Turbine engine blade blank obtained by metal casting and method for manufacturing such a blank

Abstract

The present disclosure relates to a turbine engine blade blank obtained by metal casting, the blade blank comprising a first direction (Z) along which a blade (13), a platform (12) and a root (11) are consecutively formed, the platform (12) extending in a second direction (X) substantially perpendicular to the first direction (Z), the blade (13) comprising a pressure-side face (14) and a suction-side face (15) connected to one another by a trailing edge (16) and a leading edge (17), the root comprising retaining surfaces (23, 24) in the first direction (Z) of the rotating blade intended to co-operate with corresponding surfaces of a turbine engine disc, the blade blank (100) being characterised in that it comprises at least one web (200) that extends in a third direction (Y) which is substantially perpendicular to the first and second directions (Z,X), this web connecting a retaining surface (25) in the first direction to the platform.

Description

Description Title: Turbomachine blade blank obtained by metal casting and method of manufacturing such a blank. Technical field

[0001] The present disclosure relates to the field of turbomachine blades, in particular that of blade blanks obtained by casting a molten alloy into a mold using the casting technique in a removable material, such as for example lost wax, so as to obtain final blades. Prior art

[0002] Traditionally, the lost wax casting technique consists first of all in making a model in wax, or in any other material that can be easily removed later, of the part to be made; this model being equivalent to the blade that one wants to mold and which can include an internal part forming a ceramic core which represents the cavities that one wishes to see appear inside the blade. The wax model is then dipped several times in slips made up of a suspension of ceramic particles to make, by operations called stuccoing and drying, a shell mold. The shell mold thus envelops the wax model.

[0003] The carapace mold is then dewaxed, which is an operation by which the wax or material constituting the original model is removed from the carapace. After this removal, a ceramic mold is obtained whose cavity reproduces all the shapes of the blade and which still contains, where applicable, the ceramic core intended to generate the internal cavities of the latter. The mold then undergoes a high-temperature heat treatment or "firing" which gives it the necessary mechanical properties.

[0004] The shell mold is then ready for the manufacture of the metal part by casting. After checking the internal and external integrity of the shell mold, the next step is to pour a molten metal, which fills the voids in the shell mold, then solidifies it. This produces a blade blank, i.e. a semi-finished part, corresponding substantially to the final blade but requiring one or more additional steps, for example surface treatment or finishing, in order to obtain a final blade meeting the criteria imposed geometrical structures. In the field of lost wax casting, several solidification techniques and several casting techniques are currently distinguished, depending on the nature of the alloy and the expected properties of the part resulting from the casting. This may be, for example, directional solidification with a columnar structure (DS), directional solidification with a monocrystalline structure (SX) or equiaxial solidification (EX).

[0005] After casting the alloy, the shell is broken by a shake-out operation. Then, during another step, if necessary, the ceramic core that remained enclosed in the resulting blade blank is chemically removed. The resulting metal blade blank then undergoes finishing operations to obtain the finished part.

[0006] Examples of the production of turbine blades using the lost wax casting technique are given in the applicant's patent applications FR2875425 and FR2874186.

[0007] Figure 1 illustrates a turbine engine blade 10 known from the prior art. The arrow F in Figure 1 indicates the direction of flow of gases through a turbine engine, the terms “upstream” and “downstream” being subsequently defined with respect to this arrow F.

[0008] In a first direction, also described as the longitudinal direction Z in the remainder of the description, such a blade 10 mainly comprises a root 11, a platform 12 and a blade 13. The blade 13 and the root 11 extend mainly in the longitudinal direction Z while the platform 12 extends mainly in a second direction, also described as the axial direction X in the remainder of the description, this axial direction X being substantially perpendicular to the longitudinal direction Z. The blade 10 further comprises a stilt 18 connecting the root 11 to the platform 12. The blade 13 comprises a pressure face 14 (visible in FIG. 4) and an extrados face 15 connected to each other by a trailing edge 16 downstream and a leading edge 17 upstream.

[0009] Conventionally, each blade 10 is mounted on a turbine disk, for example high pressure, the root 11 of the blade 10 being mounted in a groove in the rim of the disk, and the blade 13 extending radially outwards from the root 11 of the blade 10. The root 11 of each blade 10 is at least partly received longitudinally and retained radially in one of the grooves in the rim of the disk. The root 11 of each blade 10 here has a section (in a third direction, called transverse direction Y in the remainder of the description) in the form of lobes, the root 11 being able to longitudinally comprise a first lobe 21 and a second lobe 22. Each lobe 21, 22 respectively comprises a first retaining surface 23 and a second retaining surface 24, also commonly called bulbs or bearing surfaces, intended to cooperate with a corresponding surface of a turbomachine disk. The first retaining surface 23 is positioned between the platform 12 and the second retaining surface 24. The first and second retaining surfaces 23, 24 radially hold the root 11 of the blade in rotation in the groove of the disk.

[0010] Furthermore, still as illustrated in Figure 1, an upstream reinforcement portion 25, also commonly called an upstream spoiler, extends in the transverse direction Y, this direction Y being substantially perpendicular to the longitudinal direction Z and axial direction X, that is to say in a plane formed by the longitudinal direction Z and transverse direction Y, from the platform 12 towards the foot 11. In Figure I, the upstream reinforcement portion 25 is arranged near the upstream face 26 of the foot II, and in particular in the longitudinal extension of the upstream face 26. The upstream reinforcement portion 25 thus comprises an upstream face common to the upstream face 26 of the foot 11, a downstream face 29 of the upstream reinforcement portion opposite the upstream face 26, and a longitudinal face of the upstream reinforcement portion 30 joining the upstream and downstream faces of the upstream reinforcement portion 25. A downstream reinforcement portion 28 may further be arranged near the downstream face 27 of the foot 11, in particular in the longitudinal extension of the downstream face 27.

[0011] During a conventional process for melting an alloy in a shell mold obtained using the lost-wax casting technique, several blades are cast simultaneously in a casting cluster. The alloy is introduced into the upper part of the cluster, and thus fills the shell mold by gravity. The lower part of the mold is thus filled before the upper part. It is therefore understood that the solidification front of the alloy moves from the lower part to the upper part of the shell mold. According to current practice, the shell mold is arranged in the cluster so that the blade 13 is positioned in the lower part, and the root 11 is positioned in the upper part. Consequently, the solidification front moves from the blade 13 to the root 11, and therefore the blade 13 is cast before the root 11.

[0012] The manufacture of blades from new metal alloys, comprising for example rhenium Re and / or ruthenium Ru, allows increased stress on these parts in operation compared to commonly used alloys, of the AM1 type. However, it has been observed that these new alloys lead to the appearance of casting defects during solidification of the metal, which weakens the part and makes it non-compliant. The defects observed may for example be of the shrinkage type, that is to say a defect in the form of a cavity forming in the solid part of a cast metal part and due to the contraction of the metal during its solidification. In particular, such a shrinkage type defect may be observed on one of the upstream 25 or downstream 26 reinforcement portions of the blade 10.

[0013] The present disclosure therefore aims in particular to overcome these solidification defects which may appear on the blade blanks obtained by casting a metal alloy. Summary

[0014] To this end, the present disclosure proposes a turbomachine blade blank obtained by metal casting, comprising a first direction along which are successively formed a blade, a root and a platform extending in a second direction substantially perpendicular to the first direction, the blade comprising a pressure face and an extrados face connected to each other by a trailing edge and a leading edge, the root comprising retaining surfaces in the first direction of the rotating blade intended to cooperate with corresponding surfaces of a turbomachine disk, in which the blade blank comprises at least one web extending in a third direction substantially perpendicular to the first and second directions, this web connecting a retaining surface in the first direction to the platform.

[0015] The veil may also have the following characteristics, taken alone or in combination: - the veil is formed at the upstream end of the blade root; - the veil can be formed on the same side as the side of the extrados and / or intrados face of the blade; - the veil has a first concave curved face oriented upstream; - the veil has a second convex curved face oriented downstream.

[0016] The characteristics according to which the web has a first concave curved face oriented upstream and a second convex curved face oriented downstream make it possible to ensure better repeatability of the molding process, and in particular to avoid the formation of protuberances during the molding process.

[0017] During the solidification of the metal, these two characteristics help to avoid the formation of freckles (areas of local concentration of impurities in the metal) and recrystallized grains.

[0018] The root may further comprise, on the same side as the side of the extrados and / or intrados face of the blade, in the first direction, a first retaining surface and a second retaining surface, the first retaining surface being positioned in the first direction between the platform and the second retaining surface, the web connecting the first retaining surface to the platform.

[0019] The platform may further comprise a portion, a reinforcing portion for connection to the web, said reinforcing portion extending in the third direction and having a longitudinal face, the thickness of the web being between 0.2 and 0.8 times the thickness of the longitudinal face of the upstream reinforcing portion.

[0020] In the case of a web thickness less than 0.2 times the thickness of the longitudinal face of the upstream reinforcement portion, the presence of an underthickness type molding defect was observed.

[0021] In particular, the volume of liquid metal in the reserve to be cast is in this case insufficient and less important, which leads to its faster solidification. Also, it has been observed that the casting of this volume of liquid metal in reserve creates areas with porosity defects or shrinkage type defects.

[0022] In the case of a web thickness greater than 0.8 times the thickness of the longitudinal face of the upstream reinforcement portion, the presence of an excess thickness type molding defect was observed.

[0023] In particular, during the solidification of the metal, thermomechanical problems of the recrystallization type were observed in this case: the monocrystalline criterion is broken, which weakens the part and can make it non-functional.

[0024] The present disclosure also proposes a method for manufacturing a turbomachine blade from a model made of removable material with geometry and dimensions corresponding to those of the blade blank defined above, the method comprising: - form a shell mold around the model, the shell mold defining an imprint capable of obtaining said blade blank, - remove the model from the shell mold, - orient the shell mold so that, for the blade blank, the first direction is oriented vertically and so that the head is in the low position and the foot in the high position, and - pour metal into the shell mold, in the upper part of said mold.

[0025] During the method, a plurality of shell molds may be distributed circumferentially about an axis parallel to the first direction for the blade blank of each of the molds.

[0026] Then the veil is removed from the blade blank to obtain the blade. Brief description of the drawings

[0027] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig. 1

[0028] [Fig. 1] shows a partial perspective view of a prior art blade, from its downstream face. Fig. 2

[0029] [Fig. 2] shows a partial perspective view of a blade blank according to the present disclosure, from its upstream face. Fig. 3

[0030] [Fig. 3] shows a partial longitudinal view of the blade blank of Fig. 2, illustrating a web according to the present disclosure. Fig. 4

[0031] [Fig. 4] shows a view from the upstream face of the blade blank of Figure 2. Fig. 5

[0032] [Fig. 5] is a longitudinal view of the blade blank of Figure 2. Fig. 6A

[0033] [Fig. 6A] illustrates a casting of an alloy to obtain a blade of the prior art. Fig. 6B

[0034] [Fig. 6B] illustrates a casting of an alloy for obtaining a blade blank according to the present disclosure. Description of the embodiments

[0035] Figures 2 to 5 illustrate an example of a blade blank 100 according to the present disclosure, the blade blank 100 being shown only partially. The blade blank 100 is similar to the blade 10 shown in Figure 1, except that it further comprises a web 200. The web 200 is arranged between the upstream reinforcement portion 25 and the first retaining surface 23, so as to form an extension of material between the upstream reinforcement portion 25 and the first retaining surface 23 which delimit it. The web 200 illustrated in Figures 2-5 is formed at the upstream end 26 of the root 11 of the blade 10. According to another example, the web may be formed at the downstream end 27 of the root 11. According to yet another example, each upstream and downstream end 26, 27 may each comprise a veil.

[0036] In the example illustrated in the figures, the web 200 is formed on the same side as the side of the extrados face 15 of the blade 13. Alternatively, the web 200 can be formed on the same side of the intrados face of the blade 13. Two webs can also be provided, each being arranged on one side of the faces of the blade 13.

[0037] According to the example illustrated and better visible in Figure 5, the web 200 may have a first curved face 201, this being concave towards the upstream. The web 200 may also have a second curved face 202, this being convex towards the downstream. The first and second curved faces 201, 202 make it possible not to complicate the demolding of the blade blank in comparison with a blank which would not include the web 200.

[0038] The thickness L200 of the web 200 can be measured between the first and second curved faces 201, 202, in the axial direction X. This thickness L200 can be less than the thickness L30 of the longitudinal face of the upstream reinforcement portion 25. For example, the thickness L200 can be between 0.2 and 0.8 times the thickness L30 of the longitudinal face of the upstream reinforcement portion 30. As a result, the web 200 and the upstream reinforcement portion 25 are connected together by a connection radius of the upstream reinforcement portion R25 and by a web connection radius R200, the ratio of which is less than or equal to 0.5 (R30 / R200 < 0.5), and preferably between 0.3 and 0.4, and for example equal to 0.37. These dimensions guarantee a web thickness that does not extend beyond the connecting radii of the upstream reinforcement portion, which makes re-machining the area after removal of the web as simple as possible.

[0039] Advantageously, the web 200 eliminates the observed solidification defects and in particular the shrinkage phenomenon detailed above, on the upstream reinforcement portion 25, or alternatively on the downstream end 27 if the web 200 is arranged there.

[0040] According to the example in which the web is arranged between the upstream reinforcement portion 25 and the first retaining surface 23, as illustrated in FIGS. 2 to 5, the web 200 provides a continuous feed front of hot alloy on the upstream reinforcement portion, which improves the solidification of said portion. For comparison, FIG. 6A illustrates the solidification of the alloy during its casting to form a conventional blade without a web, and FIG. 6B also illustrates the solidification of the same alloy, to form a blade blank comprising a web 200. In FIG. 6A, in the circled area, the solidification front is interrupted on the upstream reinforcement portion 25, which creates an isolated area 35 at the end of the upstream reinforcement portion 30. There has thus already been solidification around this isolated area 35, which is then no longer supplied with molten alloy.During solidification, the alloy shrinks, which results in a reduction in the occupied volume. The isolated zone 35, due to its break in the supply of molten alloy, therefore undergoes a shrinkage phenomenon without compensation by a supply of molten alloy, which results in shrinkage of this isolated zone 35. In Figure 6B, the solidification front moves progressively from the platform 12 to the first retaining surface 23, that is to say without interruption of the solidification front. The web 200 thus provides a supply zone for molten alloy so as not to interrupt the supply in the reinforcement portion. upstream 25. Thanks to the veil 200, the solidification front remains continuous in the upstream reinforcement portion zone 25.

[0041] Furthermore, the presence of the web 200 is not compatible with the final blade. The web 200 is therefore present only on the blade blank 100, and not on the final blade. Indeed, the presence of this web 200 prevents the longitudinal insertion of the blade root into the groove of the disc rim.

[0042] Further, the veil 200 may be defined by its volume. Preferably, the volume of the veil is between 16.5 cm 3 and 18.3 cm 3 , which corresponds to a volume 3.5 to 5 times larger than the volume of the area where the shrinkage phenomenon observed on a blade of the prior art can occur.

[0043] To manufacture the blade blank 100 described above, the manufacturing method can be described as follows.

[0044] The method comprises a preliminary step of preparing a shell mold of a shape complementary to that of the blade blank that it is desired to obtain. A shell mold is thus formed around a model made of removable material of geometry and dimensions corresponding to those of said blade blank 100, the shell mold defining an imprint capable of obtaining said blade blank.

[0045] Several molds can be joined together in a casting cluster so that several pieces can be cast simultaneously. Each mold is oriented so that the resulting piece is oriented with the blade pointing downwards, and the foot pointing upwards.

[0046] The alloy is then poured into the shell mold, from the upper part of the mold.

[0047] After solidification of the alloy cast in the mold, a blade blank 100 is then obtained, comprising the web 200. Following the manufacture of said blade blank 100, it must still undergo one or more machining steps so as to obtain the final blade, and in particular a step in which the web 200 is removed from the blade blank 100, this web representing a non-functional volume of material. The longitudinal face of the upstream reinforcement portion 30 is then completed.

Claims

Claims

1. A turbomachine blade blank obtained by metal casting, comprising a first direction (Z) along which a blade (13), a platform (12) and a root (11) are successively formed, the platform (12) extending in a second direction (X) substantially perpendicular to the first direction (Z), the blade (13) comprising a pressure face (14) and an extrados face (15) connected to each other by a trailing edge (16) and a leading edge (17), the root comprising retaining surfaces (23, 24) in the first direction (Z) of the rotating blade intended to cooperate with corresponding surfaces of a turbomachine disk, characterized in that the blade blank (100) comprises at least one web (200) extending in a third direction (Y) substantially perpendicular to the first and second directions (Z, X), this web connecting a retaining surface (23) in the first direction to the platform (12).

2. Blade blank according to claim 1, in which the web (200) is formed at the upstream end (26) of the root (11).

3. Blade blank according to claim 1 or 2, in which the web (200) is formed on the same side as the side of the extrados (15) or intrados (14) face of the blade (13).

4. Blade blank according to any one of the preceding claims, in which the root (11) comprises, on the same side as the side of the extrados (15) or intrados (14) face of the blade (13), in the first direction (Z), a first retaining surface (23) and a second retaining surface (24), the first retaining surface (23) being positioned in the first direction (Z) between the platform (12) and the second retaining surface (24), the web (200) connecting the first retaining surface (23) to the platform (12).

5. Blade blank according to any one of the preceding claims, in which the web (200) has a first concave curved face (201) oriented upstream in the second direction (X).

6. Blade blank according to claim 5, in which the web (200) has a second convex curved face (202) oriented downstream in the second direction (X).

7. Blade blank according to any one of the preceding claims, in which the platform (12) comprises a reinforcing portion (25, 28) for connection to the web (200), said reinforcing portion (25, 28) extending in the third direction (Y) and having a longitudinal face (30), the thickness (L200) of the web (200) being between 0.2 and 0.8 times the thickness (L30) of the longitudinal face of the upstream reinforcing portion (30).

8. Method for manufacturing a turbomachine blade from a model made of removable material with geometry and dimensions corresponding to those of the blade blank (100) defined according to any one of the preceding claims, the method comprising: - forming a shell mold around the model, the shell mold defining an imprint capable of obtaining said blade blank (100), - remove the model from the shell mold, - orient the shell mold so that, for the blade blank, the first direction is oriented vertically and so that the head is in the low position and the foot in the high position, - pour metal into the shell mold, in the upper part of said mold.

9. The method of claim 8, wherein a plurality of shell molds are circumferentially distributed around an axis parallel to the first direction for the blade blank of each of the molds.

10. A method according to claim 8 or 9, wherein the web (200) is removed from the blade blank (100) to obtain the blade.

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