Method for assembling metal parts of different sizes and centrifugal diffuser produced by this method

Abstract

The invention relates to a method for assembling a first metal part (21) to a second metal part (22), the first and second metal parts having different sizes, the method comprising the following operations: - a) producing (110) a slot (23) in a surface of the first metal part (22); - b) positioning (120) the second metal part (22) in line with the slot (23) of the first metal part; and - c) welding (130) the second metal part (22) to the first metal part (21) through the slot (23) using a high-energy welding beam, the slot guiding the welding beam. The invention also relates to a centrifugal diffuser for turbomachinery comprising a metal cover (21) and a plurality of metal blades (22), each blade (22) being assembled with the cover (21) by means of the method hereinbefore.

Description

DESCRIPTION TITLE: Method for assembling metal parts of different masses and a centrifugal diffuser produced using this method TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for assembling a first and a second metal part having different masses, in which the second part is welded to the first part through a slot formed in the first part. The invention also relates to an assembly, obtained by this method, of a metal cover and at least one metal blade, as well as a centrifugal diffuser for a turbomachine comprising such an assembly.

[0002] The invention has applications in the field of aeronautics and, in particular, in the field of assembling metal parts for aircraft turbomachinery. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Aircraft turbomachinery, particularly gas turbine type turbomachinery, comprises several stages mounted around a central rotating shaft. An example of a turbomachine is schematically represented in Figure 1. In this example, the turbomachine 10 has a rotating shaft 11 extending along a central axis AA, around which are mounted, in an upstream-downstream direction, a fan 12, a compressor 13, a combustion chamber 14, and a turbine 15. When the turbomachine 10 is in operation, an airflow enters the turbomachine through the fan 12; this airflow is then compressed by the compressor 13, then mixed and burned with fuel in the combustion chamber 14 before being expanded in the low-pressure turbine 15 and then discharged through a nozzle 16.

[0004] At the outlet of the compressor 13, a centrifugal diffuser 20 directs the airflow towards the compression chamber 14. This centrifugal diffuser 20, more simply called a diffuser, has a partially flat circular cover to which blades are attached. Generally, the blades are attached to the cover by brazing. The brazing is usually carried out by manually applying the brazing material. The brazing process involves brazing the tips of the blades followed by high-temperature heat treatment, approximately 1150°C. This brazing operation has the drawback of generating significant deformations on the centrifugal diffuser 20; in particular, it distorts the flatness of the distributor. This brazing operation can, for example, generate distortions, as shown in Figure 2, with a rate that can vary from + / -0.2 to + / -0.5. This deformation of the distributor's flatness is partly random and therefore uncontrolled. Indeed, the brazing radii forming between the blade tips and the cover walls are difficult to control and often difficult to achieve. Depending on the amount of brazing material deposited, brazing can spread onto the blade and, by capillary action, into the radial airflow delimited by the diffuser, which can lead to a modification of the diffuser's metallurgical structure, outside the assembly area.

[0005] Because the solder application is manual, problems with poor solder wettability and / or solder deficiencies can occur, which are relatively random and difficult to avoid. The only known solution to these problems is to perform solder touch-ups, sometimes numerous ones. However, each solder touch-up requires a complete soldering cycle, and therefore a new high-temperature heat treatment. Since the heat treatment is the cause of diffuser deformation, it is understandable that the more heat treatments the diffuser undergoes, the more pronounced the deformations become.

[0006] To reduce the risks associated with brazing the blades to the cover, manufacturers of centrifugal diffusers considered replacing brazing with electron beam welding, also known as FE welding. Indeed, using FE welding would reduce the risks of brazing radii, drips, and wetting. However, FE welding requires fusing parts of different masses and, in particular, different thicknesses over a short distance. A diffuser cover is at least 2 mm thick, while the tips of the blades, to be welded to the cover, are generally between 0.3 mm and 2 mm thick. An example of a centrifugal diffuser blade profile is shown in Figure 3. This example shows that the blade thickness varies, with a maximum thickness of approximately 2 mm at the center of the blade and a minimum thickness of approximately 0.3 mm to 0.5 mm at the tips. blade tips and therefore at the top of the blade. This difference in mass between the top of the blade and the cover prevents these two areas from being fused together, in particular because the assembly is done from the outside face of the cover (that is to say the face opposite to the face on which the blade is fixed), the electron beam being positioned above the outside face of the cover.

[0007] The FE welding operation for assembling the blade and cover introduces another drawback. Traditionally, the blade and cover are joined using brazing, in a configuration known as "through-blade" and a configuration known as "non-through-blade." An example of a through-blade configuration is shown in Figure 5A, and an example of a non-through-blade configuration is shown in Figure 5B. In the through-blade configuration, the tip 22a of the blade passes through the cover 21 via a suitable opening and protrudes from the outer face 21a of the cover. In the non-through-blade configuration, the tip 22a of the blade is positioned against the inner face 21b of the cover. These two configurations, used together for the same diffuser, were defined to allow for precise positioning of the cover relative to the blades and to achieve improved mechanical strength of the joint.

[0008] While the through-hole configuration is suitable for FE welding, the non-through-hole configuration results in electron beam instability, with the beam being deflected at the blade tip during FE welding. Figure 4 schematically represents an FE electron beam during FE welding at the junction between the cover 21 and the tip 22a of the diffuser blade 22, in the non-through-hole configuration. The deflection of the FE electron beam, indicated by arrows on either side of the blade tip 22a, prevents the cover and blade from being joined by local fusion of the materials. Therefore, blades mounted in the non-through-hole configuration cannot be attached to the cover by FE welding.

[0009] Therefore, there is a real need for a solution that allows a blade to be assembled onto a diffuser cover by FE welding. SUMMARY OF THE INVENTION

[0010] To address the problems mentioned above regarding the assembly of blades onto a centrifugal diffuser cover, the applicant proposes a process assembly by high-energy welding, such as FE welding, in which the weld beam is guided by means of a slot made in the surface of the cover. The applicant also proposes an assembly of metal parts obtained by this process.

[0011] According to a first aspect, the invention relates to a method for assembling a first metal part onto a second metal part, the first and second metal parts having different masses, characterized in that it comprises the following operations: - making a slot on the surface of the first metal piece, - positioning of the second metal piece directly above the slot in the first metal piece, and - welding, through the slot, of the second metal piece onto the first metal piece with a high-energy welding beam, the slot ensuring the guidance of the welding beam.

[0012] This process allows, by guiding the welding beam through a slot, the assembly of metal parts using a high-energy welding technique, even when the metal parts have different masses.

[0013] Throughout the description, the expression "metal part" includes both a part made of metal and a part formed from an alloy.

[0014] Furthermore, two parts are considered to have "different massivity" when these two parts have relatively distinct volumes, dimensions and / or thicknesses from each other, that is to say, the ratio between the thickness of the first metal part (for example the cover in the examples detailed later) and that of the second metal part (for example the blade at its thinnest level, for the detailed examples below where the second part is a blade with evolving thickness) varies between 1 and 10.

[0015] In addition to the characteristics mentioned in the preceding paragraph, the assembly method according to one aspect of the invention may have one or more complementary characteristics from among the following, considered individually or in all technically possible combinations: - the welding operation consists of electron beam welding. - the welding operation consists of laser welding. - the second metal piece is positioned in a non-through configuration relative to the first metal piece. - the slot made during the operation of making the slot is through, with a shape substantially similar to a profile of the second metal piece.

[0016] A second aspect of the invention relates to an assembly of a first and a second metal part, obtained by the process defined above, in which the first metal part is a centrifugal diffuser cover and the second metal part is a centrifugal diffuser blade, the cover and the blade being assembled by a local melting of the metal of said metal cover and blade.

[0017] A third aspect of the invention relates to a centrifugal diffuser for a turbomachine comprising a metal cover and a plurality of metal blades, the cover having a substantially flat surface, the blades extending substantially perpendicularly to the flat surface of the cover, characterized in that each blade is assembled with the cover by means of the method as defined above.

[0018] In addition to the characteristics mentioned in the preceding paragraph, the centrifugal diffuser according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: - some of the plurality of blades are assembled with the cover in a through configuration and others of the plurality of blades are assembled in a non-through configuration. - each blade comprises a portion of blade assembled with the cover in a through configuration and a portion of blade assembled with the cover in a non-through configuration. - a portion of the blade assembled with the cover in a non-through configuration is located at one end of the blade.

[0019] A fourth aspect of the invention relates to an aircraft turbomachine, comprising a centrifugal diffuser as defined above, mounted at the outlet of a compressor of said turbomachine. BRIEF DESCRIPTION OF THE FIGURES

[0020] Other advantages and features of the invention will become apparent from the following description, illustrated by the figures in which:

[0021] Figure 1, already described, represents a schematic longitudinal cross-sectional view of an example of a turbomachine according to the prior art.

[0022] Figure 2, already described, represents a schematic side view and a schematic perspective view of a diffuser according to the prior art, deformed by the heat treatment of the brazing operation.

[0023] Figure 3, already described, represents a schematic view of the profile of a diffuser blade according to the prior art.

[0024] Figure 4, already described, represents a schematic cross-sectional view of a cover / blade junction of a diffuser according to the prior art during an FE welding operation.

[0025] Figures 5A and 5B, already described, represent schematic cross-sectional views of a cover / blade junction of a diffuser according to the prior art, respectively, in a through-blade configuration and in a non-through-blade configuration.

[0026] Figure 6 shows a schematic cross-sectional view of a cover / blade junction of a diffuser according to the invention, before welding.

[0027] Figure 7 represents a schematic perspective view of a diffuser cover according to the invention when blades are welded to said cover by means of a high-energy weld.

[0028] Figure 8 shows a schematic cross-sectional view of a blade end welded to the diffuser cover according to the invention.

[0029] Figure 9 shows a schematic perspective view of several blades of a diffuser according to the invention assembled in a through and non-through configuration.

[0030] Figure 10 represents a functional diagram of the assembly process according to the invention.

[0031] Figure 11 shows a top view and a truncated top view of an example of the diffuser according to the invention with a non-through configuration area at the blade tip. DETAILED DESCRIPTION

[0032] An example of a method for assembling a blade to a diffuser cover by high-energy welding, and an example of a blade and diffuser cover assembled by this method, are described in detail below, with reference to the accompanying drawings. These examples illustrate the features and advantages of the invention. It should be noted, however, that the invention is not limited to these examples.

[0033] In the figures, identical elements are identified by identical references. For the sake of readability, the size scales between represented elements are not respected.

[0034] In general, welding is a permanent joining technique that establishes a continuous bond between the welded parts. The term weld refers to the metal, or alloy, joining the parts to be joined, formed by the fusion of the edges to be joined, with or without the addition of a filler material. A weld can therefore result from the merging of the base metals (i.e., the parts to be joined) or from the mixing of the base metals and the filler material. During welding, there is a localized fusion of the parts to be joined, unlike brazing where the materials to be joined never melt.

[0035] High-energy welding, such as electron beam welding or laser welding, is a welding technique in which a high-energy welding beam is directed onto the parts to be joined, generating intense heat that melts the metal of those parts. The term "high energy" means that the welding beam delivers a high local power of at least 10 kW / mm². 2 In electron beam welding, or EBM welding, an electron beam bombards the parts to be joined, producing a narrow, intense, three-dimensional heat source that forms a hole or tunnel through the materials of both parts and travels along the joint to be welded. In laser welding, the electron beam is replaced by a laser beam.

[0036] The method according to the invention, a functional example of which is shown in Figure 10, proposes to join two metal parts by high-energy welding, avoiding any instability and / or deviation of the weld beam. An example of two metal parts, in particular a blade 22 and a cover 21 of a centrifugal diffuser, to be joined using the method of the invention, is shown in Figure 6. The following description will be given for a blade and a cover of a centrifugal diffuser, it being understood that the method of the invention can be implemented for any assembly of a first metal part to be joined with a second metal part.

[0037] To enable deflection-free welding of the high-energy weld beam, the method according to the invention comprises an operation 110 of forming, on the outer surface 21a of the cover 21, a slot 23 located opposite the blade 22. This slot 23 is an orifice passing completely through the cover 21, in its thickness e. This slot 23 extends, on the cover, along at least a portion of the profile of the blade 22 with a shape substantially similar to said profile; this slot 23 may be, for example, substantially straight or in the shape of an arc of a circle. In the example of Figure 6, the slot 23 is formed directly above the profile of the blade 22 in order to guide the high-energy weld beam towards the apex 22a of the blade to be welded, thus preventing said beam from being deflected.Indeed, the high-energy welding beam, also called a welding beam, electron beam, or laser beam, is directed towards slot 23 and follows its entire length. The welding beam thus allows the metal of the cover 21, located near slot 23, and the metal of the blade 22, located opposite slot 23, to be locally heated to their melting temperatures. The two molten metals fuse together, and after cooling, the two metal parts are joined.

[0038] The slot can be made using techniques commonly employed for cutting metal parts, such as laser cutting or electrical discharge machining (EDM). An example of a centrifugal diffuser cover equipped with several slots is shown in Figure 7. This cover 21 has slots 23 made for implementing the process according to the invention. These slots 23 allow the assembly, in a non-through configuration, of blades (not visible in the figure) onto the cover 21. Figure 7 also shows 24 lights used for blade assembly in a through-configuration, explained later.

[0039] The process in Figure 10 comprises, after step 110 of creating the slot 23, a step 120 of positioning the blade 22 directly over the slot 23. Indeed, for the welding beam to ensure the fusion of the metals of the cover and the blade, it is necessary that the blade be positioned opposite the slot, with its tip 22a extending substantially perpendicularly to the internal surface 21b of the cover 21. After positioning the blade 22, the high-energy welding step 130 is carried out using a suitable welding device. This welding step 130 is performed, as explained previously, by heating the metal of the tip of the blade 22 and the metal of the portion of the cover 21 adjacent to the slot 23 to their melting temperatures, so as to obtain a fusion zone Z2 which, after cooling, will ensure the joining of the two parts.

[0040] In some embodiments, some blades 22 are assembled with the cover in a non-through configuration and others in a through configuration.

[0041] In some other embodiments, the blades 22 are partially assembled with the cover in a through-welding configuration and partially in a non-through-welding configuration. An example of such an assembly is shown in Figure 9. This Figure 9 shows blades 22 having extended portions 22b and normal portions 22c. The extended portions 22b are portions of the blade 22 that project longitudinally beyond the normal portions 22c of the blade. The extended portions 22b are designed to fit into the slots 24 of the cover 21 in the through-welding configuration. These extended portions 22b, housed in the slots 24, are assembled with the cover 21 by a conventional high-energy welding operation, in which the weld beam induces fusion of the metal of the extended portion 22b and the metal of the cover around this extended portion, creating a first weld zone Z1.The normal portions 22c of the blade 22 are each positioned against a slot 23 in the cover, directly above said slot. The joining of these normal portions 22c with the cover 21 is achieved after the weld bead passes through the slot 23, i.e., along the normal portion 22c of the blade. The passage of the weld bead through the slot 23 generates a second weld zone Z2.

[0042] Thus, as explained previously, the slot 23 in the cover 21 guides and focuses the welding beam onto the tip 22a of the blade in non-through configuration areas. Since this slot 23 is positioned opposite the normal portion 22c of the blade 22, it offers an additional advantage during cover positioning. Indeed, this slot 23 allows verification, before welding, of the correct positioning of the cover 21 relative to the blades 22. Several techniques are currently used to verify the positioning of the cover relative to the blades (for example, the use of a mechanical or optical detection tool); verification using the slot 23 either replaces the usual technique or confirms the positioning verification, with the advantage of being simple to implement and requiring no additional costly equipment.

[0043] The assembly method with welding through slot 23, as described above, resolves the problem caused by the difference in mass between the blade and the cover. In embodiments where each blade is assembled partly in a through-welding configuration and partly in a non-through-welding configuration, the difference in mass is particularly pronounced at the blade tip, i.e., in the area near the end of the blade. Indeed, at the blade tip, the difference in mass results not only in a difference in the thickness of the parts (approximately 0.2 to 0.3 mm for the blade tip and approximately 2 to 3 mm for the cover) but also in a transition zone in the configuration, with the shift from the through-welding to the non-through-welding configuration.In this transition zone, the change in configuration generates significant variations in thickness, particularly due to the very thin profile of the blade. An example of a blade tip assembly is schematically represented in Figure 8, showing the through-configuration zone Zt, the non-through-configuration zone Znt, and the transition zone Ztrans. To avoid variability during the welding operation in the transition zone Ztrans, the process includes an adjustment to the positioning of the through-configuration zone Zt, which must be placed as close as possible to the edge of the blade 22 to optimally take advantage of the welding advantages offered by the through-configuration. In addition to this adjustment, and conversely, a non-through-configuration zone Znt is retained at the blade tip. A schematic example of this is shown. The diffuser according to the invention, with a non-through configuration zone Znt at the blade tip, is shown in Figure 11. This choice of a non-through configuration zone Znt at the blade tip avoids many problems. Indeed, if a through configuration zone Zt were positioned at the very tip of the blade 22, then: - On the one hand, the cover 21 welded to the blade tip would have a weakened area on its outer diameter (schematically represented by a circle in Figure 11) which could deform under the effect of the welding operation. The height of the air stream defined by the height of the inner blade at the diffuser would then be uncontrolled on either side of the blade, with, moreover, a deformed diffuser cover in this area; and - On the other hand, the use of positioning tools for this weakened area for support during the welding operation would introduce unnecessary industrial complexities, mainly due to the bulk of the elements involved (blades, cover, blade height, juxtaposition of the blades relative to each other, etc.).

[0044] Maintaining a non-through configuration zone Znt at the end of the blade not only avoids the problems stated above but also allows the thinnest area of ​​the blade 22 to be welded, ensures the retention of the cover 21 and limits manufacturing costs by avoiding a complex implementation.

[0045] Although described through a number of examples, variants and embodiments, the assembly method according to the invention, the assembly itself and the diffuser made by implementing this method include various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

DEMANDS

1. A method for assembling a first metal part (21) onto a second metal part (22), the first and second metal parts having different masses, characterized in that the second part is assembled with the first metal part at least partially in a non-through configuration and in that the method comprises the following operations: a) making (110), on a surface of the first metal part (21), a slot (23) passing through said first metal part in its thickness (e), b) positioning (120) of the second metal part (22) at the slot (23) of the first metal part, against said slot (23), and c) welding (130), through the slot (23), of the second metal part (22) onto the first metal part (21) with a high-energy welding beam, the slot ensuring the guidance of the welding beam.

2. A method according to claim 1, characterized in that the welding operation (130) consists of electron beam welding.

3. Method according to claim 1, characterized in that the welding operation (130) consists of LASER welding.

4. A method according to any one of claims 1 to 3, characterized in that the slot (23) made during operation a) has a shape substantially similar to a profile of the second metal piece (22).

5. Assembly of a first and a second metal part, obtained by the process according to any one of claims 1 to 4, wherein the first metal part (21) is a centrifugal diffuser cover and the second metal part (22) is a centrifugal diffuser blade, the cover and the blade being assembled by a local melting of the metal of said metal cover and blade.

6. A centrifugal diffuser for a turbomachine comprising a metal cover (21) and a plurality of metal blades (22), the cover having a substantially flat surface, the blades extending substantially perpendicularly to the flat surface of the cover, characterized in that each blade (22) is assembled with the lid (21) by means of the method according to any one of claims 1 to 4.

7. Centrifugal diffuser according to claim 6, characterized in that some of the plurality of blades (22) are assembled with the cover (21) in a through configuration and others of the plurality of blades are assembled in a non-through configuration.

8. Centrifugal diffuser according to claim 6, characterized in that each blade (22) comprises a portion of blade (22b) assembled with the cover (21) in a through configuration and a portion of blade (22c) assembled with the cover (21) in a non-through configuration.

9. Diffuser according to claim 8, characterized in that a portion of blade (22c) assembled with the cover (21) in a non-through configuration is located at one end of the blade.

10. Aircraft turbomachine, comprising a centrifugal diffuser according to any one of claims 6 to 9 mounted at the outlet of a compressor (13) of said turbomachine.

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