Such methods use dry fiber composite preforms in order to produce components with geometric shapes that may be unwindable, non-unwindable or not completely unwindable. The dry fiber composite preform can be a woven fabric, a multi-axis interlaid scrim or a warp-thread reinforced unidirectional preform. The above-mentioned preforms are used in the production of components made of fiber-reinforced material. They represent an intermediate process step before infiltration by resin and curing occur.
Such a method is referred to as a so-called resin film infusion (RFI) method wherein dry carbon fibers, carbon fiber woven fabrics or carbon fiber interlaid scrim are placed in a curing device before a specified non-liquid quantity of resin film is applied to them from the outside. The curing tools equipped and evacuated in this way are subsequently cured in an autoclave or another pressure receptacle by exposure to temperature and pressure. The use of pressure receptacles and the associated complex tools that are necessary are however very expensive, rendering such methods complex also in regard to temperatures and pressures to be maintained. The scope of application of such methods is thus limited.
Furthermore, the use of dry preform components is described, for example, in German Published Patent Application No. 198 13 105, which describes a method for producing fiber composite components wherein the fibers and the matrix material are formed in a tool, forming a mold cavity, the tool including at least two parts, with the air situated in the mold cavity being able to escape. In this arrangement, a porous membrane is placed into the mold cavity, in front of the apertures, with the pores of said porous membranes being of such a size that air can be evacuated without hindrance while the matrix material is retained in the mold cavity.
The foregoing solution does not involve any application of pressure. However, it is associated with a disadvantage in that the size of components that can be produced with this method is limited, because the matrix material can be introduced into the fibers, i.e., into the preforms, only in a limited way, provided a central matrix feed bush has been provided, because the matrix has to flow along the preform plane, i.e., along the fibers. Due to the distance to be covered and the resistance put up by the material, this direction of flow creates the largest flow resistance to the matrix. Thus, impregnation along the length of material flow is limited. As an alternative, the matrix is put in place over an area. To this effect, resin reservoirs, situated on the component surface, are used, which require their own expensive resin supply device up to the preform, thus at every position posing the risk of a leakage (risk of rejects).
There is a further disadvantage in that this method can meet very exacting quality standards of the component to be produced only to a limited extent. This is because as a result of the potential resin passages through the vacuum foil and the membrane up to the preform surface, matrix material can penetrate through the membrane in many locations of the component, thus sealing off said membrane from above. In this case, air evacuation no longer functions and pores form within the laminate, because of the reaction during the curing process (e.g. as a result of trapped air, chemical separation, volatile components etc.). Such pores, which can negatively affect the quality of the component, cannot be eliminated.
Other conventional low-pressure methods, such as, for example, VARI (DLR) do without a membrane and two-part vacuum chambers. They avoid pore formation by process management of the vacuum and temperature outside the boiling range of the matrix material. In this way, no pores arise in the component. However, there is a disadvantage in that temperature and vacuum management must be very exactly adhered to at every position of the component, to avoid locally entering the boiling range of the matrix, with subsequent local pore formation. In the case of large components, such precise process management can only be realized with considerable difficulty and expense. This method has a further disadvantage in that as a result of permanent suction to maintain a vacuum, matrix material can be drawn from the component, which again can create pores. Furthermore, a resin trap or similar is necessary so as to prevent damage to the vacuum pump as a result of any matrix material issuing.
It is therefore an object of the present invention to provide a method for producing fiber-reinforced plastic components made of dry fiber composite preform by an injection method and a device for implementing the method, the method being suitable even for larger components, and allowing process management which is as simple as possible while at the same time making it possible to achieve good component quality.