Dream ticket

Aerospace engineers at Sheffield University are using novel manufacturing techniques which could mean lighter, stronger landing gears for future aircraft. The research — to develop titanium landing gear parts for the Boeing 787 Dreamliner — could have significant effects on the aircraft’s fuel economy.

‘It’s a real boost to the system when research results in environmental benefits that complement the cost savings which often are the sole drivers behind our work,’ said Adrian Allen, director of Boeing’s Advanced Manufacturing Research Centre (AMRC) a £15m partnership between Boeing and the university’s Faculty of Engineering. Specialising in materials forming, metal working and castings, the department also carries out research into composite materials.

The centre was responding to a challenge from Colin Sirett, program manager for Messier-Dowty, which makes aircraft landing gear. Sirett wanted to see whether it was feasible to make landing gear parts for the Dreamliner from a new grade of titanium alloy, Ti5553.

‘Future aircraft must be lighter than today’s, but maintain the same operating capabilities.’ said Sirett. ‘Lighter landing gear is a necessary element of this challenge as, when in-flight, the gears are ‘dead weight’ which adversely contributes to the operating efficiency of the aircraft. The equation is simple — less weight, less power required to lift and carry, therefore less fuel used.’

Composed of titanium, vanadium, aluminium, molybdenum and chromium, Ti5553 is a high-strength, low weight alloy that can be made extremely hard. Boeing has been evaluating the properties of the alloy for structural duties in its new aircraft, but according to the AMRC’s head of machining dynamics, Sam Turner, although there have been detailed studies of its properties when cast and forged, relatively little work has been done on machining the material.

Such is the evolution of landing gear   structures, the 787’s gear has very little of the traditional high-strength steels that have been used since the early days of commercial aircraft design. ‘To go from steel to titanium is a big step,’ said Turner. ‘But it’s another step again to go from a known grade of titanium to an unknown one.’

Compared with other titanium grades, Ti5553 is very aggressive to tooling, and requires high forces to cut it, Turner explained. ‘The question is, how can we run faster and deeper?

‘We had to solve problems with tool wear and, because we were applying higher cutting forces, we were getting vibration and chatter from the machines.’

From analysing the behaviour of the machine tools with load cells and accelerometers, Turner’s team built up a profile of the frequency of vibration experienced by the tools, and the damping characteristics.

Turner explained that they then used predictive methods to find the ‘sweet spots’— the conditions at which they could cut as fast and deep as they needed to, without vibration. ‘The key was to take existing tooling, but push it harder,’ he said.

One contributing factor was the centre’s relationship with Sandvik, whose special metals division has worked with the centre to develop cutting tools which break up the vibration. The AMRC’s research substantially reduced the development time for working with a new material, said Sirett.

‘This work has enabled manufacturing times to be reduced, along with the cost impact of the new technology introduction. Working together with the centre we have greater confidence in being able to deliver the performance required for the 787.’

But the AMRC and Messier are not resting on their laurels. Research is already underway to evaluate further savings and environmental efficiencies by superseding titanium with new composite structures.

‘Technology is now developing at such a pace that companies must constantly keep ahead of the game,’ said Allen.

Adrian Allen will be talking about the AMRC’s research at the the Metalworking Production Summit on 23 November at the RBS Williams F1 Conference Centre in Grove, Oxfordshire.