Composite material spacer ring and its manufacturing process

Abstract

This method (200) for manufacturing a spacer ring made of composite material for a turbomachine blower includes preparing (210) an upstream skin preform, preparing (220) a downstream skin preform, preparing (230) an insert preform, inserting (251) the insert preform between the upstream and downstream skin preforms to form a rotating spacer ring preform, and curing (260) the rotating spacer ring preform. The preparation (210) of the upstream skin preform and / or the preparation (220) of the downstream skin preform includes draping (212, 222) prepreg strands onto a skin mold by automated fiber placement. Figure for the abstract: Fig. 5

Description

Description Title of the invention: spacer ring made of composite material and its manufacturing process Field of invention

[0001] The present invention relates to spacer rings for turbine blower- bomachine and more particularly their manufacturing process. Technological background

[0002] — Turbomachine fan rotors most often comprise a disk of fan with a plurality of blades attached to the disc and extending in directions substantially radial from the disc. They also include platforms inter-blades interposed between the blades to internally delimit the vein secondary flow. These inter-blade platforms are made integral with the disc by an upstream retaining flange and a downstream retaining flange.

[0003] One type of downstream retaining flange is the rotating spacer rings, better known by their English name “rotating spacer” or “flow-path” spacer ». These rotating spacer rings comprise a radial ferrule attached to a part integral with the disc and extended by a ring projecting axially towards upstream. Said ring is defined by revolution of a generatrix globally in V-shape pointing upstream. This ring includes an inner leg de- ending with an inwardly oriented axial shoulder which bears against the plates inter-blade forms and an outer leg which defines a glo- outer surface truncated cone-shaped section internally delimiting the secondary flow vein. The external leg is extended by an appendage forming a hook to ensure sealing between the fan rotor and the turbomachine casing.

[0004] — Traditionally, rotating spacer rings are made of metal, most often made of titanium. Recently, it has been proposed, to lighten them, to make them in composite material using resin transfer molding technique.

[0005] — However, producing rotary spacer rings using resin transfer molding resin transfer is not entirely satisfactory. Indeed, this process is expensive and complex to implement.

[0006] — A technique for manufacturing composite preforms is also known, called "automatic fiber placement" (better known by the acronym AFP of English "Automatic Fiber Placement"), in which a draping machine deposits on a support a strip made up of several narrow ribbons (generally with a width of 3 to 13 mm) juxtaposed, called "wicks" ("tows" in English), by through a laying head. These strands are made up of oriented fibers following the direction of elongation of the strand and embedded in a matrix. They are introduced into the head by a feed system which contains several reels each containing one of the strands to be laid. The strands are unwound from the reels and led to the head which heats them just before a roller comes to press them onto the support. The head is connected to a robot which positions it during the draping and the whole is controlled by a computer program which has been defined according to the desired fiber alignment in the final product. The automatic placement of fibers thus allows very high reproducibility in the production of composite material parts. In the aeronautical field, this technique is generally used to produce elements of simple geometry and large dimensions, such as wing or fuselage elements. On the other hand, due to the constraints imposed by the dimensions of the rollers and the width of the strands, automatic fiber placement is generally considered not to be suitable for the production of small or geometrically complex parts, such as rotary spacer rings, because such parts would require specific, non-immediate deposition and / or cutting strategies. Statement of the invention An objective of the invention is to simplify and automate the manufacture of rotary spacer rings so as to reduce their cost. To this end, the invention relates, according to a first aspect, to a method for manufacturing a spacer ring made of composite material for a turbomachine fan, said spacer ring comprising an upstream skin delimiting an upstream face of the spacer ring when it is mounted on the turbomachine, a downstream skin delimiting a downstream face of the spacer ring when it is mounted on the turbomachine, and an annular insert housed between the upstream and downstream skins, the manufacturing method comprising the following steps: preparation of an upstream skin preform, preparation of a downstream skin preform, preparation of an insert preform, insertion of the insert preform between the upstream skin preform and the downstream skin preform so as to form a ring preform rotating spreader, and baking the rotary spacer ring preform, wherein the preparation of the upstream skin preform and / or the preparation of the downstream skin preform comprises draping prepreg strands over a skin mold by automatic fiber placement. According to particular embodiments of the invention, the manufacturing method also has one or more of the following characteristics, taken in isolation or in any technically possible combination(s): draping prepreg strands over the skin mold produces a annular preform blank, upstream skin preform preparation and / or the preparation of the downstream skin preform including, following said draping, the shaping of the preform blank so as to form the upstream skin preform, respectively the downstream skin preform; the shaping of the preform blank is carried out by thermoforming; the skin mold has a revolution shape centered on an axis of revolution, a cylindrical marker being attached to the skin mold with at each point an axial direction parallel to the axis of revolution, a radial direction connecting the axis of revolution to said point and a circumferential direction or- thogonal to the axial and radial directions, each prepreg strand being draped in a direction forming at each point a non-zero angle with the local circumferential direction; the preparation of the insert preform includes the draping of pre- impregnated on an insert mold by automatic fiber placement, the mold insert having a disc shape, the prepreg strands being draped on a slice of said disc; the disc is of revolution around a central axis, a cylindrical reference is attached to the insert mold with at each point an axial direction parallel to the central axis, a radial direction connecting the central axis to said point and a circumferential direction orthogonal to the axial and radial directions, and each strand of prepreg is draped substantially parallel to the circumferential direction; draping prepreg strands onto the insert mold includes: the production of at least one stack of layers of wicks of prepreg stacked in the radial direction, said stack having an axial edge defined by draping which has a axial extension, and machining a machined axial edge of the stack, opposite the edge axial defined by draping, by clean cutting of the stack; for at least one stack, the axial edge defined by draping is curved, the machined axial edge being straight, or the axial edge defined by draping is inclined, the machined axial edge being radial; several stacks are made, said stacks comprising an em- inner stack and an outer stack radially superimposed on the inner stack, the machined axial edge of the inner stack being obtained by clean cutting of the interior stack along a surface of primary cutting and the machined axial edge of the outer stack being obtained by clean cutting of the outer stack according to a cutting surface secondary different from the primary cutting surface; the axial edge defined by draping of the outer stack extends ra- dially the machined axial edge of the inner stack, the cutting surface secondary radially extending the axial edge defined by draping of the interior stack; the axial edge defined by draping of the outer stack extends ra- dialy the axial edge defined by draping of the inner stack, the secondary cutting surface radially extending the machined axial edge of the interior stack; the machined axial edge is obtained by clean cutting of the stack according to a radial or truncated conical cutting surface; and The spacer ring is a rotating spacer ring. The invention also relates, according to a second aspect, to a spacer ring obtained by means of such a method. The invention also relates, according to a third aspect, to a fan rotor comprising such a spacer ring. According to a fourth aspect, the invention relates to a turbomachine comprising such a fan rotor. According to a fifth aspect, the invention relates to an aircraft comprising such a turbomachine. Brief description of the Figures Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which: [Fig. 1] is a top view of an aircraft according to an exemplary embodiment the invention, [Fig.2] is a simplified sectional view of a turbomachine of the aircraft of [Fig.1], [Fig.3] is a view of a detail marked III of [Fig.2], [Fig.4] is a sectional view of a rotating spacer ring of the tur- bomachine of [Fig.2], [Fig.5] is a diagram illustrating a process for manufacturing the ring rotating spreader of [Fig.4], [Fig.6] is a diagram illustrating a step in the preparation of a preform insert of the manufacturing process of [Fig.5], and Figures 7 to 25 illustrate different steps and sub-steps of the fa- construction of [Fig.5]. Detailed description of an example of implementation The aircraft 10 shown in [Fig.1] comprises turbomachines 12 to propel it. In the example shown, the aircraft 10 is an airplane. This aircraft comprises, in a conventional manner, a fuselage 14, a tailplane 16 and two wings 18. The turbomachines 12 are here two in number and are each housed under a respective wing 18. As a variant (not shown), the turbomachines 12 are arranged along the fuselage 14, for example near the tailplane 16. As a further variant (also not shown), the aircraft 10 comprises a single turbomachine 12 or at least three turbomachines 12. One of the turbomachines 12 is shown in [Fig.2]. As visible in this Figure, the turbomachine 12 is elongated along a longitudinal axis X. It typically has angular symmetry around said longitudinal axis X, that is to say that there is at least one angle for which the turbomachine is invariant by rotation around the longitudinal axis X. Here and hereinafter, the terms "interior" and "exterior", "internal" and "external", as well as their variations, are understood in reference to the X axis, an element described as "interior" or "internal" being oriented towards the X axis while an "exterior" or "external" element is oriented opposite the X axis. The term "radial" and its variations are understood in reference to a direction orthogonal to the X axis. The turbomachine 12 comprises, in a conventional manner, a nacelle 20, an internal vein 22 for circulating an air flow through the nacelle 20, a combustion chamber 24 housed in the vein 22, an engine body 26 and a gas exhaust nozzle 28. In the following, the terms “upstream” and “downstream” are understood to refer to a direction of flow of an air flow through the vein 22. The engine body 26 comprises a compressor 30, a turbine 32 and a transmission shaft 34 coupling the turbine 32 to the compressor 30 for driving the compressor 30 by the turbine 32. The compressor 30 is arranged upstream of the combustion chamber 24 and supplies the combustion chamber 24 with compressed air. The turbine 32 is arranged downstream of the combustion chamber 24 and receives the exhaust gases leaving the combustion chamber 24. The transmission shaft 34 has the longitudinal axis X as its axis of rotation. The transmission shaft 34 is guided in rotation relative to the nacelle 20 by means of of bearings (not shown). In the example shown, the turbomachine 12 is a multi-body turbomachine, in particular a double-body turbomachine, comprising a low-pressure body 40 in addition to the engine body 26. The engine body 26 then constitutes a high-pressure body, the compressor 30 being a high-pressure compressor, the turbine 32 being a high-pressure turbine and the transmission shaft 34 being a high-pressure shaft. The low pressure body 40 comprises a low pressure compressor 42, a low pressure turbine 44 and a low pressure shaft 46 coupling the low pressure turbine 44 to the low pressure compressor 42 for driving the low pressure compressor 42 by the low pressure turbine 44, The low pressure compressor 42 is arranged upstream of the high pressure compressor 30 and supplies the latter with compressed air. The low pressure turbine 44 is arranged downstream of the high pressure turbine 32 and receives the exhaust gases leaving the latter. The low pressure shaft 46 is guided in rotation relative to the nacelle 20 by means of bearings (not shown). The low pressure shaft 46 is coaxial with the high pressure shaft 34. It therefore also has the longitudinal axis X as its axis of rotation. In particular, the low pressure shaft 46 extends inside the high pressure shaft 34. The turbomachine 12 also comprises a fan 50 for driving the air flow in an external circulation vein 52 surrounding the nacelle 20. A primary air flow A (hot) is thus distinguished, consisting of the portion of the air flow driven in the internal circulation vein 22, and a secondary air flow B (cold), consisting of the portion of the air flow driven in the external circulation vein 52. The fan 50 comprises a fan rotor 54. This fan rotor 54 is rotatably mounted relative to the nacelle 20 around the longitudinal axis X. It comprises a disk 55 provided with fan blades 56 extending substantially radially outwards from the disk 55. These blades 56, when they are rotated, drive the air flow into the external circulation vein 52. The fan rotor 54 is driven in rotation by the low-pressure turbine 44, via the low-pressure shaft 46. In the example shown, this drive is direct, that is to say that the fan rotor 54 is integral in rotation with the low-pressure shaft 46. In a variant (not shown), this drive is done via a reduction gear allowing the fan rotor 54 to rotate at a speed lower than that of the low-pressure shaft 46. The fan rotor 54 is in particular arranged upstream of the internal circulation vein 22 and also drives the air flow in the latter. In the example shown, the blower 50 also comprises a stator of fan 58, also called a rectifier, comprising fixed blades 59 arranged at the periphery of the nacelle 20, in the external circulation vein 52, along a plane orthogonal to the longitudinal axis X. This fan stator 58 is here arranged downstream of the fan rotor 54. The external circulation vein 52 is here defined between the nacelle 20 and a fan casing 60 surrounding the fan 50. The turbomachine 12 is typically constituted by a turbojet with a high dilution ratio (in English “bypass ratio”), the dilution ratio being defined as the ratio of the flow rate of the secondary flow B (cold) to the flow rate of the primary flow A (hot). In the example shown, the turbomachine 12 also comprises a precompressor 62 at the inlet of the internal vein 22. This precompressor 62 comprises an alternation of fixed vanes 64 and moving blades 66 extending successively in the internal vein 22. The fixed vanes 64 are integral with the nacelle 20. The moving blades 66 are mounted on a precompressor shaft 68. This precompressor shaft 68 is fixed to the disk 55 of the fan rotor 54. With reference to [Fig. 3], the fan rotor 54 also comprises inter-blade platforms 70 interposed circumferentially between the blades 56 and flanges 72, 74 retaining said platforms 70 to the disc 55. In the example shown, the fan rotor 54 also comprises a conical top 76 mounted upstream of the disc 55 and inter-blade platforms 70. Each inter-blade platform 70 has an outer surface 78 which internally delimits a portion of the external vein 52 between the blades 56. The flanges 72, 74 are each annular in shape and centered on the longitudinal axis X. As for the inter-blade platforms 70, they each define a portion of the external vein 52 at the level of the fan 50. They comprise an upstream flange 72, located upstream of the inter-blade platforms 70, and a downstream flange 74 located downstream of the inter-blade platforms 70. The upstream flange 72 is here interposed between the rotor 76 and the inter-blade platforms 70. It comprises a radial shroud 80 fixed to the disc 55 and a lug 82 projecting axially downstream from said shroud 80. This lug 82 has an external surface 84 internally delimiting a part of the external vein 52 at the level of the fan 50 and an internal surface 86 bearing against an upstream end 88 of the inter-blade platforms 70. The downstream flange 74 is constituted by a rotating spacer ring 90. It typically has an outside diameter between 600 and 1200 mm. Referring to [Fig.4], the rotating spacer ring 90 comprises a radial ferrule 92 fixed to the precompressor shaft 68 and a ring 94 radially extending the ferrule 92 outwardly. The ferrule 92 is substantially flat. It extends substantially along a radial plane. It has an internal end 96 for attachment to the precompressor shaft 68 and an external end 98 for connection to the ring 94. The ring 94 extends around the ferrule 92 and projects axially upstream relative to said ferrule 92. It is connected to the ferrule 92 by a fillet 100 whose concavity is oriented upstream. The fillet 100 typically has a radius of curvature between 10 and 60 mm. The ring 94 is defined by revolution around the X axis of a generally V-shaped generatrix pointing upstream. It comprises an inner leg 102 and an outer leg 104 converging towards each other in the upstream direction up to an upstream end 105 of the ring 94. The inner leg 102 defines an axial shoulder 106 oriented inwards. This shoulder 106 is substantially cylindrical, that is to say that it has a zero or at least very small radial extension in comparison with its other dimensions. It is in particular substantially cylindrical of revolution. The shoulder 106 bears against a downstream end 108 ([Fig.2]) of the inter-blade platforms 70. In particular, the inner leg 102 extends the fillet 100 upstream. The outer leg 104 defines a generally frustoconical outer surface 110 widening downstream and internally delimiting a portion of the outer vein 52. The outer leg 104 has an axial extension greater than that of the inner leg 102. Knowing that the two legs 102, 104 have the same upstream limit (they both end at the upstream end 105 of the ring 94), this implies that the outer leg 104 projects downstream relative to the inner leg 102. In particular, the outer leg 104 also projects downstream relative to the ferrule 92. The upstream end 105 here defines a radial shoulder 112, substantially flat and included in a radial plane, oriented upstream. The ring 94 also comprises an appendage 114 forming a hook extending the outer leg 104 downstream. The appendage 114 is curved outwards. It has an upstream end 116 for connection to the outer leg 104 and a free downstream end 118. The distance from the downstream end 118 to the axis X is less than or equal to the distance from the upstream end 116 to the axis X; in the example shown, the two distances are substantially equal to each other. The appendage 114 ensures sealing between the fan rotor 54 and the casing 119 ([Fig. 2]) of the nacelle 20. The ring 94 also comprises a reinforcing core 120 interposed between the legs 102, 104. Said core 120 is housed at the bottom of the space 122 between the legs 102, 104, that is to say it comes against the upstream end 105 of the ring 94. The rotating spacer ring 90 is in particular formed of an upstream skin 122, a downstream skin 123 and an annular insert 124. The upstream skin 122 constitutes an upstream portion of the ferrule 92 and an upstream portion of the fillet 100, as well as the inner leg 102, the upstream end 105 and an outer portion of the outer leg 104 of the ring 94. The upstream skin 122 thus delimits an upstream face 126 of the rotating spacer ring 90. The downstream skin 123 constitutes a downstream part of the ferrule 92 and a downstream part of the fillet 100, as well as the appendage 114 and an inner part of the outer leg 104 of the ring 94. It further extends between the inner and outer legs 102, 104 downstream of the core 120. The downstream skin 123 thus delimits a downstream face 128 of the rotating spacer ring 90. The insert 124 is housed between the skins 122, 123. It constitutes the core 120. The skins 122, 123 and the insert 124 are each formed of a composite material comprising fibers embedded in a matrix. The fibers of the insert 124 are preferably oriented predominantly in the circumferential direction (i.e., orthogonal to the axial and radial directions) so as to support circumferential and radial loads during rotation of the fan rotor 54. A method 200 for manufacturing the rotating spacer ring 90 will now be described, with reference to Figures 5 to 25. As visible in [Fig.5], the method 200 comprises a first step 210 of preparing an upstream skin preform 300 ([Fig.18]). This step 210 begins with a draping 212 of prepreg strands by automatic fiber placement. As visible in |Fig.7], said prepreg strands are draped over a first upstream skin mold 302 so as to produce an annular upstream skin preform blank 304. The first upstream skin mold 302 has a shape of revolution centered on an axis of revolution (not shown). For the remainder of the description, the terms of orientation are understood in reference to a cylindrical reference point attached to the first upstream skin mold 302, shown in [Fig.7], in which we distinguish at each point: an axial direction A parallel to the axis of revolution, going from the rear towards the front a radial direction B, orthogonal to the axial direction A, connecting the axis of re- evolution at said point and going from the inside to the outside, and a circumferential direction C orthogonal to the axial and radial directions A B. The first upstream skin mold 302 has a front face 306 with a convex outer annular edge 308. Said outer annular edge 308 comprises a frustoconical outer portion 310 widening towards the rear, an annular intermediate portion 312, substantially planar, extending substantially along a radial plane and forming projecting inwardly from a front end of the outer portion 310, and an inner portion 314 extending inwardly from the intermediate portion 312, said inner portion 314 being in the shape of a truncated cone flaring forwardly. The prepreg strands are draped over said outer annular edge 308. Thus, they are draped over a convex surface, which is very suitable for the automatic placement of fibers, the laying head of a draping machine not being able to press the prepreg strands against a support having a concave shape when said concave shape has a radius of curvature smaller than that of the roller of the laying head. Each prepreg strand is in particular draped in a direction (not shown) forming at each point a non-zero angle with the local circumferential direction C, said angle preferably being between 25° and 90°. In other words, the draping direction of each prepreg strand has a radial component at every point. Preferably, different layers of prepreg strands are draped successively so that the upstream skin preform blank 304 is formed from a stack of several plies stacked in the axial direction A. Advantageously, the orientation of the draping direction of the strands alternates from one layer to another. For example, the draping direction of the strands in the even (or odd) layers is oriented substantially at 90° to the circumferential direction C, the draping direction of the strands in the odd (or even) layers being oriented substantially at 30° to the circumferential direction C. The upstream skin preform blank 304 thus comprises: a truncated external part 316, widening towards the rear, corresponding to the outer portion of the outer leg 104 of the ring 94, and an annular intermediate part 317, substantially flat and projecting inwardly from a front end of the outer portion 316, said intermediate part 317 corresponding to the upstream end 105 of the ring 94, In contrast, the upstream skin preform blank 304 does not include a portion corresponding to the inner leg 102 of the ring 94, the upstream portion of the fillet 100, or the upstream portion of the ferrule 92. Instead, it includes an inner portion 318 extending inwardly from the intermediate portion 317, said inner portion 318 being in the shape of a truncated cone flaring forward. The draping 212 is thus followed by a step 214 of shaping the upstream skin preform blank 304 to form the parts corresponding to the inner leg 102 of the ring 94, to the upstream part of the fillet 100 and to the upstream part of the ferrule 92 and thus obtain the upstream skin preform 300. This shaping is for example carried out by vacuum thermoforming. For this purpose, the upstream skin preform blank 304 is, as visible in [Fig. 8], placed on a second upstream skin mold 320. This second upstream skin mold 320 has a shape of revolution centered on an axis of revolution (not shown). For the remainder of the description, the terms of orientation are understood with reference to a cylindrical reference attached to the second upstream skin mold 320, shown in [Fig. 8], in which we distinguish at each point: an axial direction À' parallel to the axis of revolution, going from the rear towards the front a radial direction B', orthogonal to the axial direction A', connecting the axis of revolution at said point and going from the inside to the outside, and a circumferential direction C' orthogonal to the axial directions A' and radial B'. In a similar manner to the first upstream skin mold 302, the second upstream skin mold 320 has a front face 322 with a convex outer annular edge 324, said outer annular edge 324 comprising a frustoconical outer portion 326 widening towards the rear and an annular, substantially planar intermediate portion 328 extending substantially along a radial plane and projecting inwards from a front end of the outer portion 326. The outer portion 326 and the intermediate portion 328 are in particular substantially identical and advantageously perfectly identical respectively to the outer portion 310 and to the intermediate portion 312 of the first upstream skin mold 302. Unlike the first upstream skin mold 302, the outer annular edge 324 of the second upstream skin mold 320 does not include a truncated cone-shaped inner portion that flares out toward the front. Instead, said outer annular edge 324 includes: a cylindrical portion 330 extending rearwardly from an in- end interior of the intermediate part 328, an annular, substantially flat inner portion 332 extending sens- possibly following a radial plane and delimiting an inner end of the edge outer annular 324, and an annular fillet 334 connecting the cylindrical part 330 to the inner part 332. The cylindrical part 330, the inner part 332 and the annular fillet 334 together delimit a concave recess 336 in the front face 322, that is to say that the surface resulting from the combination of these three regions 330, 332, 334 is hollow relative to the surface connecting the inner end of the intermediate part 328 to the inner end of the outer annular edge 324. The outer annular edge 324 thus has the shape of the upstream skin 122. Advantageously, the second upstream skin mold 320 is obtained from the first upstream skin mold 302 by removing an insert 338 ([Fig.7]) filling the recess 336 and defining the inner portion 314 of the outer annular edge 308 of the front face 306 of the first upstream skin mold 302. The second upstream skin mold 320 is placed on a forming platform 340, then the upstream skin preform blank 304 is covered with a bladder 342 with preferably a separator 344 and a drain 346 interposed between the upstream skin preform blank 304 and the bladder 342. Sealing is achieved between the bladder 342 and the forming platform 340, then the assembly is heated, typically to a temperature between 80 and 90°C, while a vacuum is created between the bladder 342 and the forming platform 340. The bladder 342 is thus pressed against the second upstream skin mold 320 and carries with it the upstream skin preform blank 304, softened by the heat, which thus takes the shape of the outer annular edge 324 of the upstream face. 322 of said mold 320. This gives the upstream skin preform 300. Returning to [Fig. 5], the manufacturing method 200 also comprises a second step 220 of preparing a downstream skin preform 350 ([Fig. 22]). This second step 220 is here implemented in parallel with the first step 210. Alternatively, it is implemented following the first step 210, or even before said first step 210. Similar to the first step 210, the second step 220 begins with a draping 222 of prepreg strands by automatic fiber placement. As seen in [Fig.9], said prepreg strands are draped onto a first downstream skin mold 352 so as to produce an annular downstream skin preform blank 354. The first downstream skin mold 352 has a shape of revolution centered on an axis of revolution (not shown). For the remainder of the description, the terms of orientation are understood in reference to a cylindrical reference point attached to the first downstream skin mold 352, shown in [Fig.9], in which we distinguish at each point: an axial direction À' parallel to the axis of revolution, going from the rear towards the front a radial direction B'', orthogonal to the axial direction À”, connecting the axis of revolution at said point and going from the inside to the outside, and a circumferential direction C'' orthogonal to the axial directions À' and radial B'°. The first downstream skin mold 352 has a front face 356 with an edge convex outer annular edge 358. Said outer annular edge 358 comprises a frustoconical outer portion 360 widening towards the rear, an annular intermediate portion 362, substantially planar, extending substantially along a radial plane and projecting inwards from a front end of the outer portion 360, and an inner portion 364 extending inwards from the intermediate portion 362, said inner portion 364 being in the shape of a truncated cone widening towards the front. The first downstream skin mold 352 also has an outer cylindrical face 366. This outer cylindrical face 366 has a diameter smaller than the outer diameter of the front face 356. A collar 367 delimiting a shoulder 368 facing towards the rear ensures the junction between the outer cylindrical face 366 and the front face 356. The prepreg strands are draped over said outer annular edge 358 and over a front end section 370 of the outer cylindrical face 366. Thus, they are essentially draped over a convex surface, which as we have seen is very suitable for the automatic placement of fibers. If said strands are also draped over a concave surface, at the interface between the front 356 and outer cylindrical 366 faces, this does not pose any difficulty in view of the smallness of the surface concerned: it is indeed not a problem, over such a small surface, for the strands not to be pressed against the mold 352. Each prepreg strand is in particular draped in a direction (not shown) forming at each point a non-zero angle with the local circumferential direction C”, said angle preferably being between 25° and 90°. In other words, the draping direction of each prepreg strand has a radial component at every point. Preferably, different layers of prepreg strands are draped successively along the axial direction A” so that the downstream skin preform blank 354 is formed from an axial stack of several plies. Advantageously, the orientation of the draping direction of the strands alternates from one layer to another. For example, the draping direction of the strands in the even (or odd) layers is oriented substantially at 90° to the circumferential direction C””, the draping direction of the strands in the odd (or even) layers being oriented substantially at 30° to the circumferential direction C°>. The downstream skin preform blank 354 thus comprises: an axially extending cylindrical rear portion 370, a truncated outer part 372, widening towards the rear to a rear end 373 having a diameter greater than that of the part rear 370, said outer part 372 corresponding to the inner part of the outer leg 104 of the ring 94, a collar 374 which is substantially flat and extends substantially along a radial plane, said collar 374 connecting a front end of the rear part 370 at the rear end 373 of the outer part 372, said collar 374 corresponding to the upstream end 116 of the appendage 114 of the ring 94, and an annular intermediate part 376, substantially flat and projecting inwardly from a front end of the outer portion 372, said intermediate part 374 corresponding to the portion of the downstream skin 123 which extends between the inner and outer legs 102, 104 of the ring 94 in downstream of core 120. In contrast, the downstream skin preform blank 354 does not include a portion corresponding to the downstream portion of the fillet 100 or to the downstream portion of the ferrule 92. Instead, it includes an inner portion 378 extending inwardly from the intermediate portion 376, said inner portion 378 being in the shape of a truncated cone flaring forward. The apex angle of this inner portion 378 is in particular greater than that of the inner portion 318 of the upstream skin preform blank 304. The draping 222 is thus followed by a step 224 of shaping the downstream skin preform blank 354 to form the parts corresponding to the downstream part of the fillet 100 and to the downstream part of the ferrule 92 and thus obtain the downstream skin preform 350. This shaping is for example carried out by vacuum thermoforming. For this purpose, the downstream skin preform blank 354 is, as visible in [Fig. 10], placed on a second downstream skin mold 380. This second downstream skin mold 380 has a shape of revolution centered on an axis of revolution (not shown). For the remainder of the description, the orientation terms are understood with reference to a cylindrical reference attached to the second downstream skin mold 380, shown in [Fig. 10], in which we distinguish at each point: an axial direction À' parallel to the axis of revolution, going from the rear towards the front a radial direction B''', orthogonal to the axial direction A', connecting the axis of revolution at said point and going from the inside to the outside, and a circumferential direction C'”' orthogonal to the axial directions A” and radial B'”. In a similar manner to the first downstream skin mold 352, the second downstream skin mold 380 has a front face 382 with a convex outer annular edge 384, said outer annular edge 384 comprising a frustoconical outer portion 385 widening towards the rear and an annular intermediate portion 386, substantially planar, extending substantially along a radial plane and projecting inwards from a front end of the outer part 385. The second downstream skin mold 380 also has an outer cylindrical face 387 with a diameter smaller than the outer diameter of the front face 382 and a collar 388 which delimits a shoulder 389 facing towards the rear and ensures the junction between the outer cylindrical face 387 and the front face 382. The outer part 385, the intermediate part 386, the outer cylindrical face 387 and the collar 388 are in particular substantially identical and advantageously perfectly identical respectively to the outer part 360, to the intermediate part 362, to the outer cylindrical face 366 and to the collar 367 of the first downstream skin mold 352. Unlike the first downstream skin mold 352, the outer annular edge 384 of the second downstream skin mold 380 does not include a truncated cone-shaped inner portion that flares out toward the front. Instead, said outer annular edge 384 includes: an inner part 392 annular, substantially flat, extending sens- possibly following a radial plane set back from the intermediate part 386 and de- limiting an inner end of the outer annular edge 384, and an annular fillet 394 connecting the inner part 392 to an in- end interior of the intermediate part 386. The inner portion 392 and the annular fillet 394 together delimit a concave recess 396 in the front face 382, ​​that is to say that the surface resulting from the combination of these two regions 392, 394 is hollow relative to the surface connecting the inner end of the intermediate portion 386 to the inner end of the outer annular edge 384. The outer annular edge 384 thus has the shape of the downstream skin 123. Advantageously, the second downstream skin mold 380 is obtained from the first downstream skin mold 352 by removing an insert 398 ([Fig.9]) filling the recess 396 and defining the inner portion 364 of the outer annular edge 358 of the front face 356 of the first downstream skin mold 352. The second upstream skin mold 380 is placed on a forming platform 400, then the downstream skin preform blank 354 is covered with a bladder 402 with preferably a separator 404 and a drain 406 interposed between the downstream skin preform blank 354 and the bladder 402. The seal is created between the bladder 402 and the forming platform 400, then the assembly is heated, typically to a temperature between 80 and 90°C, while the vacuum is created between the bladder 402 and the forming platform 400. The bladder 402 is thus pressed against the second downstream skin mold 380 and carries with it the upstream skin preform blank 354, softened by the heat, which thus takes the shape of the outer annular edge 384 of the upstream face 382 of said mold 380. This gives the downstream skin preform 350. Returning to [Fig. 5], the manufacturing method 200 further comprises a third step 230 of preparing an insert preform 410 ([Fig. 20]). This third step 230 is here implemented after the first and second steps 210, 220. Alternatively (not shown), it is implemented in parallel with said steps 210, 220, or between said steps 210, 220, or even before said steps 210, 220. With reference to [Fig. 6], this third step 230 comprises the draping 231 of prepreg strands on an insert mold 412 ([Fig. 11]) by automatic placement of fibers. As visible in [Fig. 11], the insert mold 412 has a disc shape 414 comprising two large opposite discoidal faces 415, 416 connected to each other by a circumferential edge 418. This disc 414 is in particular of revolution around a central axis (not shown). For the remainder of the description, the orientation terms are understood with reference to a cylindrical reference mark attached to the insert mold 412, shown in [Fig. 11], in which we distinguish at each point: an axial direction P parallel to the central axis, going from back to front, a radial direction R, orthogonal to the axial direction P, connecting the axis central to said point and going from the inside to the outside, and a circumferential direction Q orthogonal to the axial directions P and radial directions R. During said draping 231, the prepreg strands are draped onto the edge 418 of the disc 414 substantially parallel to the circumferential direction Q, that is to say in a direction forming an angle of less than 5°, or even less than 1° with said circumferential direction Q. Thus, the fibers of the insert 124 are oriented predominantly in the circumferential direction, which allows the insert 124 to support significant circumferential and radial loads during the rotation of the fan rotor 54. Returning to [Fig.6], the draping 231 begins with a first sub-step 232 of producing a first stack 420 ([Fig.11]) of layers of pre-impregnated strands. During this first sub-step 232, the prepreg strands are draped in successive layers along the radial direction R. A first layer (not referenced) is first draped directly onto the edge 418 of the mold 412, then each subsequent layer is draped onto the outer face of the previous layer. For example, between 40 and 60 layers are draped successively to form this first stack 420. The axial position of each layer is defined by reference to a first axial edge 422, here a rear edge, of the first stack 420. In other words, the layers are positioned axially relative to each other so that the first axial edge 422 of the first stack 420 has a radial profile, i.e. taken in a predefined radial plane. In particular, the layers are positioned so that said first axial edge 422 has an axial extension with advantageously, as shown, an outer end 424 of the first axial edge 422 axially set back relative to the inner end 425 of the first axial edge 422. In other words, the outer end 424 of the first axial edge 422 is axially offset forward relative to the inner end 425. More particularly, the layers are positioned so that the first stack 420 comprises an inner section 427 in which the first axial edge 422 has an axial extension and an outer section 428 in which the first axial edge 422 extends substantially along a radial plane, i.e. the axial extension of the first axial edge 422 in this outer section 428 is substantially zero. The inner section 427 delimits an inner end (not referenced) of the first stack 420 and the outer section 428 delimits an outer end (not referenced) of the first stack 420. The radial profile of the first axial edge 422 is substantially continuous and derivable at the junction between said inner and outer sections 427, 428. In the inner section 427, the radial profile of the first axial edge 422 is concave with a concavity oriented radially outwards. The inner 427 and outer 428 sections have substantially the same radial thickness. Advantageously, the prepreg strands are arranged in a staggered pattern in the outer section 428. For this purpose, the outer section 428 has an alternation of layers axially offset relative to each other, said layers being offset alternately forwards and backwards. In other words, the outer section 428 includes a plurality of first layers aligned radially with each other, with interposed between them second layers axially offset forwards or backwards relative to the first layers, said second layers themselves being radially aligned with each other. This axial offset is typically between 1 and 2 mm and is for example substantially equal to 1.5 mm. Thus, alignment of the spaces between the strands is avoided, which would risk creating weaknesses within the insert 410. Preferably, the layers aligned radially with each other are grouped in groups of at least two layers, for example three, stacked successively without a radially offset layer interposed between them. Returning to [Fig.6], sub-step 232 is followed by a sub-step 233 of machining the first stack 420. As visible in [Fig.12], during this sub-step 233, the axial edge of the first stack 420 which is opposite the axial edge defined by draping 422, here therefore the front edge, is machined, thus forming a first machined axial edge 430. This machining is in particular carried out by clean cutting of the first stack 420 along a first radial cutting surface 432 by means of a cutting tool 434 having a blade 436 extending along said first cutting surface 432. Returning to [Fig. 6], sub-step 233 is followed by a sub-step 234 of affixing a shim 438 ([Fig. 13]) along the axial edge defined by draping 422. As visible in [Fig. 13], said shim 438 is placed on the edge 418 of the mold 412 and matches the shape of the axial edge defined by draping 422. It has substantially the same radial thickness as the first stack 420 and is flush with an outer face 439 of the first stack 420. Returning to [Fig.6], sub-step 234 is followed by a sub-step 235 of producing a second stack 440 ([Fig.13]) of layers of prepreg strands over the first stack 420. During this sub-step 235, the prepreg strands are draped in successive layers along the radial direction R, straddling the first stack 420 and the shim 438. A first layer (not referenced) is first draped directly onto the first stack 420 and the shim 438, then each subsequent layer is draped onto the outer face of the previous layer. For example, between 40 and 60 layers are draped successively to form this second stack 440. The axial position of each layer is defined with reference to a first axial edge 442, here a front edge, of the second stack 440. In other words, the layers are positioned axially relative to each other so that the first axial edge 442 of the second stack 440 has a radial profile, i.e. taken in a predefined radial plane. This first axial edge 442 extends one of the axial edges 422, 430, here the machined axial edge 430, of the first stack 420, i.e. the inner end 443 of the first axial edge 442 is flush with the outer end 444 of the machined axial edge 430. In particular, the layers are positioned so that said first axial edge 442 has an axial extension with advantageously, as shown, an outer end 445 of the first axial edge 442 axially set back relative to the inner end 443 of the first axial edge 442. In other words, the outer end 445 of the first axial edge 442 is axially offset rearward relative to the inner end 443. The outer end 445 is in particular interposed axially between the inner end 443 and the shim 438. More particularly, the layers are positioned so that the first axial edge 442 does not have any concave section with inwardly oriented concavity, i.e. so that no layer is axially offset forward relative to the first axial edge 442. tively to the lower layer. In addition, the layers are positioned so that each section of the first axial edge 442 has an axial extension, that is to say that the second stack 440 does not have a section in which the first axial edge 442 extends substantially along a radial plane. In the example shown, the layers are positioned so that the second stack 440 comprises an inner section 447 in which the first axial edge 442 is convex with a convexity oriented radially outwards and an outer section 448 in which the first axial edge 442 is of substantially frustoconical shape centered on the central axis. In the inner section 447, the radial profile of the first axial edge 442 is in particular substantially in the shape of an arc of a circle. The inclination of the first axial edge in the section 448 is in particular substantially equal to the inclination of the outer surface 110 of the rotating spacer ring 90 and forms for example an angle of between 20° and 45° with the edge 418 of the mold 412. The radial profile of the first axial edge 442 is substantially continuous and derivable at the junction between said inner and outer sections 447, 448. Returning to [Fig. 6], sub-step 235 is followed by a sub-step 236 of machining the second stack 440. As visible in [Fig. 14], during this sub-step 236, the axial edge of the second stack 440 which is opposite the axial edge defined by draping 442, here therefore the rear edge, is machined, thus forming a second machined axial edge 450. This machining is in particular carried out by clean cutting of the second stack 440 along a second radial cutting surface 452 by means of a cutting tool 454 having a blade 456 running along said second cutting surface 452. This second cutting surface 452 is different from the first cutting surface 432. In particular, it is axially offset relative to the first cutting surface 432. It radially extends the axial edge defined by draping 422 of the first stack 420, that is to say that it intersects the outer face 439 of the first stack 420 at the level of said axial edge 422. Preferably, the shim 438 is removed prior to the implementation of the sub-step 236. Returning to [Fig. 6], sub-step 236 is followed by a sub-step 237 of affixing a shim 458 ([Fig. 15]) along the second machined axial edge 440. As visible in [Fig. 15], said shim 458 is placed on the edge 418 of the mold 412 and matches the shape of the axial edge defined by draping 422 of the first stack 420 and the second machined axial edge 440. It has substantially the same radial thickness as the first stack 420 and the second stack 440 taken together and is flush with an outer face 459 of the second stack 440. Returning to [Fig.6], sub-step 237 is followed by a sub-step 238 of producing a third stack 460 ([Fig.15]) of layers of prepreg rovings over the second stack 440. During this sub-step 237, the prepreg strands are draped in successive layers along the radial direction R, straddling the second stack 440 and the shim 458. A first layer (not referenced) is first draped directly onto the second stack 440 and the shim 458, then each subsequent layer is draped onto the outer face of the previous layer. For example, between 40 and 60 layers are draped successively to form this third stack 460. The axial position of each layer is defined with reference to a first axial edge 462, here a front edge, of the third stack 460. In other words, the layers are positioned axially relative to each other so that the first axial edge 462 of the third stack 460 has a radial profile, i.e. taken in a predefined radial plane. This first axial edge 462 extends one of the axial edges 442, 450, here the axial edge defined by draping 442, of the second stack 440, i.e. the inner end 463 of the first axial edge 462 is flush with the outer end 464 of the axial edge defined by draping 442. In particular, the layers are positioned so that said first axial edge 462 has an axial extension with advantageously, as shown, an outer end 465 of the first axial edge 462 axially set back relative to the inner end 463 of the first axial edge 462. In other words, the outer end 465 of the first axial edge 462 is axially offset rearward relative to the inner end 463. The outer end 465 is in particular located radially above the shim 458, that is to say that the radial plane passing through the outer end 465 intersects the shim 458. More particularly, the layers are positioned such that the first axial edge 462 does not have any concave section with inwardly oriented concavity, i.e. such that no layer is axially offset forward relative to the lower layer. In addition, the layers are positioned such that each section of the first axial edge 462 has an axial extension, i.e. the third stack 460 does not have a section in which the first axial edge 462 extends substantially along a radial plane. In the example shown, the first axial edge 462 is of substantially frustoconical shape centered on the central axis. Its inclination is in particular substantially equal to the inclination of the external surface 110 of the rotating spacer ring 90 and forms for example an angle of between 20° and 45° with the edge 418 of the mold 412. Returning to [Fig.6], sub-step 238 is followed by a sub-step 239 of machining the third stack 460. As visible in [Fig.16], during this sub-step 239, the axial edge of the third stack 460 which is opposite the axial edge defined by draping 462, here therefore the rear edge, is machined, thus forming a third machined axial edge 470. This machining is in particular carried out by clean cutting of the third stack 460 along a third cutting surface 472 by means of a cutting tool 474 having a blade 476 running along said third cutting surface 472. This third cutting surface 472 is different from the first and second cutting surfaces 432, 452. In particular, this third cutting surface 472 is a frustoconical surface centered on the central axis and widening towards the rear. It radially extends the axial edge defined by draping 442 of the second stack 440, that is to say that it intersects the outer face 459 of the second stack 440 at the level of said axial edge defined by draping 442, and intersects the outer end 465 of the axial edge defined by draping 462 of the third stack 460. Preferably, the shim 458 is removed prior to the implementation of this sub-step 239. This produces the insert preform 410. It will be noted that, thanks to the sub-steps 232 to 239, this insert preform 410, of small dimensions and complex shape, is obtained without implementing a complex cutting strategy. Indeed, the insert preform 410 is simply divided into several concentric regions 420, 440, 460, each having a planar or frustoconical axial edge, and, for each of these regions 420, 440, 460, the axial edge having the most complex geometry (for example because it is curved while the other edge is straight, or because it is inclined while the other edge is radial) is formed directly during the layup, by simply programming the robot so as to offset the strips from one layer to the other, which is done very easily. It is then sufficient to machine the opposite axial edge by clean cutting to obtain the planar or frustoconical axial edge.This cutting of one of the two axial edges remains necessary, because the strands have a fixed width (typically 6.35 mm) which is the same for all the layers and which is not small compared to the width of the insert preform 410 (each layer is formed of only a few strands deposited side by side, the number of these strands being typically between 1 and 20 and most often between 3 and 9). It is therefore not possible, during layup, to adapt the distance between the axial edges by adjusting the width of the strands or the number of strands deposited in each layer. As a result, at the end of each production 232, 235, 238 of a stack of layers, the axial edge which is opposite the edge defined by draping ends up with substantially the same geometry as the edge defined by draping (this aspect is not shown in figures 11, 13 and 15, which are schematic). nevertheless, in practice, the two axial edges in question actually have substantially the same geometry). To give this axial edge the desired geometry, which is different from that of the edge defined by draping, we therefore resort to machining said axial edge. Returning to [Fig. 5], the method further comprises, in the example shown, a fourth step 240 of preparing strand preforms 480 ([Fig. 23]). This fourth step 240 is here implemented after the first, second and third steps 210, 220, 230. Alternatively (not shown), it is implemented in parallel with said steps 210, 220, 230, or between said steps 210, 220, 230, or even before said steps 210, 220, 230. With reference to [Fig. 17], prepreg strands 482 are, during this step 240, stacked successively in a strand mold 484. This strand mold 484 is curved with an internal radius of curvature substantially equal to the external radius of the rear end 373 of the external part 372 of the downstream skin preform 350. It has a radial section, that is to say taken in a plane orthogonal to the direction of curvature of the mold 484, substantially in the shape of a V widening from a bottom 486 to an opening 488. It is delimited between two walls 490, 492 converging towards the bottom 486, each wall 490, 492 extending from the opening 488 to the bottom 486. A first wall 490 has a substantially rectilinear radial profile. The second wall 492 has a radial profile in the form of an arc of a circle with a radius of curvature substantially equal to the external radius of curvature of the fillet 494 ([Fig.22]) forming the junction between the outer part 372 and the collar 374 of the downstream skin preform 350. The strands are regularly compacted in the mold 484, said stacking and compacting steps being repeated until the mold 484 is completely filled. The stack of strands is then demolded from the mold 484: a strand preform 480 is thus obtained. Advantageously, the strand preform 480 does not constitute a complete ring: the preceding steps are then repeated as many times as necessary to obtain a sufficient number of strand preforms 480 to form a complete ring. Alternatively, the strand preform 480 constitutes a complete ring: a single strand preform 480 is then produced during step 240. The prepreg strands used for manufacturing the upstream skin preform 300, the downstream skin preform 350, the insert preform 410 and, where appropriate, the strand preforms 480 advantageously all have substantially the same composition. Said strands are typically unidirectional fiber strands, said fibers being carbon fibers, for example AS7 fibers, embedded in an epoxy resin, for example an 8552 resin. Returning to [Fig. 5], the method 200 further comprises, following steps 210, 220, 230, 240, a step 250 of preparing a rotary spacer ring preform 490 ([Fig. 25]). This step 250 begins with a sub-step 251 of inserting the insert preform 410 between the upstream skin preform 300 and the downstream skin preform 350. This sub-step 251 begins with the placement 252 of the upstream skin preform 300 in a rotating spacer ring mold 500 ([Fig. 18]). As visible in [Fig. 18], this mold 500 has a shape of revolution around a main axis (not shown). For the remainder of the description, the orientation terms are understood with reference to a cylindrical reference mark attached to the mold 500, shown in [Fig. 18], in which we distinguish at each point: a vertical direction Z parallel to the main axis, going from bottom to top, a radial direction U, orthogonal to the vertical direction Z, connecting the axis main point at the said point and going from the inside to the outside, and a circumferential direction V orthogonal to the vertical directions Z and radial U. The mold 500 has in particular a discoidal shape with an upper face 502 comprising: a central plate 504, substantially discoidal, an annular peripheral plate 506, and between the central plate 504 and the peripheral plate 506, a slot 508 annular sinking downwards relative to the central plate 504 and the peripheral plate 506. The central plate 504 and the peripheral plate 506 are each substantially orthogonal to the main axis and substantially parallel to each other. The peripheral plate 506 is vertically offset upwards relative to the central plate 504. The slot 508 is delimited between a substantially cylindrical inner wall 510, centered on the main axis, and a substantially frustoconical outer wall 512 widening upwards, centered on the main axis, said walls 510, 512 converging towards a bottom 514 of the slot 508. The inner wall 510 is connected to the central plate 504 by a fillet 516 having an outer radius of curvature substantially equal to the inner radius of curvature of the fillet 100 of the rotary spacer ring 90. The central plate 504, the fillet 516, the inner wall 510, the bottom 514 and the outer wall 512 together delimit, in a hollow, a surface complementary to the upstream face 126 of the rotating spacer ring 90. The upstream skin preform 300 is thus placed in the mold 500 so that its intermediate part 317 extends into the bottom 514 of the slot 508, its ex- part interior 316 bearing against the exterior wall 512 and extending partly out of the slot 508, above the exterior plate 502. Returning to [Fig.5], substep 251 also includes cutting 253 of the upstream skin preform 300. As seen in [Fig.19], during this cutting 253, the portion 518 ([Fig.18]) of the outer part 316 of the upstream skin preform 300 which extends out of the slot 508 is removed. Still with reference to [Fig.5], sub-step 251 further comprises the positioning 254 of the insert preform 410. As visible in [Fig.20], during this positioning 254, the insert preform 410 is housed in the upstream skin preform 300, at the bottom of the slot 508, the front face of said preform 410 being oriented downwards. The positioning 254 is followed by the insertion 255 of the insert preform 410. As visible in [Fig.21], during this insertion 255 a punch 520 presses on the rear face of the insert preform 410 so as to insert it into the slot 508. This punch 520 has a flat bearing face 522, oriented downwards, with an inner edge 524 and an outer edge 524 each curved upwards. This step makes it possible to shape the rear face of the insert preform 410 so that it better matches the downstream skin preform 350. The depression 255 is followed by the positioning 256 of the downstream skin preform 350. As visible in [Fig.22], during this positioning 256, the downstream skin preform 350 is placed over the upstream skin preform 300 and the insert preform 410, its front face facing downwards. The outer portion 372 of the downstream skin preform 350 is placed against the outer portion 316 of the upstream skin preform 300 and its intermediate portion 376 is placed against the rear face of the insert preform 410. The rear portion 370 of the downstream skin preform 350 then extends substantially vertically and an annular space 528 remains clear between the rear end of the outer portion 316 of the upstream skin preform 300 and the fillet 494 forming the junction between the outer portion 372 and the collar 374 of the downstream skin preform 350. The insert preform 410 is thus inserted between the upstream skin preform 300 and the downstream skin preform 350. The sub-step 251 is followed by a sub-step 257 of placing the strand preforms 480. As visible in [Fig.23], during this sub-step 257, the strand preforms 480 are placed in the annular space 528 between the rear end of the outer part 316 of the upstream skin preform 300 and the fillet 494 of the downstream skin preform 350 so as to fill said annular space 528. Substep 257 is followed by a substep 258 of placing a mold insert 530 ([Fig.24]). As seen in [Fig.24], during this substep 258, a mold insert 530 is placed on the peripheral plate 506. This insert 530 is placed so as to cover the peripheral plate 506, the rear end of the ex- inner part 316 of the upstream skin preform 300, the strand preforms 480 and the collar 374 of the downstream skin preform 350. It comes into contact with the base of the rear part 370 of the downstream skin preform 350. This insert 530 is annular, with an internal radius of curvature substantially equal to the external radius of curvature of the rear part 370 of the downstream skin preform 350. It is substantially flat, with a large lower face 532 in contact with the peripheral plate 506, a large upper face 534 opposite the large lower face 532 and substantially parallel to the latter, and an internal edge 536 connecting said large faces 532, 534. The thickness of the insert 530 is substantially equal to the distance between the ends 116, 118 of the appendage 114 of the rotating spacer ring 90. The insert 530 is advantageously formed from several sectors (not shown) juxtaposed with each other. Sub-step 258 is finally followed by a sub-step 259 of folding the downstream skin preform 350. As visible in [Fig.25], during this sub-step 259 the rear part 370 of the downstream skin preform 350 is folded outwards, over the mold insert 530. To enable this folding, a counterform 540 is used. This counterform 540 comprises a core 542 having a lower face 544 comprising, from the outside to the inside: a truncated outer part 546 widening upwards, an annular intermediate portion 548, substantially flat, extending sens- possibly following a radial plane and projecting inwards from a lower end of the outer part 546, a 550 annular fillet with concavity oriented inwards and downwards extending upwardly from an inner end of the inter- mediator 548, and an annular, substantially flat inner portion 552 extending sens- possibly following a radial plane set back from the intermediate part 548, in the extension of an inner end of fillet 550. The core 542 also comprises an outer face 554 comprising, from top to bottom: a cylindrical portion 556 of diameter less than the outside diameter of the lower face 544, a collar 558 extending radially outward from one end lower part of the cylindrical portion 556 and defining an oriented shoulder upwards, and a 560 fillet with outwardly oriented convexity connecting an ex- end inner end of the collar 558 at an outer end of the outer part 546 of the lower face 544. The core 542 has a shape complementary to the rear face of the downstream skin preform 350. The counterform 540 also comprises a folding ring 562. Said folding ring 562 projects radially outwards from the core 542, at a distance from the collar 558. It has a substantially flat lower face 564 delimiting with the collar 558 and the cylindrical portion 556 of the outer face 554 of the core 542 an outer groove 566 whose bottom is constituted by the cylindrical portion 556. The width of said outer groove 566, constituted by the distance from the folding ring 562 to the collar 558, is substantially equal to the thickness of the mold insert 530 increased by twice the thickness of the downstream skin preform 350. The counterform 540 is preferably made of silicone. It is advantageously made of several sectors (not shown). To fold back the rear portion 370 of the downstream skin preform 350, the counterform 540 is put in place so that the groove 566 fits onto the inner edge 536 of the mold insert 530, the outer portion 546 and the intermediate portion 548 of the front face 544 of the core 542 bearing respectively against the outer portion 372 and the intermediate portion 376 of the downstream skin preform 350. In doing so, the folding ring 562 presses against the rear portion 370 of the downstream skin preform 350 and folds it against the mold insert 530. This produces a rotating spacer ring preform. Step 250 is finally followed by a step 260 of curing the rotating spacer ring preform. During this step 260, the rotating spacer ring preform is left in the mold 500, with the mold insert 530 and the counterform 540 in place, and heated conventionally to a temperature suitable for crosslinking the matrix and hardening the preform. The preform is then cooled and demolded: the rotating spacer ring 90 is thus obtained. Because the counterform 540 is made of silicone, it tends to expand during baking. It therefore presses against the downstream skin preform 350 during baking, which ensures, after baking, excellent cohesion of the upstream skin 122, the downstream skin 123 and the insert 124 with each other. Thus, thanks to the method 200 described above, it is possible to obtain in a simple and inexpensive manner a rotary spacer ring 90 made of composite material having excellent mechanical properties. This method 200 is also easily repeatable, which allows for great homogeneity in the rotary spacer rings obtained by means of this method. In particular, the method 200 cleverly solves the problem of applying the draping technique by automatic fiber placement to the fa- brication of a rotating spacer ring. In particular, the fact of carrying out thermoforming 214, 224 of the preforms 300, 350 after the draping 212, 222 makes it possible to solve the problem of managing small concave regions. This thermoforming 214, 224 is enabled by the deposition of the strands, during the draping 212, 222, in directions forming non-zero angles with the circumferential direction, even though such an arrangement of the strands is counter-intuitive since it goes against the objective of mechanical resistance usually sought on this type of part. This arrangement is itself made possible by the decoupling between the functions of maintaining the entire part and defining the surface seen by the air flow, entrusted to the skins 122, 123, with the mechanical reinforcement function, entrusted to the insert 124, for which the fibers are themselves deposited in the circumferential direction.

Claims

Claims

1. A method (200) of manufacturing a spacer ring (90) made of material composite for turbomachine fan, said spacer ring (90) comprising an upstream skin (122) delimiting an upstream face (126) of the spacer ring (90) when mounted on the turbomachine, a downstream skin (123) delimiting a downstream face (128) of the ring spacer (90) when mounted on the turbomachine, and an insert (124) annular housed between the upstream and downstream skins (122, 123), the method manufacturing (200) comprising the following steps: preparation (210) of an upstream skin preform (300), preparation (220) of a downstream skin preform (350), preparation (230) of an insert preform (410), inserting (251) the insert preform (410) between the preform upstream skin (300) and the downstream skin preform (350) of so as to form a rotating spacer ring preform, And baking (260) of the rotary spacer ring preform, wherein the preparation (210) of the upstream skin preform (300) and / or the preparation (220) of the downstream skin preform (350) comprises the draping (212, 222) of prepreg strands on a skin mold (302, 352) by automatic fiber placement.

2. The manufacturing method (200) of claim 1, wherein the draping (212, 222) of prepreg strands onto the skin mold (302, 352) produces an annular preform blank (304, 354), the pre- preparation (210) of the upstream skin preform (300) and / or the preparation (220) of the downstream skin preform (350) comprising, following said draping (212, 222), the shaping (214, 224) of the preform blank (304, 354) so ​​as to form the upstream skin preform (300), respec- tively the downstream skin preform (350).

3. A manufacturing method (200) according to claim 1 or 2, wherein the skin mold (302, 352) has a shape of revolution centered on a axis of revolution, a cylindrical reference being attached to the skin mold (302, 352) with at each point an axial direction (A, À') parallel to the axis of revolution, a radial direction (B, B'') connecting the axis of re- evolution at said point and a circumferential direction (C, C'”) or- thogonal to the axial and radial directions, each prepreg strand being draped in a direction forming at each point an angle not zero with the local circumferential direction (C, C'”).

4. A manufacturing method (200) according to any one of claims previous, wherein the preparation (230) of the insert preform (410) comprises draping (231) prepreg strands onto a insert mold (412) by automatic fiber placement, the mold insert (412) having a disc shape (414), the pre- impregnated being draped over a slice (418) of said disc (414).

5. A manufacturing method (200) according to claim 4, wherein the disk (414) is of revolution around a central axis, a cy- lindrique is attached to the insert mold (412) with at each point a axial direction (P) parallel to the central axis, a radial direction (R) connecting the central axis to said point and a circumferential direction (Q) or- thogonal to the axial and radial directions, and each pre- impregnated is draped substantially parallel to the circumferential direction- ential (Q).

6. The manufacturing method (200) of claim 5, wherein the draping (231) of prepreg strands on the insert mold (412) understand : the production (232, 235, 238) of at least one stack (420, 440, 460) of layers of stacked prepreg strands along the radial direction (R), said stack (420, 440, 460) having an axial edge defined by draping (422, 442, 462) which has an axial extension, and machining (233, 236, 239) of a machined axial edge (430, 450, 470) of the stack (420, 440, 460), opposite the axial edge defined by draping (422, 442, 462), by clean cutting of the stack (420, 440, 460).

7. Manufacturing method (200) according to claim 6, wherein, for at least one stack (420, 440), the axial edge defined by draping (422) is curved, the machined axial edge (430) being straight, or the axial edge defined by draping (442) is inclined, the machined axial edge (450) being radial.

8. A manufacturing method (200) according to claim 6 or 7, wherein several stacks (420, 440, 460) are produced, said stacks (420, 440, 460) comprising an inner stack (420, 440) and a outer stack (440, 460) radially superimposed on the stack interior (420, 440), the machined axial edge (430, 450) of the stack interior (420, 440) being obtained by clean cutting of the stack interior (420, 440) according to a primary cutting surface (432, 452) and the machined axial edge (450, 470) of the outer stack (440, 460) being obtained by clean cutting of the outer stack (440, 460) according to a secondary cutting surface (452, 472) different from the surface of primary cut (432, 452).

9. The manufacturing method (200) of claim 8, wherein the axial edge defined by draping (442) of the outer stack (440) radially extends the machined axial edge (430) of the inner stack (420), the secondary cutting surface (452) extending radially the axial edge defined by draping (422) of the inner stack (420), or the axial edge defined by draping (462) of the outer stack (460) radially extends the axial edge defined by draping (442) of the inner stack (440), the secondary cutting surface (472) radially extending the machined axial edge (450) of the stack interior (440),

10. A manufacturing method (200) according to any one of claims 6 to 9, wherein the machined axial edge (430, 450, 470) is obtained by clean cutting of the stack (420, 440, 460) along a surface of radial or truncated cone-shaped cutout (432, 452, 472).

11. Spacer ring (90) obtained by a manufacturing method (200) according to any one of claims 1 to 10.