Method for manufacturing a ceramic core for manufacturing turbomachine vanes

Abstract

A method for manufacturing a ceramic core blank intended for the manufacture of hollow turbomachine blades using the technique of lost wax casting, the blank being manufactured by additive manufacture and comprising at least one first part intended to form the cavities of the hollow blades and at least one second part configured to allow the positioning of the core in a wax mold, the second part and the first part being positioned and held with respect to one another by means of a junction portion interposed between the first part and the second part, at least one through orifice extending through the second part, the junction portion and the first part, a first end of the through orifice opening to an outer face of the second part, and a second end of the through orifice opening to an outer face of the first part.

Claims

1. A method for manufacturing a ceramic core blank for the manufacture of hollow turbomachine blades using the technique of lost wax casting, the blank being manufactured by additive manufacturing and comprising: at least one first part for forming cavities of the hollow blades, at least one second part configured to allow positioning of the ceramic core in a wax mold, the at least one second part and the at least one first part being positioned and held with respect to one another by means of a temporary junction portion interposed between the at least one first part and the at least one second part, at least one through orifice extending through the at least one second part, the temporary junction portion and the at least one first part, a first end of the at least one through orifice opening to an outer face of the at least one second part, and a second end of the at least one through orifice opening to an outer face of the at least one first part.

2. The method according to claim 1, wherein the temporary junction portion comprises a passage putting into fluid communication the at least one through orifice and a space outside the core blank.

3. The method according to claim 1, wherein the at least one through orifice comprises a first rectilinear portion extending from the first end, and a second rectilinear portion having an angle less than 180° with respect to the first rectilinear portion, and extending from the second end.

4. The method according to claim 3, wherein the angle between the first and the second rectilinear portion is greater than or equal to 100°.

5. The method according to claim 4, wherein the angle between the first and the second rectilinear portion is comprised between 110° and 120°.

6. The method according to claim 1, wherein a diameter of the first rectilinear portion of the at least one through orifice is comprised between 0.15 and 0.3 mm.

7. A method for manufacturing a ceramic core for the manufacture of hollow turbomachine blades using the technique of lost wax casting, the method comprising a step of manufacturing a blank by the method according to claim 1, and also comprising, after the manufacture of the blank: cleaning the at least one through orifice, inserting at least one positioning rod into the at least one through orifice, capping the at least one through orifice, eliminating the temporary junction portion.

8. The method according to claim 7, wherein the cleaning of the at least one through orifice is accomplished by an injection of pulsed air and/or a solvent into at least one end of the at least one through orifice.

9. The method according to claim 7, wherein the at least one positioning rod is a rod of alumina.

10. The method according to claim 7, wherein the capping of the at least one through orifice is accomplished by applying a ceramic paste to the two ends of said at least one through orifice.

11. The method according to claim 10, comprising, after capping, a hardening step allowing hardening the ceramic paste used for capping the at least one through orifice.

12. The method according to claim 7, wherein, prior to their insertion, the at least one positioning rod is coated with ceramic adhesive.

13. A method for manufacturing a hollow turbomachine blade using the technique of lost wax casting, comprising: Manufacturing the ceramic core by a method according to claim 7, manufacturing a wax model having a shape of a final part by arranging the ceramic core obtained in the preceding step in a wax mold, manufacturing a ceramic mold by plunging the wax model obtained in the preceding step several times into a slurry, pouring, after the elimination of the wax, molten metal into the ceramic mold and around the ceramic core, elimination of the ceramic mold and of the ceramic core.

14. A ceramic core blank for the manufacture of hollow turbomachine blades using the technique of lost wax casting, comprising: at least one first part for forming cavities of the hollow blades, at least one second part configured to allow positioning of the ceramic core in a wax mold, the at least one second part and the at least one first part being positioned and held with respect to one another by means of a temporary junction portion interposed between the at least one first part and the at least one second part, at least one through orifice extending through the at least one second part, the temporary junction portion and the at least one first part, a first end of the at least one through orifice opening to an outer face of the at least one second part and a second end of the at least one through orifice opening to an outer face of the at least one first part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages will be better understood upon reading the detailed description given hereafter of the different embodiments of the invention given by way of non-limiting examples. This description refers to the pages of appended drawings, in which:

(2) FIG. 1 shows schematically a plan view of a portion of a ceramic core intended to be used in the manufacture of hollow turbomachine blades using the technique of lost wax casting,

(3) FIG. 2A shows schematically a technique for cleaning an orifice according to the prior art, and FIG. 2B shows schematically a technique of cleaning an orifice according to the present disclosure,

(4) FIG. 3 shows a schematic transparent view of a portion of a ceramic core of the present disclosure,

(5) FIG. 4 is a diagram shown the method of manufacturing a ceramic core according to the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

(6) FIGS. 2A and 2B show schematically samples of a ceramic cored, in the form of test pieces, allowing illustrating the cleaning of an orifice of the core. FIG. 2A shows schematically a technique for cleaning an orifice 50 according to the prior art. The orifice 50 is non piercing. The hashed part represents the ceramic core, more precisely the polymerized paste forming the ceramic core. The latter comprises a first part 20, a second part 30 and a junction portion 60. The greyed part shows the non-polymerized ceramic paste remaining in the orifice 50 after the printing of the core blank.

(7) During additive manufacture, the core blank is made layer by layer, beginning with the first part 20 for example, then the junction portion 60, then the second part 30, while providing for the presence of the orifice(s) 50. The junction portion 60 has a toothed shape, limiting the contact surface between the junction portion 60 and the first part 20 and/or the second part 30. The junction portion 60 can thus comprise a plurality of teeth 61, in the form of spikes or of studs, interposed between these two parts.

(8) According to the specific case illustrated in FIG. 2A, the orifice 50 is non piercing and comprises a bottom 51. The operation of cleaning the orifice is carried out, for example by means of a drill 70, its passage into the orifice 50 allowing removing the paste. A technique of this type causes the deterioration or the breakage of many ceramic cores.

(9) FIG. 2B shows schematically a technique for cleaning an orifice 50 according to the present disclosure. Unlike the specific case according to the prior art, the orifice 50 is piercing. More precisely, the orifice 50 comprises a first rectilinear portion 50a extending through the second part 30, the junction portion 60 and the first part 20, and a second rectilinear portion 50b extending through the first part 20 from the end of the first rectilinear portion 50a and opening on an outer face of the first part 20. The first rectilinear portion 50a is preferably longer than the second rectilinear portion 50b, and is intended to receive a positioning rod. The angle β between the first and the second rectilinear portion 50a, 50b is less than 180°, and greater than or equal to 100°, preferably comprised between 110° and 120°.

(10) During additive manufacture, a passage 62 is provided in the junction portion 60. This passage 62 can be an orifice or a local absence of teeth 61, allowing the orifice 50 to be put into fluid communication with a region outside the ceramic core, and surrounding it. The passage 62 allows facilitating the cleaning operation of the orifice 50. In fact, at the end of additive manufacture, the cleaning of the orifice 50 can be carried out by injecting pulsed air at one or both ends of the orifice 50. The pressure exerted at the ends of the orifice 50 allows the removal of the non-polymerized paste present in the orifice, through the passage 62 of the junction portion 60 (see arrows in FIG. 2A). In place of the pulsed air, a solvent can be injected, or a mixture of air and of solvent. Alternatively, a suitable cylindrical tool can be used to push the paste, in addition to or in place of the air and/or of the solvent.

(11) FIG. 3 shows a schematic view of a part of the ceramic core 10 according to the present disclosure, accomplished by additive manufacture, comprising a first part 20, a second part 30, and a junction portion 60. The first part 20 has the shape of the cavities that it is desired to obtain at the end of the manufacture of the turbine blade. In FIG. 3, only the upper end of the first part 20, corresponding to the upper end, or tip, of the blade is visible. The second part 30 or dome, allows the retention of the ceramic core 10 during the manufacture of the wax model, and during the pour of metal into a ceramic shell mold. The first part 20 and the second part 30 are spaced from one another by a distance S comprised between 0.4 and 1.4 mm. This spacing and this positioning of the first part 20 with respect to the second part 30 are provided, and the end of the manufacture of the core blank, by the junction portion 60. After the elimination of the junction portion 60, the space S remaining between these two parts allows the formation of the bathtub at the tip of the blade, during the pouring of metal infiltrating into this space.

(12) In this example, three through orifices 50 extend through the second part 30, the junction portion 60 and the first part 20. Each of these orifices 50 comprises a first rectilinear portion 50a opening on an outer face of the second part 30, and a second rectilinear portion 50b (of which only one is visible in FIG. 3) opening to an outer face of the first part 20. A positioning rod 40 is inserted into each of these orifices 50. These positioning rods 40 can be rods of alumina, and can have a length of 13 mm and a diameter of 0.6 mm. Nevertheless, these dimensions are not limiting and can be modified depending on the considered geometry of the core.

(13) The rest of the description describes a method for manufacturing a ceramic core 10 according to the present disclosure, with reference to FIG. 4.

(14) A first step in the manufacturing of a ceramic core 10 comprises the manufacture of a core blank by additive manufacture (step S1). The blank comprises the first part 20, the junction portion 60 and the second part 30. Additive manufacture provides for the presence of through orifices 50, and of the passage(s) 62 in the junction portion 60.

(15) At the end of the manufacture of the blank, the orifices 50 are cleaned i.e. emptied of residues of non-polymerized ceramic paste remaining in the orifices 50 (step S2). To this end, pulsed air and/or solvent, for example, is injected in the ends of the orifices 50. The residual paste is thus removed by the passage 62 of the junction portion 60.

(16) A positioning rod 40 is then inserted into each through orifice 50 (step S3). More precisely, a positioning rod 40 is inserted into the first rectilinear portion 50a of each through orifice. The rods 40 are inserted from the top, i.e. by the end of the orifice 50 opening on an outer face of the second part 30, and driven into the orifice 50 so as to extend both in the second part 30 and in the first part 20. The rods 40 can be previously coated with ceramic adhesive. This adhesive solidifies during the thermal treatment described below, and allows optimal coating of the rod.

(17) After the placement of the positioning rods 40 in the orifices 50, the latter are capped (step S4). This capping is carried out by means of a ceramic paste, so as to obtain a smooth surface condition on the outer faces of the first and second parts 20 and 30. This allows subsequently avoiding surface irregularities on the wax model, and on the final part. The capping is followed by a step of hardening the ceramic paste, allowing solidifying the paste added in step S4 (step S5). This step can be carried out according to the properties of the paste, depending on whether it is, for example, photosensitive or heat-sensitive, by means in particular of a UV light source or a heat source. According to this embodiment, the hardening step is accomplished by exposure to UV light. It will be noted that after solidification of the ceramic paste, the core 10 can also follow a heat treatment step comprising debonding and sintering.

(18) The method finally comprises the elimination of the junction portion 60 (step S6). This elimination is facilitated by the toothed shape of the junction part 60, and can be accomplished by any suitable tool which can be inserted between first part and the second part. At the end of this step, the first part 20 and the second part 30 are held to one another and positioned with respect to one another solely by the positioning rods 40.

(19) The ceramic core 10 thus obtained can then be used in the manufacture of hollow turbomachine blades using a technique of lost wax casting. In particular, the ceramic core 10 can be arranged in a wax mold, while being held by the second part 30 to form the wax model having the shape of the final part, with cavities formed by the first part 20 of the ceramic core 10. The wax model is then plunged several times into a slurry in order to form the ceramic mold. After elimination of the wax, the molten metal is poured into the ceramic mold and around the ceramic core, the latter again being held in fixed position by means of the second part 30. Finally, the ceramic mold and the ceramic core 10 are then eliminated by shaking-out, in order to obtain the final part. It will be noted that the elimination of the ceramic also comprises the elimination of the alumina positioning rods 40, withdrawn during shaking-out, then leaving small orifices through the bathtub at the top of the blade, at the location where these rods were located. These orifices serve in particular as holes for dust removal or for removal of the air present in the cavities of the blade.

(20) Although the present invention has been described by referring to specific exemplary embodiments, it is obvious that modifications and changes can be carried out on these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the different embodiments illustrated/mentioned can be combined into additional embodiments. Consequently, the description and the drawings must be considered in an illustrative, rather than a restrictive sense.

(21) It is also obvious that all the features described with reference to a method are transposable, alone or in combination, into a device, and conversely, all features described with reference to a device are transposable, alone or in combination, to a method.