Patent Application
20240287905
The invention relates to the manufacture of gas turbine engine blades.
The technology of metal powder injection (metal injection molding or MIM) to manufacture metal products is known. This technology makes it possible to meet high production rate needs while having good repeatability and good reproducibility.
It is an injection molding from a mixture of metal powder and polymer binder. This mixture forming an aggregate, called “feedstock”, is extruded then cut into flakes or pellets to be used in an injection press.
After the injection, a part called “green” part held in place by the binder is obtained. This binder is then removed during the step called debinding step, which can be carried out in different ways (aqueously, thermally or chemically), which gives a part called “brown” part.
This part where nearly all of the binder has been removed is very fragile because it is composed of approximately 40% air, and is only bound by the remains of the binder. The brown part is finally sintered, step during which it is subjected to a temperature close to the melting point of the powder. This temperature allows the grains to weld together to create a solid.
After this step, a “gray” part is obtained, composed of the material of the powder only and having shrunk in relation to the volume of the molding due to the spaces left by the binder. Depending on the methods, parts with a density of 95% to 99.5% can be obtained for different applications. The part is then finished.
This technique makes it possible to create complex shapes with excellent surface finish and fine tolerances. More profitable for complex shapes, the metal powder injection molding allows the production of medium and large series of small parts for a large market. Being part of the family of replication techniques, it is very efficient in raw materials (for the powder part). It does not create waste and oil is not used.
However, the shrinkage of the part mentioned above makes it difficult to apply this technique for the manufacture of gas turbine engine blades. Indeed, a removal of up to 15% of a dimension of the blade is observed. However, it is important to accurately control the dimensions of this type of part. In addition, the thermal variations to which the blade is subjected during the manufacture can cause deformations or cracks. This is all the more sensitive as the blades are generally asymmetrical and have thicknesses in certain locations which are up to 3.5 times greater than the thickness in another location of the blade.
One aim of the invention is therefore to make the manufacture of the gas turbine engine blades easy and more reliable, in particular by injection of metal powder.
For this purpose, a method for manufacturing a gas turbine engine blade is provided according to the invention, in which:
As will be seen below, depending on their configuration, the protuberance(s) can have different functions, namely serving as a support for the part during manufacture and/or as a stiffener. Thus, they make it possible to avoid the appearance of deformation phenomena such as sagging, torsion, bending and buckling and of mechanical stresses related to the manufacturing process. The invention thus allows the manufacture of elongated parts of complex geometry, in particular asymmetrical parts, and makes it possible to control the dimensions of the part, while making possible a material removal comprised between 10 and 27% during manufacture. The invention allows high-rate production. It reduces material losses during manufacture. The entire manufacture can be done with an optimized budget.
In one mode of implementation, during manufacture, in particular during the heat treatment step, the part is in contact with a support via the protuberance (s).
The protuberances therefore serve here as support integrated into the part in order to prevent its deformation, in particular its sagging, during manufacture. This may for example be the sintering step during the implementation of the metal powder injection technique.
In one mode of implementation, the protuberance or at least one of the protuberances is a rib.
These ribs then form stiffeners that limit the deformations of the part during the temperature variations it experiences.
The method according to the invention may further have at least one of the following characteristics:
It can be provided that the protuberance(s) has/have an edge opposite to the main face, the edge extending in a plane or the edges of the protuberances extending in the same plane.
This/these edge(s) thus serve(s) as a support face for the part during manufacture.
A gas turbine engine blade, in particular an aircraft turbine engine, is also provided according to the invention, the blade comprising a base, a root and an air stream area extending between the base and the root, the blade resulting from the implementation of a method according to the invention.
Such a blade may have, on a macroscopic level, a shape and dimensions identical to those of a blade manufactured through a method of the prior art. However, it differs in its microscopic structure. Thus, it has a grain size on average larger than that of the blade obtained by a method of the prior art and it offers better resistance to creep.
A gas turbine engine comprising at least one blade according to the invention is moreover provided according to the invention.
There is also provided according to the invention a part comprising:
This part constitutes the intermediate product obtained during the implementation of the first step of the method of the invention, before the elimination of the rib(s).
One embodiment of the invention will now be presented by way of non-limiting example in support of the drawings in which:
One mode of implementation of the manufacturing method according to the invention will be presented for the production of a gas turbine engine blade.
In a first step, an intermediate part 4 comprising a blade is manufactured. This part is illustrated in its principle in
The part and the blade thus comprise a base 6, a root 8 and a vane or air stream area 10 extending between the base and the root.
The air stream area 10 has two main faces, namely an intrados face 12 visible in
The air stream area 10 comprises protuberances, here forming ribs, protruding from the intrados face 12, as illustrated in
One 20 of the ribs forms a closed central loop and in this case has an elliptical shape. The major axis of the ellipse is globally parallel to the edges 16 and 18. The rib has a center of symmetry located in line with a barycenter 22 of the part and/or of the blade and coincides therewith in the figures. This barycenter 22 forms a midpoint and central point of the blade.
The air stream area 10 also comprises in this case transverse ribs 24 each extending from the leading edge 16 to the trailing edge 18. The transverse ribs 24 are curved, which further reduces the risk that harmful phenomena such as cracks appear. Each transverse rib 24 has a center of curvature located on the same side of the rib as the center of the ellipse 22. The transverse ribs 24 are here four in number, namely two between the elliptical rib 20 and the base 6 and two others between the elliptical rib 20 and the root 8. The adjacent transverse ribs 24 are spaced from each other by a distance comprised between 5 and 25 mm.
The air stream area 10 also comprises in this case rectilinear radial ribs 26 each located in the alignment of the center 22 of the air stream area. In other words, although each radial rib 26 is interrupted before reaching this midpoint and therefore does not reach it, this point 22 would be on the rib if it were extended in a rectilinear manner.
All the radial ribs 26 here have a first end located on the elliptical rib 20 from which the radial ribs radiate.
Two of the radial ribs 26 extend up to the base 6. Two others extend up to the root 8. These ribs can be described as longitudinal because they extend over a large part of the length (more than a third) of the air stream area 10 and in a direction slightly inclined relative to the longitudinal direction. In this case, they each intercept two of the transverse ribs 24, which amounts to saying that they are intercepted by them.
Several other radial ribs 26, in this case four, extend up to the trailing edge 18. Furthermore, several other radial ribs 26, in this case six, extend up to the leading edge 16.
There is therefore in the present example a total of 14 radial ribs 26, this number being in no way limiting.
All the ribs 20, 24 and 26 form in this example an arrangement globally having a plane of symmetry. It even has two planes of symmetry perpendicular to each other and corresponding to the axes of the ellipse, so that the arrangement presents a center of symmetry coincident with the center 22. The arrangement of the ribs here resembles that of a spider web.
These symmetries concern the general arrangement of the ribs, each rib thus having a rib which occupies a position symmetrical to its own. But they do not relate to the precise dimensions of the ribs, as can be seen in particular in
Ribs are also present inside the looped rib 20. These include a rectilinear rib 34 occupying the entire major axis of the ellipse and a rib 36 occupying half of the minor axis, as illustrated in
The ribs extend only on the intrados face 12, the extrados face 14 remaining completely free of ribs.
In this case, the manufacture implements an injection of metal powder. The manufacture takes place by means of injection molding from a mixture of metal powder and polymer binder. The metal powder is here an alloy of titanium and aluminum such as Ti-48Al-2Cr-2Nb (in atomic %) commonly referred to as TiAl 48-2-2).
Once the part has been injected, a part held in place by the binder is obtained. This binder is then removed during the debinding operation, which gives the “brown” part. In this part, almost all of the binder has been removed and it is composed of about 40% air, and is bound only by the remains of the binder. It must then be sintered, a step during which it is subjected to a temperature close to the melting point of the powder, for example above 1,200° C.
After this operation, a “gray” part is obtained, composed of the powder material only and having shrunk in relation to the volume of the molding due to the spaces left by the binder.
This part 4 is made in one block. During the debinding and sintering operations, the part rests on a planar support, the ribs 20, 24, 26 being located in the lower part and the extrados face 14 facing upwards. The edge 30 of the ribs is therefore bearing on the planar support and in contact therewith. It provides local support to the air stream area. The part also rests on the manufacturing support by the base 6 and the root 8.
The ribs 20, 24, 26 not only form support but also stiffeners which make it possible to preserve the shape of the part and its integrity during these operations, particularly during sintering and then cooling.
At the end of this first manufacturing step, a part forming an intermediate product and consisting of the blade and of the ribs as illustrated in
Then, the ribs 20, 24, 26 are eliminated from the air stream area, for example by machining.
A part consisting of the single blade 32 illustrated in
On the blade 32, the air stream area 10 has a thickness which is approximately 3.5 times smaller than that of the base 6 and the root 8. This difference can have a significant impact during the cooling and shrinkage of the part in the absence of protuberances. The ribs are precisely disposed and dimensioned as explained above in order to increase this ratio from 3.5 to approximately 2 in this case. In particular, the central portion of the air stream area is made more massive with the protuberances. Globally, taking into account the location of the massiveness areas of the part 4 makes it possible to distribute the material during the design in order to avoid excessive differences in thickness over the entire part.
In addition, in the absence of support from the ribs, the air stream area 10 would sag during manufacture. This is why the ribs are disposed on the air stream area, in order to support it. The ribs which extend in different directions and at different locations in the part help to avoid different types of deformation to which the blade would otherwise be exposed during manufacture.
As can be seen, the ribs are uniformly distributed, in particular so that the bearing points of the part on the manufacturing support are also uniformly distributed. The arrangement of the ribs takes into account a reference point which remains fixed throughout the manufacture of the part which is the barycenter 22 thereof. The ribs are disposed according to this point, or even from it. Indeed, taking into account the position of the center of gravity 22 of the assembly makes it possible to better control the removal inherent to the method.
Each rib here has a thickness comprised between 1 and 8 mm. It is indeed preferable to give a significant width to the stiffeners. If they are too thin, they are difficult to inject and deform during the removal of the part. In our case, the choice of range is related to the minimum thicknesses of the part.
In addition, each rib in this case has an area of connection with the intrados face 12 having a radius comprised between 0.2 and 2 mm, which makes it possible to promote the injection and eliminate internal stress concentrations. This condition on the dimension of the radii makes it possible to limit cracking phenomena, to make the injection more favorable and to avoid tearing during the injection of the part out of the mold.
Furthermore, it will be preferably made sure to take into account in the design of the part to be manufactured and forming the blade-ribs assembly, the injection constraints and the phenomena of segregation, core porosity and internal stress which are generated and detected during sintering.
In the present example, the blade 32 is intended to form part of an aircraft turbojet engine 100 forming here a twin spool and airflow gas turbine engine like the one illustrated in
It comprises from upstream to downstream, therefore from left to right in
The high-pressure compressor 7, the combustion chamber 9 and the high-pressure turbine 11 form a high-pressure body, which together with the low-pressure compressor 5 and the low-pressure turbine 13 define a main air stream. A nacelle surrounds the fan 2 and the central part so as to form a fan compartment and to define a secondary air stream.
The turbines 11, 13 comprise blades 32 manufactured through the invention.
The invention is applicable to other manufacturing technologies, for example feedstock printing and feedstock compaction.
The manufacture could also take place using the binder jetting printing technique. The latter is an additive manufacturing method which works by binder jetting onto a powder. An automated roller distributes a thin layer of powder onto a build tray. A print head applies a liquid binder to the powder, creating a layer of the object. Then, the printing platform carrying the tray slightly goes down to allow the addition of a new layer of powder. The method is thus repeated until creation of the object. The excess powder is thus sucked up and the object is dusted using compressed air. Then the printed part is placed in an oven for baking or sintered. Finally, a finish treatment can improve the condition of the printed part. As before, the ribs are then removed from the intermediate product thus produced to obtain the blade itself.
As the invention relates to the manufacture of metal parts, in particular by the metal powder injection method, it can be used in all technical fields.
Numerous modifications can be made to the invention without departing from its scope.
The protuberances may be other than ribs and have shapes other than those presented above and be round, square, star-shaped, stud-shaped, half-ball shaped, etc. They can provide a stiffening function without providing a support function and vice versa.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2104869 | May 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2022/050856 | 5/3/2022 | WO |
