CompositesWorld

JUN 2017

CompositesWorld

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JUNE 2017 34 CompositesWorld INSIDE MANUFACTURING For the CMC components of the mixer, centerbody and core cowl, GE designed CMC prepreg material using alumina oxide fibers and alumina oxide matrices — called Ox-Ox CMC — and subsequently qualified the prepreg for the Passport 20 as well as a number of military applications. e prepreg is produced to GE's specifications by Axiom Materials (Santa Ana, CA, US). Axiom weaves the fabric for GE, using 3M Nextel 720 continuous-fila- ment ceramic oxide fibers, produced by 3M Advanced Materials (St. Paul, MN, US). e woven fabric is then pre-impregnated with an alumina oxide matrix. e ceramic matrix is a slurry of alumina and other fillers and materials. When the matrix is heated in an autoclave and then sintered, the fibers and matrix are fused together. is process differs from that for standard PMCs, where two very different organic materials, such as carbon fiber and epoxy thermoset resin, are combined and heat-molded into a new molecular structure. e fiber and matrix in Ox-Ox CMC materials have very similar chemical structures, derived from powders and 3 After cure, the vacuum bag and caul sheets are removed, the parts are de-molded and then transferred to the sintering oven. Autoclave-cured mixer parts (top two shelves) and core cowl sections (bottom shelf) are shown loaded onto the furnace's removable floor. After the loaded floor slides into the furnace, the door (shown on left) is closed and the furnace is brought to high temperature. 2 The finished layups are vacuum bagged and the parts are transferred to an autoclave for cure under high heat and pressure. Photo shows open autoclave during vacuum line installation. 1 After the metal molds are treated with a special mold release, the cut patterns are hand-laid on the molds in the specified ply schedule. Photo shows layup of a mixer in a multi-piece mold tool. Source (all step photos) | CHI various other mixtures, Hynes explains. When these materials are sintered and hardened, their chemical makeup remains the same. e design load of these parts derives from the aeroloads from the engine core airflow and external airflow — primarily a pressure load, rather than tensile or compression, Hynes says. Like carbon or glass, oxide fibers can be oriented in the layup to achieve a quasi-isotropic architecture. Manufacturing Ox-Ox CMC parts For the Passport 20 engine, CHI's Ox-Ox CMC parts comprise the mixer, the exhaust centerbody and the engine core cowl. e mixer and centerbody are both part of the engine nozzle. For these, the Axiom multiaxial prepreg fabric is cut to pre-designed patterns on automated flatbed CNC cutters supplied by Gerber Technology. An Ox-Ox CMC prepreg uses solvents that have a volatile flash- point, so they must be refrigerated until use. ey, therefore, have a limited cumulative out-time at room temperature that requires strict control procedures.

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