Process for assembling metal parts of different masses and centrifugal diffuser produced using this process

Abstract

Method for assembling metal parts of different masses and centrifugal diffuser produced using this method The invention relates to a method for assembling a first metal part (21) onto a second metal part (22), the first and second metal parts having different masses, the method comprising the operations: a) producing (110), on a surface of the first metal part (22), a slot (23), b) positioning (120) the second metal part (22) in line with the slot (23) of the first metal part, etc.) welding (130), through the slot (23), 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.The invention also relates to a centrifugal diffuser for a turbomachine 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 above method. Figure to be published with the abstract: Figure 6.

Description

Title of the invention: Method for assembling metal parts of different masses and 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 made within 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 finds applications in the field of aeronautics and, in particular, in the field of the assembly of metal parts for aircraft turbomachines. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Aircraft turbomachines, and in particular those of the gas turbine type, comprise different stages mounted around a central rotation shaft. An example of a turbomachine is shown schematically in [Fig.l]. In this example, the turbomachine 10 comprises a rotation shaft 11 extending along a central axis AA and around which are mounted, in the upstream to downstream direction, a fan 12, a compressor 13, a combustion chamber 14 and a turbine 15. When the turbomachine 10 is in operation, an air flow enters the turbomachine through the fan 12; this air flow 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 conveys the air flow to the compression chamber 14. This centrifugal diffuser 20, more simply called a diffuser, comprises a partially flat circular cover on which blades are fixed. Generally, the blades are fixed by brazing to the cover. Brazing is usually carried out by manually depositing brazing on the tips of the blades then a high-temperature heat treatment, i.e. at approximately 1150°C. This brazing operation has the disadvantage of generating significant deformations on the centrifugal diffuser 20; in particular, it deforms the flatness of the distributor. This brazing operation can, for example, cause distortions, as shown in [Fig. 2], with a rate that can vary from + / -0.2 to + / -0.5. This deformation of the flatness of the distributor is partly random and therefore uncontrolled.In fact, the brazing rays are formed between the tops of the blades and the walls of the cover. are difficult to control and often difficult to achieve. Depending on the quantity of solder deposited, the solder may spread on the blade and, by capillarity, in the radial air stream delimited by the diffuser, which can lead to a modification of the metallurgical structure of the diffuser, outside the assembly area.

[0005] Since the solder is removed manually, problems of poor wettability of the solder can also be generated and / or lack of solder, which are relatively random and difficult to avoid. The only known solution to resolve these problems is to carry out solder retouching, sometimes numerous. However, each solder retouch requires a complete soldering cycle, and therefore a new high-temperature heat treatment. Since the heat treatment is the cause of the deformations of the diffuser, it is understood that the more the diffuser is subjected to a high number of heat treatments, the more the deformations are amplified.

[0006] To reduce these hazards related to the brazing of the blades on the cover, manufacturers of centrifugal diffusers have considered replacing the brazing operation with an electron beam welding operation, also called FE welding. Indeed, using FE welding would reduce the hazards of brazing radii, drips and wetting. However, FE welding requires fusing, over a short distance, parts of different masses and in particular different thicknesses. Indeed, a diffuser cover has a thickness of at least 2 mm, while the top of the blades, to be welded on the cover, generally has a thickness of between 0.3 mm and 2 mm. An example of a profile of a centrifugal diffuser blade is shown in [Fig.3].This example shows that the thickness of the blade is scalable, with a maximum thickness of about 2mm at the center of the blade and a minimum thickness of about 0.3mm to 0.5mm at the ends of the blade 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 merged together, in particular because the assembly is done from the outer face of the cover (i.e. the face opposite the face on which the blade is fixed), the electron beam being positioned above the outer face of the cover.

[0007] The FE welding assembly operation of the blade and the cover causes another drawback. Indeed, the assembly between the blade and the cover is traditionally carried out, with the brazing technique, according to a configuration called "through blade" and a configuration called "non-through blade". An example of a through configuration is shown in [Fig. 5A] and an example of a non-through configuration is shown in [Fig. 5B]. In the through configuration, the top 22a of the blade passes through the cover 21 through a suitable slot and projects from the outer face 21a of the cover. In the non-through configuration, the top 22a of the blade is positioned against the inner face 21b of the cover. These two confi gurations, used jointly for the same diffuser, have been defined to allow positioning of the cover in relation to the blades and to obtain improved mechanical resistance of the junction.

[0008] If the through configuration is suitable for assembly by FE welding, the non-through configuration causes instability of the electron beam with a deflection of said beam at the top of the blade during FE welding. [Fig. 4] schematically represents an FE electron beam during FE welding at the junction between the cover 21 and the top 22a of the blade 22 of the diffuser, in non-through configuration. The deflection of the FE electron beam, represented by arrows on either side of the top 22a of the blade, prevents the assembly of the cover and the blade by local melting of the materials. The blades mounted in non-through configuration cannot therefore be fixed to the cover by FE welding.

[0009] There is therefore a real need for a solution allowing a blade to be assembled by FE welding on a diffuser cover. Summary of the invention

[0010] To address the above-mentioned problems of assembling blades on a centrifugal diffuser cover, the applicant proposes a high-energy welding assembly method, such as FE welding, in which the welding 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 method.

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

[0012] This method makes it possible, by guiding the welding beam via a slot, to assemble 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 metal part and a part formed from an alloy.

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

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

[0016] A second aspect of the invention relates to an assembly of a first and a second metal part, obtained by the method 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 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 comprising a substantially flat surface, the blades extending substantially perpendicular 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 which have just been mentioned in the preceding paragraph, the centrifugal diffuser according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to 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 blade assembled with the cover in a non-configuration crossing is located at one end of the blade.

[0019] A fourth aspect of the invention relates to a turbomachine for aircraft, 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 characteristics of the invention will appear on reading the following description, illustrated by the figures in which:

[0021] [Fig.l], already described, represents a schematic view in longitudinal section of an example of a turbomachine according to the state of the art.

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

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

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

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

[0026] [Fig.6] represents a schematic sectional view of a cover / blade junction of a diffuser according to the invention, before welding.

[0027] [Fig.7] shows a schematic perspective view of a diffuser cover according to the invention when blades are welded with said cover by means of high energy welding.

[0028] [Fig.8] represents a schematic sectional view of a blade end welded to the cover of the diffuser according to the invention.

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

[0030] [Fig. 10] represents a functional diagram of the assembly method according to the invention.

[0031] [Fig. 11] represents a top view and a truncated top view of an example of the diffuser according to the invention with a non-through configuration zone at the end of the blade. DETAILED DESCRIPTION

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

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

[0034] Generally speaking, welding is a permanent joining technique that establishes a continuity of nature between the welded parts. The term weld is used to designate the metal, or alloy, connecting the parts to be joined, formed by the fusion of the edges to be joined, with or without the addition of a filler product. The weld can therefore be the result of the sole mixing of the base metals (i.e. the parts to be joined) or of the mixing of the base metals and the filler product. During welding, there is local fusion of the parts to be joined, unlike a brazing assembly where there is never fusion of the materials to be joined.

[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 to produce intense heat that melts the metal of said parts to be joined. The term "high energy" means that the welding beam delivers a high local power of at least 10 kW / mm2. In the electron beam welding technique, or FE welding, an electron beam bombards the parts to be joined and produces a narrow and intense three-dimensional heat source forming a hole or tunnel opening through the materials of the two parts and moving along the joint to be welded. In the laser welding technique, the electron beam is replaced by a LASER beam.

[0036] The method according to the invention, an example of which is shown functionally in [Fig. 10], proposes to assemble two metal parts by high-energy welding, avoiding any instability and / or deviation of the welding beam. An example of two metal parts, in particular a blade 22 and a cover 21 of a centrifugal diffuser, to be assembled with the method of the invention, is shown in [Fig. 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 assembled with a second metal part.

[0037] To enable welding without deviation of the high-energy welding beam, the method according to the invention comprises an operation 110 of carrying out, on the surface ex inner 21a of the cover 21, a slot 23 located opposite the blade 22. This slot 23 is an orifice passing right through the cover 21, in its thickness e. This slot 23 extends, on the cover, along at least part of the profile of the blade 22 with a shape substantially similar to said profile; this slot 23 can be, for example, substantially rectilinear or in the shape of an arc of a circle. In the example of [Fig.6], the slot 23 is made directly above the profile of the blade 22 in order to guide the high-energy welding beam towards the top 22a of the blade to be welded in order to prevent said beam from being deflected. Indeed, the high-energy welding beam, also called welding beam or electron beam or laser beam, is directed towards the slot 23 and follows the slot 23 over the entire length of said slot.The welding beam thus makes it possible to locally bring to their melting temperature the metal of the cover 21 located in the vicinity of the slot 23 and the metal of the blade 22 located opposite the slot 23. The two molten metals aggregate so that after cooling, the two metal parts are assembled.

[0038] The slot can be made using techniques conventionally used for cutting metal parts such as, for example, LASER cutting or electro-erosion cutting (called EDM cutting, for Electro-Discharge Machining, in English terms). An example of a centrifugal diffuser cover equipped with several slots is shown in [Fig. 7]. This cover 21 includes slots 23 made for implementing the method according to the invention. These slots 23 allow the assembly, in a non-through configuration, of blades (not visible in the figure) on the cover 21. This [Fig. 7] also shows slots 24 used for the assembly of blades in a through configuration, explained later.

[0039] The method of [Fig. 10] comprises, after the operation 110 of producing the slot 23, an operation 120 of positioning the blade 22 in line with the slot 23. Indeed, for the welding beam to be able to ensure the fusion of the metals of the cover and the blade, it is necessary for the blade to be positioned opposite the slot, its top 22a extending substantially perpendicular to the internal surface 21b of the cover 21. After positioning the blade 22, the high-energy welding operation 130 is implemented by means of a suitable welding device. This welding operation 130 is carried out, as explained previously, by bringing to their melting temperature, the metal of the top of the blade 22 and the metal of the part of the cover 21 surrounding the slot 23 so as to obtain a fusion zone Z2 which will ensure, after cooling, the assembly 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 certain other embodiments, the blades 22 are partially assembled with the cover in a through configuration and partially in a non-through configuration. An example of such an assembly is shown in [Fig. 9]. This [Fig. 9] shows blades 22 having extended portions 22b and normal portions 22c. The extended portions 22b are portions of the blade 22 which extend longitudinally projecting relative to 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 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 welding beam induces a fusion of the metal of the extended portion 22b and the metal of the cover around this extended portion, creating a first melted zone ZI.The normal portions 22c of the blade 22 are each positioned against a slot 23 of the cover, in line with said slot. The assembly of these normal zones 22c with the cover 21 is obtained after passage of the welding beam in the slot 23, that is to say along the normal portion 22c of the blade. The passage of the welding beam in the slot 23 generates a second melted zone Z2.

[0042] Thus, as explained previously, the slot 23 of the cover 21 makes it possible to guide and focus the welding beam on the top 22a of the blade in the non-through configuration zones. This slot 23 being made opposite the normal portion 22c of the blade 22, it offers an additional advantage when positioning the cover. Indeed, this slot 23 makes it possible to check, before welding, whether the positioning of the cover 21 relative to the blades 22 is correct. Several techniques are currently used to check the positioning of the cover relative to the blades (for example the use of a mechanical detection tool or an optical tool); verification by means of the slot 23 makes it possible either to replace the usual technique, or to confirm the verification of the positioning, with the advantage of being simple to implement, without requiring additional expensive means.

[0043] The assembly method with welding through the slot 23, as described above, makes it possible to solve the problem caused by the difference in mass between the blade and the cover. In the embodiments where each blade is assembled partly according to the through configuration and partly according to the non-through configuration, the difference in mass is particularly present at the tip of the blade, that is to say in the zone close to the end of said blade. Indeed, at the tip of the blade, the difference in mass is reflected not only by a difference in thickness of the parts (approximately 0.2 to 0.3 mm for the top of the blade and approximately 2 to 3 mm for the cover) but also by a transition zone of the configuration mode with the passage from the through configuration to the non-through configuration. In this zone of transition, the change of configuration generates strong variations in thickness, in particular because the profile of the blade is very thin. An example of assembly at the end of the blade is shown schematically in [Fig.8] with the Zt zone of through configuration, the Znt zone of non-through configuration and the Ztrans transition zone. To avoid variabilities during the welding operation in the Ztrans transition zone, the method includes an operation of adjusting the positioning of the Zt through configuration zone which must be placed as close as possible to the edge of the blade 22 in order to take optimal advantage of the welding facilities offered by the through configuration. In addition to this adjustment operation, and conversely, it is chosen to keep a Znt non-through configuration zone at the end of the blade.A schematic example of a diffuser according to the invention with a non-through configuration zone Znt at the end of the blade is shown in [Fig. 11]. This choice of a non-through configuration zone Znt at the end of the blade makes it possible to avoid many problems. Indeed, if a through configuration zone Zt were positioned at the very end of the blade 22, then: . - on the one hand, the cover 21 welded to the top of the blade would have a weakened area on its outer diameter (shown schematically by a circle in [Fig.l 1]) which would be likely to deform under the effect of the welding operation. The height of the air stream defined by the height of the blade inside the diffuser would then be uncontrolled on either side of the blade with, in addition, a deformed diffuser cover in this area; and - on the other hand, the use of positioning tools for this weakened area for the purpose of holding it during the welding operation would introduce unnecessary industrial complexities, mainly due to the size of the elements present (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 makes it possible to avoid the problems stated above but also to weld the thinnest zone of the blade 22, to ensure the maintenance of the cover 21 and to limit manufacturing costs by avoiding complex implementation.

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

Claims

Claims

1. Method for assembling a first metal part (21) on 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. production (110), on a surface of the first metal part (21), of a slot (23) passing right through said first metal part in its thickness (e), b. positioning (120) of the second metal part (22) in line with 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) on the first metal part (21) with a high-energy welding beam, the slot ensuring the guidance of the welding beam.

2. 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. Method according to any one of claims 1 to 3, characterized in that the slot (23) produced during operation a) has a shape substantially similar to a profile of the second metal part (22).

5. Assembly of a first and a second metal part, obtained by the method according to any one of claims 1 to 4, in which 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 fusion of the metal of said metal cover and blade.

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

7. d H-. 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 blade portion (22b) assembled with the cover (21) in a through configuration and a blade portion (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. Turbomachine for aircraft, 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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