EP3953082A1

EP3953082A1 - Method for manufacturing a plurality of guide vanes sectors using casting

Info

Publication number: EP3953082A1
Application number: EP20731165.5A
Authority: EP
Inventors: Ngadia Taha NIANE; Saïd BOUKERMA; Camille Mettoux
Original assignee: Safran SA
Current assignee: Safran SA
Priority date: 2019-04-08
Filing date: 2020-03-20
Publication date: 2022-02-16
Also published as: FR3094655A1; FR3094655B1; US20220193761A1; CN113677454B; US11712737B2; WO2020208325A1; CN113677454A

Abstract

The invention relates to a method for manufacturing a plurality of monocrystalline guide vanes sectors each comprising at least a first blade extending between two platforms, using a lost-wax casting technique. The method involves pouring molten metal into a plurality of ceramic moulds (100) clustered around an axis (A) and controlled solidification of the poured metal in a furnace comprising a radiating heating element configured to be positioned around the cluster, a metal solidification front progressing within each mould in a direction (D_S) parallel to the axis of the cluster during the course of the controlled solidification. The method is characterized by the presence, in each mould (100), of a second shell separated from a first shell for the moulding of the guide vanes sector and which delimits a second cavity (130) for the moulding of a dummy blade which acts as a heat shield.

Description

Title of the invention: Method of manufacturing a plurality of distributor sectors by foundry

Technical area

The present invention relates to the general field of methods of

manufacture of metal turbomachine parts by foundry. It relates more particularly to a method of manufacturing a plurality of monocrystalline distributor sectors each comprising at least one blade extending between two platforms.

Prior art

[0002] In certain applications, and in particular in turbomachines

aeronautics, it is necessary to have metal parts or metal alloy parts which have a controlled monocrystalline structure. For example, in the distributors of the turbines of aeronautical turbomachines, the blades must withstand significant thermomechanical stresses due to the high temperature and to the centrifugal forces to which they are subjected. A controlled monocrystalline structure in the metal alloys forming these blades makes it possible to limit the effects of these stresses.

To make a metal part of this type, we know the processes of the lost wax casting type. In a manner known per se, in such a process, a wax model of the part to be produced is first produced, around which a ceramic shell is formed, forming a mold. Molten metal is then poured into the mold, and the directed solidification of the metal results in the molded part after removal from the mold. This method is advantageous for manufacturing metal parts of complex shapes, and makes it possible to obtain parts having a monocrystalline structure by using, for example, a single crystal grain supplier device such as a seed or a grain selector duct.

The manufacture of turbomachine distributor sectors is known

aeronautics by such a process. FIG. 1 shows for example a single-bladed distributor sector 1. FIG. 2 shows for example a two-bladed distributor sector 2. A distributor sector generally comprises one or more blades 3 which extend between two platforms 4 delimiting the duct. flow of the gas stream. Due to their complex shape, and in order to obtain a monocrystalline part, it is often necessary to develop ceramic molds comprising artifices such as grain supply conduits connecting a single crystal grain supply device to different parts of the mold cavity, and in particular to the part intended to form the blade (s) of the distributor sector.

[0005] FIG. 3 shows a view of the internal volume of a mold 5 for manufacturing a two-bladed distributor sector 2 such as that of FIG. 2, comprising a grain supplier device 6 housing here a monocrystalline seed connected to the parts 7 of the mold cavity intended to form the blades 3 by grain supply ducts 8.

[0006] Despite these tricks, parasitic grains are still present, in particular at the level of the distributor blade on the zones 9 identified in FIG. 3, and the part scrap rate is high. In addition, after the metal has solidified, additional, time-consuming and expensive machining is required to eliminate grain lines at critical parts such as the leading edge of the blades.

There is therefore a need for a method for manufacturing monocrystalline distributor sectors which does not have the aforementioned drawbacks.

Disclosure of the invention

The invention relates to a method of manufacturing a plurality of monocrystalline distributor sectors each comprising at least a first blade extending between two platforms, the method comprising the casting of a molten metal in a plurality of molds ceramics distributed in a cluster around an axis, and the directed solidification of the metal cast in a furnace comprising a radiating heating element configured to be disposed around the cluster, a solidification front of the metal progressing in each mold in a direction parallel to the axis of the cluster during directed solidification, in which each mold comprises:

a first shell delimiting a first mold cavity of a distributor sector, the first cavity having parts forming the platforms of the distributor sector, and a part forming a first blade having a external face with respect to the axis of the cluster corresponding to an extrados face of the first blade, a first edge and a second edge corresponding respectively to a leading edge and to a trailing edge of the first blade, the first edge being located upstream of the second edge with respect to the direction of progression of the solidification front, and

a single crystal grain supply device connected by two conduits

supply to the parts of the first cavity forming the platforms of the distributor sector upstream thereof,

characterized in that each mold further comprises a second shell separated from the first shell and located upstream of the latter with respect to the direction of progression of the solidification front, the second shell defining a second mold cavity of a blade dummy connected to the grain supply device, the second cavity having a face corresponding to an extrados face of the dummy blade parallel to the external face of the first cavity.

[0008] Throughout the discussion, we talk about shell to designate the envelope in

ceramic of the mold, and cavity to designate an internal volume of the mold in which a metal can be poured.

[0009] The method according to the invention differs in particular from the methods of the prior art by the use of molds provided with mold cavities of dummy blades. The presence of these dummy blades makes it possible to form an anti-radiation heat shield for each sector of the molded distributor, in particular for the blade or blades thereof, during the directed solidification of the cast metal. The separation between the first and the second shell prevents thermal bridges between them. The aforementioned characteristics (second molding shell of a dummy blade, and separation of the first and second shell), in particular, thus make it possible to drastically reduce the formation of parasitic grains and the number of parts rejected because of them. .

[0010] In an exemplary embodiment, each dummy blade can be independent, that is to say is not connected to platforms. [0011] In an exemplary embodiment, the part of each first cavity forming a first blade can only be in communication with the parts of said cavity forming the platforms.

[0012] In an exemplary embodiment, each mold may be devoid of a grain supply duct between the grain supplying device and the part forming the first blade, and between the grain supplying device and a second blade, if applicable.

[0013] In an exemplary embodiment, each dummy blade may have the shape of a curved strip. This shape makes it possible to obtain a dummy blade of reduced mass maintaining a heat shield function with little impact on the mass and strength of the cluster.

[0014] In an exemplary embodiment, each dummy blade may include part of a lower surface face so that each second shell forms a tongue extending inside the cluster. The shell formed around this tab can be used to hold, for example, a thermal insulator inside the cluster.

[0015] In an exemplary embodiment, a thermal insulator can be placed at

the interior of the cluster during directed solidification, the thermal insulation being held over at least one tongue of a second shell. The presence of such a thermal insulator makes it possible to improve the temperature homogeneity during directed solidification, to obtain a more stable solidification front, and thus further reduce the appearance of parasitic grains. The thermal insulation can be a carbon felt.

[0016] In an exemplary embodiment, each mold may further comprise a supply cavity having a triangular shape, the ducts

feeder and the single crystal grain feeder device being connected to said cavity at the tops of the feed cavity, the second cavity being connected to the feed cavity at one side thereof located between the two supply ducts.

In an exemplary embodiment, a junction can connect the cavity

feed to the second cavity, said junction having a length of at least 12 mm. In an exemplary embodiment, each distributor sector can further comprise a second blade, the part of the first cavity forming the second blade being located downstream of the part of the first cavity forming the first blade relative to the direction of progression of the solidification front. This arrangement makes it possible to manufacture a two-bladed distributor sector.

[0019] In an exemplary embodiment, each grain supplier device may comprise a housing in which a single crystal seed is present.

[0020] In an exemplary embodiment, the cluster may comprise between four and twelve ceramic molds, for example six ceramic molds.

Brief description of the drawings

[0021] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an exemplary embodiment thereof without any limiting nature. In the figures:

[0022] [Fig. 1] Figure 1 shows an example of a single-bladed distributor sector.

[0023] [Fig. 2] Figure 2 shows a two-bladed distributor sector.

[0024] [Fig. 3] Figure 3 shows a mold for making a two-bladed distributor sector used in a prior art process.

[0025] [Fig. 4] Figure 4 shows a cluster comprising several molds for manufacturing two-bladed distributor sectors in a method according to the invention.

[0026] [Fig. 5] Figure 5 shows a perspective view of a mold of the bunch of Figure 4.

[0027] [Fig. 6] Figure 6 shows a detailed front view of the mold of Figure 5.

[0028] [Fig. 7] Figure 7 shows a detailed rear view of the mold of the

figure 5.

[0029] [Fig. 8] Figure 8 shows an enlarged view of Figure 6 at the level of the second cavity.

[0030] [Fig. 9] Figure 9 shows an enlarged side view of the mold of the

figure 5. [0031] [Fig. 10] Figure 10 shows a sectional view along the X plane identified in Figure 6.

[0032] [Fig. 1 1] Figure 1 1 shows the main steps of a

manufacturing a plurality of dispenser sectors according to one embodiment of the invention.

[0033] [Fig. 12] Figure 12 illustrates the placement of a cluster in a furnace to achieve directed solidification of the cast metal.

Description of embodiments

[0034] Unless otherwise stated, it will be noted that in the figures, for greater readability, the shell corresponding to the ceramic material wall (or envelope) of the cluster and therefore of the molds has not been shown. In other words, we have only shown the internal volumes or cavities of a cluster comprising several molds or of a mold. These figures thus show the parts into which a molten metal can be introduced, which also corresponds to the wax model that can be used to make the mold, and to the assembly obtained after casting and directed solidification of the metal.

Figure 4 shows an installation or cluster 10 comprising a plurality of molds 100 for molding two-bladed distributor sectors 2 like that of Figure 2 by a method according to the invention, here the molds are six in number. Of course, the cluster 10 can include a different number of molds, for example a number between four and twelve. The cluster 10 has a central axis A around which the molds 100 are distributed. The cluster 10 comprises a cup 1 1 through which a liquid metal can be introduced into the cluster 10. The cup 1 1 overcomes a vertical or downward central duct 12. Near the opening of the cup 1 1 is a plurality of ducts 13 which make it possible to extract the wax before the step of casting a molten metal for each of the molds 100. A ring 14 connected to the descendant 12 by stiffeners 15 makes it possible to distribute the molten metal cast between the molds 100 and to feed them via supply conduits 16. In this example, there are two feed conduits 16 per mold 100. The entire cluster 10 can be placed on a horizontal sole 17 provided to support the 'together throughout the manufacturing process which will be described later in connection with FIG. 1 1. The sole 17 also makes it possible to avoid the complete fusion of the monocrystalline seed.

A direction D _s is defined corresponding to the direction of propagation of the solidification front of the metal progressing in the cluster during the directed solidification. The direction D _s is parallel to the axis A of the cluster 10. In the figures, such a front will progress from the sole 17 to the bucket 1 1. A direction DR is defined corresponding to a radial direction with respect to the axis A of cluster 10, which defines the terms “interior” and “exterior” in relation to cluster 10.

[0037] Figures 5 to 9 show different views of a mold 100 corresponding to a sector of the cluster 10.

The mold 100 comprises a first shell which defines a first cavity 1 10 for molding the distributor sector 2. The first cavity 110 comprises parts 1 1 1 forming the platforms 4 of the distributor sector 2, a part 1 12 forming a first blade 3 (Figures 6 and 7) and a part 1 13 forming a second blade 3. The parts 112 and 113 are thus each in communication only with the parts 11 11 forming the platforms. The conduits 13 for removing the wax, and the supply conduits 17 are connected to the parts 11 1 of the first cavity 1 10. In each mold 100, the part 1 12 forming the first blade is located upstream with respect to the direction. D _s of the part 112 forming the second blade.

Each part 1 12 and 1 13 forming a first and a second blade is oriented so that the first and the second blade have an extrados face which is located radially (in the direction DR) on the outside with respect to their intrados face. In other words, the part 1 12 forming the first blade and the part 1 13 forming the second blade each have an external face 1 12a and 1 13a relative to the axis A of the cluster 10 which corresponds to the extrados face of the first or the second blade.

In addition, the part 112 forming the first blade and the part 1 13 forming the second blade each have a first edge 112b and 1 13b corresponding to the leading edge of the corresponding blade and a second edge 112c and 1 13c corresponding at the trailing edge of the corresponding blade. The sector of distributor is oriented such that the first edges 112b and 1 13b are located upstream with respect to the direction D _s of the second edges 1 12c and 1 13c.

The mold 100 further comprises a grain supplier device

monocrystalline 120, which may for example comprise a monocrystalline seed in a housing, connected by a triangular supply cavity 121 and two supply conduits 122 to the parts 11 of the first cavity 110 forming the platforms. The device 120 and the supply conduits 121 are connected to the tops of the triangular supply cavity 121.

In the method according to the invention, each mold 100 also has a second shell, separated from the first shell and located upstream of the latter with respect to the direction D _s , defining a second mold cavity 130 d 'a dummy blade. We speak of a “dummy” blade because it simulates the presence of a blade in the distributor sector, but is not part of it. Moreover, the dummy blade which will be molded in the second cavity will be separated from the distributor sector (or withdrawn or eliminated) at the end of the manufacturing process. It is in fact only used during directed solidification, where it acts as an anti-radiation heat shield to reduce the appearance of parasitic grains.

[0043] The second cavity 130 is connected by a junction 131 only to the triangular supply cavity 121 at a middle part of one of its sides. The junction 131 has, in this example, a length L (Figure 9) of at least 12 mm.

The second cavity 130 has part of the aerodynamic profile, and

in particular an outer face 130a corresponding to an extrados face of a blade, and a first edge 130b corresponding to a leading edge of a blade. The dummy blade (and therefore the cavity for molding it) here has the shape of a curved strip. In the example illustrated, the dummy blade also comprises a part of a lower surface of the blade so that the second shell forms a tongue 132 (FIG. 10) extending inside the cluster 10. The second cavity 130 is oriented so that the external face 1 12a of the part 1 12 of the first cavity 110 forming the first blade and the external face 130a are parallel (FIG. 9). The second cavity 130 can be separated by a minimum distance DO (Figure 8) of at least 8 mm from the first cavity 1 10.

Figure 10 shows a sectional view along the X plane identified in Figure 6.

Exceptionally in this figure, there is shown the ceramic shell of the mold 100. One can thus see in particular the first shell 110a, the second shell 130c and the tongue 132 of the second shell 130c. It can thus be seen that the first shell 110a and the second shell 130c are separated so as to avoid a thermal bridge between them. In this figure, it has also been illustrated that the mold 100 can be arranged so that the distance D1 separating the first edge 130b from the second cavity of the first edge 112b, and the distance D2 separating the first edge 112b from the first edge 113b can be roughly equal.

When manufacturing single-bladed distributor sectors, one can for example ensure that the first edges 1 12b and 130b of the first cavity and the second cavity are separated by a distance corresponding to the distance between two leading edges in the distributor considered.

The cluster 10 and the molds 100 which compose it can be made of ceramic material. In a manner known per se, a wax model of cluster 10 is first obtained. Then, this wax model is covered with a ceramic shell by successive quenching in a suitable slip and sanding (tempering-stucco). The covered model is finally dewaxed and fired.

FIG. 11 illustrates the main steps of a process for manufacturing a single crystal distributor sector 1 or 2 according to the invention using several molds 100 arranged in a cluster 10 such as that presented above.

The first step E1 of the process consists in filling the molds 100 of the cluster 10 by pouring a molten metal in the cluster 10. To do this, the metal can be poured directly into the cup 11 of the installation, and it can travel by gravity until filling the molds 100.

The second step E2 of the process comprises the directed solidification of the metal present in the molds. To do this, the cluster 10 filled with molten metal is placed in an oven 200 (figure 2) having a radiating heating element 210 arranged around the cluster 10. It is also possible to have a thermal insulator 220 inside the cluster, for example a carbon felt, which is held on the tongues 132 of the second shells 130c forming the dummy blades. The thermal insulator 220 can take a cylindrical or conical shape and be placed in the cluster around the central channel 12. During this step, the solidification of the part is controlled by means of a thermal gradient in the oven 200. thermal gradient generally extends in the direction D _s . The solidification front moves in the direction D _s from the monocrystalline grain supply devices 120 to the bucket 1 1. The solidification front can be moved by for example moving the cluster 10 vertically (this is also referred to as “draw”) in the oven 200 (arrow 230). Once the part has solidified, it can be unchecked and finished machining. In particular, the method comprises a step of removing the dummy blade from the solidified assembly to obtain the distributor sector (in other words, the dummy blade is separated from the distributor sector thus manufactured).

It will be noted that the invention has been described in the context of the manufacture of a plurality of two-bladed distributor sectors. The method is of course applicable to the manufacture of a single-bladed distributor using a cluster provided with several molds each comprising a first mold cavity having only a part forming a first blade and parts forming the platforms of the sector.

Claims

[Claim 1] A method of manufacturing a plurality of sectors of

monocrystalline distributor (1; 2) each comprising at least a first blade (3) extending between two platforms (4), the method comprising (El) casting a molten metal in a plurality of ceramic molds (100) distributed in a cluster (10) around an axis (A), and the (E2) directed solidification of the cast metal in a furnace (200) comprising a radiating heating element (210) configured to be disposed around the cluster, a front of

solidification of the metal progressing in each mold in a direction (D _s ) parallel to the axis of the cluster during directed solidification, in which each mold comprises:

a first shell (110a) defining a first mold cavity (110) of a distributor sector, the first cavity having parts

(111) forming the platforms (4) of the distributor sector, and a part

(112) forming a first blade (3) having an external face (112a) relative to the axis (A) of the cluster corresponding to an extrados face of the first blade, a first edge (112b) and a second edge ( 112c)

corresponding respectively to a leading edge and to a trailing edge of the first blade, the first edge being located upstream of the second edge with respect to the direction (D _s ) of progression of the solidification front, and a device providing monocrystalline grain (120) connected by two supply conduits (122) to the parts (111) of the first cavity forming the platforms of the distributor sector upstream thereof,

characterized in that each mold (100) further comprises a second shell (130c) separated from the first shell (110) and located upstream thereof with respect to the direction (D _s ) of progression of the solidification front, the second shell delimiting a second mold cavity (130) of a dummy blade connected to the grain supplying device (120), the second cavity having a face (130a) corresponding to an extrados face of the dummy blade parallel to the outer face (112a) of the first cavity (110).

[Claim 2] A method according to claim 1, wherein the portion (112) of each first cavity (110) forming a first blade (3) is only in communication with the parts (111) of said cavity forming the platforms (4).

[Claim 3] A method according to claim 1 or 2, wherein

each dummy blade has the shape of a curved band.

[Claim 4] The method of claim 3, wherein each dummy blade comprises a portion of an underside face such that each second shell (130c) forms a tongue (132) extending inside the cluster (10). ).

[Claim 5] A method according to claim 4, wherein a thermal insulator (220) is placed within the cluster during directed solidification, the heat insulator being held on at least one tab (132) of a second. shell (130c).

[Claim 6] A method as claimed in any one of claims 1 to 5, wherein each mold further comprises a feed cavity (121) having a triangular shape, the feed conduits (122) and the grain supplying device. monocrystalline (120) being connected to said cavity at the tops of the supply cavity, the second cavity being connected to the supply cavity at one side thereof located between the two supply conduits.

[Claim 7] A method according to claim 6, wherein a

Junction (121) connects the feed cavity to the second cavity, said junction having a length of at least 12mm.

[Claim 8] A method according to any one of claims 1 to 7, wherein each distributor sector (2) further comprises a second blade (3), the part (113) of the first cavity (110) forming the second. blade being located downstream of the part (112) of the first cavity forming the first blade with respect to the direction (D _s ) of progression of the solidification front.

[Claim 9] A method according to any one of claims 1 to 8, wherein each grain supplying device (120) comprises a housing in which a single crystal seed is present. [Claim 10] A method according to any one of claims 1 to 9, wherein the cluster (10) comprises between four and twelve ceramic molds (100).