Casting method for obtaining a part including a tapering portion

Abstract

A casting method for obtaining a part that includes a tapering portion, and a turbine engine blade obtained by casting and including a tapering trailing edge, are provided. The method includes: providing an insert element having a tapering section; making a shell around the insert element; and casting a molten material into the shell including the insert element.

Claims

1. A casting method for obtaining a blade for a turbine engine that includes a tapering trailing edge, the method comprising: providing an insert element having a tapering section; making a shell around the insert element; and casting a molten material into said shell including the insert element, wherein said tapering trailing edge of the blade is constituted by said tapering section of said insert element wherein the molten material is a material from the family of metals.

2. A method according to claim 1, wherein the making the shell comprises, in order: providing a mold reproducing a shape of the blade that is to be obtained; inserting the insert element in said mold in a location corresponding to the trailing edge of the blade that is to be obtained; injecting wax into said mold and obtaining a wax model including the insert element; molding the shell around the wax model including the insert element; and firing the shell and removing the wax.

3. A method according to claim 2, wherein the mold is a reusable metal mold.

4. A method according to claim 1, wherein the insert element includes recesses into which the molten material can penetrate during casting.

5. A method according to claim 1, wherein the insert element is heated to a temperature close to that of the molten material during casting.

6. A method according to claim 1, wherein a thickness of the tapering section of the insert element is less than 1 mm.

7. A method according to claim 1, wherein the insert element includes a composite material.

8. A method according to claim 7, wherein the shell includes a cavity presenting a shape of a main portion of the obtained blade, and the obtained blade presents a transition zone between the main portion and the insert element, in which transition zone the molten material and material of the insert element are in solid solution.

9. A method according to claim 1, wherein the molten material is a titanium-aluminum alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are diagrammatic and seek above all to illustrate the principles of the invention. In the drawings, from one figure to another, elements (or portions of an element) that are identical are referenced by the same reference signs.

(2) FIGS. 1A to 1H show eight successive steps in an example of the method.

(3) FIG. 2 shows an alternative embodiment of a turbine engine blade.

(4) FIG. 3 shows another alternative embodiment of a turbine engine blade.

DETAILED DESCRIPTION OF EMBODIMENTS

(5) In order to obtain a more concrete idea about the invention, an example method is described in detail below with reference to the accompanying drawings. It should be recalled that the invention is not limited to this example.

(6) FIGS. 1A to 1H show the various steps in an example implementation of the casting method. It seeks to obtain a final part 80 having a main portion 81 and a tapering insert portion 82. In this implementation, the desired part is a turbine blade and the insert portion 82 is its trailing edge. Naturally the parts that it is desired to obtain may be much more complicated and may in particular include a plurality of insert portions of sizes and mechanical properties that may be identical or different.

(7) In FIG. 1A, a metal mold 10 is provided. The mold has a cavity 11 forming a negative of the exact shape of the final part 80, i.e., in this example, a blade-shaped hollow.

(8) As shown in FIG. 1B, an insert element 21 is inserted in the cavity 11 of the mold 10 precisely at the location that corresponds to its final position in the final part 80. In this example, it is a tapering trailing edge having a thickness of about 0.7 mm. Naturally, the insert element 21 is prepared and shaped so as to enable it to be inserted in the cavity 11: in particular it is provided with the appropriate dimensions. Recesses 22 are also formed in the insert element 21. The insert element 21 may also be subjected to physiochemical treatments in order to provide it with advantageous properties. If necessary, fastener means may enable the insert element 21 to be held in place in the cavity 11 of the mold 10. In other implementations, instead of recesses 22 or in addition thereto, the insert element 21 may have projections that are to become embedded in the cast material so as to provide cohesion between the insert element 21 and the bulk of the finished part.

(9) As shown in FIG. 1C, wax 30 is then injected into the cavity 11 of the mold 10. The wax fills the cavity 11 completely together with the recesses 22 in the insert element 21. Once solidified, the wax 30 holds the insert element 21 captive.

(10) It is then possible to unmold the wax model 40 as obtained and as shown in FIG. 1D. This model comprises a main portion 41 that is made of wax derived from the wax 30 that has solidified, together with the insert element 21 secured to the wax main portion 41. The wax model 40 thus presents the exact shape of the final part 80, the insert element 21 being situated exactly in the position of the future insert portion 82.

(11) As shown in FIG. 1E, a shell 50 is then molded around the wax model 40. For example, the wax model 40 may be embedded in a powder of refractory material 51. Successive layers of refractory material 51 may be put into place. Feed chimneys may also be provided for use in subsequent casting.

(12) As shown in FIG. 1F, the shell 50 is then fired, e.g. in a kiln. The refractory material powder 51 then transforms into a ceramic 61 forming a solidified shell 60. At the same time, under the effect of heat, the wax melts and is discharged, thus leaving behind a cavity 62. This produces a solidified shell 60 that includes the insert element 21 still in the correct position and a cavity 62 presenting the shape of the main portion 81 of the final part 80.

(13) Thereafter, as shown in FIG. 1G, a molten material 70, in this example a TiAl alloy, can be cast via the feed chimneys. The molten material 70 then fills all of the space available inside the shell 60, i.e. the cavity 62 and the recesses 22 in the insert element 21. The shell and the casting are then allowed to cool. In this implementation, the insert element 21 is made of metal. Thus, during cooling, at the interface 71 between the molten material 70 and the insert element 21, the two materials diffuse and interpenetrate. In other implementations, the insert element 21 may be made of composite material: under such circumstances, overall cohesion is provided mainly by the complementary shapes of the insert element 21 and the cast material 70 once it has solidified.

(14) Once cooling has terminated, the shell 60 is broken and the final part 80 is obtained as shown in FIG. 1H, in which the molten material 70 has solidified to give the main portion 81, while the insert element 21 is secured to the main portion 81 so as to constitute the insert portion 82. Depending on the conditions under which casting is performed, a transition zone 83 of greater or lesser size is present between the main portion 81 and the insert portion 82: in this transition zone 83, the two materials are in solid solution in varying proportions.

(15) Thus, FIG. 1H shows a first embodiment of a turbine blade obtained by casting and having a tapering trailing edge. In this example, the insert portion 82 reproduces the complete shape of the trailing edge extending the pressure side 88i and the suction side 88e of the blade to a common end 89; its thickness is then about 0.7 mm and it decreases down to its end 89.

(16) FIG. 2 shows a second embodiment of a turbine blade obtained by casting and having a tapering trailing edge. In this second example, the insert portion is a fine flat plate 182 having a thickness of 0.3 mm and arranged to extend the suction side 88e of the blade.

(17) FIG. 3 shows a third embodiment of a turbine blade obtained by casting and having a tapering trailing edge. In this third embodiment, the insert portion comprises a first fine flat plate 282a having a thickness of 0.3 mm arranged to extend the suction side 88e of the blade, and a second fine flat plate 282b having a thickness of 0.3 mm and arranged to extend the pressure side 88i of the blade.

(18) the implementations and embodiments described herein are given by way of non-limiting illustration, and on the basis of this description, a person skilled in the art can easily modify these implementations and embodiments or can envisage others, while remaining within the scope of the invention.

(19) Furthermore, the various characteristics of these implementations and embodiments may be used singly or in combination. When they are used in combination, these characteristics may be used as described above or in some other way, the invention not being limited to the specific combinations that are described in the present description. In particular, unless specified to the contrary, a characteristic described with reference to one implementation or embodiment may be applied in analogous manner to another implementation or embodiment.