Methods for the precise positioning of fiber semi-finished products and sandwich cores and for the production of fiber composite components

Abstract

A process that exhibits: Laying an auxiliary layer sequence (2) which has at least one suction film (21) onto a support surface (1t) of a laying aid (1); Applying at least one layer of fiber semi-finished product (3, 4) onto the applied auxiliary layer sequence (2); Placing a negative mold (5) onto the at least one layer of fiber semi-finished product (3, 4) placed on it, such that the at least one layer of fiber semi-finished product (3, 4) placed on it is arranged between the suction film (21) and the negative mold (5); Creating an evacuated state by evacuating an area between the suction film (21) and the negative mold (5) such that the at least one fiber semi-finished product layer (3, 4) is pressed against the negative mold (5) by the suction film (21), wherein the laying of at least one layer of fiber semi-finished products (3, 4) the application of at least one first layer of fiber semi-finished products (3) onto the applied auxiliary layer sequence (2); the placement of one or more sandwich cores (6) onto at least one first fiber semi-finished product layer (3); and comprising the laying of at least one second fiber semi-finished product layer (4) onto the at least one laid first fiber semi-finished product layer (3) and the laid sandwich core or sandwich cores (6).

Description

[0001] The invention relates to the production of fiber composite components. Load-bearing shell components are frequently used in lightweight constructions. Such shell components play an important role, for example, in aircraft construction. Furthermore, load-bearing shell components made of fiber composite materials are also used in rotor blades for wind turbines, rockets, boat hulls, and vehicle bodies.

[0002] A typical challenge in the design of such shell components is ensuring sufficient buckling resistance. Aluminum shell components are traditionally stiffened with stringers. Fiber-reinforced shell components often use sandwich structures with a lightweight, compression-resistant core. Both stringer stiffeners and sandwich structures are found in commercial and military aircraft.

[0003] Often, for example, in small aircraft construction, the production of such shell components is still carried out using the labor-intensive hand lay-up process. The high degree of manual labor involved in this process makes automation difficult and results in long cycle times. Furthermore, it often no longer meets modern requirements for process reliability and reproducibility. It is therefore primarily used for prototypes and small series.

[0004] In large aircraft construction, the production of shell components is usually carried out using prepregs in combination with autoclave processes. The handling and storage of the fiber semi-finished products, as well as the acquisition costs of the required tools and autoclaves, are crucial. As a result, this process is usually only used in large-scale production.

[0005] Resin infusion processes, which have been researched for several years, offer a compromise between labor-intensive manual / wet lamination and equipment-intensive prepreg technology. In these processes, the liquid synthetic resin is infused into a finished, dry, and vacuum-sealed layer structure made of reinforcing fibers and additives. Layers of peel ply, flow aid, and suction film are used as additives and are disposed of after demolding. Currently, there is potential for optimization of resin infusion, especially with dry layer structures.

[0006] When negative molds are used to produce shell components that have a concave curvature and / or steep and vertical surfaces, or other complex geometries, the precise insertion of the individual semi-finished fiber layers frequently presents problems. For example, the semi-finished fiber layers or core reinforcements can slip, or they can fall from steep surfaces into deeper areas of the negative mold. These problems are particularly pronounced when using dry semi-finished fiber layers. Often, attempts are made to counteract these problems by using chemical or mechanical fixation aids.

[0007] Preforms that are mechanically or chemically bonded and comprise one or more fiber layers are also referred to as textile preforms. These are semi-finished fiber products that can be sewn together, braided, or embroidered onto a carrier material. However, the sewing and embroidery threads remaining in the component can impair fiber and component quality. Furthermore, the production of such preforms involves additional work steps and a significant amount of time, which is only justifiable for larger series.

[0008] Chemical fixation aids can be, for example, adhesives or thick resin deposits that are introduced into the component in more or less precisely defined quantities during the laying process and remain there. This type of fixation aid is usually used for prototypes and small series.

[0009] The influence of these chemical fixing aids on component quality has not been fully clarified and must be demonstrated separately, which is particularly important for applications relevant to approval, such as aircraft construction.

[0010] In addition to attaching fiber layers to each other, these fixing aids are also used to attach sandwich cores to the fiber layers. Sandwich cores can be sewn into fiber layers, braided around fiber layers, or glued to reinforcement layers using a spray adhesive. The problems already discussed can also arise in these cases.

[0011] DE 103 31 358 A1 discloses a method for the automated production of an integral structural component made of fiber composite materials. This method uses a carrier with cavities and a curved upper side with several recesses. A film placed on the upper side is sucked onto the carrier through the recesses, so that it curves slightly into the recesses in the area of ​​the recesses without touching the carrier there. By unwinding the film, the recesses are exposed one by one. As soon as one of the recesses is exposed, a vacuum skin is rolled over it so that it adheres to the carrier in the area of ​​the recesses as well, thus precisely following the contour of the recess. A stringer profile is then inserted onto the vacuum skin in the area of ​​each recess. Several further skin layers are then applied on top of this.A sealing compound is applied circumferentially to the vacuum skin, adjacent to the skin layers. A structural shell is placed on top of this arrangement with its concave side, so that the sealing compound seals the gap between the vacuum skin and the structural shell. The cavity between the vacuum skin and the structural shell is then evacuated and subsequently filled using an injection process.

[0012] DE 10 2008 023 629 A1 concerns an integral hollow component made of fiber-reinforced plastic in sandwich construction.

[0013] The object of the invention is to provide easy-to-use methods for the precise positioning of fiber semi-finished products and optionally also of sandwich cores, as well as for the production of a fiber composite component. These objects are achieved by methods according to patent claims 1 and 10, respectively. Refinements and developments of the invention are the subject of subclaims.

[0014] A first aspect relates to a method in which an auxiliary layer sequence comprising at least one suction film is placed on a support surface of a laying aid. At least one semi-finished fiber layer is placed on the placed auxiliary layer sequence. A negative mold is placed on the at least one placed semi-finished fiber layer, so that the at least one placed semi-finished fiber layer is arranged between the suction film and the negative mold. By evacuating an area between the suction film and the negative mold, an evacuated state is created, so that the at least one semi-finished fiber layer is pressed against the negative mold by the suction film.The application of the at least one semi-finished fiber layer comprises the application of at least one first semi-finished fiber layer onto the applied auxiliary layer sequence, the application of one or more sandwich cores onto the at least one first semi-finished fiber layer, and the application of at least one second semi-finished fiber layer onto the at least one applied first semi-finished fiber layer and the applied sandwich core or the applied sandwich cores.

[0015] A second aspect relates to a method for producing a fiber composite component. For this purpose, a method according to the first aspect is carried out, and the at least one semi-finished fiber layer is embedded in a resin by means of a resin infusion process. The resin is subsequently cured.

[0016] The invention uses a laying aid to facilitate the deposition, in particular of dry but also non-dry semi-finished fiber layers and other components of a fiber composite component to be manufactured, and to fix them relative to one another. The use of the laying aid prevents the dry fiber layers or sandwich cores from slipping. This laying aid allows both the deposition of individual semi-finished fiber layers and the precise positioning of sandwich cores as core reinforcements in sandwich structures. When using this manufacturing method, the use of mechanical or chemical fixing aids can be dispensed with. The fixing can be carried out, among other things, to embed the semi-finished fiber layer(s) and, where provided, the sandwich cores in a resin and then cure the resin. The known resin infusion process is particularly suitable for this purpose.

[0017] The invention is explained below with reference to exemplary embodiments in the accompanying figures. In the figures, identical reference numerals designate identical features. Fig. 1 illustrates part of a method for positioning at least one semi-finished fiber layer on a laying aid; Fig. 2 illustrates part of a method for positioning at least two semi-finished fiber layers and at least one sandwich core between the semi-finished fiber layers; and Fig. 3 shows a vertical section through a stack of layers placed on a support surface of a laying aid having a convex section.

[0018] Fig. 1 shows a laying aid 1 with a support surface 1t that replicates the contour of the inside of a shell component to be manufactured, for example a wing shell of an aircraft. Individual layers of an auxiliary layer sequence 2 and subsequently one or more semi-finished fiber layers 3, 4 are placed one after the other on the support surface 1t. The individual layers of the auxiliary layer sequence 2 allow for later resin infusion. The layers of the auxiliary layer sequence 2, which can include, for example, a layer of a suction film 21, an optional layer of a flow aid 22, an optional layer of a perforated film 23 and a likewise optional layer of a peel ply 24, are placed on the laying aid 1 in the stated order. One or more semi-finished fiber layers 3, 4 are then placed on the auxiliary layer sequence 2. Any additional components for the resin infusion process (e.g. sprue, hoses, possible sensors) are positioned at appropriate locations.Once the semi-finished fiber layers 3, 4 have been completely placed on the auxiliary layer sequence 2 and the other components have been positioned, a negative mold 5 corresponding to the shell component to be produced is placed on the stack, which comprises the laying aid 1, the auxiliary layer sequence 2 placed on the laying aid 1, and the semi-finished fiber layer(s) 3, 4 placed on the auxiliary layer sequence 2, so that the elements placed on the support surface 1t, in particular the semi-finished fiber layer(s) 3, 4, are located between the support surface 1t and the negative mold 5. The suction film, which forms the layer of the auxiliary layer sequence 2 closest to the laying aid 1, is hermetically sealed to the negative mold 5.

[0019] Since the shell component to be produced is to have a sandwich structure with one or more sandwich cores 6 (for example foam cores), as in Fig. 2 illustrates, the sandwich core 6 or the sandwich cores 6 are inserted between two semi-finished fiber layers 3 and 4. This means that first, one or more semi-finished fiber layers 3 are placed on the auxiliary layer sequence 2 located on the laying aid 1. The sandwich core(s) 6 are placed thereon, and one or more semi-finished fiber layers 4 are placed over the placed sandwich core(s) 6. The semi-finished fiber layers 3, 4 can, for example, be dry semi-finished fiber layers.

[0020] To ensure that the sandwich core(s) 6 remain in the desired position on the laying aid 1 and do not slip, the laying aid 1 can optionally have recesses 10 into which the sandwich core(s) 6 are inserted. The auxiliary layer sequence 2 and the one or more semi-finished fiber layer(s) 3 are located between the sandwich core(s) 6 and the recesses 10.

[0021] Fig. 3 shows for the example according to Fig. 2 a vertical section through the arrangement with the individual layers of the auxiliary layer sequence 2 lying successively on the support surface 1t, the semi-finished fiber layers 3 and 4, the sandwich cores 6 located between the semi-finished fiber layers 3 and 4, and the negative mold 5.

[0022] By hermetically sealing the suction film 21 against the negative mold 5, the area between the suction film 21 and the negative mold 5 can be evacuated, for example via one or more inserted hoses. As a result, the ambient pressure presses the suction film 21 against the negative mold 5. This has the effect that the remaining layers of the auxiliary layer sequence 2 (i.e., layers 22, 23, 24 - if present - with the exception of the suction film 21), the semi-finished fiber layer(s) 3, 4, the sandwich core(s) 6, and the other components (if present) are pressed against the negative mold 5 by the suction film 21, thereby being fixed to the negative mold 5 and no longer being able to slip.

[0023] In this evacuated state, the negative mold 5, together with the suction film 21 and the remaining layers of the auxiliary layer sequence 2 (i.e., their layers 22, 23, 24 - if present - with the exception of the suction film 21), the semi-finished fiber layer(s) 3, 4, the sandwich core(s) 6, and the other components (if present), can be lifted off the laying aid 1 and rotated into any position if required. Lifting off is equivalent to removing the laying aid 1 from the suction film 21. A resin can then be infused into the area between the suction film 21 and the negative mold 5, or the assembly can be stored in the evacuated state and infused with a resin at a later time.The infusion process is carried out in such a way that the semi-finished fiber layer(s) 3, 4 and the sandwich core(s) 6 are embedded in the resin. After the resin subsequently cures, they combine with the resin to form the shell component to be produced, thus creating a fiber composite component. After curing, the evacuation state can be released, the suction film 21 can be removed from the negative mold 5, and the shell component can be removed from the negative mold 5.

[0024] By using the laying aid 1, precise positioning of the semi-finished fiber layer(s) 3, 4, the sandwich core 6 or the sandwich cores 6, and the other components (if present) can be achieved. This applies in particular if the support surface 1t of the laying aid 1 has a convex section 1k and the laying aid 1 is oriented during the placement of the aforementioned parts and until the evacuation state is reached such that the convex section 1k is located on the upper side of the laying aid 1, counter to the direction of gravity G.

[0025] Due to its function purely as a positioning aid for the (e.g. dry) semi-finished fiber products 3, 4, the laying aid 1 does not need to have any particular temperature or media resistance.

[0026] Since the manufacturing process eliminates the need for mechanical and chemical fixation aids, adverse effects on component quality are avoided. This eliminates the need to introduce sewing or embroidery threads or foreign substances, such as those found in spray adhesives, into the fiber composite. However, such fixation aids can still be used optionally.

[0027] In addition, additional work steps, such as the separate production of preforms, or additional material, such as spray adhesive, can be dispensed with.

[0028] In the evacuated state, the component can be transported or theoretically stored for any length of time and then infused at the required time.

[0029] The method is particularly suitable for the automated production of fiber composite components in conjunction with a cutting plotter that cuts individual or all layers 21, 22, 23, 24, 3, 4 before placing them on the laying aid 1 and / or a laying robot that places individual or several layers 21, 22, 23, 24, 3, 4 on the laying aid 1.

Claims

[1] Method comprising: Placing an auxiliary layer sequence (2), which has at least one suction film (21), on a support surface (1t) of a laying aid (1); Placing at least one semi-finished fiber layer (3, 4) on the applied auxiliary layer sequence (2); Placing a negative mold (5) on the at least one placed semi-finished fiber layer (3, 4) so ​​that the at least one placed semi-finished fiber layer (3, 4) is arranged between the suction film (21) and the negative mold (5); Creating an evacuated state by evacuating an area between the suction film (21) and the negative mold (5) such that the at least one semi-finished fiber layer (3, 4) is pressed against the negative mold (5) by the suction film (21), wherein the laying of at least one semi-finished fiber layer (3, 4) placing at least a first semi-finished fiber layer (3) on the applied auxiliary layer sequence (2); placing one or more sandwich cores (6) on the at least one first semi-finished fiber layer (3); and the laying of at least one second semi-finished fiber layer (4) onto the at least one laid first semi-finished fiber layer (3) and the laid sandwich core or the laid sandwich cores (6). [2] Method according to claim 1, in which the laying aid (1) has one or more recesses (10) on the support surface (1t); and the sandwich core or the sandwich cores (6) are inserted into the recess(es) (10) when placed and are thereby fixed. [3] Method according to one of the preceding claims, in which no chemical fixing aid is used when applying the at least one semi-finished fibre layer (3, 4). [4] Method according to one of the preceding claims, wherein the application of the auxiliary layer sequence (2) comprises the application of the auxiliary layer sequence (2) onto the support surface (1t) having a convex section (1k). [5] Method according to claim 4, wherein the laying aid (1) is aligned during the laying of the auxiliary layer sequence (2), the at least one semi-finished fiber layer (3, 4) and the negative mold (5) such that the convex section (1k) is located on the upper side of the laying aid (1) opposite to the direction of the force of gravity G. [6] Method according to one of the preceding claims, in which the suction film (21) is sealed against the negative mold (5) before evacuation. [7] Method according to one of the preceding claims, in which all semi-finished fibre layers (3, 4) are applied in a dry state. [8] Method according to one of the preceding claims, wherein the evacuation takes place in a state in which all semi-finished fiber layers (3, 4) are in a dry state. [9] Method according to one of the preceding claims, in which the laying aid (1) is removed from the suction film (21) in the evacuated state. [10] A method for producing a fiber composite component, the method comprising: Carrying out a method according to one of the preceding claims; Embedding the at least one semi-finished fiber layer (3, 4) in a resin by means of a resin infusion process; and Curing of the resin after embedding.

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