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Braided Reinforcements in Resin Transfer Molding |
Case Study 320 |
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The Subject: Aircraft Horizontal Stabilizer
The Challenge:
The Solution:
The Details:
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| Case Study 320 | Back to Top |
In the labor-intensive job of making advanced composite aerospace components, the industry searches for ways to reduce manufacturing costs. Ideally, the faster, more efficient method should provide a component with lighter weight, higher strength and durability and a better finish. Design and manufacturing teams at Raytheon Aircraft Company of Wichita, Kansas proposed resin transfer molding (RTM) as an innovative way to make large primary aircraft structures such as horizontal stabilizers.
To demonstrate this potential, Raytheon engineers designed a "typical" horizontal stabilizer, a 91.5" long tapered wing-like structure with internal spars. Size and location of the spars was determined by the need to prevent buckling. A tooling system was built for RTM consisting of mandrels for five internal cells (to form the spars) and a master mold. The five mandrels are covered with dry carbon fiber reinforcement, then placed in the master mold, with a skin of dry carbon fiber fabric for molding into a one-piece structure.
The reinforcement surrounding the mandrel needed to be stable since the mandrel would be moved and placed into position in the RTM mold. Braided carbon fiber sleeving from A&P Technology proved to be the ideal reinforcement, providing multiple directional strength, fitting the mandrel shape precisely, and staying in position during movement of the mandrels.
Some of the cells get two layers of braided carbon fiber. The cells with less demanding requirements get one layer of braided carbon fiber plus some small inserts of satin weave carbon fiber fabric at highly stressed points. Before placement in the RTM mold, the five cells are assembled and covered with a layer of carbon fiber fabric. A braided carbon fiber sleeve would be ideal for the outer skin, because it would conform to the airfoil contour and hold the cells together. At the time Raytheon was ready to mold this stabilizer, carbon fiber sleeving was not available in a large enough diameter (new braiding techniques at A&P Technology produce braided sleeving up to 54").
Raytheon had estimated that hand laying up the cores would require a certain number of man-hours. When the braided reinforcements were introduced, the time needed to prepare the five cores dropped by 30%. Raytheon proved the viability of RTM molding for large aerospace structures, and braided sleeving from A&P Technology is the preferred reinforcement, providing the needed physical properties while enabling breakthrough reductions in cost.
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