EP3395471B1 - Core for the fabrication of a turbine engine blade - Google Patents

Description

The present invention relates to the field of turbomachine blading, that in particular of blading obtained by casting a molten alloy in a mold using the lost-wax casting technique.

Conventionally, the lost-wax casting technique consists first of all in making a model in wax, or in any other material that can be easily removed later, of the part to be made; this model comprises an internal part forming a ceramic core which represents the cavities which one wishes to see appear inside the blade. The wax model is then dipped several times in slips consisting of a suspension of ceramic particles to make, by so-called stuccoing and drying operations, a 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, a ceramic mold is obtained, the cavity of which reproduces all the shapes of the blade and which still contains the ceramic core intended to generate the internal cavities thereof. The mold then undergoes a high temperature heat treatment or “baking” which gives it the necessary mechanical properties.

The shell mold is then ready for the manufacture of the metal part by casting. After checking the internal and external integrity of the shell mould, the next step consists in pouring a molten metal, which fills the voids between the inner wall of the shell mold and the core, then in solidifying it. In the field of lost-wax casting, there are currently several solidification techniques, and therefore several casting techniques, depending on the nature of the alloy and the expected properties of the part resulting from the casting. It can be directed solidification with columnar structure (DS), directed solidification with monocrystalline structure (SX) or equiaxed solidification (EX).

After casting the alloy, the shell is broken by a shake-out operation. During another step, the ceramic core which remained enclosed in the blade obtained is chemically eliminated. The metal blade obtained then undergoes finishing operations which make it possible to obtain the finished part.

Examples of the production of turbine blades by the lost-wax casting technique are given in the patent applications FR2875425 and FR2874186 of the plaintiff. Other embodiments of turbine blades are given in the patent applications FR3037829 , WO2013167847 , WO2015026535 and US5820774 .

To form the wax model of the dawn, a tool or wax injection mold is used, in which the core is placed and then the liquid wax is injected through a channel provided for this purpose.

The quest for increased engine performance notably involves more efficient cooling of the turbine blades located immediately downstream of the combustion chamber. This requirement necessitates the formation inside these blades of more elaborate internal cooling fluid circulation cavities. These blades have the particularity of having several metal walls and therefore require the manufacture of increasingly complex ceramic cores.

Due to the complexity of the cooling cavities to be formed with their partition walls, and their arrangement, the core is produced in several parts which are assembled and glued. The elementary nuclei are generally linked together at the level of the foot and the top. It is in fact a question of controlling the thickness of the walls and of the partitions formed at the time of casting. The assembly must allow the core to withstand the stresses undergone during the wax injection, dewaxing and then casting stages.

It is thus necessary to place the different parts of the core very precisely relative to each other in the wax injection mold and to guarantee that the relative positions of the different parts of the core are maintained. Maintaining the different parts of the core as proposed in the current technique consists of fixedly connecting these parts or core elements to the ceramic shell. If such a maintenance allows in theory to guarantee a precise relative positioning of the various elements of the core, it is observed that the casting of molten metal leads to a non-negligible thermal expansion of the elements of the core inducing, due to a static fixation of the constituent elements of the core with respect to each other. others to deformations of some of these elements, which contributes to increasing the scrap rate of the blades. In critical cases, one of the elements of the core can even break, obviously leading to rejecting the blade obtained but also to manufacturing a new core, which is costly and time-consuming.

The object of the invention is in particular to provide a simple, effective and economical solution to the problems of the prior art described above.

To this end, it proposes a core, according to claim 1, used for the manufacture by lost-wax casting of a turbine engine blade, extending in a longitudinal direction between a root and a head and comprising a main element and at least one first secondary element each comprising a functional part and a non-functional part, characterized in that the non-functional part of the main element and the non-functional part of the said at least one first secondary element are assembled and shaped so as to cooperate sliding with each other in the longitudinal direction and rotating around this longitudinal direction.

According to the invention, the connection of the main element and the first secondary element of the core allows relative displacement by longitudinal sliding and by rotation of the core elements with respect to each other. More particularly, when the main element is fixed in the ceramic shell, the first secondary core can expand longitudinally and in rotation in its non-functional part. Thus, it is possible to limit the deformations and breaks of the core, which reduces the scrap rate of the blades at the end of a lost wax casting operation.

Also, the use of non-functional parts of the core elements avoids modifying the functional parts of the core. Indeed, the dimensioning of these functional parts is difficult to achieve and a modification of their shapes for reasons other than those related to the final shape of the blade is not desirable. The non-functional parts are formed at a longitudinal end of the core, preferably at the base of the core.

The term “functional” used in reference to 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. Thus, a non-functional part refers to an area of a core element that has no impact on the final geometry of the part.

The longitudinal direction corresponds to a direction extending from the root of the blade to the tip of the blade, this longitudinal direction being substantially perpendicular to the axis of rotation of the turbomachine.

According to another characteristic of the invention, the slip is a linear slip, that is to say along a line, more specifically a straight line, the slip then being straight linear. The main element of the core and the first secondary element of the core are therefore positioned and guided in movement with respect to each other at the level of the foot according to a rectilinear line of the first secondary element sliding on a plane of the main element . This also makes it possible to have isostatic and non-hyperstatic positioning of the first secondary element on the main element.

The linear mode of sliding, more particularly rectilinear, is distinguished from a sliding of one surface on another surface, by preventing excessive mechanical stresses from being exerted on the first secondary element and the main element and causing buckling, the deformation or even a break of the elements of the core.

In order to allow the differential expansions between the first secondary core element and the shell as well as the absolute expansions of said two parts of the core with respect to the shell mould, a set of expansion can be provided between the shell mold and the first secondary element. This expansion clearance can be achieved by interposing a film of varnish between the first secondary element and a boss of the shell mould. It is understood that during the dewaxing and baking operation of the shell mould, the film of varnish will be eliminated resulting in the formation of a free space forming a clearance between the first secondary element and the shell mould.

Advantageously, the combination of the expansion clearance and the aforementioned linear guide greatly limits the risks of core breakage, thus making it possible to optimize the blade manufacturing process.

Said non-functional part of said at least one secondary element may comprise a rod slidably engaged in a first groove of the non-functional part of the main element. The rectilinear linear guidance can then take place at the level of the zone of contact of the rod with the bottom of the groove. The film of varnish is then deposited on a portion of the face of the rod arranged opposite the bottom of the first groove.

The first groove may comprise two lateral flanks moving away from each other in the direction of the outlet of the first groove. The use of such flanks makes it easier to center the rod in the groove. When the rod has a substantially circular cross-section, the line support can take place with a groove bottom surface which is flat.

In one embodiment, the core comprises a second secondary element, a non-functional part of which comprises a rod engaged in longitudinal sliding in a second groove of the non-functional part of the main element.

The rod of the first secondary element and the rod of the second secondary element are for example arranged symmetrically to each other with respect to a straight line extending longitudinally, the first groove and the second groove opening out in opposite directions along a direction perpendicular to the longitudinal direction.

It also relates to a method, according to claim 10, for manufacturing a blade by means of a core as described above, in which the non-functional part of the main element of the core is retained in a mold of injection of wax by an anchoring means on a wall of the mould.

• la figure 1 est une vue schématique en perspective d'une extrémité inférieure d'un noyau selon l'invention ;
• la figure 2 est une vue schématique en perspective de l'élément principal du noyau selon l'invention ;
• la figure 3 est une vue schématique selon une ligne de coupe du montage d'une tige d'un élément du noyau dans une gorge d'un autre élément du noyau.

The invention will be better understood and other details, advantages and characteristics of the invention will appear on reading the following description given by way of non-limiting example, with reference to the following figures:

• the figure 1 is a schematic perspective view of a lower end of a core according to the invention;
• the figure 2 is a schematic perspective view of the main element of the core according to the invention;
• the picture 3 is a schematic view along a section line of the mounting of a rod of one element of the core in a groove of another element of the core.

We first refer to the figure 1 representing a lower end of a core 10 according to the invention comprising a main element 12 and two secondary elements, namely a first secondary element 14 and a second secondary element 16. figure 1 , only the non-functional parts of the constituent elements of the core 10 are shown, these non-functional parts being arranged at a longitudinal end of the core 10 (double arrow L). As indicated above, a non-functional part of the core 10 is a part that does not participate in the final geometry of the part during the lost-wax casting process.

The core 10 extends in three directions perpendicular in pairs, a longitudinal direction L corresponding on the final blade to the longitudinal direction L connecting the root to the tip of the blade, an axial direction A ( figure 1 ) corresponding on the final blade to the upstream/downstream direction and a transverse direction T crossing the intrados and extrados faces of the blade ( picture 3 ). The core includes a head 17 on the figure 1 and a foot 11 which alone is represented on the figure 1 .

The main element 12 of the core 10 is intended to form in its functional part (not shown) a central cavity of the blade and the first and second secondary elements 14, 16 are intended to form in their functional parts (not shown) cavities in the intrados and extrados walls of the blade.

As is clearly visible on the figure 1 , the non-functional part of the first secondary element 14 comprises a rod or finger 18 extending substantially longitudinally and which is housed in a first groove 20 or substantially longitudinal notch of the non-functional part of the main element 12 ( figures 1 and 2 ). Similarly, the second secondary element 16 comprises in its non-functional part a rod 22 extending substantially longitudinally and which is housed in a second groove 24 or substantially longitudinal notch of the non-functional part of the main element 12 ( figures 1 and 2 ). The invention also covers embodiments in which the main element 12 of the core 10 only comprises a single groove associated with a single secondary element of the core.

As shown on the figure 2 , the first groove 20 and the second groove 24 open out in opposite directions in a direction perpendicular (double arrow T) to the longitudinal direction L, that is to say in the transverse direction T. The rod 18 of the first secondary element 12 and the rod 22 of the second secondary element 16 are symmetrical to each other with respect to a straight line D extending longitudinally L.

The first groove 20 and the second groove 24 are separated from each other by a web 26 of material from the main element 12 of the core, this web 26 being inclined obliquely with respect to a first plane containing the longitudinal direction L and the transverse direction T and a second plane containing the longitudinal direction L and the axial direction A.

According to the invention, the rod 18 of the first secondary element 14 is slidably mounted in the first groove 20 of the main element 12 of the core 10, just as the rod 22 of the second secondary element 16 is slidably mounted in the second groove 24 of the main element 12 of the core 10. In addition, each of the grooves 20, 24 is shaped so as to allow a degree of freedom in rotation of the rods 18, 22 around the longitudinal axis L.

The rods 18, 22 have a circular shape and the bottom 28 of the grooves 20, 22 is flat so that the contact between a rod 18, 22 and the bottom 28 of a groove 20, 24 is a rectilinear line contact, which makes it possible to carry out a guide according to a rectilinear support of the first secondary element of the core and of the second secondary element of the core on the main element of the core without hyperstatic connection. In this way, the friction of the three parts of the core on each other is greatly limited and the relative expansions are allowed.

In addition, each rod 18, 22 is sized so that its diameter is flush with the exit plane 30 of the groove 20, 24 in which it is engaged. Thus, it is possible to ensure linear contact between the shell 32 and the rod 18, 22 of each of the first 14 and second 16 secondary elements.

Each groove 20, 24 comprises two opposite sides 34, 36 connected to one another by the bottom wall 28 flat. The two sides 34, 36 of each groove 20, 24 move away from each other in the direction of the outlet of the groove 20, 24. As can be seen on the picture 3 , the width of the groove 20, 24 measured at the level of the bottom wall 28 is less than the diameter of the rod 18, 22.

As depicted in picture 3 , the shell mold comprises a first internal boss 38 formed on an internal face of the mold 40 and positioned so as to clamp the rod 18 of the first secondary element 14 of the core 10 in the first notch 20 of the main element 12 of the core 10. Similarly, the mold 40 comprises a second internal boss (not shown) formed on an internal face of the mold 40 and positioned so as to grip the rod 22 of the second secondary element 16 of the core 10 in the second notch 24 of the element main 12 from core 10. note that the first 38 and second bosses are thus formed on faces facing the mold in the transverse direction T and cover the outlets of the first 20 second 24 notches. It is understood that the zone 44 separating the shell mold 40 from the core 10 comprises wax.

Each boss 38 comprises two longitudinal sides 38a, 38b inclined obliquely relative to each other, converging towards each other towards the inside of the mold 40 and connected to each other by a wall 38c for clamping the rods 18, 22 of the first and second secondary elements 14, 16 of the core 10 in the bottom of the notch 20, 24. Preferably, the sides 38a, 38b are inclined at an angle between 10 and 30 ° relative to a plane containing the longitudinal direction A and the transverse direction T to the longitudinal direction and passing between the two sides 38a, 38b.

As can be seen on the picture 3 , a film of varnish 42 is interposed between the rod 18, 22 of each of the non-functional part of the first secondary element 14 and of the non-functional part of the second secondary element 16 and the wall 38c of the boss 38 opposite. It is understood that during the dewaxing and firing operation of the shell mould, the film 42 of varnish will be eliminated resulting in the formation of a free space forming a clearance between each of the first secondary element 14 and the second secondary element 22 and the shell mold 40. This free space forms a means for sliding the second non-functional parts of the first 14 and second 16 secondary elements.

If the invention has been described in relation to the cooperation with rectilinear linear sliding and rotation of a rod in a groove 20, 24, it is understood that these displacements can be obtained in other ways which come within the scope of the protection.

Thus, in another embodiment of the invention, the rod 18 of the first secondary element 14 and the rod 22 of the second secondary element 16 could have a shape other than circular, for example oval, more generally of concave shape.

Claims (10)

1. A core (10) used in manufacturing, by lost-wax casting, a turbomachine blade, the core extending along a longitudinal direction (L) between a base (11) and a head, and one main element (12) and at least one first secondary element (14), each including a functional part allowing to achieve a face of a final geometry of the blade and a non-functional part corresponding to a part which does not participate to the final geometry of the blade, characterized in that the non-functional part of the main element (12) and the non-functional part of said at least one first secondary element (14) are assembled and shaped so as to cooperate with one another by sliding in the longitudinal direction (L) and rotating around the longitudinal direction (L).
2. The core of claim 1, characterized in that the sliding motion is a linear rectilinear sliding motion and the non-functional parts are formed at one longitudinal end of the core (10), in preference at the level of the base (11) of the core (10).
3. The core of claim 1 or 2, characterized in that said non-functional part of the first secondary element (14) comprises a rod (18) engaged by sliding into a first groove (20) of the non-functional part of the main element (12).
4. The core of claim 3, characterized in that the first groove (20) includes two lateral sidewalls (34,36) that are spaced increasingly further apart from one another in a direction of an outlet of the groove (20).
5. The core of claim 4, characterized in that the sidewalls (34,36) are connected to a substantially plane bottom wall (28).
6. The core of claim 3 to 5, characterized in that the rod (18) has a substantially circular cross section.
7. The core of claim 1 to 6, characterized in that it further comprises a second secondary element (16) of which a non-functional part comprises a rod (22) engaged by longitudinally sliding into a second groove (24) of the non-functional part of the main element (12).
8. The core of claim 7, characterized in that the second groove is located on a face of the main element that is opposite the first groove.
9. The core of claim 7 or 8, characterized in that the rod (18) of the first secondary element (12) and the rod (22) of the second secondary element (16) are symmetrical to each other with respect to a line (D) extending longitudinally (L), the first groove (20) and the second groove (24) opening into opposite directions according to a direction (T) that is perpendicular to the longitudinal direction (L).
10. A method for manufacturing a blade by means of the core (10) of anyone of preceding claims, wherein the non-functional part of the main element (12) of the core (10) is retained in a wax injection mould by an anchoring means on a wall of the mould.

Images