Method for producing a structural element consisting of a fibre-composite hollow profile and load-introducing element, and structural element

Abstract

A method for producing a structural element (14) that comprises a hollow profile (1) made of continuous fibre-reinforced plastics material and a load-application element (15) is based on providing a hollow profile (1) on a liner (2), wherein the hollow profile (1) is impregnated by heating it to a temperature that is equal to or above the softening temperature of the matrix material (9) and below its cross-linking temperature, removing the liner (2) in an inner region (17) of the hollow profile (1), where the load-application element (15) is arranged, and consolidating and functionalising the structural element (14) by heating it to a temperature that is equal to or above the cross-linking temperature of the matrix material (9) and by applying a radially inwardly acting pressure to the structural element (14). The hollow profile (1) is moulded onto the load-application element (15) in a form-fitting manner.

Claims

1. A method for producing a structural element (14) comprising a hollow profile (1) made of continuous fibre-reinforced plastics material (3) that comprises a thermosetting matrix material (9) that has a softening temperature that is below a cross-linking temperature of the thermosetting matrix material, and at least one load-application element (15), wherein the method comprises at least the following method steps: a. providing a cut-to-size hollow profile (1) made of plastics material (3) that is reinforced by continuous fibres, on a liner (2), which is part of the structural element, wherein the liner (2) forms an inner lateral surface of the hollow profile (1), and wherein the hollow profile (1) is impregnated by heating said hollow profile to a temperature that is equal to or above the softening temperature of the matrix material (9) and below the cross-linking temperature of the matrix material (9); b. removing the liner (2) in an inner region (17) of the hollow profile (1) that is intended for load application; c. arranging a load-application element (15) on the inner region (17) of the hollow profile (1) that is intended for load application; d. consolidating and functionalising the structural element (14) by heating the structural element (14) to a temperature that is equal to or above the cross-linking temperature of the matrix material (9) and applying a radially inwardly acting pressure to the structural element (14), wherein the hollow profile (1) is moulded onto the load-application element (15) in a form-fitting manner.

2. The method according to claim 1, characterised in that providing the hollow profile (1) according to method step a. comprises at least the following method steps: i. manufacturing a hollow profile (1) made of plastics material (3) that is reinforced by continuous fibres, on a liner (2), the liner (2) forming the inner lateral surface of the hollow profile (1); ii. heating the hollow profile (1) to a temperature that is equal to or above the softening temperature of the matrix material (9) and below the cross-linking temperature of the matrix material (9); iii. cooling the hollow profile (1) to a temperature below the softening temperature of the matrix material (9); iv. cutting the hollow profile (1) to size and removing it from a production line (5).

3. The method according to claim 2, characterised in that the hollow profile (1) is manufactured by laying continuous fibres or continuous-fibre semifinished products, pre-impregnated with the matrix material (9), on the liner (2).

4. The method according to claim 2, characterised in that the hollow profile (1) is manufactured in a continuous manner, the matrix material (9) being fed to the continuous fibres (8) laid on the liner (2).

5. The method according to claim 4, characterised in that the matrix material (9) is fed to the continuous fibres (8) via an application of powdered resin or via an injection of resin.

6. The method according to claim 2, characterised in that the hollow profile (1) is encased in a thermally contractible covering (4) following one of method steps i. or ii. or iii. or iv.

7. The method according to claim 6, characterised in that the process of encasing the hollow profile (1) in a thermally contractible covering (4) is carried out following method step i., method step ii. subsequently being carried out such that the hollow profile (1) is heated to a temperature that is equal to or above the softening temperature of the matrix material (9) and below the cross-linking temperature of the matrix material (9), wherein a first thermal contraction of the covering (4) takes place until said covering rests on the outer lateral surface of the hollow profile (1).

8. The method according to claim 1, characterised in that the hollow profile (1) is encased in a thermally contractible covering (4) following one of method steps a. or b. or c.

9. The method according to claim 8, characterised in that the covering (4) of the hollow profile (1) comprises a shrink ring.

10. The method according to claim 8, characterised in that the covering (4) of the hollow profile (1) is applied to an outer lateral surface of the hollow profile (1) via a spiralising machine (12).

11. The method according to claim 8, characterised in that the radially inwardly acting pressure on the structural element (14) for the consolidation thereof is applied in a region not intended for load application via thermal contraction of the covering (4).

12. The method according claim 8, characterised in that the radially inwardly acting pressure on the structural element (14) for the consolidation and functionalisation thereof is applied in a region (17) intended for load application via thermal contraction of the covering (4).

13. The method according to claim 8, characterised in that the covering (4) of the hollow profile (1) comprises a shrink film.

14. The method according to claim 8, characterised in that the covering (4) of the hollow profile (1) comprises heat shrink tubing.

15. The method according to claim 1, characterised in that the radially inwardly acting pressure on the structural element (14) for the consolidation and functionalisation thereof is applied in a region (17) intended for load application via a pressure diaphragm (18).

16. The method according to claim 1, characterised in that the matrix material (9) is a thermosetting 1-component system comprising an epoxy resin and a secondary amine as the curing agent.

17. The method according to claim 1, characterised in that, in order to manufacture the hollow profile (1), continuous fibres (8) are laid on the liner (2) in a continuous manner via a creel (6).

18. The method according to claim 1, characterised in that the liner (2) is comprised of metal or plastics material, the melting temperature of the metal or the softening temperature of the plastics material being higher than the cross-linking temperature of the matrix material (9).

19. The method according to claim 1, characterised in that the liner (2) is removed from an inner lateral surface of the hollow profile (1), in an inner region (17) of the hollow profile (1) that is intended for load application, via boring or gouging.

20. The method according to claim 1, characterised in that the load-application element (15) is arranged in the inner region (17) of the hollow profile (1) intended for the load application in such a way that the load-application element (15) and the liner (2) of the hollow profile (1) form a continuous surface to which pressure can be applied.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in the following by way of embodiments and with reference to a plurality of drawings, but without being restricted thereto. In the drawings:

(2) FIG. 1 is a longitudinal section through a hollow profile produced by means of method steps according to the invention.

(3) FIG. 2 shows a detail of a process chain for continuous manufacture of a hollow profile.

(4) FIG. 3 shows a structural element according to the invention.

(5) FIGS. 4a to 4d illustrate embodiments for applying a consolidation and functionalisation pressure in the load-application region of a structural element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) FIG. 1 is a longitudinal section through a hollow profile 1 that is processed, as a semifinished product, in further method steps in order to produce a structural element. The hollow profile 1 is preferably in the shape of a hollow cylinder. The supporting, inner lateral surface is formed by a thin metal or plastics liner 2. A layer of continuous fibre-reinforced plastics material 3 is located on the liner 2. The reinforcing fibres extend in the longitudinal direction, for axially reinforcing the profile 1, and in any non-axial directions for off-axis reinforcement of the profile 1.

(7) The reinforcing-fibre laminate 3 comprises a thermosetting B-stage matrix consisting of an epoxy resin and a secondary amine, preferably imidazole or an imidazole derivative. In this case, B-stage means that the softening temperature of the epoxy resin is below the cross-linking temperature of the epoxy resin and curing agent. The outer lateral surface of the hollow profile 1 forms a shrink ring 4 that is shrunk precisely onto the reinforcing-fibre laminate layer 3 by means of a first heating process. The hollow profile 1 is processed to form the structural element 14 according to the invention in subsequent method steps.

(8) FIG. 2 shows a detail of a production line 5 for continuous manufacture of a hollow profile 1. The process chain is shown from the liner 2 being fed, through various steps of machining the hollow profile blank and a shrink ring 4 being wrapped around said blank, up to the hollow profile blank being impregnated using a heated tool 13. The profile 1 subsequently being drawn off, and the cutting to size and removal from the production line 5 are not illustrated in the process chain shown.

(9) Continuous fibres or rovings 8 are drawn off the coils 7 of a creel 6, in the machine direction 51, and laid on the liner 2 in the axial direction. Subsequently, the matrix material 9 that is solid at room temperature is applied in powder form to the blank, i.e. in this case the liner 2 coated with axial reinforcing fibres. In the following step, the blank passes through a braiding wheel 10, by means of which the braided rovings 8 are laid on the axial reinforcing fibres so as to extend in any desired direction. Off-axis reinforcement of the hollow profile 1 is thus achieved. The blank is then sprinkled with powdered matrix material 9. Further off-axis reinforcement is carried out using a spiralising machine 11 from which rovings 8 are laid on the blank so as to be at a specified angle relative to the profile axis. The blank is then again sprinkled with powdered matrix material 9.

(10) In a following method step, the blank is encased, in a continuous manner, in a shrink ring 4 by means of a shrink ring spiralising machine 12.

(11) The impregnation, i.e. the fibre infiltration by means of the matrix material, takes place in a subsequent method step by means of the blank being drawn through a heated tool 13. In this case, the blank is heated to a temperature that is equal to or above the softening temperature of the resin of the matrix material 9 but below the cross-linking temperature of the matrix material 9.

(12) As a result of the action of heat, the shrink ring 4 shrinks precisely onto the outer lateral surface of the hollow profile blank and thus functions as an outer contour-stabilising element during the impregnation.

(13) For further processing (not shown here) of the hollow profile manufactured constantly and continuously, as described, the hollow profile blank is first cooled to a temperature that is below the softening temperature of the matrix material 9. The cooling may be carried out entirely passively by means of the dwell time of the hollow profile blank in the production line 5 following the heated tool 13 being at least equal to or longer than the cooling time. The cooling can also be actively accelerated, for example by spraying the blank with cooled air. After the blank has been cooled, it is cut to size to the intended length and removed from the production line 5.

(14) FIG. 3 is a longitudinal section of a structural element 14 according to the invention, consisting of a continuous fibre-reinforced hollow profile 1 and a load-application element 15. The load-application element 15 may comprise undercuts 16. In the load-application region 17, the liner 2 of the hollow profile 1 was removed, preferably by means of boring or gouging, prior to functionalising the hollow profile 1 in order to form the structural element 14. In the load-application region 17, a form-fitting connection exists between the reinforcing-fibre laminate 3 and the load-application element 15.

(15) FIG. 4 shows variants a to d of the method step of consolidating and functionalising the structural element 14, consisting of the hollow profile 1 and the load-application element 15, in the load-application region 17. The aim of the functionalisation is to mould the hollow profile 1 onto the load-application element 15 in the load-application region 17 in order to establish a form-fitting connection. For this purpose, the structural element 14 has to be heated to the cross-linking, and thus the curing, temperature of the matrix of the reinforcing-fibre laminate 3, and furthermore a radially inwardly oriented consolidation and forming pressure has to be applied to the hollow profile 1 in the load-application region 17.

(16) In all the method steps, the load-application element 15 functions as the inner die. The selection of the method variants must be adjusted, in each individual case, to the geometry of the structural element 14 and is for example dependent on the thickness of the reinforcing-fibre laminate 3, the shape of the undercuts 16, and the fibre orientation.

(17) FIG. 4a shows the application of a consolidation and forming pressure in the load-application region 17 by means of thermal contraction of a shrink ring 4. The thermal contraction of the shrink ring 4 can likewise exert pressure for consolidating the hollow profile 1 as part of the structural element 14 in the region not intended for the load application.

(18) FIG. 4b shows the application of a radially inwardly oriented consolidation and forming pressure 21 in the load-application region 17 by means of a pressure diaphragm 18. In these method variants that are based on external high-pressure forming, the pressure is transferred from a forming tool 19 to the pressure diaphragm 18 by means of a transfer medium 20, such that the hollow profile 1 is moulded onto the load-application element 15, functioning as the inner die, in the load-application region 17.

(19) FIG. 4c shows the application of a radially inwardly oriented consolidation and forming pressure 21 in the load-application region 17 by means of pressing using a divided die 22. In this case, the contour of the die has to correspond to the contour of the load-application element 15, including the undercuts 16 thereof.

(20) FIG. 4d shows the application of a radially inwardly oriented consolidation and forming pressure 21 in the load-application region 17 by means of pressing using a divided die 22 over a sleeve 23 to be formed. Compared with the method variant shown in FIG. 4c, using the sleeve 23 prevents parts of the hollow profile 1 from jamming in the parting planes of the divided die 22.

LIST OF REFERENCE NUMERALS

(21) 1 hollow profile 2 liner 3 reinforcing-fibre laminate 4 heat shrink tubing 5 production line 51 machine direction 6 creel 7 coil 8 roving 9 matrix material 10 braiding wheel 11 spiralising machine 12 shrink ring spiralising machine 13 heated tool 14 structural element 15 load-application element 16 undercut of the load-application element 17 load-application region 18 pressure diaphragm 19 forming tool 20 pressure transfer medium 21 pressure direction 22 divided die 23 sleeve