Method for manufacturing an open part with reinforced ribs

Abstract

The invention relates to a method for manufacturing an open part (10) made of composite material and comprising a skin (12), ribs extending in an associated direction of extension, and at least one reinforced rib (14) having a reinforced head (22), the method comprising: - providing a first fibre preform (PF1) for forming the skin and the body of the ribs; - providing a second fibre preform (PF2) for forming the reinforced head of the reinforced ribs; - placing the assembly formed of the first and second fibre preforms in a moulding device (30) comprising a die (32) shaped to form the ribs of the part; and - thermocompressing the assembly to form the part; and the first preform comprises discontinuous fibres (PF12) for forming the body, while the second preform comprises continuous fibres oriented in the direction of extension.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURING AN OPEN PART WITH REINFORCED RIBS

[0003] Technical field of the invention

[0004] The present invention relates to the field of composite material parts from a fibrous reinforcement densified by a matrix, in particular turbomachine parts. It relates in particular to the methods of manufacturing by thermocompression parts such as open and ribbed composite panels, comprising reinforced ribs forming stiffeners.

[0005] Technical background

[0006] The technical background includes in particular document EP 3 950 292 Al.

[0007] An open stiffened composite panel generally comprises a composite skin joined to an intermediate structure, unlike so-called sandwich composite panels which comprise two composite skins joined on either side of an intermediate structure. This reduces the cost of the panel and simplifies its manufacture, as well as reducing its mass, which is particularly important for an aeronautical application.

[0008] Examples of application may be aircraft nacelle reverser flaps, part of reverser grids, stiffened internal or external vein panels, etc.

[0009] Composite skins generally comprise organic or mineral fibers, for example carbon or glass, woven or deconstructed, embedded in a polymer or resin matrix.

[0010] In order to maintain good bending stiffness, such an open panel generally includes a structure formed of stiffening ribs extending from the inner face of the composite skin. These ribs can be oriented in the same direction or be intersecting.

[0011] The Applicant's patent application FR 2 112 191 proposes an open panel having increased flexural rigidity and improved resistance to deformation, making it possible to significantly reduce the mass of the panel and simplify its manufacture. More specifically, the open composite panel comprises a composite skin having an inner face and an outer face and a plurality of stiffening ribs. Each rib extends from the inner face of the skin to a vertex opposite said inner face and also in a respective direction of extension. In addition, at least one rib is reinforced among the ribs. For this purpose, each reinforced rib forms a stiffener and comprises at least one elongated stiffening portion extending along the vertex of the reinforced rib, said stiffening portion comprising fibers extending substantially in the direction of extension of the reinforced rib.

[0012] It is known to produce various turbomachine parts, in particular aircraft turbomachine parts, from a composite material with the aim of improving their thermomechanical resistance capabilities and reducing their mass.

[0013] Some composite materials are usually composed of a fibrous reinforcement and a matrix.

[0014] Several technologies have been identified for manufacturing composite material parts, including injection molding (RTM), thermoplastic injection molding, and thermocompression molding. RTM injection molding requires fiber reinforcement, most often with continuous fibers. Thermoplastic injection molding of fiber reinforcement with long or short fibers (fibers in the resin and a previously empty mold) allows parts to be manufactured very quickly and at high speeds. Thermocompression molding, on the other hand, allows fiber reinforcement already pre-impregnated with a matrix to be densified by applying pressure and performing a heat treatment at high temperature.

[0015] The objective of the present invention is to propose a method for facilitating and making robust the manufacture by thermocompression of such structurally optimized ribbed panels.

[0016] Summary of the invention

[0017] The invention relates to a method for manufacturing an open part made of composite material comprising a skin and at least one rib each comprising a body and a head, the body extending from an internal face of the skin to the head, each rib extending in an associated direction of extent, the part comprising at least one rib called a reinforced rib having a reinforced head, the method being characterized in that it comprises the following steps:

[0018] - a step of providing at least one first fibrous preform intended to form the skin and the body of the at least one rib;

[0019] - a step of providing at least one second fiber preform intended to form the reinforced head of the at least one reinforced rib;

[0020] - a step of placing in a molding device comprising a punch and a die the assembly formed of the first fiber preform and the second fiber preform, the second fiber preform being arranged between the die and the first fiber preform and the die being shaped to form the at least one rib of the open part; and

[0021] - a step of thermocompression of the assembly to form the open part;

[0022] - a step of demolding the assembly to form the open part; and in that the first fiber preform comprises at least discontinuous fibers (PF12) to form at least the body of the ribs and that the second fiber preform comprises at least continuous fibers oriented in the direction of extension associated with the at least one rib.

[0023] Thus, the invention makes it possible to overcome at least some of the drawbacks presented above by a simple solution. Indeed, the invention proposes a method making it possible to facilitate and make robust the manufacture by thermocompression of such ribbed parts, in particular structurally optimized ribbed panels and more precisely comprising a reinforced structure at the top of the ribs.

[0024] Such a part or panel has increased flexural strength and stiffness due to the rib heads. The rib heads are easily added to the panel by the method of the invention.

[0025] By "extending substantially in one direction" is meant forming an angle of less than 10° with this direction, preferably less than 5°.

[0026] Similarly, "rib" means any shape in elevation outside the plane of the panel and "stiffener" or "reinforced rib" means a rib with a reinforced head, i.e. a reinforced structure at the top of its body.

[0027] The method according to the invention may comprise one or more of the following characteristics, taken individually or in combination with each other, in all technically possible combinations:

[0028] - the open part is an open panel;

[0029] - the first preform comprises layers of continuous fibers to form the skin, the discontinuous fibers being arranged in clusters on one of the layers of continuous fibers to form the body of the at least one rib;

[0030] - the first preform comprises an additional layer of continuous fibers to form the skin comprising slits, each slit extending in the associated direction of extension of the at least one rib, the discontinuous fibers being arranged in clusters between the layers and the additional layer of continuous fibers at right angles to the slits of the additional layer;

[0031] - the or each of the at least one reinforced rib extends in at least two distinct directions of extent and intersects at points of intersection and the second preform comprises ribbons of continuous unidirectional fibers extending in the at least two directions of extent and overlapping alternately at the points of intersection;

[0032] - the second preform comprises, for each reinforced rib head, at least one additional layer of continuous fiber material arranged so as to cover at least one of the ribbons of unidirectional fibers extending in the direction of extension associated with said reinforced rib head, the additional layer having an elongated shape in the direction of extension of said associated reinforced rib head, the continuous fibers of the additional layer extending in a direction different from the direction of extension of said associated reinforced rib head and the additional layer being shaped to cover the at least one ribbon of longitudinal fibers and at least partially the body associated with said reinforced rib head of the open part after thermocompression;

[0033] - a first portion of the continuous fibers of the additional layer are oriented at an angle of between 30° and 60° relative to the direction of extension of the associated rib-reinforced head and a second portion of the continuous fibers of the additional layer are oriented at an angle of between -30° and -60° relative to the direction of extension of the associated rib-reinforced head;

[0034] - the additional layer has a width in a direction perpendicular to the direction of extension of the associated rib-reinforced head such that after thermocompression, the additional layer covers the body over a covering height greater than at least three times the thickness of the additional layer, and preferably at least greater than 5 times the thickness of the additional layer;

[0035] - the matrix comprises a main surface and cavities extending from the main surface and being shaped to form the at least one rib of the open part, and the placing step comprises placing the second fiber preform at the bottom of the cavities and then placing the first fiber preform on the main surface before the thermocompression step;

[0036] - the matrix comprises a main surface and cavities extending from the main surface and being shaped to form the at least one rib of the open part and the step of providing at least one first fiber preform comprises a step of providing a so-called skin fiber preform intended to form the skin and a step of providing a so-called body fiber preform intended to form the body of the at least one rib; and the step of placing in the molding device comprises: placing the second fiber preform in the cavities, then placing the body fiber preform on the main surface in line with the cavities, then placing the skin fiber preform above the body fiber preform;

[0037] - the fibrous body preform is compressed so as to flow at least partially into the cavities before the skin preform is put in place, so as to form at least 80% of the filling of the at least one rib, and preferably at least 90%, and more preferably at least 95%;

[0038] - the first and second fiber preforms are pre-impregnated with a resin.

[0039] Brief description of the figures

[0040] The invention will be better understood and other characteristics and advantages will become apparent upon reading the detailed description which follows, comprising embodiments, given for illustrative purposes with reference to the appended figures and presented as non-limiting examples, which may serve to complete the understanding of the present invention and the description of its embodiment and, where appropriate, contribute to its definition, in which:

[0041] - Figure 1 is a schematic cross-sectional view of a first open panel obtained by a manufacturing method according to the invention;

[0042] - figure 2 is a three-dimensional schematic view of a second example of a panel obtained by the method according to the invention;

[0043] - figure 3 is a block diagram representing a method of manufacturing a part according to the invention;

[0044] - figure 4 schematically represents a sectional view of a molding device or mold for manufacturing the part illustrated in figures 1 or 3 before the thermocompression step;

[0045] - figure 5 schematically represents a sectional view of the molding device of figure 4 when the mold is closed during thermocompression;

[0046] - figure 6 schematically illustrates a perspective view of a first preform used in the manufacturing method according to the invention;

[0047] - figure 7 schematically represents a sectional view of the molding device just before closing the cover on the die on the first preform of figure 6;

[0048] - figure 8 illustrates the result of the first fiber preform of figure 6 after thermocompression;

[0049] - figure 9 schematically illustrates a perspective view of another first preform used in the manufacturing method according to the invention;

[0050] - figure 10 schematically represents a sectional view of the molding device just before closing the cover on the die on the first preform of figure 9;

[0051] - figure 11 illustrates the result of the first fiber preform of figure 9 after thermocompression;

[0052] - figure 12 schematically represents a perspective view of a second preform used in the manufacturing method according to the invention; and

[0053] - Figure 13 illustrates a partial sectional view of a part manufactured from the second preform of Figure 12. Elements having the same functions in the different implementations have the same references in the figures.

[0054] The figures are not drawn to scale. In particular, the thicknesses are enlarged to make the figures easier to read.

[0055] Detailed description of the invention

[0056] Figure 1 illustrates a schematic cross-sectional view of a first example of an open part which can be obtained by the method according to the invention, in particular of an open panel 10. By panel is meant any surface part which can also be non-planar and non-developable.

[0057] Examples of application may be aircraft nacelle reverser flaps, part of reverser grids, stiffened internal or external vein panels, etc.

[0058] The open panel 10 comprises a composite skin 12 and at least one reinforced rib 14, also called a stiffener. The open panel 10 may further comprise unreinforced ribs, i.e. having an unreinforced head.

[0059] As previously indicated, "rib" means any out-of-plane elevation shape of the panel and "stiffener" means a rib with a reinforced head, i.e. a reinforced structure at the top of its body.

[0060] The skin 12 extends along a plane of extent XY, and defines an external face 16 and an internal face 18, spaced apart from each other along a thickness direction Z perpendicular to the plane of extent XY.

[0061] The external face 16 is for example intended to face a passenger compartment and to be visible, while the internal face 18 may not be visible depending on the installation of the part, once the panel 10 is in place.

[0062] The ribs, reinforced or not, each comprise a body 20 and a head 22. The bodies 20 project from this internal face 18 of the skin in the thickness direction Z, up to the respective heads 22 of the stiffeners 14.

[0063] Furthermore, each rib body 20, reinforced or not, extends on the internal face 18 of the skin 12, in an associated direction of extent. For example, the bodies 20 of the ribs all extend in the same direction of extent X, parallel to each other as in the example illustrated in FIG. 1.

[0064] The ribs, reinforced or not, can be regularly spaced in a transverse direction Y, perpendicular to the direction of extent X and to the direction of thickness Z.

[0065] Each rib body, reinforced or not, comprises two flanks 24 extending between the internal face 18 and the head 22 of the rib, reinforced or not, opposite each other in the transverse direction Y. For each stiffener 14, the head 22 of the rib is reinforced relative to the body 20 of said rib, that is to say it has a greater stiffness and thus makes it possible to reinforce the panel 10.

[0066] The reinforced heads 22 extend along the body 20 of the reinforced rib 14.

[0067] Each reinforced head is a rigid structure elongated in the direction of extension of the body of the reinforced rib 14, i.e. the X direction in the illustrated example, in the form of a rod, made of a rigid material, which in particular has an elastic stiffness greater than or equal to that of the material making up the body of the ribs.

[0068] Figure 2 represents a three-dimensional schematic view of another example of a panel which is more complex than the first example of Figure 1 and which can also be obtained by the method according to the invention.

[0069] In this example, the panel 10 comprises ribs in elevation relative to the skin (body and head) extending in several directions of extent distinct from one another. In particular, in the illustrated example, three reinforced ribs 14A extend in a first direction of extent X, two reinforced ribs 14B extend in a second direction of extent Y, and three reinforced ribs 14C extend in directions of extent intermediate between the first and second directions of extent X, Y.

[0070] All the directions of extent form an angle between them of between 15° and 165°, and in particular equal to 90° in the example shown for the first direction of extent X and the second direction of extent Y.

[0071] The reinforced ribs 14 intersect at at least one crossing point 26. Two stiffeners 14 form the crossing point 26 and are secured to each other at the crossing point of their reinforced heads.

[0072] The manufacturing method 100 of a part, in particular an open panel, made of composite material according to the invention will now be described in detail with reference to figure 3 which is a flowchart representing the steps of the method.

[0073] The method comprises a step 1 10 of supplying or providing at least one first fiber preform PF1 intended to form the skin 12 and the body 20 of the stiffeners 14.

[0074] The first fiber preform PF1 may comprise continuous fibers and / or discontinuous fibers FDC to form the skin and the body of the stiffeners. We speak of short fibers when they have a length of less than 1 mm as opposed to long fibers which have a length of a few tens of millimeters. Thus, the first fiber preform PF1 may be in the form of stacks of layers or sheets of unidirectional fibers, known for example by the English acronym NFC for "Non-Crimp Fabrics". Alternatively, the first fiber preform PF1 may be in the form of fabrics or mats called SMC according to the English acronym for "Sheet Molding Compound". In a known manner, such mats comprise continuous or discontinuous fibers distributed randomly mainly in the plane of extension of the mat.According to another alternative, the first fiber preform PF1 can be in the form of bulk materials known for example by the English acronym BMC for “Bulk Molding Compound” comprising fibers of finite lengths and generally of a length less than 50 mm.

[0075] Preferably, the fibers of the first fiber preform PF1 are advantageously pre-impregnated with an impregnating polymer resin (or matrix). In other words, the first preform PF1 is made of a so-called pre-impregnated composite material, i.e. comprising fibers embedded in a resin. The impregnating resin comprises in particular a thermoplastic or thermosetting resin. An example of a thermoplastic resin is a polyamide, a polyetheretherketone, a polyetherketoneketone, poly(phenylene sulfide) or a polyaryletherketone. The thermosetting resin comprises, for example, an epoxide or a polyimide. The fibers are organic, mineral, metallic, thermoplastic polymer or thermosetting polymer fibers or a mixture of these fibers. An example of a fiber is carbon, glass or aramid fiber.

[0076] The method comprises a step 120 of supplying or sourcing at least one second fiber preform PF2 intended to form the head 22 of the stiffeners, i.e. the reinforced head of the reinforced ribs.

[0077] The second fiber preform PF2 comprises at least long fibers FC oriented in the direction of extension associated with the stiffeners 14.

[0078] Long oriented continuous fibers are understood to mean unidirectional continuous fibers whose length is approximately equal to a few tens of millimeters.

[0079] Preferably, the second fiber preform PF2 is also made of a so-called pre-impregnated composite material, i.e. comprising fibers embedded in a resin. Preferably, the resin for the second fiber preform PF2 is identical to that of the first fiber preform PF1.

[0080] Advantageously, the long oriented fibers of the second fiber preform PF2 intended to form the reinforced heads 22 of the reinforced ribs 14 are predominantly or exclusively in the form of several ribbons of unidirectional fibers, generally noted UD for “unidirectional”. Each ribbon of unidirectional fibers comprises a set of continuous filaments parallel to each other. The continuous filaments are thus arranged longitudinally over the entire length of the extent of the head 22 of the stiffener 14. When the part to be manufactured comprises stiffeners 14 extending in several directions of extent distinct from each other and intersecting at points of intersection 26 (see FIG. 2), the second preform PF2 advantageously comprises ribbons of continuous longitudinal fibers extending in the different directions of extent and overlapping alternately at the points of intersection.

[0081] Figure 12 shows such a second preform PF2 intended to form the heads 22 of the stiffeners 14 and in particular at a point of intersection 26. In the example illustrated, a stiffener 14A extends in a first direction of extent X and a stiffener 14B extends in a second direction of extent Y. The second preform PF2 comprises first longitudinal fiber ribbons RA extending in the first direction of extent X and second longitudinal fiber ribbons RB extending in the second direction of extent Y. The first ribbons RA and the second ribbons RB intersect at the point of intersection 26 in an alternating manner. At the point of intersection 26, a stack of a first ribbon RA then a second ribbon RB then a first ribbon RA, etc. is thus obtained.

[0082] Such a configuration of alternating ribbons according to the different directions of extension of the stiffeners advantageously makes it possible to increase the mechanical connections of the fibers of the different directions and thus to reinforce the mechanical strength of the intersection point, also called inter-stiffener node if necessary.

[0083] These ribbons can be advantageously deposited by a process of depositing ribbons on a geometric shape by mechanized draping.

[0084] Preferably, the width L of the ribbons of a bundle of longitudinal fiber ribbons UD is slightly less than or equal to the width of the head of the stiffener 14 of the part to be produced. By width is meant a dimension transverse to the direction of extension of the stiffener and therefore of the ribbons, which is also a dimension perpendicular to the direction of the longitudinal fibers of the ribbons.

[0085] Advantageously, the second preform PF2 intended to form the head of the stiffeners comprises, for each stiffener head, at least one additional layer PF21 made of long or continuous fiber material.

[0086] This additional layer PF21 is arranged so as to cover at least one of the ribbons of unidirectional UD fibers extending in the direction of extension associated with said stiffener head 22, more precisely to cover a bundle of ribbons RA, RB of unidirectional UD fibers as illustrated in FIG. 12. The additional layer(s) PF21 have an elongated shape in the direction of extension of the reinforced head 22 of the associated stiffener.

[0087] The continuous fibers of the additional layer(s) PF21 extend in a direction different from the direction of extension of said associated stiffener head, i.e. in a direction transverse or non-collinear to the direction of extension of the stiffener. Furthermore, the additional layer(s) PF21 is (are) shaped to cover the at least one ribbon RA, RB of unidirectional fibers UD and at least partially the body 20 associated with said stiffener head of the part after thermocompression.

[0088] Thus, this or these additional PF21 layers improve the transfer of stresses between the longitudinal fibers of the head and the body of the stiffener.

[0089] Preferably, each additional layer PF21 is arranged directly on each independent linear segment of the associated reinforced head. It extends transversely on either side of the longitudinal ribbons so as to constitute, after forming and thermocompression, a U-shaped fibrous continuity in a plane orthogonal to the direction of extension covering the unidirectional fibers UD of the reinforced heads and a portion of the body of the stiffener. In other words, the width L' of each additional layer PF21 is greater than the width L of the ribbons of a bundle of ribbons of unidirectional fibers UD to be covered. Preferably, the width L' of the additional layer PF21 is sufficient to extend over a covering height H along the sides 24 of the stiffener greater than three times its thickness E, and even more preferably at least 5 times its thickness E.Thickness E is the thickness of the additional PF21 layer before baking.

[0090] Figure 13 illustrates a partial sectional view of an embodiment of a part manufactured in particular from such a second preform PF2 in which the additional layers of the preform PF21 are added to the thickness of the stiffener body, i.e. the dimension of the body in the transverse direction Y. In an alternative mode, the thickness of the stiffener body is constant and the additional layers of the preform PF21 replace a portion of the material of the body of the rib over the overlap height H.

[0091] Such a second PF2 preform may be manufactured by arranging pieces of continuous fibers on a lay-up form to form the additional layer(s) PF21 and then superimposing the unidirectional fiber ribbons UD on the additional layer(s) PF21.

[0092] Alternatively, such a second PF2 preform may be manufactured by first depositing the UD unidirectional fiber ribbons and then depositing thereon at least one layer of continuous fibers extending over a small width on either side of the deposition width of the UD unidirectional fiber ribbons.

[0093] Each additional PF21 layer can be a fabric whose fibers are preferentially oriented between + / -30 and + / -6O 0 relative to the direction of extension of the associated stiffener, in other words the fabric comprises first fibers oriented between +30 and +60° relative to the direction of extension and second fibers oriented between -30 and -60° relative to the direction of extension, symmetrically to the first fibers relative to the direction of extension of the associated stiffener. The fabric is formed by two-dimensional weaving of the first fibers and second fibers are woven.

[0094] Alternatively, each additional layer PF21 may be a stack of at least two layers of unidirectional fibers that extend in directions symmetrical to the direction of extension of the associated stiffener and between + / -30 and 90° to the direction of extension of the associated stiffener.

[0095] Then, the method comprises a step 130 of placing in a molding device 30 the assembly formed from the first fiber preform PF1 and the second fiber preform PF2 as illustrated in FIG. 4.

[0096] Figure 4 schematically represents a sectional view of a molding device or mold 30 for manufacturing the part illustrated in Figure 1 or 2 before the thermocompression step.

[0097] This device 30 comprises a matrix 32 and a cover or punch 34 mounted to slide vertically, in the Z direction, in the matrix and defining with it a compression chamber 36.

[0098] The matrix 32 has a main surface 38 facing the cover 34. This main surface 38 has reliefs, and more precisely cavities 40 extending from the main surface 38 and shaped to form the stiffeners of the open panel. The shape and arrangement of the cavities 40 correspond to those of the stiffeners 14 of the part to be manufactured. Thus, each cavity 40 extends from the main surface 38 to a bottom 42. The second fiber preform PF2 is arranged between the matrix 32 and the first fiber preform PF1.

[0099] In a first embodiment, the first fiber preform PF1 and the second fiber preform PF2 are assembled by stacking one on top of the other to form an assembly and then this assembly is installed in the molding device so that the continuous fibers of the second preform intended to form the heads of the stiffeners are positioned in line with the cavities. Then the molding device 30 is closed.

[0100] Of course, if the preform PF2 comprises complementary layers PF21, these are stacked in external layers of the assembly so as to be the first in contact with the surface 38 of the molding form.

[0101] According to a first variant, the second fiber preform PF2 intended to form the heads of the stiffeners is first positioned alone in the molding device 30 so that each ribbon or bundle of ribbons associated with a stiffener head is engaged in the corresponding cavity 40 of the die 32 of the molding device 30. The first fiber preform PF1 is then placed above the second preform and in particular on the main surface 38 of the die 32 before the thermocompression step. Advantageously, the molding device 30 may comprise another punch shaped to push each ribbon or bundle of ribbons associated with a stiffener head partially into the corresponding cavity 40 or to the bottom 42 thereof.This step of driving the second preform PF2 into cavities is all the more advantageous since the second preform PF2 comprises at least one additional layer PF21 as described previously in order to promote control of the driving of the second preform PF2 centered in each cavity and the juxtaposition of the additional layer PF21 along the sides 24 of the associated stiffener.

[0102] According to a second variant, the step 130 of placement in the molding device 30 comprises:

[0103] - the installation of the second fiber preform PF2 so that each ribbon or bundle of ribbons associated with a stiffener head is at least partially engaged in the corresponding cavity 40 towards the bottom 42 thereof, then

[0104] - the placement of the PF12 body fiber preform on the main surface 38 in line with the cavities. Preferably, the PF12 body fiber preform is compressed so as to creep at least partially in the cavities 40. This creep can reach at least 80% of the filling of the stiffeners, preferably at least 90%, and more preferably at least 95%.

[0105] The placement step 130 continues with the placement of the skin fiber preform PF11 above the body fiber preform PF12 before closing the molding device for the step of thermocompression of the final assembly to form the final part.

[0106] Then, the method continues with a step 140 of thermocompression of the assembly to form the open panel as illustrated in Figure 5.

[0107] Figure 5 schematically represents a sectional view of the molding device 30 of Figure 4 when the mold is closed during thermocompression.

[0108] This thermocompression step ensures the positioning of the second fiber preform PF2 at the head of the stiffeners 14. In addition, the thermocompression makes it possible to obtain the flow of the material, at least partially, of the first fiber preform PF1 to form the body 20 of the stiffeners 14 so that it properly fills the tooling cavity. Thus, the thermocompression makes it possible to obtain the connection between the two preforms PF1 and PF2 by common consolidation. The fiber preforms are thus solidified by chemical reaction of crosslinking or polymerization for a thermosetting resin, heating and cooling for a thermoplastic matrix.

[0109] The reinforced heads 22 of the stiffeners 14 are thus integral with the respective bodies 20 of the stiffeners, and more precisely linked to the respective bodies by the polymer matrix of the composite forming the heads. The method may further comprise a step 150 of demolding the manufactured part followed by a step 160 of finishing the part in order to obtain the final part.

[0110] According to a first variant, the method according to the invention differs from the previous one in that during step 110 of supplying or providing at least one first fiber preform PF1, the first fiber preform PF1 comprises continuous fibers FC to form the skin and discontinuous fibers FDC to form the body of the stiffeners.

[0111] For example, the continuous FC fibers intended to form the skin of the part are sheets of unidirectional UD fibers or fabrics or mattresses of multiaxial multilayers - or BMC volume materials as described and defined previously.

[0112] The discontinuous fibers can be uniformly distributed superimposed on the layers of continuous fibers. Advantageously, the discontinuous fibers can be arranged in clusters or piles near the origins of the stiffeners on the skin, making it possible to reduce the creep lengths of the material of the first preform PF1 to fill the cavities and form the bodies of the stiffeners.

[0113] Such a step is illustrated in Figures 6 to 8. Figure 6 schematically illustrates the first preform PF1 in perspective. The first fiber preform PF1 comprises a fiber preform PF11 called “skin preform” intended to form the skin 12 and a fiber preform PF12 called “body preform” intended to form the body of the stiffeners 14.

[0114] The PF11 skin preform has several layers of continuous fibers, three plies in the example shown.

[0115] The body preform PF12 is formed from a cluster of discontinuous fibers arranged in clusters near the origins of the stiffeners 14 on the skin 12. In the example illustrated, the cluster is triangular in shape to form a stiffener of the same shape.

[0116] This step 110 may advantageously comprise a thermocompression step to form the first fiber preform PF1 from the skin preform PF11 and the body preform PF12 in order to consolidate them together and ensure their connection before the step 130 of placing in the molding device 30 the assembly formed by the first preform PF1 and the second preform PF2. The same molding device 30 may be used during the two thermocompression steps.

[0117] Figure 7 schematically represents a sectional view of the molding device just before closing the cover 34 on the die 32 while Figure 8 illustrates the result of this thermocompression, i.e. the first fiber preform PF1.

[0118] Preferably, the skin preform PF1 1 comprises an additional layer PF11 1 of continuous fibers. Figure 9 schematically illustrates such a first preform PF1 in perspective. The additional layer PF11 1 comprises a slot 50 for each stiffener 14, each slot 50 extending in the associated direction of extension of the stiffeners 14. In the illustrated example, the slot 50 is triangular in shape to form a stiffener of the same shape.

[0119] The discontinuous fibers of the body preform PF12 are arranged in clusters between the layers of the skin preform and the additional layer of the skin preform at the slots 50 of the additional layer PF1 11 , as illustrated in Figures 10 and 11 . Figure 10 schematically represents a sectional view of the first preform PF1 intended to be inserted into the molding device while Figure 1 1 illustrates the result of the thermocompression, that is to say the first fiber preform PF1 in which the body 20 of the stiffeners 14 is at least partially formed.

[0120] The presence of the additional layer PF11 1 of continuous fibers, provided with slots 50 at the level of the clusters of discontinuous fibers, advantageously makes it possible to guide the movement of the discontinuous fiber elements and to ensure a continuous layer of fibers on the surface of the part at the start of the stiffeners 14.

[0121] The invention as described thus advantageously makes it possible to facilitate and make robust the manufacture by thermocompression of such ribbed parts, and in particular of structurally optimized ribbed panels.

[0122] Obviously, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms and other variants that may be envisaged by those skilled in the art within the scope of the invention and in particular all combinations of the different operating modes described above, which may be taken separately or in association.

[0123] In particular, the invention, as described, uses so-called pre-impregnated composite materials, i.e., comprising fibers embedded in a resin to form all of the fiber preforms. However, the method can also be applied to so-called "dry" fiber preforms, i.e., comprising fibers held together by a binder. In this case, the resin is applied to the preforms, for example, by a film of resin arranged between the cover and the first fiber preform before closing the molding device, the preforms being impregnated during thermocompression. Alternatively, the resin can be injected into the compression chamber of the molding device after closing the latter.

Claims

CLAIMS 1. Method (100) for manufacturing an open part (10) made of composite material comprising a skin (12) and at least one rib each comprising a body (20) and a head, the body extending from an internal face (18) of the skin to the head, each rib extending in an associated direction of extent, the part comprising at least one rib called a reinforced rib (14) having a reinforced head (22), the method being characterized in that it comprises the following steps: - a step of providing (1 10) at least one first fibrous preform (PF1) intended to form the skin and the body of the at least one rib; - a step of providing (120) at least one second fiber preform (PF2) intended to form the reinforced head (22) of the at least one reinforced rib (14); - a step of placing (130) in a molding device (30) comprising a punch (34) and a die (32) the assembly formed of the first fiber preform and the second fiber preform, the second fiber preform being arranged between the die and the first fiber preform and the die being shaped to form the at least one rib of the open part; and - a thermocompression step (140) of the assembly to form the open part; - a step of demolding the assembly to form the open part; and in that the first fiber preform comprises at least discontinuous fibers (PF12) to form at least the body of the ribs and that the second fiber preform comprises at least continuous fibers oriented in the direction of extension associated with the at least one rib.

2. Method according to claim 1, in which the first preform (PF1) comprises layers (PF11) of continuous fibers to form the skin, the discontinuous fibers (PF12) being arranged in clusters on one of the layers of continuous fibers to form the body of the at least one rib.

3. Method according to claim 2, in which the first preform (PF1) comprises an additional layer (PF11 1 ) of continuous fibers to form the skin comprising slits (50), each slit extending in the associated direction of extension of the at least one rib, the discontinuous fibers being arranged in clusters between the layers and the additional layer of continuous fibers at right angles to the slits of the additional layer.

4. Method according to any one of the preceding claims, in which the or each of the at least one reinforced rib (14) extends in at least two directions. of distinct extent (X, Y) and intersect at intersection points (26) and in which the second preform (PF2) comprises ribbons (RA, RB) of continuous unidirectional fibers extending along the at least two directions of extent and overlapping alternately at the intersection points.

5. Method according to the preceding claim 4, in which the second preform (PF2) comprises, for each reinforced rib head, at least one additional layer (PF21) of continuous fiber material arranged so as to cover at least one of the ribbons of unidirectional fibers extending in the direction of extension associated with said reinforced rib head, the additional layer having an elongated shape in the direction of extension of said associated reinforced rib head, the continuous fibers of the additional layer extending in a direction different from the direction of extension of said associated reinforced rib head and the additional layer being shaped to cover the at least one ribbon of longitudinal fibers and at least partially the body associated with said reinforced rib head of the open part after thermocompression.

6. Method according to the preceding claim 5, in which a first portion of the continuous fibers of the additional layer (PF21) are oriented at an angle of between 30° and 60° relative to the direction of extension of the associated rib reinforced head and a second portion of the continuous fibers of the additional layer are oriented at an angle of between -30° and -60° relative to the direction of extension of the associated rib reinforced head.

7. Method according to the preceding claim 5 or 6, in which the additional layer (PF21) has a width in a direction perpendicular to the direction of extension of the associated rib-reinforced head so that after thermocompression, the additional layer covers the body over a covering height greater than at least three times the thickness of the additional layer, and preferably at least greater than 5 times the thickness of the additional layer.

8. Method according to any one of the preceding claims, in which the matrix (32) comprises a main surface (38) and cavities (40) extending from the main surface and being shaped to form the at least one rib of the open part, and in that the positioning step comprises the positioning of the second fibrous preform (PF2) at the bottom of the cavities then the positioning of the first fibrous preform (PF1) on the main surface before the thermocompression step.

9. Method according to one of claims 1 to 7, in which the matrix (32) comprises a main surface (38) and cavities (40) extending from the main surface and being shaped to form the at least one rib of the open part and the step of providing at least one first fiber preform comprises a step of providing a so-called skin fiber preform intended to form the skin and a step of providing a so-called body fiber preform intended to form the body of the at least one rib; and in which the step of placing in the molding device (30) comprises: - the placement of the second fiber preform (PF2) in the cavities (40), then - the placement of the fibrous body preform (PF12) on the main surface (38) in line with the cavities, then - the placement of the skin fiber preform (PF11) above the body fiber preform (PF12).

10. Method according to the preceding claim, in which the fibrous body preform (PF12) is compressed so as to flow at least partially into the cavities (40) before the skin preform (PF11) is put in place, so as to form at least 80% of the filling of the at least one rib, and preferably at least 90%, and more preferably at least 95%.

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