Manufacturing process for a stiffened thin-walled fiber composite material product, Stiffened thin-walled fiber composite material product and use of such a product

Abstract

Manufacturing process for a stiffened thin-walled fiber composite material product (3) comprising the following steps: Arranging a reinforcing element in a mold (7), wherein the reinforcing element has a base layer (5) and reinforcing yarns (1) arranged on one side of the base layer; Dividing the mold (7) by means of an elastic membrane (6) into a product chamber with the reinforcing element and into a pressure chamber, wherein the side of the base layer (5) with the reinforcing yarns (1) is arranged in the direction of the elastic membrane (6); Arranging a soft material (8) in the pressure chamber so that the soft material (8) is pressed into the spaces (4) between the reinforcing yarns (1); Creating a negative pressure in the product chamber using a vacuum pump; Filling the product chamber with a matrix until the matrix presses the elastic membrane (6) against the soft material (8); Applying pressure via the elastic membrane (6) to the matrix (8) between the reinforcing yarns (1), such that the elastic membrane (6) is pressed deeper than the soft material (8) between the reinforcing yarns (1) and the reinforcing element is impregnated with the matrix; and Curing of the matrix to produce the stiffened thin-walled fiber composite material product (3).

Description

Technical field

[0001] The invention relates to a manufacturing process for a stiffened, thin-walled fiber composite material product, to a fiber composite material product manufactured in this way, and to the use of such a product. The composite material product is, in particular, a stiffened, thin-walled natural fiber composite material product. State of the art

[0002] WO 2012 / 076 308 A1 discloses a two-layer composite material consisting of a base layer and reinforcing yarns arranged above it. At least one, preferably both, of these layers is or are made of a natural fiber, such as hemp. While a first side of the base layer represents a flat surface, the second side of the base layer, together with the reinforcing yarns arranged on the base layer, forms a three-dimensional surface with height differences between the exposed areas of the base layer and the areas containing the reinforcing yarns. Theoretically, it would suffice to restrict the filler matrix, e.g., a polymer, only to the volume of the base layer and the reinforcing yarns, so that the surface of the composite material product follows the topology of the reinforcing yarns and the spaces between them.The steep flanks and / or the small gaps between two reinforcing yarns make such material-saving matrix filling difficult, especially for industrial-scale production. One proposed manufacturing method involves placing the base layer and the reinforcing yarns arranged above it, flat side down, into a mold. The uneven side is covered with an elastic membrane, which is then pressurized. This reduces the thickness of the matrix between the mold and the membrane, between the reinforcing yarns—a process commonly known as vacuum forming or vacuum injection molding. However, the problem is that the elastic membrane does not effectively limit the amount of matrix, and this method still results in more matrix being used in the composite product than necessary. This leads to an unnecessarily high weight for the composite product.Furthermore, the use of elastic membranes is not suitable for industrial production with high volumes.

[0003] WO 2005 / 000 566 A1 discloses a manufacturing process for conventional composite materials with flat surfaces. A reinforcing element is placed in a base mold and covered with a lid mold. An elastic membrane seals the base mold containing the reinforcing element from the lid mold. The base mold has a matrix inlet for impregnating the reinforcing element and a vacuum outlet for improved and faster impregnation. The lid mold allows a control fluid to be introduced into the pressure chamber between the elastic membrane and the lid mold, thus controlling the pressure on the elastic membrane for impregnating the reinforcing element. The thickness of the composite material product can be controlled by the pressure in the pressure chamber. By varying the pressure along the elastic membrane, composite material products with continuously variable thicknesses can be produced.Additionally, an embodiment with an additional soft foam in the pressure chamber is disclosed to minimize the amount of pressure fluid required. However, the method described in this document is designed for flat surfaces or surfaces of composite material products that change thickness only slowly and does not allow for the material-saving production of the two-layer composite material products with their complex surface structures described above.

[0004] DE 691 09 255 T2 discloses a device and a method for resin injection molding of composite objects with complex configurations that have a high fiber-to-resin ratio.

[0005] US 2002 / 0 146 529 A1 Method and apparatus for forming composite parts by injecting liquid resin by creating temporary resin distribution channels on the surface of a preform to assist the distribution of the resin during injection. Description of the invention

[0006] The object of the invention is to find a manufacturing process that avoids the aforementioned problems of the prior art. In particular, the object of the invention is to find an industrial manufacturing process that allows for the most material-efficient use of the matrix for composite materials with complex surface structures and reduces the overall weight of the composite material.

[0007] This problem is solved by a manufacturing process for a stiffened thin-walled fiber composite material product according to claim 1, a stiffened thin-walled fiber composite material product according to claim 22, and the use of a stiffened thin-walled fiber composite material product according to claim 23.

[0008] Specific embodiments of the invention are the subject of further patent claims.

[0009] This is achieved through the clever interplay of the elastic membrane and the soft material with the surface structure of the reinforcing element during matrix injection and impregnation. Despite using the pressure-vacuum matrix injection process employed in industrial manufacturing, the soft material, by extending into the spaces between the reinforcing yarns, limits the amount of matrix injected into the product chamber. This allows the amount of matrix used to be controlled to a level that does not completely cover the reinforcing yarns. Furthermore, this is possible even at high injection speeds. The use of a soft material also minimizes changes to the shape and position of the reinforcing yarns, resulting in good stiffness in the manufactured composite product.The elastic membrane is so flexible that, under the pressure of the pressure chamber, it forces the matrix material, effectively confined by the soft material, from the spaces between the base layer, reinforcing yarns, and soft material into the reinforcing element (impregnation). This results in a composite material whose surface follows the topology of the reinforcing yarns and the base layer, minimizing the amount of matrix in the spaces between the reinforcing yarns. This process is particularly suitable for reinforcing yarns made of natural fibers, as these are very compact and compressible to a low degree, thus exhibiting minimal deformation under the pressure of the soft material.

[0010] A particularly advantageous feature is the arrangement of channels in the soft material, which are designed to distribute the matrix quickly and homogeneously throughout the product chamber while the matrix presses the elastic membrane against the soft material. This is especially advantageous for the present invention because the soft material pressing against the reinforcing yarns acts as a barrier to the matrix, thus slowing the distribution of the matrix from space to space. Brief description of the characters

[0011] The invention is explained in more detail with reference to the accompanying figures, which show Fig. 1 an embodiment of the reinforcing yarns; Fig. 2 an embodiment of a thin-walled fiber composite material product; Fig. 3 an embodiment of a device for the production of a stiffened thin-walled fiber composite material product; Fig. 4 a further embodiment of a device for producing a stiffened thin-walled fiber composite material product; and Fig. 5 an embodiment of a method for producing a stiffened thin-walled natural fiber composite material product. Ways to implement the invention

[0012] The invention relates to a manufacturing method and a device for producing a stiffened, thin-walled fiber composite material product (hereinafter referred to as composite material product) and a composite material product produced in this way. The composite material product is preferably a fiber composite material and comprises a reinforcing element and a matrix, wherein the matrix and the reinforcing element are connected to the matrix by positive locking.

[0013] The reinforcing element has a base layer. The base layer is preferably a flat layer. The base layer is preferably flexible. The base layer can be a fiber product or another type of material, such as a continuous layer or porous materials. Fiber products include both artificially produced fiber products, such as mats, non-woven fabrics, woven fabrics, etc., and natural fiber products, such as wood. Fibers can include both artificial fibers, such as glass, carbon, ceramic, aramid, boron, basalt, steel, and nylon fibers, and natural fibers, such as flax, hemp, jute, ramie, kenaf, sisal, henequen, bamboo, silk, or cotton. Different fiber types can also be mixed. Wood veneers can also be used as a base layer. Other materials can include metals, such as aluminum sheets, or plastics.The invention does not limit the design of the base layer, and other designs of the base layer not mentioned here are also possible.

[0014] The reinforcing element comprises a multitude of reinforcing yarns. A yarn is a linear textile structure made from one or more fibers. The reinforcing yarns are arranged on one side of the base layer. The reinforcing yarns can be either applied to the base layer or integrated into it. In one embodiment, the reinforcing yarns are attached to the base layer so that they retain their desired position during the manufacturing of the composite product. Attachment techniques include sewing, gluing, or other methods. The reinforcing yarns can also be manufactured directly with the base layer. Particularly when the base layer consists of yarns, these yarns can be combined with the reinforcing yarns to form a single textile, such as a mat, a non-woven fabric, or a woven fabric, which constitutes the reinforcing element.Alternatively, the reinforcing yarns can also be positioned on the base layer without being attached and only bonded to the base layer once the matrix has cured. According to the invention, the reinforcing yarns are arranged on one side of the base layer such that a gap exists between two adjacent reinforcing yarns. When the reinforcing yarns are placed on top of the base layer, the gaps between two adjacent reinforcing yarns have a depth corresponding to the thickness of the reinforcing yarn. If the reinforcing yarns are integrated into the base layer, they protrude from the base layer on one side by a certain height, thus also forming a gap between two reinforcing yarns with a depth corresponding to the protrusion height of the reinforcing yarns.

[0015] The following optional properties of the reinforcing yarns, both individually and especially in their (sub-)combination, have proven particularly advantageous for the properties of the composite product manufactured using the inventive method. Preferably, the reinforcing yarns 1 are arranged such that they intersect and form rectangular, trapezoidal, or otherwise shaped meshes, i.e., spaces, as shown by way of example in Fig. Figure 1 shows a particularly advantageous method. It is especially advantageous to realize the intersecting reinforcing yarns 1 as a grid fabric, so that the reinforcing yarns 1 form a second layer that can be easily arranged above the base layer. The second layer can thus be treated like a textile. Preferably, the reinforcing yarns are produced from a plurality of fibers. Preferably, the reinforcing yarns are spun with a specific twist angle of the fiber lines 2. The twist angle of a yarn is defined as the angle between the direction of the fiber line 2 of the yarn and the longitudinal axis of the yarn. The twist angle is preferably between 15° and 45°. A twist angle of 18° to 26° or between 20° and 24° has proven particularly advantageous. Preferably, the weight per unit length of the reinforcing yarns is between 500 and 6000 TEX. The spacing between two adjacent reinforcing yarns 1 is between 5 and 100 mm.Preferably, a natural fiber is used as the fiber for the reinforcing yarn.

[0016] In summary, the reinforcing element has a base layer on one side of which reinforcing yarns are arranged such that a gap forms between two adjacent reinforcing yarns. The invention is particularly advantageous for a reinforcing element, i.e., for the base layer and / or the reinforcing yarns, made of natural fibers, since these form particularly compact reinforcing yarns. However, the invention can also be applied to reinforcing elements without natural fibers.

[0017] The matrix is ​​processed in liquid form, as described in detail later, and hardens with the reinforcing element to create the composite material product. Polymers, such as thermosets (synthetic resins), elastomers, or biopolymers, are preferably used as the matrix. However, other matrix materials could also be used. From this point forward, the term "matrix" will be used.

[0018] WO2012076308 discloses further details of the described composite material products, which also include yarns in the base layer. All such composite material products described in WO2012076308 are possible embodiments of the composite material product to be manufactured. WO2012076308 is incorporated into this application by reference for further details of the composite material product to be manufactured.

[0019] Fig. Figure 2 shows an example of a desired composite material product 3, which is flat on one side 3.1 and has a topology on a second side 3.2 that follows the protrusions created by the reinforcing yarns 1 and the depressions created by the spaces 4 as closely as possible. This avoids unnecessary weight from matrix material in the spaces. The finished composite material 3 exhibits a typical ribbed structure, with the ribs being created by the reinforcing yarns 1 cured with the matrix.

[0020] Fig. 3 and Fig. Figure 4 shows two embodiments of a device for producing the composite material product described above. Fig. Figure 5 shows an exemplary embodiment of a manufacturing process for the composite material product described above.

[0021] In step 1, the reinforcement element described above, comprising the base layer 5 and the reinforcing yarns 1, is arranged in a product chamber of a mold 7. Preferably, the mold consists of at least a first part 7.1 and a second part 7.2, so that the mold 7 can be opened for arranging the reinforcement element and then closed again. The reinforcement element is placed in the mold such that the reinforcing yarns point towards the pressure chamber. The opposite side of the reinforcement element, which is generally flat, rests against the wall of the mold 7. The shape of the mold wall against which this opposite side of the reinforcement element rests defines the shape of the final composite material product.

[0022] An elastic membrane 6 separates the mold into the aforementioned product chamber and a pressure chamber. Preferably, the elastic membrane 6 is hermetically sealed within the mold, so that the pressure chamber is hermetically sealed from the product chamber by the elastic membrane 6. The elastic membrane 6 is designed to be elastic enough that, at a specific pressure differential applied in the mold between the pressure chamber and the product chamber, it conforms to the surface of the reinforcing element, i.e., to the topology formed by the base layer and the reinforcing yarns with their interstices. The elastic membrane 6 can be reused for several composite material products or used for only one composite material product at a time. Reusable elastic membranes 6 can be made, for example, from latex or silicone.To achieve the necessary flexibility for these materials, membrane thicknesses of less than 2 mm are advantageous. However, other materials that detach themselves from the cured matrix or the cured composite material product can also be used for reusable elastic membranes 6. Disposable elastic membranes 6 can, for example, be made from thin elastic polymer films. In one embodiment, these disposable elastic membranes 6 can be removed from the cured composite material product, or in an alternative embodiment, they can remain on it.

[0023] In step S2, a soft material 8 is arranged in the pressure chamber of the mold 7 such that the soft material 8 presses against the protruding reinforcing yarns 1 (still separated by the elastic membrane 6) in such a way that the soft material 8 at least partially fills the spaces between the reinforcing yarns 1. The soft material 8 is preferably an elastomer. The soft material 8 is preferably elastic enough that the reinforcing yarns 1 are not, or only negligibly, altered in shape and / or position by the soft material 8 while the soft material 8 is pressed into the spaces between the reinforcing yarns 1. The soft material 8 preferably has an elasticity / hardness of less than 50 Shore A, preferably less than 30 Shore A, preferably less than 20 Shore A, and preferably less than 10 Shore A. Measurements for Shore hardness are defined, for example, in DIN EN ISO 868 or in DIN ISO 7619-1.The soft material is preferably at least as thick as its penetration depth into the spaces 4 between the reinforcing yarns 1, so that the hard mold 7 does not press on the reinforcing yarns 1 and change their position and / or shape. The soft material 8 can, for example, be arranged in the pressure chamber such that it assumes the position described above when the mold is closed. Such an embodiment is particularly advantageous for industrial production of large quantities. Alternatively, the position of the soft material 8 relative to the reinforcing element could also be controlled by the device, e.g., by measuring the contact pressure.

[0024] In step S3, a vacuum is created in the product chamber of the mold 7. For this purpose, preferably at least one vacuum channel 9 is arranged in the mold 7, e.g., in mold half 7.1, through which the gas present in the product chamber is extracted. A vacuum pump is preferably used for this purpose. This has the advantage, firstly, that the quality of the manufactured composite material product is increased, since undesirable gas inclusions in the matrix are avoided. The vacuum also has the effect of pressing the elastic membrane 6 against the reinforcing element and thus fixing it in place. The generated vacuum also allows for very rapid filling of the product chamber, since the liquid matrix is ​​not only forced into the product chamber but also drawn into it on the other side.It is also possible to vacuum the pressure chamber during the emptying of the product chamber, so that the elastic material rests not on the reinforcing element but on the soft material 8. This further accelerates the spreading of the liquid matrix. To protect the vacuum pump, a matrix brake / trap is preferably arranged upstream of the vacuum pump. Step S3 can be performed before, during, or after the arrangement of the soft material in step S2.

[0025] In step S4, the pressure chamber is filled with the liquid matrix. The liquid matrix is ​​preferably introduced into the product chamber via a matrix inlet. The matrix can be drawn into the product chamber solely by the vacuum created. Alternatively, in addition to the vacuum, the liquid matrix can also be pumped / forced into the product chamber under pressure. The product chamber then fills with the liquid matrix until the spaces 4 between the reinforcing yarns 1, the base layer 5, and the soft material 8 are filled with the liquid matrix. In this state, the liquid matrix presses the elastic membrane 6 against the soft material 8. The soft material 8 thus limits the amount of liquid matrix that is filled into the spaces by the volume of the soft material 8 penetrating them. This allows the cured composite product to be produced with a weight reduction equal to the amount of matrix saved.Problematic in the case of . Fig. The device shown in Figure 3 could be that the soft material 8, which presses on the reinforcing yarns 1, prevents a rapid spread of the liquid matrix material.

[0026] Fig.Figure 4 shows an alternative embodiment in which channels 12 are arranged in the soft material 8 to improve the propagation of the liquid matrix between the spaces. Preferably, the channels 12 are arranged along the interface between the soft material 8 and the elastic membrane 6. The channels 12 are wide enough to allow the elastic material to expand into them, but the additional volume for the liquid matrix material is negligible or smaller than the penetration volume of the soft material 8 into the spaces 4. Preferably, the channels are arranged at least in the direction of propagation of the liquid matrix. However, additional channels can be arranged at other angles to achieve even better propagation of the liquid matrix material.

[0027] Step S4 is performed after step S2. Preferably, step S3 is started before step S4 and continued during step S4. However, step S3 could also be started simultaneously with step S4.

[0028] Alternatively, filling the product chamber in step S4 could also be done by pre-impregnating the reinforcing element, so-called “prepregs”, before the reinforcing element is placed in the mold 7.

[0029] After step S4, the pressure in the pressure chamber is increased in step S5. Either a gas or a liquid can be used as the pressure fluid in the pressure chamber. This forces the elastic membrane 6 to force the liquid matrix, located between the base layer 5, the reinforcing yarns 1, and the soft material 8, into the reinforcing element, thus impregnating it with the liquid matrix. By carefully arranging the soft material 8, the amount of matrix accumulated in the spaces in step S4 can be precisely limited to the quantity required for impregnation, thereby enabling optimal production of the composite material product 3. Preferably, the pressure in the product chamber is reduced before and / or during the increase in pressure in the pressure chamber.

[0030] In step S5, the liquid matrix is ​​cured. Afterwards, the composite material product 3 is ready and can be removed from the mold 7. To accelerate curing, the mold 7 and / or the printing fluid, in particular a hydraulic fluid, can be heated. Curing could also be initiated or accelerated by UV irradiation or by moisture.

[0031] The described invention enables the production of particularly lightweight and exceptionally stable composite material products. The reinforcing yarns allow for a reduction in the effective thickness of the composite material product, and thus its overall weight, while maintaining or even improving its stiffness. The manufacturing process also allows for the creation of highly complex shapes.

[0032] One area of ​​application would be in the automotive sector. For example, body parts that are currently made of relatively thick and therefore heavy steel or aluminum sheets could be replaced by the composite material products described above. An aluminum sheet could be used as the base layer. Interior vehicle trim, such as door panels and dashboards, can also be manufactured using the composite material product described above. Seat shells could also be made from such a composite material. For the seat shell and / or interior trim, textiles, such as natural fiber textiles, could be used as the base layer. Similar applications exist in the aerospace industry to save weight in interior and exterior trim or seats.

[0033] Other areas of application include luggage such as suitcases, housings for electrical devices, etc.

Claims

[1] Manufacturing process for a stiffened thin-walled fiber composite material product (3) comprising the following steps: Arranging a reinforcing element in a mold (7), wherein the reinforcing element has a base layer (5) and reinforcing yarns (1) arranged on one side of the base layer; Dividing the mold (7) by means of an elastic membrane (6) into a product chamber with the reinforcing element and into a pressure chamber, wherein the side of the base layer (5) with the reinforcing yarns (1) is arranged in the direction of the elastic membrane (6); Arranging a soft material (8) in the pressure chamber so that the soft material (8) is pressed into the spaces (4) between the reinforcing yarns (1); Creating a negative pressure in the product chamber using a vacuum pump; Filling the product chamber with a matrix until the matrix presses the elastic membrane (6) against the soft material (8); Applying pressure via the elastic membrane (6) to the matrix (8) between the reinforcing yarns (1), such that the elastic membrane (6) is pressed deeper than the soft material (8) between the reinforcing yarns (1) and the reinforcing element is impregnated with the matrix; and Curing of the matrix to produce the stiffened thin-walled fiber composite material product (3). [2] Manufacturing process according to claim 1, characterized by , that the soft material (8) is pressed onto the reinforcing element in such a way that, after filling the product chamber and before increasing the pressure in the pressure chamber, the volume of the matrix in the spaces (4) between the reinforcing yarns (1), the base layer (5) and the soft material (8) is less than 150%, preferably less than 120%, of the matrix volume which is pressed into the reinforcing element. [3] Manufacturing process according to any one of the preceding claims, characterized by, that the soft material (8) is pressed onto the reinforcing element in such a way that, after filling the product chamber and before increasing the pressure in the pressure chamber, the volume of the matrix in the spaces (4) between the reinforcing yarns (1), the base layer (5) and the soft material (8) corresponds to a certain volume and the pressure is exerted over the elastic material in such a way that in the cured composite material product the matrix volume occupies less than 60%, preferably less than 50%, of the volume defined by the outer surfaces of the reinforcing yarn and / or the base material. [4] Manufacturing process according to any one of the preceding claims, characterized by , that the soft material (8) has a hardness of less than 30 Shore A. [5] Manufacturing process according to any one of the preceding claims, characterized by, that the soft material (8) is so soft that when pressed against the reinforcing yarns (1) it does not cause any change in shape or position of the reinforcing yarns (1) and / or the soft material (8) is so hard that when the product chamber is filled with the matrix it can limit the filling volume in the spaces (4) between the reinforcing yarns, the base layer and the soft material. [6] Manufacturing process according to any one of the preceding claims, characterized by , that the soft material (8) has channels (12) along the elastic membrane (6) which improve the flow of the matrix between the spaces. [7] Manufacturing process according to any one of the preceding claims, characterized by , that the elastic membrane (6) is pressed in by the pressure fluid to at least 70%, preferably at least 90%, of the depth of the space (4) between the reinforcing yarns (1). [8] Manufacturing process according to any of the preceding claims, characterized by , that when pressure is applied in the pressure chamber, the elastic membrane (6) conforms to the reinforcing yarns (1) and to the base layer (5) such that the matrix volume in the spaces (4) between the reinforcing yarns, the base layer and the elastic membrane is less than 10% of the reinforcing yarn volume. [9] Manufacturing process according to any of the preceding claims, characterized by , that the elastic membrane (6) is designed to be able to expand by at least 300%. [10] Manufacturing process according to any one of the preceding claims, characterized by that the manufacturing process includes one or more of the following steps: Injection of the matrix under pressure between 1 and 50 bar; Applying a pressure between 1 and 50 bar to the elastic membrane (6) by the pressure fluid; and Curing of the matrix by heating the printing fluid and / or the mold (7). [11] Manufacturing process according to any of the preceding claims, characterized by , that the reinforcing yarns (1) consist of a yarn with a twist angle between 15° and 45°, preferably between 18° and 26°. [12] Manufacturing process according to any one of the preceding claims, characterized by , that the reinforcing yarns (1) consist of a yarn with a density per unit length between 500 TEX and 6000 TEX. [13] Manufacturing process according to any of the preceding claims, characterized by , that the reinforcing yarns (1) are arranged with a distance between 5 mm and 100 mm from each other. [14] Manufacturing process according to any of the preceding claims, characterized by , that the reinforcing yarns (1) have first reinforcing yarns and second reinforcing yarns, wherein the first reinforcing yarns cross over with the second reinforcing yarns. [15] Manufacturing process according to any one of the preceding claims, characterized by , that filling the product chamber with the matrix can also be done by impregnating the reinforcing element before arranging the reinforcing element in the mold (7). [16] Manufacturing process according to any of the preceding claims, characterized by , that the base layer (5) comprises a carbon fiber layer, a glass fiber layer, a natural fiber layer, a metal layer, a polymer layer, a wood veneer or a subcombination of these. [17] Manufacturing process according to any of the preceding claims, characterized by , that the cured stiffened thin-walled fiber composite material product (3) has a flat surface on a first side (3.1) and a surface structure on a second side (3.2) which follows a topology formed by the spaces (4) of the reinforcing yarns (1). [18] Stiffened thin-walled fiber composite material product (3) produced by a manufacturing process according to any of the preceding claims. [19] Use of a stiffened thin-walled fiber composite material product (3) according to the preceding claim for body parts of an automobile or an aircraft. [20] Use according to claim 19, characterized by that a metal sheet is used as the base layer.

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