Novel welding technology gives more fuel-efficient engines

Transport accounts for around a quarter of the UK’s carbon dioxide emissions and making aeroengines more efficient contributes to reducing this number.

A team of researchers at The University of Manchester was involved in the development of new welding techniques, which allow the use of new high temperature materials to increase fuel efficiency. Rolls-Royce now uses friction welding processes for its modern Trent aeroengines that drive the Airbus A380 and the Boeing 787.

As climate change continues to hit the headlines, aeroplane engine manufacturers are all competing to design more environmentally friendly technologies. As a general principle, engines run more efficiently and release less harmful emissions when they run at higher temperatures - more than one thousand degrees in an aircraft engine. Unfortunately, materials that can withstand such high temperatures cannot be joined by conventional welding techniques.

A research team at The University of Manchester was involved in the development of friction welding procedures and post-processing treatments, which allow Rolls-Royce to introduce specialist high temperature materials into their engines.

Bolts

Friction welding can replace heavy bolts in engine components.

Engines

More than 1200 Trent XWB engines have been ordered.

Fuel

The Trent XWB is 25% more fuel efficient than its closest competitor.

Adopting this new welding method, Rolls-Royce is now able to use materials and novel alloys that can handle engine temperatures up to 50°C higher than before. These latest models have better fuel efficiency with lower emissions of harmful NOx and CO2.

The Manchester research team was also involved in the development of "blisk" technology, which allows Rolls-Royce to weld blades to disks, reducing the weight of critical engine parts. This weight reduction also improves fuel efficiency.

Following extensive testing and industrial trials, Rolls-Royce now use the new welding technology in several of its engines. For example, the Trent 900 engine, which powers the A380 Airbus, employs nickel superalloys joined by inertia friction welding.

The number of friction welds has continued to increase in engines for the Boeing 787 and the A350 Airbus. This has contributed to the A350's new Trent XWB engine being 25% more fuel efficient than its closest competitor. Rolls-Royce has orders for more than 1200 Trent XWB engines which first saw flight in early 2013. Rolls-Royce reports that this engine has helped the company to maintain its market share.

Background

Professor Michael Preuss, Professor Philip Withers and their research team used large-scale research facilities and advanced microscopy to study the detailed structure of engine materials (including specialist high temperature alloys) which had been joined using inertia and linear friction welding. These studies identified how the welding processes and post-welding treatments affect the strength and performance of the engine materials.

Temperature

Friction welding allows Rolls-Royce to build engines that run 50°C hotter than before.

Weight

Components made using friction welding are up to 30% lighter than using the same assembly joined by using bolts.

The researchers worked to minimise residual stresses by either identifying optimum welding parameters or applying an appropriate post-weld heat treatment that relaxes the stresses sufficiently without compromising the microstructures and properties of the engine component.

The studies revealed that the chemistry of alloys has a pronounced effect on the generation of residual stresses following inertia friction welding. The researchers also showed that proposed post-weld heat treatments only partially relieved residual stresses, but they were able to develop an alternative and more effective treatment. The residual stresses were measured using neutron diffraction, shown to be a much better analytical technique than conventional hole drilling method.

Extensive laboratory and industry-based research and testing allowed the team to optimise the parameters for inertia and linear friction welding.