Innovative infusion method for out-of-autoclave and autoclave processes

Today, the reduction of manufacturing costs is a big challenge to the aircraft industry and the usage of prepreg materials is state of the art. It is known that the impregnation of dry fibre materials with a liquid resin can reduce the manufacturing costs. But for future applications of infusion processes for aircraft parts, it is essential to provide a good laminate quality and to reduce the scrap rate. Therefrom, a new infusion method for out-of-autoclave and autoclave- based processes will be investigated. A conventional vacuum infusion process uses a single-sided mould and a flexible vacuum bag to form a cavity for the composite part. The resin feed channels and other supplies distribute the resin over the composite part. The new method uses resin distribution channels beyond the vacuum bag and a pressure difference between these channels and the mould cavity. Therefore, the channels have no immediate contact to the resin and they are reusable for other parts. The channels will be pressurised with a pressure lower than the resin pressure. This enables the resin to flow primarily in this area. To stop the resin flow, pressure equalisation between resin and channels will be applied. This has the advantage that the channels will not leave any marks on the part surface. By this method, resin flow fronts can be manipulated and the risk of dry spots is reduced. This infusion process is combined with an automated mixing and dosing unit for a continuous processing of a two- component resin system. The mixing ratio and the pressure difference between the ambient and the resin pressure are automatically controlled. For autoclave applications, the resin pressure is up to 10 bars. To improve the viscosity, both components of the epoxy can be preheated to a temperature of 80°C and therefore the handling of resin systems like Hexcel RTM6-2 is permitted. The new approach will help to enhance the infusion of aircraft parts and it will also reduce the manufacturing costs of composite parts.