METHOD FOR MANUFACTURING A COMPOSITE MATERIAL STRUCTURE USING A COCURING PROCESS

Abstract

A method for manufacturing a structure by curing together a base laminate and structural components placed thereon. Particularly, the uncured structural component has a peripheral tapered foot edge so that the vacuum bag placed thereon follows all the uncured plies without an abrupt leap from the structural component foot to the base laminate.

Claims

1. A method for manufacturing a composite material structure using a co-curing process, the structure being formed by at least one structural component positioned on a base laminate, the method comprising the following steps: a) for each uncured structural component, manufacturing the uncured structural component by laying-up and forming steps so that the structural component comprises a foot configured to contact the base laminate, wherein such foot comprises a peripheral tapered foot edge, each uncured structural component being surrounded by a vacuum strip secured between curing tools; b) positioning each of the at least one uncured structural components on an uncured base laminate in areas foreseen for an attachment and to form an assembly, the vacuum strip of each uncured structural component forming a vacuum bag with complementary pieces of the same material, so that the resulting vacuum bag extends over the entire uncured base laminate; c) applying a curing cycle to the assembly resulting from step b) for curing together each of the at least one structural components with the base laminate, manufacturing the composite material structure thereby.

2. The method according to claim 1, wherein step a) further comprises laying-up staggered pre-preg plies on a foot edge area to form the peripheral tapered foot edge.

3. The method according to claim 1, wherein step a) further comprises trimming a peripheral foot edge of the at least one structural component to form the peripheral tapered foot edge.

4. The method according to claim 1, wherein step a) further comprises manufacturing separately the at least one structural component and joining adjacent to its peripheral foot edge an uncured wedge to form the peripheral tapered foot edge.

5. The method according to claim 1, wherein step b) further comprises laying-up additional pre-preg plies in a non-planar manner covering at least the peripheral tapered foot edge so that thresholds are offset.

6. The method according to claim 1, wherein step b) further comprises laying-up the uncured base laminate on a mold shaping an aerodynamic surface, so that the base laminate is a portion of an aircraft skin.

7. The method according to claim 1, wherein at least one structural component is a reinforcing longitudinal stringer.

8. The method according to claim 1, wherein the at least one structural component is a T-profile stringer.

9. The method according to claim 1, wherein the at least one structural component is an omega-profile stringer.

10. The method according to claim 7, when the reinforcing longitudinal stringer is a T-profile stringer, wherein the curing tools are two angular profiles, adapted to a shape of the T-profile stringer.

11. The method according to claim 10, wherein the two angular profiles comprise two L-profile caul plates.

12. The method according to claim 1, wherein the curing tools are made of a material able to maintain a stable shape at a solidification temperature of a matrix of the composite.

13. The method according to claim 12, wherein the curing tools are made of steel.

14. The method according to claim 12, wherein the curing tools are made of INVAR alloy.

15. The method according to claim 1, wherein the vacuum strips and the complementary pieces for forming jointly the vacuum bag comprising an impervious plastic film with an internal side either treated with a release agent or covered by a release film.

16. The method according to claim 15, wherein a breather tissue is arranged between the impervious plastic film and the release film.

17. The method according to 1, wherein at least one complementary piece comprises a first portion of the same width as a vacuum strip, and a second portion adapted to cover a remainder region of the base laminate.

18. The method according to claim 15, wherein both the at least one vacuum strip and said first portion of the at least one complementary piece comprises sealing tapes applied at any or both of the respective side edges thereof, so that at least one of contiguous strips or first portions of the complementary pieces are in contact by the sealing tapes in order to facilitate a union between the vacuum strip and the first portion of a complementary piece.

19. The method according to claim 1, wherein in step a) lateral edges of the vacuum strips are fixed to an assembly tool where the curing tools are placed, to ensure proper alignment of the vacuum strips during a placement of the uncured structural component on the base laminate.

20. A composite material structure formed by at least one structural component positioned on a base laminate manufactured by the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] These and other characteristics and advantages of the invention will become clearly understood in view of the detailed description of the invention which becomes apparent from a preferred embodiment of the invention, given just as an example and not being limited thereto, with reference to the drawings.

[0071] FIG. 1 shows a schematic plan view of a composite structure (stiffened skin) formed by a base laminate (an aircraft wing cover) on which a plurality of structural components (stringers) are positioned.

[0072] FIG. 2 shows a schematic cross-sectional representation of a conventional stringer foot edge cured together with a base laminate (conventionally co-cured).

[0073] FIGS. 3a-3b show (a) a T-profile stringer, and (b) an omega-profile stringer placed on a base laminate.

[0074] FIGS. 4a-4c show an embodiment of a structural component according to the present invention and two detailed views of different peripheral tapered foot edges.

[0075] FIGS. 5a-5b show (a) a schematic plan view of the composite structure before subjecting it to the curing cycle illustrating in particular the strips and complementary pieces with which the vacuum bag is formed; and (b) a partial side view of an embodiment of the strip and complementary piece according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076] The skilled person in the art recognizes that aspects of the present invention described hereinafter may be embodied either as a method for manufacturing by co-curing a composite structure (10), or the composite material structure (10) itself.

[0077] A manufacturing method of a structure (10) such as a cover of an aircraft wing (see FIG. 1) formed by a skin of composite (i.e., the base laminate (2)) stiffened by T-profile stringers made of composite (i.e., the structural components (1)) will now be described.

[0078] In aeronautics, structural components (1) are typically placed span-wise the wing.

[0079] Such method comprises the basic following steps:

[0080] a) for each uncured structural component (1), manufacturing it by laying-up and forming steps so that the structural component (1) comprises a foot (1.1) adapted to contact on a base laminate (2) wherein such foot (1.1) comprises a peripheral tapered edge (1.1.1); each uncured structural component (1) being surrounded by a strip (3) of vacuum bag secured between curing tools (not shown in these figures);

[0081] b) positioning each of the at least one uncured structural components (1) on an uncured base laminate (2) in the areas foreseen for the attachment, the vacuum strip (3) of each uncured structural component (1) forming a vacuum bag with complementary pieces (4.1, 4.2) of the same material so that the resulting vacuum bag extends over the entire uncured base laminate (2);

[0082] c) applying a curing cycle to the assembly resulting from the previous step for curing together each of the at least one structural components (1) with the base laminate (2), manufacturing the structure (10) thereby.

[0083] In particular, the uncured structural component (1) is manufactured by laying up pre-preg plies on a flat laminate, followed by a forming process where the web or the foot bends to the shape of the desired profile.

[0084] The forming process can be achieved either by a conventional diaphragm vacuum forming, by dedicated tooling where the laminate is enclosed heated and moved in a controlled way or by continuous forming methods.

[0085] As mentioned, the tapered foot edge may be achieved either by the forming process (if the foot bends from the flat laminate), by a special lay-up arrangement where each ply starts in a different position (staggered) or by trimming the laminate foot edge with an appropriate angle.

[0086] Then, the manufactured structural component (1), still uncured and wrapped by the vacuum strip (3) (and secured between curing tools), is positioned on the uncured base laminate (2) (already molded on a mold shaping the outer aerodynamic surface). Positioning of the structural components (1)stringersmay be performed one by one or in groups, using dedicated handling and positioning tools which are properly referenced, for instance to the base laminate or base tool.

[0087] It can be noted that the sum of an uncured structural components (1) surrounded by the vacuum strip (3), except on the foot, and in turn secured between curing tools is known as an ensemble.

[0088] FIG. 2 depicts a schematic cross-sectional representation of a conventional straightstringer foot edge co-cured with a base laminate (2). It can be seen that the foot edge is formed by the edges of the stacked plies originally forming the uncured preform. These plies are compressed by a stringer molding tool (5) that keeps them in position.

[0089] The curing tool (5) function is primarily preventing the deviation of the web (1.2) from the vertical plane and aiding the vacuum bag matching, as closely as possible, to the radius of the structural component. In some embodiments, especially with T-profile stringers, curing tool (5) does not cover the top of the web (1.2).

[0090] Applying one single curing cycle for the integration of the stringers (1) shown in FIG. 2 with the base laminate (2) (i.e., co-curing) causes prints and undulations (2.1) on the skin (2) once cured, particularly in areas where the stringer molding tool (5) ends close to the peripheral stringer foot edge.

[0091] FIGS. 3a and 3b depicts two stringers (1, 1) with a different cross-sectional profile commonly used in aeronautics. Particularly, FIG. 3a shows a T-profile stringer (1), while FIG. 3b shows an omega-profile stringer (1), both placed on a base laminate (2).

[0092] The T-profile stringer (1) (see FIG. 3a) formed by stacked plies comprises:

[0093] a web (1.2), projecting perpendicular to the base laminate (2); and

[0094] two foot (1.1), each pointing in opposite direction, serving as a resting for the T-profile stringer on the base laminate (2)

[0095] Once installed, the foot (1.1) has a surface adapted to contact the base laminate (2) which extends up to the peripheral foot edge.

[0096] Regarding the omega-profile stringer (1) (see FIG. 3b), it is formed by a substantially trapezoidal profile with an open side, from the ends of which two feet (1.1) extend outwards pointing in opposite directions. The isosceles trapezoidal profile may be understood as the web (1.2) of the omega-profile stringer (1).

[0097] FIG. 4a depicts an embodiment of a structural component (1) placed on a base laminate (2) according to the present invention. In particular, it is shown a T-profile stringer (1) with a peripheral tapered foot edge (1.1.1).

[0098] For exemplary purposes, only a T-profile stringer (1) will be depicted, but it is also applicable to the peripheral tapered foot edge of an omega-profile stringer (1) as shown in FIG. 3b.

[0099] As mentioned, this tapered or chamfered edge shape creates a smooth transition for the vacuum bag (4.1, 4.2) and prevents bridging and sinking of these edges on the base laminate (2). Thus, the undesirable effect (2.1) shown in FIG. 2 is avoided along the peripheral foot edge, which represented a weakness on the performance of the co-cured structure. Unlike that, the co-cured stiffened panels (10) as the one shown in FIG. 4a meet the quality levels acceptable in the aircraft industry.

[0100] FIG. 4b depicts a tapered edge (1.1.1) achieved either by laying up the foot edge creating this staircase pattern or by a trimming operation with an appropriate angle.

[0101] This staircase pattern created on the foot edge by following a staggered laying-up scheme may be performed either by leaving the longest plies close to the base laminate once positioned thereon; or in an inverted staggering (i.e., the shortest plies close to the base laminate) and performing a compaction on the foot edge to form the peripheral tapered foot edge (1.1.1). That is, bringing the longest plies to the base laminate by the compaction to form a ramp.

[0102] Alternatively, the peripheral tapered foot edge (1.1.1) is formed by an uncured wedge (1.1.2) positioned adjacent to a straight peripheral foot edge of a stringer (1).

[0103] Further, FIG. 4c depicts additional plies (1.1.3) laid-up so as to cover the peripheral foot edge of the stringer (1).

[0104] FIG. 5a depicts a schematic plan view of the composite structure (10) before subjecting it to the curing cycle.

[0105] In some embodiments, the lateral edges of the vacuum strips (3) are fixed to an assembly tool where the curing tools are located. To do so, a strip (3) is firstly placed on the curing tool and fixed to said assembly tool. Then, in a second step, such preform is placed within the strip (3), being surrounded thereby. It is to be noted that the underneath surface of the foot of the stringer (the one to be in contact with the base laminate) is not surrounded by this vacuum strip (3).

[0106] By keeping the lateral edges of the strip fixed to the assembly tool during placement of the uncured structural component (1) on the base laminate (2), the alignment of the strip (3) with the web (1.2) of the structural component (1) is guaranteed.

[0107] It is to be noted that strips (3) are adapted to the geometry of the uncured structural components (1) so as to avoid the so-called bridges that may cause breakage of the vacuum bag during the curing cycle.

[0108] Upon positioning of the ensembles on the base laminate (2) (both in uncured state), the vacuum bag is formed for the whole assembly by joining the vacuum bag strips (3) provided with each structural component (1) (within each ensemble) with the complementary pieces (4.1, 4.2) in order to cover the whole base laminate (2) extension.

[0109] As it can be seen, the complementary piece(s) comprise(s) a first portion (4.1) of the same width as the vacuum strips (3), and a second portion (4.2) adapted to cover edge region of the base laminate (2).

[0110] The first portion (4.1) of the complementary pieces is deemed as a continuation of the vacuum strips (3) of those structural components (1) that do not extend to the entire available length of the base laminate (2); and the second portion (4.2) thereof are deemed as supplementary pieces required to complete the vacuum bag covering all the base laminate (2) extension.

[0111] The vacuum strip(s) (3) as well as the first portion (4.1) of the complementary piece(s) may comprise sealing tapes (not shown) at any or both side edges.

[0112] Therefore, after placing the structural components (1) on the base laminate (2), the vacuum bag is formed joining the strips (3) and the first (4.1) (and second (4.2)) portions of the complementary pieces for each structural component (1) by their contiguous side edges by means of such sealing tapes.

[0113] FIG. 5b depicts a partial side view of an embodiment of the strip (3) (or complementary piece (4.1, 4.2)) according to the invention.

[0114] In particular, the vacuum strips (3) and the complementary pieces (4.1, 4.2) for forming a vacuum bag comprise an impervious plastic film (3.1) with the internal side treated with a release agent or covered by a release film (3.3), A breather tissue (3.2) can be arranged between these two films to improve vacuum stability during laminate consolidation.

[0115] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.