METHOD FOR MANUFACTURING A COMPOSITE MATERIAL PART WITH ELEVATED ELEMENTS AND CORRESPONDING PART

Abstract

The invention relates to a part (20) made of composite material for a turbomachine, in particular an aircraft, comprising:- a composite skin (22) having an inner face (28) and an outer face (26), the composite skin comprising continuous fibers; and- at least one element (24) extending in a respective direction of extension (X), each element (24) comprising a body (30) extending from the inner face (28) of the skin to a free end (32) in an elevation direction (Z) distinct from the direction of extension, each body (30) being connected to the inner face by at least one fillet (36, 36'), the body is made of composite material comprising mainly discontinuous fibers; characterized in that the part (20) further comprises an additional skin (40) of continuous fibers covering at least the at least one fillet connecting the body to the inner face of the skin. Figure for abstract: Figure 3

Description

Title of the invention: METHOD FOR MANUFACTURING A PART MADE OF COMPOSITE MATERIAL WITH ELEVATED ELEMENTS AND CORRESPONDING PART Technical field of the invention

[0001] The present invention relates to the field of parts made of composite material from a fibrous reinforcement densified by a matrix, in particular turbomachine parts. It relates in particular to parts comprising elements in elevation out of plane relative to a surface of the part and monolithic such as a stiffener or a yoke.

[0002] The invention also relates to a method of manufacturing such parts. Technical background

[0003] 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.

[0004] Certain composite materials are usually composed of a fibrous reinforcement and a matrix.

[0005] Several technologies have been identified for manufacturing composite material parts, including injection molding (or RTM - an English acronym meaning "Resin Transfer Molding"), thermoplastic injection and thermocompression. RTM injection requires fiber reinforcement, in most cases with continuous fibers.

[0006] Many turbomachine parts include out-of-plane elevation elements such as a stiffener, a yoke, a rib, a gusset.

[0007] However, these elevation elements can rise to a very significant height in relation to their thickness (their transverse dimension) or in relation to the surface on which they rest. This is the case, for example, of a rib screed 3 to 10 mm thick which rises to a distance of 30 to 50 mm high. In this case, it is sometimes difficult to guide the material so that it fills the entire shape of the elevation element. Furthermore, the organization of material at the foot of the element can present a significant mechanical weakness.

[0008] The objective of the present invention is to provide a solution making it possible to improve the method of manufacturing a part by thermocompression and thermoflow, in particular a turbomachine, in composite material with at least one raised element whose elevation height is significant relative to the surface on which it rests while having the best mechanical performance of the junction zone. Summary of the invention

[0009] The invention relates to a method for manufacturing a part made of composite material, in particular for an aircraft, comprising a composite skin having an internal face and an external face, and at least one element extending in a respective direction of extent, each element comprising a body extending from the internal face of the skin to a free end in a direction of elevation distinct from the direction of extent, each body being connected to the internal face by at least one fillet, the method comprising the following steps: - a step of providing a first fibrous preform intended to form the skin and comprising continuous fibers; - a step of providing a second fiber preform intended to form the body of the elements and comprising mainly discontinuous fibers; - a step of providing a third fiber preform intended to form the additional skin and comprising continuous fibers; - a step of placing in a molding device comprising a punch and a die the assembly formed of the first fiber preform, the second fiber preform and the third fiber preform so that the discontinuous fibers of the second preform are arranged in clusters on the first preform to form the body of the at least one element and the third fiber preform is shaped and arranged so as to at least partially cover the clusters of discontinuous fibers of the second preform; - a step of thermocompression of the assembly to form the part; and - a step of demolding the assembly to form the part.

[0010] 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 reliable method for manufacturing a part comprising at least one raised element whose elevation height is significant relative to the surface on which it rests. Indeed, the additional layer(s) above the skin and covering the connection fillets makes it possible to ensure very good mechanical strength conditioned by the fibers instead of just the resin.

[0011] The method according to the invention may comprise one or more of the following characteristics, taken in isolation or in combination with each other, according to all technically possible combinations: - the third preform intended to form the additional skin comprises slits, each slit extending in the associated direction of extension of the at least one element, the discontinuous fibers being arranged in clusters between the first fiber preform and the third fiber preform at right angles to the slits of the third preform; - the third preform intended to form the additional skin comprises a plurality of portions of continuous fibers, the portions being arranged so as to form orifices in line with the elements to be formed of the part, the discontinuous fibers being arranged in clusters between the first fiber preform and the third fiber preform in line with the orifices of the third preform; - the orifices of the third preform are partially closed by the respective portions which form the orifices so that during the thermocompression step, the discontinuous fibers of the clusters flow through the orifices to form the elements of the part to be manufactured; - the discontinuous fibers of the second fiber preform have a length of less than 50 mm, preferably less than 30 mm; - the first fiber preform, the second fiber preform and the third fiber preform are pre-impregnated with a resin; - the third preform comprises a first layer comprising first unidirectional fibers oriented at an angle of between +30° and +150° relative to the direction of extension of the at least one fillet, preferably between +40° and +140°, and a second layer comprising second unidirectional fibers oriented at an angle of between -30 and -150° relative to the direction of extension, symmetrically to the first fibers relative to the direction of extension of the associated elevation element, and preferably between -40° and -140°.

[0012] The invention also relates to a part made of composite material for a turbomachine, in particular an aircraft, comprising: - a composite skin having an inner face and an outer face, the composite skin comprising continuous fibers; and - at least one element extending in a respective direction of extent, each element comprising a body extending from the internal face of the skin to a free end in a direction of elevation distinct from the direction of extent, each body being connected to the internal face by at least one connecting fillet, the body is made of composite material mainly comprising discontinuous fibers. According to the invention, the part further comprises an additional skin of continuous fibers covering at least one fillet connecting the body to the internal face of the skin.

[0013] The part according to the invention may comprise one or more of the following characteristics, taken in isolation or in combination with each other, according to all technically possible combinations: - the continuous fibers of the additional skin extend in orientations from the inner face of the skin towards the body of the at least one element and at least one of the orientations of the continuous fibers of the additional skin extends along a curvilinear path along the at least one fillet; - the part is an open panel and the at least one element is a screed or a stiffener.

[0014] The part is advantageously produced by implementing the method according to the invention and as described previously.

[0015] The invention further relates to a turbomachine comprising a part made of composite material as mentioned above. Brief description of the figures

[0016] 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:

[0017] - [Fig.l] is a partial axial sectional view of an example of a turbomachine with to which the invention applies;

[0018] - [Fig.2] is a schematic cross-sectional view of an example of a part according to the invention comprising three elements in elevation; - [Fig. 3] is a three-dimensional schematic view of an example of a composite material part according to the invention comprising an elevation element such as a stiffener; - [Fig.4] is a three-dimensional schematic view of another example of a composite material part according to the invention comprising two elements in elevation such as a double-clamp part; - [Fig.5] is a block diagram representing a method of manufacturing a part according to the invention; - [Fig.6] schematically illustrates in perspective an example of stacking of layers of continuous fibers forming a first preform and the positioning of discontinuous fibers forming a second preform in line with the elevation elements of the part to be produced; - [Fig.7] is a sectional view of [Fig.6]; - [Fig.8] schematically illustrates in perspective an example of superposition of a layer of continuous fibers forming a third preform, the layer comprising a triangular slot at the right of the elements in elevation of the part to be produced;

[0019] - [Fig.9] is a sectional view of [Fig.8] with the tooling; - [Fig. 10] schematically illustrates in perspective the final piece obtained;

[0020] - [Fig. 11] is a sectional view of [Fig. 10]; - [Fig. 12] is a three-dimensional schematic view of a step of placing the first, second and third preforms, the third preform comprising a slot in line with an element in elevation of the part to be produced; - [Fig. 13] is a three-dimensional schematic view of another example of a step of placing the first, second and third preforms, the third preform comprising two portions with parallel edges on either side of an elevation zone of a part to be produced; - [Fig. 14] is a schematic sectional view of another example of a step of placing the first, second and third preforms, the third preform comprising two portions with parallel edges on either side of a lifting zone of a part to be produced, the two portions overlapping slightly above the lifting zone of a part to be produced; and - [Fig. 15] is a schematic sectional view of [Fig. 14] during the thermocompression step and illustrates in particular the finishing of the discontinuous fibers of the second preform through the slot of the third preform.

[0021] Elements having the same functions in different implementations have the same references in the figures. The figures are not drawn to scale. In particular, the thicknesses are enlarged to make the figures easier to read. Detailed description of the invention

[0022] [Fig. 1] represents an axial and partial sectional view of a turbomachine 1 with longitudinal axis A which comprises various parts and / or members which can be made of composite materials. Of course, the invention applies generally to all parts made of composite material having complex shapes (profiles with evolving section for example) and in various fields in which the parts allow transmission of forces, a reduction in mass while being economical.

[0023] The turbomachine 1 of [Fig.l] is a dual-flow, dual-spool turbomachine intended to be mounted on an aircraft. The turbomachine 1 comprises a fan 2 which is mounted upstream of a gas generator 3 or engine following the circulation of the gases in the turbomachine and here along the longitudinal axis A (and even from left to right in [Fig.l]). The gas generator 3 comprises, from upstream to downstream, a low-pressure compressor 4a, a high-pressure compressor 4b, a combustion chamber 5, a high-pressure turbine 6a and a low-pressure turbine 6b. The fan 2 comprises a plurality of fan blades 7 which extend along a radial axis R and whose free ends are surrounded by a fan casing 8. The longitudinal axis A is perpendicular to the radial axis R and also to a transverse axis T. The fan casing 8 is carried by a nacelle 9, the nacelle 9 and the fan casing 8 being centered on the longitudinal axis A. The fan 2 divides the air entering the turbomachine into a primary air flow that passes through the gas generator and in particular in a primary vein 10, and into a secondary air flow that circulates around the gas generator in a secondary vein 11. Outlet Guide Vanes (OGV for "Outlet Guide Vane" in English) 12 which are located downstream of the fan blades 7, extending around the longitudinal axis A and through the secondary vein to straighten the secondary air flow.

[0024] [Fig. 2] illustrates a schematic cross-sectional view of a first example of a part 20 made of composite material according to the invention. Figures 3 and 4 also each illustrate a part 20 made of composite material with a fiber reinforcement embedded in a matrix. In particular, the part 20 comprises one or more elevation elements. The part 20 of [Fig. 3] is for example a part with a stiffener as an elevation element while the part of [Fig. 4] is for example a double-clamped part.

[0025] More precisely, the part 20 comprises a composite skin 22 and at least one so-called elevation element 24, for example stiffeners ([Fig.3]), ribs, yokes ([Fig.4]), etc.

[0026] In the examples illustrated in Figures 2 to 4, the skin 22, called the main skin, extends along a plane of extent XY, and defines an external face 26 and an internal face 28, spaced apart from each other along a thickness direction Z perpendicular to the plane of extent XY.

[0027] The external face 26 is for example intended to face a passenger compartment and to be visible, while the internal face 28 is not visible, once the part 22 is in place.

[0028] The so-called elevation element(s) 24 each comprise a body 30 projecting from this internal face 28 of the skin in the thickness direction Z, up to a respective free end 32.

[0029] Furthermore, each body 30 extends on the internal face 28 of the skin 22, in an associated direction of extension.

[0030] In the example illustrated in [Fig.2], the direction of extension of the element 24 is the direction X. In the example of [Fig.4], the bodies 30 of the two elements 24, in particular the yokes, extend in the same direction of extension X, parallel to each other.

[0031] Alternatively, the bodies 30 of the elements 24 may extend in different directions of extent and intersect at points of intersection as illustrated for example in FIGS. 6 to 11.

[0032] The elements 24 can be regularly spaced along a transverse direction Y, perpendicular to the direction of extent X and to the direction of thickness Z as illustrated in particular in [Fig.2].

[0033] Each body 30 comprises two flanks 34 extending between the internal face 28 and the free end 32 of the body 30 of the respective element 24, opposite each other in the transverse direction Y. The flanks 34 extend mainly in parallel XZ planes.

[0034] Furthermore, each body 30 is connected to the internal face 28 by at least one connecting fillet 36. In other words, each body 30 widens towards the internal face 28. In the example of [Fig. 3], each of the two flanks 34 of the body 30 of the stiffener 24 flares towards the internal face 28 of the skin. Each fillet has a curvilinear profile in a plane transverse to the direction of extension of the stiffener X. Furthermore, the body 30 of each element 24 may also comprise two other flanks 34' extending between the inner face 28 and the free end 32 of the body 30 of the respective element 24, opposite each other in the direction of extension X. The other flanks 34' thus extend mainly in parallel YZ planes. The other flanks 34' may also be connected to the inner face 28 by a fillet 36' as illustrated in the example of [Fig. 4] of a double-clamped part. The body 30 of each clamp flares towards the inner face 28 of the skin 22.

[0035] According to the invention, the part 20 further comprises an additional skin 40 composed of continuous fibers covering at least the connection fillet(s) 36, 36' of the body 30 to the internal face 28 of the skin 22. More precisely, the additional skin 40 extends along the plane of extent of the main skin 22, that is to say along the plane of extent XY, and defines an external face 46 and an internal face 48, separated from each other along a thickness direction Z perpendicular to the plane of extent XY. The external face 46 of the additional skin 40 is in contact with the internal face 28 of the main skin when it is not in contact with the body of an element 24 and in particular with its connection fillet 36, 36'. The internal face 48 of the additional skin 40 forms the internal face of the final part 20.

[0036] The additional skin 40 can also partially cover the sides 34, 34' of the body 30 of the elements 24 near the connection fillets 36, 36'.

[0037] In the example illustrated in [Fig. 3], the additional skin 40 is formed of two portions 40A and 40B each covering a fillet 36 of a flank 34 of the stiffener and extending above the internal face 28 of the main skin 22 in opposite directions along the direction Y perpendicular to the direction of extension of the element 24, that is to say of the stiffener of the part.

[0038] In the example illustrated in [Fig.4], the additional skin 40 is formed from a single piece of continuous material and comprises an orifice 42 per element through which the element extends from the internal face 28 of the main skin 22 towards the free end 32. Each orifice 42 is delimited by a periphery 44 matching the shape of the body 30 of the element, in particular of the yoke, which passes through it so as to cover the or all of the connection fillets 36, 36' of the body of the element 24.

[0039] Furthermore, the continuous fibers of the additional skin 40 extend in orientations from the internal face 28 of the main skin 22 towards the body 30 of each element 24 and at least one of the orientations of the continuous fibers of the additional skin 40 extends in a curvilinear path along the corresponding fillet, i.e. it covers.

[0040] The part 20 made of composite material as illustrated in Figures 2 to 4 is composed of fiber reinforcements. The fiber reinforcements are intended to provide strength to the final part 20 obtained, in particular at the walls or junctions of the part. The fiber reinforcements are densified by a matrix to obtain the rigid final part with the elevation elements 24.

[0041] More precisely, the main skin 22 is composed of a first fibrous reinforcement, in particular with continuous fibers, the elevation element(s) 24 are composed of a second fibrous reinforcement, mainly with discontinuous fibers, and the additional skin 40 is composed of a third fibrous reinforcement with continuous fibers. The fibrous reinforcements are each obtained from fibrous preforms as described below.

[0042] The method 100 for manufacturing such parts made of composite material according to the invention will now be described in detail with reference to [Fig.5] which is a flowchart representing it.

[0043] The method comprises a step 110 of supplying or providing a first fiber preform PF1, called skin preform, intended to form the skin and comprising continuous fibers.

[0044] 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 polyetheretherketoneketone, 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.

[0045] The skin preform PF1 mainly comprises continuous fibers arranged in several layers of continuous fibers such as unidirectional fiber sheets. tional whose extension directions are different from one layer to another, fabrics or multiaxial multilayer mats of layers called NCF for "Non-Crimp Fabrics" in English. The mats are formed from a stack of layers of fibers whose direction differs from one layer to another. The continuous fibers advantageously provide the main skin 22 with high mechanical performance. The skin preform PF1 can also contain discontinuous fibers, in particular for example to provide the volume of adaptation material necessary for variable thicknesses of the part to be produced.

[0046] The method comprises a step 120 of providing or supplying a second fiber preform PF2, called a body preform, intended to form the body of the stiffeners and comprising mainly discontinuous fibers.

[0047] The PF2 body preform is mainly composed of discontinuous fibers in the form of: - bulk volume of the BMC type according to the English acronym “BulkMolding Compound” comprising fibers of finite lengths (generally less than 50 mm in length), - bulk surface of fabrics or SMC type mattresses according to the English acronym "Sheet Molding Compound") comprising continuous or discontinuous fibers distributed randomly mainly in the plane of the fabric / mattress, or - of mats of shavings or “chips” of material comprising oriented fibers (DLF for “Discontinuons Long Fiber” in English) obtained from pieces of fabric or pieces of sheets of unidirectional fibers, or - finished pieces of wicks.

[0048] Advantageously, the discontinuous fibers of the body preform PF2 have a length of less than 50 mm, preferably less than 30 mm.

[0049] Preferably, the second fiber preform PF2 is also made of 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.

[0050] The volume of material for the body preform PF2 determined to manufacture the part 20, and more precisely the elevation elements 24, must be at least equal to the volume of the elevation elements 24 to be formed. Preferably, the volume is slightly greater than that of the elevation elements 24 to be formed to promote good compaction of the material during thermocompression. Indeed, material health - minimization of porosities - is obtained by compressing the material and requires that the quantity of material placed in the tooling be at least equal to the volume of the impression to be molded. The material of the preform PF2 can be arranged near the elevation elements 24 to be formed to limit the finishing distance to travel in order to reach the elevation zone.

[0051] The method comprises a step 130 of providing or supplying a third fiber preform PF3 intended to form the additional skin. The third preform PF3 comprises exclusively continuous fibers such as unidirectional fiber sheets or bidirectional or monodirectional to multidirectional NCF fabrics.

[0052] The third preform PF3 comprises one or more layers of continuous fibers whose extension directions are different from one layer to another. The continuous fibers advantageously provide the additional skin 40 with high mechanical performance.

[0053] Furthermore, the continuous fibers of the third fiber preform PF3, intended to form the additional skin 40, are configured to extend in multiple orientations from the internal face 28 of the main skin 22 towards the body 30 of each element 24 in the final part 20. At least one of the orientations of the continuous fibers of the third fiber preform PF3 is configured to extend in a curvilinear path along the corresponding fillet, i.e. it covers.

[0054] The third fiber preform PF3 may comprise one or more layers of continuous fibers. In the case of several layers, the continuous fibers of the same layer may have a single common direction which varies from one layer to another. For example, a first layer comprises first unidirectional fibers oriented at an angle of between +30° and +150° relative to the direction of extent X of the fillet, preferably between +40° and +140°, and a second layer comprising second unidirectional fibers oriented at an angle of between -30 and -150° relative to the direction of extent X, symmetrically to the first fibers relative to the direction of extent X of the associated elevation element, preferably between -40° and -140°.

[0055] According to another example, the third fiber preform is a fabric having warp threads oriented between +35° and +55° along the direction of extension of the associated elevation element especially at the level of the connecting fillet 36 and weft fibers oriented between +125° and +145°.

[0056] Furthermore, the third fiber preform PF3, intended to form the additional skin 40, comprises free ends (fiber end edges) extending beyond the start of the connection fillets 36, 36' between the internal face 48 and the flanks 34, 34' of the elevation elements 24, so as to cover the skin preform PF1 and partially the discontinuous fibers of the body preform PF2 while providing a passage for the finishing of the discontinuous fibers of the body preform PF2 as described below and so as to be able to form the surface of the connection radii. 36.

[0057] Thus, the discontinuous fibers present in the PF2 preform result in a tensile failure mode instead of peeling. In addition, the continuous fibers of the internal surface 48 allow a failure mode by the fibers instead of inter-fibers. These two elements increase the level of failure and make it repeatable.

[0058] Then, the method comprises a step 140 of placing in a molding device 50 the assembly formed of the skin preform PF1 and the body preform PF2 and the third preform PF3 as illustrated in Figures 6 to 11. Figures 6 and 8 illustrate perspective views of the steps of assembling the preforms, [Fig. 10] represents the final part.

[0059] Figures 7, 9 and 11 respectively illustrate sectional views of Figures 6, 8 and 10. The molding device or mold 50 for manufacturing a part according to the invention is illustrated only in [Fig.9] for the sake of clarity of the figures.

[0060] With reference to [Fig.9], the device 50 comprises a die 52 and a cover or punch 54 mounted to slide vertically, in the direction Z, in the die and defining with it a compression chamber 56. The die 52 has a main surface 58 facing the cover 54. This main surface 58 has reliefs, and more precisely cavities 60 extending from the main surface 58 and shaped to form the elevation elements 24 of the final part 20. The shape and arrangement of the cavities 60 correspond to those of the elements 24 of the part to be manufactured. Thus, each cavity 60 extends from the main surface 48 to a bottom 62.

[0061] In the example illustrated, the final part ([Fig.10]) comprises a stiffener 24 of triangular shape.

[0062] Figures 6 and 7 schematically illustrate in perspective and in section an example of stacking of several layers of continuous fibers (three in the illustrated example) forming a skin preform PF1 and the positioning of discontinuous fibers forming a body preform in clusters on the skin preform PF1 in line with the elements in elevation of the part to be produced. The discontinuous fibers are advantageously arranged in clusters or piles near the origins of the elements 24 in elevation on the main skin making it possible to reduce the finishing lengths of the material of the second preform PF1 to fill the cavities and form the bodies of the elements 24.

[0063] In the example illustrated, the discontinuous fibers are arranged in a triangular-shaped cluster corresponding to the shape and dimensions of the element 24, for example a triangular stiffener, of the part 20 to be manufactured ([Fig. 10]).

[0064] Figures 8 and 9 schematically illustrate in perspective and in section the assembly formed by the skin preform PF1, the body preform PF2 and the third preform PF3. The third preform PF3 is superimposed on the stack of figures 6 and 7. The third preform PF3 comprises a passage 70 in line with the elements 24 in elevation of the part to be produced. In the example illustrated, the passage 70 is triangular in shape, that is to say adapted to the shape of the triangular cluster of discontinuous fibers forming the body preform PF2 and especially to the triangular geometric shape of the cavities 60. The third fiber preform PF3, thus shaped, is arranged so as to at least partially cover the clusters of discontinuous fibers of the second preform PF2 while leaving a passage 70 for the finishing of the discontinuous fibers of the second preform PF2 to form the elements 24 in elevation of the part to be produced.

[0065] In Figures 8 and 10, the inner surface layer of the third fiber preform PF3 consists of a first portion arranged inside the contour of the elevation element 24 and a second portion forming the entire peripheral portion, outside the contour of the elevation element 24. Alternatively, one or both portions of this inner surface layer of the third fiber preform PF3 may consist of two or more distinct portions to improve the adequacy of the orientation of the fibers of each portion of this layer with respect to the different orientations in the XY plane of the elevation elements 24 to be formed.

[0066] The assembly formed by the first fiber preform PF1, the second fiber preform PF2 and the third fiber preform PF3 is installed in the molding device 50 so that the passages 70 of the third preform PF3, and therefore the clusters of discontinuous fibers of the second preform PF2, are positioned in line with the cavities 60 ([Fig.9]). In one embodiment, the three preforms PF1, PF2, PF3 are assembled superimposed on each other using a positioning template and then installed in the molding device. In another embodiment, the preforms PF1, PF2, PF3 are installed one by one in the molding device stacked successively on top of each other. The molding device 50 is then closed.

[0067] [Fig. 12] schematically illustrates an example of such an assembly E in perspective in which the third preform PF3 comprises a slot 72 for each elevation element 24 to be formed. In the illustrated example, there is only one slot 72. Each slot 72 extends in the associated direction of extension X or the directions of extension, if applicable, of the elements 24 to be formed.

[0068] The discontinuous fibers of the body preform PF2 are arranged in clusters between the first skin preform PF1 and the third preform PF3 in line with the slots 72 of the third preform PF3, as illustrated in FIGS. 9 and 12.

[0069] Such a slot 72 can be made by an incision in the third preform PF3.

[0070] Alternatively, the third preform PF3 intended to form the additional skin 40 comprises a plurality of portions of continuous fibers. The portions are arranged so as to form passages 70 or orifices in line with the elements 24 to be formed of the part and in such a way that the free edge ends of the passages 70 in the preform PF3 extend into the connection fillets 36 at the start of the elevation elements 24. The discontinuous fibers are arranged in clusters between the first fiber preform PF1 and the third fiber preform PF3 in line with the passages of the third preform PF3.

[0071] [Fig. 13] schematically illustrates an example of such an assembly E' in perspective in which the third preform PF3 comprises two parts 74A, 74B of continuous fibers arranged so as to form a passage 70 in line with the elements 24 to be formed of the part. The passage 70 is delimited by the edges 76A, 76B of the parts 74 arranged on either side of the elevation element to be produced. In the example illustrated, the edges are parallel and extend in the direction of extension. The cluster of discontinuous fibers is arranged between the first preform PF1 and the third fiber preform PF3 in line with the passage 70 of the third preform PF3. Such a third preform makes it possible to form an additional skin 40, in two portions 40A and 40B as for the part of [Fig.3].Each portion 40A, 40B covers a fillet 36 of a flank 34 of the stiffener and extends above the internal face 28 of the main skin 22 in opposite directions along the direction Y perpendicular to the direction of extension of the element 24, that is to say of the stiffener of the part.

[0072] Furthermore, the edges 76A, 76B of the portions 74 arranged on either side of the elevation element to be produced may overlap one 76A above the other 76B over a distance D of a few millimeters in the state of the flat preform PF3 and in the assembly with the preforms PF1 and PF2 before the thermocompression step, as illustrated in [Fig. 14]. Advantageously, this configuration allows each portion 40A, 40B of the additional skin 40 to cover and match the corresponding fillet of the body and a portion of the flank of the body of the element of the final part. In this case, the passage 70 opens during the finishing of the discontinuous fiber material of the second preform during the thermocompression step as illustrated in [Fig. 15]. Before the start of the finishing, the passage 70 is closed by the overlapping of the edges 76A, 76B of the parts 74 of the third preform PF3 ([Fig. 14]).

[0073] Then, the method continues with a step 150 of thermocompression of the assembly to form the final part. This thermocompression step makes it possible to compress the material, that is to say the assembly of the three fiber preforms PF1, PF2, PF3, so as to cause the discontinuous fiber material of the body preform PF2 to flow so that it fills the cavities 60 of the mold up to the bottom 62 of the latter in order to form the elements 24 in elevation. During this thermocompression step, the discontinuous fiber material of the body preform PF2 passes through the passage(s) 70 of the third fiber preform PF3 to fill the cavities 60 of the mold. Thus, the final part 20 obtained comprises an additional skin 40 covering the connection fillets 36, 36' of the bodies of the elevation elements 24, thus ensuring good mechanical performance of the junction zone between the elevation elements 24 and the main skin 22 even in the event of significant elevation of the elements relative to the surface of the main skin on which they rest.

[0074] This method is particularly advantageous with fiber preforms pre-impregnated with a resin. Indeed, the matrix associated with the fibers acts as a lubricating element promoting the fining of the discontinuous fibers of the second preform PF2 to form the elevation elements. During the thermocompression step, the material of the assembly must be heated so as to sufficiently reduce the viscosity of the matrix, typically to a viscosity of less than 100 poise, and preferably to a viscosity of less than 10 poise.

[0075] Thus, thermocompression makes it possible to obtain the connection between the preforms PF1, PF2 and PF3 by common consolidation. The fibrous preforms are thus solidified by chemical reaction of crosslinking or polymerization for a thermosetting resin, heating and cooling for a thermoplastic matrix.

[0076] The bodies 30 of the elements 24 are thus integral with the internal surface 28 of the main skin 22, and more precisely linked to the internal surface 28 of the main skin 22 by the additional skin 40 and the polymer matrix of the composite materials of the preforms.

[0077] The method then comprises a step 160 of demolding the manufactured part followed optionally by a step 170 of finishing the part (deburring, finishing, etc.) in order to obtain the final part.

[0078] 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 when the ribs extend over significant heights relative to the surface on which they rest.

[0079] 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. 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, for example aqueous or soapy. 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 it. The process must then include a step of removing the binder to then incorporate the matrix between the fibers and consolidate the assembly.

Claims

Claims

1. Part (20) made of composite material for a turbomachine, in particular an aircraft, comprising: - a composite skin (22) having an internal face (28) and an external face (26), the composite skin comprising continuous fibers; and - at least one element (24) extending in a respective direction of extension (X), each element (24) comprising a body (30) extending from the internal face (28) of the skin to a free end (32) in a direction of elevation (Z) distinct from the direction of extension, each body (30) being connected to the internal face by at least one fillet (36, 36'), the body is made of composite material comprising mainly discontinuous fibers; characterized in that the part (20) further comprises an additional skin (40) of continuous fibers covering at least the at least one fillet connecting the body to the internal face of the skin.

2. Part according to claim 1, in which the continuous fibers of the additional skin (40) extend in orientations from the internal face (28) of the skin (22) towards the body (30) of the at least one element (24) and at least one of the orientations of the continuous fibers of the additional skin (40) extends in a curvilinear path along the at least one fillet (36, 36').

3. A part according to claim 1 or 2, the part being an open panel and the at least one element being a clevis or a stiffener.

4. Method for manufacturing a part made of composite material according to one of the preceding claims, the method comprising the following steps: - a step of providing (110) a first fiber preform (PF1) intended to form the skin (22) and comprising continuous fibers; - a step of providing (120) a second fiber preform (PF2) intended to form the body (30) of the elements (24) and comprising mainly discontinuous fibers; - a step of providing (130) a third fiber preform (PF3) intended to form the additional skin (40) and comprising continuous fibers; - a step of placing (140) in a molding device (50) comprising a punch (54) and a die (52) the assembly formed of the first fiber preform (PF1), the second fiber preform (PF2) and the third fiber preform (PF3) such that the discontinuous fibers of the second preform are arranged in clusters on the first preform to form the body of the at least one element and the third fiber preform is shaped and arranged so as to at least partially cover the clusters of discontinuous fibers of the second preform; - a step of thermocompression (150) of the assembly to form the part; and - a step of demolding (160) of the assembly to form the part.

5. Method according to the preceding claim 4, in which the third preform (PF3) intended to form the additional skin (40) comprises slots (72), each slot (72) extending in the associated direction of extension of the at least one element (24), the discontinuous fibers being arranged in clusters between the first fiber preform (PF1) and the third fiber preform (PF3) at right angles to the slots (72) of the third preform (PF3).

6. Method according to claim 4, in which the third preform (PF3) intended to form the additional skin (40) comprises a plurality of portions (74) of continuous fibers, the portions being arranged so as to form orifices (70) in line with the elements to be formed of the part, the discontinuous fibers being arranged in clusters between the first fiber preform (PF1) and the third fiber preform (PF3) in line with the orifices of the third preform (PF3).

7. A method according to claim 6, wherein the orifices (70) of the third preform (PF3) are partially closed by the respective portions which form the orifices so that during the thermocompression step, the discontinuous fibers of the clusters flow through the orifices to form the elements of the part to be manufactured.

8. Method according to any one of claims 4 to 7, in which the discontinuous fibers of the second fiber preform (PF2) have a length of less than 50 mm, preferably less than 30 mm.

9. A method according to any one of claims 4 to 8, wherein the first fiber preform (PF1), the second fiber preform (PF2) and the third fiber preform (PF3) are pre-impregnated with a resin.

10. A method according to any one of claims 4 to 9, wherein the third preform (PF3) comprises a first layer comprising first unidirectional fibers oriented at an angle of between +30° and +150° relative to the direction of extension of the at least one fillet (36, 36'), preferably between +40° and +140°, and a second layer comprising second unidirectional fibers oriented at an angle of between -30 and -150° relative to the direction of extension, symmetrically to the first fibers relative to the direction of extension of the associated elevation element, and preferably between -40° and -140°.

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