The invention relates to a method for manufacturing an aerospace structural component, and an aerospace vehicle comprising the aerospace structural component.

Aerospace structural component of fibre reinforced materials may comprise a support struc ture which stiffens the aerospace structural component. The support structure may comprise orthogonal, non-regular or non-orthogonal stiffeners. Furthermore, grid-like or topology op- timized support structures are known to stiffen the aerospace structural components in which the stiffeners are arranged in a grid-like or topology optimized manner. The stiffeners extend along the aerospace structural component and have junctions or notches. At those junctions the fibres in stiffener direction of one of the stiffeners are at least partially not connected as described for example in DE 10 2012 210 043 Al.

Thus, there is the need for providing an improved method for manufacturing a stiffener struc- ture for an aerospace structural component and an improved stiffener structure.

The object is solved by the features of the independent claims. Advantageous embodiments are subject matter of the dependent claims and the following description. According to the invention, a method for manufacturing an aerospace structural component comprising a stiffener structure is provided, wherein the stiffener structure comprises stiffen ers extending along the aerospace structural component, and wherein the stiffeners form at least one stiffener junction, the method comprising the steps: a) Providing a shape of a stiff ener structure, the shape defining at least one stiffener shape and at least one position of a stiffener junction, b) Providing at least two unidirectional rods and at least two support ele ments, each support element being configured to position and fix at least one unidirectional rod in a mould tool element of the stiffener structure, c) Forming a base structure for the stiff ener structure by arranging the at least two unidirectional rods in the at least two support ele ments along the at least one stiffener shape, while interleaving the at least two unidirectional rods at the at least one position of the sti ffener junction, d) Arranging the base structure in at least one mould tool element of the stiffener structure, e) Closing the at least one mould tool element of the stiffener structure, f) Injecting a matrix material into the at least one mould tool element of the stiffener structure, such that the base structure is embedded in the matrix mate rial, g) Curing and/or consolidating the matrix material resulting in a stiffener structure for an aerospace structural component.

The invention provides a method for manufacturing a stiffener structure for an aerospace structural component in which unidirectional rods provide the base structure for the stiffeners. At first, the unidirectional rods are arranged such in the support element that the general shape of the stiffener structure is formed by the unidirectional rods, e.g. a grid-like shape or a topol ogy optimized shape. The support elements place the unidirectional rods in different layers, i.e. with the help of the support elements, the unidirectional rods stay in place and can be in terleaved with each other at the stiffener junctions since the unidirectional rods of different stiffeners are arranged in different layers. Therefore, the layers in which the unidirectional rods of different stiffeners are arranged in at the stiffener junctions are different. Therefore, at the stiffener junctions, the unidirectional rods are interleaved with each other. This means, that the unidirectional rods extend through the junctions without interruption independently from which stiffener at the stiffener junction they originate. Then, the resulting base structure is arranged in a mould tool element. After the mould tool element is closed, matrix material is injected into the mould tool element to connect with the base structure such that the base structure is embedded in the matrix material. Due to this connection, the unidirectional rods and the interleaved parts at the junctions of the stiffeners are embedded in the matrix material. Due to the interleaved unidirectional rods, the stability of the stiffener structure is improved such that the stiffener structure may be carried out in a light weight and cost-efficient manner.

In an example, the stiffener structure with stiffeners extending in different directions is mono- lithic . This means, that the whole stiffener structure comprises a continuous matrix material, such that the matrix material forms a single piece. This further increases the flexibility and stability of the stiffener structure since no breaking points are formed by the manufacturing process.

In an example, a unidirectional rod is cut to the length that a stiffener shall have. The stiffener extends over at least one junction in the stiffener structure, such that the unidirectional rods inside the stiffener are interleaved with further unidirectional rods of another stiffener at the junction. This further improves the stability of the stiffener structure.

In an example, the support element defines a cross-section of a stiffener. The cross-section is defined perpendicular to the longitudinal extension of the unidirectional rods, i.e. the direction from one stiffener junction to another stiffener junction along the stiffener between both stiff ener junctions. This means, that the side surfaces of the support element facing away from the stiffener form the complete cross-sectional shape of the stiffener. This provides an improved stability of the basic structure in the mould tool element and further of the stiffener structure at the position of the support element. The support element may further comprise a lumen through which the matrix material can flow during the injection process. This results in a con tinuous extension of the matrix material along the stiffener and the stiffener structure.

In another example, the support element defines only one side of the cross sectional shape and/or a partial cross section of a stiffener. In this example, the support element only has one surface which forms at least a part of the cross-sectional shape of the stiffener. This surface may be used for supporting the base structure in a mould tool element. In this example, the stiffener structure comprises a matrix material that may automatically extend along the stiff ener and the stiffener structure without being interrupted by the support element since the support element does extend over the whole cross section of the stiffener. In an example, the shape of the stiffener structure defines a grid of stiffeners with a plurality of stiffener j unctions .

In an example, the matrix material is a thermoplastic material, preferably polyetherketon- eketone (PEKK) or polyetheretherketone (PEEK).

In another example, the matrix material is a thermoset material, preferably epoxy resin or pol- yester.

In both examples mentioned above, the matrix material may comprise fibres, preferably short fibers.

In an example, the stiffener structure is a skeleton framework. In that example, the stiffener structure does not need to be attached to a supporting skin component.

According to an example, step e) comprises the sub-steps: el) Covering the at least one mould tool element of the stiffener structure with a skin component for an aerospace structural com ponent such that the skin component connects to the plurality of support elements of the base structure, and e2) Closing the at least one mould tool element of the stiffener structure with a mould tool element of the skin component.

According to an example, the skin component is pre-cured and/or pre-consolidated. This facil- itates the attachment of the skin component to the stiffener structure.

According to an example, step g) further comprises the sub-steps: gl) Co-curing and/or co- consolidating the matrix material and the skin component.

In an example, the skin component comprises a lightning strike material or further functional materials or layers e.g. films, primers or paintings.

According to an example, prior to step e) the method comprises the further steps: h) Arrang ing at least one functional element and/or at least one functional interface element in the base structure along the unidirectional rods, wherein the at least one functional element preferably is a glass fibre element, a signal line, an electrical line, or a holding plate with apertures for a glass fibre element or a signal/electrical line, and wherein the functional interface element may preferably be an interface for a glass fibre element, a signal line, or an electrical line.

The inclusion of functional elements into the base structure provi des an embedding of the functional element into the stiffener structure. This means, that for example the functional element extending along the stiffener structure are protected in the matrix material and further to not need to be installed later. Furthermore, by providing functional interfaces elements which may connect to the functional elements inside the stiffener structure, e.g. glass fibres, electrical or signal lines, the installation of such lines along the aerospace structural compo- nent from which the stiffener structure is attached to is simplified. This may provide a stiffen er structure which includes for example electrical wires and interfaces to connect external electrical wires to the electrical wires inside the stiffener structure. The same holds for the further examples of functional elements.

In an example, step h) comprises the sub-steps: hl) Arranging at least one functional interface element for the at least one functional element at the base structure and hi) Connecting the at least one functional interface element to the at least one functional element.

In an example, if the stiffener structure and the skin component are made from a thermoset material the stiffener structure is co-bonded to the skin component. In another example, a sec- ondary bonding may be performed. In yet another example, the stiffener structure is welded to the skin component using a thermoplastic film.

In an example, if the stiffener structure and the skin component are made from a thermoplast material the stiffener structure may be welded to the skin component, e.g. by induction weld- ing or ultrasonic welding, etc. In another example, the skin component may be placed in-situ on the stiffeners. In yet another example, a co-consolidation of the skin component and the stiffener may be performed.

According to an example, step f) comprises the sub-step: fO) Applying pressure to the at least one mould tool element of the stiffener component prior to injecting the matrix material. In an example, pressure is applied to the mould tool element and to a closing tool element that closes the mould tool element, the pressure sealing the closed mould tool element during the injection of the matrix material.

According to an example, the support element is an inlay plate. This provides a simple and efficient way to support the unidirectional rods in the mould and/or in the stiffener structure and to place the unidirectional rods in different layers in the stiffener structure.

According to an example, the inlay plate comprises at least one holding component compris- ing an aperture or a groove for inserting and positioning a unidirectional rod. The apertures of grooves for inserting a position in a unidirectional rod hold the unidirectional rods in place inside the base structure and therefore inside the stiffener structure.

According to an example, the holding component comprises a structural element preferably a crack stopper element, a load bearing element, and/or a skin component connector. The struc- tural element may therefore increase the functionality of the stiffener structure.

In an example, the structural element may also be an insert for connecting to brackets or for directly connecting the stiffener structure to an aerospace structural component or further components.

According to an example, prior to step d), the method further comprises the step: i) arranging a reinforcement element in the base structure such that the reinforcement element comprises an angle in the range between 0° and 90°, preferably 45°, to a direction along a unidirectional rod. The reinforcement element may provide a reinforcement of the stiffener structure along a direction being angled to the unidirectional rods and the support elements. This improves the prevention of cracks in the stiffener, parti cularly due to a reduction of thermal tension be- tween the unidirectional rods and the matrix in isotropic regions.

According to an example, the matrix material comprises short fibre material. This further in creases the stability and flexibility of the stiffener structure. According to the invention, also an aerospace structural component comprising a stiffener structure is provided, the stiffener structure being produced according to the method being described above, the stiffener structure comprising at least two stiffeners forming at least one stiffener junction, at least two unidirectional rods, at least two support elements, and a matrix material, wherein the at least two unidirectional rods extend along the at least two stiffeners and are interleaved at the at least one stiffener junction, wherein each of the at least two sup- port elements is connected to at least one unidirectional rod in the at least two stiffeners, and wherein the at least two unidirectional rods and the at least two support elements are embed- ded in the matrix material.

Due to the unidirectional rods being embedded in matrix material of the stiffener structure, this stiffener structure comprises an improved stability and flexibility. Furthermore, the stiff ener structure may be carried out in a lightweight and cost-efficient manner.

In an example, the stiffener structure may further comprise a reinforcement element, wherein the reinforcement element is arranged at an angle in the range between 0° and 90°, preferably 45°, to a direction along a unidirectional rod or a stiffener extension, respectively. The rein forcement element may provide a reinforcement of the stiffener structure along a direction being angled to the unidirectional rods and the support elements.

According to an example, the aerospace structural component comprises a skin component, wherein the stiffener structure is attached to the skin component.

The attachment of the stiffener structure to the skin component provides an aerospace struc tural component which comprises an improved stability. The stiffener structure and the skin component support each other such that the stabi lity of the skin component as well as the sta bility of the stiffener structure is improved. The result is an aerospace structural component which comprises a skin with a lightweight stiffener structure.

According to an example, the aerospace structural component is a component of an aircraft fuselage structure. According to an example, the stiffener structure and the skin component are made from a fi bre-reinforced material, preferably carbon fibre -reinforced plastic or glass fibre-reinforced material.

According to the invention, also an aerospace vehicle is provided, the aerospace vehicle com prising at least one aircraft fuselage structure and at least one stiffener structure according to the above description or at least one aerospace structural component according to the above description, wherein the at least one stiffener structure or the at least one aerospace structural component form a portion of the at least one aircraft fuselage structure.

The effects and further embodiments of an aerospace vehicle according to the present inven tion are analogous to the effects and embodiments of the description mentioned above. Thus, it is referred to the above description of the method, the stiffener structure and the aerospace structural component.

In the following the invention is described by the means of an exemplary embodiment using the attached drawing.

Fig. 1 shows a schematic drawing of an aerospace vehicle comprising an air craft fuselage structure with a stiffener element;

Fig. 2 shows a schematic drawing of an aerospace structural component com prising a stiffener of the stiffener structure;

Fig. 3 shows a schematic drawing of unidirectional rods of different length;

Fig. 4a-c show schematic drawings of different kind of support elements:

Fig. 5 shows a schematic drawing of the base structure comprising unidirec tional rods and support element;

Fig. 6a, b shows a schematic drawing of a tool element comprising the base struc ture with junctions comprising interleaved unidirectional rods; Fig. 7a-d show schematic drawings of different mould to elements which are closed;

Fig. 8 shows a schematic drawing of a tool element with applied pressure el ements; and

Fig. 9 shows a schematic flowchart of the method for manufacturing an aero space structural component.

Fig. 1 shows an aerospace vehicle 50 which comprises a fuselage that is made of several fuse lage sections 52. The fuselage section 52 comprises an aerospace structural component 19 which forms the fuselage section 52. The aerospace structural component 19 comprises a skin component 17 and a stiffener structure 10, the stiffener structure 10 comprising a plurality of stiffeners 12 which may cross at stiffener junctions 23.

Fig. 2 shows a portion of the aerospace structural component 19 comprising a stiffener 12 of the stiffener structure 10. The stiffener 12 is shown with an open end section in which unidi rectional rods 16 are visible which are embedded in the matrix material 18. The stiffener 12 is attached to the skin component 17. The unidirectional rods 16 extend along the whole length of the stiffener 12 in the stiffener structure 10 without any interruption. Even when two stiff eners 12 cross at a stiffener junction 23, the unidirectional rods 16 are not interrupted since they are interleaved as shown for example in Fig. 5 and further described below.

As shown in Fig. 3, for manufacturing the stiffener structure 10, unidirectional rods 16 may be cut in adequate lengths fitting to the length of the stiffeners 12 in which the uni directional rods 16 will be placed.

Furthermore, support elements 20, 20’ are provided, examples of support elements 20, 20’ are shown in Figs. 4a to 4c. Fig. 4a shows a support element 20, 20’ which is provided as an inlay plate. The inlay plate comprises apertures 22 as holding components for the unidirectional rods 16 which have the same cross-section as the unidirectional rods 16. Therefore, the unidi rectional rods 16 may be fed through those apertures 22. The apertures 22 hold the unidirec- tional rods 16 at a particular position with respect to the support element 20, 20’. Further more, the support element 20, 20’ arranges the unidirectional rods being arranged in the aper tures 22 in layers.

Furthermore, the support element 20, 20 being shown in Fig. 4a comprises surface elements 21 which face away from the unidirectional rods 16. Those surface elements 21 define the shape of a cross-section of a stiffener 12 in which the support element 20, 20’ will be placed.

The support element 20, 20’ may further comprise a structural element 27. The structural el ement 27 may provide further structural features to the support element 20. The structural element 27 may for example be a crack stopper element, a load bearing element, and/or a skin component connector. The crack stopper element will stop or decrease the spreading of cracks which may occur due to an overload of the stiffener structure 10. The load bearing element may for example be configured to bear a load which is connected to the stiffener structure 10 at the position of the support element 20. The skin component connector may for example provide means for connecting the stiffener structure 10 to a skin component 17 in a mechani cal manner, e.g. with a click fastener or screws etc.

Fig. 4b shows another exemplary embodiment of the support structure 20, 20’. As the support structure 20, 20’ being shown in Fig. 4a, the support structure 20, 20’ of Fig. 4b is an inlay plate. The difference to the embodiment of Fig. 4a, is that the support structure 20, 20’ of Fig. 4b comprises grooves 24 as holding components for the unidirectional rods 16. The grooves 24 comprise end sections 28 which are configured to receive unidirectional rods 16. This means, that the end sections 28 comprise the same diameter as the unidirectional rods 16. The width of the grooves 24 is smaller than the width of the unidirectional rods 16.

However, in this embodiment, the support element 20, 20’ may be made of a material which is flexible such that the unidirectional rods 16 may be pushed through the groove 24 into the end section 28. Since the groove 24 has a smaller diameter than the unidirectional rods 16 being in the end section 28, the unidirectional rods 16 will be fixed in the end section 28.

Fig. 4c shows a further exemplary embodiment of the support element 20, 20’. This embodi ment comprises only one surface element 21 which may define a portion of the outline of the cross-section of the stiffener 12. The further surfaces 26 of the support element 20, 20’ are configured such that they will be placed inside the cross-section of the stiffener 12. This means that except for the surface element 21, the surfaces 26 of the support element 20, 20’ will be placed inside the stiffener 12.

This exemplary embodiment further comprises apertures 22 for feeding through the unidirec- tional rods 16 as the embodiment of Fig. 4a.

Fig. 5 shows the base structure 25 of a stiffener structure 10 with a junction 23. The base structure 25 is mounted by placing the unidirectional rods 16 into the support elements 20,

20’, wherein the support elements 20, 20’ arrange the unidirectional rods 16 in different lay ers. The support element 20 arranges the unidirectional rods 16 in a first and a third layer, wherein the support element 20’ arranges the unidirectional rods 16 in a second and fourth layer. The first, the second, the third and the fourth layer do not cross. This means, that the unidirectional rods 16 are interleaved at the junction 23 such that all unidirectional rods 16 extend through the junction 23 without any interruption, independently of the stiffener 12 they are be arranged in.

Fig. 6a shows the base structure 25 being arranged in a mould tool element 38. The mould tool element 38 comprises a mould 30 which has the shape of the stiffener structure 10 to be produced. In this example, the support elements 20, 20’ define the shape of the cross-section of a stiffener 12 and therefore fit into the mould 30 of the mould tool element 38 such that they contact all walls of the mould 30. However, in an example, the support elements 20, 20’ may be slightly smaller than the mould 30 such that a matrix material 18 being introduced into the mould 30 may flow around the support element 22 form out a monolithic structure. Furthermore, the support element 20, 20 may comprise a lumen through which the matrix material 18 may flow through the support element 20, 20’.

Furthermore, Fig. 6a shows an exemplary embodiment, in which support elements 20 support two unidirectional rods 16 and support element 20’ supports a single unidirectional rod 16.

The layers in which the support element 20 supports each of the two unidirectional rods 16 are different than the layer in which support element 20’ supports the single unidirectional rod 16. Moreover, a reinforcement element 29 is shown. The reinforcement element 29 is integrated into the base structure 25. Furthermore, the reinforcement element 29 comprises an angle in the range between 0° and 90° to a direction along a unidirectional rod 16. The reinforcement element 29 may provide a reinforcement of the stiffener structure 10 along a direction being angled to the unidirectional rods 16 and the support elements 20.

Although the example of Fig. 6a shows a mould 30 for three stiffeners 12 having two junc- tions 23, the mould 30 may comprise any number of stiffeners 12 and any number of junc- tions 23. Furthermore, the example of Fig. 6a shows a grid-like shape with orthogonal angles at the junctions 23 and regular distances between the stiffeners 12. In another exemplary em bodiment, the mould 30 may comprise non-ortho gonal angles between the stiffeners 12 and further nonregular distances between the stiffeners 12. Furthermore, the mould 30 may also provide a shape for a stiffener structure 10 which is topology optimized for particular compo nents.

Fig. 6b shows a base structure 25 which comprises unidirectional rods 16 being arranged in support elements 20. The unidirectional rods 16 are interleaved at the junction 23.

The base structure 25 further comprises functional elements 31 and functional interface ele ments 33. Functional elements 31 may e.g. be glass fibres, electrical lines or signal lines. The functional elements 31 extend along a portion of the base structure 25 which forms a stiffener 12 to be produced. At the junctions 23, the functional elements 31 are interleaved with the unidirectional rods 16. The functional elements 31 may further be interleaved with further functional elements 31 at the junction 23, the further functional elements 31 extending along another portion of the base structure 25 of a further stiffener 12 to be produced.

Functional interface elements 33 may be interfaces for the functional elements 31 for connect ing the functional elements 31 which are arranged inside the stiffener structure 10 to external elements, like external glass fibres, external electrical wires, or external signal lines.

The functional interface elements 33 are supported by holding elements 35 which fix the posi tion of the functional interface elements 33 in the mould 30 of the stiffener structure 10. Due to the fixed position of the functional interface elements 33 in the mould 30, the functional interface elements 33 have a determined position in the stiffener structure 10 to be produced.

The inclusion of the functional elements 31 and the functional interface elements 33 provides an improved stiffener structure 10 which comprises an integrated functional infrastructure, wherein the functional infrastructure may for example comprise an integrated electrical wire network, an integrated glass fibre network, and/or an integrated signal wire network.

Fig. 7a shows a male mould tool element 38 for producing the stiffener structure 12, the male mould tool element 38 comprising a channel 36 which is connected to the mould 30 in a fluid communicating manner. The channel 36 is configured to provide a matrix material 18 to the mould 30. The opening end of the channel 36 into the mould 30 may for example have a point-like shape, a sequence of point-like openings, a linear shape along the mould 30, or comprise a sequence of linear openings.

The base structure 25 with the support elements 20, 20’ and the unidirectional rods 16 is ar ranged in the mould 30. A closing tool element 14 for the male mould tool element 38 closes the mould 30. The closing tool element 14 may for example be a rigid caul plate and/or an upper tool cover. The mould 30 and the portion of the closing tool element 14 which is ar ranged above the mould 30 define the cross-sectional shape of the stiffener 12 and the stiffen er structure 10 to be produced.

Fig. 7b shows a female mould tool element 34 for producing the stiffener structure 12. The female mould tool element 34 comprises a channel 36 which is connected to the mould 30 in a fluid communicating manner which is configured to provide a matrix material 18 to the mould 30.

The base structure 25 with the support elements 20, 20’ and the unidirectional rods 16 is ar ranged on the closing tool element 14 which is arranged on a carrying structure 32. The fe male mould tool element 34 covers the portion of the base structure 25. That portion may be a stiffener 12 of the stiffener structure 10 to be produced. In an exemplary embodiment a single female mould tool element 34 may cover the complete base structure 25 such that the base structure 25 is enclosed between the single female mould tool element 34 and the closing tool element 14.

In another exemplary embodiment, a plurality of female mould to elements 34 may cover the complete base structure 25. Thus, the base structure 25 may be enclosed between the closing tool element 14 and female mould tool elements 34.

The exemplary embodiment of Fig. 7c shows a male mould tool element 38 comprising the base structure 25 wherein a skin component 17 covers the mould tool element and the base structure 25. In this embodiment, the closing tool element 14 covers the skin component 17 such that the skin component 17 and base structure 25 are in a sandwich position between the closing tool element 14 and the male mould tool element 38.

The exemplary embodiment of Fig. 7d shows the same configuration with a female mould tool element 34. In this embodiment, the skin component 17 covers the closing tool element 14. The base structure 25 is arranged on the skin component 17. The female mould tool ele- ment 34 or the plurality of female mould tool elements 34, respectively, then covers the base structure 25.

Fig. 8 shows an exemplary embodiment in which the stiffener structure 10 is connected to a skin component 17 during the manufacture of the stiffener structure 10. If the stiffener struc- ture 10 shall not be connected to a skin component 17, then the skin component 17 will not be present in the assembly of Fig. 8.

For the manufacturing of the stiffener structure 10, pressure is applied to the mould tool ele- ment 38 and the closing tool element 14. A first pressure device component 39 is arranged on the closing tool element 14. The first pressure device component 39 comprises one end which has a shape that is complementary to the closing tool element 14 such that the first pressure device component 39 fits on the closing tool element 14.

In an analogous manner, a second pressure device component 40 may be arranged below the male mould tool element 38. The second pressure device component 40 is configured such that a matrix material 18 may flow through the channel 36 into the mould 30. The matrix ma terial 18 may be provided by a line 44 from a reservoir (not shown).

The first pressure device component 39 and the second pressure device component 40 sand- wich the male mould tool element 38 and the closing tool element 14. Pressure being indicat ed by arrows 46 is provided on the male mould tool element 38 and the closing tool element 14 such that the mould 30 is sealed. Then, matrix material 18 may be introduced through the channel 36 into the mould 30.

After the injection of the matrix material 18 into the mould 30, the matrix material 18 may be cured or consolidated depending on which matrix material 18 is used. In an example, the ma trix material 18 is a thermoplastic material, preferably polyetherketoneketone (PEKK) or pol- yetheretherketone (PEEK). In another example, the matrix material 18 is a thermoset material, preferably epoxy resin or polyester.

The skin component 17 may for example be pre-cured or pre-consolidated such that the ma trix material 18 may connect to the skin component 17 during the curing/ consolidation.

Furthermore, the skin component 17 may comprise a lightning strike material or further func tional materials or layers which may for example be films, primers and/or paintings.

It should be noted, that the embodiments according to Fig. 7a and 7b may provide a stiffener structure 10 which may be self-supporting, i.e. the stiffener structure 10 to be produced may be a skeleton framework. In this case, the stiffener structure 10 may be a standalone structure which does not comprise an attachment to the skin component 17. However, if the stiffener structure 10 does not have self-supporting features, the stiffener structure 10 may be attached to the skin component 17 to provide an aerospace structural component 19 after the manufac turing of the stiffener structure 10.

In an example, if the stiffener structure 10 and the skin component 17 are made from a ther moset material the stiffener structure 10 is co-bonded to the skin component 17. In another example, a secondary bonding may be performed. In yet another example, the stiffener struc ture 10 is welded to the skin component 17 using a thermoplastic film. In an example, if the stiffener structure 10 and the skin component 17 are made from a ther- moplast material the stiffener structure 10 may be welded to the skin component 17, e.g. by induction welding or ultrasonic welding, etc. In another example, the skin component 17 may be placed in-situ on the stiffener structure 10. In yet another example, a co-consolidation of the skin component 17 and the stiffener structure 10 may be performed.

Fig. 9 shows a flowchart of the method 100 for manufacturing an aerospace structural compo- nent 19 comprising a stiffener structure 10. In a first step a), the shape of the stiffener struc- ture may be provided 101, the shape defining at least one stiffener shape and at least one posi- tion of the stiffener junction. The stiffener shape provi des the direction in which the stiffener extends and start or end at a stiffener junction or may extend through a stiffener junction.

The shape of the stiffener structure may be provided by choosing the topology of the stiffener structure. That shape may in an example be grid-like with an orthogonal or non-orthogonal shape, being a regular or non-regular grid. In another example, that shape may have a topolo- gy optimized shape.

Then, in the step b), at least two unidirectional rods and at least two support elements may be provided 102. The support elements may be configured to position and fix at least one unidi- rectional rod in a mould tool element of the stiffener structure. The mould tool element of the stiffener structure comprises the shape of the stiffener structure in the mould.

In a step c), the base structure for the stiffener structure may be formed 103. The base struc- ture may be formed by arranging the at least two unidirectional rods in the at least two support elements. The unidirectional rods may be arranged along the at least one stiffener shape. At the stiffener junctions, the unidirectional rods may be interleaved such that each unidirectional rod may be part of a different stiffener at the stiffener junction. Both uni directional rod will extend through the stiffener junctions without interruption.

Furthermore, in step h), at least one functional element may be arranged 104 in the base struc- ture along the unidirectional rods. This may provide additional functional features for the stiffener structure. The functional elements may for example be glass fibre elements, signal lines, electrical lines, or holding plates for holding the glass fibre elements and/or the signal lines or the electrical lines. Moreover, functional interface elements may be provided into the base structure. The functional interface elements may connect the functional elements with external functional components. The functional interface element may for example be an in terface for a glass fibre element, a signal line, or an electrical line.

In step i), a reinforcement element is arranged 113 in the base structure such that the rein forcement element comprises an angle in the range between 0° and 90°, preferably 45°, to a direction along a unidirectional rod. The reinforcement element may provide a reinforcement of the stiffener structure along a direction being angled to the unidirectional rods and the sup port elements. This improves the prevention of cracks in the stiffener, particularly due to a reduction of therm al tension be-tween the unidirectional rods and the matrix in isotropic re gions.

The base structure may be arranged 105 in the at least one mould tool element of the stiffener structure in step d). Arranging the base structure in the mould tool element may be performed by placing the unidirectional rods with the support elements into the mould tool element. Since the base structure compri ses the shape of the stiffener structure and the mould tool ele ment also comprises the shape of the sti ffener structure, the base structure may be easily ar ranged into the mould tool element.

In a step e), the at least one mould to element may be closed 106. For closing the at least one mould tool element, a closing tool element may be used. The mould tool element may be a male mould tool element or a female mould tool element. If the stiffener structure shall be connected to the skin component during the manufacturing process, before closing the mould tool element, a skin component may be arranged between the mould tool element and the closing element, such that the skin component connects to the base structure. In that case, the skin component may cover 109 the mould tool element in a step el). Then, the closing tool element may close 110 the mould tool element in a step e2).

In a step fO), pressure may be applied 111 to the mould tool element and the closing tool ele ment. This will seal the mould of the mould tool element to prevent the matrix material to flow out of the mould during the injection. Then, in a step f) matrix material may be injected 107 into the at least one mould tool element of the stiffener structure. The injection of the matrix material into the mould tool element within that the base structure into the matrix material. The combination of the matrix material and the base structure will form the stiffener structure. The matrix material may be a fibre reinforced material wherein the fibres may for example be short fibres. This will improve the structural integrity of the stiffener structure.

In a step g) the matrix material may be cured and/or consolidated 108. The matrix material will assume the shape of the mould comprising the embedded uni directional rods and support elements. This will result in a stiffener structure. In case that the skin component and the stiff ener structure shall be manufactured together, in a step gl), the matrix material and the skin component may be co-cured and/or co-consolidated 1 12. This will result in an aerospace structural component comprising a skin component and a stiffener structure.