Resin transfer molding (RTM) of transmission top case

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Resin transfer molding (RTM) of transmission top case

Crist, S.R. / Henry, Z.S.

Metallic materials are traditionally used in the fabrication of helicopter transmission gearboxes. However, the metallic gearbox is usually susceptible to corrosion, especially in unfavorable environments. Although the metallic part itself is not expensive, frequent replacement is very costly in terms of labor and downtime. Composite materials are known to have far better corrosion resistance and damage tolerance than their metallic counterparts. In addition, composite materials have superior strength (strength-to-density ratios), which implies a weight reduction. Among various composite manufacturing techniques, resin transfer molding (RTM) has been recognized as one of the most promising processes to fabricate components that require all-tooled surfaces or integrated components. A helicopter main transmission top case was identified as an excellent candidate for redesign using RTM. BMI resin (Cytec 5250-4 RTM resin) and IM7 2-D braided graphite fiber were used to make the top case preform. Computer simulation of resin flow inside the mold cavity was performed, and the result was utilized to optimize the tool design. This program demonstrated that the RTM process is capable of making complicated structural parts.