Method for producing a hollow blade

Abstract

The invention relates to a method for producing a blade (8), the method comprising the following steps: (d) perforating the outer wall of the blade (8) using electrical discharge machining to form cooling channels (17), characterised in that: - in step (a), the blade (8') comprises cooling slots (16) that extend from the inner wall (13) towards the outer wall, each having a first end (16a) opening into the internal cavity (14) and a second end (16b) located between the inner wall (13) and the outer wall; and - in step (d), each perforation is made from the outer wall to the second end (16b) of each cooling slot (16), such that each cooling channel (17) opens into a respective cooling slot (16).

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURING A HOLLOW VANE

[0003] Technical field of the invention

[0004] The invention relates to the field of methods for manufacturing hollow blades for turbomachines, particularly aircraft.

[0005] The invention relates in particular to the field of manufacturing processes for hollow blades, comprising a step of drilling by electro-erosion machining, also known by the English acronym EDM (for “electrical discharge machining”).

[0006] Technical background

[0007] An aircraft turbomachine, such as a turbojet, typically comprises, from upstream to downstream in the direction of gas flow, a 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.

[0008] The blower allows the suction of an air flow divided into a primary flow and a secondary flow. The primary flow passes through a primary vein of the turbomachine while the secondary flow is directed towards a secondary vein surrounding the primary vein.

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

[0010] Turbines are typically equipped with blades regularly distributed around a rotating wheel about the longitudinal axis. A blade extends radially between a root and a tip. A blade also includes a blade connected to the root by a platform, for example. The blade has an aerodynamic shape and typically includes an outer wall comprising a pressure face and an extrados face connected by a leading edge and a trailing edge.

[0011] Because high-pressure turbine blades are located downstream of the combustion chamber, they are subjected to high temperatures. Therefore, these blades are typically made of metallic or composite materials, particularly ceramic matrix composites (CMCs). These materials have the advantage of being able to withstand high temperatures. However, such blades can be subjected to temperatures higher than those that metallic or ceramic matrix composite materials can withstand.

[0012] In this context, it has been proposed to equip the blades with a cooling system. The cooling system comprises a cooling circuit arranged inside the blades and allowing the passage of air from the compressors inside the blades. The cooling circuit comprises internal cavities delimited by an internal wall of the blade and which allow internal cooling of the blades. In addition, it has been proposed to drill the external wall of the blades to form cooling passages opening into the internal cavities to create an air film around the blade and optimize the cooling of the blades. The passages are typically made by electroerosion drilling after the blade has been manufactured using an electroerosion device. Indeed, electroerosion processes are the only ones compatible with the complex geometries of the blades and to guarantee material health during drilling.

[0013] The EDM device typically comprises at least one electrode that is either moved a predetermined distance or moved to a given condition. Once this distance or condition is reached, the drilling depth is considered to have been reached. It is particularly important to control this distance or condition. Indeed, if these parameters are incorrect, then there is a risk that the surface of the internal cavity opposite the drilled surface will be impacted by the electrodes or even pierced. Such an impact can generate mechanical defects on the blade or even its rupture and aerothermal defects by disturbing the air flow in the blade.

[0014] With the aim of further improving blade cooling, it is now proposed to significantly reduce the thickness of the internal cavities in order to maximize internal heat exchange. However, current EDM drilling processes cannot guarantee impact-free drilling given the very small thickness of the cavities. Also, still with the aim of improving blade cooling, the cooling passages have a complex geometry that is difficult to envisage using EDM drilling processes.

[0015] In this context, there is a need to provide a method for manufacturing a hollow blade having thin internal cavities, allowing the creation of cooling passages of complex geometry.

[0016] Summary of the invention

[0017] To this end, the invention proposes a method of manufacturing a hollow blade for a turbomachine, the method comprising the following steps:

[0018] (a) manufacturing a blade comprising: an outer wall comprising a leading edge, a trailing edge, a pressure face and an extrados face which connect the leading edge to the trailing edge, and an inner wall delimiting an internal cavity,

[0019] (d) drilling the outer wall of the blade by electroerosion to form cooling channels.

[0020] The process is remarkable in that:

[0021] - in step (a), the blade comprises cooling slots extending from the inner wall towards the outer wall and each having a first end opening into the inner cavity and a second end located between the inner wall and the outer wall, and - in step (d), each drilling is made from the outer wall to the second end of each cooling slot so that each cooling channel opens respectively into a cooling slot.

[0022] According to the manufacturing method of the invention, two main steps are implemented.

[0023] According to the first stage of blade manufacturing, a blade with cooling slots is proposed.

[0024] According to the second step of manufacturing the blade according to the invention, cooling channels are produced by electroerosion drilling of the blade. According to this step, the drilling of these cooling channels opens into the second end of the cooling slots.

[0025] Thus, at the end of these steps, the blade is provided with cooling passages which extend from the external wall to the internal cavity of the blade in order to create a film of air around the blade and improve its cooling.

[0026] Such a manufacturing process, which is articulated around two manufacturing steps, which are the manufacturing of a blade provided with slots and the drilling of channels, allows the production of air passages, constituted by the combination of these slots and channels, of any geometry and without impact despite internal cavity thicknesses less than or equal to 1 mm. Indeed, the presence of cooling slots prior to drilling by electroerosion, guarantees a maximum drilling depth much less than the thickness of the internal cavity. Also, the presence of such cooling slots makes it possible to initiate complex geometries for the production of cooling air passages, for example bent or even truncated cones.

[0027] The method of the invention therefore makes it possible to provide blades whose aerothermal and mechanical properties are improved. The invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another:

[0028] - step (a) includes the following sub-step (aO):

[0029] (aO) manufacturing a core for forming the internal cavity, the core comprising a body and appendages for forming the cooling slots, each appendage extending from the body and comprising a first end connected to the body and a second end opposite the body,

[0030] - step (a) includes the following sub-steps carried out after step (aO)

[0031] (a1) make a model of the dawn around the core,

[0032] (a2) make a shell mold of the dawn around the model,

[0033] (a3) remove the model,

[0034] (a4) optionally, heat treat the shell mold,

[0035] (a5) pour a metal into the shell mold, and

[0036] (a6) remove the core,

[0037] - between steps (a) and (d), the method comprises the following steps:

[0038] (b) providing a virtual reconstruction of the blade obtained in step (a) and determining spatial coordinates of the cooling slots,

[0039] (c) providing an electroerosion device comprising at least one electrode configured to electroerosion pierce the blade to form the cooling channels, the position of the electrode with respect to the blade being determined according to the spatial coordinates obtained in step (b),

[0040] - in step (b), the virtual reconstruction is carried out by imaging, in particular by tomography,

[0041] - in step (aO), at least one of the appendages extends along an axis perpendicular to an axis of elongation of the core,

[0042] - in step (aO), at least one of the appendages extends along an axis inclined relative to an axis of elongation of the core, - in step (aO), at least one of the appendages has a truncated cone shape, the first end having a diameter greater than the diameter of the second end,

[0043] - at step (aO), the core is produced by additive manufacturing,

[0044] - in step (aO), the core is produced by injection molding.

[0045] Brief description of the figures

[0046] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which: Figure 1 is a schematic representation in longitudinal section of a half-turbomachine of an aircraft according to the invention, Figure 2 is a schematic representation of a blade pierced by the method according to the invention, Figure 3 is a schematic representation in cross section of the blade of Figure 2, Figure 4 is a schematic representation of a blade according to a first exemplary embodiment, Figure 5 is a schematic representation of a blade according to a second exemplary embodiment, Figure 6 is a schematic representation of a blade according to a third exemplary embodiment, Figure 7 is a block diagram of the method of the invention, Figure 8 is a schematic representation of a core according to a first exemplary embodiment,Figure 9 is a schematic representation of a core according to a second exemplary embodiment, Figure 10 is a schematic representation of a core according to a third exemplary embodiment, Figure 11 is a schematic representation of a blade before the drilling step and in which the core of Figure 8 has been implemented, Figure 12 is a schematic representation of a blade before the drilling step and in which the core of Figure 9 has been implemented, Figure 13 is a schematic representation of a blade before the drilling step and in which the core of Figure 10 has been implemented, Figure 14 is a schematic representation of an electroerosion device implemented in the method of the invention, Figure 15 is a schematic representation of a blade during the drilling step and in which the core of Figure 8 has been implemented,Figure 16 is a schematic representation of a blade during the piercing step and in which the core of Figure 9 has been implemented, Figure 17 is a schematic representation of a blade during the piercing step and in which the core of Figure 10 has been implemented.,

[0047] Detailed description of the invention

[0048] Figure 1 illustrates an example of a turbomachine 1, in particular an aircraft. The turbomachine 1 extends around and along a longitudinal axis X.

[0049] In the present application, the terms “upstream” and “downstream” are defined in relation to the direction of circulation of the gases in the turbomachine 1 along the longitudinal axis X.

[0050] The terms “axial”, “axially”, “radial”, “radially”, are defined in relation to the longitudinal axis X of the turbomachine 1.

[0051] The terms "internal", "interior", "external", "exterior",

[0052] "externally" are defined relatively to the distance from the longitudinal axis X along a radial axis perpendicular to the longitudinal axis X.

[0053] The turbomachine 1 comprises, from upstream to downstream, a fan 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). The fan 2 allows the suction of an air flow F dividing into a primary flow F1 and a secondary flow F2. The primary flow F1 passes through the engine of the turbomachine 1 while the secondary flow F2 is directed towards a secondary vein.

[0054] The primary flow F1 is compressed within the low pressure compressor 3 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 turbines 6 and low pressure turbines 7. The gases finally escape through the nozzle, the cross-section of which allows the acceleration of these gases to generate propulsion.

[0055] 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.

[0056] With reference to Figure 2, the turbomachine 1, in particular the high-pressure turbine 6, comprises blades 8 extending radially from a disk (not shown) movable or fixed in rotation relative to the longitudinal axis X. Each blade 8 extends along an elongation axis Y perpendicular to the longitudinal axis X. Each blade 8 extends along this elongation axis Y between a head 10 and a root 12 and comprises a blade 9. The root 12 is for example connected to the blade 9 by a platform 11. The root 12 of each blade 8 is respectively mounted in a disk to retain the blade 8 on the disk.

[0057] The blade 9 has an aerodynamic shape and comprises an external wall comprising a lower surface face 9i and an upper surface face 9e connected by a leading edge 9a and a trailing edge 9b.

[0058] With reference to Figure 3, the blade 8 further comprises at least one inner wall 13. The inner wall 13 is located inside the outer wall. The inner wall 13 extends for example along the elongation axis Y between the head 10 and the root 12 of the blade 8. The inner wall 13 has an extrados surface 13e located on the side of the extrados face 9e and a intrados surface 13i located on the side of the intrados face 9i. The blade 8 is made of an electrically conductive material. The material is for example a metallic material or a composite material. Advantageously, the composite material is a ceramic matrix composite (CMC) material. Such materials have the advantage of resisting high temperatures and therefore of allowing the implementation of these blades 8 near the combustion chamber 5, in an environment subjected to high temperatures.

[0059] In order to further improve the temperature resistance of the blades 8, each blade 8 comprises at least one internal cavity 14 for the circulation of air, for example taken from the low-pressure compressor 4, inside the blade 8. The internal cavity 14 is delimited by the internal wall 13 and preferably extends along the elongation axis Y of the blade 8. It extends, for example, from the head 10 to the root 12 of the blade 8.

[0060] The thickness e of the internal cavity 14 as measured along an axis Z perpendicular to the elongation axis Y is for example between 0.5 mm and 2 mm, preferably equal to 1 mm. Such a thickness e of the internal cavity 14 makes it possible to maximize the heat exchanges inside the blade 8 to improve its cooling.

[0061] In order to further improve the temperature resistance of the blades 8, each blade 8 further comprises, according to the invention, cooling air passages 15 provided in the external wall and which open into the internal cavity 14. The air passages 15 thus allow the passage of air from the internal cavity 14 to the external wall of the blade 8 in order to create a film of air around the blade 8 to cool it.

[0062] The air passages 15 have, for example, a circular cross-section. They advantageously have a diameter of the order of a micrometer. The air passages 15 are advantageously aligned and / or distributed in a staggered pattern.

[0063] According to an exemplary embodiment shown in Figure 4, at least one air passage 15, and preferably each air passage 15, extends along the axis Z perpendicular to the elongation axis Y of the internal cavity 14. According to another exemplary embodiment shown in Figure 5, at least one air passage 15, and preferably each air passage 15, is bent. Such a configuration makes it possible to adapt the circulation of the cooling air flow in the blade 8. Indeed, the cooling air can circulate in a first zone of the blade 8 and be ejected into a second zone of the blade 8.

[0064] According to an exemplary embodiment shown in Figure 6, at least one air passage 15, and preferably each air passage 15, is frustoconical. The air passage 15 widens for example in the direction of the internal cavity 14. Such a configuration makes it possible to improve the flow of the cooling air flow to the internal cavity 14, in particular when the distance separating the external and internal walls 13 is significant.

[0065] A method of manufacturing such a hollow blade 8 according to the invention will now be described.

[0066] Referring to Figure 7, the manufacturing process comprises the following steps:

[0067] (a) manufacturing a blade 8' comprising the outer wall and the inner wall 13 delimiting the inner cavity 14. In step (a), the blade 8' further comprises cooling slots 16 extending from the inner wall 13 towards the outer wall and each having a first end 16a opening into the inner cavity 14 and a second end 16b located between the inner 13 and outer walls, then

[0068] (b) preferably, providing a virtual reconstruction of the blade 8' obtained in step (a) and determining spatial coordinates of the cooling slots 16, then

[0069] (c) preferably, providing an electroerosion device 100 comprising at least one electrode 102 configured to pierce by electroerosion the blade 8' of step (a) to form cooling channels 17, the position of the electrode 102 with respect to the blade 8' being determined according to the spatial coordinates obtained in step (b), and (d) piercing the external wall of the blade 8' by electroerosion to form the cooling channels 17, each piercing being carried out from the external wall to the second end 16b of each cooling slot 16 so that each cooling channel 17 opens respectively into a cooling slot 16.

[0070] According to a particularly advantageous embodiment of the invention, step (a) comprises the following chronological sub-steps:

[0071] (aO) manufacturing a core 18 intended to form the internal cavity 14, the core 18 comprising a body 19 and appendages 20 intended to form the cooling slots 16, each appendage 20 extending from the body 19 and comprising a first end 20a connected to the body 19 and a second end 20b opposite the body 19,

[0072] (a1) make a model of the dawn around the core 18,

[0073] (a2) make a shell mold of the dawn around the model,

[0074] (a3) remove the model,

[0075] (a4) optionally, heat treat the shell mold,

[0076] (a5) pour a metal into the shell mold,

[0077] (a5') solidify the metal and remove the shell mold, and

[0078] (a6) remove core 18.

[0079] With reference to figures 8 to 10, preferably, the sub-step (aO) of manufacturing the core 18 is carried out by additive manufacturing or by molding. The core 18 may be made of ceramic material, refractory metal or a mixture thereof. The appendages 20 and the body 19 of the core 18 may be monolithic or form two separate pieces and then secured together by gluing, welding or any other fixing means. The appendages 20 and the body 19 may comprise the same material or different materials.

[0080] The body 19 of the core 18 extends along an elongation axis Y' parallel to the elongation axis Y of the blade 8. Each appendage 20 has an external diameter of between 0.1 mm and 0.5 mm, preferably 0.35 mm and a length L of between 0.5 mm and 2 mm, preferably 1 mm.

[0081] According to a first exemplary embodiment illustrated in figure 8, at least one of the appendages 20 extends along an axis Z' perpendicular to the elongation axis Y' of the core 18.

[0082] According to a second exemplary embodiment illustrated in Figure 9, the axis Z' of at least one of the appendages 20 is inclined at an angle other than 90° relative to the elongation axis Y' of the core 18.

[0083] According to a third exemplary embodiment illustrated in FIG. 10, at least one of the appendages 20 has a truncated cone shape, the first end 20a having a diameter greater than the diameter of the second end 20b.

[0084] The sub-step (a1) of manufacturing the model of the blade 8 is preferably carried out by injection molding of wax around the core 18.

[0085] Sub-step (a2) of manufacturing the shell mold can be carried out, for example, by successively dipping the model in slips. The slips comprise, for example, a ceramic material. The dipping can be completed by a step of drying the shell mold.

[0086] Sub-step (a3) ​​can be carried out by pre-baking the shell mold at a first temperature allowing the shell mold to be dewaxed.

[0087] Substep (a4) can be carried out by baking the shell mold at a second temperature higher than the first temperature. Such a substep makes it possible to increase the strength of the shell mold.

[0088] Sub-step (a5) can be carried out under vacuum. The metal is molten during this sub-step. The metal is, for example, a metal alloy.

[0089] Sub-step (a5) may be followed by a sub-step a5' of solidification of the metal and removal of the shell mold. The shell mold is for example broken. Sub-step (a6) may be carried out by mechanical or chemical treatment. For example, the blade 8' may be placed in a chemical bath to dissolve the core 18. At the end of sub-step (a6), the blade 8' is obtained according to step (a) as illustrated in Figures 11 to 13.

[0090] According to a particularly advantageous embodiment of the invention, step (b) of virtual reconstruction of the blade 8 is carried out by imaging, in particular by tomography, in particular by X-ray tomography. Such a step makes it possible to precisely determine the position of the cooling slots 16.

[0091] In step (c), and with reference to FIG. 14, the electroerosion device 100 comprises a drilling guide 101 and at least one electrode 102 carried by the guide 101. Preferably, the device 100 is of the multi-drilling type. Such a device 100 has the advantage of allowing the drilling of a plurality of cooling channels 17 simultaneously. This allows an economic gain of at least 30% compared to a single-drilling electroerosion device with which only one cooling channel 17 can be produced at a time. Thus, the device 100 comprises, for example, between four and thirty electrodes 102.

[0092] The electrodes 102 are arranged parallel to each other and each make it possible to produce a cooling channel 17 by electroerosion. Each electrode 102 has an elongated shape. Each electrode 102 is configured to pierce by electroerosion a cooling channel 17 from the external wall of the blade 8 to the second end 20b of the cooling slot 16.

[0093] According to step (c) of the invention, each electrode 102 is adjusted in position in the guide 101 according to the spatial coordinates of the cooling slots 20 obtained in step (b). Such adaptive drilling makes it possible to guarantee the position of the cooling channels 17 according to the position of the cooling slots 16 and thus to obtain compliant cooling passages 15. During step (d), the blades 8' are drilled by electroerosion (EDM for "Electrical Discharge Machining" in English) as for example illustrated in Figures 15 to 17 according to the different cores 18 implemented. For this purpose, the electrodes 102 are moved towards the external wall of the blade 8'. The blades 8 obtained at the end of step (d) thus have cooling passages 15 as described above.

[0094] Such an electroerosion process is compatible with the aerodynamic shape of the blades 8 and makes it possible to guarantee material health when drilling the cooling channels 17.

[0095] Thanks to the two-step manufacturing of the hollow blades 8 according to the invention, by firstly producing cooling slots 16 and then drilling cooling channels 17, it is possible to produce cooling passages 15 without impact even when the internal cavities 14 have a thickness e less than or equal to 1 mm. Also, thanks to such a two-step process, it is possible to create cooling passages 15 that are bent, truncated or of any other geometry.

[0096] Adaptive EDM drilling according to the advantageous steps (b) and (c) makes it possible to simplify such a two-step process. Indeed, it is possible to correctly aim the cooling slots 16 when EDM drilling the cooling channels 17. The cooling passages 15 thus have the desired configuration.

Claims

CLAIMS 1. Method for manufacturing a hollow blade (8) for a turbomachine (1), the method comprising the following steps: (a) manufacturing a blade (8') comprising: an outer wall comprising a leading edge (9a), a trailing edge (9b), a pressure face (9i) and an extrados face (9e) which connect the leading edge (9a) to the trailing edge (9b), and an inner wall (13) delimiting an internal cavity (14), (d) drilling the external wall of the blade (8) by electroerosion to form cooling channels (17), characterized in that: - in step (a), the blade (8') comprises cooling slots (16) extending from the inner wall (13) towards the outer wall and each having a first end (16a) opening into the inner cavity (14) and a second end (16b) located between the inner wall (13) and the outer wall, and - in step (d), each drilling is carried out from the external wall to the second end (16b) of each cooling slot (16) so that each cooling channel (17) opens respectively into a cooling slot (16), and in that the method further comprises between steps (a) and (d), the following steps: (b) providing a virtual reconstruction of the blade (8') obtained in step (a) and determining spatial coordinates of the cooling slots (16), (c) providing an electroerosion device (100) comprising at least one electrode (102) configured to electroerosion pierce the blade (8') to form the cooling channels (17), the position of the electrode (102) with respect to the blade (8') being determined according to the spatial coordinates obtained in step (b).

2. Method according to the preceding claim, characterized in that step (a) comprises a following sub-step (aO): (aO) manufacturing a core (18) for forming the internal cavity (14), the core (18) comprising a body (19) and appendages (20) for forming the cooling slots (16), each appendage (20) extending from the body (19) and comprising a first end (20a) connected to the body (19) and a second end (20b) opposite the body (19).

3. Method according to the preceding claim, characterized in that step (a) comprises the following sub-steps carried out after step (a0): (a1) make a model of the blade (8) around the core (18), (a2) make a shell mold of the blade (8) around the model, (a3) ​​remove the model, (a4) optionally, heat treat the shell mold, (a5) pour a metal into the shell mold, and (a6) remove the core (18).

4. Method according to any one of the preceding claims, characterized in that in step (b), the virtual reconstruction is carried out by imaging, in particular by tomography.

5. Method according to any one of claims 2 to 3 or 4 in combination with claim 2, characterized in that in step (a0), at least one of the appendages (20) extends along an axis (Z') perpendicular to an axis of elongation (Y') of the core (18).

6. Method according to any one of claims 2 to 3 or 4 in combination with claim 2, characterized in that in step (a0), at least one of the appendages (20) extends along an axis (Z') inclined relative to an axis of elongation (Y') of the core (18).

7. Method according to any one of claims 2 to 3 or 4 in combination with claim 2, characterized in that in step (a0), at least one of the appendages (20) has a frustoconical shape, the first end (20a) having a diameter greater than the diameter of the second end (20b).

8. Method according to any one of claims 2 to 3 or 4 to 7 in combination with claim 2, characterized that in step (a0), the core (18) is produced by additive manufacturing.

9. Method according to any one of claims 2 to 3 or 4 to 7 in combination with claim 2, characterized that in step (a0), the core (18) is produced by injection molding.

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