Freeform Fabrication of Functional Silicon Nitride Components by Direct Photo Shaping

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S.VENTURA*, S.NARANG*, P.GUERIT*, S.LIU*, D.TWAIT**, P.KHANDELWAL***, E. COHEN**** and R. FISH**** *SRI International, 333 Ravenswood Avenue, Menlo Park California 94025 "**HoneywellCeramic Components, 2525 West 19 0th Street, Torrance, California 90504 ***Rolls-Royce Allison, P.O. Box 420, Speed Code W-05, Indianapolis, Indiana 46206-0420 "****Universityof Utah, Department of Computer Science, 3190 Merrill Engineering Bldg., Salt Lake City, Utah 84112 ABSTRACT This paper describes a new multilayer solid freeform fabrication process, "Direct Photo Shaping" (DPS), where visible digital light projection is used as a maskless tool to build images on photocurable ceramic dispersions (ceramic powders in photopolymerizable liquid monomers) by flood exposure. For each layer, the projected image is changed according to the CAD data describing the object being built and solidification takes place by photocuring the exposed areas. Multiple layers are dispensed and photocured to fabricate the object of interest. A final rinse with a suitable solvent allows the removal of any uncured ceramic dispersion. The porous free formed "green" ceramic object can then be fired and sintered into a highly dense ceramic part. Digital Light ProcessingTM technology (developed by Texas Instruments) enables SRI International to project digital, high resolution, high brightness, high contrast visible light to photocure and form components with a good degree of accuracy. This paper describes the Direct Photo Shaping process and its advantages, and how DPS is being applied to the fabrication of ceramic (Honeywell AS800) gas turbine components for military and commercial applications. ASS00 test specimens with flexural strength in excess of 800MPa were fabricated by DPS. A first-stage AS800 turbine vane for the Rolls-Royce Allison Model 501-K industrial gas turbine was fabricated by DPS and tested in a gas-burner test rig at 1204'C. Initial tests show that ceramic samples with optimized surface finish (comparable to that achieved by ceramic bisque machining) can be fabricated by applying a pixel anti-aliasing filter along the boundaries of the sample projected slice images.

INTRODUCTION The Solid Freeform Fabrication (SFF) approach holds great promise for rapid prototyping of ceramic components through simplification of the processing cycle, including the elimination of the time consuming steps of pattern making and mold fabrication. SFF of ceramics will allow fast turnaround design validation of new advanced ceramic components for gas turbine engines. In comparison with conventional spark ignition engines, gas turbine engines offer greater fuel efficiency, lower particulate levels, and multiple fuel capability. Turbine engine technology is critical not only to maintaining US military superiority but also to continuing commercial prominence in the aviation, marine and industrial sectors. Selective laser sintering [1], 3-D ink jet printing [2], laser stereolithography [3], fused deposition [4] and layer object manufacturing [5] are examples of rapi

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