Method for manufacturing a turbomachine blade

Abstract

The method for manufacturing a blade (32) of a turbomachine (100) comprises: - manufacturing a part (4) comprising an air flow path zone (10) and a layer (20) covering the zone, the layer having cavities (21) forming a periodic pattern, the manufacture taking place by injecting a mixture comprising a binder and a powder; - removing a larger part of the binder from the part; - sintering the part; and - removing the layer (20) from the part to obtain the blade (32).

Description

[0001] Manufacturing process of a turbomachine blade

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the manufacture of turbomachine blades.

[0004] STATE OF THE ART

[0005] Metal injection molding (MIM) is a technology used to manufacture metal products. This technology can meet the needs of high production rates while maintaining good repeatability and reproducibility.

[0006] It is an injection molding process using a mixture of metal powder and polymer binder. This mixture, forming a granulate, called "feedstock," is extruded and then cut into flakes or pellets for use in an injection molding machine.

[0007] After injection, we obtain a part called a "green", held in place by the binder. This binder is then removed during the so-called debinding step, which can be carried out in different ways (aqueous, thermal or chemical), which gives a part called "brown".

[0008] This piece, with almost all of its binder removed, is very fragile because it is composed of approximately 40% air and is held together only by the remnants of the binder. The brown piece is finally sintered, a step during which it is subjected to a temperature close to the melting point of the powder. This temperature allows the grains to bond together to create a solid.

[0009] After this step, we obtain a "grey" part, composed of the powder material only and having shrunk compared to the volume of the casting due to the spaces left by the binder. Depending on the process, parts with a density of 95% to 99.5% can be obtained for different applications. The part is then finished.

[0010] This technique allows for the creation of complex shapes with excellent surface finish and fine tolerances. More cost-effective for complex shapes, metal powder injection molding allows for the production of medium and large series of small parts for a wide market. As part of the family of replication techniques, it is very economical in terms of raw materials (for the powder part). It does not create waste and does not use oil.

[0011] However, the shrinkage of the part mentioned above makes it difficult to apply this technique to the manufacture of turbomachine blades. In fact, shrinkage of up to 15% of one dimension of the blade is observed. However, it is important to precisely control the dimensions of this type of part. In addition, the thermal variations to which the blade is subjected during manufacture can cause deformations or cracks. This is all the more sensitive since the blades are generally asymmetrical and have thicknesses in certain places that are up to 3.5 times greater than the thickness in another place on the blade.

[0012] One aim of the invention is therefore to make the manufacture of turbomachine blades easier and more reliable, in particular by injecting metal powder.

[0013] STATEMENT OF THE INVENTION

[0014] For this purpose, the invention provides a method for manufacturing a turbomachine blade, in which:

[0015] - a part is manufactured comprising an air vein zone and a layer covering the zone, the layer having cavities forming a periodic pattern, the manufacturing taking place by injection of a mixture comprising a binder and a powder;

[0016] - more of the binder is removed from the part;

[0017] - the part is sintered; and

[0018] - the layer of the part is removed to obtain the blade.

[0019] The layer thus prevents the appearance of cracks linked to the injection step, but also avoids the appearance of deformation phenomena such as sagging, twisting, bending, buckling and mechanical stresses linked to the sintering and machining steps. The invention thus allows the manufacture of elongated parts of complex geometry, particularly asymmetrical, and to control the dimensions of the part. It allows high-speed production. Providing cavities in the layer has the advantage of saving material and therefore reducing manufacturing costs. Finally, the cavities reduce the risk of tearing during demolding.

[0020] The manufacturing method according to the invention may also have at least one of the following characteristics:

[0021] - the cavities are arranged in a staggered pattern;

[0022] - the cavities form at least one line of identical cavities, the line being parallel to a length of the air vein zone;

[0023] - the cavities form at least a first line and a second line, those of the first line being identical to each other, those of the second line being identical to each other, finally those of the first line being different from the cavities of the second line;

[0024] - the cavities of the first line have a profile presenting a different orientation from the cavities of the second line;

[0025] - each cavity has a closed profile;

[0026] - each cavity has a profile which presents at least one axis of symmetry;

[0027] - each cavity has a hexagonal profile;

[0028] - each cavity is configured so that the cavity can be described by a parametric surface excluding any singular point;

[0029] - each cavity has lateral faces having connection zones with a bottom of the cavity and with an external face of the layer, the connection zones having a fillet having a radius between 0.2 mm and 1 mm;

[0030] - the cavities are arranged so that a distance between two adjacent cavities is greater than or equal to 3 mm, for example greater than or equal to

[0031] 6 mm; and

[0032] - the cavities extend into a larger part of the layer.

[0033] The cavities can be expected to extend over the entire thickness of the layer.

[0034] The layer can be expected to extend over the entire air vein area.

[0035] According to one embodiment, the layer covers an intrados of the air vein zone. It can be provided that the thickness of the layer is uniform.

[0036] This promotes uniform debinding of the part.

[0037] According to one embodiment, the layer is placed in direct contact with a support, in particular during the sintering step.

[0038] The layer therefore serves here as support integrated into the part to prevent its deformation, in particular its sagging, during sintering.

[0039] It can be provided that the part comprises a foot, the layer forming a plane merged with an edge of the foot.

[0040] According to one embodiment, at least one machining operation is carried out so as to standardize a thickness of the layer.

[0041] The layer therefore serves as reinforcement during machining by stiffening the blade exposed to significant deformations during the roughing operation involving high cutting forces.

[0042] According to one embodiment, the layer and an extrados face are machined in several passes, each having a depth of between 0.2 mm and 1 mm and / or a scanning pitch of between 0.1 mm and 10 mm.

[0043] These machining parameters during the finishing operation make it possible to respect the geometric specificities in accordance with the aeronautics field and the complexity of the profile shape of the air vein zone.

[0044] According to the invention, a part is also provided comprising:

[0045] - a turbomachine blade, the blade comprising an air vein zone, and

[0046] - a separate layer of the blade, extending over the air vein zone and presenting cavities forming a periodic pattern.

[0047] This part constitutes the intermediate product obtained during the implementation of the process of the invention, before the removal of the layer.

[0048] According to one embodiment of this part, the material used is an alloy of titanium and aluminum. Also provided according to the invention is a turbomachine blade, in particular an aircraft turboshaft engine blade, the blade comprising an airflow zone, the blade resulting from the implementation of a method according to the invention.

[0049] Such a blade may have macroscopically a shape and dimensions identical to those of a blade manufactured using a prior art method. However, it differs therefrom in its microscopic structure. Thus, it has an average grain size larger than that of the blade obtained by a prior art method and it offers better creep resistance.

[0050] The invention further provides a turbomachine comprising at least one blade according to the invention.

[0051] DESCRIPTION OF FIGURES

[0052] We will now present an embodiment of the invention by way of non-limiting example with the support of the drawings in which: Figures 1 and 2 are perspective views of the intrados side of an intermediate part obtained in an embodiment of the method of the invention; Figure 3 is a larger scale view of the intrados side of the part of Figures 1 and 2; Figures 4 and 5 are views of the same part on the extrados side; Figures 6 and 7 illustrate the positioning and holding in position of the intermediate part in its part holder for the first machining phase; Figures 8 and 9 illustrate the path taken by the cutter for the first machining phase; Figures 10 and 11 illustrate the positioning and holding in position of the intermediate part in its part holder for the second machining phase; Figures 12 and 13 illustrate the path taken by the cutter for the second machining phase;Figure 1 is a view similar to Figures 4 and 5 showing the blade obtained from this intermediate part; and Figure 15 is a half-sectional view of an aircraft turbojet incorporating such a blade. We will present an embodiment of the manufacturing method according to the invention for producing a turbomachine blade.;

[0053] In a first step, an intermediate part 4 is manufactured comprising a blade. This part is illustrated in Figures 1 to 5.

[0054] The part and the blade thus comprise a foot 6, a heel 8 and a blade or air vein zone 10 extending between the foot and the heel.

[0055] The air vein zone 10, visible in figures 2 and 4, has two main faces, namely a lower surface face 12 visible in figure 3 and an upper surface face 14, visible in figures 4, 5 and 14. The two faces are each delimited by a leading edge 16 and a trailing edge 18 forming the two longitudinal edges of the blade. Each main face 12, 14 extends from the root to the heel.

[0056] As illustrated in Figure 2, the part 4 comprises a layer 20 extending over the air vein zone, in this case over the intrados face 12. The layer has a uniform thickness along the entire length of the layer, the minimum value of which is 2 mm at the heel, in the present example.

[0057] On the cavities

[0058] The layer has cavities 22, visible in Figures 1 to 3, open on the side of an external face 21 of the layer 20 opposite the air stream zone 10. Each cavity extends over the entire thickness of the layer. The cavities 22 extend in a larger part of the layer 20 and the latter extends over the entire air stream zone 10.

[0059] This layer forms a plane merged with the edge of foot 26 visible in figure 1.

[0060] In order to facilitate the manufacture of the mold and the injection step, each cavity 22 has a geometry that can be described by a parameterized surface, excluding any singular point, the profile of which is closed and has at least one axis of symmetry. In one embodiment illustrated in Figure 3, the cavities 22 have a hexagonal shape whose vertices are rounded. It can be envisaged in another embodiment that the cavities 22 have a profile having a cylindrical or elliptical shape.

[0061] The cavities 22 here form a periodic pattern. This means that the pattern is reproduced identically along one or more lines in a plane parallel to a longitudinal direction of the layer and parallel to the width of the layer.

[0062] The cavities 22 form in this case three lines of identical cavities 33, 34, 35, visible in figure 1, each line being parallel to a length of the air stream zone 28. More precisely, the cavities 22 form three lines, namely first, second and third lines. The cavities of the first line 33 are identical to each other. The cavities of the third line 35 are identical to each other and to those of the first line 33. In addition, the cavities of these two lines all have the same orientation. In this case, one side of the hexagon is parallel to the leading 16 and trailing 18 edges. They are therefore the image of each other by a translation.

[0063] The cavities of the second line 34 are identical to each other and different from the cavities of the first and third lines, in this case larger than these. The cavities of the second line all have the same orientation. They are therefore the image of each other by a translation. But they do not have the same orientation as those of the other two lines. In this case, two edges of the hexagon are parallel to the leading and trailing edges. They are the image of the cavities of the first and third lines by an indirect similarity.

[0064] The cavities are arranged in a staggered pattern.

[0065] To limit the risks of tearing and cracking during the ejection of the intermediate part 4 from the mold, it is preferable that two adjacent cavities 22 are at least 3 mm apart, a value taken for the example illustrated in figure 3.

[0066] Each cavity 22 has six lateral faces having connection zones with a bottom of the cavity and with the external face 21 of the layer 20, the connection zones having a fillet 30 having a radius between 0.2 mm and 1 mm. The fillet is convex at the external face and concave at the bottom. On the steps of the method

[0067] Obtaining the intermediate part

[0068] In this case, the manufacturing process involves the injection of metal powder.

[0069] In a first step, an injection molding is carried out from a mixture of metal powder and polymer binder. The metal powder here is an alloy of titanium and aluminum such as Ti-48Al-2Cr-2Nb (in atomic %), commonly called TiÀl 48-2-2. This produces a rough version of the part in Figures 1 to 3, namely the blade equipped with the layer. This is the "green" version. In this rough version, the powder is held in place by the binder.

[0070] This binder is then removed during the debinding operation, resulting in the "brown" part. In this part, almost all of the binder has been removed and it is composed of approximately 40% air, and is only bound by the remains of the binder.

[0071] It is then sintered, a step during which it is subjected to a temperature close to the melting point of the powder, for example above 1200°C.

[0072] After this operation, we obtain a “grey” part, composed of the powder material only and having shrunk in relation to the volume of the casting due to the spaces left by the binder.

[0073] This part 4 is manufactured in one block. During the debinding and sintering operations, the part is placed in direct contact with a flat support, the external face 21 of the layer 20 being located in the lower part and the extrados face 14 facing upwards. This layer is therefore in contact with the flat support. The latter provides local support for the air stream zone 10.

[0074] This layer forms a support but also a stiffener which helps preserve the shape of the part and its integrity during these operations, in particular during sintering and then cooling.

[0075] At the end of this first manufacturing phase, a part 4 is therefore obtained forming an intermediate product consisting of the blade 34 and the layer 20 as illustrated in figures 1 to 5. Machining

[0076] Then, the layer of the air vein zone is removed by two machining phases 200 and 300.

[0077] For this purpose, the part is positioned and held in position in a part holder 202 for the machining phase 200. Figure 6 shows a front view of a section of the intermediate part taken in its part holder 202, and Figure 7 the top view of the part in the same configuration. The external face 21 of the layer 20 is placed in direct support on a table 208. Thus, choosing as a reference for positioning the external face of the layer, covering 80% of the intermediate part, makes it possible to avoid dispersions linked to possible shape defects generated by the process and provides robustness to the clamping. Three point contacts 204 which can be materialized by pins or other supports are placed, namely one against the foot 6 in the longitudinal direction and two against the leading edge 16 in the width direction.In other embodiments, the first stop can be placed at the heel 8, the intrados 14 or the extrados 16 and the other two against the trailing edge 18. Two flanges 206 placed at the extrados 14 complete the rigid holding in position of the intermediate part on the table along the width and from above against the extrados face. The number of direct contacts of the flange on the extrados can be unique, or greater than or equal to two. The table, the stops and the flanges form the workpiece holder. In addition, this workpiece holder will be cleared on the foot 6 and heel 8 side in order to free up the accessibility of the milling tools to all these areas.

[0078] In this configuration, the machining of foot 6 and heel 8 is then carried out, which will serve as a reference for installation and a clamping zone for the second machining phase.

[0079] The machining path for phase 200 is illustrated in a top view of the intermediate part in Figure 8, and in a front view of a section of the intermediate part on the two parts of Figure 9. The machine tool used comprises five or six axes and the machining program follows the following operations: a. a face milling cutter 210 comes to dress at the level of the foot 6 then the heel 8 a first plane on the extrados side 14, b. the workpiece holder 202 rotates, and c. the second plane is dressed at the level of the heel 8 then the foot 6 on the intrados profile side 12.

[0080] In another embodiment, the machine tool only comprises three axes, which does not allow the rotation of the workpiece holder 202. Thus, to be able to machine on both sides, the workpiece must be disassembled and turned over. An additional machining phase is therefore to be provided, separating operations (1 a) and (1 c).

[0081] Then, the part is positioned and held in position in another part holder 302 for the second machining phase 300 as illustrated in Figure 10, representing the front view of a section of the intermediate part taken in its part holder 302, and Figure 11, representing the top view of the part taken in its part holder 302. The foot 6 and the heel 8 are placed in direct contact with the table 308, forming a sufficiently precise contact zone to respect the geometric tolerances during adjustment and clamping as well as the compatibility of the cutting forces necessary for the second machining phase 300. Three point contacts 304 which can be materialized by pins or other supports are placed, namely two against the foot 6 and one against the heel 8. Two flanges 306 placed at the level of the foot 6 and the heel 8 ensure that the intermediate part is held in a rigid position.This time the rigid support takes place exclusively by the foot and the heel, leaving the air vein zone 10 accessible for machining, the workpiece holder being clear in this zone.

[0082] The machining path for phase 300 is illustrated in a top view of the intermediate part in Figure 12, and in a front view of a section of the intermediate part in Figure 13. The machine tool used comprises five or six axes and the machining program follows the following operations:

[0083] 2a. a two-sided 310 type milling cutter carries out a roughing operation on layer 20 of the intermediate part to bring this face to a thickness identical to that on the extrados side 14 which may be 2 mm,

[0084] 2b. The milling cutter carries out a finishing operation on this same intrados face 16 progressing along the part by sweeping movements in spirals or helicals until the final profile or after 2 to 10 successive passes, 2c. the part holder 302 rotates, and

[0085] 2d. The cutter carries out a finishing operation on the extrados face 14 progressing along the part by sweeping movements in spirals or helicals until the final profile or can be done in 2 to 10 successive passes.

[0086] This order of operations makes it possible to carry out the roughing operation with the maximum amount of material, thus sufficiently stiffening the intermediate part subjected to significant cutting forces linked to the large volume of material in layer 20 and the discontinuity of the layer due to the presence of cavities 22.

[0087] The passes preferably produce a material removal value between 0.2 mm and 1 mm and the sweep pitch has a value between 0.1 mm and 10 mm depending on the roughness, the desired peak heights and the geometry of the milling tools.

[0088] In another embodiment, the machine tool only comprises three axes, which does not allow the rotation of the workpiece holder 302. Thus, to be able to machine on both sides, the workpiece must be disassembled and turned over. An additional machining phase is therefore to be provided, separating operations (2a), (2b) from operation (2c).

[0089] The cutting tools of the 210, 310 cutters used may have the following characteristics:

[0090] - the material is a “micro grain” type carbide in a single block or in an attached plate;

[0091] - a coating of any type is deposited; and

[0092] - the cutting angle is between -5° and +10°.

[0093] Cutting speeds can be expected to be between 20 m / mm and 100 m / mm and feed rates between 0.01 mm and 1 mm.

[0094] Soluble or whole oils can be used under a pressure ranging from 5 bars to 150 bars (one bar being worth 10 5 Pa).

[0095] A micro-spray lubricant, with CO2 or nitrogen, can also be used. This then produces a part consisting of the single blade 32 illustrated in Figure 14. The blade comprises the root 6, the heel 8 and the airflow zone 10. The two intrados 12 and extrados 14 faces are smooth.

[0096] On the blade 32, the air stream zone 10 has a thickness which is less than that of the root 6 and the heel 8. This difference can have a significant impact during the cooling and shrinkage of the part in the absence of the layer 20. The layer and its cavities 22 are arranged and dimensioned as explained above in order to reduce this ratio. Overall, taking into account the location of the massiveness zones of the part 4 makes it possible to distribute the material during the design in order to avoid excessively large differences in thickness over the entire part.

[0097] Furthermore, in the absence of support by the layer 20, the airflow zone 10 would collapse during manufacturing. This is why the layer is provided in excess of the airflow zone, in order to support it. The periodic pattern of the cavities 22 makes it possible to reduce the risks of various types of deformation to which the blade would otherwise be exposed during manufacturing while minimizing costs.

[0098] Furthermore, care should preferably be taken to take into account in the design of the part to be manufactured and forming the blade-layer assembly the injection constraints and the phenomena of segregation, core porosity and internal stress generated and detected during sintering.

[0099] In the present example, the blade 32 is intended to be part of an aircraft turbojet 100 forming here a double-flow and double-spool turbomachine like that illustrated in figure 15. The turbomachine has a main axis XX which serves as the axis of rotation of the rotor relative to the stator.

[0100] It comprises from upstream to downstream, therefore from left to right in Figure 15, a fan 2, a low-pressure compressor 5, an intermediate-pressure compressor, a high-pressure compressor 7, a combustion chamber 9, a high-pressure turbine 11 and a low-pressure turbine 13. These elements, with the exception of the fan, form a central part of the turbojet engine. Their mobile parts rotating around the axis XX form the rotor. The high-pressure compressor 7, the combustion chamber 9 and the high-pressure turbine 11 form a high-pressure body, which together with the low-pressure compressor 5 and the low-pressure turbine 13 define a main airflow vein. A nacelle surrounds the fan 2 and the central part so as to form a fan compartment and to define a secondary airflow vein.

[0101] The turbines 11, 13 comprise blades 32 manufactured using the invention.

[0102] The invention is applicable to other manufacturing technologies, for example feedstock printing and feedstock compaction.

[0103] Manufacturing could also take place using binder jetting. This is an additive manufacturing method that works by spraying binder onto powder. An automated roller spreads a thin layer of powder onto a build plate. A print head applies a liquid binder to the powder, creating a layer of the object. Then, the print platform carrying the plate lowers slightly to allow the addition of a new layer of powder. The process is repeated until the object is created. The excess powder is then vacuumed and the object is dusted off using compressed air. The printed part is then placed in an oven for baking or sintering. Finally, a finishing treatment can improve the condition of the printed part. As before, the layer of the intermediate product thus produced is then removed to obtain the blade itself.

[0104] The invention relates to the manufacture of metal parts, in particular by the process of injecting a mixture comprising a binder and a powder, and can be used in all technical fields.

Claims

Demands 1. Method for manufacturing a turbine blade (32) of a turbomachine (100), wherein: - a part (4) is manufactured comprising an air vein zone (10) and a layer (20) covering the zone, the layer having cavities (22) forming a periodic pattern, the manufacture taking place by injection of a mixture comprising a binder and a powder; - a larger part of the binder is removed from the piece; - the part is sintered; and - we remove layer (20) of the part to obtain the blade (32).

2. Method according to the preceding claim in which the cavities (22) are opened on an external face (21) of the layer (20) opposite the air vein zone (10).

3. A method according to at least one of the preceding claims in which the cavities (22) are arranged in a staggered pattern.

4. A method according to at least one of the preceding claims wherein the cavities (22) form at least one line of identical cavities, the line being parallel to a length of the air vein zone (10).

5. A method according to at least one of the preceding claims wherein the cavities (22) form at least a first line and a second line, the cavities of the first line being identical to each other, the cavities of the second line being identical to each other, the cavities of the first line being different from the cavities of the second line.

6. Method according to the preceding claim wherein the cavities (22) of the first row have a profile having a different orientation from the cavities of the second row.

7. A method according to at least one of the preceding claims in which each cavity (22) has a closed profile.

8. A method according to at least one of the preceding claims in which each cavity (22) has a profile which has at least one axis of symmetry.

9. A method according to at least one of the preceding claims in which each cavity (22) has a hexagonal profile.

10. A method according to at least one of the preceding claims in which each cavity (22) is configured so that the cavity can be described by a parameterized surface excluding any singular point.

11. A method according to at least one of the preceding claims in which each cavity (22) has lateral faces having connection zones with a bottom of the cavity and with an external face of the layer, the connection zones having a fillet having a radius between 0.2 mm and 1 mm.

12. A method according to at least one of the preceding claims wherein the cavities (22) are arranged so that a distance between two adjacent cavities is greater than or equal to 3 mm, for example greater than or equal to 6 mm.

13. A method according to at least one of the preceding claims wherein the cavities (22) extend into a greater part of the layer (20).

14. A method according to at least one of the preceding claims in which the cavities (22) extend throughout a thickness of the layer (20).

15. A method according to at least one of the preceding claims wherein the layer (20) extends over the entire air vein area (10).

16. A method according to at least one of the preceding claims wherein the layer covers an intrados of the air vein area (12).

17. A method according to at least one of the preceding claims wherein a thickness of the layer (20) is uniform.

18. A method according to at least one of the preceding claims in which the layer (20) is placed in direct contact with a support, in particular during the sintering step.

19. Method according to any one of the preceding claims, the part comprising a foot (6), the layer (20) forming a plane coinciding with an edge of the foot (26).

20. A method according to at least one of the preceding claims in which at least one machining operation is carried out so as to standardize a thickness of the layer (20).

21. A method according to at least one of the preceding claims in which the layer (20) and an extrados face (14) are machined in several passes, each having a depth between 0.2 mm and 1 mm.

22. A method according to at least one of the preceding claims in which the layer (20) and an extrados face (14) are machined in several passes, each having a sweep pitch between 0.1 mm and 10 mm.

23. Item (4) comprising: - a turbomachine blade (32), the blade comprising an air duct zone (10), and - a layer (20) distinct from the dawn, extending over the air vein area (10) and having cavities (22) forming a periodic pattern.

24. Turbomachine blade (32), in particular aircraft turbomachine blade (100), the blade comprising an air duct zone (10) and resulting from the implementation of a method according to at least one of claims 1 to 22.

25. Turbomachine (100) comprising at least one blade (32) according to the preceding claim.

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