Semi-finished product and method for producing a structural component

A semi-finished product for the manufacture of a structural component has a plurality of prepreg tapes, each having unidirectionally arranged reinforcing fibers embedded in a thermoplastic matrix material, and with a plurality of connecting strands containing a thermoplastic material. The prepreg tapes and the connecting strands are either joined to form a textile sheet structure or the prepreg tapes are arranged to form a multiaxial fabric, individual layers of the fabric being joined by the connecting strands. Further, a method for manufacturing a curved structural component from such a semi-finished product is described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/EP2019/076079 filed Sep. 26, 2019, published in German, which claims priority from German Application No. 102018217018.5 filed Oct. 4, 2018, the disclosures of which are incorporated herein by reference.

The present invention relates to a semi-finished product and method for manufacturing a structural component, in particular a structural component, which has a curved or double-bent shape or form.

In the field of aircraft and spacecraft construction in particular, structural components made of fibre composite material are used which have a curved, dome-shaped or otherwise spherical shape in at least two directions. Such components are used in aircraft construction, e.g. as pressure bulkheads or fuselage shells.

For the production of such multi-curved structural components, typically a multitude of mat-shaped semi-finished fiber products are first stacked to form a laminate or layered structure. The semi-finished fiber products may be in the form of fiber mats pre-impregnated with a matrix material. The laminate structure formed is then shaped and the matrix material is cured.

US 2005/0035115 A1 describes a process for the production of fiber composite components, wherein a layered structure, which has reinforcing fiber layers embedded in thermoplastic matrix material, is received between heating mats and inductively heated to a forming temperature. In a closed cavity of a compression mold, the layered structure is formed together with the heating mats by means of a pressurized fluid. A similar method is described in U.S. Pat. No. 5,591,369 A.

DE 10 2010 050 740 A1 describes a method of manufacturing a structural component, wherein a plurality of semi-finished layers of a fiber-reinforced thermoplastic plastics material are stacked and selectively joined together at points in order to fix a position of the semi-finished layers relative to one another. The type of connection is intended to prevent the formation of folds during subsequent press forming.

It is an object of the present invention to provide a semi-finished product and a method for manufacturing a structural component from a fiber-reinforced thermoplastic material, each of which further reduces wrinkle formation during forming.

This task is solved by the objects of the independent claims, respectively.

According to a first aspect of the invention, a semi-finished product is provided for manufacturing a structural component. The semi-finished product comprises a plurality of prepreg tapes extending along each other, each having unidirectionally arranged reinforcing fibers embedded in a thermoplastic matrix material, and a plurality of connecting strands comprising a thermoplastic plastic material. The connecting strands and the prepreg tapes are joined together to form a textile sheet structure in which each of the connecting strands crosses a plurality of the prepreg tapes. The connecting strands and the prepreg tapes are joined together along a respective connecting line in a first end region of the textile sheet structure and in a second end region of the textile sheet structure opposite to the first end region.

An idea underlying the invention is to provide a semi-finished product in the form of a textile sheet structure formed from prepreg tapes with unidirectional fibers and connecting strands comprising a thermoplastic material. In particular, the thermoplastic material of the connecting strands may be the same thermoplastic material as the matrix material contained in the prepreg tapes or at least have a similar composition. The textile structure, i.e., a structure of intersecting strands, offers the advantage that the semi-finished product has anisotropic deformation properties. In particular, the textile structure allows the prepreg tapes to slide along each other, which prevents wrinkling during deformation. The formation of wrinkles is further prevented by the fact that a material joint of the strands, i.e., a material joint between prepreg tapes and thermoplastic connecting strands, is only provided along connecting lines located opposite each other, whereby the prepreg tapes and the connecting strands can slide along each other or are not connected at the other crossing points. The unidirectional thermoplastic prepreg tapes are elongated, single-ply tape material in which continuous reinforcing fibers extending in only one direction are embedded in a thermoplastic matrix material. Such prepreg tapes offer the advantage that they are easily deformable but less susceptible to the formation of ondulations. In contrast to semi-finished products consisting purely of woven reinforcing fibers, the semi-finished product according to the invention no longer requires subsequent infiltration with matrix material in order to produce a structural component from the semi-finished product.

According to another aspect of the invention, a semi-finished product for manufacturing a structural component is provided. The semi-finished product comprises a plurality of prepreg tapes each having unidirectionally arranged reinforcing fibers embedded in a thermoplastic matrix material. Optionally, a plurality of connecting strands comprising a thermoplastic plastic material are further provided. The prepreg tapes are arranged to form a multiaxial fabric comprising a plurality of superimposed layers of prepreg tapes, wherein the prepreg tapes within a layer run parallel to one another, and wherein the layers are joined relative to one another at individual points, in particular sewn, knitted, woven, welded or joined by another textile process, preferably by means of the connecting strands.

According to this aspect of the invention, a multilayer semi-finished product is provided, wherein the individual layers are formed from parallel prepreg tapes and the individual layers are connected only at points by the connecting strands. For example, joints may be provided along parallel lines. Due to the merely punctual connection of the layers and the parallel extension of the prepreg tapes and thus of the reinforcing fibers within the individual layers, the individual layers can slide relative to each other and the fibers within the individual layers can slide relative to each other, thus preventing wrinkling. The advantages mentioned above for the use of prepreg tapes with thermoplastic material apply analogously to this aspect of the invention.

The semi-finished products described allow in particular an efficient deposition of flat semi-finished product layers. This means that it is no longer necessary to deposit and fix individual prepreg tapes to form a flat layer.

According to a further aspect of the invention, a method of manufacturing a structural component having a curved shape is provided. According to this method, a layered structure is first formed from a plurality of layers, the layers each comprising at least one semi-finished product formed as described above. The layers can optionally be thermoplastically joined, for example by welding, in particular ultrasonic welding, at a joining point which is located in the region of a vertex of the curved shape to be produced. Thus, a discrete, e.g., point-shaped, material joint of the layers of the layered structure is produced at a point at which no or only slight relative movements of the individual layers to one another occur during forming in order to produce the curved shape. In a further step, the layered structure is formed into the curved shape at a forming temperature that is lower than a melting point of the thermoplastic materials of the semi-finished product. After forming, the formed layered structure is heated to a temperature that is higher than the melting point of the thermoplastic materials of the semi-finished product, i.e., higher than the melting point of the thermoplastic matrix material of the prepreg tapes and higher than the melting point of the thermoplastic material of the connecting strands of the semi-finished product. Finally, the layered structure is consolidated by applying a compression pressure and cooled down again under this pressure to a solidification temperature that is lower than the melting point of the thermoplastic materials of the semi-finished product.

Consequently, another idea of the invention is to reduce wrinkling by forming the layered structure at a temperature that is lower than the melting point of the thermoplastic materials of the semi-finished product. Since the thermoplastic materials are still solid during forming, the layers of the layered structure do not yet stick together outside the optional joint, so that sliding of the layers against each other is still possible, especially if the layers also shear differently due to different fiber directions during the forming process. In this way, the individual prepreg tapes of a respective layer themselves and the individual layer can slide against each other, which prevents wrinkling of the reinforcing fibers. Due to the fixing of the layers or plies relative to each other in an area of the layered structure which contains an apex of the curved shape of the structural component after forming further facilitates sliding of the layers relative to each other in more deformed areas.

By reducing the formation of wrinkles, the mechanical strength of the components is improved. Due to the textile structure of prepreg tapes and connecting strands, which each have one, preferably the same, thermoplastic material, a large flat component can be produced in a very simple and quick manner after forming.

Advantageous embodiments and further designs result from the subclaims referring back to the independent claims in connection with the description.

In particular, the prepreg tapes may comprise a width between 3 mm and 15 mm. In particular, it can also be provided that a width is between 0.001 percent and 5 percent of a length of the prepreg tapes. In general, the prepreg tapes are thus narrow, which further improves the formability of the semi-finished product.

According to an embodiment of the semi-finished product, it is provided that the prepreg tapes extend in a first direction and the connecting strands extend in a second direction transverse to the first direction, and wherein an outermost first prepreg tape in relation to the second direction and an outermost second prepreg tape located opposite to the first prepreg tape are respectively joined with the connecting strands by way of a material joint to form the connecting lines. According to this embodiment, the connecting lines run along outermost prepreg tapes of the textile semi-finished product that are located opposite to each other. This prevents fraying or disintegration of the semi-finished product, while the sliding of the individual tapes relative to each other is impeded as little as possible.

According to a further embodiment of the semi-finished product, the prepreg tapes and the connecting strands are interwoven with each other. Accordingly, the prepreg tapes each run parallel to each other, e.g., in a first direction, and the connecting strands extend transversely to the prepreg tapes, e.g., in a second direction, and also run parallel to each other. For example, the prepreg tapes may be provided as warp strands and the connecting strands may be provided as weft strands, or vice versa. Optionally, the connecting strands and the prepreg tapes are woven in an atlas weave in which the weft strand passes under a warp strand and then across more than two warp strands. The formation of the textile sheet structure by weaving prepreg tapes and connecting strands in particular offers the advantage that the reinforcing fibers run approximately parallel to each other within the sheet structure. Furthermore, weaving can be easily automated.

According to a further embodiment, the prepreg tapes and the connecting strands are interwoven with each other.

According to a further embodiment of the semi-finished product, the connecting strands each comprise a first end region and a second end region opposite to the first end region, the first and second end regions each projecting beyond the connecting lines. Accordingly, the connecting strands form protrusions or a kind of tab which protrude over an edge or edge region of the sheet structure. These tabs can be used for coupling to other semi-finished products of the same or similar construction in a material joint, which facilitates the processing of the semi-finished product.

According to a further embodiment of the semi-finished product, the connecting strands are formed as foil tapes consisting of the thermoplastic material or as threads consisting of the thermoplastic material. Tapes, i.e., strands with flat, rectangular cross-sections, have a low cross-sectional thickness, so that a very thin semi-finished product can be realized. Threads, i.e., strands with several filaments twisted into an approximately circular cross-section, offer the advantage of greater mechanical strength.

Optionally, the connecting strands consist of thermoplastic plastic material, preferably the thermoplastic matrix material of the prepreg tapes. As a result, the connecting strands dissolve to a certain extent when the semi-finished product is heated to a temperature higher than the melting temperature of the thermoplastic materials and additionally improve the cohesion between the reinforcing fibers.

According to an embodiment of the method, the individual layers of the layered structure are each formed from several semi-finished products in which the connecting strands project beyond the connecting lines, as described above. In particular, at least the first end regions of the connecting strands of a first semi-finished product are thermoplastically joined to prepreg tapes of a respective further semi-finished product. Optionally, the second end regions of the connecting strands of the further semi-finished product can also be thermoplastically joined to prepreg tapes of the first semi-finished product. In this way, large flat layers can be produced in a simple manner. For the thermoplastic joint, a welding process such as ultrasonic welding can be used, for example.

According to a further embodiment of the method, it can be provided that the layered structure is formed in such a way that the prepreg tapes in different layers extend in different directions. For example, the layers are stacked in such a way that the prepreg tapes of two adjacent layers or plies extend in different directions. Thus, the reinforcing fibers in different layers also extend in different directions, which improves the mechanical strength of the structural component.

According to a further embodiment of the method, the layered structure is formed by sequential stacking of the layers on a flat deposition surface and the forming takes place in a further step, e.g., in a cavity of a forming tool, wherein the cavity is formed by a part of the forming tool with a contour surface corresponding to the curved shape of the structural component and a flat abutment member. Stacking on a flat surface offers the advantage that a large number of layers can be deposited quickly, with little risk of wrinkling. Forming takes place in a separate (press) forming step.

According to a further embodiment of the method, the layered structure is formed by sequential stacking of the layers on a curved deposition surface and thereby simultaneously forming into the curved shape, wherein a contour surface of a form part of a forming tool is formed by the deposition surface corresponding to the curved shape of the structural component, wherein the forming tool additionally comprises a flat abutment member for forming a cavity with the forming part. Thereby, each layer is deposited separately on a curved surface and thus at least partially already formed into the desired shape. This offers the advantage that the individual layers do not have to slide against each other for forming, or only to a small extent, which further reduces the risk of wrinkling.

Optionally, it can be provided that layers of the layered structure deposited on the curved contour surface of the form part are thermoplastically joined at further bonding points in addition to the optional bonding point located in the region of the apex. This fixes the layers in their position.

According to a further embodiment of the method, it is provided that the heating of the layered structure takes place in the cavity of the forming tool. If the layers have already been deposited on the form part, the cavity is first closed by the deposition part, thereby compacting the individual layers.

According to a further embodiment of the method, the form part of the forming tool is designed as a flatly extending first form plate, whereby the abutment member is designed as a flatly extending second form plate. The form part and the abutment member are thus each designed as flat, curved metal plates. Compared to solid presses, the form parts have a low heat capacity. Therefore the cavity can be heated up quickly and with little energy input.

The form may also be formed as a partially solid mold, e.g., with a surface portion forming the contour surface and with a base portion formed as a stiffening structure supporting the surface portion.

According to one embodiment, in order to apply the compression pressure, a magnetic field is generated by means of a magnet device, which is coupled into a magnetizable material associated with the first form plate and/or into a magnetizable material associated with the second form plate in such a way that the layered structure is subjected to the compression pressure by the form plates. In particular, a magnetic field directed transversely to the contour surface is generated. Accordingly, the compression pressure is generated by means of a magnetic force which can, for example, act directly on the form plates, e.g., if the first and/or the second form plate is formed from a magnetizable metal material and the magnetizable material is associated with the respective form plate in this way. Alternatively, the magnet device can also have magnetizable elements coupled to the form plates as magnetic material, which press the form plates together relative to each other by the effect of the magnetic field. Due to their flat extension, the form plates allow the formation of a magnetic field extending through the cavity in which the layered structure is located. On the one hand, this achieves a very even distribution of pressure. Furthermore, this offers the advantage that the form plates can be designed relatively thin, which reduces the tool costs. In particular, the force for compressing the form halves can act through the form halves and the component. This is particularly advantageous for large, flat components.

According to a further embodiment of the method, the forming tool is placed on a form half for heating and cooling or consolidation, whereby the compression pressure is applied by the forming tool during cooling. In particular, the form half can serve here as a kind of support for the forming tool, which is particularly advantageous when using form plates. Furthermore, the form half can also serve as a heat sink.

According to a further embodiment, it is provided that the forming tool for cooling or consolidation is arranged in a cavity formed by two form halves of a compression tool and the compression pressure is applied through the form halves. Accordingly, it is provided that the forming tool, in the cavity of which the layered structure is accommodated, is compressed between two form halves adapted to an outer contour of the forming tool. In this way, the final desired curved shape of the structural component can be produced very precisely. The pressing tool also serves as a heat sink for cooling the layered structure. Heating the layered composite in the cavity of the forming tool and cooling it in the cavity of a separate pressing tool accelerates the method and saves energy.

According to a further embodiment of the method, the heating of the layered structure is carried out by inductive heating of the form plates or by means of infrared radiation. Inductive heating, i.e., heating by generating alternating magnetic fields by means of an alternating electrical voltage, offers the advantage that the form plates themselves act as a heating device. This allows to realize efficient heating of the cavity. Infrared radiation can be generated advantageously with little constructional effort. Since the form plates have a low heat capacity, both heating by means of infrared radiation and inductive heating of the form plates are suitable for generating rapid temperature changes in the cavity, which accelerates both the heating and the cooling of the layered structure.

According to a further embodiment, it is provided that a vacuum is generated in the cavity of the forming tool. In particular during forming and/or for applying the compression pressure. By generating a vacuum in the cavity of the forming tool, air that may be present between or in the layers of the layered structure is extracted from the layered structure. This prevents pore formation in the structural component and thereby increases the mechanical strength of the structural component. Furthermore, the vacuum can be used at least partially to generate the compression pressure or the pressure for forming. This further accelerates the method.

As used herein, a “curved component” or “curved shape” is generally understood to mean a geometric body having at least a first surface and a second surface oriented opposite thereto, the first and second surfaces each being curved in at least two directions. In particular, this may include geometries that cannot be unwound onto a plane. For example, a curved body is understood herein to mean an at least partially dome-shaped, spherical, parabolic or bowl-shaped body.

A vertex of the curved shape of the component may be given, for example, by the centroid of one of the surfaces forming the curved shape of the body. In particular, the vertex may lie on an intersection of symmetry lines of the curved shape.

With regard to directional indications and axes, in particular to directional indications and axes relating to the course of physical structures, it is understood herein by a course of an axis, of a direction or of a structure “along” another axis, direction or structure that these, in particular the tangents resulting in a respective location of the structures, each run at an angle of less than or equal to 45 degrees, preferably less than 30 degrees and in particular preferably parallel to one another.

With respect to directional indications and axes, in particular to directional indications and axes relating to the course of physical structures, it is understood herein by a course of an axis, of a direction or of a structure “transversely” to another axis, direction or structure that these, in particular the tangents resulting in a respective location of the structures, each run at an angle of greater than or equal to 45 degrees, preferably greater than or equal to 60 degrees and in particular preferably perpendicular to one another.

Reinforcing fiber herein may generally be fibers that are thread-shaped or piecewise thread-shaped, such as carbon, glass, ceramic, aramid, boron, mineral, natural or plastic fibers or mixtures thereof.

A “melting point” or a “melting temperature” is understood herein in relation to a thermoplastic material as a temperature above which the material is in a flowable, viscous state. Above the melting temperature, a component made of thermoplastic material may be bonded by way of a material joint, in particular fused, with another component made of thermoplastic material, which is also above the melting temperature.

In the figures, the same reference signs denote identical or functionally identical components, unless otherwise stated.

FIGS.1,2and16each show a semi-finished product1for manufacturing a structural component B. As shown inFIGS.1,2and16, the semi-finished product comprises a plurality of prepreg tapes2and a plurality of connecting strands3.

FIG.3shows, by way of example, of a schematic, interrupted sectional view of a prepreg tape2. As can be seen inFIG.3, the prepreg tape2comprises several reinforcing fibers21extending in one direction or unidirectionally. The reinforcing fibers21may, for example, be in the form of fiber bundles. As further shown inFIG.3, the reinforcing fibers21are embedded in a thermoplastic matrix material20. As shown in particular inFIGS.1,2and16, the prepreg tapes2are realized as narrow, strip-shaped tapes. As shown inFIG.3, the prepreg tapes2may have a width b2, e.g., in a range between 1 mm and 15 mm, and a length l2, e.g., in a range between 0.5 m and 100 m.

FIGS.4and5show, by way of example, possible designs of the connecting strands3. In particular, the connecting strands3can each be made of a thermoplastic material or comprise a thermoplastic material. InFIG.4, an example of a reinforcing strand3is shown in cross-section, which is realized as a foil tape33consisting of thermoplastic material30. As exemplified inFIG.4, the foil tape33may be realized with a rectangular cross-section.FIG.5shows an example of a reinforcing strand3in cross-section, which is formed as a thread34consisting of thermoplastic material30. As schematically and exemplarily shown inFIG.5, the thread34may be formed of a plurality of twisted filaments35forming an approximately circular cross-section of the thread34. Optionally, the reinforcing strands3contain the same thermoplastic material used as the matrix material of the prepreg tapes.

In the semi-finished product1shown inFIG.1by way of example, the prepreg tapes2and the connecting strands3are interwoven with each other and thereby form a textile, single-layer sheet structure4. As exemplarily shown inFIG.1, the connecting strands3run transversely to the prepreg tapes2, each of the connecting strands3crossing several of the prepreg tapes2. In particular, each connecting strand3runs in sections on opposite sides of the prepreg tapes2. The prepreg tapes2run along each other and do not cross each other within the sheet structure4. InFIG.1the connecting strands3are exemplarily shown as foil tapes33.

As can be seen inFIG.1, the prepreg tapes2extend in a first direction R1and the connecting strands3extend in a second direction R2transverse to the first direction R1. In order to prevent fraying of the fabric, inFIG.1an outermost first prepreg tape2A and an outermost second prepreg tape2B, which is located opposite to the first prepreg tape, are connected by way of a material joint to the connecting strands3with respect to the second direction R2. As exemplarily shown inFIG.1, the connecting strands3are connected in a material joint to the first prepreg tape2A in the region of a first end portion31and to the second prepreg tape2A in the region of a second end portion32, which is located opposite to the first end portion31with respect to the second direction R2. The first and second prepreg tapes2A,2B define respective opposite edges of the textile sheet structure4. As exemplified inFIG.1, in particular each of the connecting strands3may be materially joined to the first and second prepreg tapes2A,2B. Generally, the connecting strands3and the prepreg tapes2are materially joined to each other in a first end region41of the sheet structure4and in a second end region42of the sheet structure4opposite to the first end region41, in each case along a respective connecting line5A,5B. InFIG.1, the connecting lines5A,5B each run along the first direction R1or along the first and second prepreg tapes2A,2B. The material joint may be created by ultrasonic welding, for example.

As further shown inFIG.1, it may be provided that the first end region31of the connecting strands3protrudes or projects beyond the first prepreg tape2A and the second end region32of the connecting strands3protrudes or projects beyond the second prepreg tape2B with respect to the second direction R2, thereby forming a projecting tab. Generally, it may be provided that the end regions31,32of the connecting strands3project beyond the connecting lines5A,5B, respectively.

In the semi-finished product1shown by way of example inFIG.2, the prepreg tapes2and the connecting strands3are interwoven with each other and thus form a textile, single-layer sheet structure4. As schematically shown inFIG.2, the connecting strands3run transversely to the prepreg tapes2, each of the connecting strands3crossing several of the prepreg tapes2. In particular, each connecting strand3runs in sections on opposite sides of the prepreg tapes2. InFIG.2, the connecting strands3are exemplarily shown as foil tapes33.

As exemplarily shown inFIG.2, the connecting strands3are each materially joined to one of the prepreg tapes2in the region of a first end portion31and in the region of a second end portion32, which is located opposite to the first end portion31with respect to the second direction R2. As a result, the connecting strands3and the prepreg tapes2are materially joined to one another in a first end region41of the sheet structure4and in a second end region42of the sheet structure4, which is located opposite to the first end region41, in each case along a respective connecting line5A,5B. InFIG.2, it is shown by way of example that the connecting lines5A,5B each run along intersections of the prepreg tapes2and the connecting strands3and obliquely to a longitudinal extent of the prepreg tapes2and the connecting strands3. The material joint can be created by ultrasonic welding, for example.

As further shown inFIG.2, it may be provided that one or more of the connecting strands3have the first end portion31projecting beyond the first connecting line5A and the second end portion32projecting beyond the second connecting line5B to form a projecting tab.

The semi-finished products3shown inFIGS.1,2allow the prepreg tapes to slide against each other due to their textile structure, which reduces the risk of wrinkles forming when the semi-finished product is deformed.

The semi-finished product1shown schematically and as an example inFIG.16has a multi-layer structure. The prepreg tapes2are arranged to form a flat, multi-axial fabric6, which comprises several superimposed layers60of prepreg tapes2. As shown schematically inFIG.16, the prepreg tapes2extend parallel to each other within a respective layer60. In adjacent layers60, the prepreg tapes2extend in different directions, e.g., transversely to each other. InFIG.16, only two plies or layers60are shown for simplicity. The individual layers60are sewn or otherwise connected, e.g. welded, knitted, entangled or linked, relative to each other at individual, preferably discrete, e.g. periodically repeating points or spots. For reasons of clarity, this is only shown at a single point inFIG.16. As shown by way of example, for connecting the individual layers60a connecting strand3can be used. In this case, the connecting strand3wraps around two intersecting prepreg tapes2at a crossing point, for example. The connecting strand3is preferably formed as a thread34.

In the semi-finished product1shown by way of example inFIG.16, the prepreg tapes2within a layer60and the layers60can slide against each other, thus reducing the risk of wrinkling during forming of the semi-finished product1.

In the following, with respect toFIGS.6to15, a method for manufacturing a curved structural component B, e.g., a structural component B as exemplarily shown inFIG.17, is explained.

FIG.17shows an example of a curved structural component B in the form of a pressure dome for an aircraft (not shown). The structural component B may in particular have a circular peripheral edge E. As shown inFIG.17, the structural component may, for example, be dome-shaped or cupola-shaped and thus be curved in several curvature directions. InFIG.17, a vertex P of the curved shape of the structural component B is drawn in, which is given by an intersection of symmetry lines S1, S2of the structural component B.

For production of the structural component B, a layered structure100is first formed which has a plurality of superimposed layers110, the layers110each containing at least one semi-finished product1, as described by way of example with reference toFIGS.1,2and16.

The layers110are realized as flatly extending mats.FIGS.6to8exemplarily show the production of a single layer110from several of the semi-finished products1shown inFIG.1. For forming of the layer110, first end sections31of the connecting strands3of a first semi-finished product11are first thermoplastically or materially joined to prepreg tapes2of a respective further semi-finished product12, e.g. by ultrasonic welding. The second end sections32of the connecting strands3of the further semi-finished product12are further thermoplastically joined to prepreg tapes2of the first semi-finished product11, for example also by ultrasonic welding. As shown inFIG.6, the first end portions31of the connecting strands3of the first semi-finished product11overlap the outermost second prepreg tape2B of the second semi-finished product12and the second end portions32of the connecting strands3of the first semi-finished product12overlap the outermost first prepreg tape2A of the first semi-finished product11.

The semi-finished product1shown inFIG.2can be connected to other such semi-finished products1in the same way.

FIG.7shows a layer110formed by several semi-finished products1as described above. The individual semi-finished products1were trimmed at opposite ends1A,1B before being joined to form a layer110. In this way, different circumferential shapes of the layers110can be produced, e.g., an approximately circular circumference, as shown by way of example inFIG.7. Optionally, the layer110formed by the semi-finished products1can also be cut further in order to set the exactly desired circumferential shape of the layer110, e.g. circular, as shown inFIG.8.

Of course, it is also conceivable to form a layer110from one respective semi-finished product1.

When using semi-finished products1formed as multiaxial fabrics, as exemplified inFIG.16, one layer110of the layered structure100contains several layers60of the semi-finished product1.

The layered structure100is generally formed by stacking or placing several layers110on top of each other, as exemplified in an exploded view inFIG.9. As shown schematically inFIG.9, the layered structure100can in particular be formed in such a way that the prepreg tapes2in different layers110extend in different directions R110. In particular, it can be provided that the prepreg tapes2of adjacent layers110of the layered structure100extend in intersecting directions R110.

As exemplified inFIG.11, the layered structure100can be formed, for example, by sequentially stacking the layers110on a flat deposition surface150a. Alternatively, the layered structure100can also be formed by stacking the layers110on a curved deposition surface150a, as shown schematically inFIG.12. In the latter case, due to the shape unstable nature of the textile sheet structure4or the multiaxial fabric6, the individual layers110are at least partially deformed in accordance with the curved support surface150a. The curved deposition surface150acan be provided, for example, by a contour surface210aof a forming tool200corresponding to the curved shape of the structural component B. The forming tool200will be explained in detail below.

After formation of the layered structure100, the layers110are optionally thermoplastically joined, e.g., by ultrasonic welding, at a joining point120, which is located, for example, in the region of the apex P of the curved shape to be produced. Generally, the joining position is selected in such a way that no or only very little displacement of the layers110relative to each other is necessary in the corresponding area during subsequent deformation. If the layers110have been placed on a curved deposition surface150a, an additional thermoplastic joining is optionally carried out at further joining points121away from the apex point P, e.g., also by ultrasonic welding.FIG.10shows a schematic top view of a layered structure100, which is formed from layers110with a circular circumference. The joint120is formed in the region of the center with respect to a radial direction. This is the region that forms the apex P of the structural component B shown as an example inFIG.17.

In a further step, forming the layered structure100into the curved shape occurs. This forming step is performed at a forming temperature that is lower than a melting point of the thermoplastic materials20,30of the semi-finished product1. The forming temperature is thus lower than a melting point of the matrix material20of the prepreg tapes2and lower than a melting point of the thermoplastic material30of the connecting strands3. As a result, the prepreg tapes2and the reinforcing strands3of the semi-finished products1contained in the layers110are in a solid aggregate state, which reduces friction or viscous adhesion between and within the layers110. In addition, during the forming process, the reinforcing fibers within the individual prepreg tapes are still supported by solid matrix material, so that the fibers are better protected from buckling even in the event of a compressive load in the longitudinal direction of the fibers due to the forming process. This prevents the formation of wrinkles, waviness or ondulations in the fiber layers during forming.

The forming can take place, for example, in a cavity205of a forming tool200, as shown schematically inFIG.13. The forming tool200comprises a form part210having a contour surface210acorresponding to the curved shape of the structural component B, and an abutment member220. The abutment member220and the form part portion210are positionable relative to each other in a closed position, as exemplified inFIG.13. In the closed position, a cavity205is formed between the contour surface210aand an inner surface220aof the abutment member220. Optionally, a seal215may be disposed between the abutment member220and the form part210to hermetically seal the cavity205in the closed position of the forming tool200.

As exemplarily shown inFIG.13, the form part210can be formed as a flatly extending first form plate211and the abutment member220can be formed as a flatly extending second form plate221. The inner surface220aof the abutment member220can be designed to correspond to the shape of the structural component B to be produced or to be complementary to the contour surface210aof the form part210.

For forming the layered structure100formed on the flat deposition surface150a(FIG.11) or to further form the already partially formed layered structure100created on the curved deposition surface150a(FIG.12), a force F is applied to the form part210and the abutment member220such that the layered structure100is pressed together between the form part210and the abutment member220. The force F may be applied, for example, by creating a vacuum in the cavity205of the forming tool200by means of an evacuation device or pump230fluidically coupled to the cavity205, as exemplified inFIG.13. This simultaneously ensures that any air pockets that may be present in the layered structure100are removed or reduced. Alternatively, or in addition thereto, the force F may also be generated by generating a magnetic field which is coupled into a magnetizable material associated with the first form plate211and/or into a magnetizable material associated with the second form plate221such that the layered structure is subjected to the compression pressure by the form plates. For example, it may be provided that the first and/or the second form plates211,221and/or a substructure, such as the form half310is formed of a magnetizable metal material and a magnetic field is generated which pulls or compresses the first and the second form plates211,221relative to each other. This is exemplified inFIG.15. Accordingly, the magnetizable material is associated with the form plates211,221in that they are themselves formed from a magnetizable material or contain a magnetizable material. The magnetizable material may also be associated with the first form plate211in that the form half310is formed from or comprises a magnetizable material. A magnet device240comprising a plurality of electric induction coils241distributed along the contour surface210aof the form part210may be provided to generate the magnetic field. Permanent magnets (not shown) may also be provided instead of electric induction coils241. In general, the magnet device240may comprise magnetic field generators arranged to generate a magnetic field. In the following, reference is made by way of example to induction coils241as magnetic field generators, whereby the features disclosed in this regard also apply in an analogous manner to other magnetic field generators. The magnet device240can be located in the lower structure of the form half310, as shown inFIG.15, or for example also on the other side, above the upper form plate221. In the latter case in particular, the magnet device240may comprise an at least partially flexible or articulated support structure which is coupled to the second form plate221so that the induction elements241are flexibly connected to one another and can adapt to the form plate221in order to transmit the pressure as uniformly as possible. In particular, the magnet device240is arranged to generate a magnetic field directed transversely to the contour surface210a.

FIG.13also shows the result of a further optional method step in which reinforcing profiles130were applied to a layer110of the layered structure100opposite to the contour surface210a. The reinforcing profiles130may, for example, have a double T-shaped cross-section, as schematically shown inFIG.13, and also comprise a thermoplastic plastic material. For example, the reinforcing profiles130may be formed from a fiber reinforced thermoplastic material. The forming tool200is then moved to the closed position, as shown inFIG.13. In this case, the abutment member220or the second form plate221is provided with recesses223through which a girder of the reinforcement profile223extends. For this purpose, the second form plate221can, for example, be formed in two parts, a first part having the recesses223in the form of slots which are open on one side and are closed by a second part. Alternatively, the stiffening profiles130can also be inserted into enveloping bulges or recesses (not shown) of the second form plate221or of the abutment member220. This improves tightness of the cavity205. The stiffening profile130in general may be pressed against the layered structure100in the cavity205by means of the abutment member220.

In a further step, the formed layered structure100is heated to a temperature that is higher than the melting point of the thermoplastic materials20,30of the semi-finished product1. This melts the thermoplastic matrix material20of the prepreg tapes2and the thermoplastic material30of the connecting strands3, whereby the individual layers110of the layered structure100fuse together and are thereby joined. The optional stiffening profiles130are thereby also fused to the uppermost layer110.

Preferably, the heating takes place in the cavity205of the forming tool200. Optionally, a vacuum is also generated in the cavity205by means of the pump205. A heating device250can be provided for heating the cavity205. InFIG.13, the heating device250is exemplarily designed as an induction heating device252, which comprises one or more induction coils253to induce an alternating magnetic field in at least one of the form plates211,221, which inductively heats the form plate211,221so that the cavity205is heated. InFIG.13, the heating device250is located on the side of the form part210as an example. In the example ofFIG.13, this preferably excites the first form plate211, so that the layered structure100heats up starting from the latter and the optional stiffening profiles130are heated predominantly in the region in which they are in contact with the layered structure100.

InFIG.15, the heating device250is exemplarily designed as an infrared radiator251, which is arranged on the side of the abutment member220. Optionally, another infrared radiator (not shown) may be arranged on the side of the form part210. In general, the infrared radiator251is arranged to generate thermal radiation in order to heat the cavity205. Of course, an induction heating device252may also be provided inFIG.15, as explained with reference toFIG.13. Furthermore, it is conceivable that the magnet device240, which is provided per se for applying the compression pressure, is also used as a heating device. For this purpose, it can be provided that a direct current flows through the induction coils241to generate the magnetic direct field for applying the compression pressure and an alternating electric current flows through the induction coils241to heat the cavity205.

Optionally, and independently of the design of the heating device250or the heat supply for heating, the forming tool200may be deposited on a form half310during heating, as exemplified inFIG.15. The form half310may have a form surface310a, which may be shaped to correspond to a rear surface210bof the form part210of the forming tool200. Advantageously, an insulating layer311is arranged between the form surface310aof the form half310and the rear surface210bof the form part210in order to avoid heating of the form half310to the greatest possible extent. This has the advantage that the form half310is exposed to smaller temperature fluctuations and consequently deforms less strongly due to thermal expansion. In particular, the form half310serves as a support for the forming tool200. This allows the form plates211,221to be made relatively thin. This speeds up the heating of the cavity205and reduces tool costs. As further shown inFIG.15, the magnet device240may be integrated into the form half310, for example.

In a further method step, consolidating of the layered structure100occurs by applying a compression pressure and cooling to a solidification temperature that is lower than the melting point of the thermoplastic materials20,30of the semi-finished product1. During consolidation, the layered structure100cools down or heat is dissipated from the layered structure. As a result, the thermoplastic material20,30solidifies and the structural component B is formed.

Consolidation can also take place in the cavity205of the forming tool200. For cooling, the heating device250is switched off and/or the forming tool205and the heating device250are physically separated from each other. As exemplarily shown inFIG.15, the consolidation or cooling can also take place on the form half310. In this case, the compression pressure can be generated by the vacuum device205and/or by the magnet device240. Generally, the compression pressure200can be applied by the forming tool200.

Alternatively, the forming tool200can be arranged in a cavity305formed by two form halves310,320of a pressing tool300for consolidation or cooling, and the compression pressure can be applied through the form half310,320, as schematically shown inFIG.14. The exemplary pressing tool300shown inFIG.14comprises a first form half310and a second form half320. The first form half310can be formed with a first form surface310aanalogous to the form half described with reference toFIG.15. The second form surface320comprises a second form surface320awhich is formed to correspond to an outer surface220bof the abutment member220. The form halves310,320are movable relative to each other between an open position and a closed position by means of a movement device330, for example in the form of a hydraulic drive.FIG.14shows the pressing tool300in a closed position or stance in which the second form surface320afaces the first form surface310aand the form halves310,320or the form surfaces310a,320aof the form halves310,320define the cavity305.

As schematically indicated by arrows A1, A2inFIG.14, the form halves310,320press the form part210and the abutment member220and thus the layered structure100, which is located in the cavity205of the forming tool200, together. Thus, the compression pressure is applied by the pressing tool300. Optionally, during consolidation or cooling, the cavity305of the pressing tool300and/or the cavity205of the forming tool200may be evacuated. Optionally, if the layered structure100is heated together with the form plates211and221outside the pressing tool, the cavity205of the forming tool200may already be evacuated before being placed in the cavity305of the pressing tool300, which facilitates the holding together of the layered structure100and the form plates211,221and removes air previously present in the layered structure100even before melting.

During consolidation or cooling of the layered structure100, the form halves310,320have a temperature that is lower than the melting temperature of the thermoplastic materials20,30. As a result, the form halves310,320form heat sinks, which accelerates the cooling of the cavity205. The cooling may be further accelerated in that the form halves310,320are formed of a metal material having a high thermal conductivity, such as aluminum or the like. Advantageously, the heat capacity of the form halves310,320is many times, for example ten times, the heat capacity of the form plates211,212of the forming tool200.

Although the present invention has been explained above with reference to example embodiments, it is not limited to these, but can be modified in a variety of ways. In particular, combinations of the above embodiments are also conceivable.

REFERENCE LIST

1semi-finished product1A,1B endings of the semi-finished product2prepreg tapes2A first prepreg tape2B second prepreg tape3connecting strands4sheet structure5A,5B connecting lines6multiaxial fabric11first semi-finished product12second semi-finished product20thermoplastic matrix material21reinforcing fibers30thermoplastic plastic material31first end section of the connecting strands32second end section of the connecting strands33foil tape34Thread35filaments41First end region of the sheet structure42second end region of the sheet structure60layers100layered structure110layer120joining point130reinforcing profiles150adeposition surface200forming tool205cavity of the forming tool210form part211first form plate210acontour surface of the form part210bback surface of the form part215seal220abutment member220ainner surface of the abutment member221second form plate230pump240magnet device250heating device251infrared radiator252induction heating device300pressing tool305cavity of the pressing tool310first form half310aform surface of the first form half320second form half320aform surface of the second form half330movement deviceB structural componentb2width of the prepreg tapesE peripheral edge of the structural componentF forcel2length of the prepreg tapesP apexR1first directionR2second directionS1, S2symmetry linesR110direction