Additive Manufacturing

JAN 2018

ADDITIVE MANUFACTURING is the magazine devoted to industrial applications of 3D printing and digital layering technology. We cover the promise and the challenges of this technology for making functional tooling and end-use production parts.

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Page 15 of 43

JANUARY 2018 Additive Manufacturing 14 TAKING SHAPE The design of the aerospike's exhaust manifold is essentially inverse to the tradi- tional bell-shaped rockets used to launch recent space shuttles. Those rockets lose efficiency when the thrust spreads out from the bottom of the bell-shaped manifold as the craft ascends and the atmospheric pressure decreases. This is why today's shut- tle missions require multiple stages to reach orbit: Decreasing atmospheric pressure during ascent requires different thrust capabilities than the initial booster rockets that are jettisoned just minutes after launch. The Amaero team—which consists of Marten Jurg, an engineer with Amaero and a PhD candidate at Monash University in Australia, as well as other PhD candidates from the school—designed their aerospace engine around the additive process from the outset. Printed on an EOS M280 using Hastelloy X (a high-strength, nickel-based superalloy), Jurg says that build chamber size constraints, feature size, materials performance and key parameters such as the angle, thickness and arrangement of features were all considered in light of the group's collective years of experience in the alloy system using selective laser melting (SLM). All design choices were made to reduce the amount of machining necessary for postprocessing. "Drawing from experience in the Hastelloy alloy system, we knew what was and wasn't possible," Jurg says. This experience informed Amaero's design choices, and by working back and forth with the fluids engineers, the team was able to rapidly iterate and create geometries and features that would meet key performance criteria while still maintaining AM buildability. The team first focused on what Jurg calls the "big-ticket items," such as the engine's three-chamber design, truncated aerospike and cooling configuration. Jurg points to the conformal cooling channels as just one of the aspects of Amaero's aerospike that would not have been possible to manufacture traditionally. Numerous features were completely reconceptualized for additive design, including the conformal cooling, injector manifold, the elimination of high temperature seals (by making the combustion chamber a single piece), and the fluid flow path and control mechanisms. The cooling passages alone, he says, "constantly change size and orientation to cater for the specific local heat flux, which is critical to ensuring continuous operation." Achieving the right manipulation of tubes traditionally would be an extremely difficult process, he says—one that might take years to perfect. Since Amaero's engine was intended to be finished in just a matter of months, the Amaero team had to radically rethink its design approach. For this they created calcu- lation tools that allowed them to rapidly iterate through the fundamental aspects of the design and quickly converge on a design solution. "We aimed to show through this project the benefit of working with AM design from the outset, not taking a traditional design and making it work with AM," Jurg says. "In this project, through concurrent design methodology and consolidation of components, the timeframe could be re- duced significantly while also increasing the overall performance." The team behind the aerospike engine has formed a new venture called NextAero to move this work forward, looking at future applications in propulsion technologies. Meanwhile, Jurg says that Amaero is using its aerospike "to show the potential of addi- tive manufacturing to those who may not understand the process, and how by working with AM designers, it is possible to build items with a new level of performance." Still shot of Amaero's 3D-printed aero- spike engine during a firing test. Once hailed as "the holy grail of the spaceship movement," the aerospike is a single- stage-to-orbit engine that NASA tested extensively in the 1990s. Featuring an inverted-bell shape and complex cooling channels, the aerospike is notoriously difficult to manufacture through traditional methods.

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