Patent Application
20200116029
The present invention relates to a method for producing turbine engines solid blades.
It is advantageously implemented with metal materials that are difficult to transform into parts having a complex shape, like titanium aluminide.
It can also be implemented using ceramic-based materials.
It has a particularly important though nonexclusive use in the field of the solid blades or blades used in the aeronautical sector or the energy field, whether these blades or vanes are stationary or rotate.
For example, a turbine engine comprises at least one stationary nozzle guide blade assembly or stator, and a rotating blade assembly or rotor.
The stator is made up by stationary guide blades held between an inner ring and an outer ring or between two half-casings. In the case of a turbine, the stator makes it possible to guide and distribute the flow of the fluids over the blades of the rotor which are therefore rotated.
Conventionally, aeronautical blades are produced from either rough casting or as forged, partially or totally reworked.
It has already been proposed to produce stator stationary blades in several portions to facilitate operations particularly for piercing or machining before the assembly of the various portions (EP 3 103 580).
The distribution of the stresses present in a rotating blade is radically different to that observed in a stationary blade.
In particular, for blades all including a core, a root and a tip, the stresses at the root (embedded for a stationary blade and a rotating blade), as far as over approximately half of the core, can have a ratio of 1 (stationary blade) to 100 (rotating blade).
Indeed, if the thrust force is substantially the same in both cases, a rotating blade is subjected also to a centrifugal acceleration.
This is why this solution is limited to stationary blades. This is confirmed by the fact that the various portions are assembled by mechanical engagement.
The documents EP 2 772 614 and EP 1 481 755 which relate to hollow blades can also be mentioned.
The stresses linked to the centrifugal force are small in a hollow blade compared to those to which a solid blade is subjected.
This is the result of the respective positions of the center of gravity of the blade and of the respective masses of the blades.
It is for this reason that the teaching of these documents is limited to hollow blades.
When the rough piece is only partially machined and in particular when the profile of the blade is finished without mechanical reworking, a straightening, shaping and/or sizing operation is then essential to ensure functional dimensioning.
For small-sized turbine blades, in the case of forming a developmental prototype, or for perfecting operations, or for series blades made from easily machinable and inexpensive materials, ranges, said to be cut from the block, are used.
Such solutions have disadvantages in the case where it is desired to use titanium aluminide (gamma TiAl), which has good temperature resistance, but a significant brittleness at room temperature.
More specifically, these known solutions pose the following problems in particular.
In the case of a range obtained from a forged rough bar, using the entire surface for mechanical machining is possible but requires a complex machining range to be able to follow the deformations linked to the stress relaxations, or to use a self-adapting range. In addition, using a forged blank requires at least three process families: material development, forging, and machining, with a relatively long production cycle.
In the case of a range obtained with a rough casting, using the entire surface for mechanical machining is certainly possible but requires, again in this case, a complex machining range to be able to follow the deformations linked to the stress relaxations, said method generating, in any case, a significant scrap rate linked to the casting defects resulting after machining.
Using a rough casting finally requires three to five process families: material development, casting, possibly hot isostatic pressing, possibly straightening, and finally machining, and in this case again with a relatively long production cycle.
In the case of a range said to be cut from the block for mechanical machining, it is a matter in this case of starting from a slug (made by casting or extrusion) and transforming this simple geometry into that of the part by removing the surplus of material by machining.
Given the difficulty in machining gamma TiAl (again quite low cutting conditions, considerable tool wear, fragility of the material at room temperature, etc.) and the high cost of the material, this approach here again presents serious disadvantages for the production of blades in series.
It has been proposed to overcome these disadvantages using the method of producing turbine blades made from metal alloy described in FR2997885.
This method relates to simultaneously producing, from an aluminum and titanium alloy bar having a simple and/or axisymmetric geometry, at least two mutually interlocked blanks by waterjet cutting in the bar, then each of said resulting blanks is machined separately in order to obtain the blades having a final profile.
This method has the advantage of making several parts from the same bar and thus of limiting the amount of material lost when producing the blanks.
It also makes it possible to recover a material of good quality and, all else being equal, in greater quantity for recycling it. It should be noted here that only the feedheads are recoverable via the casting approach, the gates being cropped.
The applicant has continued the research thereof to try to further reduce the amount of material to be recycled, after obtaining the blade blanks, as well as the cost of these blanks.
For this purpose, the invention notably proposes a method for obtaining a turbine engine solid blade comprising a core, a tip and a root, said method comprising:
a step of producing a blank from at least two parts, at least one of them being a solid part, said at least two parts being assembled by a diffusion connection technique without melting and,
a step of machining this blank in order to produce a blade with a defined profile.
It should be noted that “solid part” means a part that is not in powder form at the time of assembly.
Furthermore, in the context of the present invention, a machining step is understood to be an operation of removing at least 25% of material mass relative to the mass of the finished part.
Thus, this method is based on a design for obtaining a blade that is radically different to that used in the production methods currently implemented for solid and rotary blades.
Indeed, all these methods make it possible to produce blade blanks from a single part, whereas the method according to the invention consists in producing the blade from at least two assembled parts.
This approach is not the approach of a person skilled in the art since increasing the number of operations before obtaining the blank of a blade seems a priori more complicated than producing this blank in one go.
In addition, assembly is often associated to risks of embrittlement and therefore of deterioration in quality, which rules out the use of assembly for rotating blades subjected to substantial loads, particularly at the root thereof which is fixed on a hub or a disc and at the central portion of the core thereof which must be able to withstand impact.
In the context of the invention, the assembly used is not mechanical assembly including a step of engaging two adjacent parts one in the other, nor bonding assembly.
It is assembly by diffusion, i.e. assembly provided mainly by the diffusion of chemical elements between the two assembled parts, and without melting.
Thus, assembly by diffusion is achieved by means of processes that take place in a solid medium, either entirely (diffusion welding), or by combining a liquid phase (diffusion brazing with disappearance of the liquid phase at the end of the brazing stage).
In linear friction methods, spark plasma sintering methods and similar methods, solid state diffusion is not the only operating mechanism since viscoplasticity occurs in a very localized manner at the interface.
It has been found that assembly of this type does not cause degradation of the mechanical characteristics of the blade, which makes it possible to use this method for both stationary and rotating blades.
In practice, the production of each constituent part of the blade is simplified since it is possible to choose the most appropriate method for each of them.
It is also possible to choose the method that generates the least material loss.
Furthermore, each constituent part can be obtained from a bar made of a metal alloy but also from waste recovered from other productions, notably waste from a waterjet cutting method. This will then be a solid part in accordance with the invention.
Such a solid part can also be made of ceramic-based material and, for example, be made up of a ceramic-impregnated ceramic fiber matrix.
The method according to the invention ultimately makes it possible to simplify the production, to limit the quantity of materials used as well as the quantity of materials to be recycled, without affecting the robustness of the obtained part.
In advantageous embodiments, one and/or the other of the following arrangements are furthermore and/or additionally used:
at least two of said parts are solid;
at least one of said parts is obtained using powder, being formed directly on said at least one solid part;
at least one solid part is a block made of a metal alloy;
the core of said blade is obtained from a block cut at the periphery of a cylindrical rough piece with a solid section, to take advantage of the radius of curvature thereof in producing the outer surface of said core;
the core of said blade is obtained from a block cut in a cylindrical rough piece with an annular section, to take advantage of the radius of curvature thereof in producing the outer surface and/or the inner surface of said core;
at least one solid part is ceramic-based, in particular made of a ceramic matrix composite;
the powder is a metal alloy powder or a ceramic powder;
the metal alloy is titanium aluminide (gamma TiAl);
said at least two parts are assembled using a linear friction welding method;
said at least two parts are assembled using a method of diffusion welding under pressure;
at least one solid part is machined prior to the assembly thereof.
The invention also relates to a solid blade made of titanium aluminide and/or of a ceramic-based material, which solid blade is obtained by the method according to the invention.
The invention also relates to a turbine engine comprising at least one such blade.
The invention will be better understood and other aims, advantages and features thereof will appear more clearly on reading the description which follows and which is given with reference to the appended drawings wherein:
The elements common to the various figures will be designated by the same references.
Referring firstly to
In a known manner, the core has a crescent moon-shaped section, the root 2 has a generally parallelepiped shape and the tip 3 is generally U-shaped.
This figure shows that the three constituent portions of a turbine engine blade have very distinct shapes.
The method according to the invention proposes taking advantage of these differences in shape to minimize the proportion of the material necessary for the production of the blade which is lost or which must be recycled.
Therefore, the method according to the invention proposes separating the blade into at least two parts. In the examples described with reference to
The invention is, however, not limited to this use and the blade could be, for example, separated into two parts, each of them corresponding to different stress zones, as will be described with reference to
Reference is firstly made to
In practice, as will be explained in the following description, a block designed for a part can be used to produce a portion of another part. However, to simplify the explanations, the terminology core, root and tip used to designate the portions of a blade that are obtained from a block of material will be retained.
Thus,
It is therefore understood that the height of the rough piece 4 is substantially equal to the length of the cores to be obtained. As will be explained in the following description, this depends on the type of link with the ends of the blade and on the nature of these ends (solid or powder-based).
Thus, the outer surface 10 of a core 1 is located on the outer periphery 40 side of the rough piece 4, while the inner surface 11 thereof is oriented on the internal periphery 41 side of the rough piece 4.
Cutting is carried out by waterjet as the cutting planes are not axial.
Thus, eight blocks 42 are obtained and, in each of them, a core 1 can be machined.
It should be noted that the invention is not limited to the use of a cylindrical rough piece with an annular section but can also be based on a conical rough piece with an annular section. Such a rough piece may be chosen to make cores, the section of which is wider on one side than the other. In both cases, the rough piece can also be cut along axial planes.
In general, it is known that, in a metal rough piece, porosities can exist at the center thereof. It is thus necessary to carry out post-treatments to be certain that a metal rough piece has suitable qualities, throughout the entire thickness thereof.
However, these post-treatments are very expensive.
It is therefore understood that a rough piece with an annular section, such as the rough piece 4, can be used without the need for post-treatments, the peripheral portion of a rough piece being always of better quality than the central portion thereof. In practice, defects may be present but they are often acceptable.
As for the rough piece 4, the height of the rough piece 7 is substantially equal to the length of the cores 1 to be obtained.
Post-treatments have been necessary to ensure the same quality through the entire thickness thereof. It consists of hot isostatic pressing in particular to close the solidification defects for the rough pieces produced by casting. This pressing is not necessary for a rough piece obtained by extrusion. Moreover, heat treatment is, in any case, often necessary to obtain the minimum properties required for use.
Reference is now made to
This rough piece 5 and the rough piece 4 or the rough piece 7 are typically obtained from different slugs and the material thereof is not necessarily identical. Given the thickness thereof, the rough piece has had to undergo appropriate post-treatments to provide a same quality through the thickness thereof. Moreover, the diameter thereof may be less than the inner diameter of the rough piece 4 and the height thereof less than that of the rough piece 4 or of the rough piece 7 since the two rough pieces are made independently. Thus, the rough piece 5 may, for example, be obtained by extrusion so that the dimensions thereof are defined as tightly as possible, to minimize the amount of material used.
To minimize the spatial requirement thereof, the roots 2 just like the tips 3 are arranged flat on each other.
These various blocks 50 and 51 are also illustrated in
This cutting is produced in this case with a saw. With waterjet cutting, the blocks could have a shape closer to the root or the tip of the final blade, as is illustrated, for example, in
Reference is now made to
Such a rough piece or bar 6 is illustrated as a top view in
This figure also illustrates, in thin lines, the location and the spatial requirement of six cores 1, positioned at the periphery of the rough piece 6 and of a root 2 and of a tip 3 which are positioned in the central portion of the rough piece 6.
It is understood that the cores 1 extend over the entire height of the rough piece 6, the height of which is therefore substantially equal to the length of the cores. As previously described with regard to
Of course, in the center of the rough piece 6, it is possible to provide for the spatial requirement of a plurality of roots 2 and tips 3, in practice six in the present case, which are stacked according to the height of the rough piece 6.
Cutting the blocks 61 and 62 makes it possible to separate a central rough piece 63 which extends over the entire height of the rough piece 6 and to obtain blocks 61 which are all substantially identical.
The blocks 61 are made in the peripheral portion of the cylindrical block 6 which is of better quality than the central rough piece 63 and which, in practice, often does not require any post-treatment.
It is noted that the section of the rough piece 63 is a hexagon. Indeed, it is relatively easy to cut a block according to the height thereof, with a blade saw, forming cut faces. This is not the case if the aim is to obtain a rough piece with a cylindrical section.
It is understood that, if the height of the block 63 is necessarily substantially equal to the height of the cores 1, it is however possible to optimize the arrangement of the roots 2 and of the tips 3 in the rough piece 63 to reduce the diameter thereof and therefore the diameter of the rough piece 6.
Of course, the central rough piece 63 is used for the formation of roots and/or tips insofar as the quality of the material allows it, i.e. in practice if the rough piece 6 has undergone appropriate post-treatments. In this case, the six blade rough pieces are advantageously obtained from the same material batch.
In the opposite case, only the peripheral portion of the rough piece 6 is used for the formation of cores (as is illustrated in
The roots and the tips are then obtained from a rough piece that does not belong to the same material batch as the rough piece 6.
Thus,
The height of the rough piece 8 is at least equal to the length of the parts 12 that are intended to be obtained.
For best use of the material of the rough piece 8, the two parts 12 are arranged tip-to-tail.
It is understood that a blade blank can then be obtained from the block 80, 81 and, for example, from a block 50, as illustrated in
As will be seen hereafter in the description, the tip 3 can also be obtained from powder.
Thus, two parts 12 similar to those illustrated in
This variant has the advantage of being able to produce blade blanks from the same material batch.
Reference will now be made to the other figures to illustrate how a blank of a turbine engine blade can be obtained from the blocks illustrated in
In general, two types of method can be distinguished: those in which a blank of the blade is obtained only from solid parts and those in which the blank includes at least one part obtained using powder.
Moreover, in both types of method, the blank of the blade can be obtained from two or three parts.
Thus, for the methods of the first type, the core, the root and the tip of the blade are all obtained from the blocks illustrated in
In the methods of the second type, it will be possible to use, for example, the blocks illustrated in
Focus will turn next to the method of the first type, in which all the parts used for obtaining a blade blank are solid parts.
As shown in the previous figures, this core blank can, moreover, be obtained from two or three solid parts.
Focus will first turn to obtaining a blade blank from three solid parts.
The solid parts intended to obtain a core may thus consist of the blocks 42, 71 and 61 described with reference to
Moreover, the solid parts intended to obtain roots or tips of the blade may consist of the blocks 50 and 51 illustrated in
When the block corresponding to a core is the type of the blocks 42 and 71 that are illustrated in
As explained with reference to
The various modes of assembly of these solid parts will now be described with reference to
In general, it can be envisaged to assemble blocks together, the obtained blank then being machined to obtain a blade.
It would also be possible to consider machining each block or at least some of them to obtain the part for which it is intended or a shape close thereto.
However, assembly at least partly by blocks is preferred since it makes it possible to limit the number of machining operations and, as will be shown, this offers more flexibility in the use of the solid parts in order to obtain the blade.
In the examples illustrated in
By contrast, the blocks intended for obtaining a tip or a root have not yet been machined.
In the example illustrated in
It should also be noted that blocks having the geometry illustrated in
In this type of assembly, the faces 510 of the block 51 and 14 of the core 1 which are assembled together have the same surface. It is the same for the faces 500 of the block 50 and 13 of the core 1.
In this case, the blocks from which the cores 1 are formed, for example the blocks 4, 7 or 6, may have a height less than the length of the cores.
In this type of assembly, the mutually assembled faces 510 of the block 51 and 12 of the core 1 do not have the same surfaces and it is the same for the faces 13 of the core 1 and 500 of the block 50.
In any case, assembly is carried out using a connection technique without melting.
This can in particular be a linear friction welding method, for example the LFW (Linear Friction Welding) method.
Since this LFW method generates an upset at the joint between two parts, it is necessary to provide excess lengths.
In this case, the blocks from which the cores 1 are formed may have a height greater than the length of the cores.
It is also possible to use a spark plasma sintering or SPS method which avoids any significant upset of material at the joint between two parts (unlike the LFW method).
Furthermore, assembly of the three parts is carried out simultaneously or successively, in particular according to the constraints of the assembly methods used.
In a variant, the core and the root can be made from a same block, such as the blocks 80, 81 illustrated in
In this case, a blade blank will be obtained from one of these blocks 80, 81 or 90, 91 and from another block corresponding to the tip of the blade.
It may be a block 51, as illustrated in
It is understood that, in the first case, the blank will comprise elements from different slugs of material. By contrast, if the blank is obtained from, for example, the blocks 90 and 92, the blank of the core will be made from a single material.
This assembly will not be described in greater detail. It can be of the end-to-end or end-to-face type, as illustrated in
These two figures illustrate two solid parts, for example the block 90 and the block 93, the block 90 having been previously machined to obtain the core 1 of the final blade.
In a variant,
It is understood that this variant of the method makes it possible to obtain a blade which is produced as one unit in the zone which is subjected to the most stress.
In the modes of implementation illustrated in
The invention is, however, not limited to this implementation example and one of these blocks could be directly used, or pre-machined to the final geometry thereof, leaving excess thicknesses at the interface zones.
Reference is now made to
Reference is first made to
Thus, the core 1 can be obtained from one of the blocks 42, 71 or 61 described with reference to
Of course, the block for producing a core could also be the type of block 71 illustrated in
The blocks 102 and 103 are formed directly on the ends of the block 42 from powder densified by a technique of diffusion welding under pressure, such as the so-called SPS (spark plasma sintering) technique.
For this purpose, the cleanliness of the interface is checked beforehand and particularly that there is no abrasive grain (resulting from waterjet cutting) encrusted in the surface of the material.
This technique is described schematically with reference to
It uses tooling comprising a first fixed portion 110 closed on one side by a second fixed portion 115 and on the other side by a third portion 111, these three portions defining a cavity 112, in which the second portion 111 is mounted such as to be translatable along the longitudinal axis X of the cavity 112.
Inside the cavity 112, a third part 113 is provided which is also movable along the longitudinal axis X. It is made in two half-shells to allow demolding. This part 113 is intended to hold a core 1 or a block, such as the block 42, in which a core can be made.
This part 113 delimits two sub-cavities 122a and 122b, into which powder 114 is introduced in appropriate quantities.
This powder may be a metal alloy powder such as TiAl, or a ceramic powder, such as silicon carbide (SiC).
The application of this pressure makes it possible to pack the powder inside the cavities 122a and 122b, the volume of which has decreased between the step illustrated in
In this regard, it should be noted that, in the example illustrated in
In any case, the block 42 (or the core of the blade if the block is previously machined) is at least partly inserted into the blocks 102 and 103, with the result that the linking surface between the block 42 and the block 102 or the block 103, respectively, is larger than in the case of an end-to-end assembly.
In addition, the portion of the blade that endures the most stress, in this case the core, can be continuous over the entire blade, which reinforces the strength thereof.
Thus, preferably, the length of the core will be chosen to completely pass through the root (and thus be level with the outer surface of the root, on the final blade), the core/root linking zone being that which is most loaded in a rotating blade.
Of course, the invention is not limited to these two examples and the blocks could have another simple geometry such as a washer or a profile even closer to the end to be obtained.
These two figures are intended to show the interlock between the solid core and the tip and the root which are obtained from powder.
Thus, these two figures show that the junction between the core and the ends is produced in the latter, and therefore outside the zones of greater stress of the blade. This helps to reinforce the mechanical strength of the obtained blade.
Furthermore, if the powder has a higher production cost than a raw material, it is understood that the method which has just been described makes it possible to produce end parts, the quoted measurements of which are very close to the tip or to the root of the final blade. Thus, this method makes it possible to reduce the steps for machining the blank, and the material used.
Thus, the obtained blade will have, on the tip 3 side, interlocking between the solid core and the tip 3 as illustrated in
As illustrated in
Moreover, the provision of powder is used to produce a functional zone of the part which is subjected to high stresses.
This is particularly the case for the root of a rotor blade, which root is connected to the inner disc of the rotor.
Moreover, in the case of a stator blade, the root and the tip of the blade are the two zones of the blade subjected to the greatest stresses.
Finally, the mass of material provided initially (before machining) with the powder can correspond to the total mass of the final blade. Moreover, after machining, the mass of material provided with the powder represents a substantial proportion of the mass of the final blade (for example approximately 10%).
Another variant (not shown in the figures) of the method consists in producing a blank of the blade from two solid parts and from a part obtained from powder.
By way of example, this blank can be obtained from a block 42, 71 or 61, as illustrated in
All the examples described confirm that the method according to the invention makes it possible to minimize the material used and the material waste, the separation of the blade into two or three portions offering more flexibility in using the material.
To illustrate the savings in material that can be achieved with the method according to the invention, indicated in the table above is the total mass (g) of material used to obtain a blade (mass/blade) in various scenarios.
The reference (with value 100) corresponds to a blade obtained using the method described in the document FR 2 997 885.
Furthermore, once the blank of the blade has been obtained, machining is carried out to remove the excess thicknesses and obtain the blade with the final dimensions thereof, such as the blade illustrated in
Two tensile tests at room temperature were carried out on various types of test pieces to show the consequences of an assembly carried out using a connection technique without melting on a part.
These tensile tests at room temperature were carried out according to the French standard NF EN ISO 6892-1.
The typical values of ultimate tensile strength (Rm), and of yield stress (Rp02) are given in the two tables below.
The minimum values required are conventionally given by the manufacturer and correspond to a sizing of the blade that allows it to withstand the stresses to which it is subjected.
Thus, in a first test, several test pieces were made:
test piece 1: obtained by casting and solid
test piece 2: obtained by assembling two solid parts, using the SPS technique
test piece 3: obtained by assembling a solid part and a part formed by powder.
Table 1 confirms that the techniques for assembly without melting make it possible to obtain parts, the mechanical characteristics of which are comparable to or greater than those required for the function.
In a second test, several test pieces were made:
test piece A: obtained by casting and solid
test piece B: obtained by powder consolidated by the SPS technique
test piece C: obtained by assembling a solid part and powder consolidated by the SPS technique.
Table 2 surprisingly shows that the techniques without melting of the SPS type that are used with powder even make it possible to obtain parts, the mechanical characteristics of which are greater than those required for the function and those corresponding to a solid part.
In general, the designer of the blades will choose the most suitable production method according to the stresses to which they are subjected.
As is obvious and as also follows on from the above, the present invention is not limited to the embodiments more specifically described. On the contrary, it covers all the variants thereof and in particular those in which a solid part, for example the core, is based on ceramics and not on metal, in particular a ceramic matrix composite composed of ceramic fibers woven and impregnated with ceramics, such as silicon carbide (SiC), the ends being made from ceramic or metal powder for example.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1752018 | Mar 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/000051 | 3/12/2018 | WO | 00 |
