GKN sees applications for three approaches to AM. One is large deposition technology to create pre-forms by feeding wire into a laser or electron beam to melt the metal and build up the part. Another is fine deposition technology to add local features such as bosses or pads to a simple forging using wire-fed laser melting. “This is in production in Sweden for parts of the [Rolls-Royce Trent] XWB engine,” Oldfield says.
The third approach is powder-bed additive manufacturing, which enables complex parts to be “printed” using a laser or electron beam to melt layer after layer of metal powder. The three approaches have different speeds, accuracies and scales. “Large deposition can produce parts on a big scale,” says Oldfield. 'With powder bed, you can pick up the part, it is good for high-value, high-performance parts that you want to optimize to a high degree.”
Powder-bed machines are restricted in size, and there are issues with ensuring consistency, but they are “completely flexible,” Oldfield says. Ultimately, this freedom will result in radical new approaches to designing parts. “Imagine a manifold with material only where there is flow—and no housing, just attachment points. There will be massive cost savings, and weight savings at the same time,” he says.
General Electric is stepping up its additive manufacturing efforts to support future engines including the GE9X and CFM Leap. The effort is led by Morris Technologies, a small prototyping company specializing in AM that was acquired by GE last year. “We want to take it out of the model shop and into the production shop as quick as we can,” says GE Aircraft Engines President David Joyce.
Initial parts have been made using direct metal laser melting for the first Leap-1, assembly of which began in April. Laser melting is used to build up intricate swirl passages in the combustor's fuel nozzles. “To get the low nitrous oxide [emissions], these passages are very byzantine, and complicated if you have to braze them,” says Joyce, adding that laser melting can create a more architecturally complex part that is lighter and easier to build.
A new joint venture with Parker Aerospace will focus on AM processes for fuel systems. Beyond this, Joyce says, obvious targets for applications include turbine blades and tip repairs. “The big challenge is what material systems we can use and how we can use them,” he says. “I don't see it being used for big disks, but definitely for blades and repairs, particularly on blisks, as well as the manufacture of fuel nozzles and brackets.”
But in the long term, Leap chief project engineer Gareth Richards believes, the concept could be used for far larger parts. “Additive manufacturing is the downfall of subtraction manufacturing. Ever since the Industrial Revolution, we've had to begin with a big block of metal, and in the future it won't be like that,” he says. “We're already considering how to make compressor cases additively. It might take weeks to build up, but that's still shorter than the current 18-month cycle.”
Manufacture of such components traditionally includes a lot of “white space” between times when the part is being worked on. “With additive, you don't have that. You don't have any forgings, sheets, bars and tubes. You don't have to carry all these parts. This is the vision,” says Richards, who adds that “25 percent-plus of the engine could be made using this process within the next number of years.”
Engine manufacturer Pratt & Whitney also is moving quickly to embrace AM, partnering with the University of Connecticut to set up a research center with an initial $4.5 million investment and another $3.5 million to follow over the next five years. “We are looking at additive manufacturing to wring out development lead time,” says Engineering Vice President Tom Prete. “We see it offering a great improvement in cost and time to market. It's fast, lean, efficient and green—because its use of materials is less wasteful.”