AEROSPACE ENGINEERING
Optimised tools for tomorrow’s sustainable aircraft by Steve Weston, Industry and Tech Centre Manager – Aerospace, Sandvik Coromant They are necessary when working with difficult-to-machine materials. Tomorrow’s sustainable aircraft will rely increasingly on next generation powder-based, heat resistant super alloys (HRSAs) and advanced ceramic matrix composites (CMCs), as they can withstand high temperatures for more efficient fuel burn and low emissions. However, these materials are required to be heat resistant, creep resistant and keep good material properties under extreme temperatures. This presents challenges at the machining stage.
able aircraft fuel and liquid hydrogen, to create lower emissions. As always, the ability to run hotter means there is a more efficient fuel burn. If we couple this with higher compression ratios, which most new and future engines can support, then the result is greater efficiency. That means less fuel is combusted with increased power and reduced noise.
The UK Innovation Strategy report says that new technologies and processes will be key to manufacturing and machining these advanced materials at scale. Collaboration within the industry will also be essential, which is already being demonstrated at the Advanced Manufacturing Research Centre (AMRC) in Sheffield, UK.
With aero engines, the core of the engine is relatively small and the fan on the front is relatively large. So, a limiting factor is how fast you can rotate the fan. To remedy this, over the last five to 10 years, gearboxes have been introduced between the fan and the core of the engine. They enable the fan to run more slowly while the engine core runs faster for high compression and better fuel efficiency.
Sandvik Coromant was one of the original members to join the AMRC when it was founded in 2000, along with Boeing and Messier Dowty (today Safran Landing Systems). They were later joined by the likes of British Aerospace, Rolls-Royce, GKN Aerospace and Airbus, and today, the AMRC has approximately 118 members in total. Most of the centre’s projects are collaborative by nature, funded and selected by all members, and the AMRC now employs over 500 highly qualified researchers and engineers from around the globe. All are devoted to multi-million pound projects that can support a strong, pro-innovation economy. In the aerospace sector, if we are talking about sustainability, then new technologies and processes should focus on the ability to combust new fuel types, like sustain36
THE SINGAPORE ENGINEER April 2022
Innovations for sustainability
However, HRSA components are needed to make this work. Such materials are metallurgically-composed to retain their properties when exposed to extreme temperatures. But this also means the stresses generated when machining these materials are high. The unique capability of these nickel-, iron- and cobalt-based super alloys to perform close to their melting point also gives them generally-poor machinability. One part that is increasingly used in aerospace is the blisk, a component that comprises both a rotor disk and blades. Unlike traditional disks, which have slots in the outside diameter that blades fit into, blisks combine the disk and blades into a single component and are lighter than conventional disks with
blades. This decreases the number of components in the compressor while, at the same time, decreasing drag and increasing the efficiency of air compression in the engine by around 8%. Blisks are generally located on the cold compressor side of aircraft engines and are usually made of titanium in the first instance, then migrating to HRSA materials when they are closer to the combustion chamber. Machining these components effectively, and to the highest standards, requires optimised tools and process knowledge relevant to these advanced materials. Sandvik Coromant’s internal project areas focus strongly on a variety of key aero engine components and features. They include disks, blisks, shafts and casings, among others. In particular, we are seeing increased use of blisks in today’s gas turbine engines and expect this trend to continue, as the last ounces of potential power and fuel efficiency are extracted from current engine architectures. However, blisks present unique machining challenges because they are often made from HRSAs. The components demand tight dimensional and geometrical tolerances, while maintaining high standards of surface integrity and surface finish.
More secure machining In response to these machining challenges, Sandvik Coromant offers a number of tooling solutions to support cost-effective, high-quality machining of aero engine components. One such method, that Sandvik Coromant recommends, is high feed side milling. The technique involves a small radial
