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Hartford, Conn.Pratt & Whitney is flying dozens of parts in aircraft engines manufactured through the 3-D printing or “additive” process. Asked how these parts can endure the thermal and dynamic stresses required of aviation parts—when they are laid down one layer at a time and presumably have seams or a “grain” afterwards—company chief engineer for manufacturing Lynn Gambill told Air Force Magazine each layer of a metal part is laid down before the layer beneath it has cooled. The layers bond together seamlessly, resulting in a homogenous part; a single crystal “with no grain.”  The secret, she said, is in Pratt’s metallic powder, part of a proprietary process. The technique is also capable of producing parts within parts at the time of manufacture, such as a gear free to move within an outer part. “The powder serves as a placeholder” to separate the inner from the outer parts, Gambill said. The unused powder is removed after printing, leaving the inner part free to move. Unused power is also reclaimed for re-use, reducing the cost of material. The 3-D process saves material and money, and allows prototyping of parts that can speed the development process, Gambill said.