METHOD FOR JOINING FIBER-PLASTIC COMPOSITE COMPOSITES AND STABILIZING DEVICE

Description

[0001] The invention relates to a method for joining fiber-reinforced plastic (FRP) components, in particular aircraft components, and to a method for producing an aircraft part, for example a control surface element.

[0002] Furthermore, the invention relates to a stabilizing device which, in particular during a joining process, can be inserted into a recess of a fiber-plastic composite (FRP) component for the purpose of maintaining its shape and / or providing its shape, and which comprises: a preferably elongated base body with a cavity that can be filled with a fluid, an opening that is preferably arranged on the base body, and a movable pressing element for transmitting an outwardly directed compressive force to the FKV component, wherein the pressing element has at least partially a higher flexibility than the base body, wherein the compressive force can be generated by filling the cavity with the fluid, wherein the pressing element has a bag which is arranged within the cavity and which can be filled with the fluid to generate the compressive force, wherein the bag is designed to protrude at least partially through the opening in the filled state in order to generate the compressive force on a boundary surface of the FKV component which delimits the recess.

[0003] Furthermore, the invention relates to a tool with such a stabilizing device.

[0004] In the aviation industry, components made of fiber-reinforced plastic (FRP) are widely used due to their high stability and low weight. In the manufacture of aircraft parts, such as a control surface element, several components made of FRP material, also referred to below as FRP components, are often joined together by joining, for example by welding. During the welding of FRP components, however, the heat and pressure applied can lead to undesirable deformation of the FRP components. This can cause problems, particularly in reinforcing structures with hollow profiles, because if there is no counterpressure during the welding process, these can collapse and thus lose their shape and thus their reinforcing effect.

[0005] It is known from the prior art to insert an inflatable or liquid-fillable bladder made of silicone rubber into cavities of components made of FRP material in order to strengthen them during a welding process. One such method is known from US 5,710,414 A. The disadvantage is that the flexible bladder exerts pressure on the surrounding component evenly in all directions. The component can therefore be deformed in an undesirable way because the bladder also exerts compressive forces on areas that do not experience any counterpressure from the welding. If heat from the welding process reaches these areas, they are softened and deformed by the pressurized bladder. Furthermore, due to its flexibility, the bladder is difficult to place precisely in narrow cavities. In addition, it can tear and melt and burst in hot spots.

[0006] Devices and methods for processing and stabilizing components during production are known from US 2019 / 0275747 A1, EP 3 711 933 A1, US 2017 / 0036310 A1, US 5,366,684 A and US 2005 / 0035115 A1.

[0007] EP 1 070 661 A2 discloses an auxiliary device that can be used in joining FRP components. The auxiliary device has several bladders that can be inflated using a fluid to press against the FRP components.

[0008] WO 2019 / 094428 A2 relates to the manufacture of a rotor blade for a wind turbine. During production, an internal bladder is used to mold thermoplastic material.

[0009] In light of these statements, it is therefore an object of the present invention to at least partially alleviate the disadvantages of the prior art. Preferably, the object of the invention is to provide a method and a stabilizing device of the type mentioned above, which enable targeted and shape-preserving stabilization of an FRP component during joining, in particular during a welding process. The stabilizing device should be easily and precisely insertable into cavities.

[0010] This object is achieved by a method according to claim 1. According to the invention, the method comprises the following steps: i) providing a first and a second FRP component, wherein the first FRP component has a recess;ii) introducing a stabilizing device into the recess of the first FRP component, wherein the stabilizing device has a preferably elongated base body with a cavity, an opening, and a pressing element, which pressing element has at least partially a higher flexibility than the base body, wherein the pressing element has a bag which is arranged within the cavity and which can be filled with a fluid to generate an outwardly directed compressive force, wherein the bag, in the filled state, is designed to protrude at least partially through the opening in order to generate the compressive force on a boundary surface of the first FRP component which delimits the recess, wherein the pressing element further has a thermally insulating element which is arranged on the outside of the base body, such that the compressive force can be transferred to the first FRP component via the thermally insulating element;iii) filling the cavity with the fluid so that the pressing element is pressed against the boundary surface of the first FRP component that defines the recess; iv) connecting the first FRP component to the second FRP component at a connection point by joining, in particular by welding, wherein the pressing element exerts an outwardly directed compressive force on the connection point to stabilize the shape of the recess.

[0011] Advantageously, the pressing element can be used to exert a compressive force in a targeted manner on the connection point, which is a weld point, for example, and thus to maintain the shape of the recess and thus of the first FRP component during joining, in particular welding. Viewed from the base body, the pressing element is pressed outwards against the boundary surface on the inside of the first FRP component and thus against the connection point, while the shape of the base body is essentially retained. This is due to the fact that the pressing element is more flexible than the base body, i.e. has less rigidity. The base body therefore essentially retains its shape, while the pressing element exerts the compressive force on the boundary surface on the inside of the first FRP component, on the outside of which the connection point is located.The compressive force is directed outwards (viewed from a center of the stabilizing device). The stabilizing device thus exerts a compressive force on the first FRP component. Due to the greater flexibility, the pressing element can be deflected relative to the base body. Preferably, the pressing element is elastically deformable. Advantageously, this also compensates for tolerances in the event of component defects. The flexibility of the pressing element can be achieved in particular in that the pressing element at least partially comprises a material that is more flexible, i.e. less stiff, than the material of the base body. It can also be provided that the pressing element and the base body are made of the same material or a similarly stiff material, but that the pressing element has a joint or has a thinner wall thickness than the base body.By using a correspondingly thin wall thickness, sufficient flexibility of the pressure element can be achieved even with inherently hard and rigid materials. While the pressure element is pressed against the boundary surface on the first FRP component, the shape of the base body changes only slightly at most. In contrast, in the prior art, such as in US Pat. No. 5,710,414 A, the compressive force of the stabilizing device is distributed evenly in all directions, so that the hollow profile can be deformed in an undesirable manner. The first and second FRP components consist at least partially, preferably entirely, of a fiber-plastic composite material. In this disclosure, a fiber-plastic composite material (FRP material) refers to a material consisting of reinforcing fibers and a plastic matrix.Examples of FRP materials from which the FRP components can be partially or completely made are carbon fiber reinforced plastic (CFRP) or glass fiber reinforced plastic (GFRP). The first FRP component and the second FRP component can, for example, be components of a control surface element to be produced for an aircraft, for example a spoiler or a droop panel. According to the invention, the stabilizing device is inserted into a recess in the first FRP component. The first FRP component can have a reinforcing structure with one or more hollow profiles, wherein the recess is formed by the one or more of the hollow profiles. The hollow profiles and thus the recess can be undercut or not undercut. The recess can, for example, be a hole, a cavity, or a curvature of the first FRP component.Since reinforcement structures are often used in aircraft components (see, for example, WO 2016 / 023056 A1 as an example of a reinforcement structure), it is advantageous if the base body has an elongated shape in order to support entire regions of such structures during joining and to facilitate insertion. According to the invention, the base body has a cavity that can be filled with a liquid and / or gaseous fluid. The cavity is preferably located within the base body. The fluid can be, for example, air, water, or oil. Furthermore, the stabilizing device has an opening that is preferably arranged on the base body. When the stabilizing device is inserted, the fluid can transmit the compressive force through the opening to the boundary surface and thus to the connection point. The opening connects the cavity to the exterior of the stabilizing device and, in one embodiment, can be freely, i.e.not be covered. Alternatively, the opening can be covered, for example by a preferably flexible wall structure or by a film element. The only important thing is that the pressure force from the fluid can be transmitted outwards through the opening. By filling the cavity with the fluid, the pressing element is pressed against the boundary surface on the inside of the first FRP component and thus against the connection point, since the pressing element has a higher degree of flexibility than the base body. The shape of the base body is thus essentially retained, as already explained, while the pressing element is at least partially deformed and pressed against the boundary surface. The material from which the pressing element is at least partially made can, for example, be a film material or a rubber-like material.While the pressure element presses against the boundary surface and thus against the connection point, the first FRP component and the second FRP component can be welded together. Advantageously, the compressive force generated by the stabilizing device on the connection point prevents a change in the shape of the recess or of the first FRP component during joining. The first and second FRP components are preferably joined by welding. For example, an induction welding process, an ultrasonic welding process, a resistance welding process, a conduction welding process, or a laser welding process is used to weld the first FRP component to the second FRP component. If a welding process is used for joining, the connection point can also be referred to as a weld point.The compressive force generated by the stabilizing device acts as counterpressure for the pressure applied during welding and counteracts the simultaneously softening material, which softens due to the effects of temperature. The counterpressure stabilizes or consolidates the shape of the recess and thus of the first FRP component. In a preferred embodiment, the compressive force of the pressing element is directed essentially only in one spatial direction. In most applications, it is particularly advantageous if, in the intended use state of the stabilizing device, the compressive force acts essentially only upwards, relative to an inertial system. This supports the recess of the first FRP component from below. Thus, the second FRP component can be welded to the first FRP component from above without changing the shape of the first FRP component.

[0012] The present method is therefore suitable for stabilizing an FRP component during a joining process for connecting two FRP components. Joining can be carried out, for example, by welding, screwing, riveting, or gluing. It is provided that the pressing element has a bag arranged within the cavity. The bag can be filled with the fluid to generate the compressive force, wherein the bag, when filled, passes at least partially through the opening and generates the compressive force on the connection point. The bag can be made of a rubber material or a plastic material, for example. Preferably, the bag extends substantially over the entire length of the cavity. In a particularly preferred embodiment, the bag can be a tubular film that is closed at one end and connected to a fluid supply, in particular a gas supply, at the other end.When the bag is filled with the fluid (filled state), it is forced through the opening due to its lower flexibility compared to the base body. When filled, the bag preferably essentially fills the entire cavity of the base body. The bag is thus so flexible that, when filled, it essentially conforms to the shape of the cavity.

[0013] A particularly easy-to-design and thus advantageous variant of the invention results when a gas, especially air, is used as the fluid. The gas can be filled into the cavity or bag using a compressor or pump. As already mentioned, however, the fluid can also be a liquid, for example, oil or water.

[0014] To stabilize the recess and thus the first FRP component, it is advantageous if the fluid used to generate the compressive force is pressurized, and the pressure is between 1.0 bar and 8.0 bar, preferably between 1.5 bar and 5.0 bar, in particular between 2.0 bar and 3.0 bar. Such a fluid pressure can effectively counteract the forces during joining, particularly welding. At higher compressive forces, the recess and thus the first FRP component could be disadvantageously deformed by the stabilizing device. Compressive forces that are too low (for example, below 1 bar, depending on the component) would have an insufficient stabilizing effect.

[0015] Particularly when the FRP components are joined by welding, it is advantageous if the thermal insulation element, in particular a thermal insulation plate, is pressed against the boundary surface during joining, in particular welding. The thermal insulation element prevents the heat introduced for welding from being dissipated too quickly. This can facilitate the welding process. It also prevents the heat introduced in the first FRP component from being distributed away from the weld point, which contributes to further stabilizing the first FRP component. The thermal insulation element can be arranged loosely on the outside of the base body, for example. Alternatively, the thermal insulation element can be connected to the bag described above. In a further embodiment, the thermal insulation element can be connected to the base body, for example via a film element or a rubber element.The thermal insulation element is preferably made of ceramic or a polymer material, a fiber reinforced composite material, or fiber cement, or a mixture of these materials. In a particularly preferred embodiment, the thermal insulation element is a particularly flat thermal insulation panel.

[0016] In one embodiment of the invention, it is provided that the first FRP component has a reinforcement structure and the recess is at least partially formed by a section of the reinforcement structure. Reinforcement structures are used in aircraft parts, in particular in control surface elements such as spoilers or droop panels, etc. In this embodiment, the recess is formed by a hollow profile of the reinforcement structure. A reinforcement structure can, for example, have one or more connecting webs, viewed in cross-section. The reinforcement structure can, for example, connect two surface elements to one another. The connecting web(s) can form a structural pattern, thereby forming a hollow profile. The structural pattern can, for example, be triangular, trapezoidal, rectangular, or wave-shaped. The structural pattern can be present individually or repeated.In an example structural pattern, for example, two essentially vertical connecting webs are connected to each other via a horizontal connecting web. This structural pattern can be present individually, thus forming a single hollow profile. However, the structural pattern can also be repeated, forming multiple hollow profiles.

[0017] In order to counteract any unintentional displacement of the FRP components, it is advantageous if at least the first FRP component is fixed during joining.

[0018] In one embodiment, it can be provided that the connection point is cooled or heated by the fluid before joining, during joining and / or after joining, preferably with the fluid being circulated. Cooling or heating a connection point is particularly advantageous in a welding process for joining. The fluid can be liquid or gaseous. In a particularly preferred embodiment, it can be provided that the fluid is circulated between a temperature control device, in particular a cooling and / or heating device, and the cavity. As a result, thermal energy is dissipated from the first FRP component or supplied to it. The temperature control device can, for example, keep the fluid within a temperature range during circulation.

[0019] The invention further relates to a method for producing an aircraft part, for example a control surface element, in particular a spoiler, comprising the steps: i) Arranging a first surface element made of FRP material on a table; ii) Placing an intermediate element with a reinforcement structure made of FRP material on the first surface element; iii) Connecting the intermediate element to the first surface element by joining, in particular welding, at at least one connection point to obtain a first FRP component; iv) Placing a second FRP component in the form of a second surface element on the first FRP component; v) Connecting the first FRP component to the second FRP component by applying the method for joining fiber-plastic composite (FRP) components in one of the embodiment variants described above.

[0020] The control surface element can be, for example, a spoiler or a droop panel. The first surface element can be, for example, an upper or lower outer skin of a spoiler. The second surface element can be the other of the upper or lower outer skins, corresponding to the first surface element. When connecting the first surface element to the intermediate element, a stabilizing device is typically not yet necessary because the intermediate element rests on the first surface element and the connection points in step iii) are typically not located at points with underlying recesses, so no stabilization by the stabilizing device is necessary. If necessary, a stabilizing device can also be used in this step, and the joining method described above can be applied.Typically, the connection points, in particular weld points, in step iii) are located at locations where the intermediate element rests directly on the first surface element, without any recesses such as cavities underneath or in between. A change in shape due to sinking of recesses therefore typically does not occur in step iii). The first surface element only needs to be supported from below, for example by the table. Any stable base can be referred to as a table. In step v), however, at least one connection point, in particular at least one weld point, is located at a location where there is a recess underneath, which is at least partially formed by the reinforcing structure of the first FRP component.In order to prevent a change in the shape of the recess and thus of the first FRP component, the stabilizing device is inserted into the recess and the joining process described above is applied.

[0021] After joining, in particular after welding, the first and second FRP components, the stabilizing device can be removed from the recess, preferably after the fluid has been at least partially drained from the cavity. The stabilizing device can be reused.

[0022] The object mentioned at the outset is also achieved by a stabilizing device according to claim 10. The stabilizing device can be inserted into a recess of a fiber-plastic composite (FRP) component, particularly during a joining process, in particular during a welding process, for the purpose of maintaining and / or shaping the shape of the component. The stabilizing device according to the invention comprises: a preferably elongated base body with a cavity that can be filled with a fluid, an opening that is preferably arranged on the base body, and a movable pressing element for transmitting an outwardly directed compressive force to the FRP component, wherein the pressing element has at least partially greater flexibility than the base body, wherein the compressive force can be generated by filling the cavity with the fluid, wherein the pressing element has a bag,which is arranged within the cavity and which can be filled with the fluid to generate the pressure force, wherein the bag is designed to protrude at least partially through the opening in the filled state in order to generate the pressure force on a boundary surface of the FKV component that defines the recess, characterized in that the pressing element further comprises a heat-insulating element that is arranged on the outside of the base body, so that the pressure force can be transferred via the heat-insulating element to the adjacent FKV component.

[0023] With regard to the advantages and the design of the features of the stabilizing device, reference is also made to the explanations in connection with the method described above. The cavity in the base body can be filled with a fluid, for example a gas, in particular air, or a liquid, in particular water or oil. If, as described above and below, the pressing element has a bag arranged in the cavity, this is filled with the fluid. The base body is preferably elongated. The pressing element is movable relative to the base body. By filling the cavity (or optionally the bag in the cavity) with the fluid, the pressing element, in the inserted state in the recess, is pressed against the boundary surface on the inside of the first FRP component. The shape of the base body is essentially retained. The pressure force of the fluid is transferred to the FRP component via the opening.Due to the greater flexibility of the pressure element, it can be deflected relative to the base body. The pressure element is preferably elastically deformable. The flexibility of the pressure element can be achieved, for example, by the pressure element at least partially comprising a material that is more flexible, i.e. less stiff, than the material of the base body. It can also be provided that the pressure element and the base body are made of the same material or a similarly stiff material, but the pressure element has a joint or has a thinner wall thickness than the base body. A geometric solution is also possible, for example by providing local reinforcements or weakenings in the material. By using a correspondingly thin wall thickness, sufficient flexibility of the pressure element can be achieved even with inherently hard and stiff materials.An example of this is aluminum: A base body made of aluminum with a thick wall thickness allows the base body to be essentially undeformed under the pressure of the fluid. However, a thin aluminum plate used as a pressure element can be deformed accordingly.

[0024] It is provided that the pressing element has a bag which is arranged within the cavity and which can be filled with the fluid to generate the compressive force, wherein the bag is designed to protrude at least partially through the opening in the filled state in order to generate the compressive force on the component. The opening can be free so that the bag can pass through unhindered. Alternatively, the opening can also be covered, for example by a film element, a rubber element or a flexible wall structure. The bag can be made of a plastic material or a rubber material. In a particularly preferred embodiment, the bag can be a tubular film which is closed at one end and connected to a fluid supply, in particular a gas supply, at the other end. When filled, the bag essentially fills the entire cavity and essentially adapts to its shape.

[0025] If joining is performed by welding the FRP components, it is advantageous, as already explained in connection with the method according to the invention, for the pressing element to have a thermal insulation element arranged on the outside of the base body, so that the compressive force can be transferred to the adjacent component via the thermal insulation element. The thermal insulation element is preferably designed as a flat, i.e., non-curved, plate. The thermal insulation element is preferably a thermal insulation plate.

[0026] In a preferred embodiment, the thermal insulation element consists of a ceramic material, a polymer material, an FKV material, a concrete material, a cement material, fiber concrete or a mixture of the aforementioned materials.

[0027] In one embodiment of the invention, the base body consists of a polymer material, an FKV material, a metal or a mixture of the aforementioned materials.

[0028] To stabilize recesses formed by hollow profiles, it is advantageous if the base body has a substantially U-shaped or substantially C-shaped cross-section. The cross-sectional shape of the base body can have a longitudinal web, from whose opposite longitudinal edges a first transverse web and a second transverse web protrude. The first transverse web forms a first angle with the longitudinal web. The second transverse web forms a second angle with the longitudinal web. The first and second angles can, for example, be substantially 90°. The first and / or second angles can also be less than 90°, so that the cross-sectional shape of the base body tapers towards the free ends of the transverse webs. It is also possible for the first and / or second angles to be greater than 90°. The transverse webs can also have projections facing one another at the ends facing away from the longitudinal web. One transverse web can be higher than the other transverse web.Preferably, the cross-sectional shape of the base body is substantially uniform over its entire length. The opening of the stabilizing device on the base body can be formed by an open end of the C or U. If crossbars with projections are provided, the opening can be formed between the projections. The projections can also be designed such that they taper in cross-section toward the opening. This allows the compressive force to be transferred more effectively to the connection point, especially if a bag is provided.

[0029] Since reinforcing structures in aircraft components such as spoilers often taper towards one side, it is advantageous if the cross-sectional shape of the base body also tapers towards the opening. If the cross-section is essentially C- or U-shaped and the opening is formed by the open end of the C or U, the cross-sectional shape of the base body tapers towards the open end of the C or U.

[0030] The stabilizing device can be a component of a tool for joining fiber-reinforced plastic (FRP) components. Such a tool can comprise: a table, preferably with a holding device for fixing an FRP component; a joining device, in particular a welding device; a stabilizing device in one of the embodiments described above.

[0031] The joining device can be used to join, in particular weld, FRP materials together. In particular, the welding device can be designed as an induction welding device. Alternatively, the welding device can be, for example, an ultrasonic welding device, a resistance welding device, a conduction welding device, or a laser welding device. The joining device can be arranged on a robot, in particular on a robot arm.

[0032] This disclosure also relates to the combination of the tool as described above with the first and second FRP components as described above.

[0033] In the following, the invention is explained in more detail with reference to figures, to which, however, it is not intended to be limited.

[0034] They show: Fig. 1 a stabilizing device according to the invention, which is partially inserted into a recess of a first FKV component; Fig. 2 a stabilizing device according to the invention in a recess of a first FKV component in cross section; Fig. 3 a base body of a stabilizing device according to the invention; Fig. 4 a stabilizing device according to the invention with a heat insulating element; Fig. 5 a sequence of the method according to the invention for joining two FRP components; Fig. 6 a sequence of the method according to the invention for producing an aircraft part; and Fig. 7 a section of an aircraft part during production.

[0035] Fig. 1 shows a stabilizing device 1 according to the invention, which, for illustrative purposes, is only partially inserted into a recess 2 of a first FRP component 3 (FRP: fiber-plastic composite). A second FRP component 4 is attached to the first FRP component 3, but not yet connected to it. Naturally, the first 3 and the second FRP component 4 can also represent larger components with multiple recesses 2, for example, components for aircraft parts 20 such as control surface elements. An example of a control surface element is a spoiler 21 (see Fig. 7 ).

[0036] The first FKV component 3 has, in the illustration shown, a reinforcement structure 5 with a hollow profile 7 in the shape of an inverted U, which is connected to a first surface element 6. The recess 2 is formed by the hollow profile 7. In Fig. 1 only a single recess 2 is shown; however, an FKV component can of course have several recesses 2 and thus a larger extent than in Fig. 1 shown (see for example Fig. 7 ). For example, the reinforcement structure 5 can have a structural pattern that is continued in the direction of arrow 41, so that several similar hollow profiles 7 with recesses 2 are present. The second FRP component 4 is formed by a second surface element 40 in the illustration shown.

[0037] In Fig. 1 the second FKV component 4 is attached to the first FKV component 3. The second FKV component 4 is to be joined to the first FKV component 3 at a connection point 8. In the embodiments of the invention described below, the joining takes place by welding, for example induction welding or ultrasonic welding. The connection point 8 can therefore also be referred to as weld point 8. In principle, however, the joining can also be carried out by screwing, gluing or riveting. The weld point 8 is indicated by the dashed line and is located on the outside of the recess 2 at the connection point between the first FKV component 3 and the second FKV component 4. The weld point 8 is elongated and oriented approximately parallel to the recess 2.

[0038] To prevent the hollow profile 7, and thus also the recess 2, from being deformed during welding due to the heat and pressure applied, according to the invention, the stabilizing device 1 is inserted into the recess 2 in the direction of arrow 9 prior to welding, preferably essentially completely. In the embodiment shown, the stabilizing device 1 has an elongated base body 10, in particular made of metal, which encloses a cavity 11 inside. In the embodiment shown, the stabilizing device 1 has essentially the same cross-sectional shape as the recess 2. The size of the stabilizing device 1 is adapted to the size of the recess 2.

[0039] Fig. 2 shows the stabilizing device 1 in the recess 2 in cross section. As in Fig. 2 As can be seen, the base body 10 has a substantially C-shaped cross-section that tapers towards the top. In the embodiment shown, the cross-sectional shape of the base body 10 has a longitudinal web 44, on whose opposite longitudinal edges 45a, b a first transverse web 46a and a second transverse web 46b protrude. The first transverse web 46a forms a first angle α 1 with the longitudinal web 44. The second transverse web 46b forms a second angle α 2 with the longitudinal web 44. The angles α 1, 2 can be 90°, for example. At least one of the angles α 1, 2 (or both) can also be less than 90°, so that the cross-sectional shape of the base body 10 tapers towards the top, as in the embodiment shown. It is also possible for at least one of the angles α 1, α 2 (or both) to be greater than 90°. As shown, the transverse webs 46a, b can also have mutually facing projections 47a, b at the ends facing away from the longitudinal web.One transverse web 46 of the C-profile of the stabilizing device 1 can be higher than the other transverse web 46 of the C-profile. Preferably, the cross-sectional shape of the base body 10 is substantially the same over its entire length. On the upper side of the base body 10, the stabilizing device 1 also has an opening 12 between the transverse webs 46, in particular between their projections 47a, b, which connects the cavity 11 to the environment. The projections 47a, b can taper towards the opening 12. This allows the bag 14, which will be described in more detail later, to pass more easily through the opening 12. The stabilizing device 1 further has a pressing element 13. In the embodiment shown, the pressing element 13 is made at least partially of a material that has greater flexibility, i.e., lower rigidity, than the material of the base body 10.In the embodiment shown, the pressing element 13 comprises a bag 14 located inside the cavity 11 and made of a plastic material. Furthermore, the pressing element 13 has a ceramic heat-insulating element 15 in the form of a heat-insulating plate 16, which is arranged on the outside of the base body 10 above the opening 12 and can rest against the projections 47a, b. The heat-insulating element 15 protects the bag 14 from high heat input and also ensures that heat is not transferred from the welding point 8 to other locations during welding, thus preventing the heat required for welding from being lost. By filling the bag 14 with a fluid, preferably a gas, in particular air, the bag 14 expands in the cavity 11 and exerts a compressive force F via the heat insulating element 15 on a boundary surface 17 delimiting the recess 2 on the inside of the first FKV component 3.Due to the greater rigidity and thus lesser flexibility of the base body 10 compared to the bag 14, the shape of the base body 10 remains essentially the same when the pressing element 13 exerts the compressive force F on the boundary surface 17. When filled, the bag 14 protrudes at least partially through the opening 12. The compressive force F is thus transmitted via the opening 12. As a result, the compressive force F is directed onto the weld point 8 and its immediate surroundings, while the base body 10 hardly deforms and exerts no or only a slight compressive force on the boundary surface 17. To generate the compressive force F, the fluid is pressurized between 1.0 and 8.0 bar. If the pressure is too high (for example 15 bar), there is a risk that the recess would be deformed by the stabilizing device 1.If the pressure were too low (for example, below 1 bar), the pressure force F would be too low and the recess 2 could be deformed during welding. The opening 12 can additionally be covered with a foil element, a rubber element, or a flexible wall element (not shown).

[0040] When the pressure element 13 exerts a compressive force F on the boundary surface 17 of the recess 2, the welding process can begin to join the first FRP component 3 to the second FRP component 4. The compressive force F prevents the recess 2 or the hollow profile 7 from deforming during welding, for example, by collapsing. The stabilizing device 1 thus provides a counterpressure that counteracts the pressure exerted during welding, preventing the hollow profile 7 from collapsing.

[0041] Fig. 3 shows an oblique view of the elongated base body 10 of the stabilizing device. It can be seen that the cross-section of the base body 10 is essentially C-shaped and tapers towards the opening 12. The corners 18 of the inner surface of the base body 10 are rounded to prevent damage to the bag 14 when filled. The base body 10 can further have an insertion opening 42 on at least one of the two end faces. The bag 14 can be inserted into the cavity 11 and supplied with fluid through one of these insertion openings 42.

[0042] Fig. 4 shows the base body 10 of the stabilizing device 1 together with the heat insulating element 15. It can be seen that the heat insulating element 15 also has an elongated shape and is essentially trapezoidal in cross section, wherein the legs 19 of the trapezoid have a curved or rounded shape.

[0043] Fig. 5 depicts the sequence of the method according to the invention for joining, in particular welding, FRP components 3, 4. In step 101, the first 3 and the second FRP component 4 are prepared. In step 102, the stabilizing device 1 is inserted into a recess 2 of the first FRP component 3. In step 103, the cavity 11 or the bag 14 in the cavity is filled with the fluid, so that the pressing element 13 exerts a compressive force F on the connection point 8. In step 104, the first FRP component 3 is connected, in particular welded, to the second FRP component 4. The stabilizing device can then be removed from the recess, preferably after the fluid has been at least partially drained from the cavity 11. The stabilizing device is reusable.

[0044] The method can also be used in a method for producing an aircraft part 20, for example a control surface element such as a spoiler 21 (see also Fig. 7 ). In Fig. 6 The individual steps are shown here. In step 201, a first surface element 6 is arranged on a table 22. The table 22 can have a holding device 23 for fixing FKV components 3, 4. In step 202, an intermediate element 43 with a reinforcement structure 5 is placed on the first surface element 6 and then, in step 203, is joined, in particular welded, to it at a connection point 8a, preferably a weld point 8a. This results in a first FKV component 3. In a step 204, a second surface element 40, which forms a second FKV component 4, is placed on the first FKV component 3. Subsequently, in step 205, the second FKV component 4 is joined to the first FKV component 3 at point 8, wherein the method according to Fig. 5 is applied.

[0045] Fig. 7shows a section of an aircraft part 20 in the form of a spoiler 21 during production. Here, two stabilizing devices 1 are at least partially inserted into recesses 2 of a first FRP component 3. The first FRP component 3 has a reinforcing structure 5 as an intermediate element 43 and a first surface element 6. The reinforcing structure 5 forms hollow profiles 7. In the illustrated reinforcing structure 5, two essentially vertical connecting webs 48a are connected via a essentially horizontal connecting web 48b. This structural pattern continues and forms the reinforcing structure 5. A second FRP component 4 in the form of a second surface element 40 is placed on the first FRP component 3 and is to be connected to it by welding at the weld points 8. The stabilizing devices 1 stabilize the recesses 2 during welding as explained above.The spoiler 21 is manufactured using a tool 24. The tool 24 comprises a table 22, preferably with a holding device 23, at least one stabilizing device 1, and a joining device 25, preferably a welding device. This can be attached, for example, to an end effector of a robot (not shown).

Claims

1. A method for joining fibre-reinforced plastic (FRP) components (3, 4), in particular aircraft FRP components, comprising the following steps: i) Providing a first (3) and a second (4) FRP component, the first FRP component (3) having a recess (2); ii) Inserting a stabilising device (1) into the recess (2) of the first FRP component (3), wherein the stabilising device (1) has a preferably elongated base body (10) with a cavity (11), an opening (12) and a pressing element (13), which pressing element (13) has, at least partially, a higher flexibility than the base body(10), wherein the pressing element (13) comprises a bag (14), which is arranged inside the cavity (11) and which can be filled with a fluid to generate an outwardly directed pressure force (F), wherein the bag (14), when in filled state, is arranged, to at least partially protrude through the opening (12), in order to generate the pressure force (F) onto a delimiting surface (17) of the first FRP component (3), which is delimiting the recess (2), wherein the pressing element (13) further comprises a heat-insulating element (15), which is arranged on the outside of the base body (10), so that the pressure force (F) can be transmitted via the heat-insulating element (15) to the first FRP component (3); iii) Filling the cavity (11) with a fluid such that the pressing element (13) is pressed against a delimiting surface (17) of the first FRP component (3), which delimits the recess (2) ; iv) Connecting the first FRP component (3) to the second FRP component (4) by joining at a connecting point (8), in particular by welding, wherein the pressure force (F), which is directed towards the outside, is exerted onto the connecting point (8) by means of the pressing element (13) for stabilising the shape of the recess (2).

2. The method according to claim 1, wherein the bag (14) is filled with the fluid in order to generate the pressure force (F), wherein the bag (14) passes at least partially through the opening (12) in the filled state and generates the pressure force (F) on the connecting point (8).

3. The method according to claim 1 or 2, wherein a gas, in particular air, is used as fluid.

4. The method according to any one of claims 1 to 3, wherein the fluid for generating the pressure force (F) is pressurised and the pressure is between 1.0 bar and 8.0 bar, preferably between 1.5 bar and 5.0 bar, in particular between 2.0 bar and 3.0 bar.

5. The method according to any one of claims 1 to 4, wherein the pressing element (13) has a heat-insulating element (15), in particular a heat-insulating plate (16), which is pressed against the delimiting surface (17) of the first FRP component (3) during the joining.

6. The method according to any one of claims 1 to 5, wherein the first FRP component (3) has a reinforcing structure (5) and the recess (2) is formed at least partially by a section of the reinforcing structure (5).

7. The method according to any one of claims 1 to 6, wherein at least the first FRP component (3) is fixed during the joining.

8. The method according to any one of claims 1 to 7, wherein the connecting point (8) is cooled or heated by the fluid before joining, during joining, and / or after joining, preferably wherein the fluid is circulated.

9. A method for producing an aircraft part (20), for example a control surface element, in particular a spoiler (21), comprising the steps of: i) Arranging a first surface element (6) of FRP material on a table (22); ii) Placing an intermediate element (43) having a reinforcing structure (5) of FRP material on the first surface element (6); iii) Connecting the intermediate element (43) to the first surface element (6) by joining, in particular welding, at at least one connecting point (8a), in order to obtain a first FRP component (3); iv) Placing a second FRP component (4) in the form of a second surface element (40) on the first FRP component (3); v) Connecting the first FRP component (3) to the second FRP component (4) by applying the method according to any one of claims 1 to 8.

10. A stabilising device (1) which can be inserted in particular during a joining process for the shape-retaining and / or shaping support of a fibre-reinforced plastic (FRP) component (3) into a recess (2) thereof, comprising: a preferably elongated base body (10) with an internal cavity (11), which can be filled with a fluid, an opening (12), which is preferably arranged on the base body (10), and a movable pressing element (13) for transmitting a pressure force (F), which is directed towards the outside, to the FRP component (3), wherein the pressing element (13) has at least partially a higher flexibility than the base body (10), wherein the pressure force (F) can be generated by filling the cavity (11) with the fluid, wherein the pressing element (13) comprises a bag (14), which is arranged inside the cavity (11) and which can be filled with a fluid to generate a pressure force (F), wherein the bag (14), when in filled state, is arranged, to at least partially protrude through the opening (12), in order to generate the pressure force (F) onto a delimiting surface (17) of the FRP component (3), which is delimiting the recess (2), characterised in that, the pressing element (13) further comprises a heat-insulating element (15), which is arranged on the outside of the base body (10), so that the pressure force (F) can be transmitted via the heat-insulating element (15) to the first FRP component (3).

11. The stabilising device (1) according to claim 10, wherein the heat-insulating element (15) is a heat-insulating plate (16) and the heat-insulating element (15) consists preferably of a ceramic material, a polymer material, an FRP material, a concrete material, a cement material, fibre-reinforced concrete or a mixture of said materials.

12. The stabilising device (1) according to claim 10 or 11, wherein the base body (10) is made of a polymer material, an FRP material, a metal or a mixture of said materials.

13. The stabilising device (1) according to any one of claims 10 to 12, wherein the base body (10) is substantially U-shaped or substantially C-shaped in cross section.

14. The stabilising device (1) according to any one of claims 10 to 13, wherein the cross-sectional shape of the base body (10) tapers toward the opening (12).

15. A tool (24) for joining fibre-reinforced plastic (FRP) components (3, 4), comprising: - a table (22), preferably having a holding device for fixing an FRP component (3, 4); - a joining device (25), in particular a welding device; - a stabilising device (1) according to any one of claims 10 to 14.