METHOD FOR ASSEMBLING METAL PIECES OF DIFFERENT MASSIVENESS AND CENTRIFUGAL DIFFUSER PRODUCED BY THIS METHOD

Abstract

A method for assembling a first metal part to a second metal part, the first and second metal parts having different sizes, the method including the following operations a) producing a slot in a surface of the first metal part; b) positioning the second metal part in line with the slot of the first metal part; and c) welding the second metal part to the first metal part through the slot using a high-energy welding beam, the slot guiding the welding beam.

Claims

1. A method for assembling a first metal piece to a second metal piece, the first and second metal pieces having a different massiveness, the second piece being assembled with the first metal piece at least partially in a non-through configuration, and the method comprising the following operations of: a) making, on a surface of the first metal piece, a slot passing right through said first metal piece in its thickness (e), b) positioning the second metal piece in line with the slot of the first metal piece, against said slot, and c) welding, through the slot, the second metal piece to the first metal piece with a high energy welding beam, the slot providing guide for the welding beam.

2. The method according to claim 1, wherein the welding operation consists of electron beam welding.

3. The method according to claim 1, wherein the welding operation consists of LASER welding.

4. The method according to claim 1, wherein the slot formed during operation a) includes a shape substantially similar to a profile of the second metal piece.

5. An assembly of a first and a second metal piece, obtained by the method according to claim 1, wherein the first metal piece is a centrifugal diffuser cover and the second metal piece is a centrifugal diffuser blade, the cover and the blade being assembled by locally melting the metal of said metal cover and blade.

6. A centrifugal diffuser for a turbomachine including a metal cover and a plurality of metal blades, the cover including a substantially planar surface, the blades extending substantially perpendicularly to the planar surface of the cover, wherein each blade is assembled with the cover by means of the method according to claim 1.

7. The centrifugal diffuser according to claim 6, wherein 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.

8. The centrifugal diffuser according to claim 6, wherein each blade includes a blade portion assembled with the cover in a through configuration and a blade portion assembled with the cover in a non-through configuration.

9. The diffuser according to claim 8, wherein a blade portion assembled with the cover in a non-through configuration is located at one end of the blade.

10. A turbomachine for aircraft, including a centrifugal diffuser according to claim 6 mounted at the outlet of a compressor of said turbomachine.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] Further advantages and characteristics of the invention will become apparent upon reading the following description, illustrated by the figures in which:

[0031] FIG. 1, already described, represents a schematic longitudinal cross-section view of an example of a turbomachine according to the state of the art.

[0032] 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 soldering operation.

[0033] FIG. 3, already described, represents a schematic view of the profile of a diffuser blade according to the state of the art.

[0034] FIG. 4, already described, represents a schematic cross-section view of a cover/blade junction of a diffuser according to the state of the art during a EBW operation.

[0035] FIGS. 5A and 5B, already described, represent schematic cross-section 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.

[0036] FIG. 6 represents a schematic cross-section view of a cover/blade junction of a diffuser according to the invention, before welding.

[0037] FIG. 7 represents a schematic perspective view of a diffuser cover according to the invention when blades are welded to said cover by means of high energy welding.

[0038] FIG. 8 represents a schematic cross-section view of a blade end welded to the diffuser cover according to the invention.

[0039] 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.

[0040] FIG. 10 represents a functional diagram of the assembly method according to the invention.

[0041] FIG. 11 represents a top view and a truncated top view of an example of the diffuser according to the invention with a zone of non-through configuration at the blade tip.

DETAILED DESCRIPTION

[0042] 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 hereinafter, with reference to the appended drawings. These examples illustrate characteristics and advantages of the invention. It is reminded, however, that the invention is not limited to these examples.

[0043] In the figures, identical elements are marked by identical references. For reasons of legibility of the figures, the size scales between the elements represented are not respected.

[0044] Generally speaking, welding is a permanent assembly technique which establishes a continuity of nature between the welded pieces. The term weld is used to designate the metal, or alloy, connecting the pieces to be assembled, formed by melting the edges to be assembled, with or without the addition of a filler material. The weld may therefore be the result of the base metals alone (i.e. the pieces to be assembled) or of the mixture of the base metals and the filler material. During welding, there is local melting of the pieces to be assembled, unlike in soldering where there is never melting of the materials to be assembled.

[0045] High energy welding, such as electron beam welding or LASER welding, is a welding technique in which a high energy welding beam is applied to the pieces to be assembled to produce intense heat for melting the metal of the pieces to be assembled. The term high energy means that the welding beam delivers a high local power of at least 10 KW/mm.sup.2. In electron beam welding, or EBW, a beam of electrons bombards pieces to be assembled and produces a narrow, intense, three-dimensional heat source forming a hole or tunnel opening through the materials of the two pieces and travelling along the joint to be welded. In the laser welding technique, the electron beam is replaced with a LASER beam.

[0046] The method according to the invention, an example of which is functionally represented in FIG. 10, provides for assembling two metal pieces by high energy welding, avoiding any instability and/or deflection of the welding beam. An example of two metal pieces, in particular a blade 22 and a centrifugal diffuser cover 21, to be assembled using the method of the invention, is represented in FIG. 6. The following description will be given for a blade and a centrifugal diffuser cover, it being understood that the method of the invention may be implemented for any assembly of a first metal piece to be assembled with a second metal piece.

[0047] To allow welding without deflection of the high energy welding beam, the method according to the invention includes an operation 110 of making, on the external surface 21a of the cover 21, a slot 23 located facing the blade 22. This slot 23 is an opening 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 may be, for example, substantially rectilinear or with the shape of an arc of a circle. In the example of FIG. 6, the slot 23 is made vertically aligned with 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 avoid deflection of said beam. The high energy welding beam, also referred to as the welding beam, electron beam or laser beam, is directed towards the slot 23 and follows the slot 23 along the entire length of said slot. The welding beam thus enables the metal of the cover 21 located in the vicinity of the slot 23 and the metal of the blade 22 located facing the slot 23 to be brought locally to their melting temperature. The two molten metals aggregate so that, after cooling, the two metal pieces are assembled.

[0048] The slot can be made using techniques conventionally used for cutting metal pieces, such as LASER cutting or EDM (Electro Discharge Machining) cutting. An example of a centrifugal diffuser cover with several slots is represented in FIG. 7. This cover 21 includes slots 23 made for implementing the method according to the invention. These slots 23 enable blades (not visible in the figure) to be assembled on the cover 21, in a non-through configuration. FIG. 7 also shows apertures 24 used for assembling blades in a through configuration, explained later.

[0049] The method of FIG. 10 includes, after the operation 110 of making the slot 23, an operation 120 of positioning the blade 22 in line with the slot 23. Indeed, for the welding beam to ensure melting of the metals of the cover and the blade, it is necessary that the blade is positioned facing the slot, its top 22a extending substantially perpendicular to the inner surface 21b of the cover 21. Once the blade 22 has been positioned, the high energy welding operation 130 is implemented using an adapted welding device. This welding operation 130 is executed, as explained previously, by bringing the metal of the top of the blade 22 and the metal of the part of the cover 21 adjacent to the slot 23 to their melting temperature, so as to obtain a melting zone Z2 which will ensure, after cooling, the assembly of both pieces.

[0050] In some embodiments, some blades 22 are assembled with the cover in a non-through configuration and others in a through configuration.

[0051] In some 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 represented in FIG. 9. FIG. 9 shows blades 22 including extended portions 22b and normal portions 22c. The extended portions 22b are portions of the blade 22 which project longitudinally from the normal portions 22c of the blade. The extended portions 22b are designed to be inserted into the apertures 24 of the cover 21 in the through configuration. These extended portions 22b, housed in the apertures 24, are assembled with the cover 21 by a conventional high energy welding operation in which the welding beam induces melting of the metal of the extended portion 22b and the metal of the cover around this extended portion, creating a first molten zone Z1. The normal portions 22c of the blade 22 are each positioned against a slot 23 in the cover, in line with said slot. The assembly of these normal zones 22c with the cover 21 is obtained after the welding beam has passed through the slot 23, i.e. along the normal portion 22c of the blade. Passage of the welding beam through the slot 23 generates a second molten zone Z2.

[0052] Thus, as previously explained, the slot 23 in the cover 21 makes it possible to guide and focus the welding beam on the top 22a of the blade in the zones of non-through configuration. As this slot 23 is made facing 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 in relation to the blades 22 is correct. Several techniques are currently used to check positioning of the cover in relation to the blades (for example the use of a mechanical detection tool or an optical tool); checking by means of the slot 23 makes it possible either to replace the usual technique or to confirm the positioning check, with the advantage of being simple to implement, without requiring additional costly means.

[0053] The assembly method with welding through slot 23, as described above, solves the problem caused by the difference in massiveness between the blade and the cover. In the embodiments in which each blade is assembled partly in the through configuration and partly in the through configuration, the difference in massiveness is particularly present at the blade tip, i.e. in the zone close to the end of said blade. In fact, at the blade tip, the difference in massiveness not only results in a difference in the thickness of the pieces (about 0.2 to 0.3 mm for the top of the blade and about 2 to 3 mm for the cover) but also in a transition zone in the configuration mode when shifting from the through configuration to the non-through configuration. In this transition zone, the change of configuration generates significant variations in thickness, especially as the blade profile is very thin therein. An example of a blade tip assembly is schematically represented in FIG. 8 with the zone Zt for the through configuration, the zone Znt for the non-through configuration and the transition zone Ztrans. To avoid variability during the welding operation in the transition zone Ztrans, the method includes an operation of adjusting positioning of the through configuration zone Zt, which has to be positioned as close as possible to the edge of the blade 22 in order to take optimum advantage of the weldability offered by the through configuration. In addition to this adjustment operation, and in contrast, it is chosen to retain a zone of non-through configuration Znt at the blade tip. A schematic example of a diffuser according to the invention with a zone of non-through configuration Znt at the blade tip is represented in FIG. 11. This choice of a zone with a non-through configuration Znt at the blade end avoids many problems. Indeed, if a zone with a through configuration Zt were positioned at the very end of the blade 22, then: [0054] on the one hand, the welded cover 21 at the top of the blade would have a weakened zone on its external diameter (depicted by a circle in FIG. 11) 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 internal to the diffuser would then be uncontrolled on either side of the blade with, moreover, a deformed diffuser cover in this zone; and [0055] on the other hand, the use of tooling to position this weakened zone for the purpose of holding it in place during the welding operation would introduce unnecessary industrial complexity, mainly due to the overall size of the elements involved (blades, cover, blade height, juxtaposition of the blades in relation to each other, etc.).

[0056] Keeping a zone of non-through configuration Znt at the blade tip makes it possible not only to avoid the problems set out above but also to weld the thinnest zone of the blade 22, to ensure that the cover 21 is held in place and to limit manufacturing costs by avoiding complex implementation.

[0057] Although described through a number of examples, alternatives and embodiments, the assembly method according to the invention, the assembly itself and the diffuser produced by implementing this method comprise various alternatives, modifications and improvements which will be obvious to the person skilled in the art, it being understood that these alternatives, modifications and improvements are within the scope of the invention.