FR3085418A1 - TURBOMACHINE BLADE COMPRISING AN INTERNAL HONEYCOMB PART - Google Patents

Abstract

The invention relates to a turbine engine blade (1) comprising an upper surface (13), a lower surface (14), a base (16), and a top (15), characterized in that said blade (1) comprises an internal part honeycomb formed by a plurality of cells directed along a main axis of elongation (θ) of the blade (1) and which open at the foot (16) of the blade (1), said blade (1 ) also comprising a casing (3) surrounding the internal honeycomb part along the upper surface (13) and the lower surface (14), as well as a bath (17) comprising a bottom wall (17a ) covering the internal honeycomb part on the top (15) of the blade (1).

Description

Invention background

The present invention relates to the general field of turbine engine blades, and more particularly to mobile turbine engine blades for aircraft.

The moving blades of a turbomachine are subjected to significant mechanical stresses, in particular the blades of a high pressure turbine because of the high speed of rotation of the high pressure turbine.

The turbomachine blades, and particularly the high pressure turbine blades, must therefore have a structure making it possible to withstand the significant mechanical stresses to which said blades are subjected.

There is a need to find blades which have better resistance to mechanical stresses.

In addition, the blades can be used in an environment having a high temperature, as is particularly the case for high pressure turbine blades which can be subjected to temperatures of the order of 1000 ° C., and may therefore need a cooling system so as not to be damaged during the operation of the turbomachine.

Thus, and particularly for high pressure turbine blades, there is a need to find blades with better mechanical strength when used at high temperatures, for example of the order of 1000 ° C.

Subject and summary of the invention

The main object of the present invention is therefore to solve such a problem by proposing a turbomachine blade comprising an upper surface, a lower surface, a foot, and a top, said blade comprising an internal honeycomb part formed by a plurality of alveoli directed along a main axis of elongation of the blade and which open at the foot of the blade, said blade also comprising an envelope surrounding the internal honeycomb part along the upper surface and the lower surface, and a bathtub comprising a bottom wall covering the internal honeycomb part on the top of the blade.

Such a solution allows to improve the performance of the blade cooling system without weakening the blade, thereby improving the mechanical strength of the blade at high temperatures.

The turbomachine vane can also include the following additional characteristics, these additional characteristics being able to be combined with one another according to the technical possibilities:

- cooling channels are formed at a trailing edge of the blade;

- The bottom wall of the tub comprises at least one orifice communicating with the internal part, the number of orifices formed in the bottom wall of the bath being less than the number of cells of said internal part;

- the blade is made of nickel-based super alloy;

According to a second aspect, the invention relates to a turbomachine comprising a blade according to any one of the preceding characteristics.

The turbomachine may further comprise a high pressure turbine which comprises a blade according to any one of the preceding characteristics.

According to a third aspect, the invention relates to a method of manufacturing a blade according to any one of the preceding characteristics.

According to a first variant of the manufacturing process, said manufacturing process comprises the following steps:

- Manufacturing of a main ceramic core having a shape complementary to the internal honeycomb part, by a process for forming a mixture comprising a ceramic powder and a plastic binder;

- manufacture of a ceramic tub core;

- Manufacturing by foundry of the blade around the main core and the tub core, the main core and the tub core being kept separate so as to form the bottom wall of the tub;

- elimination of the main core and the tub core.

According to an additional characteristic of the first variant of the manufacturing process, a ceramic trailing edge core is manufactured and is assembled with the main core at the level of the part corresponding to the trailing edge of the blade, the edge core of leakage then being eliminated with the main core and the tub core.

According to a second variant of the manufacturing process, said manufacturing process, the blade is produced by a process for forming a mixture comprising a metal powder and a plastic binder.

According to an additional characteristic of the second variant of the manufacturing process, said manufacturing process comprises the following steps:

- manufacture of the internal part by shaping a mixture comprising a metal powder and a plastic binder, and elimination of the plastic binder;

- Manufacture of a first part of the envelope intended to surround the internal part forming the upper surface of the blade by shaping a mixture comprising a metal powder and a plastic binder, and elimination of the plastic binder;

- Manufacture of a second part of the envelope intended to surround the internal part forming the lower surface of the blade by shaping a mixture comprising a metal powder and a plastic binder, and elimination of the plastic binder;

- Assembling the first part of the envelope and the second part of the envelope around the internal part so as to form the lower surface and upper surface of the blade and sintering of the assembly;

- assembly of a bathtub at the top of dawn.

According to another possible characteristic of the second variant of the manufacturing process, said manufacturing process comprises the following steps:

- manufacture of the internal part by shaping a mixture comprising a metal powder and first plastic binder;

- overmolding of the envelope around the internal part with a mixture comprising a metal powder and a second plastic binder, the first plastic binder having a melting temperature higher than the second plastic binder;

- elimination of the first plastic binder and the second plastic binder, and sintering.

According to an additional characteristic of the second variant of the manufacturing process, said manufacturing process comprises the following steps:

- manufacture of the internal part by shaping a mixture comprising a metal powder and first plastic binder;

- elimination of the first plastic binder;

- overmolding of the envelope around the internal part with a mixture comprising a metal powder and a second plastic binder;

- elimination of the second plastic binder, and sintering.

According to an additional characteristic of the second variant of the manufacturing process, said manufacturing process comprises the following steps:

- Provision of a plastic strip around the internal part before the envelope is overmolded around the internal part, the plastic strip having a melting temperature higher than the melting temperature of the second plastic binder used for the manufacture of the envelope;

- elimination of the strip after overmolding the envelope around the internal part.

According to another possible characteristic of the second variant of the manufacturing process, said manufacturing process comprises the following steps:

injection of a plastic material into the cells of the internal part, the plastic material having a melting temperature higher than the melting temperature of the second plastic binder used for the manufacture of the envelope;

- elimination of the plastic material after overmolding of the envelope around the internal part.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an embodiment thereof devoid of any limiting character. In the figures:

- Figure 1 shows a perspective view of a blade according to the invention;

- Figure 2 shows a sectional view perpendicular to a main axis of elongation of the blade of Figure 1 along the plane II;

- Figures 3a, 3b, 3c, 3d and 3e show ceramic cores for the manufacture of a blade according to a variant of the invention;

- Figures 4a and 4b show views of a blade according to a variant of the invention for which the cores have not yet been removed, said cores being shown by transparency;

- Figure 5 shows schematically the different stages of a method of manufacturing a blade according to a variant of the invention in which the blade is manufactured by foundry;

- Figure 6 schematically shows the different stages of a method of manufacturing a blade according to a variant of the invention in which the blade is produced a method of forming a mixture comprising a metal powder and a binder plastic;

- Figure 7 shows schematically the different stages of a method of manufacturing a blade according to a variant of the invention in which the blade is produced by overmolding of an envelope around an internal honeycomb part ;

- Figure 8 shows schematically the different stages of a method of manufacturing a blade according to another possible variant of the invention in which the blade is produced by overmolding of an envelope around an internal part in nest d 'bee;

- Figures 9a, 9b and 9c schematically represent different stages of the variant of the manufacturing process in which the blade is produced by overmolding the envelope around the internal honeycomb part.

Detailed description of the invention

As shown in FIGS. 1 and 2, a movable blade 1 of a turbomachine according to the invention has a profiled shape and includes a leading edge 11, a trailing edge 12, an upper surface 13, and a lower surface 14.

The blade 1 comprises a main axis of elongation Θ, which is perpendicular to the axis of the turbomachine. The blade 1 also includes a foot 15 by which said blade 1 is fixed to a disc, as well as a top 16 located at an end opposite to the foot 15 along the main axis of elongation Θ.

At its apex 15, the vane 1 comprises a bathtub 17 which is formed by a cavity open to said apex 15 of the vane 1. The bathtub 17 makes it possible to reduce the contacts between of the annular surface of the casing inside which the blade 1 is rotated and the top 15 of said blade 1.

The blade 1 comprises an internal honeycomb part 2 formed by a plurality of cells 21 of identical shape directed along the main axis of elongation Θ. In the example illustrated in the figures, the cells 21 have a cross section of hexagonal shape, this shape having the advantage of providing very good mechanical characteristics to the internal part 2. However, the cells 21 are not limited to a hexagonal shape, the cells 21 may for example have a square section or a circular section.

In addition, the cells 21 preferably have an internal diameter between 0.05mm and 0.5mm. By diameter is understood here the largest dimension of the cell 21 taken perpendicular to the main axis of elongation Θ.

In addition, the walls which form the cells 21 preferably have a thickness of between 0.1mm and 1mm.

The cells 21 are directed along the main axis of elongation θ and open at the foot 16 of the blade 1. The internal part 2 therefore forms a network of channels formed by the plurality of cells 21, this network of channels making it possible to circulate a cooling flow inside the blade 1 which is introduced into this network of channels by the foot 16 of the blade 1.

The internal honeycomb part 2 makes it possible on the one hand to provide the blade 1 withstand mechanical stresses, and on the other hand allows a cooling flow to circulate inside the blade so to obtain efficient and uniform cooling of the blade 1.

The blade 1 also includes an envelope 3 which surrounds the internal part 2 along the upper surface 13 and the lower surface 14 of the blade 1. The envelope 3 forms the outer surface of the blade 1, and gives thus its profiled shape at dawn 1. The casing 3 also forms the foot 16 of the blade 1. In the embodiment illustrated in Figures 1 and 2, the internal part 2 has a profiled shape corresponding to the shape of the blade 1, and the envelope 3 is a thin layer which surrounds said internal part 2 following the profiled shape of said internal part 2. Such an embodiment makes it possible to obtain good cooling of the blade 1. However, the internal part 2 can have different shapes.

The bathtub 17 at the top 15 of the blade 1 comprises a bottom wall 17a which covers the internal part 2 on the top of the blade 1, and thus at least partially obstructs the network of channels formed by said internal part 2. The bottom wall 17a of the bathtub 17 makes it possible to retain the cooling flow circulating in the internal part 2, thus preventing the entire cooling flow from escaping through the top of the blade 1, which would adversely affect aerodynamic performance from dawn 1.

According to a possible variant, the bottom wall 17a comprises at least one orifice 17b which communicates with the internal part 2, in other words which opens at a first end at the top 15 of the blade 1 and which opens at the second end in a cell 21 of the internal part

2. This at least one orifice 17b is a dusting hole which makes it possible to evacuate part of the cooling flow circulating inside the blade 1 through the top 15. The number of orifice 17b is less than the number cells 21, and is preferably between 1 and 4.

The blade 1 is preferably a movable turbine blade of a turbojet engine, and even more preferably a high pressure turbine blade. Indeed, the blade 1 according to the invention makes it possible to advantageously replace the turbine blades of the state of the art, and particularly the high pressure turbine blades, which include an internal cooling circuit as well as a cooling by creation. a film of cold air around said blades of the state of the art.

The blade 1 is preferably made of a nickel-based super alloy in order to withstand the high operating temperatures of turbomachine turbines, and particularly for the high pressure turbine.

According to an advantageous variant, the blade 1 comprises cooling channels 12a at the trailing edge 12 for cooling by convection of said blade 1. These cooling channels 12a are channels perpendicular to the main axis of elongation θ distributed along the profiled part of the blade 1, which open at a first end in the internal part 2, and which open at a second end outside the blade at the trailing edge 12 of the blade 1. Preferably, the cooling channels 12a open out at the trailing edge 12a on the pressure side 14.

Furthermore, the internal part 2 of the blade 1 may include a chamber located at the top 15 of the blade, under the bottom wall 17a of the bathtub 17, which forms one end of the internal part 2. This chamber is a cavity which connects all the cells 21 of the internal part 2, so that the cooling flow which circulates through the cells 21 converges towards said chamber. Furthermore, the chamber can be connected to the cooling channels 12a in order to supply them with cooling flow. In addition, when the bottom wall 17a of the bathtub 17 comprises at least one orifice 17b for dusting, said at least one hole for dusting opens into the chamber.

Several variants of the manufacturing process are possible for manufacturing the blade 1 according to the invention. According to a first variant illustrated in Figures 3a, 3b, 3c, 3d, 4a, 4b and 5, the blade 1 is made by foundry around a ceramic core. According to a second variant illustrated in FIGS. 6 and 7, the blade 1 is produced by shaping a mixture comprising a metal powder and a plastic binder. In Figure 4a, the tub core 5 is not shown.

The cells 21 open at the foot 16 of the blade 1 in order to serve as an input to the cooling flow. To do this, as visible in FIG. 4a, the main core 4 intended to form the cells 21 protrudes from the foot 16 of the blade.

As illustrated in FIGS. 3a, 3b, 3c, 3d, 4a, 4b and 5, according to the first variant, the method of manufacturing the blade 1 comprises the following steps:

- Ell: manufacture of a main core 4 having a shape complementary to the internal part 2 of honeycomb, by a process for forming a mixture comprising a ceramic powder and a plastic binder, also called "feedstock" according to Anglo-Saxon terminology. In this step, in order to achieve the complex shape of the main core 4, the mixture comprising the ceramic powder and the plastic binder is shaped (green state), then the plastic binder is removed so that only the ceramic remains (brown state) , then the part is sintered in order to consolidate it (final part). The mixture comprising the ceramic powder and the plastic binder, or feedstock, has the properties of plastic thanks to the presence of the plastic binder, and thus the various types of additive manufacturing process for the shaping of a plastic material can be used. , such as injection (CIM for “Ceramic Injection Molding” according to English terminology), extrusion, three-dimensional CLIP printing (for “Continuous Liquid Interface Production” according to English terminology), or three-dimensional jet jet printing (or "binder jetting" according to Anglo-Saxon terminology). The plastic binder is typically removed thereafter by heating the part, for example at the start of the sintering step, or else is removed using a solvent.

- E12: manufacture of a ceramic tub core 5. The tub core 5 can be manufactured in a conventional manner, the shape of the tub core 5 not being particularly complex.

- E13: manufacture by foundry of the blade 1 around the main core 4 and the tub core 5, the main core 4 and the tub core 5 being kept separate so as to form the bottom wall 17a of the tub 17. This step is typically carried out by lost wax casting, which is a molding technique known to those skilled in the art for the manufacture of a blade. Thus, to do this, a wax model which has the shape of the blade 1 to be produced is produced around the main core 4 and the tub core 5, then a ceramic shell is produced around the wax model, the model in wax is then removed so as to obtain an empty ceramic shell with a shape complementary to Taube to be manufactured inside which the main core 4 and the tub core 5 are located, metal is poured into the shell, the the shell is then removed when the metal is solidified. In this step, the internal part 2 is produced by the metal coming into the interstices of the main core 2 so as to form the partitions delimiting the cells 21, and the casing 3 is produced by the metal coming surrounded outside the core main 5. In addition, the main core 4 and the tub core 5 being kept spaced from each other, the metal settling between said main core 4 and said tub core 5 forms the bottom wall 17a of the bath 17.

- E14: elimination of the main core 4 and of the tub core 5. The elimination of the cores 4 and 5 is typically carried out by chemical dissolution using an acid which dissolves the ceramic in order to keep only the metal. Following this step of eliminating the main core 4 and the tub core 5 Final mole 1 is obtained.

In addition, the method of manufacturing Taube 1 can also include the manufacture of a ceramic trailing edge core 6. The trailing edge core 6 is assembled with the main core 4 at the part corresponding to the trailing edge 12 of Taube 1. The trailing edge core has a shape complementary to the cooling channels 12a. Once the three cores 4, 5 and 6 are assembled, the blade 1 is obtained by casting around said cores 4, 5 and 6. The leading edge core 6 makes it possible to produce the cooling channels 12a at the leading edge 12. Finally, the cores 4, 5 and 6 are eliminated in order to obtain Taube 1 final with the internal part 2 honeycomb, the bathtub 17 at the top 15, and the cooling channels 12a at the leading edge 12 .

FIGS. 3a to 3e illustrate variants of the main core 4, of the tub core 5, as well as of the trailing edge core 6. In FIGS. 3a, 3b and 3e the tub core 5 is not shown in order to better illustrated the main core 4. FIG. 3e illustrates the variant according to which Taube 1 comprises a chamber connecting the cells 21 under the wall 17a of the bath 17. To do this, a ceramic plate is located at the upper end of the main core 4 so as to connect the various ceramic rods which are intended to form the cells 21. The plate can also be connected to the trailing edge core

6.

According to the second manufacturing variant, the blade 1 is not obtained by foundry but by shaping a mixture comprising a metal powder and a plastic binder, also called "feedstock" according to English terminology.

This second manufacturing variant includes several possible implementations. In particular, the second manufacturing variant comprises a first implementation in which the internal part 2, a first part of the casing 3 forming the upper surface 13 of the blade 1, and a second part of the casing 3 forming the 'intrados 14 dawn 1 are manufactured separately and then assembled together. The second manufacturing variant also includes a second possible implementation in which the casing 3 is overmolded around the internal part 2.

According to the first possible implementation illustrated in FIG. 6, the method of manufacturing the blade 1 comprises the following steps:

- E21: manufacture of the internal part 2 by shaping a mixture, or feedstock, comprising a metal powder and a plastic binder, and elimination of the plastic binder. The feedstock having the properties of plastic thanks to the presence of the plastic binder, the different types of additive manufacturing process for the shaping of a plastic material can be used for the manufacture of the internal part 2. For example, the part internal 2 can be produced by injection (MIM for “Metal Injection Molding” according to English terminology), by extrusion, by three-dimensional CLIP printing (for “Continuous Liquid Interface Production” according to English terminology), or by three-dimensional printing with binder jet (or "binder jetting" according to English terminology). The plastic binder is then removed, for example by being melted or with a solvent.

- E22: manufacture of the first part of the envelope 3 intended to surround the internal part 2 forming the upper surface 13 of the blade 1 by forming a mixture, or feedstock, comprising a metal powder and a plastic binder , and elimination of the plastic binder. The first part of the envelope 3 can be manufactured in the same way as the internal part 2.

The plastic binder is then removed, for example by being melted or with a solvent.

- E23: manufacture of a second part of the casing 3 intended to surround the internal part 2 forming the lower surface 14 of the vane 1 by forming a mixture comprising a metal powder and a plastic binder, and elimination plastic binder. The second part of the envelope 3 can be made in the same way as the first part of the envelope 3 and the internal part 2. The plastic binder is then removed, for example by being melted or with a solvent.

- E24: assembly of the first part of the casing 3 and the second part of the casing 3 around the internal part 2 so as to form the lower surface 14 and the upper surface 13 of the vane 1 and sintering of assembly. The internal part 2, the first part of the casing 3, and the second part of the casing 3 are therefore assembled in the brown state, then are sintered in order to pass into their final state.

- E25: assembly of the bathtub 17 at the top 15 of the dawn 1. The bathtub 17 can be manufactured apart from the rest of the dawn in a conventional manner.

Furthermore, according to a possible variant, the method does not include a step E25 of assembling the bathtub 17, the bathtub 17 being formed by assembling the first part of the casing 3 and the second part of the envelope 3.

The feedstocks used for manufacturing the internal part 2 and the two parts of the casing 3 can be identical. For the manufacture of blade 1 made of nickel-based super alloy, the metal powder used is made of nickel super alloy.

According to the second possible implementation of the second manufacturing variant illustrated in FIGS. 7 and 9a-9c, the method of manufacturing the blade 1 comprises the following steps:

- Ε2Γ: manufacture of the internal part by shaping a mixture, or feedstock, comprising a metal powder and first plastic binder. The internal honeycomb part 2 as illustrated in FIG. 9a is obtained.

- E22 ': overmolding of the envelope 3 around the internal part 2 with a mixture comprising a metal powder and a second plastic binder, the first plastic binder having a melting temperature higher than the second plastic binder. The fact that the first plastic binder has a higher melting temperature than the second plastic binder means that the first plastic binder is not removed during the molding operation of the casing 3 around the internal part 2. As illustrated in the FIG. 9b, the internal part 2 is placed in a mold 7, here composed of two half-molds 71, which defines a housing 8 inside which said internal part 2 is installed for overmolding. The housing 8 of the mold 7 has the shape of the vane 1. Then, once the internal part 2 is installed in the housing 8 of the mold 7, as illustrated in FIG. 9c, the mixture comprising the metal powder and the second plastic binder is injected into said housing 8 in order to form the envelope 3.

- E23 ': elimination of the first plastic binder and of the second plastic binder, and sintering. This step is for example carried out by heating the part inside the mold 7.

The bathtub 17 is then assembled at the top of the part obtained after sintering, so as to obtain the final blade 1. The bathtub 17 can be obtained in a conventional manner separately from the rest of the blade 1. The bathtub 17 can also be formed with the casing 3.

According to another possible solution illustrated in FIGS. 8 and 9a9c, the manufacturing process comprises the following steps:

- E21: manufacture of the internal part 21 by shaping a mixture comprising a metal powder and first plastic binder. This step is similar to step Ε2Γ of the implementation of the method illustrated in FIG. 6. The internal part 2 in honeycomb as illustrated in FIG. 9a is obtained.

- E22: elimination of the first plastic binder. The first plastic binder can for example be removed by being melted, or else by a solvent.

- E23: overmolding of the envelope 3 around the internal part with a mixture comprising a metallic powder and a second plastic binder. In this solution, it is not necessary for the second plastic binder to have a melting temperature lower than the first plastic binder because the first plastic binder has already been removed, the internal part 21 is in the brown state. As indicated previously, the overmolding operation is illustrated in FIGS. 9b and 9c.

- E24: elimination of the second plastic binder, and sintering. Here again, these operations can be carried out by heating the part in the mold 7.

The bathtub 17 is then assembled at the top of the part obtained after sintering, so as to obtain the final blade 1. The bathtub 17 can be obtained in a conventional manner separately from the rest of the blade 1. The bathtub 17 can also be formed with the casing 3.

In order not to fill the cells 21 of the internal part 2 of the mixture comprising the metal powder and the second plastic binder during step E22 'or E23 of overmolding the envelope 3, a possible solution consists in placing a strip in plastic around the internal part 2 before the overmolding operation. The plastic strip thus prevents the feedstock of the envelope 3 from entering inside the cells 21. The plastic strip is then removed with the second plastic binder, and good cohesion between the internal part 2 and the envelope 3 is ensured. by sintering.

Another solution to prevent the cells 21 of the internal part 2 from being filled by the feedstock of the envelope 3 consists in filling said cells 21 by injecting a plastic material before step E22 'or E23 of overmolding, said plastic material comprising a melting temperature higher than the second plastic binder. After the overmolding step E22 ′ or E23, the plastic material is removed with the second plastic binder, and good cohesion between the internal part 2 and the casing 3 is ensured by sintering. The plastic material may for example be the first plastic binder used for the manufacture of the internal part 2.

Claims (14)

1. Dawn (1) of a turbomachine comprising an upper surface (13), a lower surface (14), a foot (16), and a top (15), characterized in that said blade (1) comprises an internal part (2) honeycomb formed by a plurality of cells (21) directed along a main axis of elongation (Θ) of the blade (1) and which open at the foot (16) of the blade (1), said blade (1) also comprising a casing (3) surrounding the internal honeycomb part (2) along the upper surface (13) and the lower surface (14), as well as a bath (17) comprising a bottom wall (17a) covering the internal honeycomb part (2) on the top (15) of the blade (1). 2. Dawn (1) according to claim 1, in which cooling channels (12a) are formed at a trailing edge (12) of the blade (1). 3. Dawn (1) according to any one of claims 1 to 2, in which the bottom wall (17a) of the bathtub (17) comprises at least one orifice (17b) communicating with the internal part (2), the number of orifice formed in the bottom wall of the bath (17) being less than the number of cells (21) of said internal part (2). 4. Dawn (1) according to any one of claims 1 to 3, wherein said blade (1) is made of nickel-based super alloy. 5. Turbomachine comprising a blade (1) according to any one of claims 1 to 4. 6. Turbomachine according to claim 5, in which a high pressure turbine comprises a blade (1) according to any one of claims 1 to 4. 7. A method of manufacturing a blade (1) according to any one of claims 1 to 4, comprising the following steps: - (Ell): manufacture of a main ceramic core (4) having a shape complementary to the internal part (2) of honeycomb, by a process for forming a mixture comprising a ceramic powder and a plastic binder; - (E12): manufacture of a ceramic tub core (5); - (E13): manufacture by foundry of the vane (1) around the main core (4) and the tub core (5), the main core (4) and the tub core (5) being kept separate forming the bottom wall (17a) of the bathtub (17); - (E14): elimination of the main core (4) and the tub core (5). 8. A method of manufacturing a blade according to claim 7, in which a ceramic trailing edge core (6) is manufactured and is assembled with the main core (4) at the part corresponding to the trailing edge ( 12) of the blade (1), the trailing edge core (6) then being eliminated with the main core (4) and the tub core (5). 9. A method of manufacturing a blade (1) according to any one of claims 1 to 4, wherein the blade (1) is manufactured by a method of forming a mixture comprising a metal powder and a plastic binder. 10. The manufacturing method according to claim 9, comprising the following steps: - (E21): manufacture of the internal part (2) by forming a mixture comprising a metal powder and a plastic binder, and elimination of the plastic binder; - (E22): manufacture of a first part of the envelope (3) intended to surround the internal part (2) forming the upper surface (13) of the blade (1) by shaping a mixture comprising a metal powder and a plastic binder, and removal of the plastic binder; - (E23): manufacture of a second part of the casing (3) intended to surround the internal part (2) forming the lower surface (14) of the blade (1) by forming a mixture comprising a metal powder and a plastic binder, and removal of the plastic binder; - (E24): assembly of the first part of the casing (3) and the second part of the casing (3) around the internal part (2) so as to form the lower surface (14) and the upper surfaces (13) of the blade (1) and sintering of the assembly; - (E25): assembly of a bathtub (17) at the top (15) of the blade (1). 11. Method according to claim 9, comprising the following steps: - (Ε2Γ): manufacture of the internal part (2) by shaping a mixture comprising a metal powder and first plastic binder; - (E22 ⁷ ): overmolding of the envelope (3) around the internal part (2) with a mixture comprising a metal powder and a second plastic binder, the first plastic binder having a melting temperature higher than the second plastic binder; - (E23 '): elimination of the first plastic binder and the second plastic binder, and sintering. 12. Method according to claim 9, comprising the following steps: - (E21): manufacture of the internal part (2) by shaping a mixture comprising a metal powder and first plastic binder; - (E22): elimination of the first plastic binder; - (E23): overmolding of the envelope (3) around the internal part (2) with a mixture comprising a metal powder and a second plastic binder; - (E24): elimination of the second plastic binder, and sintering. 13. The method of claim 11 or claim 12, wherein the method comprises the following steps: - provision of a plastic strip around the internal part (2) before the envelope is overmolded around the internal part (2), the plastic strip having a melting temperature higher than the melting temperature of the second plastic binder used for the manufacture of the envelope (3); - elimination of the strip after overmolding of the envelope (3) around the internal part (2). 14. The method of claim 11 or claim 12, wherein the method comprises the following steps: - injection of a plastic material into the cells (21) of the internal part (2), the plastic material having a melting temperature 5 higher than the melting temperature of the second plastic binder used for the manufacture of the envelope (3); - elimination of the plastic material after overmolding of the envelope (3) around the internal part (2).