Method for producing a reinforced fiber semi-finished product and reinforced fiber semi-finished product

Abstract

Method for producing a reinforced fiber semi-finished product, comprising the steps - Providing a dry fiber semi-finished product, - Arranging at least one reinforcement layer on at least one surface of the dry fiber semi-finished product, - joint impregnation of the at least one reinforcement layer and the dry fiber semi-finished product to produce the reinforced fiber semi-finished product, characterized in that the dry fiber semi-finished product is completely and the at least one reinforcement layer is partially impregnated with the matrix.

Description

[0001] The invention relates to a method for producing a reinforced semi-finished fiber product according to the preamble of patent claim 1, as well as the correspondingly reinforced semi-finished fiber product.

[0002] For the production of fiber-reinforced components, impregnated fiber semi-finished products, such as prepregs or sheet molding compounds (SMC), are used. These typically comprise a fiber semi-finished product impregnated with a matrix. In very simplified terms, the impregnated fiber semi-finished product is initially produced in sheet form and cut to the desired length. In a subsequent processing step, the impregnated fiber semi-finished product is inserted into a forming tool, pressed into the desired shape, and cured into a fiber composite component. This component can then be post-processed if necessary.

[0003] Until the impregnated semi-finished fiber product is pressed and cured, its matrix is ​​in a soft, uncured state, making handling difficult due to the resulting flexibility and resulting in low dimensional stability. There is therefore a risk that individual fiber bundles of the semi-finished fiber product will be displaced from their predetermined position during transfer, transport, or a closing movement of a pressing tool. This risk is particularly high when unidirectional semi-finished fiber products consisting of a number of fiber bundles (so-called fiber rovings) are used as semi-finished fiber products, as the essentially parallel fiber bundle orientation results in particularly low slip resistance, especially when the semi-finished fiber product is subjected to a shear force perpendicular to its fiber orientation.In this case, the individual fiber bundles can be shifted relative to each other due to the low sliding strength, which means that a component produced from this has local weak points and must be sorted out as scrap.

[0004] But this risk also exists in other arrangements with multi-directional semi-finished fiber products, such as mats, non-crimp fabrics, woven fabrics or knitted fabrics, despite higher sliding stiffness.

[0005] From document DE 10 2011 005 323 A1, a method is known for producing a tensile member coated with a polymer layer, comprising the following steps: producing at least one tensile member by impregnating at least one fiber structure containing carbon fibers with at least one polymer precursor, pultruding the impregnated fiber structure, and coating at least some of the at least one tensile member produced in this step with a layer of a polymer by extrusion. The fiber structure used can comprise at least two fiber layers and / or fiber regions, which preferably differ with respect to the type of fibers contained therein.

[0006] From document EP 1 342 544 A1 a method is known for producing a preform comprising a plurality of layers of a reinforcing material, the method comprising the following steps: providing individual layers of a fibrous reinforcing material, providing a reinforcing resin material, providing means for connecting the layers, the method comprising the single step of connecting the individual, not yet connected, layers of the reinforcing material to one another by bringing the not yet connected layers of the reinforcing material into contact with one another and, at the same time, at least partially impregnating the individual layers of the reinforcing material with the resin material to form the molding material, thereby avoiding the need for an additional binder for connecting the individual reinforcing layers prior to impregnation.

[0007] From the document DE 10 2006 002 198 A1 a method is known for producing a fiber composite component with at least two adjacent first and second sub-elements, each with a fiber structure and matrix systems embedding the fiber structure, wherein the first sub-element is consolidated while leaving a transition region provided for connection to the second sub-element with a fiber structure unwetted by the matrix system and wherein the second sub-element is subsequently consolidated after the matrix system of the second sub-element has penetrated into the transition region of the first sub-element.

[0008] From the document EP 1 321 282 A1 a prepreg is known with a web-shaped fabric of filaments and with a resin for impregnation, in which the fabric is impregnated over the fabric thickness in a first thickness range and is not impregnated or is impregnated to a much lesser extent in a second thickness range and the first and second thickness ranges each extend over the entire fabric width, so that the filaments in the second thickness range are permeable to air transversely to the longitudinal extent of the prepreg.

[0009] The object of the invention is therefore to provide a manufacturing method for a fiber semi-finished product which at least reduces the disadvantages described and enables stable and, as far as possible, displacement-proof processing.

[0010] The object is achieved by means of a method according to patent claim 1 and a reinforced fiber semi-finished product according to patent claim 11. Advantageous embodiments and further developments emerge from the respective dependent patent claims.

[0011] Accordingly, a method for producing a reinforced fiber semi-finished product is disclosed, comprising the steps - Providing a dry semi-finished fiber product, - Arranging at least one reinforcement layer on at least one surface of the dry semi-finished fibre product, - joint impregnation of the at least one reinforcement layer and the dry semi-finished fiber product to produce the reinforced semi-finished fiber product, wherein the dry semi-finished fiber product is completely impregnated with the matrix and the at least one reinforcement layer is partially impregnated with the matrix.

[0012] A reinforcement layer is applied to one or more surfaces of the dry, not yet matrix-impregnated, semi-finished fiber product. This can be done, for example, by simply laying it on top, creating a multi-layer stack.

[0013] The joint impregnation step preferably comprises a superficial application and pressing of the matrix into the at least one reinforcement layer and / or the dry semi-finished fiber product. It is therefore possible to apply the matrix to one or more surfaces of the stack structure, i.e., one of the reinforcement layers and / or the semi-finished fiber product, and to work it into the individual layers starting from the corresponding surface. The penetration of the matrix in the depth direction of the stack structure can occur in particular by pressing in, i.e., by applying pressure, and can lead to particularly good penetration of as many layers of the stack structure as possible. For this purpose, it is possible, for example, to apply pressure by rolling.

[0014] Press-fitting also makes it possible to create a particularly resilient connection between the at least one reinforcement layer and the semi-finished fiber product using the matrix. Additional adhesive or other bonding agents for connecting the reinforcement layers to the matrix or the semi-finished fiber product are therefore unnecessary.

[0015] Each of the reinforcement layers can thus act as a stabilization of the semi-finished fiber product that has been impregnated in the meantime, so that its sliding resistance is significantly increased and undesired displacement of the impregnated semi-finished fiber product or individual components, in particular the fiber bundles, during transport, but also during subsequent compression molding, can be avoided.

[0016] For example, a first reinforcement layer is arranged on a first surface and a second reinforcement layer on a second surface of the still-dry semi-finished fiber product. Typically, the dry semi-finished fiber product has a substantially flat, plate-like spatial shape, defining two large surfaces: an upper surface (first surface) and a lower surface (second surface) opposite the upper surface, to which reinforcement layers can be applied.

[0017] The joint impregnation step comprises fully impregnating the dry semi-finished fiber product and partially impregnating the reinforcement layer with the matrix. Partial impregnation can occur by applying the matrix only to and penetrating the sections to be impregnated. Alternatively, however, the matrix can be applied to specific areas and flow from there, allowing the matrix to escape again in these areas. In this case, no, or at least no significant, impregnation of these areas is formed. This is particularly possible in the depth or thickness direction of the reinforcement layer, so that a matrix is ​​first applied to an outer surface of the reinforcement layer and then transported further in the thickness direction, thereby impregnating the semi-finished fiber product arranged there.At the same time, the matrix is ​​essentially removed from the surface and / or in the thickness direction from the reinforcement layer.

[0018] The reinforcement layer also makes it possible to create a visible structure, allowing a coating of the semi-finished fiber with a defined visual appearance and / or support structure to be applied and impregnated with the matrix to fix it. This eliminates the need for subsequent bonding of films with the corresponding appearance.

[0019] For example, the impregnation step can take place in a sheet molding compound (SMC) manufacturing process or in a prepreg manufacturing process. A prepreg is a semi-finished product consisting of continuous fibers impregnated with a matrix of thermosetting or thermoplastic material, with the matrix being in an uncured state. SMC refers in particular to fiber semi-finished products made of shorter fibers, in contrast to continuous fibers, typically with a length of approximately 25 to 50 mm, whereby a thermosetting matrix can be used in particular for SMC. Both manufacturing processes are well known per se, so a detailed description of the procedures will be omitted.

[0020] Furthermore, the at least one reinforcement layer can comprise metal fibers, glass fibers, carbon fibers, plastic fibers, natural fibers, cellulose fibers, or a natural fiber layer, a nonwoven layer, a cellulose layer, or a plastic film. Depending on the intended use, this can provide additional functionality in addition to the intended anti-slip stabilization of the semi-finished fiber product.

[0021] If, for example, metal fibers are applied as a reinforcement layer, it is possible to provide electromagnetic shielding for the resulting component. In addition, a magnetizable surface can be created in this way, which allows, for example, the correspondingly designed semi-finished product or the resulting component to be reliably secured using magnetic forces or even transported (at least over short distances), for example, using a robot arm. Complex gripping tools could be eliminated in this case. The use of glass or plastic fibers, on the other hand, can provide additional electrical insulation.

[0022] According to further embodiments, the dry semi-finished fiber product may comprise a unidirectional fiber layer of parallel arranged fiber bundles or a multidirectional fiber layer, in particular a mat, a woven fabric, a scrim, a knitted fabric or a knitted fabric.

[0023] The reinforcement layers are preferably thin, meaning they are smaller than the dry or impregnated fiber semi-finished product. For example, the cellulose layer is formed as a paper layer and the plastic layer as a film.

[0024] Furthermore, the reinforcement layer can comprise a textile fabric, in particular a mat, a woven fabric, a scrim, a knitted fabric, or a knitted fabric. A film, in particular a plastic film or a cellulose layer, has already been described.

[0025] Furthermore, a reinforced semi-finished fiber product is provided, comprising a semi-finished fiber product and at least one reinforcement layer arranged on an outer surface of the impregnated semi-finished fiber product. The semi-finished fiber product is produced by the method according to the invention.

[0026] For example, the reinforced semi-finished fiber product can be manufactured using a process according to the given description. The resulting reinforced semi-finished fiber product or matrix is ​​not yet cured. In an optional subsequent step, it can be pressed into a three-dimensional shape and cured to create a fiber composite component.

[0027] The invention is explained in more detail below with reference to the figure using an exemplary embodiment.

[0028] The figure shows an exemplary representation of an apparatus for carrying out a method for producing a reinforced semi-finished fiber product 20. First, a dry semi-finished fiber product 21, i.e., one not yet impregnated with a matrix, is provided. For this purpose, for example, a number of fiber bundles (fiber rovings) 11 are fed from a creel 12 to a sheet molding compound (SMC for short) system 17. In this system, the dry semi-finished fiber product 21 is produced from the fiber bundles 11, for example, as a unidirectional fiber layer by arranging the fiber bundles 11 in parallel. Since the functioning of an SMC system 17 is known, a detailed explanation will be omitted.

[0029] In addition, a first 13 and a second reinforcement layer 14 are fed from a separate first 15 and second roll 16, respectively. The first reinforcement layer 13 is arranged on a first surface 18, and the second reinforcement layer 14 is arranged on a second surface 19 of the dry semi-finished fiber product 21. The arrangement comprises, in particular, a flat application of the two reinforcement layers 13, 14. Subsequently, the two reinforcement layers 13, 14 are jointly impregnated (not shown) with the dry semi-finished fiber product 21 to produce the reinforced semi-finished fiber product 20.

[0030] Thus, a reinforced semi-finished fiber product 20 is created, which comprises a semi-finished fiber product impregnated with a matrix and the two reinforcement layers 13, 14 arranged on the two outer surfaces 18, 19 of the temporarily impregnated semi-finished fiber product, wherein the reinforcement layers 13, 14 are connected to the impregnated semi-finished fiber product by means of the matrix.

Claims

[1] Method for producing a reinforced fiber semi-finished product, comprising the steps - Providing a dry semi-finished fiber product, - Arranging at least one reinforcement layer on at least one surface of the dry semi-finished fibre product, - joint impregnation of at least one reinforcement layer and the dry semi-finished fiber product to produce the reinforced semi-finished fiber product, characterized by that the dry semi-finished fiber product is completely impregnated with the matrix and at least one reinforcement layer is partially impregnated with the matrix. [2] Method according to claim 1, characterized by that the partial impregnation is carried out in such a way that the matrix is ​​only applied in the sections to be impregnated and penetrates them. [3] Method according to claim 1, characterized bythat the partial impregnation is carried out in such a way that the matrix is ​​applied in certain areas and flows from there, so that the matrix escapes again in these areas. [4] Method according to claim 3, characterized by that the matrix continues to flow in the direction of a depth or thickness direction of the reinforcement layer, so that first a matrix is ​​applied to an outer surface of the reinforcement layer and then transported further in the thickness direction, whereby the semi-finished fiber product arranged there is impregnated and at the same time the matrix is ​​substantially removed from the surface and / or in the thickness direction from the reinforcement layer. [5] Method according to at least one of the preceding claims, wherein the step of joint impregnation comprises a superficial application and pressing of matrix into the at least one reinforcement layer and / or the dry semi-finished fiber product. [6] Method according to one of the preceding claims, wherein a first reinforcement layer is arranged on a first surface and a second reinforcement layer is arranged on a second surface of the dry semi-finished fiber product. [7] A method according to any one of the preceding claims, wherein the impregnating step is carried out in a sheet molding compound (SMC) manufacturing process or in a prepreg manufacturing process. [8] Method according to one of the preceding claims, wherein the at least one reinforcing layer comprises metal fibers, glass fibers, carbon fibers, plastic fibers, natural fibers, cellulose fibers and / or a natural fiber layer, a nonwoven layer, a cellulose layer, a plastic film. [9] Method according to one of the preceding claims, wherein the dry semi-finished fiber product comprises a unidirectional fiber layer of parallel arranged fiber bundles or a multidirectional fiber layer, in particular a mat, a woven fabric, a scrim, a knitted fabric or a knitted fabric. [10] Method according to one of the preceding claims, wherein the reinforcing layer comprises a textile fabric, in particular a mat, a woven fabric, a scrim, a knitted fabric or a knitted fabric. [11] Reinforced semi-finished fiber product comprising a semi-finished fiber product and at least one reinforcement layer arranged on an outer surface of the semi-finished fiber product, characterized by that the semi-finished fiber product is produced by a method according to one of the preceding claims.

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