The invention relates to methods of impregnating a fiber preform with an impregnation composition, to methods of densifying such impregnated fiber preforms, and to associated devices.
The “poly-flex” method is known in which a fiber preform is draped on tooling having a surface with the profile desired for the final product. The preform is then covered by a deformable impermeable membrane and resin is injected between the membrane and the preform. On the other side of the membrane, isostatic pressure is exerted against the membrane by a fluid that serves to deform the face of the membrane situated facing the preform. The fluid forces the resin between the fibers and maintains pressure during a stage of curing the resin. A drawback of the “poly-flex” method is that it enables the profile and the definition of the surface of the part that is to be fabricated to be controlled on one side only of the part. The surface of the resulting part that is situated beside the membrane may be rougher and its profile is not always under control. Consequently, the “poly-flex” method can be found to be not entirely satisfactory for fabricating turbine engine blades. The “poly-flex” method is described in U.S. Pat. No. 7,866,969 B2.
Also known is the resin transfer molding (RTM) method in which the tooling comprises two half-shells that confine a cavity when they are placed one on the other. The fiber preform is inserted in the cavity between the two half-shells and is then injected with the resin. The resin is polymerized while keeping the two half-shells closed. A drawback of that method is associated with the resin shrinking during cross-linking, which can lead to a loss of pressure inside the cavity and to micropores forming that can affect the mechanical strength of the resulting part. Furthermore, in the resin transfer molding (RTM) method, it is possible for the impregnation of the preform by the resin to be incomplete. Specifically, in that method, the resin is injected via distinct points and it needs to pass through the fiber preform in order to infiltrate the entire preform, which can lead to certain zones of the preform not being impregnated.
Also known is U.S. Pat. No. 5,382,150, which describes a method in which a stack of pre-impregnated plies is consolidated between two half-shells. The method described in U.S. Pat. No. 5,382,150 also includes a curing step in an autoclave, which can be expensive.
Also known is US 2011/0195230, which describes curing a laminate.
There thus exists a need for novel methods for controlling the profile and the definition of two opposite faces of an impregnated fiber preform.
There also exists a need for novel methods for controlling the profile and the definition of two opposite faces of a composite material part comprising a fiber preform densified by a matrix.
There also exists a need to have novel methods enabling parts to be made out of composite material and presenting little microporosity.
There also exists a need to have novel devices specially adapted to performing such methods.