Gear Production
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F E AT U R E to unify the entire structure. When completed, the hybrid gear weighed 0.7081 lb (0.32 kg), 20 percent lighter than its AISI 9310 steel counterpart, which weighed 0.8847 lb (0.4 kg). Dynamic Testing Figure 1. All-steel gear, showing tooth ring (1), hub (2) and the web section (3), which represented the largest mass of the gear and thus the best candidate for replacement with a composite. fabricated from an all-steel aerospace gear in which the steel between the hub and the gear teeth was electro-discharge machined out in a hexagonal shape (Figure 1). This gap, known as the web, represented the largest mass of the gear and thus was the best candidate for replacement with a composite. The gear tested had 42 teeth, measured 3.5 inches (89 mm) in diameter and 0.196 inch (5 mm) thick. The trick was to fabricate a composite web that reconnected the hub, web and teeth in such a way as to maintain dimensional accuracy of the teeth. This was done by placing the hub into the center of a tooling fxture that featured a fat steel plate with a circular cutout the same diameter of the gear's web (see image on page 23). A series of aerospace-grade carbon fber fabric plies pre-impregnated with an epoxy resin was placed around the hub. The carbon fber plies, supplied by Toray (Tokyo, Japan), are branded T700SC. The weave of the carbon fber is visible in Figure 2 and was placed in 0and ±60-degree orientations so as to optimize material strength. A total of three circular "prepreg" webs were fabricated, each composed of 12 plies of carbon fber. One web surrounds the hub. The other two sandwich the frst. The tooth ring (minus the material excised from its center) was placed in the middle of this sandwich, inside the locating rings on the tooling fxture, to help maintain dimensional accuracy. A bond in the form of an adhesive strip connects the outside composite webs to the tooth ring 24—GEAR Production Supplement The next step for NASA Glenn was to conduct a series of tests to assess the abilities of the hybrid gear against the all-steel standard. Two types of dynamic tests were conducted to determine if hybrid gears might be considered as possible candidates in rotorcraft drive systems. The frst test assessed vibration and noise using four speeds and four levels of torque; the second was an endurance test designed to run for a large number of meshing cycles. The dynamic tests for noise and vibration used a test gear box in which two mating gears rotate against each other. The gear on the left side of the test rig is the driving gear, while the gear on the right side is the driven gear (Figure 3). All vibration measurements were made on the driven gear. The following confgurations were used on the test rig: • All-steel gears on both sides Figure 2. This completed hybrid gear has a visible carbon fber weave.