Autoclave to VARTM

However, autoclave processing remains expensive, especially for medium-to large-size production runs with low cycle times compared to most other processes. Capital cost is high, fiber placement equipment is usually even more expensive, maintenance, and operating expenses tend to be higher than for ovens, presses, and similar equipment. 

As reviewed in conventional RTM, the preform is placed into a closed, matched tool and resin is injected under pressure about 100 to 200 psi (0.69 to 1.38 MPa). Early RTM processes lacked the consistency needed for aerospace components, in both dimensional tolerances and mechanical properties. Fiber volume fractions were significantly lower than the 60 to 65 wt% typical of prepregs. Problems with predicting flow fronts as well as flaws that were introduced into the preform when closing the matched metal molds often led to high void contents and dry spots. 

Improvements in both materials and processes have made RTM a viable option for aerospace manufacturing. However, it normally takes 10 to 15 years for a new technology to become accepted in the aerospace industry. Use of RTM began about 1998 when Lockheed Martin (Fort Worth, Texas, U.S.A.) selected RTM for many of the F/A-22 Raptor s structural components. RPs comprise approximately 27 wt% of the F/A-22 s structural weight (24% TS and 3% TP). RTM accounts for more than 400 parts, made with epoxy resins. The wing s sine wave spars were probably the first structural application of RTM composites in an aircraft. For a vertical tail on another Lockheed Martin aircraft, the RTM process reduced the part count from 13 to one, eliminated almost 1,000 fasteners, and reduced manufacturing costs by more than 60%. 

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