May 06, 2013
Credit: Dufieux Industries
“Metallics are dead, long live metallics!” This could be the rallying call for a manufacturing domain that is reinventing itself in the wake of a dramatic loss of ground to composites.
In their drive for lower weight and higher performance, where metal is used, aircraft manufacturers have moved away from traditional aluminum sheet-metal fabrication to computer-controlled machining of parts from lighter, stronger alloys. But both metals and machines are expensive. The finished part can weigh a fraction of the raw material from which it is cut, incurring high costs in machine time and waste metal.
So industry is developing ways to pre-form the raw material into shapes that are close to that of the final part, dramatically reducing the metal and machining needed, and significantly cutting manufacturing costs and lead times. Various methods are being developed to join simple shapes to create “near net-shape” pre-forms for complex components, including laser-beam, friction-stir and linear friction welding.
Additive manufacturing, where metal is deposited layer by layer to build up complex shapes, also is gaining ground, including in creating pre-forms that require minimal finishing by machine and in adding individual features to parts that would otherwise demand complex and costly machining from solid metal.
Investment in advanced metallic manufacturing technology reflects the reality that airframes and engines will use a mix of composites and metals for decades to come. “Our portfolio is split pretty evenly between composites and metallics, and between aerostructures and engine components,” says Rich Oldfield, director of technology at GKN Aerospace. “The drivers are similar across metallic products in airframe and engines, and the basic driver is the buy-to-fly ratio.”
Buy-to-fly is the weight ratio between material purchased and finished product. “In an extreme case, we do not use 90% of the metal,” he says. “We can recycle that, but these materials are expensive to buy and the value of the recycled material is lower, so we lose value. Also, the part spends a long time on the machine to remove all that material.”
Beginning with a shape that is closer to the final part can dramatically change the cost equation for metallics. “We get a double benefit if we go to near net-shape pre-forms. We buy less material and spend less time on the machine. As a result, there is a big drive to get to near net-shape manufacturing,” says Oldfield.