ASSEMBLY COMPRISING A LIGHTHEAD AND A MASK AND METHOD FOR MANUFACTURING THE ASSOCIATED LIGHTHEAD

Abstract

The invention relates to an assembly comprising: - a first blade (12) comprising a first external surface intended to be coated with a coating deposited by projecting a flow of material, a second external surface intended to be uncoated, and a third external surface intended to be coated with the coating in decreasing thickness; - a masking tool (22) comprising a first mask (23, 24, 25) mounted on the first blade (12) so as to leave the first external surface uncovered and to extend opposite the second external surface, characterized in that the first mask (23, 24, 25) extends at least partially opposite the third external surface and is located at a distance from the second and third external surfaces to define, with these external surfaces, a flow path for a portion of the material flow. (Shorthand figure: Figure 4)

Description

Title of the invention: ASSEMBLY COMPRISING A BLADE AND A MASK AND METHOD FOR MANUFACTURING THE ASSOCIATED BLADE Technical field of the invention

[0001] The invention relates to the field of assemblies comprising a blade for an aircraft turbomachine and a tooling for masking the blade when projecting a flow of material onto the blade.

[0002] The invention also relates to the field of blade manufacturing comprising a step of projecting a flow of material. Technical background

[0003] An aircraft turbomachine, such as a turbojet or turbomotor, typically comprises, from upstream to downstream in the direction of gas flow, a movable fan rotating about a longitudinal axis, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, a low-pressure turbine and a gas exhaust nozzle.

[0004] The blower allows the intake of an airflow which splits into a primary airflow and a secondary airflow. The primary airflow passes through a primary channel of the turbomachine while the secondary airflow is directed towards a secondary channel surrounding the primary channel.

[0005] The primary airflow is compressed within the compressors. The compressed air is then mixed with a fuel and burned within the combustion chamber. The combustion gases pass through the turbines and then escape through the nozzle, the cross-section of which allows these gases to be accelerated to generate propulsion.

[0006] Turbines and compressors are respectively formed of a plurality of turbine and compressor stages. Each turbine stage and each compressor stage typically comprises an annular distributor and a rotating wheel centered on the longitudinal axis. Each distributor comprises a radially external platform and a radially internal platform connected by blades. The blades are typically fixed in rotation, while each rotating wheel comprises at least one annular row of rotating movable blades.

[0007] Each blade extends radially and comprises a blade having an aerodynamic shape. The blade typically comprises an external surface having an intrados face and an extrados face connected by a leading edge and a trailing edge.

[0008] The blades, in particular the blades of high-pressure turbine distributors, are located downstream of the combustion chamber and are therefore subjected to high temperatures. Thus, these blades are typically made of metallic or composite materials, particularly ceramic matrix composites (CMCs), which have the advantage of withstanding high temperatures. However, such blades cannot be subjected to temperatures exceeding those that metallic or ceramic matrix composite materials can withstand.

[0009] In this context, it has been proposed to equip the blades with a coating that forms a thermal or environmental barrier, thus making it possible, in particular, to broaden the temperature range in which these blades can be used. The coating comprises, for example, a ceramic layer that exhibits resistance to high temperatures. Such a coating is typically produced by spraying a stream of material.

[0010] However, applying such a coating to a blade presents numerous challenges. Indeed, in order to preserve the mechanical properties of the blade, the coating must be applied only to certain external surfaces of the blade, leaving other surfaces uncoated. Furthermore, the surfaces between the coated and uncoated areas must have a coating of decreasing thickness to maintain surface continuity.

[0011] To this end, one solution could be to implement a masking tool with a windowed card comprising a wall positioned substantially perpendicular to the surface to be masked and to the projection flow. However, such a tool would have the major drawback of confining the projection flow, generating vortices and the recirculation of resolidified particles. This would result in a degradation of the coating's microstructure, its cohesion, and its adhesion to the blade. Furthermore, such a solution would not allow for a coating with decreasing thickness on the surfaces connecting the coated and uncoated areas.

[0012] In this context, to overcome the aforementioned drawbacks, it has been proposed to spray the coating over the entire surface of the blade without the use of masking tools. According to this solution, the blade manufacturing process includes a step of spraying the material flow followed by a step of sandblasting the blade to remove the coating from the surfaces intended to be uncoated. Such a sandblasting step represents an additional step, which increases the manufacturing costs of the blade. Furthermore, this step is performed manually, so its reproducibility is not guaranteed, increasing variability in the manufacturing ranges of the blades. Also, such a solution does not allow for a coating of decreasing thickness on the surfaces connecting the coated and uncoated areas.

[0013] Therefore, there is a need to provide a solution that allows the manufacture of a blade having a coating of decreasing thickness with properties mechanical and improved grip, while being inexpensive and easy to manufacture. Summary of the invention

[0014] To this end, the invention proposes an assembly comprising:

[0015] - a first blade for an aircraft turbomachine, the blade (comprising a a first external surface intended to be coated with a coating deposited by projecting a flow of material, a second external surface intended to be uncoated, and a third external surface connecting the first and second external surfaces, and intended to be coated with the coating in a decreasing thickness from the first external surface to the second external surface,

[0016] - a masking tool comprising a first mask which is mounted on the first blade so as to leave the first external surface free, and to extend in relation to the second external surface.

[0017] The assembly is remarkable in that the first mask extends at least partly in relation to the third external surface and is located at a distance from the second and third external surfaces to define with these external surfaces a flow passage for part of the material flow.

[0018] According to the invention, the first mask delimits with the blade the flow passage of a part of the material flow at the level of a part of the second external surface and the third external surface.

[0019] This flow passage allows the deposition of only a portion of the material flow projected during the coating formation. This results in the coating being deposited on at least a portion of the second surface with a decreasing thickness.

[0020] Thanks to the distanced position of the first mask relative to the blade, it is therefore possible to create a coating of decreasing thickness on the surface of the targeted blade while masking the third external surface which is therefore devoid of the coating.

[0021] Thanks to the invention, it is therefore possible to mask the surfaces of the blade and consequently to avoid additional sandblasting steps to remove the coating on these areas.

[0022] Thanks to the invention, it is also possible to overcome the phenomena of confinement of the projection flow, ensuring a coating with a microstructure conforming to expectations.

[0023] The invention may comprise one or more of the following features, taken individually or in combination with each other:

[0024] - the first mask and the second and third external surfaces opposite which The first mask is located, and the masks are separated by a distance of between 1 mm and 5 mm, preferably between 1 mm and 3 mm.

[0025] - the first blade comprises an intrados face and an extrados face connected by a leading edge and trailing edge, the first mask extending along at least part of the intrados surface to the trailing edge,

[0026] - the first mask extends in a plane forming an angle between 0° and 30° relative to the third external surface,

[0027] - at least one ring sector having a longitudinal axis, the ring sector comprising the first blade and at least a second blade comprising a first external surface intended to be coated with the coating deposited by projection of the material flow, a second external surface intended to be devoid of the coating and a third external surface connecting the first and second external surfaces and intended to be coated with the coating in a decreasing thickness from the first external surface to the second external surface,

[0028] - a second mask which is mounted on the second vane so as to leave the the first external surface of the second blade, and extending opposite the second external surface of the second blade, the second mask extending at least partially opposite the third external surface of the second blade and is located at a distance from the second and third external surfaces of the second blade to define with these external surfaces a flow passage for part of the material flow,

[0029] - the ring sector comprises at least one first platform from which extends radially from each blade,

[0030] - at least one first masking platform that fits onto the first platform, the first and second masks extending beyond the masking platform,

[0031] - insertion openings for the blades formed in the first platform of masking,

[0032] - a second platform, each blade extending between the first and second platforms,

[0033] - a second masking wall fitting onto the second platform,

[0034] - the masking tool is a single piece.

[0035] The invention also relates to a method for manufacturing a blade for an aircraft turbomachine, the method comprising the following steps:

[0036] (a) provide an assembly according to any one of the preceding characteristics, and

[0037] (b) project the flow of material onto the first external surface of the blade.

[0038] The method according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0039] - during step (b), the flow of material is projected at the entrance of the passage flow located opposite the trailing edge,

[0040] - step (b) includes the following step:

[0041] (b2) project the flow of material in a direction parallel to the longitudinal axis,

[0042] - step (b) includes the following steps before step (b2):

[0043] (bO) provide a projection nozzle extending along a main axis,

[0044] (bl) orient the projection nozzle such that the main axis of the projection nozzle is oriented parallel to the longitudinal axis,

[0045] - step (b) comprises the following step carried out after step (b2):

[0046] (b4) project the flow of material in a direction inclined with respect to the axis longitudinal,

[0047] - step (b) comprises the following steps between steps (b2) and (b4):

[0048] (b3) orient the projection nozzle such that the main axis is oriented at an angle between 0° and 45° relative to the longitudinal axis. Brief description of the figures

[0049] Other features and advantages will become apparent from the following description of non-limiting embodiments of the invention with reference to the accompanying drawings in which:

[0050] [Fig. 1] is a schematic longitudinal cross-sectional representation of half an aircraft turbomachine according to the invention,

[0051] [Fig.2] is a perspective view of a distributor sector that can be fitted to the turbomachine of [Fig.1],

[0052] [Fig.3] is a schematic cross-sectional representation of a blade that can be fitted to the distributor of [Fig.2],

[0053] [Fig. 4] is a perspective view of a masking tool mounted on a distributor sector,

[0054] [Fig. 4a] is a partial perspective view of a plurality of masking tools mounted on a distributor,

[0055] [Fig. 4b] is a perspective view of a masking tool,

[0056] [Fig.5] is a schematic cross-sectional representation of the masking tooling mounted on the distributor sector according to [Fig.4],

[0057] [Fig. 6] is a perspective view of the masking tooling mounted on a distributor sector, after the material flow projection step,

[0058] [Fig.7] is a schematic cross-sectional representation of the masking tooling mounted on the distributor sector, according to another embodiment,

[0059] [Fig.8] is a schematic cross-sectional representation of the masking tooling mounted on the distributor sector, according to another embodiment,

[0060] [Fig.9] is a synoptic diagram of a method for manufacturing a blade, according to the invention. Detailed description of the invention

[0061] An example of an aircraft turbomachine 1 is shown in [Fig. 1]. The turbomachine 1 extends around and along a longitudinal axis X.

[0062] In the present application, the terms "upstream" and "downstream" are defined with respect to the direction of gas flow in the turbomachine 1 along the longitudinal axis X.

[0063] The terms "axial", "axially", "radially", "radially", "longitudinally", are defined with respect to the longitudinal axis X.

[0064] The terms "internal", "interior", "external", "outside", "externally" are defined with respect to the distance of the longitudinal axis X along a radial axis.

[0065] The turbomachine 1 comprises, from upstream to downstream, 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 such as a high-pressure turbine 6 and a low-pressure turbine 7, and a nozzle (not shown).

[0066] The blower 2 allows the intake of an airflow F which divides into a primary airflow Fl and a secondary airflow F2. The primary airflow Fl passes through a primary channel of the turbomachine 1 while the secondary airflow F2 is directed towards a secondary channel surrounding the primary channel.

[0067] The primary airflow Fl is compressed within the low-pressure compressor 3 and then the high-pressure compressor 4. The compressed air is then mixed with a fuel and burned within the combustion chamber 5. The gases formed by the combustion pass through the high-pressure turbine 6 and low-pressure turbine 7. The gases finally escape through the nozzle, the cross-section of which allows the acceleration of these gases to generate propulsion.

[0068] The fan 2 is, for example, shrouded. It is surrounded by an annular casing 2b centered on the longitudinal axis X. The casing 2b is, for example, surrounded by a nacelle (not shown) of the turbomachine 1. According to another example, the fan 2 is not shrouded.

[0069] The high-pressure turbine 6, for example, comprises at least one turbine stage, each stage comprising a distributor 8 and a runner. Not shown, the runner comprises a rotating disc centered on the axis longitudinal X and blades extending radially from the disk and regularly distributed around the longitudinal axis X.

[0070] The distributor 8 comprises a ring centered on the longitudinal axis X. Preferably, the ring is sectored and comprises a plurality of sectors of ring 9. Each sector of ring 9 extends, for example, over an angular sector centered on the longitudinal axis X, with an angle between 10° and 45°. According to another advantageous example, the ring is a single piece. In this example, the distributor 8 thus comprises a ring that extends over an angular sector of 360°.

[0071] With reference to [Fig.2], each ring sector 9 comprises an outer platform 10 and an inner platform 11 connected by at least one blade 12. The outer and inner platforms 10, 11 extend over the angular sector of the ring sector 9.

[0072] In particular, the external platform 10 comprises an external body 13 and two radial walls 14 extending radially outwards from the external body 13. The internal platform 11 comprises an internal body 15 and two radial walls 16 extending radially inwards from the internal body 15. The radial walls 14, 16 are respectively axially opposed.

[0073] Preferably, each ring sector comprises at least one first blade 12a, one second blade 12b and one third blade 12c. The first, second and third blades 12a, 12b, 12c are regularly distributed over the angular sector.

[0074] Each blade 12 extends along an elongation axis Y extending radially with respect to the longitudinal axis X.

[0075] Each blade 12 comprises a blade 17 extending along the Y-axis between the external and internal platforms 10, 11. Each blade 17 has an aerodynamic shape and comprises an external surface having an intrados face 17i and an extrados face 17e connected by a leading edge 17a and a trailing edge 17b.

[0076] As more clearly seen in [Fig. 3], each blade 12 further comprises a ventilation wall 18 which extends the intrados and extrados faces 17i, 17e to the trailing edge 17b. The ventilation wall 18 has a thickness less than the thickness measured between the intrados and extrados faces 17i, 17e at the leading edge 17a, for example. The intrados face 17i can be connected to the ventilation wall 18 by a step.

[0077] The blade 12 is, for example, made of metallic or composite material. Advantageously, the composite material is a ceramic matrix composite (CMC). Such materials have the advantage of withstanding high temperatures and therefore allow these blades 12 to be used in close proximity to the combustion chamber 5, in an environment subjected to high temperatures.

[0078] In order to improve the temperature resistance of the blades 12, each blade 12 may include openings (not shown) to allow the passage of cooling air inside the blades 12. The openings are for example on the lower surface 17i or the upper surface 17e of the blade 17. The openings are preferably provided on the ventilation wall 18.

[0079] In order to further improve the temperature resistance of the blades 12, each blade 12 according to the invention further comprises a coating 19.

[0080] The blade 12 has a first external surface SI coated with the coating 19, a second external surface S2 without the coating 19 and a third external surface S3 connecting the first and second external surfaces SI, S2 at least partly coated with the coating 19.

[0081] Preferably, the first external surface S1 is located on the leading edge 17a of the blade 12, and the second external surface S2 covers the upper surface 17e of the blade 12 and extends to the ventilation wall 18. The ventilation wall 18 is thus devoid of the coating 19, as is the upper surface 17e. This allows the efficient passage of cooling air without disturbing the airflow. The third external surface S3 connects the first and second surfaces S1 and S2. The third external surface S3 is thus located on at least part of the lower surface and at least part of the upper surface 17e connected to the leading edge 17a. The third external surface S3 is coated at least partially with the coating 19, which has a decreasing thickness on this third external surface S3. The thickness of the coating 19 decreases from the first external surface SI towards the trailing edge 17b.The third external surface S3 thus ensures surface continuity between the first and second external surfaces SI, S2.

[0082] The coating 19 comprises a material selected for example from ceramics, such as zirconia, in particular yttrium oxide stabilized zirconia, also known as yttria zirconia.

[0083] The coating 19 is applied by projecting a flow of material 20, in particular by thermal spraying. The projection of the material flow 20 is carried out in particular from a spraying device comprising a spray nozzle 21. Advantageously, the spray nozzle 21 has a principal axis Z substantially parallel to the longitudinal axis X of the distributor 8.

[0084] To achieve this coating 19, the invention provides a masking tool 22. With reference to Figures 4, 4a, 4b and 5, the masking tool 22 preferably extends over an angular sector. The angular sector is preferably equal to the angular sector of the ring sector 9 of the distributor 8.

[0085] Thus, as can be seen in [Fig.4a], a plurality of masking tools 22 are mounted on the distributor 8.

[0086] The masking tooling 22 comprises a material, for example, metallic, ceramic, polymeric, or composite. The metallic material is, for example, a nickel-chromium alloy such as alloy grade 718. As another example, the metallic material is aluminum or an aluminum alloy, copper, or steel. The advantage of such materials is that they are capable of withstanding temperatures of 300°C or higher and can therefore be used during the material flow projection step.

[0087] The masking tool 22 is preferably monobloc. It is thus made of a single monolithic piece. The masking tool 22 is produced, for example, by welding, machining from solid material, or by additive manufacturing, for example by selective laser melting, also known by the English acronym SLM for "selective laser melting".

[0088] The masking tool 22 is mounted on at least the first blade 12a of the distributor 8. The masking tool 22 makes it possible to mask the second external surface S2 of the first blade 12 in order to allow the first flow to be projected onto the first external surface SI without contaminating this second external surface S2. The masking tool 22 is advantageously mounted on the first, second, and third blades 12a, 12b, 12c of the ring sector 9 of the distributor 8. This makes it possible to mask several blades 12 simultaneously in order to reduce the time required to mask each blade 12 and thus increase production rates.

[0089] The masking tooling 22 includes at least a first mask 23, and advantageously second and third masks 24, 25. Preferably, the masking tooling 22 further includes first and possibly second masking platforms 26, 27 connected to each other by the mask(s) 23, 24, 25.

[0090] Each mask 23, 24, 25 is mounted on a vane 12 so as to leave the first external surface SI free and to extend in relation to the second external surface S2 in order to mask this second external surface S2 during the projection of the flow of material and prevent the deposition of the coating 19 on this second external surface S2.

[0091] According to the invention, each mask 23, 24, 25 also extends at least partially in relation to the third external surface S3 and at a distance from the second and third external surfaces S2, S3. Advantageously, the distance d separating the blade 12 from the mask 23, 24, 25 is between 1 mm and 5 mm, preferably between 1 mm and 3 mm.

[0092] Each mask 23, 24, 25 comprises a masking wall 28 of complementary shape to the second and third surfaces S2, S3 and a free edge 29 of the masking wall 28 opposite the trailing edge 17b of the blade 12.

[0093] Each mask 23, 24, 25 defines respectively with these second and third external surfaces S2, S3 a flow passage PI of a part 20' of the material flow 20. The flow passage PI has an inlet PI 1 of a part 20' of the material flow 20 which is opposite the trailing edge in a direction parallel to the longitudinal axis X.

[0094] Each mask 23, 24, 25 advantageously extends in a plane forming an angle between 0° and 30° with respect to the third external surface S3. Thus, each mask 23, 24, 25 can be parallel to the third external surface S3 or be angled. This allows the width of the flow passage PI to be modulated by reducing or increasing the distance d.

[0095] The first and second masking platforms 26, 27 extend over an angular sector equal to the angular sector of each ring sector 9 of the distributor 8. The first and second masking platforms 26, 27 have a shape complementary to the external and internal platforms 10, 11 of the ring sector 9 of the distributor 8. The first and second masking platforms 26, 27 are nested respectively on the external and internal platforms 10, 11

[0096] In particular, the first and second masking platforms 26, 27 respectively comprise first and second axial walls 30a, 30b and first and second radial walls 31a, 31b. The first radial wall 31a extends radially outwards from the first axial wall 30a and the second radial wall 31b extends radially inwards from the second axial wall 30b. The first axial wall 30a advantageously covers an inner face of the outer body 13 of the outer platform 10, while the second axial wall 30b covers an outer face of the inner body 15 of the inner platform 11. The first and second radial walls 31a, 31b respectively cover one of the radial walls 14 of the outer and inner platforms 10, 11.

[0097] To facilitate the attachment of the masking tool 22, the second masking platform 27 may include at least one fixing tab 27a to the distributor 8 or to the ring sector 9. The fixing tab 27a has, for example, an opening 27b for bolting the masking tool 22 to the distributor 8 or to the ring sector 9.

[0098] Such a configuration of the masking tooling 22 therefore allows both the masking of the blades 12 and the external and internal platforms 10, 11 of the distributor 8 as illustrated in [Fig. 4]. Also, such a configuration of the masking tooling 22 allows the implementation of a plurality of masks 23, 24, 25 for masking a plurality of blades 12 during a single step of projecting the material flow, i.e. without the need to stop the material flow projection step to arrange a new mask on the blade 12 to be coated as illustrated in [Fig. 6].

[0099] To facilitate the installation of the masking tool 22 on the ring sector 9 of the distributor 8, the masking tool 22 may include insertion holes 32 for the vanes 12. The holes 32 are provided on the first and / or second masking platform 26, 27. Preferably, the masking tool 22 includes first holes 32a provided on the first masking platform 26 and second holes 32b provided on the second masking platform 27.

[0100] The first orifices 32a are aligned with the second orifices 32b along a radial axis. The blades 12 pass through the first and second orifices 32a, 32b. Each orifice 32, 32a, 32b can be slotted. According to this example, each orifice 32, 32a, 32b has a slot for inserting the blade 12. Each mask 23, 24, 25 extends radially between the first and second masking platforms 26, 27 from the slots.

[0101] These orifices 32, 32a, 32b allow axial translation mounting of the masking tool 22 on the ring sector 9 of the distributor 8.

[0102] According to an embodiment illustrated in [Fig. 7], the masking wall 28 of each mask 22, 23, 24 may be perforated. According to this embodiment, the masking wall 28 of each mask 22, 23, 24 has through openings 33. Preferably, these openings 33 have an axis extending at an angle between 10° and 90°, preferably between 10° and 80°, with respect to the plane of the masking wall 28.

[0103] According to another embodiment illustrated in [Fig. 8], each mask 22, 23, 24 may include an additional masking wall 28' arranged opposite the masking wall 28, referred to as the main masking wall. The main and additional masking walls 28, 28' define between them a second flow passage P2 which extends parallel to the first flow passage PL. The first and second flow passages PL, P2 are thus separated by the main masking wall 28. The second flow passage P2 allows the circulation of a portion 20" of the material flow that has been diverted by the main masking wall 28.

[0104] According to this embodiment, each masking wall 28, 28' can be perforated. Each masking wall 28, 28' has through openings 33'. Preferably, these openings 33' have an axis extending at an angle between 10° and 90°, preferably between 10° and 80°, relative to the plane of the masking wall 28, 28'.

[0105] The additional masking wall 28' allows the flow of material to be limited on the extrados face 17e of an adjacent blade 12.

[0106] A manufacturing process for at least one of these blades 12 will now be described with reference to [Fig.9].

[0107] The manufacturing process according to the invention comprises the following steps:

[0108] (a) supply an assembly comprising at least one blade 12 and at least one tooling masking element 22 mounted on the vane 12,

[0109] (b) project the material flow 20 onto the first external surface SI of the blade 12.

[0110] Step (a) may include the following substeps:

[0111] (aO) provide at least one blade 12,

[0112] (al) provide at least one masking tool 22,

[0113] (a2) mount the masking tool 22 on the blade 12.

[0114] Step (b) can be carried out by:

[0115] (b2) projection of the material flow along a direction parallel to the longitudinal axis X of ring sector 8, and

[0116] (b4) optionally, projection of the material flow along an inclined direction relative to the longitudinal axis X of the ring sector 8, for example at an angle of inclination between 0° and 45°.

[0117] In particular, step (b) may include the following steps:

[0118] (bO) provide the projection nozzle 21,

[0119] (bl) orient the projection nozzle 21 such that the principal axis Z of the projection nozzle 21 is oriented parallel to the longitudinal axis X of the ring sector 9 or of the distributor 8, and

[0120] (b2) project the material flow 20 onto the first external SI surface of the blade 12, along a direction parallel to the longitudinal axis X of the ring sector 8.

[0121] Preferably, the material flow is projected at the inlet PI 1 of the flow passage PI located opposite the trailing edge 17b.

[0122] Step (b) may further include the following steps after steps (bl) and (b2):

[0123] (b3) orient the projection nozzle 21 such that the main axis Z of the nozzle projection 21 is oriented at an angle between 0° and 45° with respect to the longitudinal axis X of the ring sector 9 or the distributor 8, and

[0124] (b4) project the material flow 20 onto the first external SI surface of the blade 12, along a direction inclined relative to the longitudinal axis X of the ring sector 8.

[0125] During step (b), a part 20' of the material flow 20 thus flows into the flow passage PI allowing a decreasing deposition of the coating 19 on the third external surface S3 of the blade 12.

Claims

Demands

1. An assembly comprising: - a first blade (12, 12a, 12b, 12c) for an aircraft turbomachine (1), the blade (12, 12a, 12b, 12c) comprising a first external surface (S1) intended to be coated with a coating (19) deposited by projection of a flow of material (20), a second external surface (S2) intended to be free of the coating (19), and a third external surface (S3) connecting the first and second external surfaces (S1, S2), and intended to be coated with the coating (19) in a decreasing thickness from the first external surface (S1) to the second external surface (S2), - a masking tool (22) comprising a first mask (23, 24, 25) which is mounted on the first blade (12, 12a, 12b, 12c) so as to leave the first external surface (S1) free, and to extend with respect to the second external surface (S2), characterized in that the first mask (23, 24,25) extends at least partially opposite the third external surface (S3) and is located at a distance from the second and third external surfaces (S2, S3) to define with these external surfaces (S2, S3) a flow passage (PI) of a part (20') of the material flow (20).

2. Assembly according to the preceding claim, characterized in that the first mask (23, 24, 25) and the second and third external surfaces (S2, S3) opposite which the first mask (23, 24, 25) is located are separated by a distance (d) between 1 mm and 5 mm, preferably between 1 mm and 3 mm.

3. Assembly according to any one of the preceding claims, characterized in that the first blade (12, 12a, 12b, 12c) comprises an intrados face (17i) and an extrados face (17e) connected by a leading edge (17a) and a trailing edge (17b), the first mask (23, 24, 25) extending opposite at least a part of the intrados face (17i) to the trailing edge (17b).

4. Assembly according to any one of the preceding claims, characterized in that the first mask (23, 24, 25) extends in a plane forming an angle between 0° and 30° with respect to the third external surface (S3).

5. Assembly according to any one of the preceding claims, characterized in that it comprises: - at least one ring sector (9) having a longitudinal axis (X), the ring sector (9) comprising the first blade (12, 12a) and at least one second blade (12, 12b) comprising a first external surface (S1) intended to be coated with the coating (19) deposited by projection of the material flow (20), a second external surface (S2) intended to be free of the coating (19), and a third external surface (S3) connecting the first and second external surfaces (S2, S2) and intended to be coated with the coating (19) in a decreasing thickness from the first external surface (S1) to the second external surface (S2), and in that: - the masking tooling (22) comprises a second mask (24) which is mounted on the second blade (12, 12b) so as to leave the first external surface (S1) of the second blade (12, 12b) free, and to extend opposite the second surface external (S2) of the second blade (12, 12b),the second mask (24) extending at least partially opposite the third external surface (S3) of the second blade (12, 12b) and is located at a distance from the second and third external surfaces (S2, S3) of the second blade (12, 12b) to define with these external surfaces (S2, S3) a flow passage (PI) for a part (20') of the material flow (20).

6. Assembly according to the preceding claim, characterized in that: - the ring sector (9) comprises at least a first platform (10, 11) from which each blade (12, 12a, 12b, 12c) extends radially, and in that: - the masking tooling (22) comprises at least a first masking platform (26, 27) fitting onto the first platform (10, 11), the first and second masks (23, 24) extending in projection from the masking platform (26, 27).

7. Assembly according to the preceding claim, characterized in that the masking tooling (22) includes openings (32) for inserting the blades (12, 12a, 12b, 12c) formed in the first masking platform (26, 27).

8. Assembly according to any one of claims 6 or 7, characterized in that the ring sector (9) comprises a second platform (11), each blade (12, 12a, 12b, 12c) extending between the first and second platforms (10, 11), and in that the masking tooling (22) comprises at least one second masking wall (27) fitting onto the second platform (11).

9. Assembly according to any one of the preceding claims, characterized in that the masking tooling (22) is one piece.

10. Method of manufacturing a blade (12, 12a, 12b, 12c) for an aircraft turbomachine (1), the method comprising the following steps: (a) providing an assembly according to any one of the preceding claims, and (b) projecting the flow of material (20) onto the first external surface (SI) of the blade (12, 12a, 12b, 12c).

11. A manufacturing method according to the preceding claim in combination with claim 3, characterized in that during step (b), the material flow (20) is projected at the right of an inlet (PI 1) of the flow passage (PI) located opposite the trailing edge (17b).

12. A manufacturing method according to claim 10 or 11 in combination with claim 5, characterized in that step (b) comprises the following step: (b2) projecting the material flow (20) in a direction parallel to the longitudinal axis (X).

13. A manufacturing method according to the preceding claim, characterized in that step (b) comprises the following steps before step (b2): (b0) providing a projection nozzle (21) extending along a principal axis (Z), (bl) orienting the projection nozzle (21) such that the principal axis (Z) of the projection nozzle (21) is oriented parallel to the longitudinal axis (X).

14. A manufacturing method according to claim 12 or 13, characterized in that step (b) comprises the following step carried out after step (b2): (b4) projecting the material flow (20) in a direction inclined with respect to the longitudinal axis (X).

15. A manufacturing method according to claims 13 and 14, characterized in that step (b) comprises the following steps between steps (b2) and (b4): (b3) orient the projection nozzle (21) such that the main axis (Z) is oriented at an angle between 0° and 45° with respect to the longitudinal axis (X).

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