ACG's first generation of out-of-autoclave composite prepregs were developed to cure and de-mould in a stable condition after initial cure at temperatures as low as 60°C using low cost tooling and oven vacuum bag processing, but without need for the high temperatures and pressures of the autoclave normally associated with aerospace prepreg processing. One typical application of these prepregs is LTM^®45EL, which was used in the construction of Scaled Composites' SpaceShipOne space vehicle and its carrier plane WhiteKnightOne. Parts made from ACG's LTM^® prepregs are then post-cured, in a freestanding state, away from the mould to a higher temperature, thus completing the curing reaction and generating the required mechanical and thermal resistance properties.

In contrast, traditional composite prepreg materials, such as those typically used on the Lockheed/Boeing F-22 'Raptor' stealth fighter aircraft or the Boeing 787 commercial airliner, require autoclave pressures of 6 or 7 atmospheres and high temperatures - typically 180°C - to bring about the cure. The composite or Invar mould tools required to withstand these conditions are expensive. This presents particular problems for one-off prototypes or limited production aircraft with only a small number of parts over which to amortize costs. This could result in the tooling constituting 75% of the airframe costs. A low temperature, oven vacuum bag cure resolves this problem, allowing the use of low cost tooling materials, as well as removing size limitations imposed by an autoclave.

First generation out-of-autoclave systems, developed during the 1990's, had some success, but were deficient when compared to high temperature autoclave cured materials in a number of areas, specifically:

• mechanical performance
• laminate quality
• damage tolerance

Next generation out-of-autoclave prepregs and infusion systems exhibit none of these deficiencies and offer levels of performance, toughness and laminate quality comparable with high temperature/pressure systems, as well as improved handling and work-life at room temperature when compared to their predecessors.

MTM^®44-1, MTM^®45-1, MTM^®46 and MVR444 (detailed below) form ACG's new generation out-of-autoclave processing systems currently in use or under qualification for a variety of civil and military applications.

MTM^®44-1 is a dual cure temperature (130°C / 180°C [266°F / 356°F]), high performance epoxy matrix developed for both resin film infusion (RFI) and prepreg processing. It has been optimised for low pressure vacuum bag processing and, in addition to resin film and prepreg formats, it may be supplied in partial or selectively impregnated (ZPREG^®) formats to reduce lay-up time, minimise surface defects, and ensure very low internal void content. After a freestanding postcure, the system is capable of 150°C (302°F) wet Tg and exhibits a high level of damage tolerance. This, together with its low density, makes it a strong candidate for primary structures on aircraft, produced out of autoclave. The process cost savings can equally be applied to many less critical structures, such as fairings, which have, historically, been designed for autoclave processing.

MTM^®45-1 is a variable cure temperature, high performance, toughened epoxy matrix, developed for both resin film infusion and prepreg processing. It has been designed for low pressure vacuum bag processing and, in addition to resin film and prepreg formats, it may be partially or selectively impregnated (ZPREG^®) formats to reduce lay-up time, minimise surface defects and ensure very low internal void content. After a freestanding postcure, the system is capable of 150°C (302°F) wet Tg and exhibits a high level of damage tolerance. This, together with its low density, makes it a strong candidate for primary structures on aircraft, produced out of autoclave. The process cost savings can equally be applied to many less critical structures, such as fairings, which, historically, have been designed for autoclave processing. MTM^®45-1 may be initially cured at temperatures as low as 80°C (176°F), allowing lower cost tooling materials to be selected for prototypes and very short production runs.

MTM^®46 is a long outlife, flexible cure epoxy resin matrix for the manufacture of aerospace components using oven/vacuum bag moulding processes. The rheology of MTM^®46 has been developed specifically for the production of high quality laminates using low pressure processes. The 60 day room temperature working life and excellent tack and drape properties facilitates the lay-up of very large complex structures. A full range of standard prepregs is also available autoclave processing. MTM^®46 offers excellent hot/wet performance, making it the ideal candidate for the low cost primary and secondary structures in FAR23 aircraft. It is also suitable for secondary structures in civil aircraft and helicopters.

MVR^®444 is a single component epoxy resin matrix for the manufacture of aerospace quality composite components using infusion processes such as VARTM (Vacuum Assisted Resin Transfer Moulding), RTM (Resin Transfer Moulding) or RIFT (Resin Infusion under Flexible Tooling). MVR^®444 may be infused at temperatures as low as 70°C (158°F) and may be cured at temperatures between 90°C and 180°C (194°F and 356°F). It also exhibits excellent performance after hot/wet conditioning.