Method for manufacturing a self-stiffened intermediate casing and intermediate casing obtained using this method

Abstract

One aspect of the invention relates to a method for manufacturing a self-stiffened intermediate casing for a turbomachine comprising the steps of: - draping at least one first preform, - draping at least one second preform, - positioning the first and the second preform side by side in order to form an assembly comprising a uniform inner surface and a raised outer surface, - draping the inner surface of the assembly so as to consolidate the assembly, and - co-curing the consolidated assembly. A further aspect of the invention relates to a self-stiffened intermediate casing for a turbomachine obtained using this method.

Description

DESCRIPTION TITLE: Process for manufacturing a self-stiffened intermediate crankcase and intermediate crankcase obtained by this process TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for automatically manufacturing a self-stiffened intermediate housing for a turbomachine. It also relates to a self-stiffened intermediate housing obtained by this method.

[0002] The invention has applications in the field of aeronautics and, in particular, in the field of manufacturing composite parts with complex geometries such as certain turbomachine parts. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] In an aircraft turbomachine, such as a twin-spool turbojet, the term "intermediate casing" typically refers to a casing whose hub is located between the low-pressure compressor casing and the high-pressure compressor casing. Indeed, a turbojet engine conventionally comprises four external casings arranged, from upstream to downstream, in the following order: the air intake casing, the fan casing, the intermediate casing, and the thrust reverser casing. These four casings form the outer boundary of the gas stream within the turbojet. An example of such a turbojet, extending along the central axis A, is schematically represented in Figure 1.This turbojet 10 comprises, from upstream to downstream, the air inlet casing 11, which forms the inlet of the turbojet, the fan casing 12, which is arranged around the fan blades 15, the intermediate casing 13, which is connected to radial arms 16 and supports all the rotors and stators of the turbojet, and the thrust reverser casing 14 which extends to the outlet of the turbojet.

[0004] The intermediate housing is a generally cylindrical structural component supporting an intermediate housing shell, or VCI. The intermediate housing may also support one or more stiffeners with mechanical functions. Some stiffeners may, for example, form radial arms and / or allow the attachment of equipment (such as a pipe or a computer), or even form a fireproof partition. An intermediate casing supporting a ferrule and / or stiffeners is called a "self-stiffening casing".

[0005] Traditionally, self-stiffening crankcases are machined from a single piece of metal. Crankcases made from composite materials have also been proposed, for example, through 3D weaving and liquid resin injection molding (a process known as RTM for Resin Transfer Molding). The shells and stiffeners are manufactured separately and bonded to the crankcase structure. However, these manufacturing techniques for self-stiffening crankcases are expensive and complex to implement because they require a large number of operations that are rarely automated.

[0006] There is therefore a real need for an automated technique to manufacture self-stiffening crankcases at a lower cost. SUMMARY OF THE INVENTION

[0007] To address the aforementioned problems of complexity in manufacturing techniques for self-stiffened housings, the applicant proposes a manufacturing process for an automated self-stiffened housing in which several composite preforms are assembled and held together by draping and co-curing the assembly.

[0008] The term "co-firing" refers to the simultaneous firing of several composite preforms, manufactured separately and assembled to form a single piece subjected to firing.

[0009] In the remainder of the description and claims, the term "baking" shall be understood as baking in the literal sense, for example for materials such as epoxy resins which must be baked, or consolidation, for example for thermoplastic-type materials which require consolidation.

[0010] A "pre-impregnated preform" is a semi-finished composite element consisting of resin-impregnated fibers shaped by molding. In the remainder of this description, pre-impregnated preforms will be referred to simply as preforms.

[0011] In the following description, the concepts of inside and outside are defined in terms of radial positioning relative to the central axis A of the turbojet engine. Thus, An interior surface is a surface closer to the central axis A than an exterior surface of the same part.

[0012] According to a first aspect, the invention relates to a method for manufacturing a self-stiffened intermediate casing for a turbomachine, comprising the following steps: a) manufacturing by draping at least one first preform, b) manufacturing by draping at least one second preform, c) positioning the first and second preforms side by side to form an assembly having a uniform inner surface and a raised outer surface, d) draping the inner surface of the assembly so as to consolidate said assembly, and e) co-baking the consolidated assembly.

[0013] This process allows for the automated manufacturing of self-stiffening intermediate housings, ensuring cost savings compared to current techniques, as well as consistent quality.

[0014] In addition to the features mentioned in the preceding paragraph, the manufacturing process according to one aspect of the invention may have one or more of the following complementary features, considered individually or in all technically possible combinations: the first preform has a substantially U-shaped cross-section, an upstream leg of the U-shaped section forming a housing flange, and a downstream leg of the U-shaped section forming a portion of a stiffener; the second preform has a substantially L-shaped cross-section, and an arm of the L-shaped section forming, together with the downstream leg of the U-shaped section of the first preform, the stiffener; the draping of the inner surface of the assembly has a substantially L-shaped cross-section; the process includes, between step c) assembly and step d) draping, a step of applying a filler material to fill a space, on the inner surface, between the first preform and the second preform. The first preform, the second preform, and the drape are substantially cylindrical. The first preform, the second preform, and the drape are partially cylindrical. The process includes, in addition to steps a) and b) of manufacturing the first and second preforms, a further step of manufacturing at least one third preform, this third preform being assembled with the first and second preforms during step c) of assembly. Each preform consists of at least two adjoining preformed sectors. The process includes, before or after step d) of draping, a step of forming pleats locally, to form at least one additional stiffener.

[0015] A second aspect of the invention relates to a self-stiffened intermediate casing for a turbomachine, obtained by the manufacturing process as defined above. BRIEF DESCRIPTION OF THE FIGURES

[0016] Other advantages and features of the invention will become apparent from the following description, illustrated by the figures in which:

[0017] Figure 1, already described, represents a turboshaft engine comprising an intermediate casing according to the prior art;

[0018] Figure 2 represents, according to a schematic cross-sectional view, a portion of a self-stiffened intermediate housing according to the invention;

[0019] Figure 3 represents, from a functional view, the steps of the manufacturing process of a self-stiffened intermediate housing according to the invention;

[0020] Figure 4 shows, according to simplified perspective views, the different preforms assembled according to the manufacturing process of the invention to obtain an example of a self-stiffening intermediate crankcase sector;

[0021] Figure 5 shows, in a schematic cross-sectional view, a dimensioned example of the preforms shown in Figure 4; and

[0022] Figure 6 represents, according to a schematic cross-sectional view, another example of preforms assembled according to the process of the invention to obtain another example of a self-stiffened intermediate housing. DETAILED DESCRIPTION

[0023] An example of an embodiment of a method for the automated manufacture of a self-stiffened intermediate housing is described in detail below, with reference to the accompanying drawings. This example illustrates the features and advantages of the invention. It should be noted, however, that the invention is not limited to this example.

[0024] In the figures, identical elements are identified by identical references. For the sake of readability, the size scales between represented elements are not respected.

[0025] An example of a self-stiffening intermediate housing 100 is shown schematically in cross-section in Figure 2. This self-stiffening intermediate housing 100, hereafter referred to simply as the housing, comprises a basic structure 110, supporting a housing flange 120, a main stiffener 130, mounting areas 140, and additional stiffeners 135. The basic structure 110 has a substantially cylindrical shape and can be formed from a single piece or from several assembled sectors. Figure 2 shows an example of a sector of the basic structure 110. It is understood that several sectors, substantially identical in terms of dimensions, can be produced separately according to the manufacturing process described below and subsequently assembled, for example, with an overlap area between each sector to ensure continuity of material.

[0026] This housing 100 according to the invention is manufactured from several preforms, assembled together, and the assembly is reinforced by draping a surface of said assembly. An example of the manufacturing process for a housing according to the invention is shown in Figures 3 and 4. These Figures 3 and 4 show the manufacturing steps of a portion of the housing 100, and in particular the upstream portion of the housing 100 incorporating the housing flange 120 and the main stiffener 130.

[0027] According to this example, the manufacturing process 200 according to the invention comprises: a step 210 of manufacturing by draping a first preform P1, a step 220 of manufacturing by draping a second preform P2, a step 230 of positioning the first and second preforms P1, P2, side by side and aligned so that the two preforms, assembled, form the basic structure 110, with a substantially uniform inner surface Pi and an outer surface with reliefs, a step 240 of draping the inner surface of the assembly so as to consolidate said assembly, and a step 250 of baking the draped assembly.

[0028] In the example shown in Figures 3 and 4, the first preform P1 corresponds to the upstream ferrule of the housing. This preform P1 (drawing A in Figure 4) has a roughly U-shaped cross-section, that is, a cross-section comprising a base 121 and an upstream leg 122 and a downstream leg 123 extending substantially perpendicularly on either side of the base 121. The second preform P2 (drawing B in Figure 4) corresponds to the downstream ferrule of the housing and has a roughly L-shaped cross-section, that is, a cross-section comprising a base 131 and an arm 132 extending perpendicularly from the base 131. The legs 122 and 123 of preform P1 may be of different heights. The downstream leg 123 of preform P1 and the arm 132 of preform P2 are preferably of the same height.

[0029] After manufacturing the preforms, respectively P1 and P2, in steps 210 and 220, said preforms P1 and P2 are aligned with each other (step 230), that is to say, they are positioned in continuity with each other, with the downstream leg 123 of preform P1 attached to the arm 132 of preform P2. This alignment, or juxtaposition, of preforms P1 and P2 generates an assembly P4 comprising: a quasi-continuous inner surface Pi, formed by the bases 121 and 131 of preforms P1, P2, and an outer surface with relief, that is to say, comprising prominences formed by the legs 122, 123 of preform P1 and the arm 132 of preform P2.

[0030] After step 230 of positioning the preforms P1 and P2, step 240 consists of draping the inner surface Pi of the assembly P4 so as to consolidate The assembly. This draping of the inner surface, represented by reference P3 in drawing C of Figure 4, covers not only the said inner surface of the assembly but also the upstream surface 122a of the upstream leg 122 of the preform P1. This draping P3 therefore has an L-shaped cross-section, the arm 124 of which has a shape and dimensions similar to those of the upstream leg 122 of the preform P1, and the shape and dimensions of the base 125 of which are similar to those of the bases 121 and 131 of the juxtaposed preforms P1 and P2. The draping P3 thus forms the inner face 110i of the base structure 110, while the raised outer surface of the juxtaposed preforms P1 and P2 constitutes the outer face 110e of the base structure 110.

[0031] Each preform P1, P2 can be made from a single piece. Alternatively, preforms P1, P2 can be composed of two or more preformed sectors, joined together to form a preform. These different preform sectors will be draped using the same draping process P3 during step 240.

[0032] The P1, P2 preforms, as well as the P3 draping, can be made using various known composite draping techniques such as, for example, the automated fiber placement technique (known as AFP for Automated Fiber Placement, in Anglo-Saxon terms), from carbon fibers and epoxy or carbon fibers and thermoplastic (PAEK).

[0033] Once the P3 drape is in place, the assembly P5, consisting of the preforms P1, P2 and the P3 drape, forms a monolithic structure, which is then subjected to a heat treatment by curing (step 250). The curing in step 250 is carried out, according to a standard process in the field of composite part manufacturing, in an oven or an autoclave, at a temperature depending on the material used, for example, approximately 180°C for an epoxy resin or approximately 360°C for a thermoplastic material.

[0034] According to some embodiments, manufacturing process 200 includes an intermediate step, between steps 230 and 240, of depositing a filling material, also called a gap filler. This filler is deposited at the joint of the two preforms P1 and P2, on the inner surface Pi, in order to fill any gap due to a lack of material. Indeed, the assembly of preforms P1 and P2 can create a gap, that is to say a A void without material forms a hollow in the inner surface Pi. Placing a filling material fills this gap, ensuring that the inner surface is smooth and even to receive the draping P3.

[0035] According to a dimensioned example, the preforms P1 and P2 in Figure 4 can each have twelve plies, and the drape P3 can have sixty plies. The assembly P5 can, for example, have a base structure 110 and housing flange 120 thickness of 9.72 mm and a main stiffener 130 thickness of 3.24 mm, with a material plie of 0.135 mm. Once cured, the assembly P5 forms the housing 100. In the dimensioned example in Figure 5, the base structure 110 of the housing 100 has a length of 485 mm. Of course, the values ​​shown in Figure 5 are only examples. The preforms P1, P2, and the drape P3 can be produced with a higher or lower number of plies, and the dimensions of these elements P1, P2, and P3 can vary depending on the turbomachine in question and the requirements.

[0036] The manufacturing process 200 was described previously for an assembly P5 consisting of two preforms P1, P2, and a drape P3. This assembly is designed to produce, after curing, a housing 100 comprising a housing flange 120 and a main stiffener 130. Those skilled in the art will understand that other housing structures can be obtained using the same process 200 by adjusting the number of preforms to suit the desired structure. For example, several preforms can be positioned side by side, with a drape covering the inner surface formed by the assembly of these juxtaposed preforms. An example of another assembly P5 is shown for illustration in Figure 6. In this example, three preforms P1, P6, P7, having a roughly U-shaped cross-section, are assembled with a preform P2, which has an L-shaped cross-section.The inner surface Pi is covered with a drape P3 having an L-shaped cross-section, as explained previously. This example of assembly P5 allows, after firing, the production of a housing 100 having a housing flange 120, a main stiffener 130 and two other stiffeners 135, these two stiffeners 135 being obtained by the juxtaposed legs of preforms P6 and P7 and by the arm of preform P2 juxtaposed with the downstream leg of preform P7.

[0037] In certain embodiments, not shown in the figures, the housing 100 obtained with the manufacturing process 200 may include a housing flange downstream, that is to say a casing flange positioned at the end of the base structure 110 opposite to that where the upstream casing flange 120 is positioned.

[0038] In some embodiments, intermediate elements or additional stiffeners are formed on the basic structure 110 by adding folds locally. The stiffeners 135 of Figure 2 can, for example, be formed by a succession of folds at chosen locations. Thus, instead of forming stiffeners 135 as explained in Figure 6, the stiffeners 135 can be obtained by applying several folds successively on top of each other at chosen locations. Similarly, intermediate elements, such as fastener locations 140, can be formed by applying several folds locally on top of each other. These folds can be deposited on the outer face 110e of the assembly P5 or on the inner face 110i of said assembly P5. These folds are baked at the same time as all the other elements of the assembly P5.Therefore, only one cooking step 240 is carried out during the manufacturing process 200 regardless of the number of preforms and / or folds added.

[0039] Regardless of the manufacturing method, process 200 offers the advantage of being less expensive than current manufacturing techniques because it is automated, requires only a single firing step, and eliminates the need for human intervention to bond the components together. Its automation also ensures a consistent level of quality.

[0040] The figures described above show a section of a housing 100. It is understood that a housing can be manufactured in its entirety using the method according to the invention. A housing with a substantially cylindrical shape, or any other structure extending over 360°, can therefore be produced in a single piece using this method. Conversely, housings or structures can be manufactured in sections, for example, two half-housings or structures extending over 180° or even less. The sections of housings or structures manufactured using the method according to the invention are then partially cylindrical. The manufacturing method according to the invention also makes it possible to manufacture housings or structures with complex geometries, such as a double or triple curvature geometry; in this case, the shape and cross-section of the preforms to be assembled are determined according to the geometry of the housing.

[0041] Although described through a number of examples, variants and embodiments, the manufacturing process according to the invention and the housing obtained by this process include various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

DEMANDS

1. A method (200) for manufacturing a self-stiffening intermediate casing (100) for a turbomachine, comprising the following steps carried out one after the other: a) manufacturing (210) by draping at least one first preform (P1), b) manufacturing (220) by draping at least one second preform (P2), c) positioning side by side (230) of the first and second preforms (P1, P2) to form an assembly (P4) having a uniform inner surface (Pi) and a raised outer surface (110e), d) draping (240) of the inner surface (Pi) of the assembly so as to consolidate said assembly, and e) co-baking (250) of the consolidated assembly.

2. Method according to claim 1, characterized in that the first preform (P1) comprises a substantially U-shaped section, an upstream leg (122) of the U-shaped section forming a housing flange (120), a downstream leg (123) of the U-shaped section forming a portion of a stiffener (130).

3. Method according to claim 2, characterized in that the second preform (P2) has a substantially L-shaped section, an arm (132) of the L-shaped section forming, with the downstream leg (123) of the U-shaped section of the first preform, the stiffener (130).

4. A method according to any one of claims 1 to 3, characterized in that the draping (P3) of the inner surface of the assembly (P4) has a substantially L-shaped section.

5. A method according to any one of claims 1 to 4, characterized in that it comprises, between step c) of assembly and step d) of draping, a step of laying a filling material to fill a space, on the inner surface (Pi), between the first preform and the second preform.

6. A method according to any one of claims 1 to 5, characterized in that the first preform (P1), the second preform (P2) and the drape (P3) are substantially cylindrical.

7. A method according to any one of claims 1 to 5, characterized in that the first preform (P1), the second preform (P2) and the drape (P3) are partially cylindrical.

8. A method according to any one of claims 1 to 7, characterized in that it comprises, in addition to the steps a) and b) of manufacturing the first and second preforms, an additional step of manufacturing at least one third preform (P6, P7), this third preform being assembled with the first and second preforms during the assembly step c).

9. A method according to any one of claims 1 to 8, characterized in that each preform (P1, P2) is made up of at least two joined preformed sectors.

10. A method according to any one of claims 1 to 9, characterized in that it comprises, before or after draping step d), a local pleating step to form at least one additional stiffener (135).

11. Self-stiffened intermediate housing (100) for turbomachine, characterized in that it is obtained by the manufacturing process (200) according to any one of claims 1 to 10.

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