METHOD FOR PRODUCING A STRUCTURAL COMPONENT

Abstract

A method is specified for producing a structural component, in particular for an aircraft, ground vehicle, or watercraft, or for a rotor blade of a wind turbine, in which method an arrangement of fibers and plastic material is laid in a mold and subjected to an increased pressure and an increased temperature, wherein a mold is used which comprises at least one recess in which a reinforcing element is arranged. The object is to be able to cost-effectively produce a structural component of this type. For this purpose, it is provided that the reinforcing element is laid in the recess together with a core, wherein a differential volume between the recess and core, at least in a predetermined region, is chosen such that it is smaller than a segment of the reinforcing element arranged in said region by a predetermined amount.

Claims

1. A method for producing a structural component, in particular for an aircraft, ground vehicle, or watercraft, or for a rotor blade of a wind turbine, in which method an arrangement of fibers and plastic material is laid in a mold and subjected to an increased pressure and an increased temperature, wherein a mold is used which comprises at least one recess in which a reinforcing element is arranged, characterized in that the reinforcing element is laid in the recess together with a core, wherein a differential volume between the recess and core, at least in a predetermined region, is chosen such that it is smaller than a segment of the reinforcing element arranged in said region by a predetermined amount and the pressure is applied by a membrane which delimits an oil pressure chamber.

2. The method according to claim 1, wherein the differential volume comprises at least one displacement region outside of the predetermined segment.

3. The method according to claim 2, wherein at least one displacement region is arranged on a side of the reinforcing element that faces away from the arrangement of fibers and plastic material.

4. The method according to claim 2, wherein the displacement region is connected to the predetermined segment via a throttle point.

5. The method according to claim 1, wherein the reinforcing element has a height, and the recess has a depth that is smaller than the height.

6. The method according to claim 1, wherein a reinforcing element is used which comprises a web protruding away from the arrangement of fibers and plastic material, and a distance between the core and a wall of the recess in the region of the web is smaller than a thickness of the web.

7. The method according to claim 1, wherein a reinforcing element is used which comprises at least a first leg that bears against the arrangement of fibers and plastic material, wherein the recess has a first subregion for accommodating the first leg and the first subregion has a depth that is smaller than a thickness of the first leg.

8. The method according to claim 7, wherein the first subregion comprises a first extension in a direction parallel to the arrangement of fibers and plastic material, which extension extends a length of the first subregion beyond the length of the first leg, wherein the first extension has a depth that is smaller than the depth of the first subregion outside of the extension.

9. The method according to claim 7, wherein a reinforcing element is used which comprises a second leg at an end facing away from the first leg, wherein the recess comprises a second subregion for accommodating the second leg and the second subregion has a depth that is smaller than a thickness of the second leg.

10. The method according to claim 9, wherein the second subregion comprises a second extension in a direction parallel to the arrangement of fibers and plastic material, which extension extends a length of the second subregion beyond the length of the second leg, wherein the second extension has a depth that is smaller than a depth of the second subregion outside of the extension.

Description

[0022] The invention is described below on the basis of a preferred exemplary embodiment in connection with the drawing. Here:

[0023] The sole FIGURE shows a schematic illustration of a mold for producing a structural component.

[0024] A mold 1 for producing a merely schematically illustrated structural component 2 comprises a lower die 3 and an upper die 4. The lower die 3 comprises a recess 5.

[0025] To produce the structural component, an arrangement 6 of fibers and plastic material is laid into the lower die 3. The arrangement 6 is preferably formed by what are referred to as prepregs, in which a plastic material has already been applied to fibers. Carbon fibers or other high-tensile fibers can preferably be used as fibers. A thermoplastic material, in particular polyamide, for example PA6, is preferably used as plastic material.

[0026] The fibers of the prepregs can be arranged unidirectionally, that is, such that they all run in the same direction. It is also possible, however, to use prepregs in which multiple fiber layers are present, the fibers of which run in different directions. It is also possible to use unidirectional prepregs, that is, prepregs in which all fibers run in the same direction, and to arrange multiple prepregs of this type in different directions in the lower die 3. The fiber direction is determined by the subsequently desired load-bearing capacity of the structural component 2. For example, a fuselage or a cabin of an aircraft, ground vehicle, or watercraft can be produced from the structural component 2.

[0027] The FIGURE shows a mold 1 in which the structural component obtains an essentially flat formation. However, the mold 1 can also be embodied such that shapes which are at least slightly rounded can be produced, for example for an engine cover. The mold 1 can also be embodied such that shell-like structural components 2 can be produced.

[0028] The aforementioned prepregs can be laid in the mold 1 by hand or by tape layers. The thickness of the structural component 2 can be set by using more or fewer prepregs.

[0029] In addition, a reinforcing element 7 is laid in the recess, which reinforcing element 7 is in the present case embodied in a Z shape and comprises a web 8 which projects essentially perpendicularly from the arrangement 6 of fibers and plastic material. The reinforcing element 7 comprises a first leg 9 that bears against the arrangement 6 of fibers and plastic material and a second leg 10 at the other end of the reinforcing element 7.

[0030] The reinforcing element 7 is laid in the recess 5 together with a core 11.

[0031] The recess 5 comprises a first subregion 12 for accommodating the first leg 9. The first subregion 12 comprises a first extension 13 that extends a length 11 of the first subregion beyond the length of the first leg 9. However, the first extension 13 has a depth that is smaller than a depth t1 of the first subregion 12 outside of the extension 13.

[0032] The recess 5 additionally comprises a second subregion 14 for accommodating the second leg 10. The second subregion 14 comprises an extension 15 that extends a length 12 of the second subregion 14 beyond the length of the second leg 10. The second extension 15 has a depth that is smaller than a depth t2 of the second subregion 14 outside of the extension.

[0033] The core 11 has a volume that is smaller than the volume of the recess 5. Accordingly, when the core 11 has been laid in the recess 5, a differential volume or a cavity results. Theoretically, this differential volume should be identical to the volume of the reinforcing element 7.

[0034] However, one departs from such a sizing and purposely chooses the differential volume or the cavity for the reinforcing element such that it is somewhat smaller than the volume of the reinforcing element 7. It is thus possible to maintain a constant pressure on the structural component 2 being formed from the arrangement 6 of fibers and plastic material and from the reinforcing element 7 during the heating, that is, during the application of an increased temperature, and above all also during the cooling, that is, during the decrease in temperature. Due to manufacturing tolerances, that is, tolerances in the reinforcing element 7, and also due to different thermal expansions between the working materials and the material of the lower die 3 and the core 11, this pressure can, in an unfavorable case, be lost or decrease so markedly that the desired quality of the structural component 2 can no longer be guaranteed.

[0035] The reinforcing element can also be embodied with the aforementioned thermoplastic material, such as polyamide. When an increased temperature and an increased pressure are applied to the arrangement 6 of fibers and plastic material via the upper die 4, which is indicated by arrows 16, then the increased temperature also propagates to the reinforcing element and causes the semi-finished product of the reinforcing element to then become liquid or flowable. Even if the reinforcing element 7 only attains a viscous or syrup-like state, it is necessary to keep the reinforcing element 7 under the pressure described above. This is achieved in that the volume of the reinforcing element 7 is, at least in segments, smaller than the corresponding differential volume between the core 11 and the lower die 3. As a result, the semi-finished product of the reinforcing element 7 is slightly “squashed” and the “squashed” semi-finished product is under a hydrostatic pressure. This has the advantage that a uniform pressure distribution can be achieved in a simple manner. The pressure can decrease slightly due to differing thermal expansion coefficients, but it does not drop to zero. The structural component 2 being produced is thus under constant pressure.

[0036] The segment-wise reduction of the differential volume can be achieved, for example, in that a distance dl between the core 11 and the opposing wall 17 of the recess is chosen such that it is somewhat smaller than the corresponding thickness of the web 8 in this region. Alternatively or additionally, it can be provided that the depth t1 of the first recess 12 is chosen such that it is somewhat smaller than the thickness of the first leg 9. Furthermore, it can be alternatively or additionally provided that the depth t2 of the second recess 14 is chosen such that it is somewhat smaller than the corresponding thickness of the second leg 10.

[0037] When material from the legs 9, 10 is displaced, this displaced material can flow into the first extension 13 and the second extension 15, respectively. Because the first extension 13 and the second extension 15 have a smaller cross section than the corresponding subregions 12, 14, however, a certain throttling effect occurs in this case, so that an adequate pressure can still be maintained. The throttling effect can be achieved not only by a reduction in the depth of the extensions 13, 15, but also by another cross section reduction.

[0038] Material that is displaced from the region of the web can likewise be displaced into a displacement region, which is formed, for example, by one of the extensions 13, 15 or by both extensions 13, 15. However, this material must then pass by the legs 9, 10, which in turn is only possible against an increased resistance.

[0039] The application of an increased pressure and an increased temperature preferably occurs via an oil which is introduced in an oil pressure chamber in the upper die 4. The oil pressure chamber is separated from the arrangement 6 of fibers and plastic material by a membrane that is not illustrated in greater detail. The oil can, for example, have a temperature in the range of 350° C. to 410° C. when the increased temperature is desired. After the pressing, that is, after the application of pressure, a decrease in temperature to approximately 30° C. can occur.

[0040] The membrane can be relatively smooth on the side facing the arrangement 6, that is, it can have an R.sub.z value of less than 0.1 μm, so that an extremely smooth surface of the structural component 2 results.

[0041] The pressure curve and the temperature curve during the application to the arrangement of fibers and plastic material in the mold 1 should rise in as parallel a manner as possible, and should fall again in as parallel a manner as possible.