EP1980343A1 - Tool for manufacturing foundry ceramic cores for turbomachine vanes - Google Patents

Abstract

The tool for manufacturing a ceramic foundry core (10) for turbomachine blade with a leading edge and a trailing edge, comprises first and second imprints (530, 540) of the core movable in a direction F'1 with respect to other direction F'2 between a molding position and an unmolding position, sub parts movable with respect to the imprints except on the low thickness part, and mechanical ejectors (570). The core comprises a thick side part of the leading edge and a part (10A1) of low thickness on the side of the trailing edge. The mechanical ejectors are fixed on the imprints. The tool for manufacturing a ceramic foundry core (10) for turbomachine blade with a leading edge and a trailing edge, comprises first and second imprints (530, 540) of the core movable in a direction F'1 with respect to other direction F'2 between a molding position and an unmolding position, sub parts movable with respect to the imprints except on the low thickness part, and mechanical ejectors (570). The core comprises a thick side part of the leading edge and a part (10A1) of low thickness on the side of the trailing edge. The mechanical ejectors are fixed on the imprints such that the low thickness part is unmolded according to a main opening direction and one of the two imprints. Two matrices are horizontally movable between opened and closed positions. The imprints comprise decorations (510) for forming cavities in the core. An independent claim is included for a process for manufacturing a foundry core.

Description

The present invention relates to the manufacture of parts such as metal blades of turbomachines, having internal cavities with complex geometry forming in particular cooling circuits, according to the lost wax casting technique. It relates to casting tooling of the foundry core for these parts.

The manufacture of the blades according to this technique involves the production of a model, wax or other equivalent temporary material, which comprises an inner part forming a foundry core and the cavities of the blading. To form the model, a wax injection mold is used in which the core is placed and the wax is injected. The wax model obtained is then soaked several times in slips consisting of a suspension of ceramic particles to make a shell mold. We remove the wax and cook the carapace mold. Blading is achieved by casting a molten metal into the shell mold which occupies the voids between the inner wall of the shell mold and the core. Thanks to an appropriate germ or selector and controlled cooling, the metal solidifies in a desired structure. Depending on the nature of the alloy and the expected properties of the part resulting from the casting, it may be directed solidification with columnar structure (DS), directed solidification with monocrystalline structure (SX) or equiaxed solidification (EX) respectively. The first two families of parts concern superalloys for parts subjected to strong thermal and mechanical stresses in the turbojet engine, such as HP turbine blades.

After solidification of the alloy, the shell and the core are unchecked. The result is the desired blading.

The foundry cores used are composed of a ceramic material with a generally porous structure. They are made from a mixture consisting of a refractory filler in the form of particles and a more or less complex organic fraction forming a binder. Examples of compositions are given in patents EP 328452 , FR 2371257 or FR1785836 . As is known, the foundry cores are shaped by molding in a core box using for example an injection at the hurry. This shaping is followed by a debinding operation during which the organic fraction of the core is removed by a means such as sublimation or thermal degradation, depending on the materials used. A porous structure results. The core is then consolidated by heat treatment in an oven. A finishing step is possibly necessary to eliminate and deburr the traces of joint planes and obtain the geometry of the core. Abrasive tools are used for this purpose. It may still be necessary to strengthen the core, so that it is not damaged in subsequent cycles of use. In this case, the core is impregnated with an organic resin.

The gas turbine engine high pressure turbine blade cores have a fine trailing edge area. There is also a demand for parts with portions of walls or areas always thinner. As a result, the mold filling limits are often reached and lead to the development of more fluid ceramic pastes or the modification of the injection parameters. In particular, injection rates or pressures greater than the traditional conditions of use for filling the mold cavities are used.

However, these techniques have certain limitations. The ceramic material has abrasive properties and the shear stresses generated by the new, more severe filling conditions are the cause of premature wear of the fine areas of the tools resulting in an increase in the number of production stops and maintenance costs. tooling. In addition the demolding operation can cause deformation of the core when the paste has infiltrated into the mechanisms of the core box. Thus, these conditions for filling and demolding the core in the core box are at the origin of cracks and burrs type indications which cause the disposal of large quantities of cores after their ejection and control. Defects can also be revealed only after the debinding and baking heat treatment.

In order to improve the quality of the filling in the imprint, the present applicant has proposed in the patent application FR 0651682 to thicken the kernel teeth in the trailing edge area then machine the thickened teeth to return to the required thickness. The teeth designate the part of the core near the trailing edge and which after casting of metal the channels for evacuation of the cooling air.

Another method of remedying these manufacturing problems according to the invention is now proposed with a tool for manufacturing a foundry core, for a turbomachine blade with a leading edge and a trailing edge, the core comprising a a thick portion on the leading edge side and a thin portion on the trailing edge side, the mold comprising first and second impressions movable in a direction relative to each other between a molding position and a demolding position, with moving sub-parts relative to the imprints. This tooling is characterized in that the parts of the fingerprints corresponding to said thin portion of the core do not comprise a moving sub-piece, mechanical ejectors being provided on one or other of the impressions, so that after injection of the core, the part of small thickness is demolded in the main direction of opening and in that at least one of the two indentations, in its portion corresponding to the zone of small thickness, is shaped so as to obtain parts in extra thickness locally facilitating the filling of the mold to injection, these parts being intended to be machined to reduce their thickness.

By thin zone is meant a thickness e less than 0.5 mm. Thicknesses as low as 0.1 mm are aimed at.

The two cavities are preferably movable in translation between the open and closed positions. More particularly, the imprints comprise decorations on the surface and protruding for the formation of cavities in the core.

The invention also relates to a method for manufacturing a foundry core, comprising at least one thin zone, in particular a fine trailing edge, for a turbomachine blade in particular, comprising forming into a suitable tooling a mixture comprising a filler of ceramic particles and an organic binder, extraction from the mold, debinding and a heat treatment of consolidation of the core, characterized in that a core blank is formed in said tooling with said part in overthickness and that said part is machined extra thickness after extracting the blank of the mold and before or after the heat treatment operation.

While the skilled person seeks to develop lower viscosity materials or to modify the injection parameters, in particular the flow rate without forgetting the pressure, it has appeared that the reduction of the games and the mechanical deformations of the mold and the core in the fine areas allowed a significant improvement in the quality of it. It is overcome by the invention of any development, initial and after each maintenance, long and tedious adjustment of sub moving parts and special development on mold wear, even with a decrease in wall thicknesses up to 0.1 mm on the delivered core.

Thanks to the invention, it also reduces the costs of obtaining and operating the core boxes or mold and therefore foundry cores. While the amount of cores having mold release injection crack, baking crack and injection burr indications, obtained by injection into a mold with a fine trailing edge reaches several tens of%, the solution allows the fast obtaining of the best level of quality of the cores, the elimination of the burrs related to the game of the sub-parts of the box with nucleus and the reduction of the manufacturing hazards of the cores having fine trailing edges. The target limit goes down to thicknesses of 0.1 mm.

The core material preferably comprises 80 to 85% mineral filler and 15 to 20% organic binder. The composition advantageously corresponds to one of those described in the patent EP 328452 of the Applicant, in particular to the less fluid composition, but also the one which has the smallest variation of shrinkage in production series of cores.

• La figure 1 est une vue en coupe d'une aube de turbine refroidie avec sa zone de bord de fuite étroite,
• La figure 2 est une vue en perspective du noyau de l'aube de la figure 1,
• La figure 3 est une vue d'une boîte à noyau ouverte,
• La figure 4 est une coupe de principe d'une boîte à noyau selon l'art antérieur, c'est à dire présentant des sous pièces mobiles obliques au niveau du bord de fuite,
• La figure 5 est une coupe de principe d'une boîte à noyau dans les zones fines conformément à l'invention,
• La figure 6 est une illustration du principe de l'action des éjecteurs sur le noyau céramique.

Other features and advantages will emerge on reading the following description of an embodiment of the method of the invention with reference to the appended drawings in which:

• The figure 1 is a sectional view of a cooled turbine blade with its narrow trailing edge zone,
• The figure 2 is a perspective view of the nucleus of the dawn of the figure 1 ,
• The figure 3 is a view of an open core box,
• The figure 4 is a basic section of a core box according to the prior art, that is to say exhibiting oblique moving sub-parts at the trailing edge,
• The figure 5 is a basic section of a core box in the fine areas according to the invention,
• The figure 6 is an illustration of the principle of the action of ejectors on the ceramic core.

The following description corresponds to the application of the invention to the formation of a foundry core for a high pressure turbine blade in a gas turbine engine for aeronautical or land use. This example is not limiting.

As we see on the figure 1 , such a turbine blade 1 comprises an intrados face IN an extrados face EX, a leading edge BA and a trailing edge BF. The dawn includes several internal cavities, here 7: 1A to 1G. The cavities are separated from each other by partitions: 1AB, 1BC, etc. The trailing edge comprises an opening 1 H or a plurality of openings on its long fed from the last cavity 1 G by GH channels 1 'parallel to each other for the exhaust of the cooling fluid in the gas stream. The cooling fluid consists of air taken from the compressor.

When making this type of blade by casting a molten metal in a carapace mold, it must incorporate therein a core which occupies the voids of the cavities to be formed in the blade. This core 10, shown schematically on the figure 2 is of complex geometry. It comprises a portion corresponding to the cavities of the blade 10A, a portion 10B corresponding to the cavities of the root of the blade and a portion 10C forming a gripping handle during manufacture. At the head of the blade we also see a part 10D corresponding to what is designated by bathtub in the jargon of the domain. This part is here separated from the part 10A by a transverse recess. This recess forms the bottom wall of the bathtub after casting.

It includes a thin zone 10A1 corresponding to the trailing edge. This part in the example of the figure 1 encompasses portions 10G in part, 10GH and 10H. 10G is the part of the core forming the cavity 1G of the blade. 10GH is the part of the core corresponding to the channels 1GH, and 10H corresponding to the cavities 1H. The thin zone generally extends a few millimeters from the edge of the core corresponding to the trailing edge.

It is recalled that the molds are most often composed of two indentations, one lower than the other upper, which are strongly pressed against each other at the time of molding and then removed to allow the extraction of the molded part. . Unlike other processes where the mold is lost (sand casting, lost wax, etc.), it is imperative to ensure that the injected parts do not get stuck in the imprints and that they can instead go out without any deterioration. The surfaces parallel to the extraction direction are avoided; they differ from an angle called "draft" which can vary from 3 to 5 degrees. Some difficult parts of extraction require a system of sliding rods called ejectors. Moreover, the geometry of the part to be molded may include undercuts and not allow demolding by simply separating the lower and upper impressions in the demolding direction. These then comprise for these parts against the remains of moving sub-parts arranged to ensure demolding.

The figure 3 represents an injection box 300, forming a core mold, in the open position. It comprises a lower plate 310 and an upper plate 320 respectively fixed to the lower and upper matrices of the injection molding machine, not shown. This type of box comprises two impressions, one said lower 330 the other upper 340. When the box is in the closed position, is injected via an injection channel 350 the paste (mixture of polymer and ceramic) which fills the 360 space for the kernel. Each imprint includes on its inner wall relief elements forming the decorations to reserve the recessed portions of the core.

On the figure 4 the section of a conventional mold for turbine blade core 10 is shown in section. It comprises impressions 330 and 340 with decorations 370 for the cavities intended to protect the partitions of the finished blade. The curvature of the nucleus along its rope is important. The direction of the kernel portion located at the trailing edge forms an angle of the order of 45 to 60 degrees with the direction of the thicker portion located on the leading edge side. This curvature does not make fingerprints without moving parts because we can not avoid the parts against the remains.

The usual technique is to design the cavities of the mold with sub-pieces 330a and 340a at the trailing edge 10A1 of the core 10 which have a certain mobility indicated by the arrows F1 and F2. Usually, the number of partitions having the same orientation in the solid part of the core is greater than in the direction of decorations at the trailing edge. In the prior art, therefore, the mobile sub-part is reserved for the trailing edge outlets and the direct demoulding of the lower and upper impressions to the solid part of the core. By the invention the tooling is simplified in its critical part at the trailing edge and the mobile sub-parts are kept in the thicker and simpler areas of production. The decorations 370a at the sub-pieces are oriented in spares in the direction of the arrows. They make it possible to extract the core after injection of the material into the mold.

As explained above, the injection of material in this area 10A1 is all the more delicate as it is fine. It is necessary to increase the pressure, but the paste is then introduced more easily in the games between the moving parts. Moreover, mobility also leads to deformations on this part of the nucleus.

The object of the invention is to provide a core comprising thin zones having such a complex structure without having in particular deformation of these areas during injection and demolding operations.

Deformations lead to the appearance of cracks in the fine areas or burrs in the mechanisms of the core box. The cracks lead to the rejection of the nucleus. Burrs accelerate the wear of the core box and increase the number of production stops. Wear of the core box reduces its life.

According to the invention, a modified mold is made, that is to say a mold or some areas that were movable in the matrix become fixed.

Such a mold comprises figure 5 , a lower cavity 530 and an upper cavity 540 between the two plates 560 and 580 of the injection molding machine. The core 10 is injected into the space between the two cavities. Sets 510 enter the core to reserve the partitions cavities. In this figure, we see the core 10 as the trailing edge 10A1. Ejectors 570 are formed in the lower recess 530 under the trailing edge portion 10A1.

We did not represent the other part of the nucleus. It is thicker and fingerprints in this part are likely to include moving parts.

The axis of the decorations 510 is oriented in the main opening direction of the tool indicated by the arrows F'1 and F'2. The decors 510 of the trailing edge are demolded by mechanical ejectors 570 sliding along the axis of the arrows, here vertical. These are metal rods that are actuated from outside the mold. They are located in the lower part 530 of the mold.

The mold preferably has no hinge contrary to the prior art (see reference 160 on the figure 4 ) but can be attached to the upper platens 580 and lower 560 of the injection press as shown in FIG. figure 5 .

For the manufacture of the core with this tooling, the steps are as follows,

The two indentations 530 and 540 are placed in the press along their joint plane P;

The paste is injected into the space left free by the imprints;

After injection of the paste and formation of the core 10, the upper imprint of the lower imprint is spaced along the directions F'1 and F'2; the core 10 remains stuck to the lower imprint;

The core is extracted with the help of ejectors 570 which print upward pressure on the part 10A1 of the core.

A sufficient number of ejectors are determined and distributed so as to ensure a low pressure at their point of contact with the core. This distribution of the total pressure in several low pressures makes it possible to avoid any buckling of the core during its ejection. In addition the ejectors maintain a direction as parallel as possible to the demolding axis.

An example of the distribution of ejectors and their points of contact with the nucleus is shown in figure 6 . The base 61 of the injection mold is shown in the lower part of the figure - the lower half of the mold is not shown to reveal the ejectors over their entire length. Core 62 includes core body 62a, tub 62b, core foot 62c, and feed core 62d. It can be seen that the ejectors are distributed over the entire core 62 and that in the figure they are seven in number: two ejectors 63 of the bath 62b, an ejector 64 of the core body 62a, an ejector 65 of the connection zone foot / core body, two 62c core foot ejectors 62c, and a 62d injection core ejector 67. The ejectors 63 to 67 print a bottom-up motion to the ceramic core 62 and lift it from the imprint.

For the manufacture of the core, a suitable mixture was made. It is in particular an organic binder associated with a mineral filler. For example the mixture is made according to the teaching of the patent application EP 328452 . The core has a good hold in hand and its constitution allows the work by means of a milling tool by removal of chips or abrasion.

In the case of injecting the trailing edge with thickened teeth as reported in the patent application FR 0651682 of the present applicant, the next step is to machine, in this blank 10, the thickened areas that are added in the mold.

Once the kernel edges have been machined, if necessary, before baking, the following processes, known per se, are carried out in the process of manufacturing the foundry cores. For debinding, that is to say the removal of the organic binder, the core is heated to a temperature sufficient to degrade the organic components it contains. The other steps consist in heating the core to the sintering temperature of the ceramic particles that compose it. If additional consolidation is necessary, impregnation with an organic resin

For cores machined after baking the finish and the control pass directly.

Claims (5)

Tooling for making a foundry core for a turbomachine blade with a leading edge and a trailing edge, the core (10) comprising a thick part on the leading edge side and a weak part (10A1) thickness of the trailing edge side, comprising first and second cavities (530, 540) of the core movable in a direction (F'1 respectively F'2) relative to one another between a molding position and a demolding position, with, where appropriate, moving subparts relative to the cavities, characterized in that the indentations on said thin portion do not comprise a moving subpart, mechanical ejectors (570) being provided on the one or the other of the imprints, so that the thin portion (10A1) is demolded in the main direction of opening and in that at least one of the two imprints, in its portion corresponding to the thin area, is co nformée so as to obtain portions in excess locally facilitating the filling of the mold injection, these parts being intended to be machined to reduce their thickness. Tooling according to claim 1 wherein both matrices are movable in translation between the open and closed positions. Tooling according to claim 1 or 2, the impressions of which comprise decorations (510) for the formation of cavities in the core (10). A process for manufacturing a foundry core, comprising at least one thin zone, in particular a fine trailing edge, for a turbomachine blade in particular, comprising forming in a tool according to claim 1 a mixture comprising a feedstock ceramic particles and an organic binder, extraction from the mold, debinding and a heat treatment for consolidation of the core, characterized in that a blank of core with said thickened portion and that said part is machined extra thickness after extracting the blank of the mold and before or after the heat treatment operation. Method according to claim 4, wherein said thickened portion corresponds to at least one channel for evacuating cooling air from the fine blade.

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