Engine-maker Safran is exhibiting a turbine rear frame made with additive manufacturing (AM) at this year's Paris Air Show.
Produced under the RISE technology program, the 3 ft.-dia. component is the largest Safran has ever produced with additive manufacturing, demonstrating the growing use of the technique in turbofan design and manufacturing.
The turbine rear frame is a third lighter than one made with conventional casting and machining techniques, says Delphine Dijoud, Safran Aircraft Engines' vice president engineering deputy, as she updated on the company's progress at the Safran Tech site in Itteville, France, in early June.
The production cycle lasted just three weeks, instead of 18 months. That shorter cycle is one of AM's benefits, and design changes can thus be incorporated late in the development process. For the turbine rear frame, Safran is targeting a production cycle of one week or less eventually, Dijoud says.
As a powdered metal suitable for the hot section of an engine, Safran engineers chose a nickel superalloy. AM is not the most economical way to melt metal, Francois-Xavier Foubert, CEO of Safran Additive Manufacturing Campus, noted. But it makes sense if eliminating welds yields benefits – such as cutting weight significantly – or the part, which can have a more complex shape, integrates more functions, also making the overall design lighter, he explained.
A favorable buy-to-fly ratio is another strong point for AM. While conventional techniques require 3-10 lb. of metal to manufacture a 1 lb. component, AM just needs 1.5 lb., Foubert said. Current techniques need virtually zero machining after the AM process and the turbine rear frame is thus “net shape,” he stressed.
Safran already uses AM in engines, as it has 14 part types – made from aluminum, nickel superalloys or titanium – in production. The proportion of 25% of AM on the RISE demonstrator will be that of future engine production, Foubert said.
AM machine-tools enable the production of increasingly large parts. From the early 2030s, components up to 2 m (6.6 ft.) in diameter could be made with AM, Foubert predicted. At the same time, more powerful, more numerous lasers on a single machine-tool can melt thicker layers of metal powder, improving productivity.
A caveat, for designers, is the temptation to create new nuances of metal powder. A machine-tool supports only one nuance of powder, so more nuances mean more machine-tools. As they cost €3-5 million ($3.4-5.7 million) each, manufacturers rather tend to limit the number of machine-tools. On the other hand, a machine-tool supports multiple part designs, Foubert emphasized.
While the use of AM may grow, other processes will still compete. Thanks to the casting process' lower cost, foundries may retain less complex parts. Moreover, they may retain sophisticated metallurgy, such as single-crystal parts. The forging process may remain most suitable for highly loaded components, Foubert added.
Nevertheless, engine manufacturers may sometimes have a choice between the three. “Forging, casting or AM – we will pick the cheapest, as long as we preserve sovereignty,” Eric Dalbies, Safran's EVP, strategy and CTO, said. While a mine cannot be relocated, the atomization process that transforms the metal into powder can be brought in house or, at least, close enough. Airbus and Safran could therefore ask Aubert & Duval, a jointly owned metal supplier, to create an atomization facility for titanium, Dalbies said.
