Cluster model and shell for obtaining an accessory for the independent handling of formed parts and associated method

Abstract

A cluster model and a shell for the production, by lost wax casting, of a plurality of turbomachine elements, are provided. The shell includes a central sprue that is fluidly connected to a casting cup for receiving molten metal; a plurality of shell elements; a plurality of bottom feed conduits for the shell elements; and a handling accessory shell that is independent of the plurality of shell elements and of their metal supply circuit, such that there is no fluid connection to the shell elements. The handling accessory shell is fluidly connected to the central sprue so as to allow top-pour casting of the handling accessory shell.

Claims

1. A cluster model, about which is intended to be formed a shell for production, by lost wax casting, of a plurality of turbomachine elements, said model having a longitudinal axis and comprising: a replica of a casting cup suitable for the injection of molten metal into the shell; a replica of a central sprue extending along the longitudinal axis, suitable for being fluidically connected to the casting cup for receiving the molten metal; a plurality of replicas of shell elements each intended for obtaining one of the turbomachine elements, each shell element including a first bottom end portion and a second top end portion; a plurality of replicas of bottom feed conduits for the shell elements, suitable for being fluidically connected to the central sprue and the second bottom end portions of the shell elements so as to allow bottom-pour casting of the shell elements; and a replica of a handling accessory shell that is independent of the plurality of shell elements and of a metal supply circuit thereof, such that there is no fluidic connection to the shell elements, the handling accessory shell being suitable for being fluidically connected to the central sprue so as to allow top-pour casting of the handling accessory shell.

2. A shell for production, by lost wax casting, of a plurality of turbomachine elements, said shell having a longitudinal axis and comprising: a casting cup suitable for the injection of molten metal into the shell; a central sprue extending along the longitudinal axis, of the shell that is fluidically connected to the casting cup for receiving the molten metal; a plurality of shell elements each intended for obtaining one of the turbomachine elements, each shell element including a first bottom end portion and a second top end portion; a plurality of bottom feed conduits for the shell elements that are fluidically connected to the central sprue and the second bottom end portions of the shell elements so as to allow bottom-pour casting of the shell elements; and a handling accessory shell that is independent of the plurality of shell elements and of a metal supply circuit thereof, such that there is no fluidic connection to the shell elements, the handling accessory shell being fluidically connected to the central sprue so as to allow top-pour casting of the handling accessory shell.

3. The shell according to claim 2, wherein the handling accessory shell comprises radial arms fluidically connecting a handling ring shell, centered about the longitudinal axis, to the central sprue.

4. The shell according to claim 3, wherein the handling accessory shell comprises a central element of central axis coinciding with the longitudinal axis of the shell, attached to the central sprue or to the casting cup, the radial arms fluidically connecting the handling ring shell to the central element.

5. The shell according to claim 2, wherein the shell elements arranged about the longitudinal axis, being spaced circumferentially apart from one another, and defining an inner space centered about the longitudinal axis wherein the central sprue is located.

6. The shell according to claim 2, wherein each shell element is fluidically connected, at the level of the second top end portion thereof, to a single wax discharge conduit connected to the casting cup.

7. The shell according to claim 2, wherein each shell element is fluidically connected, at a level of the second top end portion thereof, to a single wax discharge conduit, and wherein the shell comprises at least one first assembly and one second assembly of a plurality of wax discharge conduits respectively connected to one another by at least one first lateral conduit and one second lateral conduit, said at least one first lateral conduit and one second lateral conduit being respectively fluidically connected to the casting cup via at least one first and one second main wax discharge conduits extending respectively between the casting cup and said at least one first and one second lateral conduits.

8. The shell according to claim 2, wherein the shell turbomachine elements are shell bladed elements, each designed for obtaining a single movable blade.

9. A method for producing, by lost wax casting, a plurality of turbomachine elements, using the shell according to claim 2, the method comprising: casting the metal in the shell for forming at least the turbomachine elements.

10. The method according to claim 9, further comprising producing a material other than metal for forming the handling accessory.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may be better understood on reading the following detailed description, non-limiting examples of implementation thereof, as well as examination of the figures, schematic and partial, of the drawing appended, wherein:

(2) FIG. 1 shows a partial perspective view of a first example of embodiment of a shell according to the invention, for the production, by lost wax casting, of a plurality of turbomachine elements, and

(3) FIG. 2 shows a partial perspective view of a second example of embodiment of a shell according to the invention, for the production, by lost wax casting, of a plurality of turbomachine elements, forming an alternative embodiment of FIG. 1.

(4) In all of said figures, identical references may designate identical or similar elements.

(5) In addition, the various portions shown in the figures are not necessarily according to a uniform scale, to make the figures more readable.

DETAILED DISCLOSURE OF SPECIFIC EMBODIMENTS

(6) It is noted that, in the entire description, the possible terms top, bottom, above and below are understood according to the orientation of the views on the figures.

(7) In addition, it is noted that the invention makes it possible to produce turbomachine elements, that may for example be compressor or turbine moveable blades, or even turbine or compressor stator blades, produced alone or by sectors including a plurality of blades.

(8) It is also noted that although the features mentioned below are described in relation to the shell 1, it must be understood that they apply in a similar way to the cluster model, about which said shell 1 is intended to be formed.

(9) In reference to FIG. 1, a first example of embodiment is shown of a shell according to the invention, for the production, by lost wax casting, of a plurality of turbomachine elements, in particular bladed elements.

(10) For the production of the shell, a cluster model (not shown) is first of all produced about which the shell 1 preferentially made of ceramic is intended to be formed. Said cluster model essentially consists of sacrificial elements made of wax, but not exclusively. However, in the interest of simplicity, it is known as wax model.

(11) The implementation of the step for producing the ceramic shell 1 is carried out in a known way by dipping the wax model into successive baths (not shown).

(12) After the drying thereof, the shell 1 obtained has a general cluster shape, and comprises shell elements that will be described hereafter, with the shell 1 shown in FIG. 1 in a position such as subsequently adopted when it is filled with molten metal.

(13) The shell 1 comprises first of all a metal casting cup 2, which can be fully or partially covered by the shell 1. Said casting cup 2 is fluidically connected to a central sprue 3 extending along the longitudinal axis X of the shell 1. Said central sprue 3 preferentially takes the form of a hollow cylinder of axis X that extends from the bottom of the casting cup 2 up to the level of the bottom ends 4a of the shell bladed elements 4.

(14) The central sprue 3 advantageously connects, in a known manner, to the bottom feed conduits 5, visible in FIG. 2 subsequently described, of the shell bladed elements 4 intended to form the metal parts in the form of bladed elements. In other words, the molten metal is injected into the casting cup 2, then passes through the central sprue 3 and is injected, in the bottom portion, into the bottom feed conduits 5 so as to make it possible to fill the shell bladed elements 4 via the bottom, that is to say from bottom to top.

(15) The shell bladed elements 4 are said to be bladed because after elimination of the wax replica, they each form within same a cavity corresponding to a blade. Said shell bladed elements 4 extend upwards, by being arranged about the axis X, and also about the central sprue 3 extending along said same axis, downwards from the bottom of the casting cup 2. The shell bladed elements 4 form the peripheral wall of the shell 1, of longitudinal axis X. They are spaced circumferentially apart from one another, and define an inner space centred about said axis X, space wherein the central sprue 3 is therefore located.

(16) Moreover, in accordance with the invention, the shell 1 comprises a handling accessory shell 6 that is totally independent of the shell bladed elements 4 and of the metal supply circuit thereof.

(17) Said handling accessory shell 6 comprises for example a central element 7 of revolutionary, cylindrical or conical shape, of central axis coinciding with the central axis X of the shell 1, oriented vertically.

(18) Said central element 7 is attached to the central sprue 3, or even to the casting cup 2 directly. Radial arms 8, further visible in FIG. 2, connect the central element 7 to a handling ring shell 9 centred about the axis X. The radial arms 8 and the handling ring shell 9 are for example arranged just below the casting cup 2.

(19) Advantageously, the radial arms 8 and the central arm 7 are fluidically connected to the central sprue 3, same fluidically connected to the casting cup 2, in order to make it possible to produce the handling accessory in metal. In accordance with the invention, top-pour casting is produced in order to obtain said handling accessory. Thus, the invention implements both bottom-pour casting so as to allow the formation of turbomachine bladed elements and top-pour casting so as to allow the formation of the handling accessory, the bladed elements and the handling accessory thus being produced in a totally independent way in order to avoid the appearance of production defects as previously explained.

(20) Moreover, in said example of embodiment in FIG. 1, each shell bladed element 4 is fluidically connected, at the level of the top end 4b thereof, to a single wax discharge conduit 10, again called wax puller or again dewaxing vents 10. Said wax discharge conduits 10 are oriented substantially vertical in the position of the shell 1 illustrated in FIG. 1.

(21) Furthermore, FIG. 1 also shows that, for reinforcing the holding of the handling ring shell 9, it may be provided a plurality of ceramic holding reinforcements 11 connecting the ring shell 9 to the casting cup 2.

(22) In the example of embodiment in FIG. 2, the choice was made not to link the wax puller to a part formed by a shell bladed element 4, in other words not to combine a wax puller with each shell bladed element 4. Thus, in said example, a first 12a, a second 12b, a third 12c and a fourth 12d assembly of four wax discharge conduits 10 respectively combined with four shell bladed elements 4 are each fluidically connected to one another by respectively the first 14a, second 14b, third 14c and fourth 14d lateral conduits.

(23) The wax discharge conduits 10 are therefore partially connected to one another in order to make them rigidly connected. In this way, it is possible to avoid having excessive vibrations during the shake-out step in particular. Indeed, said vibrations could be harmful by causing recrystallisation, and therefore the appearance of recrystallised grains on the formed parts.

(24) At the level of each of the four lateral conduits 14a-14d is fluidically connected a main wax discharge conduit 13a, 13b, 13c or 13d, or wax puller 13a-13d, same fluidically connected to the casting cup 2.

(25) In other words, the discharge of the wax, in said example, is carried out in the casting cup 2 via the first 13a, second 13b, third 13c and fourth 13d main wax discharge conduits, each being fluidically connected to a plurality of shell bladed elements 4.

(26) Advantageously, such an embodiment according to the example in FIG. 2 may make it possible to improve the casting and safety aspects. This may also make it possible to reduce or increase again the stresses in the blade during the solidification phase and more precise discharge of the wax. In this way, it may therefore be possible to optimise the dewaxing system.

(27) After obtaining the shell 1 and eliminating the essential of the cluster model enclosed within same, the shell 1 is preheated at high temperature in a dedicated furnace, for example between 1,000 and 1,200 C., in order to promote the fluidity of the metal in the shell 1 during the casting.

(28) Upon exiting from the preheating of the shell 1, the metal exiting a smelting furnace is cast in the shell bladed elements 4 via the casting cup 2, with the shell 1 in the position such as shown in FIG. 1 or 2, that is to say with the casting cup 2 open upwards and always the axis X oriented vertically.

(29) The molten metal therefore successively follows the casting cup 2, then the central sprue 3, the central element 7, the radial arms 8 and the ring shell 9 for forming the handling accessory in top-pour casting, and almost simultaneously the central sprue 3, the bottom feed conduits 5 and the shell bladed elements 4 for forming the turbomachine bladed elements by bottom-pour casting.

(30) After the cooling of the metal following the casting, the shell 1 is destroyed, then the moveable blades are extracted from the cluster for possible machining operations and finishing and inspection operations.

(31) Advantageously, stiffeners may be added on each radial arm 8 of the handling ring in order to stiffen the cluster and avoid allowing it to sag under its own weight.

(32) In addition, the embodiment of a handling ring, and more generally of a handling accessory, that is totally independent of the bladed elements makes it possible to be able to reduce the dimensions of the handling ring in relation to same formed by the feed system in a top-pour casting solution such as previously described in the part relating to the prior art. Said reduction of dimension may therefore result in a reduction of the metal mass, in particular greater than 50%. Furthermore, such a handling accessory, and in particular such a handling ring, may be produced other than in metal, and in particular in ceramic, because it is only used for the handling and no longer for the feeding of shell bladed elements 4. Therefore, the metal mass may even be reduced to zero if a material other than metal is used. Said reduction of size and metal mass of the handling accessory may be carried out whilst keeping sufficient mechanical properties.

(33) Moreover, bottom-pour casting of the cluster may make it possible to protect the metallurgical health of the formed parts. Thus, it is possible to reduce the risks of core breakage and offset because the corrosion velocities of the metal are very low, typically between 0.2 and 0.6 m/s. In addition, it is possible to reduce the metallurgical defects such as those of inclusion, oxidation, recrystallised grains, interference, among other things, as previously described in relation to the prior art.

(34) In general, the invention makes it possible to obtain an aeration of the cluster and an increase of the stiffening thereof with a better resistance to casting and finishing. The principle according to the invention aiming to isolate the handling ring from the bladed elements makes it possible to reduce the plastic deformations and stresses during the solidification and cooling.

(35) Indeed, the invention seeks to limit the thermomechanical stresses caused by thermal gradients in the direction of the directed solidification. The risks of recrystallised grains and cold cracks are mitigated with the solution of the invention. As this concerns a directed solidification method, the mould is cooled heterogeneously, the bottom cooling first, causing traction of the hot metal by the cold metal. By controlling the temperature in the bottom of the mould, it is possible to control the temperature gradient according to the direction of solidification. A balance of the metal masses of the top portion in relation to the bottom portion is established, and the stresses on all of the parts produced are mitigated and better distributed.

(36) Furthermore, it should be noted that a numerical validation of the solution of the invention by estimation of the plasticity criterion of the Von Mises criterion type at the end of solidification shows that the stresses are significantly mitigated in the order of 45 to 50% when the cluster is directly connected to the casting cup 2, as according to the examples in FIGS. 1 and 2 according to the invention, rather than being connected to a feed system in the form of a ring as according to the conventional top-pour casting solution of the prior art. Therefore, the probability of forming metallurgical defects, in particular of recrystallised grain type, is lower.

(37) Advantageously, the principle of the invention previously described may be applied to any type of cluster configuration.

(38) Of course, the invention is not limited to the examples of embodiments that have just been described. Various modifications may be made by the person skilled in the art.