Geodesic draping process

Abstract

Geodesic draping method The invention relates to a method for draping fibrous strips onto a developable draping form comprising at least one frustoconical portion extending around an axis of revolution (A) so as to obtain a fibrous preform, said frustoconical portion extending along the axis of revolution (A) between a first end contour (P1) and a second end contour (P2), the fibrous strips comprising fibers extending along at least one determined direction, the method being characterized in that the fibrous strips are deposited on the draping form so that the fibers of said fibrous strips each extend along a trajectory corresponding to a trajectory of the straight lines of the developed surface of the draping form, and in that each fibrous strip extends from one of the end contours (P1, P2) and emerges onto one of the end contours (P1, P2) of the frustoconical portion.Figure for the summary: Fig. 10.

Description

Title of the invention: Geodesic draping method Technical field

[0001] The present invention relates to the general field of methods for draping a shape using fibrous strips. Prior art

[0002] It is known to produce parts from composite material by draping on a form of strata or layers of dry or pre-impregnated fibrous strips. In certain current techniques, draping is carried out manually by an operator. These techniques can generate relatively high production costs for parts and risks of positioning errors in the layers or fibrous strips. This leads to a certain variability in the mechanical performance of the parts obtained, or even to parts whose mechanical properties are insufficient.

[0003] Mechanized solutions have thus been developed to reduce the production cost of these composite material parts, such as the automatic fiber placement technique, also known as AFP for “Automated Fiber Placement”. Such a technique is notably described in document FR 3 066 719. The fibers are then automatically deposited in the form of fibrous strips called “wicks”.

[0004] In the prior art, when it is desired to drape a developable truncated draping shape Fo comprising generatrices gOb g02 and extending between a first end contour pOi and a second end contour p02, the strands m0 and mi deposited are oriented according to the Cartesian coordinate system of the draping shape Fo, as schematically illustrated in [Fig.l]. Thus, the trajectories of the fibers or strands of fibers deposited intersect the generatrices gOi, g02 of the developable shape Fo with the same angle. [Fig.2] shows the developed surface FOd of the developable shape Fo. It is thus possible to deposit several fiber layers, each fiber layer having a different fiber orientation. It is thus possible to achieve quasi-isotropic draping.In the example illustrated schematically in figures 1 and 2, it is thus possible to produce a first fibrous layer formed by the strands me intersecting the generatrices goi, g02 of the developable form Fo with a first angle and a second fibrous layer formed by the strands mi intersecting the generatrices gOi, g02 of the developable form Fo with a second angle different from the first angle.

[0005] However, it has been found that the strands deposited with this method can exhibit significant deformations and undulations. The strength and mechanical characteristics of the draped piece obtained by this method can therefore be insufficient.

[0006] It is also known to deposit the rovings with a “spiral” winding, as described in document US8677622. However, this draping method generates large variations in thickness, with certain areas of the draping shape being covered by a lot of fibers and other areas by very few fibers. In addition, the part thus draped has a great heterogeneity in the orientations of the fibers, with not all areas having the same proportion of fibers for each orientation. It is therefore extremely difficult to achieve quasi-isotropic draping with this method. Statement of the invention

[0007] The present invention aims to overcome the aforementioned drawbacks. It has been found in particular that the further the truncated lay-up shape is from the shape of a cylinder, that is to say the more it has a significant slope relative to its axis, the more difficult it is to apply the wicks without undulations or deformations. Indeed, when the wick is deposited on a significant slope with the method(s) of the prior art, the two longitudinal edges of the wick do not travel the same distance on the lay-up shape. Thus, the deposited wick undulates or deforms. This phenomenon is even more marked when the section of the lay-up shape is reduced or when the width of the applied wick is large.

[0008] To this end, the invention proposes a method for draping fibrous strips onto a developable draping form comprising at least one portion of frustoconical shape extending around an axis of revolution so as to obtain a fibrous preform, said portion of frustoconical shape extending along the axis of revolution between a first end contour and a second end contour, the fibrous strips comprising fibers extending along at least one determined direction, the method being characterized in that the fibrous strips are deposited on the draping form so that the fibers of said fibrous strips each extend along a trajectory corresponding to a trajectory of the straight lines of the developed surface of the draping form, and in that each fibrous strip extends from one of the end contours and opens onto one of the end contours of the portion of frustoconical shape.

[0009] Thus, the deposition of the fibers of the fibrous strips so as to follow the trajectories of the straight lines of the developed shape of the draping shape ensures satisfactory draping of the fibrous strips, i.e. without undulation or deformation. This draping mode is called "geodesic", insofar as the fibrous strips are deposited so that the fibers of said fibrous strips are superimposed on the straight lines of the developed surface of the draping shape.

[0010] Furthermore, with the method of the invention, the draping of the fibrous strips that are too short is limited. Indeed, the draping of the fibrous strips that are too short can cause the rest of the draping to become detached, while their presence does not provide any real improvement in the mechanical properties. Furthermore, the short fibrous strips are more difficult to deposit, in particular with the automatic fiber draping method. With the method of the invention, the deposited fibrous strips are not cut but are extended until they reach an end contour, even if this means that in certain cases they make more than one complete turn of the draping form. A fibrous strip can therefore belong simultaneously to two draping layers.Therefore, the formation of local overthicknesses in the resulting draped preform is limited, since the overthickness created by the overlapping of the strips with other strips is used to create a new, fully-fledged layer.

[0011] According to a particular embodiment of the invention, the method comprises at least:

[0012] - the deposition of a first set of parallel fibrous strips on the form of draping so as to form a first draping layer on the draping form, a portion of the fibrous strips of the first set extending at the level of the first draping layer so as to form a portion of a second draping layer superimposed with the first draping layer, then

[0013] - the deposition of a second set of parallel fibrous strips on the first draping layer so as to complete the second draping layer and to begin a third draping layer, the fibrous strips of the second set being draped parallel to the fibrous strips of the first set belonging to the second draping layer.

[0014] Thus, the fibrous strips of the second set are draped following the fibrous strips of the first set which belong to the second layer. In order to avoid local excess thicknesses in the draped preform obtained, the second set of parallel fibrous strips is deposited following and parallel to the first set previously deposited, in order to produce a second uniform layer without excess thickness, even if the latter is formed by two sets of parallel fibrous strips.

[0015] Such draping can thus be carried out so that a portion of the fibrous strips of the second set extends at the level of the second draping layer so as to form a portion of the third draping layer which is superimposed with the second draping layer.

[0016] According to another particular embodiment of the invention, the draping method further comprises the successive deposition(s) of one or more additional sets of parallel fibrous strips on the draping form, each set additional set of parallel fibrous strips being deposited so as to complete the draping layer started by the preceding set of parallel fibrous strips, the fibrous strips of the additional set being draped parallel to the fibrous strips of the preceding set belonging to said draping layer started, a portion of the fibrous strips of the additional set extending above said draping layer thus completed so as to form at least a portion of additional draping layer covering the draping layer thus completed.

[0017] According to another embodiment of the invention, each set of fibrous strips deposited extends between the first fibrous strip deposited along a reference trajectory and a last fibrous strip deposited along a final trajectory, the angle formed between the reference trajectory and the generatrix of the draping shape which intersects the first end contour at the same point as the reference trajectory corresponding to the angle formed between the final trajectory and the generatrix of the draping shape which intersects the first end contour at the same point as the final trajectory.

[0018] According to another particular embodiment of the invention, the reference trajectory and the final trajectory correspond to generators of the draping shape.

[0019] The layup is thus simplified, making it easier to obtain a homogeneous layup. In addition, if the number of sets deposited is sufficient, the layup obtained is then quasi-isotropic.

[0020] According to a particular embodiment of the invention, the draping method comprises a step of producing at least one excess thickness of the fiber preform.

[0021] According to a first variant of the embodiment described in the preceding paragraph, the excess thickness is formed by draping between an intermediate end contour arranged between the first end contour and the second end contour, and one of the contours among the first end contour and the second end contour.

[0022] According to a second variant, the excess thickness is formed by draping between two intermediate end contours each arranged between the first end contour and the second end contour.

[0023] According to another particular embodiment, the draping method further comprises draping a plurality of stiffness fibrous structures onto the draping form, the stiffness fibrous structures being draped such that the fibers of said stiffness fibrous structures are superimposed on generatrices of the developed surface of the draping form.

[0024] According to another particular embodiment of the invention, the draping of the fibrous strips is carried out by automatic placement of fibers.

[0025] The use of draping by automatic fiber placement makes it possible to improve the repeatability and quality of the process while limiting manufacturing costs.

[0026] The invention further relates to a fiber preform comprising at least one developable portion of truncated cone shape extending around an axis of revolution, said developable portion extending along the axis of revolution between a first end contour and a second end contour, the developable portion of said preform comprising a plurality of fiber layers formed by fiber strips, characterized in that the fibers of the fiber strips of at least two successive fiber layers correspond to straight lines of the developed surface of the developable portion of the fiber preform and in that each fiber strip extends from one of the end contours and opens onto one of the end contours.

[0027] Such a fiber preform thus has better mechanical characteristics and better homogeneity of said mechanical characteristics, because it comprises few short fiber strips and no unwanted excess thicknesses.

[0028] The invention also relates to a method for manufacturing a part made of composite material comprising at least one developable part of truncated cone shape, the method comprising at least:

[0029] - the production of a fiber preform by the draping process as described above cededly,

[0030] - densification of the fiber preform by a matrix so as to obtain a part in composite material.

[0031] In particular, in the case where the fibrous strips are not pre-impregnated with a matrix precursor, the above manufacturing method may comprise:

[0032] - the production of a fiber preform by the draping process as described above cededly,

[0033] - consolidation of the fiber preform by one or more matrix precursors,

[0034] - sintering the fiber preform so as to form the matrix in the porosities of said fiber preform.

[0035] In the case where the fibrous strips are pre-impregnated with one or more matrix precursors, the manufacturing process may comprise:

[0036] - the production of a fiber preform by the draping process as described above cededly,

[0037] - heat treatment of the matrix precursor(s) so as to form the matrix in the porosities of the fiber preform.

[0038] If the fibrous strips are pre-impregnated with a binder, the latter can be removed during a debinding operation before densification or consolidation of the preform.

[0039] The invention also provides a part made of composite material comprising at least one developable part of truncated cone shape obtained by the method of manufacturing a part made of composite material as described.

[0040] Finally, the invention proposes an aircraft engine comprising a part made of composite material as described above. Brief description of the drawings

[0041] [Fig.l] [Fig.l] is a schematic perspective view of a developable draping form on which fibrous strands according to the prior art are draped.

[0042] [Fig.2] [Fig.2] is a schematic representation of the developed surface of the shape of [Fig.l] according to the prior art.

[0043] [Fig.3] [Fig.3] is a schematic perspective view of a draping form developable.

[0044] [Fig.4] [Fig.4] is a schematic representation of the developed surface of the shape of [Fig.3].

[0045] [Fig.5] [Fig.5] is a schematic sectional view of an AFP dispensing head.

[0046] [Fig.6] [Fig.6] is a developed schematic view of the draping form on in which the draping of a first set of parallel fibrous bands is in progress.

[0047] [Fig.7] [Fig.7] is a schematic perspective view of the draping shape on in which the draping of the first set of parallel fibrous strips is in progress.

[0048] [Fig.8] [Fig.8] is a developed schematic view of the lay-up form on which the lay-up of the first set of parallel fibrous strips is in progress and in a more advanced state than in [Fig.6].

[0049] [Fig.9] [Fig.9] is a schematic perspective view of the draping shape on in which the draping of the first set of parallel fibrous bands is in progress and in a more advanced state than in [Fig.7].

[0050] [Fig. 10] [Fig. 10] is a developed schematic view of the lay-up form on which the lay-up of the first set of parallel fibrous strips is completed.

[0051] [Fig. 11] [Fig. 11] is a developed schematic view of the lay-up form on which the lay-up of a second set of parallel fibrous strips is completed.

[0052] [Fig. 12] [Fig. 12] is a developed schematic view of the layup form on which the layup of a third set of parallel fibrous strips superimposed on the first and second sets of parallel fibrous strips is completed, with only the third set being illustrated. Description of the embodiments

[0053] The invention makes it possible to produce a fiber preform having the shape of the part to be obtained by draping a plurality of fiber strips on a draping form. The fiber preform is intended to form the fiber reinforcement of the part to be obtained.

[0054] The draping form comprises an internal or external draping surface intended to be draped by the fibrous strips. The draping of the draping form is carried out by applying fibrous strips to the draping surface of said draping form. Preferably, the draping is carried out on the external surface of the draping form, which is more accessible. However, it does not depart from the scope of the invention if the draping is carried out on the internal surface of the draping form.

[0055] The layup surface is developable. By extension, the term “developable layup shape” refers to a layup shape whose layup surface is developable. The layup surface has at least one portion of a frustoconical shape. The layup shape may be a conical or frustoconical shape. The layup shape may also have a complex developable shape, comprising portions at least partially of a frustoconical shape. For example, the layup shape may have a developable crown formed by a plurality of lobes distributed over a circumference, said lobes having, for example, a partially frustoconical shape. Such a layup shape may, for example, allow the layup of a fiber preform intended to form the fiber reinforcement of a turbojet flow mixer, the layup shape itself having overall the shape of a turbojet flow mixer.An example of a turbojet flow mixer is described in document FR 3 061 749.

[0056] Figures 3 and 4 illustrate an example of a draping shape F. The draping shape F extends around a central axis A. Thus, the draping surface of the draping shape F extends around the central axis A. In the example illustrated in [Fig. 3], the draping shape F and the draping surface have a circular section. The central axis A then corresponds to the axis of revolution of the draping surface. However, it does not depart from the scope of the invention if the section of the draping surface is an ellipse, provided that said draping surface remains developable. The central axis A then corresponds to the axis passing through the center of all the elliptical sections.

[0057] The draping shape F, or the draping surface, extends along the central axis A between a first end contour Pi and a second end contour P2. The first end contour Pi corresponds to the end contour of the draping shape F, or the draping surface, of smaller dimension. The second end contour P2 corresponds to the end contour of the draping shape F, or the draping surface, of larger dimension.

[0058] The draping surface of the draping shape F comprises an infinity of generators g, as illustrated in [Fig.3].

[0059] If the draping surface is conical or truncated, it is defined by an angle of inclination a which corresponds to the angle formed between the central axis A of revolution and the generatrices g, as illustrated in [Fig.3]. It will also be defined by a length R which corresponds to the length extending in the same direction as a generatrix g between the second end contour P2 and the central axis A. The length R is preferably angularly constant. It is thus defined by an opening angle 0 which corresponds to the opening angle of the developed surface of the draping shape F, as illustrated in [Fig.4]. The mathematical relationship linking the inclination angle a to the opening angle 0 is as follows: 0 = 2 ir sin(a).

[0060] The fibrous webs are preferably in the form of fibrous strands or fabric plies. The term "strand" means a set of long fibers or filaments that are substantially parallel to each other and joined together in a non-woven web. The fibrous webs may comprise continuous and long fibers. In the case where the fibrous webs are in the form of fabric plies, they are generally formed by the woven interlacing of fibers in two directions, which are usually perpendicular to each other.

[0061] The fibers of the fibrous strips may be ceramic, glass, or carbon fibers. The ceramic fibers may be fibers made of a non-oxide material, such as silicon carbide (SiC), or of an oxide material, such as alumina, or of a material comprising predominantly alumina. The glass fibers may comprise a mixture predominantly based on silica.

[0062] The fibrous strips may be dry, i.e. not impregnated with a resin, pre-impregnated or loaded with particles. The fibers of the dry fibrous strips may however be coated with a temporary binder, for example organic, which will be removed or not before the densification of said fibrous strips.

[0063] The fibrous webs may be impregnated with a thermoplastic or thermosetting material, which may comprise solid fillers. The fibrous webs may also be impregnated with a thermoplastic or thermosetting material not comprising solid fillers. The fibrous webs may be impregnated solely with an organic phase consisting of a thermoplastic material.

[0064] The thermoplastic materials that can impregnate the fibrous webs can be chosen from: polyaryletherketones (PAEK) such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK), polyetherimides (PEI), polyphenylene sulfide (PPS), polyvinyl alcohol (PVA), aliphatic polyethers and polysulfone (PSU). The thermosetting materials that can impregnate the fibrous webs can be chosen from: epoxies, phenolics and polybismaleimides (BMI).

[0065] The preliminary impregnation of the fibrous strips can be carried out by any conventional technique, for example by full bath dipping, by application by licking roller or even by spraying.

[0066] The fibrous strips may be applied to the F-form by manual draping. Preferably, in order to improve the repeatability and quality of the application of the fibrous strips to the F-form while reducing the operating time, the fibrous strips are applied to the F-form by automatic fiber placement.

[0067] [Fig. 5] schematically illustrates the structure of a deposition head 1 of a device for implementing an automatic fiber placement technique. The structure of the deposition head 1 is well known. The deposition head 1 is fed by the fiber strips 3, preferably in the form of one or more wicks. Advantageously, each fiber strip 3 is formed by a set of several wicks.

[0068] The strip or wick 3 can be conveyed by a conveying element 5 to a pressure application element 7 located on the side of the draping form F. The conveying element 5 is here in the form of a pair of counter-rotating rollers 5a and 5b between which the strip or wick 3 is present. The conveying element 5 makes it possible to advance the strip or wick 3 to the pressure application element 7. The pressure application element 7 applies pressure to the strip or wick 3 in order to carry out the deposition on the draping form F. The pressure application element 7 is here in the form of a roller.

[0069] The deposition head 1 may, in addition, comprise a heating element 9 located in the vicinity of the pressure application element 7. This heating element 9 makes it possible, in the case of a strip or wick 3 impregnated with a thermoplastic polymer, to heat said impregnated strip or wick 3 during its deposition in order to fluidify the thermoplastic polymer and thus to confer the desired adhesive power to the strip or wick 3 deposited.

[0070] During deposition, the deposition head 1 is movable in order to apply the strip or wick 3 along a first determined trajectory on the draping form F. Once the application has been carried out along this first trajectory, a cutting element 8 of the deposition head 1 cuts the strip or wick 3. After this cutting, the deposition of a first fibrous strip is thus obtained, formed by a first section of the strip or wick 3, along a first trajectory on the draping form F.

[0071] The draping operation is then continued by advancing the strip or wick 3 in the deposition head 1 to the pressure application element 7 by actuating the conveying element 5. The deposition head 1 can be moved in order to deposit the wick or strip 3 along a second trajectory on the draping form F. The deposition of a second fibrous strip, formed by a second section of the strip or wick 3 along a second trajectory is then obtained in a manner similar to that described previously.

[0072] The draping form F can obviously be rotated around its central axis A during draping to facilitate the deposition of the fibrous strips.

[0073] The draping is then continued by depositing several fibrous strips in the same manner as described previously.

[0074] According to the invention, the fibrous strips are deposited on the draping form F so that the fibers of said fibrous strips are superimposed parallel to straight lines of the developed surface of the draping form. Thus, the paths of the fibrous strips extend along straight lines of the developed surface of the draping form.

[0075] The method according to the invention comprises the deposition of a first set 100 of parallel fibrous strips on the draping form F following trajectories as illustrated in Figures 6 to 10.

[0076] A first fibrous strip of the first set 100 is deposited along a reference trajectory TiA. Preferably, the reference trajectory TiA of the first fibrous strip of the first set corresponds to a generatrix g of the draping shape F.

[0077] The first set 100 of parallel fibrous strips is defined by a reference inclination. The reference inclination is the value of the angle formed between the reference trajectory T[A and the generatrix of the draping shape F which intersects the first end contour Pi at the same point as the reference trajectory TiA. In the case where the reference trajectory TiA coincides with a generatrix, as is the case in FIGS. 6 to 10, the reference inclination is 0°.

[0078] At least one fibrous strip of the first set 100 of parallel fibrous strips extends along a generator trajectory T1B. As illustrated in FIGS. 6 and 7, the fibrous strip of the first set 100 extending along a generator trajectory T1B is preferably the first fibrous strip extending along the reference trajectory T1A, the reference trajectory T1A and the generator trajectory T1B thus being the same.

[0079] A plurality of adjacent fibrous strips are then deposited along trajectories Ti parallel to the reference trajectory TiA, said fibrous strips extending from the second end contour P2 to the first end contour P i-

[0080] By continuing to deposit adjacent fibrous strips belonging to the first set 100 along trajectories Ti parallel to the reference trajectory TiA, a fibrous strip is finally deposited extending from the second end contour P2 until returning to the second end contour P2 along an extended trajectory Tic. This extended trajectory Tic can complete a complete turn of the draping surface F, as illustrated in FIGS. 6 and 7. The extended trajectory Tic does not meet the first end contour Pb but goes around the first end contour Pp

[0081] In the case where the reference trajectory TiA of the first fiber strip of the first set 100 corresponds to a generator g of the draping shape F and in the case where the extended trajectory TiC makes a complete turn of the draping surface F, the extended trajectory TiC intersects the reference trajectory TiA at an angle equal to the opening angle 0 of the draping shape F.

[0082] The deposition of the first set of parallel fibrous strips is then continued as illustrated in FIGS. 8 and 9, the fibrous strips of the first set 100 thus deposited simultaneously forming the first draping layer and a portion of the second draping layer. Indeed, these fibrous strips of the first set 100 deposited after the fibrous strip extending along the extended TiC trajectory each have a first portion forming the first draping layer followed by a second portion forming the portion of the second draping layer.

[0083] The deposition of the first set 100 of parallel fibrous strips is optionally continued by the deposition of fibrous strips close to the second end contour P2, which extend from the second end contour P2 and open onto said second end contour P2 after a reduced length, without intersecting the reference trajectory T[A. These fibrous strips of the first set 100 follow end trajectories T[D, as illustrated in [Fig.8].

[0084] As illustrated in [Fig. 10], the deposition of the first set 100 of parallel fibrous strips is completed by the deposition of parallel fibrous strips extending between the second end contour P2 and the first end contour Pi following the extended trajectory T1C by covering the first layup layer 100, until a fibrous strip extending along a final trajectory T1E is deposited, said final trajectory T1E being defined so that the angle formed between the final trajectory T1E and the generatrix of the layup shape F which intersects the first end contour Pi at the same point as the final trajectory TiE corresponds to the reference inclination of the first set 100 of parallel fibrous strips. Thus, the final trajectory TiE has the same “inclination” as the reference trajectory T1A with respect to the layup shape F.

[0085] In the example illustrated in Figures 6 to 10, the reference inclination of the first set 100 of parallel fibrous strips is 0°, that is to say that the reference trajectory TiA is a generator of the draping shape F. Thus, the final trajectory T 1E will also be a generator of the draping shape F. Thus, in the example illustrated in [Fig. 10], the deposition of the first set 100 of parallel fibrous strips is completed by the deposition of fibrous strips extending between the second end contour P2 and the first end contour Pi following the extended trajectory Tic until a fibrous strip extending along a generator of the draping shape F is deposited, which will be the final trajectory TiE.

[0086] As illustrated in [Fig. 10], after depositing the first set 100 of parallel fibrous strips a first draping layer completely or almost completely covering the draping surface F as well as a portion of a second draping layer. The draping carried out on the draping surface F thus comprises a zone Zi formed by a single draping layer and a zone Z2 formed by two draping layers.

[0087] When the angle 0 is less than or equal to 180°, the angle between the reference trajectory Tia and the extended trajectory TiC is equal to 0. When the angle 0 is less than or equal to 180°, the area of ​​the portion of the second layer deposited corresponds to a percentage of the area of ​​the first layer which is equal to (18O°-0) / 0. When the angle 0 is less than or equal to 180°, the angular offset around the central axis A between the reference trajectory TiA and the final trajectory TiE is equal to 36Ox(18O°-0) / 0.

[0088] When the angle 0 is greater than 180°, the angle between the reference trajectory and the extended trajectory is equal to 0-180°. When the angle 0 is greater than 180°, the area of ​​the portion of the second layer deposited corresponds to a percentage of the area of ​​the first layer which is equal to (0-180°) / 0. When the angle 0 is less than or equal to 180°, the angular offset around the central axis A between the reference trajectory and the final trajectory is equal to 360x(180°-0) / 0.

[0089] In the example illustrated in Figures 6 to 10, the angle 0 is 120°, or less than 180°. Thus, the angle between the reference trajectory T[A and the extended trajectory T[C will be equal to 120°, the area of ​​the portion of the second layer deposited will correspond to 50% of the area of ​​the first layer and the angular offset between the reference trajectory TiA and the final trajectory TiE will be equal to 180°.

[0090] A second set 200 of parallel fibrous strips is then deposited on the draping form F following trajectories T2, as illustrated in [Fig.11].

[0091] A first fibrous strip of the second set 200 is deposited along a reference trajectory T2A corresponding to the final trajectory Tm of the first set 100 of parallel fibrous strips, in the zone Zi comprising only a single draping layer. The first fibrous strip of the second set 200 is thus draped directly following the fibrous strips of the first set 100 belonging to the second layer portion and parallel to said fibrous strips of the first set 100 belonging to the second layer. In the example illustrated in [Fig.l 1], the reference trajectory T2A is a generator coincident with the generator trajectory T2b.

[0092] A plurality of adjacent fibrous strips are then deposited along trajectories T2 parallel to the reference trajectory T2A, said fibrous strips extending from the second end contour P2 to the first end contour P i. The fibrous strips of the second set 200 are thus deposited parallel to the first strip of the second set 200 in the zone Zi comprising only a single draping layer, in order to continue the production of the second draping layer. If the reference trajectory T2A is not itself a generator, we end up depositing a fibrous strip of the second set 200 of parallel fibrous strips which extends along the generator trajectory T2B.

[0093] By continuing to deposit adjacent fibrous strips belonging to the second set along trajectories T2 parallel to the reference trajectory T2A, a fibrous strip is finally deposited extending from the second end contour P2 until returning to the second end contour P2 along an extended trajectory T2C. This extended trajectory T2C can make a complete turn of the lay-up surface F, as illustrated in [Fig. 11]. The extended trajectory T2C does not meet the first end contour Pb but goes around the first end contour Pb

[0094] The deposition of the second set 200 of parallel fibrous strips is then continued as illustrated in [Fig. 11], the fibrous strips of the second set 200 thus deposited simultaneously forming the second draping layer and a portion of the third draping layer. Indeed, these fibrous strips of the second set 200 deposited after the fibrous strip extending along the extended trajectory T2C each have a portion forming the second draping layer followed by a portion forming the portion of the third draping layer.

[0095] The deposition of the second set 200 of parallel fibrous strips is continued by the deposition of fibrous strips close to the second end contour P2, which extend from the second end contour P2 and open onto said second end contour P2 after a reduced length, without intersecting the reference trajectory T2A. These fibrous strips of the second set 200 follow end trajectories T 2D, as illustrated in [Fig. 11].

[0096] As illustrated in [Fig.l 1], the deposition of the second set 200 of parallel fibrous strips is completed by the deposition of parallel fibrous strips extending between the second end contour P2 and the first end contour Pi following the extended trajectory T2C by covering the second lay-up layer, until a fibrous strip extending along a final trajectory T2E is deposited, said final trajectory T2e being defined so that the angle formed between the final trajectory T2E and the generatrix of the lay-up shape F which intersects the first end contour Pi at the same point as the final trajectory T2E corresponds to the reference inclination of the first set 100 of parallel fibrous strips. Thus, the final trajectory T2E has the same “inclination” as the reference trajectories TiA and T2A with respect to the lay-up shape F.

[0097] In the example illustrated in Figures 6 to 11, the reference inclination of the first set 100 and the second set 200 of parallel fibrous strips is 0°, that is to say that the reference trajectories TiA and T2A are generators of the draping shape F. Thus, the final trajectory T2E will also be a generator of the draping shape F. Thus, in the example illustrated in [Fig.l 1], the deposition of the second set 200 of parallel fibrous strips is completed by the deposition of fibrous strips extending between the second end contour P2 and the first end contour P i following the extended trajectory T2C until a fibrous strip extending along a generator of the draping shape F is deposited, which will be the final trajectory T2E.

[0098] As illustrated in [Fig.l 1], after the deposition of the second set of parallel fibrous strips, a second draping layer is obtained, completely or almost completely covering the first draping layer, as well as a portion of the third draping layer. In the particular case illustrated in [Fig.l 1], the second set of parallel fibrous strips makes it possible to produce a third complete draping layer. The draping produced on the draping surface F thus comprises a zone Z3 formed by three draping layers.

[0099] When the angle 0 is less than or equal to 180°, the angle between the reference trajectory T2A and the extended trajectory T2C is equal to 0. When the angle 0 is less than or equal to 180°, the area of ​​the portion of the second layer deposited corresponds to a percentage of the area of ​​the first layer which is equal to (180°-0) / 0. When the angle 0 is less than or equal to 180°, the angular offset around the central axis A between the reference trajectory T2A and the final trajectory T2E is equal to 360x(180°-0) / 0.

[0100] When the angle 0 is greater than 180°, the angle between the reference trajectory and the extended trajectory is equal to 0-180°. When the angle 0 is greater than 180°, the area of ​​the portion of the second layer deposited corresponds to a percentage of the area of ​​the first layer which is equal to (0-18O°) / 0. When the angle 0 is less than or equal to 180°, the angular offset around the central axis A between the reference trajectory and the final trajectory is equal to 36Ox(18O°-0) / 0.

[0101] In the example illustrated in [Fig. 11], the angle 0 is 120°, or less than 180°. Thus, the angle between the reference trajectory T2A and the extended trajectory T2C will be equal to 120°, the area of ​​the portion of the second layer deposited will correspond to 50% of the area of ​​the first layer 100 and the angular offset between the reference trajectory T2A and the final trajectory T2E will be equal to 180°.

[0102] We can then proceed to deposit a third set 300 of parallel fibrous strips on the draping form F following trajectories T3, as illustrated in [Fig.12],

[0103] A first fibrous strip of the third set 300 is deposited along a reference trajectory T3A corresponding to the final trajectory T2E of the second set 200 of parallel fibrous strips. The first fibrous strip of the third set 300 is thus draped directly after the fibrous strips of the second set 200 and parallel to said fibrous strips of the second set 200. In the example illustrated in [Fig.12], the reference trajectory T3A is a generator merged with the generator trajectory T3B.

[0104] A plurality of adjacent fibrous strips are then deposited along trajectories T3 parallel to the reference trajectory T3A, said fibrous strips extending from the second end contour P2 to the first end contour P i. If the reference trajectory T3A is not itself a generator, a fibrous strip from the third set of parallel fibrous strips is finally deposited, which extends along the generator trajectory T3B.

[0105] By continuing to deposit adjacent fibrous strips belonging to the third set 300 along trajectories T3 parallel to the reference trajectory T3A, a fibrous strip is finally deposited extending from the second end contour P2 until returning to the second end contour P2 along an extended trajectory T3C. This extended trajectory T3C can complete a complete turn of the draping surface F, as illustrated in [Fig. 12]. The extended trajectory T3C does not meet the first end contour Pb but goes around the first end contour Pi.

[0106] The deposition of the third set 300 of parallel fibrous strips is then continued as illustrated in [Fig. 12], the fibrous strips of the third set 300 thus deposited simultaneously forming the third draping layer, a fourth draping layer and a portion of the fifth draping layer.

[0107] The deposition of the third set 300 of parallel fibrous strips is continued by the deposition of fibrous strips close to the second end contour P2, which extend from the second end contour P2 and open onto said second end contour P2 after a reduced length, without intersecting the reference trajectory T3A. These fibrous strips of the third set 300 follow end trajectories T 3D, as illustrated in [Fig. 12].

[0108] As illustrated in [Fig. 12], the deposition of the third set 300 of parallel fibrous strips is completed by the deposition of parallel fibrous strips extending between the second end contour P2 and the first end contour Pi following the extended trajectory T3C by covering the third lay-up layer, until a fibrous strip extending along a final trajectory T3E is deposited, said final trajectory T3e being defined so that the angle formed between the final trajectory T3E and the generatrix of the lay-up shape F which intersects the first end contour Pi at the same point as the final trajectory T3E corresponds to the reference inclination of the first and second sets 100 and 200 of parallel fibrous strips. Thus, the final trajectory T3E has the same “inclination” as the reference trajectories TiA, T2A and T3A with respect to the lay-up shape F.

[0109] In the example illustrated in Figures 6 to 12, the reference inclination of the sets 100, 200 and 300 of parallel fibrous strips is 0°, that is to say that the reference trajectories TiA, T2A and T3A are generators of the draping shape F. Thus, the final trajectory T3E will also be a generator of the draping shape F. Thus, in the example illustrated in [Fig.12], the deposition of the third set 300 of parallel fibrous strips is completed by the deposition of fibrous strips extending between the second end contour P2 and the first end contour P i following the extended trajectory T3C until a fibrous strip extending along a generator of the draping shape F is deposited, which will be the final trajectory T3E.

[0110] As illustrated in [Fig. 12], after the deposition of the third set 300 of parallel fibrous strips, a fourth draping layer is obtained, completely or almost completely covering the third draping layer, as well as a fifth draping layer partially covering the fourth draping layer. The draping carried out on the draping surface F thus comprises a zone Z4 formed by four draping layers and a zone Z5 formed by five draping layers.

[0111] Preferably, successive deposits of a plurality of sets of parallel fibrous strips are thus carried out. Several layers of draping are thus produced on the draping form F.

[0112] In the particular case illustrated in Figures 6 to 12, it can be seen that the first set 100 of parallel fibrous strips and the third set 300 of parallel fibrous strips are identical. The relationship between the number Y of sets of parallel fibrous strips and the number of lay-up layers Z is as follows: Y = Z x 0 / 180°. It is preferably sought to obtain integer values ​​for both the number Y of sets of parallel fibrous strips and the number of lay-up layers Z. In the example illustrated in Figures 6 to 12, 0 = 120°, which gives: Y = Z x 2 / 3. It can be seen in [Fig. 11] that by depositing Y=2 sets of parallel fibrous strips, exactly Z=3 lay-up layers are obtained. It is therefore preferable to deposit an even number of sets of parallel fibrous strips for the case of an angle 0 of 120°.

[0113] According to another example, if one wishes to produce a truncated fiber preform whose inclination is approximately 20°, one can choose a layup shape having an inclination angle a of 20.106°, because such an angle will make it possible to produce exactly 16 complete layup layers by depositing exactly 11 sets of parallel fiber strips. This particularly advantageous case is also interesting insofar as it makes it possible to finish the layup at the same angular position as the start of the layup. One thus obtains a fiber preform with a quasi-isotropic material.

[0114] In the example illustrated in Figures 6 to 12, the draping shape extends between the first end contour Pi and the second end contour P2. The shape of draping could also comprise one or more intermediate end contours arranged between the first end contour Pi and the second end contour P2, and fulfilling the same function as an end contour during draping. The intermediate end contour is preferably comprised in a plane parallel to the planes comprising the first end contour Pi and the second end contour P2.

[0115] Thus, in order to produce a fiber preform having an excess thickness or several excess thicknesses, the draping method of the invention could be carried out for example between the first end contour Pi and the second end contour P2, then between the intermediate end contour and one of the contours among the first end contour Pi and the second end contour P2. Thus, according to a particular embodiment of the invention, the draping method comprises, after the formation of the draped fiber layers, a step of producing at least one excess thickness of the fiber preform. The excess thickness is for example formed by draping between the intermediate end contour and one of the contours among the first end contour Pi and the second end contour P2 or by draping between two intermediate end contours.

[0116] The fibrous layers draped over the form F may be solely fibrous layers whose fibrous strips follow geodesic trajectories. However, the draping method according to the invention may further comprise a step of draping one or more fibrous layers in which the fibrous strips are deposited so that the fibers of said fibrous strips each extend along a non-geodesic trajectory corresponding to a trajectory of the generatrices g of the draping form F. This substantially increases the rigidity and strength of the fiber preform obtained by draping.

[0117] The fibrous layers draped over the draping form form a fibrous preform, which has at least one developable portion comprising at least one portion of frustoconical shape.

[0118] The fibrous preform thus obtained can be densified in a well-known manner by a matrix to obtain a part made of composite material, for example an engine exhaust cone or a rear inverter body.

[0119] The invention also relates to a method for manufacturing a part made of composite material comprising at least one developable part of truncated cone shape, the method comprising at least the following steps:

[0120] - production of a fiber preform by the draping process as described above cededly,

[0121] - consolidation of the fiber preform by one or more matrix precursors, and

[0122] - sintering of the matrix precursor(s) to form the matrix in the porosities of the fiber preform.

[0123] In a case where the wicks are composed solely of a binder, the consolidation step comprises the following sub-steps:

[0124] - debinding of the preform,

[0125] - injection of one or more matrix precursors into the preform, and

[0126] - cooking the preform in an autoclave so as to form the matrix in the porosities of the fiber preform.

[0127] In another case in which the wicks are composed of a binder and a matrix, the consolidation step comprises a sub-step of cooking the matrix in an autoclave.

Claims

Claims

1. Method for draping fibrous strips on a developable draping form comprising at least one portion of frustoconical shape extending around an axis of revolution (A) so as to obtain a fibrous preform, said portion of frustoconical shape extending along the axis of revolution (A) between a first end contour (Pi) and a second end contour (P2), the fibrous strips comprising fibers extending in at least one determined direction, the method being characterized in that the fibrous strips are deposited on the draping form so that the fibers of said fibrous strips each extend along a trajectory corresponding to a trajectory of the straight lines of the developed surface of the draping form, and in that each fibrous strip extends from one of the end contours (Pb P2) and opens onto one of the end contours (Pb P2) of the portion of frustoconical shape.

2. A draping method according to claim 1, said method comprising at least: - depositing a first set (100) of parallel fibrous strips on the draping form so as to form a first draping layer on the draping form, a portion of the fibrous strips of the first set (100) extending at the first draping layer so as to form a portion of a second draping layer superimposed with the first draping layer, then - depositing a second set (200) of parallel fibrous strips on the first draping layer so as to complete the second draping layer and to begin a third draping layer, the fibrous strips of the second set (200) being draped parallel to the fibrous strips of the first set (100) belonging to the second draping layer.

3. A method of draping according to claim 2, further comprising successively depositing one or more additional sets (300) of parallel fibrous strips on the draping form, each additional set (300) of parallel fibrous strips being deposited so as to complete the draping layer started by the previous set (100, 200) of parallel fibrous strips, the fibrous strips of the additional set (300) being draped parallel to the strips fibrous strips of the previous set (200) belonging to said started draping layer, a part of the fibrous strips of the additional set (300) extending above said draping layer thus completed so as to form at least a portion of additional draping layer covering the draping layer thus completed.

4. A draping method according to claim 2 or 3, wherein each set (100, 200, 300) of fibrous strips deposited extends between a first fibrous strip deposited along a reference trajectory (T ia, T2A, T3A) and a last fibrous strip deposited along a final trajectory (TiE, T2E, T3E), the angle formed between the reference trajectory (TiA, T2A, T3A) and the generatrix of the draping shape which intersects the first end contour (Pi) at the same point as the reference trajectory (TiA, T2A, T3A) corresponding to the angle formed between the final trajectory (TiE, T2E, T3E) and the generatrix of the draping shape which intersects the first end contour (Pi) at the same point as the final trajectory (TiE, T2E, T3E).

5. A draping method according to claim 4, wherein the reference trajectory (TiA, T2A, T3A) and the final trajectory (TiE, T2E, T3E) correspond to generators of the draping shape.

6. A draping method according to any one of claims 1 to 5, wherein the draping of the fibrous strips is carried out by automatic placement of fibers.

7. A method of draping according to any one of claims 1 to 6, the method further comprising draping a plurality of stiffening fibrous structures over the draping form, the stiffening fibrous structures being draped such that fibers of said stiffening fibrous structures overlap generatrices of the developed surface of the draping form.

8. A draping method according to any one of claims 1 to 7, the method comprising a step of producing at least one excess thickness of the fiber preform.

9. Fibrous preform comprising at least one developable portion of truncated cone shape extending around an axis of revolution, said developable portion extending along the axis of revolution between a first end contour and a second end contour, the developable portion of said preform comprising a plurality of fibrous layers formed by fibrous strips, characterized in that the fibers of the fibrous strips of at least two successive fibrous layers cor- correspond to straight lines of the developed surface of the developable part of the fibrous preform and in that each fibrous strip extends from one of the end contours and opens onto one of the end contours.

10. Method for manufacturing a part made of composite material comprising at least one developable part of truncated cone shape, the method comprising at least: - the production of a fiber preform by the draping method according to one of claims 1 to 8, - the densification of the fiber preform by a matrix so as to obtain a part made of composite material.

11. Part made of composite material comprising at least one developable part of truncated cone shape obtained by the method of claim 10.

12. Aircraft engine comprising a composite material part according to claim 11.

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