CompositesWorld
Issue link: https://cw.epubxp.com/i/830100
NEWS CompositesWorld.com 35 CMCs for the Hot Zone e precision-cut patterns are hand-laid on custom metal molds, previously treated with a special mold release. Layup is assisted by laser projection systems provided by Gerber subsidiary Virtek Vision International. Molds were provided by GE or by AIP Aerospace (Santa Ana, CA, US), CHI's previous owner. e mixer assembly — the most complex of the components produced — is 965 mm in diameter and 610 mm long. e mixer is molded in a multi-segment metal tool that is assembled for layup and is then disassembled after autoclave cure to allow the tool to be safely removed from the part. After layup, the part is vacuum bagged using nylon bags from Airtech International (Huntington Beach, CA, US) and cured in an autoclave under high temperature and high pressure (details not disclosed) — and then de-molded prior to sintering. Because the autoclave cycle leaves the ceramic in the green state—that is, compacted but not fully cured — Hynes explains, "We have to be very careful in de-molding this complex part before it is fully hardened in the sintering oven." e engine exhaust centerbody is a cone-shaped structure approximately 460 mm in diameter (on the front end) and 610 mm tall. It fits inside the mixer and protrudes aft of the mixer trailing edge. For this part, the cut patterns are hand laid into concave (female) molds and covered with a caul plate — made from an undisclosed material — to apply and equalize pressure. It, too, is then vacuum-bagged, autoclave-cured and demolded before entering the sintering cycle. e core cowl is made in four parts, each approximately 1.52m long and curved to form a cylinder that encloses the engine core. ese parts, too, are laid up in single-sided, concave molds, covered with caul plates and vacuum bagged. And they, too, are autoclave cured, demolded and finished in the sintering furnace. In each case, the cured parts are then transferred after demolding to the sintering furnace. e custom-designed furnace features a computer-controlled, removable floor, a design that protects workers from having to enter the furnace. After the parts are loaded, the floor is activated to automatically slide under the furnace and 4 After the parts are removed from the sintering furnace and cooled, they are machined on this Fooke 5-axis CNC milling machine. The photo shows a centerbody being positioned for machining. 5 Quality control inspection includes surface measurements by this Romer Coordinate Measuring Machine. Photo shows mixer being measured. 6 At this point, the parts undergo nondestructive inspection. Photo shows mixer in NDI. The mixer appears black in this photo because, prior to the laser IR inspection, each CMC component is treated with a temporary nonreflective coating to improve the quality of the thermographic image. 7 Following cure, machining and inspection, metal details and ceramic components are joined and then the finished parts are packed here in the assembly area within the CMC-dedicated building for shipment to General Electric.