FR3124408A1 - CERAMIC CORE USED FOR THE MANUFACTURE OF BLADE BY LOST WAX CASTING - Google Patents

Abstract

Ceramic core (40) used for the manufacture by lost-wax casting of a turbine engine blade, the core (40) extending in a longitudinal direction (X) between a root and a head (41), the core (40) comprising a first non-functional part (44) arranged at the level of the foot or the head (41), the first non-functional part (44) comprising at least one boss (60; 62; 64) extending perpendicular to the longitudinal direction (X), the boss (60; 62; 64) having a distal end portion, with respect to the first non-functional part (44), which has a parabolic convex shape. Abstract Figure: Figure 3

Description

CERAMIC CORE USED FOR THE MANUFACTURE OF BLADE BY LOST WAX CASTING

This description relates to a ceramic core used for the manufacture by wax casting of a turbine engine blade. This description relates to the mold for the manufacture of such a core. This description also relates to an assembly for the manufacture of a turbomachine blade using lost wax, the assembly comprising a mold for the manufacture of the blade and such a core.

A turbomachine conventionally extends along an axis and comprises, from upstream to downstream in the direction of gas circulation within the turbomachine, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a turbine high pressure, a low pressure turbine and an exhaust nozzle. The high pressure turbine is coupled in rotation to the high pressure compressor, via a high pressure shaft, so as to form a high pressure body. The low pressure turbine is coupled in rotation to the low pressure compressor, via a low pressure shaft, so as to form a low pressure body. The fan is connected to the low pressure shaft, either directly or via a speed reducer.

The blades of the low pressure and high pressure turbines of a turbomachine are subjected to the very high temperatures of the gases coming from the combustion chamber, which can lead to premature degradation of said blades and limit their service life.

In order to control the temperature of these blades, the latter may comprise internal cooling circuits. Air from the low-pressure compressor, for example, is sent to the cooling circuits of these blades, so as to limit their temperature.

In the remainder of the description, the terms axial, radial and circumferential are used with reference to the axis of the turbomachine.

There illustrates a turbomachine high-pressure turbine blade 10. Said blade 10 comprises, radially from the inside outwards, a foot 12, a platform 18 and a blade 16. The blade 16 comprises intrados 20 and extrados 22 surfaces connected upstream by a leading edge 24 and downstream, by a trailing edge 26.

The radially outer end 14 or crown of the blade 16 comprises a hollow part in the shape of a so-called bathtub 30. The latter is delimited by a bottom transverse to the blade 16 and by a peripheral wall forming its edge in the extension of the wall of the blade 16. The blade 16 further comprises a plurality of internal cavities communicating with a cooling air inlet located at the level of the root 12 of the blade 10 and opening at the level of perforations 28 distributed over the blade 16. The perforations 28 are located at the level of the intrados 20 and extrados 22 surfaces of the blade 16 and at the level of the leading 24 and trailing 26 edges of the blade 16.

The perforations 28 at the trailing edge 26 have the shape of slots, the other perforations 28 having generally circular or oval shapes. Other shapes may be provided, in particular at the mouth of each perforation 28.

Such blades 10 are manufactured by a lost wax casting or foundry process. For this, a metallic material is molded in a so-called “shell” mould. The shell mold comprises a cavity, that is to say a hollow shape delimiting in particular the blade 10 to be produced. One or more ceramic cores 40 can be mounted in the shell mold, at the level of the cavity, so as to form recessed zones in the part to be manufactured, in particular when the latter has a complex geometry. The cores 40 are in particular intended to delimit the cavities defining the cooling circuits as well as the tub 30 at the level of the top 14 of the blade 16.

There illustrates a known core 40 for making a turbine blade 10. This extends in a first direction X and comprises a first part 42 and a second part 44 spaced apart from each other in the first direction X.

The first part 42 forms, during the subsequent molding process of the blade 10, cavities or channels intended to form at least part of the cooling circuit of the blade 10. In this, the first part 42 of the core 40 is referred to as “functional” in that it makes it possible to produce the final geometry of the blade, in particular an internal face delimiting the cooling circuit.

Still during the subsequent molding process of the blade 10, the second part 44 is in particular intended to form the bath 30 of the blade 10. In this, the second part of the core is said to be "non-functional" in that it has, in part, no impact on the final blade geometry.

The ceramic cores 40 are themselves manufactured by molding a ceramic paste, also called slip 60, in a so-called “core injection” mould. This paste is mainly composed of a ceramic powder and a binder. The core injection mold is also composed of two shells 52 pressed against each other at a parting plane. The two shells 52 each delimit a part of the cavity of the core 40 to be made.

The core 40 thus obtained is then covered with wax in a wax injection mould, or covered with any other easily achievable material, so that a wax model of the blade 10 is produced. The wax model is then dipped several times in slips made of a suspension of ceramic particles to make, by operations called stuccoing and drying, the shell mould.

The carapace mold is then dewaxed, which is an operation by which the wax or the material constituting the original model is removed from the carapace. After this elimination, the shell mold presents the cavity which reproduces all the shapes of the blade 10 and which still contains the core 40 intended to generate the internal cavities thereof. The dewaxing of the shell mold makes it possible to simultaneously carry out a high-temperature heat treatment or “cooking” of the shell mold, which gives it the necessary mechanical properties. The shell mold is then ready for the manufacture of the blade 10 by casting a molten metal, which comes to occupy the cavity between the inner wall of the shell mold and the core 40, then to solidify it.

During this process, several phenomena come into play, such as the intrinsic deformation of the core 40 during its manufacture, the deformations and displacements of the core 40 induced by the forces during the injection of the wax or during the casting of the metal , and the effects of thermal expansion and thermal shrinkage. The core 40 is conventionally maintained, respectively, in the wax injection mold and in the shell mold according to 6 isostatism points. However, this is not enough to keep the core in place throughout the foundry process. Thus the control of the dimensions of the blade manufactured, in particular the dimensions of the walls of the blade 10 and the dimensions of the internal cavities of the blade 10, is not easy and the scrap rate of the blades 10 thus manufactured is high. .

Furthermore, providing a hyperstatic solution to absorb the deformations and displacements of the core 40 is not suitable in that this causes the core to break due to the forces induced therein.

The present description aims to propose a solution to these drawbacks.

Summary

A core is proposed, in particular made of a ceramic material, used for the manufacture by lost-wax casting of a turbine engine blade, the core extending in a longitudinal direction between a root and a head, the core comprising a first non-functional part arranged at the level of the foot or the head, the first non-functional part comprising at least one boss extending perpendicularly to the longitudinal direction, the boss having an end portion distal with respect to the first non-functional part having a parabolic convex shape.

Such a boss is capable of forming a point of contact to hold the core in position in a wax injection mold or in a shell mold during the manufacture by investment casting of a turbine engine blade, in particular when the core is deformed, displaced or dilated due to the forces induced during the injection of the wax, the casting of the metal or even due to thermal gradients. The point of contact may, for example, be intended to be formed, depending on the manufacturing step, either between the first non-functional part of the core and a wax injection mold, or between the first non-functional part of the core and a shell mold whose walls form a cavity in which the core is placed. The point of contact can also be intended to be formed between sub-elements of the first non-functional part. Unintentional movement of the first non-functional part of the core relative to the adjacent element is thus limited, or even prevented. The core is then better held in position during the manufacture by lost-wax casting of a turbine engine blade, ensuring better control of the dimensions of the walls of the turbine engine blade thus obtained, while reducing the risks of core breakage. .

The convex parabolic shape of the distal end portion of the boss makes it possible to form a single point of contact for the first non-functional part of the core, thus limiting the forces induced in the core. Thus, the risks of core breakage are limited, or even prevented.

Furthermore, the positioning of the boss at the level of the first non-functional part of the core makes it possible not to alter the final geometry of the turbomachine blade.

The term "functional" used in reference to the parts of the core makes it possible to indicate whether the part thus qualified makes it possible to produce a face of the final geometry of the blade, that is to say an external face such as a face intrados or extrados, for example, or an inner face delimiting the blade cooling circuit. Thus, a non-functional part refers to an area of a core element which has no impact, in whole or in part, on the final geometry of the blade.

In a particular embodiment, the distal end portion of said at least one boss may have a spherical shape.

The first non-functional part may comprise a first face intended to be placed opposite a first wall of a mold for manufacturing a blade in which the core is able to be placed, said at least one boss comprising at least one boss of a first type projecting from the first face. The mold can be a wax injection mold or a shell mold for the lost wax production of a blade.

The first non-functional part may comprise a second face intended to be placed opposite a second wall of a mold in which the core is able to be placed, the second face being opposite the first face, said at least one boss comprising at least one boss of a second type projecting from the second face.

The core may include an intrados face, the first face of the non-functional part may coincide, in whole or in part, with the intrados face of the core. The core may include an extrados face, the second face of the non-functional part may coincide, in whole or in part, with the extrados face of the core. The intrados face and the extrados face of the core are intended to form, by form complementarity, respectively, internal faces of the blade which are each arranged opposite to the external intrados and extrados faces of the 'dawn. The intrados face and the extrados face of the core are not as such aerodynamic surfaces.

The first non-functional part may comprise a first element and a second element separated from each other in a direction perpendicular to the longitudinal direction. The first element may comprise a face disposed facing the second element, said at least one boss comprising at least one boss of a third type projecting from said face of the first element.

The second element may include a housing in which is received by shape complementarity said at least one boss of the third type projecting from said face of the first element.

Said at least one boss may be integral with the first non-functional part of the core.

According to another aspect, a first mold (or “core injection mold”) is proposed for the manufacture of the core as described above, the first mold comprising a cavity, the cavity comprising at least a first zone intended to form, in whole or in part, the first non-functional part of the core, the first region of the cavity having a recess adapted to form said at least boss of the core.

The first mold may comprise a first shell and a second shell each delimiting a part of the cavity. The first shell and the second shell can be adapted to be pressed against each other at a joint plane.

The first mold may include a removable insert delimiting the first zone of the impression. Such a feature allows easy and quick adjustment of the size of the boss through a plurality of inserts each having a recess having particular dimensions.

According to another aspect, an assembly is proposed for the manufacture of a turbomachine blade using lost wax, the assembly comprising a second mold for the manufacture of the blade and a core as described above, the second mold comprising walls delimiting a molding cavity, the core being placed in the cavity of the second mold so as to form a passage between the core and the walls of the second mold, said at least one boss of the first non-functional part of the core being adapted to form a clearance between the distal end of the boss and the walls of the second mold or between the distal end of the boss and a sub-element of the first non-functional part of the core.

The second mold can be a wax injection mold or a shell mold for the lost wax production of a blade.

The game can be formed in a first configuration of the core, called "at rest", in which the core is subjected to no mechanical or thermal stress.

Said at least one boss can be adapted to form a point of contact between the distal end of the boss and the walls of the second mold or between the distal end of the boss and a sub-element of the first non-functional part of the core in a second configuration of the core in which the latter is expanded, deformed or moved in the mold cavity, in particular due to the forces induced during the injection of the wax, the casting of the metal or even due to an increase of the temperature.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawings, in which:

is a perspective view of a prior art turbine blade;

is a perspective view of a prior art core for manufacturing the blade of the ;

is a partial perspective view of a core according to the present description;

is a sectional view of the core of the in section plane III-III;

is a perspective view of the core of the arranged, according to a first configuration, in a mold for the manufacture of a lost-wax blade;

is a perspective view of the core of the disposed, according to a second configuration, in a mold for the manufacture of lost-wax blades.

Claims (9)

Ceramic core (40) used for the manufacture by lost-wax casting of a turbine engine blade, the core (40) extending in a longitudinal direction (X) between a root and a head (41), the core (40) comprising a first non-functional part (44) arranged at the level of the foot or the head (41), the first non-functional part (44) comprising at least one boss (60; 62; 64) extending perpendicular to the longitudinal direction (X), the boss (60; 62; 64) having a distal end portion, with respect to the first non-functional part (44), which has a parabolic convex shape. Core (40) according to Claim 1, in which the first non-functional part (44) comprises a first face (50) intended to be placed facing a first wall of a mold (70) for the manufacture of a blade in which the core (40) is able to be placed, said at least one boss (60; 62; 64) comprising at least one boss of a first type (60) projecting from the first face (50). Core (40) according to Claim 2, in which the first non-functional part (44) comprises a second face (52) intended to be placed facing a second wall of the mould, the second face (52) being opposite the first face (50), said at least one boss (60; 62; 64) comprising at least one boss of a second type (62) projecting from the second face (52). Core (40) according to claim 2 or 3, the core (40) comprising an intrados face and/or an extrados face, and in which the first face (50) and/or the second face (52) of the first non-functional part (44) of the core (40) coincides, in whole or in part, respectively with the intrados face and the extrados face of the core (40). A core (40) according to any preceding claim, wherein the first non-functional portion (44) comprises a first element (44a) and a second element (44b) spaced apart in a perpendicular direction (Y) to the longitudinal direction (X), and in which the first element (44a) comprises a face (54a) arranged opposite the second element (44b), said at least one boss (60; 62; 64) comprising at at least one boss of a third type (64) projecting from said face (54a) of the first element (44a). Core (40) according to Claim 5, in which the second element (44b) comprises a housing in which is received by form fit said at least one boss of the third type (64) projecting from the said face (54a) of the first element (44a). A core (40) according to any preceding claim, wherein said at least one boss (60;62;64) is integral with the first non-functional portion (44) of the core (40). A first mold for the manufacture of the core (40) according to any one of the preceding claims, the first mold comprising a cavity, the cavity comprising at least a first zone intended to form, in whole or in part, the first non- functional (44) of the core (44a), the first region of the recess having a recess adapted to form said at least boss (60; 62; 64) of the core (40). Assembly for the lost-wax manufacture of a turbomachine blade, the assembly comprising a second mold (70) for manufacturing the blade and a core (40) according to any one of Claims 1 to 7, the second mold (70) comprising walls delimiting a mold cavity (72), the core (40) being placed in the cavity (72) of the second mold (70) so as to form a passage between the core (40) and the walls of the second mold (70), said at least one boss (60; 62; 64) of the first non-functional part (44) of the core (40) being adapted to form a clearance (j) between the distal end of the boss (60; 62) and the walls of the second mold or between the distal end of the boss (64) and a sub-element (44a; 44b) of the first non-functional part (44) of the core (40).