about a revolutionary approach to the design and production of a novel gearbox housing for Leonardo Helicopters’ Next Generation Civil Tiltrotor Demonstrator.

“Up until now the Tilt-Rotor drive system (or gearbox) housing, could only be produced by casting, due to its complex shape and size. This in turn has limited us to the use of particular metallic alloys such as aluminium or magnesium, which are easy to cast but whose performances are not the most appropriate for this specific function. So the idea of the AMATHO project is to develop from scratch the same component but using Additive Manufacturing which allows the use of higher quality materials in order to optimise performance and reduce weight, leading to fuel reduction and its associated environmental benefits“ says Professor Giuseppe Sala of the Aerospace Structures and Design Department at Politecnico di Milano, Italy.

“We’re aiming towards a one-shot process. AM will enable us to come up with an integrated design which incorporates built-in features and functions, using the right materials, so that laborious post-process machining and finishing – which is presently required with casting processes – can be reduced or ultimately eliminated. And once we solve this specific design problem for the gearbox housing of Leonardo’s NextGen Civil Tilt-Rotor Demonstrator, we’ll be able to consolidate the process as a technical asset for Europe’s aeronautics industry, and subsequently apply it to other aircraft components“.

“The design requirements of the housing are very stringent in terms of loading, fatigue, tension, and it must also be able to withstand the presence of potentially aggressive fluids such as lubricants and oil. Fortunately, the project’s material of choice is suited to the AM process, explains Professor Sala: “The only way to solve all these issues together is to go for metallic alloys and our goal is to use titanium alloys. Usually they’re not so easy to process using conventional manufacturing, but it’s a lucky coincidence that titanium alloys are more easily processable when using additive manufacturing than aluminium or magnesium alloys“.

Titanium doesn’t just have a weight-tostrength advantage over those other metals, it also performs better in terms of mechanical endurance, thermal behaviour, and is more resistant to aggressive fluids. And there are other benefits too, according to Professor Sala:

“The breakthrough is to use the right materials to produce the right shape using the correct technology, which is additive manufacturing. We can embed some channels for lubricant flow and incorporate special sandwich walls to increase the structural efficiency, so we expect that most of the weight-saving will come from the improvement of design and the exploitation of the features that are offered by additive manufacturing, rather than from the simple reduction of weight due to the intrinsic properties of the material, so we expect a strong exploitation of AM capabilities“.

Some of the more specific objectives of the AMATHO project include the analysis and determination of the most relevant of additive manufacturing processes by comparing powder feed direct energy deposition techniques such as Direct Laser Deposition (DLD) and powder bed fusion techniques including Selective Laser Melting (SLM) and Electron Beam Melting (EBM). The powder precursors (which include magnesium, aluminium, titanium alloy and stainless steel) are being investigated as well, in terms of chemical nature, particles granulometry and morphology.

Additionally, static, fatigue, fracture mechanics, damage tolerance, corrosion endurance, chemical compatibility, machinability, weldability and heat-treatability testing are being worked out and final trade-off processes accomplished for choosing optimal materials and processes. Characterisation methodologies and NDI (non-destructive inspection) techniques are being assessed as well.

To test activity on dedicated specimens, smaller, but fully representative full-scale gearbox housing components (to be considered as proof of concept) are manufactured through the traded-off technologies and tested to check their compliance with functional aspects of the rotorcraft drive system housing. In parallel, design rules and methodologies for detail design, optimisation and structural substantiation of AM components will be defined.

One of the factors that is key to AMATHO is the exploitation of Borealis, a Horizon 2020 research and innovation project whose objective is to exploit advanced R&D results in mechatronics and laser processing, culminating in the development of a novel machine that produces large and complex products at high-speed using multi-material additive manufacturing deposition and ablation. Clean Sky’s AMATHO Project Officer Andrzej Podsadowski points out that Borealis, and its achievements in pushing the European industry’s additive manufacturing capabilities forward, is most beneficial to AMATHO by making it possible to use AM to produce larger components:

“When the project was started, the biggest element that could be manufactured by additive manufacturing was in the order of size of 20 or 25 cm diameter, and this gear box housing is 1 m by 1 m. I remember the evaluation because part of the Clean Sky call criteria for AMATHO was to propose production in a one-shot process“.

Hitherto, additive manufacturing meant that only small parts could be produced that would have to be welded together, adding time, cost and complexity to the manufacturing process. Borealis has increased the scale for AM, and opened the door to the design of larger components, making the one-shot process ambitions of AMATHO a viable prospect.

“Right now EASA and FAA are working on certification standards for additive manufacturing components in aeronautics because this is new for them as well“ says Podsadowski. “For Europe’s aviation industry, this is something we would like to exploit further, and Clean Sky’s AMATHO project clearly demonstrates that additive manufacturing is not just a game changer for cost but also for new design possibilities“.