OOA curing achieves the desired fiber content and elimination of voids by placing the layup within a closed mold and applying vacuum, pressure, and heat by means other than an autoclave. An RTM press is the typical method of applying heat and pressure to the closed mold. There are several out of autoclave technologies in current use including resin transfer molding RTM), Same Qualified Resin Transfer Molding (SQRTM), vacuum-assisted resin transfer molding (VARTM), and balanced pressure fluid molding. The most advanced of these processes can produce high-tech net shape aircraft components. RTM fabrication process

1. Precision molds are created and prepared.

2. Preforms (reinforcing graphite fiber layers) are placed into the mold. (SQRTM uses vacuum compacted prepreg layups)

3. Layups and internal mold components (mandrels) are placed in mold.

4. Mold is closed.

5. Mold is placed in a press and clamped to contain internal pressures. (Some molds are self clamping)

6. Plumbing and instrumentation are connected to the mold.

7. A very high vacuum is drawn on the mold.

8. Mold is warmed to injection temperature.

9. Resin is injected into the closed mold. Vacuum is maintained and resin injected at high pressure to create hydrostatic pressure and eliminate voids. (SQRTM process injects only a small amount of resin)

10. Mold is heated to cure temperature & held for cure cycle maintain similar to the standard autoclave curing cycle (maintaining resin pressure).

11. Mold is removed from the press.

12. Part is removed from the mold. SQRTM is an RTM process adapted to prepreg technology.

The prepreg is placed in a closed mould and during the cure cycle, a small amount of resin is injected into the cavity through ports positioned around the part. This resin does not go into the laminate, but only presses up against the edge of the laminate in order to establish hydrostatic pressure on the prepreg, similar to the goal of autoclave curing. This pressure is similar to the autoclave, on the order of 6-7 bars (90-100 psi). Hydrostatic pressure minimizes voids by keeping dissolved air, water and resin monomers in solution in the resin. The tool can either be self-clamped and self-heated or heated and clamped by a press. The equipment is composed of a tool, a press, an injector, and a vacuum pump.

VARTM is one of three processing alternatives that proponents claim can achieve aerospace-grade results without resort to autoclave cure. VARTM denotes a variety of related resin infusion processes now commonly used in the marine, transportation and infrastructure markets.

The processes differ radically from prepreg processing in that fiber reinforcements and core materials are laid up dry in a one-sided mold and vacuum bagged. Liquid resin then is introduced through one or more ports strategically placed in the mold, and drawn by vacuum through the reinforcements by means of a series of designed-in channels and/or carefully placed infusion media that facilitate fiber wetout. Unlike the autoclave, VARTM cure requires neither high heat nor high pressure. VARTM's comparatively low-cost tooling makes it possible to inexpensively produce large, complex parts in one shot.