METHOD FOR MANUFACTURING AN ANNULAR CASING FOR AN AIRCRAFT TURBOMACHINE

Abstract

A method of manufacturing an annular casing for an aircraft turbomachine, this casing comprising an annular body made of composite material, the method comprising: a step of winding a strip of fibers (10) onto the periphery of a drum (12), rotating rollers (22, 24) being used to apply and compress the strip of fibers (10) onto the periphery of the drum (12), a step of mounting a sectored annular shell (20) onto the outer periphery of the drum (12), and a step of injecting a resin into the preform (13) and RTM molding this preform (13), characterized in that the fibers of the strip are coated with a sizing substance, and in that the strip of fibers (10) undergoes a heating and cooling cycle). Figure for abstract: Figure 2

Description

Title of the invention: METHOD FOR MANUFACTURING AN ANNULAR CASING FOR AN AIRCRAFT TURBOMACHINE Technical field of the invention

[0001] The present invention relates to a method of manufacturing an annular casing for an aircraft turbomachine. Technical background

[0002] An aircraft turbomachine comprises several annular casings. To lighten a casing, it is known to make it from a composite material. In the present application, the term "composite material" means a material comprising fillers such as fibers embedded in a polymer matrix. The polymer matrix is generally a resin.

[0003] A fan casing can for example be made of composite material.

[0004] A method of manufacturing a casing of this type comprises for example: a. a step of winding a strip of fibers onto the periphery of a drum to form an annular preform, b. a step of mounting a sectored annular shell on the external periphery of the drum so that the preform is inserted between the drum and this shell, and c. a step of injecting a resin into the preform and RTM molding this preform, the preform being compressed by the annular shell and being heated during RTM molding,

[0005] The abbreviation or acronym RTM comes from the Anglo-Saxon Resin Transfer Molding and is a manufacturing process that consists of injecting a polymerizable resin into a mold containing a preform made from fibers. The resin impregnates the preform and polymerizes to solidify the preform. Polymerization takes place during compression and heating in the mold.

[0006] The first step of the process therefore consists of winding a strip of fibers around the periphery of a drum, generally over several turns. The fibers can here be coated with a substance, commonly called sizing, which in particular facilitates the weaving and shaping of the strip such as its winding. The addition of water to the fibers also facilitates the sliding of the fibers between them. This substance can also be used to facilitate the weaving of the fibers between them when the strip is woven, which is not necessarily the case.

[0007] The second step of the process consists of mounting sectors of a hull on the pe external rim of the drum and therefore around the preform. These shell sectors will be used to compress the preform on the drum.

[0008] The third step is to inject the resin into the mold to impregnate and solidify the preform, and thus form the casing. The mold is placed in an oven to heat the fiber strip. The shell sectors are used to compress the preform onto the drum.

[0009] During the second step, thin metal plates can be inserted between the shell and the preform, at the junction zones between the shell sectors. These plates prevent the fibers from being pinched between the shell sectors.

[0010] A problem encountered during the manufacture of a casing is a phenomenon of buckling of the fibers in these junction zones of the hull sectors and randomly on the external part of the casing. This buckling is due to the combination of two factors: the proliferation of the fibers and the quality of winding and weaving of the fiber strip on the drum which can lead to an excess wound length of this strip compared to the external diameter of the drum. Furthermore, the greater the thickness of the casing, the greater the risk of buckling of the fibers.

[0011] At the end of the manufacture of a casing, the buckling of the fibers is checked by an operator. If the buckling of the fibers exceeds a criticality threshold, the casing can be scrapped.

[0012] There is therefore a need to reduce the risk of buckling of the fibers during the manufacture of a casing by the aforementioned method.

[0013] One solution could, for example, be to use a vacuum tarpaulin to compress the preform onto the drum. However, compressing the preform after it has been wound does not completely prevent the (bulging of the fibrous preform).

[0014] Another solution would be to heat the strip of fibers or even to compress it before winding it onto the drum. However, this solution would not prevent the fibers from swelling when winding the strip.

[0015] The present invention provides a simple, effective and economical solution to the problem mentioned above. Summary of the invention

[0016] The invention thus proposes a method of manufacturing an annular casing for an aircraft turbomachine, this casing comprising an annular body made of composite material, the method comprising: a. a step of winding a strip of fibers onto the periphery of a drum to form an annular preform, the fibers being coated with a sizing substance, rotating rollers being used to apply and compressing the strip of fibers on the periphery of the drum, b. a step of mounting a sectored annular shell on the external periphery of the drum so that the preform is inserted between the drum and this shell, and c. a step of injecting a resin into the preform and RTM molding this preform, the preform being compressed by the annular shell and being heated during RTM molding, characterized in that the fibers of the strip are coated with a sizing substance, and in that the strip of fibers is heated in a first zone to a first softening temperature of said substance, then is cooled in a second zone to a second stiffening temperature of said substance, the first and second zones being contiguous and at least one of these zones being a zone for winding the strip of fibers onto the drum and compressing this strip of fibers onto the drum by means of at least a portion of said rollers.

[0017] The present invention thus proposes rollers for compressing the strip of fibers on the drum during its winding. The method thus proposes a first phase of compression of the strip of fibers, before the second phase of compression of the preform produced by the sectorized shell.

[0018] In addition to this compression, the fiber web undergoes a cycle of forced heating and then forced cooling. At least part of this cycle takes place during the compression of the fiber web. Heating the fiber web softens the fiber sizing substance and facilitates the shaping of the fiber web. Cooling the fiber web stiffens it again. The combination of compression and heating of the fiber web reduces the risk of fiber swelling during winding. The softening of the substance allows the web to deform sufficiently to absorb the compaction. The combination of compression and cooling of the fiber web allows the compacted fiber web to be frozen by the resolidified substance.

[0019] Furthermore, the fact of carrying out the compression and part of the thermal cycle during the winding step of the process has no significant impact on the duration of this process, which is therefore not or only slightly extended.

[0020] The method according to the invention may comprise one or more of the following characteristics, taken independently of one another or in combination with one another:

[0021] - the first zone is a zone for winding and compressing the strip of fibers by a first roller or several first rollers, and the second zone is a zone for winding and compressing the fiber strip by a second roller or more second rolls;

[0022] - the fiber strip is heated by the or each first roller in the first winding area;

[0023] - the or each first roller comprises an internal heating circuit, by electrical example or by passage of a heating fluid,

[0024] - the fiber strip is cooled by the or each second roller in the second winding area;

[0025] - the or each second roller comprises an internal cooling circuit, for example by passage of a cooling fluid;

[0026] — the or each first roller comprises an internal electric heating circuit, by resistance or induction;

[0027] - the fiber strip is heated in the first zone by a heating system external, and is cooled in the second zone by an external cooling system;

[0028] - at least two or three first rollers compress the fiber strip in the first winding zone, and at least two or three rollers compress the fiber web in the second winding zone;

[0029] — the first winding zone is located between the second winding zone and a third zone, the fiber strip being preheated in this third zone by an external heating system;

[0030] - a preheating zone is located upstream of the first zone relative to the winding direction, the fiber strip being preheated in this third zone by an external heating system;

[0031] - the first zone is a zone remote from the drum, and the second zone is a zone for winding and compressing the fiber strip by a first roller or several first rollers;

[0032] - the fiber strip is cooled by the or each first roller in the second area ;

[0033] - the or each first roller comprises an internal cooling circuit, for example by passage of a cooling fluid;

[0034] - the fiber strip is cooled in the second zone by a cooling system external development;

[0035] - the rollers are carried by a fixed support structure, preferably in a manner removable, on a support;

[0036] — the support is the support axis of the drum or is external to the drum;

[0037] - each of the rollers has an axis of rotation whose position is adjustable relative to an axis of rotation or revolution of the drum; in particular, the axes of rotation of the rollers may be inclined relative to the axis of the drum;

[0038] - each of the rollers comprises or is formed by a plurality of segments an adjacent rings that have different shapes and / or diameters;

[0039] — the annular segments of each roller are aligned on the same axis of rotation or at least some of these segments are on the contrary misaligned to allow fine adjustment of the compaction by zone;

[0040] — each of the first and second rollers is in one piece;

[0041] — the segments are independent of each other and have rotation speeds different from each other;

[0042] — the first temperature is greater than or equal to the softening temperature sizing;

[0043] — the first temperature is greater than or equal to 80°C;

[0044] — the second temperature is lower than the softening temperature of sizing;

[0045] — the second temperature is low enough to allow the stiffening of the preform;

[0046] — the second temperature is less than or equal to 40°C, or even 30°C, and corresponds for example at room temperature (e.g. around 20-25°C). Brief description of the figures

[0047] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0048] [Fig-1] [Fig.l] is a schematic perspective view of a drum around which a strip of fibers is wound,

[0049] [Fig.2] [Fig.2] is a schematic perspective view of a drum around which a strip of fibers is wound, and illustrates a first step of a method according to the invention:

[0050] [Fig.3] [Fig.3] is a schematic perspective view of compression rollers of the fiber strip during its winding;

[0051] [Fig.4] [Fig.4] is a view similar to that of [Fig.2] and illustrates areas successive winding of the strip of fibers onto the drum;

[0052] [Fig.5] [Fig.5] is a schematic perspective view of one of the compression rollers;

[0053] [Fig.6] [Fig.6] includes views similar to that of [Fig.2] and illustrates a step of disassembly of the support structure of the compression rollers;

[0054] [Fig.7] [Fig.7] is a very schematic cross-sectional view of a housing in compression course by rollers; and

[0055] [Fig.8] [Fig.8] is a flowchart showing steps of a method according to the invention of manufacturing an annular turbomachine casing. Detailed description of the invention

[0056] [Fig. 8] is a flowchart schematically illustrating steps of a method according to the invention for manufacturing an annular casing for an aircraft turbomachine. This casing is for example a fan casing.

[0057] The method essentially comprises three steps designated a), b) and c).

[0058] Step a), is a step of winding a strip of fibers onto the periphery of a drum.

[0059] [Fig.l] shows a step of winding a fiber strip 10 onto the outer periphery of a drum 12 to form an annular preform 13, in accordance with the prior art.

[0060] The drum 12 has a generally cylindrical shape and has an axis of revolution A. It is generally mounted to rotate around the axis A by a first support structure 14 which is for example fixed to the ground.

[0061] The drum 12 comprises an external annular surface around which the strip of fibers 10 is surrounded. This surface is not necessarily regular and may for example have a diameter which varies between the axial ends of the drum 12.

[0062] At each of its axial ends, the drum 12 comprises an annular rim 16 oriented radially outwards relative to the axis A. The strip of fibres 10 is wound between these rims 16.

[0063] During step a), the strip of fibers 10 can be delivered by an installation which is not shown and which comprises for example at the outlet a roller 18 for distributing the strip of fibers 10. This roller 18 has an axis of rotation B which is parallel to the axis A. This roller 18 can also have a diameter which varies along its axis B.

[0064] The fiber strip 10 is a woven or non-woven strip, that is to say it is obtained by weaving or not weaving fibers. The fibers are for example carbon fibers.

[0065] The fibers are coated with a sizing substance, which is for example epoxy-based. This substance has for example a glass transition temperature of between 60 and 120°C, and for example between 100 and 120°C.

[0066] Step b) of the method comprises the mounting of a sectored annular shell 20 on the external periphery of the drum 12 and around the preform 13. This shell 20, schematically represented in [Fig.l], is arranged all around the drum 12 and the preform 13 in order to compress the latter on the drum 12.

[0067] The shell 20 is sectorized and comprises shell sectors which are arranged next to each other on the periphery of the drum 12 and around the axis A.

[0068] Step c) of the method is a step of injecting a resin into the preform 13 and RTM molding of this preform 13.

[0069] The resin is for example of the epoxy type. It is injected into the mold comprising the drum 12 and the shell 20, or in which the drum 12 and the shell 20 are arranged, so as to impregnate the strip of fibers 10.

[0070] The resin is intended to extend over the entire circumference of the preform 13, over its entire axial extent and over its entire thickness.

[0071] RTM molding consists of compressing and heating the mold, for example in an oven, so as to cause the polymerization and hardening of the resin. Compression is obtained by exerting a force on each sector of the shell 20, oriented in a radial direction towards the axis A.

[0072] A casing is then obtained in composite material based on fibers embedded in a polymer matrix.

[0073] The particularity of the invention is that, during the winding step a) of the method, rotating rollers 22, 24 are used to apply and compress the strip of fibers 10 on the periphery of the drum 12, as shown in [Fig.2].

[0074] During winding, the strip of fibers 10 is compressed in a first winding zone ZI by one or more first rollers 22, and heated in this first winding zone ZI to a first softening temperature T1 of the substance which coats the fibers of the strip 10.

[0075] Then, still during winding, the strip of fibers 10 is compressed in a second winding zone Z2 by one or more second rollers 24, and cooled in this second winding zone Z2 to a second stiffening temperature of the substance Z2.

[0076] As seen in the drawing, the first and second winding zones Z1, Z2 are contiguous. This means that cooling takes place continuously just after heating and during winding of the fiber strip 10.

[0077] Heating the fiber strip 10 to temperature T1 makes it possible to soften the fiber coating substance and to facilitate the shaping of the fiber strip 10 as well as its compression on the drum 12.

[0078] Cooling the fiber strip 10 to temperature T2 allows the fiber coating substance to resolidify and its compressed form to set.

[0079] Advantageously, Tl is greater than Tg, and T2 is less than Tg.

[0080] Tl is for example between 60 and 120°C, and is for example of the order of 80°C.

[0081] T2 is for example between 20 and 30°C, and is for example of the order of the tem room temperature.

[0082] In the example shown in [Fig.2], the number of rollers 22 in the zone Z1 is three even if this number is not limiting. These rollers 22 have axes of rotation C parallel to each other.

[0083] The fiber strip 10 can be heated by these rollers 22 in the zone Zl, that is to say that the rollers 22 can have a dual function of compressing and heating the fiber strip 10. For this, the rollers 22 can comprise an internal circuit C1 for the passage of a heating fluid ([Fig.3]). The heating fluid is for example a liquid such as water or oil.

[0084] Alternatively, the rollers could comprise an internal electric heating circuit, for example comprising at least one heating resistor or an induction system.

[0085] In the example shown, the number of rollers 24 in zone Z2 is three even if this number is not limiting.

[0086] The fiber strip 10 can be cooled by these rollers 24 in the zone Z2, that is to say that the rollers 22 can have a dual function of compression and cooling of the fiber strip 10. For this, the rollers 24 can comprise an internal circuit C2 for the passage of a cooling fluid. The cooling fluid is for example a liquid such as water.

[0087] The rollers 24 have axes of rotation C parallel to each other.

[0088] Alternatively or as an additional feature, zones Z1 and Z2 could be heated and cooled respectively by external systems. Zone Z1 would be heated by an external heating system SI which would, for example, spray hot air onto the fiber strip 10, or heat the fiber strip by radiation, infrared, convection, etc. Zone Z2 would be cooled by an external cooling system S2 which would, for example, spray cold air onto the fiber strip 10. Alternatively, zone Z2 could be covered with an external cooling system S2 comprising, for example, a sealed bag containing dry ice.

[0089] In the example shown, the rollers 22, 24 are arranged above the drum 12, that is to say that the zones Z1 and Z2 are located in an upper part of the drum 12.

[0090] The rollers 22, 24 are here carried by a second support structure 26 which can be fixed, preferably removably, on the first support structure 14 (figures 2 and 3).

[0091] The support structure 26 comprises for example two hoops 28 between which are arranged physical axes of rotation of the rollers 22, 24 around the axes C. The rollers 22, 24 are mounted free to rotate on these physical axes which are parallel to each other and to the axis A of the drum 10.

[0092] The zone Z1 occupied by the rollers 22 has an angular extent a of the order of 10 and 30° for example around the axis A. The zone Z2 occupied by the rollers 24 has an angular extent [3 of the order of 10 and 30° for example around the axis A.

[0093] [Fig.4] illustrates an alternative embodiment of the invention in which the first winding zone Zl is located between the second winding zone Z2 and a third zone Z3 in which the fiber strip 10 is preheated by an external heating system S3.

[0094] Zone Z3 may be located on drum 12 or at a distance from drum 12.

[0095] When located on the drum, it is a third winding zone Z3. When it is at a distance from the drum 12, the zone Z3 is located “in the void”, before coming into contact with the drum 12. This latter configuration can be advantageous for greater heating efficiency of the preform and application of the compaction force as close as possible to the point of contact.

[0096] The preheating is for example carried out at a temperature between T1 and T2. This zone Z3 has for example an angular extent y of the order of 10 and 30° for example around the axis A.

[0097] As schematically illustrated by the arrows F1 in [Fig.5], the axis C of rotation of each of the rollers 22, 24 has a position which is adjustable relative to the axis A of the drum. This makes it possible to adjust the level of compression of the strip of fibers 10 when it is wound onto the drum 12. This adjustment can be made at each roller 22, 24 or at the support structure 26.

[0098] This adjustment also makes it possible to position at least part of the rollers so that their axes C are inclined relative to the axis A of the drum 12.

[0099] As can also be seen in the drawings, the rollers 22, 24 do not necessarily extend over the entire axial dimension of the strip of fibers 10 or of the drum 12. In the example shown, the rollers 22, 24 are located on a middle part of the strip of fibers 10, at the level of which the thickness or radial dimension of this strip of fibers is the greatest (and where the risk of fibers swelling is the greatest).

[0100] [Fig.5] also shows that each of the rollers 22, 24 may be formed by a plurality of adjacent annular segments 28 which have different shapes and / or diameters and which are aligned on the same axis C of rotation. The segments 28 are advantageously independent of each other and may have different rotation speeds from each other (arrows F2). This makes it possible to avoid shear problems between the fiber strip 10 and the roller 22, 24.

[0101] [Fig. 6] illustrates the removable nature of the structure 26 for supporting the rollers 22, 24. The rollers 22, 24 are also preferably mounted removably on the structure, so as to adapt their profiles to the profiles of the strip of fibers 10 and the casing to be formed.

[0102] In the examples illustrated in Figures 2 to 6, the rollers 22, 24 are located in separate planes passing through the axis A. In the variant of [Fig.7], a plane passing through the axis A crosses three rollers 22', 24' which have separate axes of rotation C' and not necessarily parallel to the axis A of the drum 12. This variant shows that the forces F3 compression rollers 22', 24' on the fiber strip 10 are oriented perpendicular to the surface to be compressed of the fiber strip 10 but are not necessarily oriented perpendicular to the axis A.

[0103] According to a variant of the method, the winding zone Z1 is no longer a heating zone but is a cooling zone. There is no zone Z2 and the preliminary zone Z3 is a heating zone.

[0104] It is therefore understood that the strip of fibers 10 is heated in the zone Z3 up to the softening temperature T1 of the substance, then is cooled in the zone Z1 up to the stiffening temperature T2 of this substance.

[0105] As mentioned above, the fiber strip may be cooled by the or each first roller 22 in the zone Z1. In this case, the or each first roller 22 may comprise an internal cooling circuit C1, for example by passing a cooling fluid.

[0106] Alternatively, the fiber strip 10 can be cooled in the zone Zl by an external cooling system SI.

Claims

Claims

1. A method of manufacturing an annular casing for an aircraft turbomachine, this casing comprising an annular body made of composite material, the method comprising: a. a step of winding a strip of fibers (10) onto the periphery of a drum (12) to form an annular preform (13), rotating rollers (22, 24) being used to apply and compress the strip of fibers (10) onto the periphery of the drum (12), b. a step of mounting a sectorized annular shell (20) onto the outer periphery of the drum (12) so that the preform (13) is interposed between the drum (12) and this shell (20), and c.a step of injecting a resin into the preform (13) and RTM molding this preform (13), the preform (13) being compressed by the annular shell (20) and being heated during the RTM molding, characterized in that the fibers of the strip are coated with a sizing substance, and in that the strip of fibers (10) is heated in a first zone (Z1 or Z3) to a first temperature (T1) for softening said substance, then is cooled in a second zone (Z2 or Z1) to a second temperature (T2) for stiffening said substance, the first and second zones (Z1, Z2, or Z3, Z1) being contiguous and at least one of these zones being a zone for winding the strip of fibers onto the drum (12) and for compressing this strip of fibers onto the drum by means of at least a portion of said rollers (22, 24).

2. A method according to claim 1, wherein the first zone (Z1) is a zone for winding and compressing the fiber strip (10) by a first roller or several first rollers (22), and the second zone (Z2) is a zone for winding and compressing the fiber strip (10) by a second roller or several second rollers (24).

3. A method according to claim 2, wherein the fiber web (10) is heated by the or each first roller (22) in the first zone (Zl), and is cooled by the or each second roller (24) in the second zone (Z2).

4. Method according to claim 3, in which the or each first roller (22) comprises an internal heating circuit (Cl), for example electrical or by passage of a heating fluid.

5. A method according to one of claims 2 to 4, wherein the fiber web (10) is cooled by the or each second roller (24) in the second winding zone (Z2).

6. Method according to claim 5, in which the or each second roller (24) comprises an internal cooling circuit (C2), for example by passing a cooling fluid.

7. Method according to claim 2, wherein the fiber web (10) is heated in the first winding zone (Z1) by an external heating system (SI), and is cooled in the second winding zone (Z2) by an external cooling system (S2).

8. Method according to one of the preceding claims, in which a preheating zone (Z3) is located upstream of the first zone (Z1) relative to the winding direction, the strip of fibers (10) being preheated in this third zone (Z3) by an external heating system (S3).

9. Method according to one of the preceding claims, in which the first zone (Z3) is a zone remote from the drum (12), and the second zone (Zl) is a zone for winding and compressing the strip of fibers (10) by a first roller or several first rollers (22).

10. A method according to claim 9, wherein the fiber web (10) is cooled by the or each first roller (22) in the second zone (Zl).

11. Method according to claim 10, in which the or each first roller (22) comprises an internal cooling circuit (Cl), for example by passing a cooling fluid.

12. A method according to claim 9, wherein the fiber web (10) is cooled in the second zone (Zl) by an external cooling system (SI).

13. Method according to one of the preceding claims, in which the rollers (22, 24) are carried by a support structure (26) fixed, preferably removably, on a support.

14. Method according to one of the preceding claims, in which each of the rollers (22, 24) has an axis of rotation (C) whose position is adjustable relative to an axis (A) of rotation or revolution of the drum (12).

15. A method according to any preceding claim, wherein each of the rollers (22, 24) comprises or is formed by a plurality of adjacent annular segments (28) which have different shapes and / or diameters.

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