Device for preforming a hollow composite profile and method for preforming a hollow composite profile, in particular of the composite stiffener type

Abstract

The invention relates to a device (100) for preforming a hollow composite profile comprising a male profile and a female profile, comprising: a male punch (110), a bell (120) facing the punch, and a deformable bladder (130) arranged in the bell and capable of being pressurized; and which is configured to receive a strip of semi-finished composite material (200) between the punch and the bladder; the bladder comprising a wall (131) with a softened wall portion, and a stiffened wall portion which is preformed so as to have a predefined profile whose shape at rest corresponds to the male profile of the profile, and which is configured to come into contact with the strip of material; and which is configured to preform the profile by deforming the bladder under pressure, so as to apply and then compact the strip of material against the punch. figure for abstract: figure 5

Description

Title of the invention: Device for preforming a hollow composite profile and method for preforming a hollow composite profile, in particular of the composite stiffener type TECHNICAL FIELD OF THE INVENTION

[0001] The field of the invention is that of composite structures and their manufacturing processes.

[0002] More specifically, the invention relates to a device, or tool, for preforming a hollow composite profile, in particular of the composite stiffener type.

[0003] The invention also relates to a method for preforming a hollow composite profile, implemented by such a device.

[0004] The invention also relates to a hollow composite profile preform, in particular of the composite stiffener type, obtained by means of such a preforming method.

[0005] The invention also relates to a method for manufacturing a composite structure, in particular of the composite panel type, comprising the preforming of a hollow composite profile, in particular of the composite stiffener type, by means of a preforming method according to the invention.

[0006] Finally, the invention also relates to a composite structure, in particular of the composite panel type, obtained by means of such a method.

[0007] The invention finds applications in particular in the manufacture of stiffener preforms for reinforcing composite skins, for forming composite parts such as aircraft fuselage panels.

[0008] The invention finds applications in the technological industries of aeronautics and space, but can also find applications in the field of land or marine vehicles, or even in the construction or energy industries. STATE OF THE ART

[0009] Aircraft structures, in particular aircraft fuselages, are generally made of composite skins reinforced by reinforcing elements.

[0010] For example, such reinforcing elements may be stiffeners, sometimes also called stringers, stringers, or spars in English terminology.

[0011] Such stiffeners may in particular themselves be made of composite material, for example of the same material as the composite skin which they are intended to reinforce.

[0012] Known stiffeners are generally in the form of hollow composite profiles, that is to say in the form of an elongated element having a section with a concave profile, called female, and a convex profile, called male, opposite the female profile. In particular, the hollow composite profile is open, that is, it does not define a closed but rather an open section.

[0013] Subsequently, reference is made in the presentation of the state of the art and in the statement of the invention as well as in the detailed description to the term "stiffener", the invention which will be set out below can however be generalized to any generic hollow composite profile.

[0014] For example, the section of a stiffener may have a so-called omega profile (Q), but may also have a U, V, D, L or Delta shape, for example.

[0015] [Fig.l] schematically represents a generic composite panel 1, comprising a composite skin 2 and a plurality of stiffeners 3 with an omega profile, here three in number, which are molded onto the composite skin 2.

[0016] [Fig.2] schematically represents a stiffener 3 having an omega profile, taken in isolation.

[0017] The stiffener 3 has a male profile 4, also called an external profile, and a female profile 5, also called an internal profile, opposite the male profile 4.

[0018] The male profile 4 forms a convex profile while the female profile 5 forms a concave profile of the stiffener 3.

[0019] The female profile 5 is generally oriented towards the composite skin 2, as can be seen in [Fig.l].

[0020] Composite stiffeners are generally obtained from a prepreg strip, for example comprising a carbon fiber reinforcement and a resin matrix, which is shaped into the desired profile and then pre-baked in order to preform the composite stiffener. The result obtained is a composite stiffener preform, which can for example be subsequently co-baked with a composite part such as a composite skin, to obtain a composite structure. Pre-baking ensures that the prepreg retains the preform given to it while allowing subsequent baking.

[0021] According to an alternative, the composite stiffeners can also be obtained from a “dry” reinforcing strip, for example comprising a thermoplastic powder which is hot-shaped, then for example infused with resin, preferably under vacuum during the operation of manufacturing the stiffened panel.

[0022] Prepregs, dry reinforcements, in particular “powdered” reinforcements, and any other known compound that can be used for shaping, are referred to in the remainder of the description generically as “semi-finished composite material”.

[0023] The shaping of the semi-finished composite material can be done in different ways.

[0024] For example, a first known technique comprises holding the semi-finished composite material by means of side clamps, then shaping the material. semi-finished composite by advancing a male punch between the side clamps.

[0025] A second known technique comprises pressing the semi-finished composite material between a male punch and a female die.

[0026] A third known technique comprises covering a male punch with the semi-finished composite material, followed by covering the assembly with a waterproof tarpaulin and placing it under vacuum in order to press the semi-finished composite material against the punch.

[0027] The first and second techniques mentioned above have the disadvantage of the appearance of strong tensions at the so-called male angles of the semi-finished composite material during shaping, resulting in an insufficient thickness of material at these angles.

[0028] [Fig.3] schematically illustrates a so-called male angle (i.e. convex on the male profile 4 itself convex) of a stiffener obtained according to this first or second preforming technique, corresponding to detail A of [Fig.2].

[0029] As shown, the male angle has a reduced thickness at the radius of curvature.

[0030] The third technique mentioned above has the disadvantage of insufficient tension at the so-called female angles of the semi-finished composite material during shaping, resulting in excessive material thickness at these angles.

[0031] [Fig.4] schematically illustrates a so-called female angle (i.e. concave on the male profile 4 which is convex) of a stiffener obtained according to this third preforming technique, corresponding to detail B of [Fig.2].

[0032] As shown, the female angle has an increased thickness at the radius of curvature.

[0033] The excess or insufficient thickness of a stiffener at its corners can lead to structural fragility at these areas, and there is thus a significant risk of structural defects in the stiffener obtained.

[0034] There is thus a need to obtain composite stiffeners which have structural integrity over their entire profile. Statement of the invention

[0035] The present invention aims to remedy all or part of the drawbacks of the state of the art cited above.

[0036] To this end, the invention relates to a device for preforming a hollow composite profile comprising a male profile and a female profile, comprising: a male punch corresponding to the shape of the female profile of the hollow composite profile, a bell configured to be arranged opposite the punch, and at least one deformable bladder arranged inside the bell and configured to be put under pressure; the device being configured to receive a strip of semi-finished composite material between the punch and the at least one bladder; the at least one bladder comprising a wall with a softened wall portion and a stiffened wall portion, the stiffened wall portion being preformed so as to have a predefined profile whose shape at rest corresponds at least in part to the male profile of the hollow composite profile, the stiffened wall portion being configured to come at least partially into contact with the strip of semi-finished composite material; the device being configured to preform the hollow composite profile by deformation of the at least one bladder under the effect of pressure, so as to apply and then compact the strip of semi-finished composite material against the punch.

[0037] In particular, by predefined profile is meant a profile of the stiffened wall portion which has a predetermined shape, given to the stiffened wall during its manufacture for example.

[0038] By "at rest" is meant a state of the bladder when it is not mechanically stressed, other than possibly by atmospheric pressure and gravitational force, in particular as opposed to a working state where the bladder is deformed under the effect of internal pressure.

[0039] The stiffened wall portion is more rigid, that is to say less flexible and less easily deformable, than the softened wall portion.

[0040] The preform is initially printed at the stiffened wall portion, which in particular makes it possible to apply the semi-finished composite material against the so-called female angles of the punch, and thus to avoid stresses in the female angles of the male profile of the profile and in particular to avoid excess material thickness there.

[0041] The deformation of the stiffened wall portion, which is applied against the semi-finished composite material, allows the latter to fit the male angles of the punch, and thus to avoid stresses in the male angles of the male profile of the profile and in particular to avoid a deficit in material thickness.

[0042] It should be noted that the stiffened wall portion retains at least part of its initial preform when the bladder is pressurized, the stiffened wall portion however also being partly deformed when the bladder is pressurized. Thus, the bladder has a so-called rest configuration, i.e. when it is not pressurized, in which the stiffened wall portion is in its initial geometry, with a profile corresponding at least partly to the male profile of the hollow composite profile. The bladder further has a so-called working configuration, i.e. when it is pressurized, in which the stiffened wall portion retains part of its initial geometry, but is also partly deformed, so that the profile of the stiffened wall portion corresponds in- entirely to the male profile of the hollow composite profile.

[0043] In other words, the combination of an initial preform of the bladder, at the level of its stiffened wall portion, and a capacity for deformation of the latter, when the bladder is pressurized, makes it possible to conform the semi-finished composite material to the punch without introducing detrimental mechanical stresses into the profile obtained.

[0044] Particularly advantageous characteristics of the device according to the invention are presented below.

[0045] - Said stiffened wall portion is formed by a thickened wall portion, and said softened wall portion is formed by a thinned wall portion.

[0046] In particular, such a bladder can easily be obtained by extrusion of material, for example elastomer.

[0047] - At least a part of said softened wall portion has a profile configured to be folded accordion-style when the at least one bladder is not pressurized and to be unfolded when the at least one bladder is pressurized.

[0048] This contributes to the application without mechanical stress of the semi-finished composite material against the punch.

[0049] - The at least one bladder is made of elastomeric material, preferably reinforced with less partly with a woven soul.

[0050] This makes it possible to significantly reinforce the bladder, particularly when it is exposed to numerous inflation / deflation cycles, and in particular to guarantee the lasting geometric conformity of the stiffened part.

[0051] - The bell comprises two internal cavities, and the device comprises two bladders, each arranged in a separate internal cavity, in a substantially symmetrical manner.

[0052] Such an arrangement allows the simultaneous expansion of two symmetrical bladders, and thus an application of the semi-finished composite material against the punch with an exact correspondence of the shapes of the stiffened wall portions and of the punch.

[0053] It should be noted that the cavities are open here, that is to say that they open towards the punch and that they are accessible.

[0054] - The bell comprises a central rib separating the two internal cavities of the bell, the central rib being configured to contact the strip of semi-finished composite material so as to bring the punch into contact with the strip of semi-finished composite material at said central rib.

[0055] In other words, the central rib separates the interior space of the bell into two substantially symmetrical cavities, that is to say that the central rib is located in a plane of symmetry of the bell.

[0056] Thus, the strip of semi-finished composite material can be taken between the rib central and the punch when the device is closed. This makes it possible in particular to hold the strip of semi-finished composite material laterally in position, and thus to ensure symmetrical deformation of the strip of semi-finished composite material by the two inflating bladders.

[0057] - The hollow composite profile to be preformed has a so-called omega profile, and the shape at rest of the predefined profile of the stiffened wall portions of each of the bladders is substantially L-shaped.

[0058] - The device comprises a means for temporarily holding the strip of material semi-finished composite inside the bell.

[0059] In particular, the strip of semi-finished composite material is held when the at least one bladder is not pressurized, and the hold is released when the at least one bladder is pressurized.

[0060] - The temporary holding means comprises one or more clamps arranged at inside the bell, configured to hold the strip of semi-finished composite material in the bell in the absence of pressurization of the at least one bladder.

[0061] - The device further comprises a thermal regulation means, configured to heating the punch, and preferably also for cooling the punch.

[0062] The invention also relates, in a second aspect, to a method for preforming a hollow composite profile comprising a male profile and a female profile, implemented by means of a device as described above; the method comprising the following steps: - a step of placing a strip of semi-finished composite material in the device, between the punch and the at least one bladder; - a step of closing the device, so that the strip of semi-finished composite material is applied at least in part against the punch; - a step of pressurizing the at least one bladder, so that the strip of semi-finished composite material is applied entirely against the punch, then compacted against the punch, under the action of the stiffened wall portion partially deforming under the effect of the pressure; - a step of consolidating the strip of semi-finished composite material comprising heating and then cooling the strip of semi-finished composite material, thereby preforming the hollow composite profile; - a step of removing the hollow composite profile preform thus formed, comprising depressurizing the at least one bladder, opening the device and demolding the hollow composite profile preform.

[0063] According to advantageous embodiments:

[0064] - The pressurization step is a progressive pressurization of the at least a bladder.

[0065] This allows for a progressive application without introducing constraints of the strip of semi-finished composite material against the punch.

[0066] - The progressive pressurization follows a linear pressurization instruction.

[0067] - The semi-finished composite material strip is a prepreg strip comprising a reinforcement formed by a stack of fabrics, preferably carbon fibers.

[0068] According to a third aspect, the invention also relates to a hollow composite profile preform, preferably of the composite stiffener type, obtained by the preforming method as described above, so that the hollow composite profile preform has a thickness of composite material that is substantially constant over its entire profile.

[0069] Such a profile, obtained by the aforementioned method, is free from mechanical constraints introduced during its manufacture, and has constant structural properties over its entire profile.

[0070] According to a fourth aspect, the invention relates to a method for manufacturing a composite structure, the composite structure preferably being a composite panel, in particular an aircraft fuselage, the method comprising the following steps: - a step of obtaining at least one hollow composite profile preform by means of a preforming method as described above, the hollow composite profile preferably being a composite stiffener; - a step of draping a composite part onto the hollow composite profile preform, the composite part preferably being a composite skin; - a step of co-firing at least one hollow composite profile preform and the composite part, to obtain the composite structure.

[0071] The invention also relates, in a fifth aspect, to a composite structure, preferably of the composite panel type, in particular of an aircraft fuselage, obtained by the manufacturing method as described above. BRIEF DESCRIPTION OF THE FIGURES

[0072] Other advantages, aims and particular characteristics of the present invention will emerge from the following non-limiting description of at least one particular embodiment of the devices and methods which are the subject of the present invention, with reference to the appended drawings, in which: • [Fig.l] is a schematic view of a composite panel comprising a composite skin and a plurality of stiffeners; • [Fig.2] is a schematic view of the profile of a stiffener presenting a omega profile; • [Fig.3] is a detail view of a male angle of the stiffener of [Fig.2], when obtained by means of a first or second preforming method known from the prior art; • [Fig.4] is a detail view of a female angle of the stiffener of [Fig.2], when obtained by means of a third preforming method known from the prior art; • [Fig.5] schematically represents, in a sectional view, a device for preforming a composite stiffener according to the invention, following a first step of a method for preforming a composite stiffener according to the invention; • [Fig.6] is a schematic view of the preforming device, similar to the view of [Fig.5], following a second stage of the preforming process; • [Fig.7], [Fig.8] and [Fig.9] are schematic views of the preforming device, similar to the views of Figures 5 and 6, during a third step of the preforming process; • [Fig. 10] is a schematic view of the preforming device, similar to the views of Figures 5 to 9, following the third step of the preforming process • [Fig. 11] is a schematic view of the preforming device, similar to the views of Figures 4 to 10, during a fifth step of the preforming process; • [Fig. 12] is a block diagram of a method for preforming a composite stiffener according to the invention; • [Fig. 13] is a detail view of a male angle and a female angle of the stiffener of [Fig. 2], when obtained by means of the preforming method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0073] The present description is given without limitation, each characteristic of an embodiment being able to be combined with any other characteristic of any other embodiment in an advantageous manner.

[0074] It should be noted, from now on, that the figures are not necessarily to scale.

[0075] Figures 1 described above illustrate such a generic composite panel 1, comprising a composite skin 2 and a plurality of stiffeners 3, here three in number; and [Fig.2] described above illustrates a generic stiffener 3 having an omega profile.

[0076] Figures 3 and 4 described above schematically illustrate respectively a male angle and a female angle of a stiffener obtained by the known techniques of prior art.

[0077] The invention described below has as its objective the production, in particular the preforming, of a stiffener 3 as illustrated in Figures 1 and 2 but which does not have the structural defects of the known stiffeners as illustrated in Figures 3 and 4.

[0078] It is recalled that the invention is not limited to stiffeners and can be generalized to any generic hollow composite profile having a male profile and a female profile.

[0079] It is noted that hereinafter, the terms "hollow composite profile" and "hollow composite profile preform", and "stiffener" and "stiffener preform" may be used interchangeably, the preform of a profile designating a profile that can generally be used in a subsequent manufacturing process, while the term profile designates a generally finished product. The devices and methods described hereinafter may be adapted depending on the desired result, i.e. obtaining a profile preform or a finished profile.

[0080] [Fig. 5] to 11 schematically represent a device 100 for preforming a composite stiffener, at different stages of a preforming method which is described in more detail below.

[0081] The device 100 is configured to preform a stiffener made of composite material from a semi-finished composite material, for example a prepreg, also known as a “prepreg” in English terminology, or even a so-called “dry” fabric or reinforcement, for example comprising a hot-melt thermoplastic powder, which is infused with a resin matrix after preforming.

[0082] Subsequently, the description is made with reference to a prepreg as a semi-finished composite material, without being limited to this type of material.

[0083] The device 100 makes it possible to preform an elongated stiffener, for example from a strip of prepreg.

[0084] Such a stiffener may have a length of several meters, up to approximately 10 to 20 meters in length, for example 15 meters in length.

[0085] As is known, a prepreg comprises a matrix impregnating a reinforcement.

[0086] For example, the matrix may be a thermosetting resin or a thermoplastic polymer.

[0087] For example, the reinforcement may be a weave of carbon fibers, and in particular a stack of carbon fiber fabrics.

[0088] The composite stiffener formed by means of the device 100 can be used to reinforce a structure, in particular a structure which is itself composite, and in particular of large size.

[0089] For example, the composite stiffener obtained can be used to reinforce a structure comprising a composite skin, in particular to form an aircraft fuselage panel.

[0090] Any other application, in particular requiring the reinforcement of structures, composite or not, can however also be envisaged.

[0091] The device 100 comprises a male punch 110, or male core, and a bell 120 configured to be placed opposite the punch 110. For example, the bell 120 may be located above the punch 110, and be configured to be positioned thereon.

[0092] In particular, the punch 110 and the bell 120 are elongated in length, in order to allow the preforming of an elongated stiffener.

[0093] The bell 120 comprises a wall, which is configured so that the wall of the bell 120 and the punch 110 together define a closed chamber when the bell 120 is placed opposite the punch 110.

[0094] In particular, the bell 120 can be closed at its longitudinal ends.

[0095] The bell 120 has, for example, a U-shaped section, although such a shape is not limiting.

[0096] The male punch 110 has a male profile, or external profile, corresponding to the female profile of the stiffener to be preformed.

[0097] In other words, the punch 110 has a convex profile corresponding to the shape of the female profile of the stiffener to be preformed.

[0098] In the example illustrated, the punch 110 has an omega profile, without such a profile being limiting, Delta, L or Z profiles being able to be used.

[0099] The device 100 may comprise thermal regulation means 140 (see [Fig. 1 1]), configured to thermally regulate the punch 110 and allowing the heating, and preferably also the cooling of the prepreg 200.

[0100] As an alternative, the thermal regulation means may be external to the device 100.

[0101] The punch 110 and the bell 120 may both be made of metallic material.

[0102] Preferably, the punch 110 is made of aluminum, to allow effective thermal regulation.

[0103] The device 100 further comprises at least one deformable bladder 130, arranged inside the bell 120.

[0104] The bladder 130 is configured to be pressurized with a gas, for example air, to be inflated and deformed under the effect of the pressure.

[0105] For this purpose, the device 100 may comprise a means for compressing a gas, such as a compressor (not shown).

[0106] Alternatively, the device 100 may comprise a means of connection (not shown) to a source of pressurized gas external to the device 100.

[0107] The at least one bladder 130 may for example be made of elastomeric material.

[0108] Preferably, the at least one bladder 130 comprises a core made of woven material, which makes it possible to increase the lifespan of the bladder and in particular to guarantee its geometric conformity over the long term.

[0109] The at least one bladder 130 preferably extends over the entire length of the device 100, inside the bell 120, that is to say that the at least one bladder is substantially elongated in length.

[0110] In particular, the bladder 130 can be obtained by extrusion of a constant profile of material, for example elastomer, which makes it possible to form a bladder 130 of significant length.

[0111] In the example illustrated, the device 100 comprises two bladders 130, which are here substantially identical, and which are arranged symmetrically in the bell 120.

[0112] In this example, the bell 120 comprises a central rib 121, forming a wall delimiting two cavities 122 of the bell 120.

[0113] Each cavity 122 receives respectively one of the bladders 130.

[0114] Each of the bladders 130 comprises a wall 131, the wall 131 being able to comprise an attachment portion 132 by which each bladder 130 is secured to the central rib 121, or simply shaped to the central rib 121 to allow the correct positioning of the bladder 130 in the cavity 122.

[0115] Furthermore, the wall 131 may comprise a contact portion 133, configured to be brought into contact with the prepreg 200 during the preforming of the stiffener.

[0116] The wall 131 may also comprise an expansion portion 134, which is deformable and which is configured to expand when the bladder 130 is pressurized.

[0117] The bell 120 comprises an interior surface 125, and the expansion portion 134 may in particular be configured to contact the interior surface 125 when the bladders 130 are inflated.

[0118] The wall 131 of each bladder 130 comprises a stiffened wall portion and a softened wall portion, that is to say that the wall 131 comprises a more rigid wall portion, in other words less flexible, and another less rigid wall portion, in other words more flexible.

[0119] For example, the stiffened wall portion comprises at least the contact portion 133, and may also comprise the attachment portion 132. The softened wall portion may comprise the expansion portion 134.

[0120] The stiffened wall portion may be formed by a thickened wall portion, and the softened wall portion may be formed by a thinned wall portion.

[0121] For example, as seen in Figures 5 to 11, the attachment portion 132 and / or the contact portion 133 are thickened, and the expansion portion 134 is thinned.

[0122] According to a variant not illustrated, the stiffened wall portion can be formed by a wall portion comprising a rigid core, and the softened wall portion may be formed by a wall portion comprising a less rigid core, or no core. According to this variant, the stiffened wall portion and the softened wall portion may have the same substantially constant thickness, or else have different thicknesses as described previously.

[0123] The thickened wall portions have increased stiffness, while the thinned wall portions have reduced stiffness.

[0124] The stiffened wall portion, comprising the contact portion 133, is preformed (for example by extrusion) so as to have a predefined profile whose shape at rest corresponds at least in part to the male profile of the hollow composite profile.

[0125] By predefined profile is meant a profile of the stiffened wall portion which has a predetermined shape, given to the stiffened wall during its manufacture for example.

[0126] This shape is that which the portion of wall adopts when it is at rest, that is to say when it is not mechanically stressed (other than possibly by atmospheric pressure and gravitational force).

[0127] The resting shape of the stiffened wall portion, and in particular of the contact portion 133, is visible in [Fig.5] in particular, in which the bladders 130 are not inflated and the pressure does not act on the stiffened wall portion.

[0128] As can also be seen in this figure, the stiffened wall portion may have a substantially L-shape, also corresponding to the shape of the contact portion 133 in the illustrated example. The stiffened wall portion may also have a substantially U-shape, including the substantially L-shape, when the attachment portion 132 is also stiffened as in the illustrated example.

[0129] In the example illustrated, the two bladders 130 arranged symmetrically each comprise an L-shaped contact portion 133.

[0130] The expansion portion 134, which is in particular a softened and here thinned wall portion, can be configured to be folded in an accordion shape when the bladder 130 is not pressurized, i.e. depressurized, and to be unfolded when the bladder 130 is pressurized.

[0131] In particular, the expansion portion 134 is configured to be brought into contact with the inner surface 125 of the bell 120 when the bladder 130 is pressurized.

[0132] The device 100 is configured to receive a prepreg, and in particular a prepreg strip 200, between the punch 110 and the bladder 130.

[0133] The prepreg strip 200 has a substantially flat shape when it is placed in the device 100.

[0134] In particular, the prepreg strip 200 can be held in the bell 120, which comprises a means for temporarily holding the prepreg.

[0135] For example, the temporary holding means comprises a plurality of clamps 123 formed on the wall of the bell 120 inside the latter.

[0136] According to an alternative, the temporary holding means can be formed by a lower stop, on which the prepreg strip 200 rests when it is put in place.

[0137] In particular, the central rib 121 of the bell has a free edge 124, and the clamps 123 are formed at the height of the free edge 124.

[0138] In this way, when the prepreg strip 200 is placed in the device 100 and in particular in the bell 120, the free edge 124 is in contact with the prepreg strip 200.

[0139] In such a configuration, the prepreg strip 200 is located between the punch 110 and the bladders 130, which are themselves arranged between the prepreg strip 200 and the inner surface 125 of the bell 120.

[0140] In other words, a first face 201 of the prepreg strip 200 is oriented towards the bladders 130, while a second face 202 opposite the first face 201 is oriented towards the punch 110.

[0141] The operation of the device 100 for preforming a composite stiffener will now be described, with reference to FIGS. 5 to 11.

[0142] In particular, the device 100 can be configured for implementing a method 300 for preforming a composite stiffener, comprising the steps 301 to 305 described below and illustrated by the block diagram of [Fig. 12].

[0143] [Fig.5] illustrates the device 100 following a step 301 of placing the prepreg strip 200 in the device 100.

[0144] As described above, the prepreg strip 200 is arranged between the punch 110 and the at least one bladder 130, and here the two bladders 130.

[0145] For example, the prepreg strip 200 can be held in the bell 120 by means of clamps 123 as described above.

[0146] During installation, the bladders 130 are housed in the cavities 122 and the contact portion 133 of the wall of the bladders 130 is partially in contact with the prepreg strip 200.

[0147] In particular, the stiffened wall portion and in particular the contact portion 133 of each bladder 130 is partially in contact with the prepreg strip 200.

[0148] The expansion portion 134 is folded accordion-style during this step.

[0149] [Fig.6] illustrates the device 100 following a step 302 of closing the device 100, during which the punch 110 and the bell 120 are brought closer to each other.

[0150] In particular, the punch 110 can be brought closer in the direction of the bell 120

[0151] At the end of step 302, the prepreg strip 200 is partly in contact with the punch 110.

[0152] In particular, a central portion of the prepreg strip 200 is engaged between the punch 110 and the free edge 124 of the bell 120.

[0153] In this way, the prepreg strip 200 is held in position against the punch 110.

[0154] It should be noted that at the end of this step, the prepreg strip 200 is not yet deformed and remains substantially flat.

[0155] [Fig.7] illustrates the device 100 during a step 303 of pressurizing the bladders 130.

[0156] Preferably, the pressurization of the bladders 130 is progressive during this step.

[0157] For example, the pressurization follows a progressive pressure increase instruction such that it allows the progressive application of the prepreg strip on the punch 110.

[0158] The pressurization step 303 may comprise a single pressure increase, for example linear, or for example several pressure increase phases, for example linear but with different slopes.

[0159] For example, the bladders 130 may be pressurized until they reach a first pressure, then be pressurized until they reach a second pressure, in particular higher than the first pressure.

[0160] For example, the final pressure reached is approximately 3 bars relative to the atmosphere.

[0161] As illustrated in [Fig.6], during step 303, the prepreg strip 200 is progressively deformed or "unwound" against the punch 110, starting with the male corners of the punch 110.

[0162] The prepreg strip 200 is detached from the clamps 123 during this step, which give way under the force exerted by the pressure in the bladders 130 and lift the temporary hold of the prepreg strip 200.

[0163] [Fig.8] illustrates the device 100 during step 303 at a time following that of [Fig.7].

[0164] As can be seen in [Fig.8], the prepreg strip 200 has been deformed even further and gradually conforms to the shape of the male punch 110.

[0165] The prepreg strip 200 is deformed under the action of the bladders 130 which deform under the effect of the pressure, the stiffened wall portion and in particular the contact portion 133 bending around the male angle of the punch 110.

[0166] As can be seen in Figures 7 and 8, during this step, the stiffened wall portion partly retains its shape at rest, in particular at the angle formed by its predefined L-shaped profile, thus guaranteeing the geometry of the preform in the concave, or female, angle on the punch.

[0167] [Fig.9] illustrates the device 100 at the end of step 303 at a time following that of [Fig.8], the prepreg strip 200 being almost entirely conformed to the shape of the male punch 110.

[0168] The stiffened wall portion, and in particular the contact portion 133, is entirely folded around the male angle of the punch 110. The angle formed by the predefined L-shaped profile of the contact portion 133 is entirely applied in the female angle of the punch 110. In other words, the stiffened wall portion gradually takes on the male shape of the punch 110, and forms what is similar to a flexible matrix of female shape.

[0169] During step 303, the expansion portion 134 unfolds from its accordion shape as the pressure increases in the bladders 130, but is not necessarily in contact with the interior surface 125 of the bell 120.

[0170] The pressure exerted on the prepreg strip 200 is therefore low, due to the absence of counter-pressure by the inner surface 125 of the bell 120, and this results in a particularly progressive and stress-free deformation of the prepreg strip 200.

[0171] The use of two symmetrical bladders 130 ensures that the thickened contact portion 133 forming the female die comes into contact in exact correspondence with the angles of the male punch 110.

[0172] [Fig. 10] illustrates the device 100 following step 303, at a time following that of [Fig. 9], the prepreg strip 200 being entirely conformed to the shape of the male punch 110.

[0173] The contact portion 133 is folded around the male angle of the punch 110 and its preformed profile corresponds with the female angle of the punch 110, the contact portion 133 being entirely in contact with the prepreg strip 200.

[0174] The prepreg strip 200 is in the shape of the omega profile, taken between the male punch and the contact portion 133 forming a female matrix.

[0175] In other words, at the end of step 303, the contact portion 133 of each of the bladders 130 has a substantially S-shape, one of the branches of the predefined L-shape at rest having been folded during step 303.

[0176] In particular, at the end of step 303, the expansion portion 134 is unfolded and is in contact with the inner surface 125 of the bell 120.

[0177] This first pressurization phase allows the progressive shaping of the prepreg strip 200 without introducing stresses into the material.

[0178] Further, during step 303, pressurization may be continued at a higher pressure, i.e., the bladders 130 may be pressurized to a second pressure higher than the first pressure.

[0179] This second pressurization phase makes it possible to compact the prepreg 200 which is shaped to the shape of the punch 110 at the end of the first pressurization phase, described above.

[0180] Here, compacting means compressing the fibers of the reinforcement of the semi-finished composite material.

[0181] During this second pressurization phase, in particular the expansion portion 134 is in contact with the inner surface 125 which exerts a counter-pressure on the bladders 130, which has the effect that the bladders 130 apply a pressure on the prepreg strip 200 which thus compacts.

[0182] The method 300 further comprises a step 304 of consolidating the prepreg, to obtain a composite stiffener preform with sufficient rigidity. The composite stiffener preform thus obtained is suitable for implementing a subsequent molding process, in particular for continuing its molding process on the composite skin. It is specified, however, that the stiffener preform can also be baked in isolation in order to obtain a composite stiffener alone, if necessary.

[0183] The curing step 304 notably comprises the heating, or pre-baking, of the prepreg strip 200.

[0184] For example, during this step, the punch 110 is heated by the thermal regulation means 140 of the punch, as illustrated schematically in [Fig. 1 1], for example until a temperature of the order of 80°C is reached.

[0185] The device 100 and the prepreg strip 200 are then cooled, for example also by the thermal regulation means 140.

[0186] At the end of step 304, the prepreg strip 200 is consolidated and constitutes a composite stiffener preform, in particular capable of being molded with the composite panel.

[0187] The method 300 also comprises a step 305 of removing the composite stiffener preform thus formed.

[0188] Step 305 notably comprises the depressurization, i.e. the bringing to atmospheric pressure, of the bladders 130, the opening of the device 100, i.e. the separation of the punch 110 and the bell 120 so as to free access to the composite stiffener preform thus formed, as well as the demolding of the composite stiffener preform from the punch 110.

[0189] [Fig. 13] schematically illustrates detail A and detail B of a stiffener such as that illustrated in [Fig.2], obtained by means of the device 100 and / or by the preforming method 300.

[0190] As can be seen, the thickness of the stiffener profile at the male angle and the female angle is substantially identical to the thickness of the profile outside the male angle and the female angle, in other words the thickness of the stiffener profile is substantially constant over its entire profile.

[0191] In particular, the male angles do not have any underthickness of the stiffener profile.

[0192] The same applies to the female angles of the stiffener, which does not have any excess thickness of the stiffener profile.

[0193] The characteristics of such a stiffener can be determined for example by measuring the thickness of the stiffener along its profile.

[0194] A composite stiffener obtained by means of the device 100 and / or by the preforming method 300 thus has improved structural integrity compared to stiffeners obtained by known methods, and in particular does not have any stress defects in the male and / or female angles of the stiffener profile.

[0195] This results in an improved, safer and more reliable composite stiffener, which provides a significant advantage particularly in applications such as the aeronautical field.

[0196] Such a stiffener is distinguished from the known technique, which, as explained above, does not make it possible to obtain composite stiffeners having a substantially constant profile thickness, particularly at the angles of the profile.

[0197] The invention also relates to the manufacture of a composite structure, for example a composite panel, in particular for an aircraft fuselage, which comprises the following steps:

[0198] - A step of obtaining at least one hollow composite profile preform, by for example a stiffener, by means of a preforming process as described above.

[0199] - A step of draping a composite part, the composite part being for example a composite skin.

[0200] This step may be a step of obtaining a composite part known in the art and adapted to obtain the desired composite structure, for example by a step of placing fibers using a fiber placement head.

[0201] - A co-cooking step, i.e. simultaneous cooking, of at least one preform of hollow composite profile and composite part, to obtain the composite structure.

[0202] For example, this step is a step of co-curing molding of the hollow composite profile and the composite part, in particular in an autoclave and after having applied the composite part to the hollow composite profile preform by a fiber placement step, and in which a molding core is arranged inside the hollow composite profile preform.

[0203] It is recalled that the invention is not limited to the examples described or illustrated.

Claims

Claims

1. Device (100) for preforming a hollow composite profile comprising a male profile and a female profile, characterized in that the device comprises: a male punch (110) corresponding to the shape of the female profile of the hollow composite profile, a bell (120) configured to be arranged opposite the punch, and at least one deformable bladder (130) arranged inside the bell and configured to be pressurized; the device being configured to receive a strip of semi-finished composite material (200) between the punch and the at least one bladder;the at least one bladder comprising a wall (131) with a softened wall portion and a stiffened wall portion, the stiffened wall portion being preformed so as to have a predefined profile whose shape at rest corresponds at least in part to the male profile of the hollow composite profile, the stiffened wall portion being configured to come at least partially into contact with the strip of semi-finished composite material; the device being configured to preform the hollow composite profile by deformation of the at least one bladder under the effect of pressure, so as to apply and then compact the strip of semi-finished composite material against the punch.;

2. The device (100) of claim 1, wherein said stiffened wall portion is formed by a thickened wall portion, and said softened wall portion is formed by a thinned wall portion.

3. Device (100) according to one of claims 1 or 2, in which at least a part of said softened wall portion has a profile configured to be folded in an accordion shape in the absence of pressurization of the at least one bladder and to be unfolded when the at least one bladder is pressurized.

4. Device (100) according to any one of claims 1 to 3, in which the at least one bladder (130) is made of elastomeric material, preferably reinforced at least in part with a woven core.

5. Device (100) according to any one of claims 1 to 4, in which the bell comprises two internal cavities (122), and the device comprises two bladders (130), each arranged in a separate internal cavity, in a substantially symmetrical manner.

6. Device (100) according to claim 5, wherein the bell (120) comprises a central rib (121) separating the two internal cavities (122) of the bell, the central rib (121) being configured to come into contact with the strip of semi-finished composite material so as to bring the punch into contact with the strip of semi-finished composite material at the level of said central rib (121).

7. Device (100) according to one of claims 5 or 6, in which the hollow composite profile to be preformed has a so-called omega profile, and in which the resting shape of the predefined profile of the stiffened wall portions of each of the bladders is substantially L-shaped.

8. Device (100) according to any one of claims 1 to 7, comprising means for temporarily holding the strip of semi-finished composite material inside the bell.

9. Device (100) according to claim 8, wherein the temporary holding means comprises one or more clamps (123) arranged inside the bell (120), configured to hold the strip of semi-finished composite material in the bell in the absence of pressurization of the at least one bladder.

10. Device (100) according to any one of claims 1 to 9, further comprising a thermal regulation means (140), configured for heating the punch, and preferably also for cooling the punch.

11. Method (300) for preforming a hollow composite profile comprising a male profile and a female profile, implemented by means of a device (100) according to any one of claims 1 to 10; the method comprising the following steps: - a step (301) of placing a strip of semi-finished composite material (200) in the device, between the punch (110) and the at least one bladder (130); - a step (302) of closing the device, so that the strip of semi-finished composite material is applied at least in part against the punch; - a step (303) of pressurizing the at least one bladder, so that the strip of semi-finished composite material is applied entirely against the punch, then compacted against the punch, under the action of the stiffened wall portion deforming in part under the effect of the pressure;- a step (304) of consolidating the strip of semi-finished composite material comprising heating then cooling the strip of; semi-finished composite material, thereby preforming the hollow composite profile; - a step (305) of removing the hollow composite profile preform thus formed, comprising depressurizing the at least one bladder, opening the device and demolding the hollow composite profile preform.

12. The method (300) of claim 11, wherein the pressurizing step is a gradual pressurization of the at least one bladder.

13. The method (300) of claim 12, wherein the progressive pressurization follows a linear pressurization setpoint.

14. Method (300) according to any one of claims 11 to 13, in which the strip of semi-finished composite material is a strip of prepreg comprising a reinforcement formed by a stack of fabrics, preferably carbon fibers.

15. Hollow composite profile preform, preferably of the composite stiffener type, obtained by the preforming method (300) according to any one of claims 11 to 14, so that the hollow composite profile preform has a thickness of composite material which is substantially constant over its entire profile.

16. A method of manufacturing a composite structure, the composite structure preferably being a composite panel, in particular an aircraft fuselage, the method comprising the following steps: - a step of obtaining at least one hollow composite profile preform by means of a preforming method (300) according to any one of claims 11 to 14, the hollow composite profile preferably being a composite stiffener; - a step of draping a composite part onto the hollow composite profile preform, the composite part preferably being a composite skin; - a step of co-firing the at least one hollow composite profile preform and the composite part, to obtain the composite structure.

17. Composite structure, preferably of the composite panel type, in particular of an aircraft fuselage, obtained by the manufacturing method according to claim 16.

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