Advanced manufacturing techniques for fabricating developmental hardware.
NASA Glenn Research Center's Engineering Development Division has been working in support of innovative gas turbine engine systems under development by Glenn's Combustion Branch. These one-of-a-kind components require operation under extreme conditions. High-temperature ceramics were chosen for fabrication was because of the hostile operating environment. During the designing process, it became apparent that traditional machining techniques would not be adequate to produce the small, intricate features for the conceptual design, which was to be produced by stacking over a dozen thin layers with many small features that would then be aligned and bonded together into a one-piece unit. Instead of using traditional machining, we produced computer models in Pro/ENGINEER (Parametric Technology Corporation (PTC), Needham, MA) to the specifications of the research engineer. The computer models were exported in stereolithography standard (STL) format and used to produce full-size rapid prototype polymer models. These semiopaque plastic models were used for visualization and design verification. The computer models also were exported in International Graphics Exchange Specification (IGES) format and sent to Glenn's Thermal/Fluids Design & Analysis Branch and Applied Structural Mechanics Branch for profiling heat transfer and mechanical strength analysis.
In addition, the computer models of the design were used to produce full-scale, two-dimensional drawings, which were in turn used to manufacture negative photolithographs for high-resolution chemical etching of the many small features into the ceramic components. However, not all of the components could be produced in this manner, which was the original goal, because of the time and budget constraints of the project. Instead, diamond core drilling was used to manufacture some larger features in the thicker sections. Also, one section of the design had many small turning vanes that had to be manufactured using electrical discharge machining, and the housing for the vanes was manufactured with computer numerical control (CNC) milling machining.
As development continued on the components, we decided to produce a working, full-scale stainless steel version to demonstrate the operation and verify the flow characteristics of the analytical models. The layers were cut from thin sheets (0.010 and 0.020 in.) of 300 series stainless steel using a 300-W yttrium-aluminum-garnet (YAG) laser cutting system. The plates received a thin copper coating on one side by a vapor deposition process called sputtering. Afterward, they were aligned and stacked on a fixture and compressed in a vacuum furnace to bond the assembly into a sealed unit.
Other components were produced using another rapid prototype process called Laser Engineered Net Shaping (LENS) which uses powdered metal fed into a laser beam and melted into a pattern of overlapping layers. The part required some secondary machining and then was ready for brazing to the rest of the system.
The planning and developing of this new hardware has only been possible through the hard work of the skilled technicians using the advanced manufacturing techniques and state-of-the-art equipment available at Glenn.
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Glenn contact: Chip Redding, 216-433-3468, Chip.Redding@nasa.gov
Author: Chip Redding
Headquarters program office: OAT
Programs/Projects: SEC
Last updated: January 20, 2005
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