Method for manufacturing a blade

Abstract

The invention relates to a method for manufacturing a blade for an aircraft turbine engine, the method being characterised in that it comprises the following steps: (a) providing a root (13) comprising a composite material; (c) forming a sleeve (14) around the root (13), the sleeve (14) extending around an axis of elongation, the step (c) comprising the following chronological substeps: (c1) depositing a first layer (16) around the root (13) along an axis of revolution centred on the root (13) by means of gas dynamic cold spraying; and (c2) depositing a second, metal layer (18) around the first layer (16) along the axis of revolution by means of concentrated energy deposition.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURED A BLADE

[0003] Technical field of the invention

[0004] The invention relates to the field of manufacturing processes for blades for aircraft turbomachinery.

[0005] The invention relates more particularly to the field of manufacturing blades comprising a base made of composite material and a sleeve located around the base of the blade.

[0006] Technical background

[0007] An aircraft turbomachine typically comprises, from upstream to downstream in the direction of gas flow, a movable fan rotating about a longitudinal axis, a low-pressure compressor and a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine, and a gas exhaust nozzle.

[0008] The blower draws in an airflow that splits into a primary airflow and a secondary airflow. The primary airflow passes through a primary duct of the turbomachine, while the secondary airflow is directed towards a secondary duct surrounding the primary duct.

[0009] The primary airflow is compressed within the compressors. The compressed air is then mixed with fuel and burned in the combustion chamber. The combustion gases pass through the turbines and then escape through the nozzle, whose cross-section allows these gases to be accelerated to generate propulsion.

[0010] Turbomachine components such as fans, compressors, and turbines include blades that influence the airflow. For example, compressor blades compress the primary airflow, while fan blades compress the secondary airflow. A fan, for instance, comprises blades evenly spaced around its longitudinal axis and free to rotate about this axis. The blades extend radially from a disk centered on the longitudinal axis. The blades can have a variable pitch angle. In this case, they also rotate about their axes of extension, which are perpendicular to the turbomachine's longitudinal axis.

[0011] Each turbine blade comprises a blade and a root. The blade extends from an outer end opposite the root, called the tip, to an inner end connected to the root. The blade has an aerodynamic shape and thus presents an upper and lower surface connected to the lower surface by a leading and trailing edge. The root is located opposite the blade tip and allows the blade to be anchored to a disk or housing of the turbomachine. The root also provides a support for the blade's rotation around its axis of extension. To reduce the blade's weight, the blade and root are typically made of an organic matrix composite material, also known as an organic matrix composite. The composite material includes, for example, reinforcing fibers embedded in a polymer matrix.

[0012] Each blade also includes a sleeve mounted around the foot and connected to the disc, and an insert inserted into both the sleeve and the foot. The sleeve has a generally tubular shape and includes an internal passage opening at its axial ends for mounting the foot within the sleeve. The sleeve is metallic to ensure its functions of supporting the blade's rotation around its axis of extension and anchoring the blade.

[0013] The sleeve is typically bonded and co-molded with the foot. A blade manufacturing process involving such a foot bonded and co-molded to a sleeve presents numerous challenges. Indeed, such a process includes the following steps:

[0014] - manufacturing a fibrous preform of the foot, for example by three-dimensional weaving,

[0015] - manufacturing of the sleeve, - surface treatment of the sleeve to improve the bonding of the sleeve to the foot,

[0016] - application of a bonding primer into the sleeve,

[0017] - application of a layer of glue inside the sleeve,

[0018] - insertion of the fibrous preform into the sleeve,

[0019] - compaction of the fibrous preform to achieve a target fiber volume ratio,

[0020] - inserting the insert, and

[0021] - co-molding of the fibrous preform in an injection mold, for example by resin transfer molding also known by the English acronym RTM for "Resin Transfer Molding".

[0022] The insertion of the fiber preform into the sleeve is done manually, making this step long and tedious. This step can also lead to defects in the fiber preform.

[0023] Furthermore, after the co-molding stage, the quality of the bonding of the sleeve around the foot and the quality of the foot within the sleeve are generally checked by tomography. However, the difference in density between the composite material of the foot and the metal of the sleeve results in significant noise in the tomographic images. Quality control of the foot is therefore particularly difficult after the co-molding stage. Consequently, it is difficult to guarantee the fiber volume percentage within the foot.

[0024] Furthermore, prior to gluing, although particular care is taken to preserve the sleeve and foot, these parts can become contaminated before being glued. Such contamination can lead to delamination or geometric defects, also resulting in rejects of these parts.

[0025] Also, after the co-molding stage, shrinkage of the composite material from the foot can be observed. Such shrinkage applies a high preload to the bonded sleeve, which is susceptible to detachment from the foot.

[0026] Finally, the large number of steps in the process makes it lengthy, complex, and expensive. Therefore, there is a need for a fast and easy-to-implement process for manufacturing a turbine blade for an aircraft turbomachine, comprising a composite material base and a sleeve surrounding the base, and enabling effective and efficient quality control of both the base and the sleeve.

[0027] Summary of the invention

[0028] To this end, the invention proposes a method for manufacturing a blade for an aircraft turbomachine, characterized in that the method comprises the following steps:

[0029] (a) provide a foot comprising a composite material,

[0030] (c) form a sleeve around the foot, the sleeve extending around an axis of elongation, step (c) comprising the following chronological substeps:

[0031] (c1) deposit a first layer around the foot along an axis of revolution centered on the foot, by dynamic projection using cold gas, and

[0032] (c2) deposit a second metallic layer around the first layer along the axis of revolution, by deposition under concentrated energy.

[0033] According to the process of the invention, the sleeve is formed directly on the foot in two stages.

[0034] Directed Energy Deposition (DED) is a process that creates a metallic layer with the mechanical properties of a sleeve. The second metallic layer deposited using this process exhibits the properties of a forged or cast part.

[0035] Therefore, such a process makes it possible to produce any type of part with complex geometry.

[0036] However, such a process involves a high-temperature thermal cycle exceeding the melting point of the second-layer material, typically above 1660°C. Therefore, this process can lead to the melting of the substrate on which it is applied. Such a thermal cycle is incompatible with a composite substrate, and consequently with a blade featuring a composite root, as the composite matrix would not withstand such temperatures.

[0037] The invention therefore proposes to form a first layer using a dynamic cold gas spraying process, for example, the process known as "cold spray." This process allows the first layer to be formed without the addition of heat. This preserves the chemical and mechanical integrity of the foot, which is made of composite material, and keeps the area heat-affected by the concentrated energy deposition process away from the foot.

[0038] The combination of these processes therefore ensures that isotherms that could affect the foot do not penetrate deeply enough into the foot, thus preserving the composite material of the foot from thermal degradation.

[0039] Also, the implementation of the concentrated energy deposition process improves the interface between the base and the first layer because it allows the diffusion, recrystallization and therefore the relaxation of the stresses of the agglomerated particles forming the first layer to be activated.

[0040] Thanks to the combination of these two processes, it is therefore possible to form a sleeve precisely, eliminating a multitude of steps related to gluing and co-molding the sleeve.

[0041] Furthermore, by combining these two processes, it is possible to eliminate a sleeve manufacturing step in favor of a sleeve forming step directly on the foot. This eliminates the step of inserting the foot into the sleeve, thus simplifying the process and reducing assembly defects between the foot and the sleeve.

[0042] Furthermore, thanks to the combination of these two processes, and in particular to the direct formation of the sleeve on the foot, it is possible to supply a composite foot as early as step (a), that is, before the sleeve is formed around the foot, thus eliminating the need for the subsequent co-molding step. Thanks to the invention, it is therefore also possible to effectively control the quality of the composite foot between steps (a) and (b) and to guarantee a target fiber volume percentage in the foot.

[0043] The invention may include one or more of the following features, taken individually or in combination with each other:

[0044] - step (c1) is carried out by a dynamic cold gas projection device, mobile or fixed, the base being mobile or fixed,

[0045] - step (c2) is carried out by a mobile or fixed concentrated energy deposition device, the foot being mobile or fixed,

[0046] - the first layer comprises a metallic material, preferably a titanium alloy,

[0047] - the second layer comprises a titanium alloy,

[0048] - the first layer has an initial thickness between 5 µm and 200 µm,

[0049] - the second layer has a second thickness greater than the first thickness of the first layer,

[0050] - between steps (a) and (c), a step (a') of foot control, for example by tomography,

[0051] - after step (c), a step (d) of machining the sleeve,

[0052] - after step (a), a step (b) of inserting an insert into the foot.

[0053] Brief description of the figures

[0054] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which: Figure 1 is a schematic longitudinal cross-sectional view of half an aircraft turbomachine, Figure 2 is a schematic perspective view of a blade equipping the turbomachine of Figure 1 without the insert and external, Figure 3 is a schematic view of a blade foot of Figure 2 equipped with a sleeve and an insert, Figure 4 is a perspective view of the sleeve, Figure 5 is a cross-sectional view of the sleeve, Figure 6 is a schematic view of a manufacturing process according to the invention, Figure 7 is a schematic cross-sectional view of the blade during step (c2) of the process according to the invention, Figure 8 is a schematic cross-sectional view of a sleeve manufacturing device that can be implemented during step (c2).

[0055] Detailed description of the invention

[0056] An example of an aircraft turbomachine 1 according to the invention is shown in Figure 1. The turbomachine 1 extends around and along a longitudinal axis A.

[0057] In this application, the terms "axial", "axially", "radial" and "radially" are defined with respect to the longitudinal axis A.

[0058] The terms "upstream", "downstream" are defined in relation to the direction of gas flow in the turbomachine 1 along the longitudinal axis A.

[0059] The terms "internal", "interior", "external", "exterior",

[0060] "Externally" are defined with respect to the distance from the longitudinal axis A along an axis extending radially with respect to the longitudinal axis A.

[0061] The turbomachine 1 comprises, from upstream to downstream in the direction of gas flow F along the longitudinal axis A, a blower 2, at least one compressor such as a low pressure compressor 3 and a high pressure compressor 4, a combustion chamber 5, at least one turbine 6 such as a high pressure turbine and a low pressure turbine, and a nozzle (not shown).

[0062] The low-pressure turbine rotor is connected to the blower 2 and the low-pressure compressor rotor 3 by a low-pressure shaft (not shown). The high-pressure turbine rotor is connected to the high-pressure compressor rotor 4 by a high-pressure shaft (not shown).

[0063] The turbomachine 1 also includes a rectifier 10. The rectifier 10 allows the airflow at the outlet of an upstream rotor to be rectified in order to provide maximum thrust at the outlet of the turbomachine 1. In the particular example of Figure 1, the rectifier 10 is located downstream of the fan 2 and allows the secondary airflow F2 to be rectified.

[0064] The blower 2 allows the intake of an airflow which splits into a primary airflow F1 and a secondary airflow F2. The primary airflow F1 passes through a primary channel of the turbomachine 1 while the secondary airflow F2 is directed towards a secondary channel surrounding the primary channel.

[0065] The primary airflow F1 is compressed within the low-pressure compressor 3 and then the high-pressure compressor 4. The compressed air is then mixed with fuel and burned in the combustion chamber 5. The gases formed by combustion pass through the high-pressure turbine and the low-pressure turbine. Finally, the gases escape through the nozzle, the cross-section of which accelerates these gases to generate propulsion. The secondary airflow F2 passes through the rectifier 10, which accelerates the flow velocity of the secondary airflow F2 to generate propulsion.

[0066] The turbomachine 1 includes blades 11. The blades 11 equip, for example, the blower 2, the rectifier 10, the compressors 3, 4, the turbines 6. The blades 11 equipping the rectifier 10 are known by the English term "Outlet Guide Vane" (OGV).

[0067] The blades 11 are movable or fixed in rotation around the longitudinal axis A. Typically, the blades 11 of the blower 2 are movable in rotation around the longitudinal axis A and the blades 11 of the straightener 10 are fixed in rotation around the longitudinal axis A.

[0068] The blades 11 extend radially with respect to the longitudinal axis A. They advantageously have a variable pitch angle. Such blades 11 are rotatable about their axes of length X. The blades 11 are driven in rotation about their axes of length X by an actuation device (not shown) allowing modification of the pitch angle of the blades 11.

[0069] Each blade 11 is mounted in an annular disk centered on the longitudinal axis A. Each disk is mobile or fixed in rotation around the longitudinal axis A.

[0070] Each blade 11 comprises a blade 12 and a foot 13.

[0071] With reference to Figure 2, the blade 12 extends longitudinally along the elongation axis X between a first end 13a, also called the head, and a second end 13b opposite the first end 13a. The elongation axis X of the blade 12 extends radially with respect to the longitudinal axis A of the turbomachine 1 after the mounting of the blade 11 in the turbomachine 1.

[0072] The blade 12 has an aerodynamic profile. The blade 12 thus comprises an upper surface 12e and an lower surface 12i connected by a leading edge 12a and a trailing edge 12b. The blade 12 therefore extends along a transverse axis between the leading edge 12a and the trailing edge 12b.

[0073] Blade 12 comprises a composite material. The composite material includes a polymer matrix and a fibrous reinforcement embedded within the matrix. The composite material is, for example, an organic matrix composite (CMC).

[0074] The matrix is, for example, a thermoplastic or thermosetting polymer matrix. The thermosetting material is, for example, chosen from epoxy resins.

[0075] The fiber reinforcement comprises fibers such as carbon fibers or glass fibers. These fibers are arranged, for example, in a fiber preform. The fiber preform is then woven in a 3D pattern. The 3D weave is, for example, of the interlock type.

[0076] The foot 13 of each blade 11 is located opposite the head of the blade 12. The foot 13 has, for example, a cylindrical shape centered on the axis of elongation X and extends from the second end 13b of the blade 12.

[0077] The foot 13 of each blade 11 comprises a composite material. The composite material comprises a polymer matrix and a fibrous reinforcement embedded in the matrix. The composite material is, for example, an organic matrix composite (OMC).

[0078] The matrix is, for example, a thermoplastic or thermosetting polymer matrix. The thermosetting material is, for example, chosen from epoxy resins.

[0079] The fiber reinforcement comprises fibers such as carbon fibers or glass fibers. These fibers are arranged, for example, in a fiber preform. The fiber preform is then woven in a 3D pattern. The 3D weave is, for example, of the interlock type.

[0080] Preferably, the foot 13 and the blade 12 form a single piece and are formed as a single unit. The foot 13 and the blade 12 are formed by the same three-dimensional weave of fibers.

[0081] With reference to figure 3, each blade 11 further comprises a sleeve 14 situated around the foot 13 and advantageously an insert 15 situated inside the sleeve 14 and received in the foot 13.

[0082] The insert 15 has a substantially cylindrical shape. The insert 15 extends along the elongation axis X between an external end 15a and an internal end 15b. The insert 15 is received in the foot 13 and in the sleeve 14. For this purpose, the external end 15a of the insert 15 is housed in the foot 13 and the internal end 15b is, for example, located outside the sleeve 14.

[0083] The insert 15 comprises and advantageously consists of a metallic material. The metallic material is chosen, for example, from aluminium, stainless steels, titanium or their alloys.

[0084] Referring to Figure 4, the sleeve 14 has a generally tubular shape centered on the elongation axis X of the blade 12. The sleeve 14 comprises a cylindrical body 14a extending between first and second axial ends 14b, 14c. Advantageously, the sleeve 14 includes two annular end flanges 14d, 14e located at the first and second axial ends 14b, 14c. The end flanges 14d, 14e form, for example, raceways for bearings enabling the rotation of the blade 11 around its elongation axis X. The sleeve 14 further includes an internal passage 14f opening at the first and second axial ends 14b, 14c. In other words, the sleeve 14 is hollow.

[0085] The sleeve 14 comprises, and advantageously consists of, a metallic material. The metallic material is chosen, for example, from aluminium, stainless steels, titanium or their alloys.

[0086] The sleeve 14 provides the interface between the blade 12 and the disc. It thus constitutes a support for attaching the blade 11 to the disc. It also forms a support for the rotation of the blade 11 around its axis of extension X.

[0087] With reference to Figure 5, the sleeve 14 has a first layer 16 and a second metallic layer 18 arranged on the first layer 16. The first layer 16 has a first thickness e1. This first thickness e1 is advantageously between 5 pm and 200 pm, in particular between 10 pm and 15 pm.

[0088] The first layer 16 comprises a metallic material, advantageously a titanium alloy. The titanium alloy is preferably grade Ti17.

[0089] The first layer 16 is formed by a dynamic cold gas projection process, in particular the process known by the English name "cold spray".

[0090] The second layer 18 has a second thickness e2 greater than the first thickness e1. The second thickness e2 is advantageously between 10 µm and 300 µm. The second layer 18 comprises a metallic material distinct from, or advantageously identical to, the metallic material of the first layer 16. The second layer 18 thus comprises a metallic material, advantageously a titanium alloy. The second layer 18 is formed by a concentrated energy deposition process, also known by the acronym DED for "Directed Energy Deposition".

[0091] A manufacturing process for the blade 11 according to the invention will now be described with reference to Figure 6.

[0092] The process includes the following chronological steps:

[0093] (a) provide foot 13,

[0094] (a') optionally control foot 13,

[0095] (b) insert insert 15 into foot 13,

[0096] (c) form the sleeve 14 around the foot 13 by:

[0097] (c1) depositing the first layer 16 around the foot 13 by dynamic cold gas projection, then

[0098] (c2) depositing the second layer 18 around the first layer 16 by deposition under concentrated energy, and

[0099] (d) Optionally, machine sleeve 14.

[0100] Step (a) may include the following substeps:

[0101] (aO) weave a three-dimensional fibrous preform of foot 13, and (a1) inject a resin into the fibrous preform.

[0102] Substep (a1) can be performed by molding, such as resin transfer molding (RTM) or draping. Therefore, step (a1) can be carried out in an injection mold.

[0103] A surface preparation step can be carried out after the foot 13 has been supplied according to step (a). The surface preparation step can be, for example, chemical machining of the foot 13.

[0104] Step (a') of checking foot 13 can be performed by tomography. This step is preferably carried out before step (c) of manufacturing the sleeve 14 around foot 13, which makes the checking more precise and reliable. Indeed, the images of foot 13 acquired by tomography are less affected by noise that could be generated by the metallic sleeve 14. Step (b) of inserting the insert 15 is carried out after manufacturing foot 13 and before manufacturing sleeve 14. This ensures a consistent fiber volume ratio in the target foot 13.

[0105] According to step (c), the sleeve 14 is formed directly around the foot 13. The cold gas dynamic spraying step (c1) is carried out with a powder comprising particles. The particles include, for example, a metallic material. The metallic particles advantageously include a titanium alloy, in particular grade TA6V. The particles have, for example, a size between 10 µm and 150 µm.

[0106] The particles are transported by a gas. The gas is, for example, nitrogen or argon. The temperature of the gas is between 500°C and 1200°C, preferably between 1000°C and 1200°C. The gas pressure is between 30 bar and 70 bar, preferably 50 bar.

[0107] The deposition at stage (c1) is a deposition along an axis of revolution centered on the foot 13 such that the first layer 16 has an annular shape of revolution conforming to the final sleeve 14. The axis of revolution is thus the elongation axis X of the sleeve 14.

[0108] The deposition at step (c1) can be three-dimensional or rotational.

[0109] The deposition at step (c1) is carried out by a dynamic cold gas projection device.

[0110] In one embodiment, the cold gas dynamic projection device is mobile and the base 13 is fixed or mobile. The cold gas dynamic projection device and optionally the base 13 are mobile, for example, in rotation around the base 13 or along one of the three-dimensional axes, or helically.

[0111] In another embodiment, the cold gas dynamic projection device is fixed and the foot 13 is rotationally mobile. The foot 13 is rotationally mobile either along one of the three-dimensional axes or helically mobile. With reference to Figure 7, the concentrated energy deposition step (c2), also known by the English acronym DED for "Directed Energy Deposition," is carried out as follows:

[0112] - place a media 20 on the first layer 16, and

[0113] - merge media 20 during the placement of media 20 onto the first layer 16.

[0114] The media 20 is, for example, in powder or wire form. The media 20 comprises a metallic material selected from titanium alloys, specifically grade TA6V. The media is deposited, for example, using a nozzle mounted on an articulated arm.

[0115] The melting of the medium 20 is achieved by a heat source 22. The heat source 22 is, for example, a laser beam, an electron beam, or a plasma. The medium 20 is heated during deposition to a temperature above its melting point. The temperature is, for example, greater than or equal to 1660°C.

[0116] During step (c2), the molten media 20 F is located on the surface of the first layer 16. This allows the creation of the second layer 18 after hardening.

[0117] The Z zone adjacent to the molten media 20 F and which is thermally affected by heat (ZAT) is concentrated and contained in the first layer 16. The first layer 16 thus allows the foot 13 to be preserved from thermal degradation during the deposition of the second layer 18.

[0118] The deposit at stage (c2) is a deposit along the axis of revolution centered on foot 13 so that the second layer 18 has an annular shape of revolution centered on the first layer 16.

[0119] The deposition at step (c2) is carried out by a concentrated energy deposition device.

[0120] In one embodiment, the concentrated energy deposition device is mobile and the foot 13 is either fixed or mobile. The concentrated energy deposition device and optionally the foot 13 are mobile, for example, in rotation around the foot 13 or along one of the three-dimensional axes, or helically.

[0121] In another embodiment, the concentrated energy deposition device is fixed and the foot 13 is rotationally mobile. The foot 13 is rotationally mobile either along one of the three-dimensional axes or helically mobile. Between steps (c1) and (c2), an optional substep of surface treatment of the first layer 16 can be carried out. The surface treatment is, for example, sandblasting.

[0122] Machining step (d) can be chemical machining or mechanical machining such as cutting.

[0123] With reference to figure 8, step (c) of the process can be carried out within a device 100 for manufacturing the sleeve 14 around the foot 13.

[0124] The device 100 includes a housing 101 and a positioning element 102 for the foot 13 in the housing 101. The device 100 may further include a sealing ring 103 mounted around the foot 13 and resting on the housing 101.

[0125] The enclosure 101 advantageously includes a hatch 101a for the insertion of the foot 13 into the enclosure 101. The sealing of the enclosure 101 is improved by the sealing ring 103 which is preferably mounted around the hatch 101a.

[0126] The device 100 may further include a protective coating 104 of the insert 15 to limit the risks of contamination of the insert 14 during step (c) of forming the sleeve 14. The protective coating 104 may be arranged around the inner end 15b of the insert 15.

[0127] The device 100 further includes a tool for making the sleeve 14 configured to deposit the first and second layers 16, 18 along the axis of revolution around the foot 13. The tool includes a deposition device under concentrated energy and a dynamic projection device by cold gas.

[0128] Thanks to the combination of these two processes, it is therefore possible to form the sleeve 14 simply by reducing the manufacturing steps. Indeed, by combining these two processes, it is possible to eliminate a manufacturing step for the sleeve 14 in favor of a step of forming the sleeve 14 directly around the foot 13. This also eliminates the manual steps of gluing, inserting the foot 13 into the sleeve 14, and co-molding these two parts.

[0129] Finally, thanks to the combination of these two processes, it is possible to provide the foot 13 in the form of a densified fibrous preform before the sleeve 14 is formed around the foot 13. It is therefore possible to control the quality of the foot 13 before the sleeve 14 is formed around the foot 13. Thanks to the process of the invention, it is also possible to repair the sleeve 14 by repeating step (c2).

Claims

DEMANDS 1. A method for manufacturing a blade (11) for an aircraft turbomachine (1), characterized in that the method comprises the following steps (a) provide a foot (13) comprising a composite material, (c) forming a sleeve (14) around the foot (13), the sleeve (14) extending around an elongation axis (X), step (c) comprising the following chronological substeps: (c1) deposit a first layer (16) around the foot (13) along an axis of revolution (X) centered on the foot (13), by dynamic projection with cold gas, and (c2) deposit a second metallic layer (18) around the first layer (16) along the axis of revolution (X), by deposition under concentrated energy.

2. Method according to the preceding claim, characterized in that step (c1) is carried out by a mobile or fixed cold gas dynamic projection device, the foot (13) being mobile or fixed.

3. A method according to any one of the preceding claims, characterized in that step (c2) is carried out by a mobile or fixed concentrated energy deposition device, the foot (13) being mobile or fixed.

4. A method according to any one of the preceding claims, characterized in that the first layer (16) comprises a metallic material, preferably a titanium alloy.

5. A method according to any one of the preceding claims, characterized in that the second layer (18) comprises a titanium alloy.

6. A method according to any one of the preceding claims, characterized in that the first layer (16) has a first thickness (e1) between 5 pm and 200 pm.

7. Method according to the preceding claim, characterized in that the second layer (18) has a second thickness (e2) greater than the first thickness (e1) of the first layer.

8. A method according to any one of the preceding claims, characterized in that it comprises, between steps (a) and (c), a step (a') of checking the foot (13), for example by tomography.

9. A method according to any one of the preceding claims, characterized in that it comprises, after step (c), a step (d) of machining the sleeve (14).

10. A method according to any one of the preceding claims, characterized in that it comprises, after step (a), a step (b) of inserting an insert (15) into the foot (13).

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