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metal injection dies that are used to create the wax patterns. This is followed by numerous steps of covering the wax pattern with multiple layers of ceramic coatings; melting the wax out of the ceramic mold; and pouring the hot metal into the mold tree created from the multi-step preparation process. The key to reducing the cost and lead time in the production of turbine engine castings has been the introduction of ceramic 3D-printing (additive manufacturing and 3D-printing are used interchangeably in this paper). With ceramic 3D-printing, the molds are printed directly enabling the casting to be made without the cost of any hard tooling. Figure 2 shows multiple ceramic molds for turbine airfoils positioned on the platform of a Renaissance Services 3D-printing machine. In contrast to Figure 1, Figure 3 shows
how the casting process flow changes with the use of 3D-printed molds. In this case, the entire front-end of the traditional investment casting process is eliminated, while the remainder of the flow remains consistent with the current methods used by foundries.
1.2 Small Turbine Engines The scope and target for the Air Force program focuses on small turbojet engines 4” to 10” in diameter.
The
primary application of these engines is for missions related to expendable and attritable aircraft. Figure 4 depicts an exploded view of a relatively common turbojet engine with three regions: the up- front compressor, the middle region combustor, and the back-end turbine. The diagram also identifies the three primary part families where castings are typically used in those three regions. The impellers and diffusers made from aluminum or titanium for the front section; the housings and cases made from steel or titanium for the middle section; and the high temperature nickel rotors and stators used for the turbine section.
30 ❘ August 2023 ®
Figure 6: ISDES Location in Turbojet Engine, Replacing Three Separate Components
Figure 7: ISDES - 3D CAD Model Showing Two Rows of Airfoils
Figure 8: ISDES – 3D-Printed Ceramic Mold and Aluminum Casting
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