Manufacturing process for a component with a porous fiber matrix structure

Abstract

A manufacturing process for a component (1) comprising the following steps: - Introducing a fiber structure into a mold, - Introducing a blowing agent into the mold, and - Hardening of the fiber structure and the blowing agent, wherein the blowing agent expands and together with the fiber structure forms a porous fiber matrix structure (12); wherein the fiber structure is a pre-impregnated prepreg, the introduction of the fiber structure is a lining of the mold with the fiber structure, and the introduction of the blowing agent is a planar application of the blowing agent onto the fiber structure; wherein by repeating the two insertion steps a stack of alternating fiber structure layers and blowing agent layers is produced, wherein the type, quantity and / or distribution of the fiber structure and / or blowing agent is variable per fiber structure layer or blowing agent layer; and a transition is formed between, on the one hand, a monolithic top layer or outer skin and, on the other hand, a very light, highly porous core made of a porous fiber matrix structure.

Description

TECHNICAL FIELD

[0001] The invention relates to a manufacturing method for a component and in particular to a manufacturing method for a component with a porous fiber matrix structure. BACKGROUND OF THE INVENTION

[0002] Composite materials with a hard cover layer and a lightweight core are known. However, these composite materials are complex to manufacture and feature a rather abrupt transition between the cover layer and core, which leads to an equally abrupt change in the physical properties of the individual layers. This rather abrupt transition can, for example, cause shear stresses and lead to component failure.

[0003] DE 10 2011 109 700 A1 describes a fiber-reinforced plastic composite component, a fiber-matrix semi-finished product and a manufacturing process.

[0004] DE 698 11 011 T2 describes a fiber web and methods for producing a shaped article by impregnating the web with a liquid resin and a curing agent therefor.

[0005] DE 10 2013 114 770 A1 describes a process for the in situ production of sandwich components reinforced with reinforcing fibers.

[0006] DE 102 50 023 A1 describes a molded part made of a polyurethane matrix containing nonwoven fabric.

[0007] DE 17 04 565 A describes a fiber-reinforced plastic composite material.

[0008] DE 20 2009 001 846 U1 describes lightweight structures made of a fiber composite material based on wood fiber mats, in particular for rotor blades in wind turbines.

[0009] DE 10 2010 014 398 A1 describes a process for manufacturing an SMC multi-layer component. SUMMARY OF THE INVENTION

[0010] It is an object of the invention to provide a simplified manufacturing method for a component and in particular for an improved component with a porous fiber matrix structure.

[0011] This object is achieved by a manufacturing method for a component having the features of the independent claim. Advantageous embodiments and further developments can be found in the subclaims and the following description.

[0012] It is proposed to provide a manufacturing method for a component which includes the following steps, not necessarily in this order: - Introducing a fiber structure into a mold, - Introducing a blowing agent into the mold, and - Hardening of the fiber structure and the blowing agent, wherein the blowing agent expands and together with the fiber structure forms a porous fiber matrix structure.

[0013] A porous fiber matrix structure can be understood as a composite of the expanded blowing agent and the fibers of the fiber structure, which are also expanded by the blowing agent. In other words, the result is a foamed, highly porous fiber composite component, or in yet another word, a fiber-reinforced foam.

[0014] Introducing the fiber structure into the mold can involve lining the mold with the fiber structure. The mold can be a simple plane or at least represent part of the component to be manufactured. The component can therefore have any shape, i.e., be flat or have more or less complex curves or angles. Curing involves heating with or without additional pressure. Curing can take place in an autoclave or in a closed mold under pressure. Heating can take place, for example, at 120°C to 180°C.

[0015] The fiber structure can be a fiber-reinforced plastic, particularly a carbon fiber-reinforced plastic. For particularly homogeneous porosity and particularly good mechanical properties of the component, the fiber structure can comprise short, randomly oriented fibers. The fibers can be recycled. The fiber structure can be a pre-impregnated prepreg or a non-pre-impregnated (dry) fiber fabric. The pre-impregnated prepreg is provided with an impregnation component before being placed in the mold, while the (dry) fiber fabric is provided with an impregnation component after being placed in the mold. The impregnation component can be a resin. The impregnation component can include an expansion additive. The impregnation component can be thermoset. The fiber structure can therefore be designed for temperatures between -50 °C and 300 °C, making it far superior to conventional foam materials.

[0016] The blowing agent can be chemical or physical. It can be powdered and free-flowing or liquid. An example of a chemical blowing agent is sodium bicarbonate. The heat applied during curing of the component releases a volatile component of the blowing agent, which causes the fiber structure to expand or foam.

[0017] The blowing agent can be introduced into the mold by applying it flatly to the fiber structure, or it can be introduced into the mold and thus into the fiber structure by gravity, negative pressure, or positive pressure. The expansion of the blowing agent can be foaming.

[0018] The manufacturing process for a component with a porous fiber matrix structure simplifies the production of composite materials, especially sandwich structures for lightweight construction. Even highly complex shapes, such as double-curved components, can be created with comparatively little effort. In particular, only one manufacturing step is required.

[0019] The manufacturing process can be implemented in two variants, which are presented below.

[0020] According to the invention, the fiber structure is a pre-impregnated prepreg, the introduction of the fiber structure into the mold is a lining of the mold with the fiber structure, and the introduction of the blowing agent into the mold is a surface application of the blowing agent to the fiber structure.

[0021] By repeating the two introduction steps “introducing the fiber structure” and “introducing the blowing agent,” a stack is created consisting of alternating fiber structure layers and blowing agent layers. The type, amount, and / or distribution of the fiber structure and / or blowing agent per fiber structure layer or blowing agent layer can be varied in order to achieve different degrees of expansion across the height of the stack. In particular, the amount of blowing agent applied over the entire surface of the fiber structure can differ between different fiber structure layers of the stack. In this way, for example, more blowing agent can be applied to a center section of the stack than to an edge region of the stack, so that this center section expands further during curing than the edge region. In this way, for example, a stack can be created with a highly porous center section and a non-porous or barely porous edge region.In other words, the type, amount and / or distribution of the blowing agent in a middle blowing agent layer in the stack can be designed for a porous expansion of the fiber structure by the blowing agent, and the type, amount and / or distribution of the blowing agent in an outer blowing agent layer in the stack can be designed for the formation of a non-porous or hardly porous cover layer.

[0022] The components produced by the process of the present invention have a very smooth transition between, on the one hand, a monolithic cover layer or outer skin and, on the other hand, a very light, highly porous core. The cover layer and the core of the component can be made of the same material, which is advantageous, for example, with regard to approval restrictions in aeronautical engineering. The cover layer and the core of the component can have the same physical properties, so that, for example, no residual stresses or thermal distortion occur. The cover layer and the core of the component can be produced in a single process step. The cover layer can have a closed surface and relatively high strength, stiffness, and hardness. The core has a relatively low density, and consequently low weight and large pores.In this way, a “bionic” structure similar to a bone with a stable outer skin and a spongy core can be created.

[0023] The distribution of the blowing agent quantities, and thus the porosity, across the stack height can be varied continuously or in stages. With regard to the blowing agent quantity and thus the porosity, the stack can be constructed symmetrically or asymmetrically with respect to its innermost layer.

[0024] In one embodiment, after porous expansion and curing, the fiber structure comprises a fiber-reinforced cover layer, the outer layers in the stack comprise a woven fabric, scrim, or unidirectional laminate, and the middle layers in the stack, or the core, comprise a reinforcing fabric. The fiber-reinforced cover layer can comprise unidirectional prepreg tapes, and the fabric of the outer layers can comprise twill or canvas, which, due to its increased fiber undulation, smoothly transitions into the open-pore middle layers of the core and improves the bond between the cover layer and the core. The core can comprise nonwoven fibers with a high dead weight. The core can have isotropic properties or increased strength in the direction of the stack height.

[0025] In the second variant of the manufacturing process, which is only described for better technical understanding, the fiber structure is a dry fiber fabric. The introduction of the fiber structure into the mold involves lining the mold with the fiber structure, and an impregnation component and the blowing agent are introduced into the mold and thus into the fiber structure using negative or positive pressure. The dry fiber fabric can be a fleece, a woven fabric, a knitted fabric, a scrim, a material, a felt or similar. The impregnation component and the blowing agent can, for example, be sucked or injected simultaneously or sequentially from one side of the mold to the other through or along the dry fiber fabric. The impregnation component and the blowing agent can, however, also be pressed or injected through the mold transversely to the layers of the dry fiber fabric, for example from top to bottom, or they can simply flow or sink through it under gravity.If the impregnation component and the blowing agent are introduced into the fiber structure in such a way that uniform mixing occurs, uniform porosity is also created (without a covering layer with properties different from the core).

[0026] The type, quantity and / or distribution of the fiber structure in the mold can be handled variably, i.e. the same or different fiber structures can be used within the mold and distributed evenly or differently.

[0027] In an example described solely for the purpose of better technical understanding, the mold has a first internal volume during the introduction of the fiber structure, the impregnation component, and the blowing agent, which expands to a larger, second internal volume after a predetermined time. The first internal volume is designed to form a cover layer, and the second internal volume is designed for porous expansion of the fiber structure.

[0028] In another embodiment, the mold is not completely filled with the fiber structure, the impregnating component, and the blowing agent, cured for a first period of time at a first pressure, and cured for a second period of time at a second pressure that is lower than the first pressure. The first pressure is designed to form a cover layer, and the second, lower pressure is designed to porously expand the fiber structure into the remaining space in the mold.

[0029] In one embodiment, the fiber structure, after porous expansion and curing, has a cover layer of unidirectional, multiaxial fibers, and the outer layers in the stack have a woven fabric, scrim, or unidirectional laminate to improve the bonding of the cover layer and core.

[0030] Furthermore, only for better technical understanding, a component is described which was produced by the manufacturing process described above and therefore comprises a fiber structure and a blowing agent, wherein the expanded blowing agent together with the expanded fiber structure forms a porous fiber matrix structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further features, advantages, and possible applications of the present invention will become apparent from the following description of the exemplary embodiments and the figures. All described and / or illustrated features, individually and in any combination, constitute the subject matter of the invention, regardless of their composition in the individual claims or their references. In the figures, identical reference numerals represent identical or similar objects. Fig. 1 shows a schematic overview of a manufacturing process for a component with a porous fiber matrix structure. Fig. 2a and b shows a cross-section through such a component with a porous fiber matrix structure. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0032] Fig. 1 shows a schematic overview of a manufacturing process for a component 1, which includes the following steps, not necessarily in this order: - Step S1, introducing a fiber structure into a mold, - Step S2, introducing a blowing agent into the mold, and - Step S3, curing of the fiber structure and the blowing agent.

[0033] During curing, the blowing agent expands and forms together with the fiber structure a porous fiber matrix structure 12. Such a porous fiber matrix structure 12 is in Fig. 2a and b. The porous fiber matrix structure 12 is understood to be a composite of the expanded blowing agent and the fibers of the fiber structure, which are also expanded by the blowing agent. Thus, a foamed, highly porous fiber composite component or a fiber-reinforced foam is created.

[0034] The manufacturing method according to the invention simplifies the production of composite materials, particularly sandwich structures for lightweight construction, for example. Highly complex shapes, such as double-curved components, can be produced with comparatively little effort. The manufacturing method according to the invention can be implemented, among other things, using two alternatives, which are presented below.

[0035] In the variant of the manufacturing process according to the invention, the fiber structure is a pre-impregnated prepreg, the introduction of the fiber structure into the mold is a lining of the mold with the fiber structure, and the introduction of the blowing agent into the mold is a surface application of the blowing agent onto the fiber structure. Fig. The manufacturing process shown in Figure 1 therefore comprises a preliminary step S0 of pre-impregnating the fiber structure.

[0036] Fig. 2a and b show a component 1 which was produced by the manufacturing process described above and therefore comprises a fiber structure and a blowing agent, wherein the expanded blowing agent together with the expanded fiber structure forms a porous fiber matrix structure 12.

[0037] By repeating the two introduction steps "introducing the fiber structure" and "introducing the blowing agent," a stack of alternating fiber structure layers and blowing agent layers is created. The type, amount, and / or distribution of the fiber structure and / or blowing agent per fiber structure layer or blowing agent layer can be varied in order to achieve different degrees of expansion across the height of the stack. In particular, the amount of blowing agent applied to the fiber structure can differ between different fiber structure layers of the stack. In this way, more blowing agent can be applied to a central part of the stack than to an edge region of the stack, so that this central part expands further during curing than the edge region. In this way, a stack, as in the Fig. 2a and b, with a highly porous and therefore light central part made of a porous fiber matrix structure 12 and a non-porous or hardly porous and therefore stable edge region made of a cover layer 11.

[0038] The components 1 thus produced by the method of the present invention exhibit a very smooth transition between a monolithic, protective cover layer 11 and a very lightweight, highly porous core made of a porous fiber matrix structure 12 and are manufactured in a single process. In this way, a "bionic" structure similar to a bone with a stable outer skin and a spongy core can be created.

[0039] In the second variant of the manufacturing process, the fiber structure is a dry fiber fabric. The introduction of the fiber structure into the mold is, as above, a lining of the mold with the fiber structure and an impregnation component and the blowing agent are introduced into the mold and thus into the fiber structure using negative or positive pressure. The impregnation component and the blowing agent can be sucked or injected from one side of the mold to the other through or along the dry fiber fabric. The impregnation component and the blowing agent can also be pressed or injected transversely to the layers of the dry fiber fabric, e.g. from top to bottom through the mold, or simply flow or sink through it under gravity.If the impregnation component and the blowing agent are introduced into the fiber structure in such a way that uniform mixing occurs, a uniform porosity (without a cover layer with properties different from the core) of the porous fiber matrix structure 12 is also created.

[0040] However, it is also possible to produce a component 1 as in the Fig. 2a and b. During the introduction of the fiber structure, the impregnation component, and the blowing agent, the mold has a first internal volume, which expands after a predetermined time to a larger, second internal volume. The first internal volume is designed for forming a cover layer 11, and the second internal volume is designed for porous expansion of the fiber structure into a porous fiber matrix structure 12. The Fig.However, the component 1 shown in Figure 2 can also be produced by not completely filling the mold with the fiber structure, the impregnation component, and the blowing agent, curing it for a first period of time at a first pressure, and curing it for a second period of time at a second pressure that is lower than the first pressure. The first pressure is designed to form a cover layer 11, and the second, lower pressure is designed to porously expand the fiber structure into the remaining space of the mold to form a porous fiber matrix structure 12.

[0041] Additionally, it should be noted that "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations.

Claims

[1] A manufacturing method for a component (1), comprising the following steps: - Introducing a fiber structure into a mold, - Introducing a blowing agent into the mold, and - Hardening of the fiber structure and the blowing agent, wherein the blowing agent expands and together with the fiber structure forms a porous fiber matrix structure (12); wherein the fiber structure is a pre-impregnated prepreg, the introduction of the fiber structure is a design of the mold with the fiber structure, and the introduction of the blowing agent is a surface application of the blowing agent to the fiber structure; wherein by repeating the two introduction steps, a stack of alternating fiber structure layers and blowing agent layers is produced, wherein the type, quantity and / or distribution of the fiber structure and / or blowing agent per fiber structure layer or blowing agent layer is variable; and whereby a transition is formed between a monolithic cover layer or outer skin and a very light, highly porous core made of a porous fiber matrix structure. [2] Manufacturing method according to the preceding claim, wherein the fiber structure is provided with a further fiber-reinforced cover layer after the porous expansion and curing and middle layers in the stack have a reinforcing fabric and outer layers in the stack have a fabric, scrim or unidirectional laminates. [3] Manufacturing process according to one of the preceding claims, wherein the blowing agent is a powdered, free-flowing, chemical blowing agent. [4] Manufacturing process according to one of the preceding claims, wherein the impregnation component is thermosetting.

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