Method for manufacturing carbon fiber panels stiffened with omega stringers

Abstract

The present disclosure refers to a method for manufacturing carbon fiber panels stiffened with omega stringers for the construction of aircraft structures, such as fuselage sections, wing panels, etc. One tubular pressure member is provided for each omega stringer of the structure to be manufactured, wherein the tubular pressure member is configured with the shape of the omega stringer. Each tubular pressure member is enclosed between the omega stringer and part of the laminate, and autoclave pressure is applied to the interior of the tubular pressure member, so that the tubular pressure member is used to consolidate the omega stringers and/or part of the laminate from the interior of these two elements, while these two elements are being co-cured or co-bonded in an autoclave. Imperfections on those internal surfaces such as resin wrinkles of the structure are reduced.

Claims

1. A method for manufacturing carbon fiber panels stiffened with omega stringers comprising: providing at least one omega stringer in a cured or un-cured state; providing at least one tubular pressure member manufactured with a cross-sectional shape of a channel defined by an omega stringer, and having at least the same length as the omega stringer; placing the tubular pressure member inside the channel of the omega stringer without use of a rigid support core; inserting a tubular vacuum bag inside the tubular pressure member; bringing in contact a laminate of uncured carbon fiber plies with the omega stringer, such that the tubular pressure element is enclosed by the laminate and the omega stringer; and applying autoclave pressure to an interior of the tubular vacuum bag such that the tubular vacuum bag forces the tubular pressure member to expand and exert pressure against part of the omega stringer and part of the laminate, wherein the tubular pressure member is a self-supporting body, wherein the tubular pressure member is made of an elastomeric material having an outer surface covered by a layer of release film material adhered to the outer surface, and wherein the layer of release film and a layer of composite material are joined to the elastomeric material during vulcanization of the elastomeric material.

2. The method according to claim 1, wherein the internal surface of the elastomeric material is covered with the layer of composite material adhered to that internal surface.

3. The method according to claim 1, wherein the tubular pressure member is a release film pre-form.

4. The method according to claim 3, wherein the thickness of the release film pre-form is within a range 0.1 to 0.7 mm.

5. The method according to claim 3, wherein the release film pre-form comprises a polytetrafluoroethylene (PFTE) or a fluorinated ethylene propylene (FEP) composition.

6. The method according to claim 1, wherein the tubular pressure member has a trapezoidal cross-sectional configuration.

7. The method according to claim 1, wherein an external vacuum bag is arranged enclosing the omega stringer and the laminate, and wherein the method further comprises joining edges of free ends of individual tubular vacuum bags with the external vacuum bag, such as during a curing process the autoclave pressure is applied to the interior of the tubular vacuum bags, and vacuum is applied to a space between the external vacuum bag and the individual vacuum bags and the omega stringer and laminate being cured.

8. The method according to claim 1, wherein the elastomeric material of the pressure member is made of rubber.

9. The method according to claim 1, wherein the layer of composite material is fiber glass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the disclosure herein are henceforth described with reference to the accompanying drawings, wherein:

(2) FIG. 1 shows an schematic representation of a tubular pressure member according to an exemplary embodiment of the disclosure herein when it is made of an elastomeric material, wherein drawing (a) is a perspective view, drawing (b) is a cross-sectional view, and drawing (c) is a longitudinal section of one of the faces of the tubular caul plate.

(3) FIG. 2 shows an schematic representation of a cross-sectional view of the assembly formed by the omega stringer joined with a skin plate, the elastomeric tubular pressure member and the, tubular vacuum bag, while autoclave pressure, represented by arrows, is being applied to the assembly.

(4) FIG. 3 is a representation a tubular pressure member according to another exemplary embodiment of the disclosure herein when it consist of a release film perform, wherein drawing (a) is a cross-sectional view of the same, and drawing (b) is a perspective view.

(5) FIG. 4 is a similar representation than FIG. 2 but using a release film perform as a tubular pressure member.

(6) FIG. 5 is a similar representation than FIG. 4 while autoclave pressure, represented by arrows, is being applied to the assembly.

DETAILED DESCRIPTION

(7) FIG. 1 represents a preferred embodiment of a tubular pressure member (1) according to the disclosure herein, which in this case is formed by the superposition of three different elements, all of them with the same trapezoidal configuration corresponding to a specific shape of an omega stringer, therefore the tubular pressure member (1) is formed by four sides and four corners between consecutive sides. The length of the tubular pressure member is at least the same that the length of the omega stringer to which it will be coupled.

(8) More specifically, the tubular pressure member (1) comprises a tubular core (2) made of an elastomeric material such as rubber, which is entirely covered on its outer surface by a layer of release film (3) made of a known material suitable to facilitate removing the tubular pressure member (1) from the composite structure (5) being manufactured, once the curing process has been completed.

(9) The tubular pressure member (1) is internally reinforced with a layer of a composite material (4) such as a fiber glass, which provides structural stability to the tubular core (2) but still allowing the elastomeric core to expand. Both the layer of release film (3) and the layer of composite material (1) are integrally joined to the tubular elastomeric core during its vulcanization.

(10) FIG. 2 shows the tubular pressure member (1) of FIG. 1 fitted or coupled inside the channel defined by an omega stringer (6), and since the trapezoidal shape of the pressure member is substantially the same as the trapezoidal shape of that channel, the tubular pressure member fits to the shape of the stringer channel such as that channel is filled by the tubular pressure member (1).

(11) At this stage, the omega stringer (6) is a pre-form of uncured plies, and it is received within a groove of a metallic male tool or mandrel (8). A laminate (7) of uncured carbon fiber plies which will form the skin panel of the structure is then layered up on the outer surface of the male tool (8) and on the omega stringer foot (10).

(12) It can be observed in this figure, how the part of the laminate (7) which overlaps the channel of the omega stringer (6), is also in contact with one of the sides of the tubular pressure member (1), and how the tubular pressure member (1) is enclosed or surrounded by part of the omega stringer (1) and also part of the laminate (7), so that the tubular pressure member (1) is in direct contact with these parts through the layer of release film (4). A tubular vacuum bag (11) is placed inside the tubular pressure member (1).

(13) A main reason for damaging this type of tubular vacuum bags, is that they are forced to inflate when pressure is applied to their interior, but occasionally these bags cannot inflate properly in all its areas and reach all the internal surface properly, and then excessive pressure is applied to some local areas of the vacuum bag.

(14) FIG. 2 shows only one omega stringer (6) and part of a laminate (7), however it would be clear for a skilled person, that a complete structure (5) is formed by a large laminate (7) to form for example the tubular skin of a fuselage section, and a plurality of omega stringers (6) as the one shown in FIG. 2.

(15) In the method of the disclosure herein, the assembly shown in FIG. 2 is covered completely with an external vacuum bag (12), and then the entire assembly is placed inside an autoclave (not shown) for curing the structure (5) in a known manner, by the simultaneous application of heat and pressure. Vacuum is also applied between vacuum bag (11) and the structure (5).

(16) As shown in FIG. 2, the autoclave pressure (represented by arrows) is applied to the interior of the tubular pressure member (1) through the tubular vacuum bag (11) which inflates and forces the tubular pressure member (1) to expand outwardly due to its elasticity, which in turn exerts pressure on the internal surfaces of the omega stringer (6) and the overlapping part of the laminate (7) to consolidate these parts of the structure.

(17) Due to the pressure exerted by the tubular pressure member (1), it is assured that after curing, the internal surfaces of the omega stringer (6) and the laminate (7) in direct contact with it are obtained as smooth surfaces free of wrinkles, and that the piece is accurately obtained with the desired geometry.

(18) The tubular pressure member (6) and tubular vacuum bags (11) are removed from the completed structure (5), and they are prepared to be used in subsequent manufacturing cycles. This tubular pressure member (6) made of an elastomeric material can be used repeatedly is several manufacturing cycles, at least 25 cycles.

(19) Alternatively, in another preferred embodiment of the disclosure herein, the tubular pressure member (1) is a release film preform as shown in FIG. 3. A release film is a well known material widely used in this industry for manufacturing high-quality composite parts. A known release film typically comprises a fluorinated ethylene propylene composition (FEP) or a polytetrafluoroethylene (PTFE) composition.

(20) In this preferred embodiment of the disclosure herein, the tubular pressure member (1) is manufactured with release film for example by a molding process, and it has been found that a suitable thickness of the this release film for this use is within the range 0.1 to 0.7 mm, and preferably 0.25 mm, so that this tubular pressure member (1) can be handled without being deformed and at the same time is has the required degree of elasticity.

(21) FIGS. 4 and 5 shows the tubular pressure member (1) made of a release film buried inside an omega stringer (6) and a laminate (7). The tubular pressure member (1) is forced to expand by increasing the pressure inside a tubular vacuum bag (11) placed in the interior of the tubular pressure member (1), as described previously with respect to FIG. 2.

(22) A tubular pressure member (1) made of a release film perform cannot be reused, but it is much cheaper than a tubular pressure member made of elastomeric material.

(23) While at least one exemplary embodiment of the 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. Other preferred embodiments of the present disclosure are described in the appended dependent claims and the multiple combinations thereof.