RTM-Light is the process of producing composite components within a vacuum-clamped two part (male/female) matched mould.
Compared with the traditional RTM process, RTM-light tooling is relatively lightweight and thus considerably lower cost. The process relies on atmospheric pressure as a mould closing force as opposed to the mechanical clamping methods and heavily reinforced mould structures used in RTM.
Unlike infusion processes that use a vacuum bag, the RTM-light process uses a semi rigid upper mould and so can still provide good definition of the moulded "B" surface and extra detail such as encapsulated inserts, cores or surface textures are readily mouldable. The mould is built with double seals – an outer vacuum seal and an inner resin seal. The flange area between the seals is evacuated to provide the main clamping force. This double seal also provides excellent security against vacuum leaks through the seals. Vacuum is applied to the mould cavity and the resin is introduced under low pressure (< 1 bar) into a peripheral feed channel running around the outside edge of the component. This peripheral injection strategy provides the most efficient route to fill the mould, with the minimum of reaction pressure against the clamping force.
The resin fills the mould cavity and is vented near the centre of the component. Any excess resin is contained within a catch-pot positioned at this point. The vacuum is drawn from the mould cavity via the catch-pot. The catch-pot prevents excess resin from being drawn into the vacuum pump. The primary mould, usually representing the "A" surface of the component, is built as a relatively stiff structure with a simple framework to prevent distortion. The upper mould is often a much lighter structure and consists of a 4-6mm laminate over the mould cavity and a reinforced and stiffened flange area. A simple frame can be incorporated to aid handling and to prevent distortion.
Due to the use of vacuum to provide a even clamping force, the RTM-light process can be successfully used to mould large structures using relatively simple and low-mass tooling.