Method for manufacturing shrouded impeller

Abstract

The method includes the preliminary steps of placing a disk and a shroud coaxially with each other wherein one of the disk and the shroud includes a plurality of blades projecting toward the other of the disk and the shroud, each blade having a base and a tip; wherein the other of the disk and the shroud comprises a plurality of grooves in its outer surface opposite the blades; wherein each groove has a side surface and a bottom; and wherein the shroud and the disk are arranged in contact with each other along the blade, wherein each of the plurality of grooves extends along a respective one of the plurality of blades. Each blade is then welded to the other of the disc and the shroud along a respective groove by a swinging laser beam applied from outside of the impeller and moving along the groove.

Description

Technical Field

[0001] The present disclosure relates to the field of turbomachinery. Embodiments disclosed herein particularly relate to a method for manufacturing a shrouded impeller for a turbomachine. Background Art

[0002] Several turbomachines use rotating impellers to convert mechanical power to pressure power of a gas stream or vice versa. In particular, turboexpanders include an impeller mounted on a shaft to expand a compressed gas stream and convert the energy of the compressed fluid into mechanical power that can be used on a rotating shaft of the expander. Centrifugal compressors and centrifugal pumps include rotating impellers to compress a gas stream using mechanical power applied to a rotating shaft of the compressor.

[0003] Typically, an impeller includes a disk, also called a hub, having a plurality of blades integral therewith. The blades may have a so-called three-dimensional shape or twist. Some impellers specifically to which the present disclosure relates also include a shroud. The disk, the shroud, and the blades arranged therebetween define a flow channel in which a gas stream flows and exchanges energy with the rotating impeller. Typically, the blades are formed by machining a blank and forming the disk and the blades into a single, integral body. The shroud is then welded to the ends of the blades, typically by arc welding (US42302657). Laser welding has also been attempted in the past (US8408873) in an effort to reduce thermal deformation and stresses in the impeller caused by conventional arc welding techniques.

[0004] Laser welding proved to have severe limitations, particularly with respect to the maximum size of shrouded impellers that could be manufactured using this technique.

[0005] Therefore, there remains a need for improvement in the art of laser welding of shrouded impellers. Summary of the invention

[0006] According to the present disclosure, there is provided a method for manufacturing an impeller with a shroud, the method comprising a preliminary step of placing a disk and a shroud coaxially with each other. One of the disk and the shroud comprises a plurality of blades protruding toward the other of the disk and the shroud, each blade having a base and a tip. The other of the disk and the shroud comprises a plurality of grooves in its outer surface opposite to the blade; wherein each groove has a side surface and a bottom. The shroud and the disk are arranged to contact each other along the blade, and each of the plurality of grooves extends along a corresponding one of the plurality of blades. The method further comprises the steps of: welding each blade to the other of the disk and the shroud along the corresponding groove by an oscillating laser beam applied from the outside of the impeller and moving along the groove (i.e., using a laser beam having an oscillating motion);

[0007] In some embodiments, the step of welding each blade to the other of the disk and the shroud along a corresponding groove may include the following steps:

[0008] Scanning a laser beam at least once along each groove in an oscillating motion and causing the bottom of the groove to melt and then solidifying the melted bottom to weld the disc and the shield along the groove;

[0009] The grooves are filled with a metallic filling material by producing a series of superimposed layers of metallic material, each layer being melted by the laser beam in an oscillating motion and subsequently solidified.

[0010] In a particularly preferred embodiment, once the disk and the shroud have been placed coaxially to each other, a preliminary peripheral welding can be performed in order to temporarily connect the shroud and the disk to each other in the correct mutual angular position. Each blade provided on one of the shroud and the disk is then welded to the other of the disk and the shroud along a corresponding groove by performing the following steps:

[0011] a) scanning a laser beam in a swinging motion following a first trajectory extending along the groove, and locally welding the disc and the shield along the first trajectory;

[0012] b) if the width of the groove requires, scanning the laser beam in a wobbling motion along a further track parallel to the first track and laterally offset therefrom in the direction of the width of the groove;

[0013] c) if necessary, repeating step (b) until the entire bottom of the groove is welded to the corresponding blade;

[0014] d) forming a metal filling material layer in the groove by the following steps:

[0015] d1. Scanning the laser beam along the first filling track extending along the groove with a swinging motion while conveying a metal filling material in the groove and melting the metal filling material with the laser beam;

[0016] d2. If the width of the groove requires, the laser beam is scanned in a swinging motion along another fill track parallel to the first fill track and laterally offset from the first fill track in the width direction of the groove;

[0017] d3. If necessary, repeat step (d2) until the entire width of the groove is filled with the molten and solidified metal filling material layer;

[0018] e) Repeating step (d) with subsequent layers of metallic filler material until the height of the recess is filled with multiple layers of molten and solidified metallic filler material.

[0019] Once steps (a), (b) and (c) have been completed for one blade, step (d) may be performed. However, preferably, the next blade is welded along the corresponding groove by performing steps (a), (b) and (c). Preferably, steps (a), (b) and (c) are performed for all blades and steps (d) and (e) are performed thereafter, starting with one of the blades. Similarly, in the event that a groove needs to be filled with a metallic filler material, steps (d) and (e) may be performed for one blade at a time. However, preferably, step (d) is performed once for each blade and then repeated for different blades in sequence so that all grooves are gradually filled with subsequent layers of metallic filler material.

[0020] Typically, the shroud and disk welded to each other using the above steps may be semi-finished products, i.e., additional machining and possible hardening or finishing steps may be required to achieve the shape and structure of the final impeller. As can be seen from the specific implementation of the embodiment, once the impeller has reached its final shape, the shroud and disk can have a thickness and diameter that is much larger than the final disk and shroud. Larger machining allowances on the shroud and disk are useful for reducing thermal deformation during welding. In one or more steps, additional metal material will be removed by machining to obtain the final shape of the impeller, which may be combined with heat treatments intended to modify the mechanical properties of the impeller (for example, for hardening purposes) and / or to reduce internal stresses or for other reasons.

[0021] Further features and embodiments of the disclosed method are described in more detail below with reference to the accompanying drawings and are set out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Reference will now be made briefly to the accompanying drawings, in which:

[0023] Figure 1 A schematic machining device including a base and a laser head is shown;

[0024] Figure 2 A laser welding apparatus in one embodiment is shown;

[0025] Figure 3 A schematic diagram showing a laser head during the steps of a welding process;

[0026] Figure 4 An exemplary embodiment of the motion trajectory of the oscillating laser spot during welding is shown;

[0027] Figure 5 Shown according to Figure 7 A cross-sectional view of a semi-finished shield along line VV in FIG.

[0028] Figure 6 Shown according to Fig. 9 A cross-sectional view of the semi-finished disk and the associated blades along the line VI-VI in FIG.

[0029] Figure 7 Shown according to Figure 5 A plan view of the semi-finished shield along line VII-VII in FIG.

[0030] Figure 8 Shown along Figure 7 A cross-sectional view taken along line VIII-VIII in FIG.

[0031] Fig. 9 Shown according to Figure 6 A view of line IX-IX in FIG.

[0032] Fig.10 shows a cross-sectional view according to a radial plane containing the axis of rotation of the finished impeller; and

[0033] Figures 11A-11J The sequence of welding one blade to the shroud of a semi-finished impeller is schematically shown. DETAILED DESCRIPTION

[0034] The following description specifically relates to a shrouded impeller for a centrifugal compressor. However, the method disclosed herein can also be used to manufacture an impeller for a pump or a turboexpander.

[0035] Briefly, the method welds the blades to the shroud (or disk) of the impeller by providing a plurality of grooves in the shroud (or disk), each groove being substantially coextensive with the corresponding blade. Each blade is then welded to the shroud (or disk) of the impeller from the outside of the impeller by melting the bottom of the corresponding groove and then solidifying the molten material using an oscillating laser, which performs one or more scans along the groove. Once the bottom of the groove has melted and solidified, thereby forming a first layer of weld material, the groove is filled with additional metal material, which is delivered (for example, in the form of powder or wire) into the groove and melted by multiple scans of the laser beam. The oscillating motion of the laser beam produces a pool of molten metal that is larger than the laser spot. This enables the groove to be quickly filled with molten and subsequently solidified metal material by producing superimposed layers of molten and subsequently solidified metal material. Each layer is in turn formed by at least one strip, preferably a plurality of molten and solidified metal material strips arranged side by side. Each strip is formed by scanning the oscillating laser following a trajectory along the longitudinal extension of the groove.

[0036] Now turning to the attached figure, Figure 1The impeller is shown in an axonometric view. The impeller 1 comprises a disk or hub 3 and a shroud 5. A plurality of blades 7 are arranged between the disk 3 and the shroud 5. The blades 7 may be three-dimensional blades. Each blade comprises a base 7.1 connected to the disk and an end 7.2 connected to the shroud.

[0037] In some embodiments, the disk 3 and blades 7 can be machined from a single blank by milling, while the shroud is manufactured separately and then connected to the blade tips by laser welding to form the final shrouded impeller 1. Specifically, the disk 3 has an inner surface 3.1 (see also Fig.10 ), to which the base 7.1 of the blade 7 is connected, and from which the blade 7 protrudes toward the shroud 5. The opposite outer surface of the disk 3 is marked 3.2. The shroud 5 has an inner surface 5.1 facing the inside of the impeller 1, which is connected to the tip 7.2 of the blade 7. The opposite outer surface of the shroud 5 is marked 5.2. Flow channels 9 are formed between the inner surface 3.1 of the disk 3 and the inner surface 5.1 of the shroud 5 and between adjacent blades 7.

[0038] In other embodiments, the blades and shrouds may be manufactured by machining (eg, milling) a blank, and the disk may be manufactured separately and subsequently welded to the blade base to form a shrouded impeller.

[0039] In a presently preferred embodiment, the shroud 5 is manufactured separately and welded to the tips 7 . 2 of the blades 7 , which are machined together with the disk 5 from a single blank.

[0040] When the shroud 5 is welded to the tip 7.2 of the blade 7 extending from the inner surface 5.1 of the disk 5, the outer surface 5.2 of the shroud 5 is machined to provide a plurality of grooves 11 therein. Each groove has a bottom 11.1 and a side surface 11.2 and extends longitudinally along a curve, which extends along the tip 7.2 of the corresponding blade 7 when the shroud 5 is welded to the blade 7.

[0041] As described in more detail below, the shroud is welded to the blade tip 7.2 using an oscillating laser. The welding process comprises two stages for each blade 7 and the corresponding groove 11. In the first stage, the metal material forming the bottom of the groove and the metal material forming the tip 7.2 of the corresponding blade 7 are melted by heating with laser power and then solidified to form a welded connection between the shroud 5 and the disk 3. In the second stage, the groove 11 is gradually filled with a metal material, which is supplied in the form of a powder or wire and melted by the laser power and then solidified in the groove.

[0042] The following detailed description relates to the laser welding process performed along a single groove as outlined above. The same process is repeated for each groove until the shroud 5 is welded to the disk 3 along a number of weld lines equal to the number of blades 7. For ease of description, the process is described below as being performed on a single groove, with the first and second stages being performed sequentially along the same groove. Once both stages of the process have been performed on the first groove, the next groove and blade are processed, and so on, until the shroud 5 is fully welded to all blades 7. However, it should be understood that the first stage of bottom welding can be performed sequentially for all grooves; and once the bottom of each groove 11 has been welded to the corresponding blade tip 7.2, the next stage of groove filling can be performed.

[0043] In some embodiments, the grooves are welded to the respective blades in an order adapted to reduce the risk of thermal deformation of the impeller, for example starting with the first groove, followed by the second groove, the second groove being angularly staggered 180° relative to the first groove; the third groove to be welded is staggered 90° relative to the second groove; the fourth groove to be welded is staggered 180° relative to the third groove, etc. The same order is followed in the second stage to fill each groove.

[0044] exist Figure 2 A laser device for performing a welding process is schematically shown in FIG. Typically, the device comprises a support for an impeller 1 and a laser head. The laser head and the impeller are provided with movement along a numerically controlled axis so that the laser beam generated by the laser head can scan each groove 11 of the shield 5.

[0045] More specifically, in Figure 2 In the embodiment schematically shown in FIG. 2 , the device 21 comprises a tilting table 23 on which the disc 3 of the impeller 1 can be blocked. The tilting table 23 can be provided with a numerically controlled movement around one or two numerically controlled rotation axes, which are preferably oriented at 90° to each other. The device 21 also comprises a laser head 25, which can be provided with a movement according to a numerically controlled translation axis, for example two numerically controlled translation axes orthogonal to each other. In a different embodiment not shown, the laser head 25 can be mounted on a robot arm, for example on an anthropomorphic robot arm.

[0046] Figure 3 A schematic diagram of a laser head 25 and an impeller 1 during the welding step of a welding process is shown in FIG. The laser head 25 comprises an oscillating laser, i.e. a laser source and associated optical devices that transmit the oscillating motion to the laser beam generated by the laser source. For example, an oscillating laser source is disclosed in US 2020 / 0376594.

[0047] In some embodiments, the laser head comprises a laser source 25.1, a collimator 25.2, a set of movable mirrors 25.3 and focusing optics 25.4. The movable mirrors 25.3 may be controlled by a suitable actuator to produce an oscillating motion.

[0048] The oscillating laser source can be moved relative to the impeller so that the laser spot generated by the laser optics 25.2-25.4 moves along a main track T, for example parallel to the groove 11, and is also provided with an oscillating motion about a center point. The center point moves along the main track. The resulting track of the laser spot on the metal material to be welded is a combination of a continuous line along the main direction and a periodic motion. If the oscillating motion is, for example, a circular motion around the center point and the main track is a continuous line along which the center point moves, the laser spot will be according to Figure 4 The depicted line moves.

[0049] The oscillating motion combined with the main motion of the laser spot along its main trajectory produces a pool of molten metal whose size is larger than the laser spot and is given by the diameter of the circular oscillating motion. Figure 4 In FIG. 1 , the mark S represents the laser spot, and W is the width of the molten metal pool.

[0050] As will become clearer from the following detailed description of the welding process, the oscillating motion of the laser spot S allows welding of large impellers, where the thickness of the blades can be a multiple of the diameter of the laser spot S and therefore the width of the groove 11 is relatively wide, while the number of laser scans is relatively small.

[0051] To better understand the welding process, Figure 5 A cross-sectional view of a semi-finished shroud before being welded to the disk of the impeller is shown. The impeller is symmetrical about the axis of rotation AA, so that Figure 5 Only half of the impeller is shown in the cross-sectional view of . The outline of the final impeller shape is shown in dashed lines. From the superimposed dashed final outline of the impeller, it can be understood that the shroud is a semi-finished product, since its thickness is significantly greater than the thickness of the final impeller shroud shown in dashed lines. In addition, the semi-finished shroud 5 comprises a circumferential protrusion 5.3, which will be removed in the final machining step and is used to temporarily connect the semi-finished shroud to the semi-finished disk during the welding process.

[0052] Semi-finished plate 3 Figure 6 The diagram is shown in a partial cross-sectional view along a radial plane containing the axis of rotation of the impeller.

[0053] The final impeller Fig.10 The reference numeral 1.1 indicates the impeller inlet.

[0054] like Figure 7 and Fig. 9As best shown in the figure, the groove 11 arranged on the outer surface of the semi-finished shroud 5 has a longitudinal extension, the shape of which corresponds to the shape of the tip 7.2 of the corresponding blade 7, so that when the shroud 7 and the disk 5 are placed on top of each other, the groove 11 extends together with the blade tip 7.2, that is, extends along the tip 7.2 of the corresponding blade 7.

[0055] like Figure 8 As shown in the cross-sectional view of , each groove 11 has a bottom 11.1 and two side walls 11.2. When the shroud 5 is placed on top of the disk 3, the outer surface of the bottom 11.1 contacts the tip 7.2 of the corresponding blade 7 machined into the disk 3.

[0056] Before welding the blades 7 to the shroud 5, a preliminary welding step is performed to temporarily connect the semi-finished shroud to the semi-finished disk 3. The temporary welding is performed along the circumferential line, connecting the circumferential protrusion 5.3 ( Figure 5 ) is connected to the circumferential edge 3.5 of the semi-finished disk 3 ( Figure 6 The correct mutual angular position of the semi-finished shroud 5 and the semi-finished disk 3 can be determined with the aid of blind holes in the tips 7.2 of some of the blades 7 formed integrally with the semi-finished disk 3 and corresponding through holes in the bottoms 11.1 of some of the grooves 11. The dowels are introduced into the through holes in the bottoms 11.1 of the grooves and into the corresponding blind holes of the blades 7.

[0057] Once the semi-finished shroud 5 and the semi-finished disk 3 have been provisionally assembled and welded to each other along the circumferential protrusion 5 . 3 to form the semi-finished impeller 1 , the semi-finished impeller is mounted on a tilting table 23 for welding along each blade 7 .

[0058] FIG. 11A to FIG. 11J The order of steps of the welding process for welding one blade 7 to the shroud 5 is described above. As described above, the process is divided into two stages: a first stage, which involves melting the groove bottom 11.1 and the blade tip 7.1, and then solidifying the molten material; and a second stage, filling the groove 11 with an additional filler metal material, which is supplied in the form of powder or wire. As described above, these two stages are usually not performed sequentially on the same groove 11. Instead, all grooves 11 are first welded with the groove bottom and then filled with the additional metal material.

[0059] exist FIG. 11A to FIG. 11J In the sequence of Figure 7 The line VIII-VIII of the groove 11 and the blade tip 7.2.

[0060] Once the semi-finished impeller 1 has been locked on the tilting table 23, in a first step the laser head 25 is positioned at one end of the groove 11 so that the laser beam B will generate a laser spot at one end of the groove 11, close to one of the side walls 11.2 of the groove. The laser head 25 moves according to a swinging motion combined with a main motion along a trajectory extending from one end of the groove 11 to the opposite end. The main motion can be transmitted to the laser head 25, the impeller 1 or both, i.e. it can be obtained by combining the motion of the tilting table 23 and the motion of the laser head 25 relative to the fixed structure supporting the laser head 25 and the table 23.

[0061] In some embodiments, the movement may start at the radially outermost end of the groove 11. Figure 4 The combination of the linear motion of the laser beam and the swinging motion of the laser beam B melts the metal material, thereby forming the shroud 5 and the blades 7. Fig.11A , the steps before melting are shown. More specifically, the bottom 11.1 of the groove 11 and the uppermost part of the blade tip 7.2 are melted. The width W of the molten area (molten metal pool) in the transverse direction of the groove 11 depends on the diameter of the circular oscillating motion and can be a multiple of the diameter of the laser spot S. The width of the molten pool (i.e., the molten metal pool) is generally smaller than the width W of the groove 11.

[0062] When the laser spot S moves along a linear trajectory T along the longitudinal extension of the groove 11, the molten metal behind the laser spot S gradually solidifies, thereby producing a weld bead formed by the molten and solidified material of the bottom 11.1 of the groove 11 and by the molten and solidified material of the blade tip 7.2. Fig. 11B Shown in.

[0063] As mentioned above, due to the diameter of the molten pool ( Figure 4 W in ) is usually smaller than the width of the groove 11, so the above steps can be repeated two or more times, and the laser beam is scanned two or more times along the groove 11. Each scan is laterally offset relative to the previous one along the transverse direction of the groove 11. If the width of the groove 11 is equal to the diameter of the molten pool, a single scan is sufficient.

[0064] By moving the laser beam B along an additional track deviating from the first track in the transverse direction of the groove 11, for example Fig. 11C As shown, another molten pool is formed, which moves from one end of the groove to the opposite end in the longitudinal direction of the groove 11. Subsequently, the molten material solidifies. If necessary, the oscillating laser beam can move along a plurality of additional tracks along the groove 11, each track being offset from the previous track in the transverse direction (i.e., in the width direction of the groove 11) until ( Fig.11D) until the entire bottom of the groove 11 and the entire tip 7.2 of the corresponding blade 7 have melted and subsequently solidified. A weld bead as large as the groove 11 is thereby formed. The width of the groove 11 corresponds substantially to the width of the blade 7 or is preferably greater than the width of the blade 7, so that the width of the resulting weld layer is equal to or greater than the thickness of the blade 7.

[0065] Due to the use of an oscillating laser, i.e., the oscillating motion of the laser beam B is combined with the main motion along the longitudinal welding trajectory T, the number of laser scans required to produce a welding layer as large as the width of the groove is much smaller than the ratio between the width of the groove 11 and the laser spot diameter. The time required to produce the welding layer is very short, and the welding method can also be used in the case of large-sized impellers with relatively large thickness of the blades 7.

[0066] The further stage of welding and filling the groove 11 with metallic material now takes place ( FIG. 11E to FIG. 11J ). As mentioned above, this additional stage can be carried out after welding and solidification of the groove bottom 11.1, or after the bottom 11.1 of one, some or all other grooves 11 has been melted and welded to the tip 7.2 of the corresponding blade 2. This second method is preferred because the risk of thermal deformation of the semi-finished impeller 1 is reduced.

[0067] The second stage of welding includes adding metal material in the groove 11 so as to fill the groove. For example, the metal material can be dispensed in the form of a wire or in the form of a powder. The added metal material is placed under the oscillating laser beam B while the oscillating laser beam B moves according to a trajectory T along the corresponding groove 11, and the linear motion along the main trajectory T is combined with the oscillating motion of the laser beam B to produce a molten pool having a width greater than the diameter of the laser spot S.

[0068] exist Figure 3 , a nozzle 31 for distributing metal powder toward the molten pool formed along the bottom of the groove 11 during this welding stage is schematically shown as an exemplary embodiment of a metal distributing device. As mentioned above, the metal material can also be delivered in other forms, such as in the form of wire.

[0069] exist Fig.11E , a first weld bead is shown formed by melting and solidifying the added metal material along one side of the groove 11. This step is repeated two or more times, such as Fig.11F , 11GThe sequence is shown until a layer of molten and subsequently solidified added metal material is formed. The number of laser scans required to complete a layer depends on the diameter of the laser spot S, the width of the oscillating motion (e.g., the diameter of the circular oscillating motion), and the width of the groove 11. If the width of the groove 11 is very small and equal to the diameter of the molten metal material pool formed by the oscillating laser, a single scan is sufficient to produce a layer of molten and subsequently solidified metal material.

[0070] This process is repeated as many times as necessary (see FIG. 11H to FIG. 11J ) to form a filling sufficient for subsequent machining of the impeller 11. In some cases, the entire groove 11 can be filled until the outer surface 5.2 of the semi-finished shroud is reached with a final layer of melted and solidified added metal material.

[0071] The multiple scanning process in combination with the oscillating movement of the laser beam B allows the entire groove 11 or a portion thereof to be filled quickly as required, even in the case of large impellers 1, where the thickness of the blade tip 7.2 and therefore the width of the groove 11 requires multiple scanning with the laser beam along the transversely offset main trajectory T. In some cases, the diameter of the oscillating movement can be adapted to the lateral dimensions of the groove, so that in the case of larger blades 7, a wider oscillating movement is used, resulting in a larger molten pool with each laser scan.

[0072] The above-described process enables an efficient welding process for even large-sized impellers, avoiding the use of arc welding and thereby reducing the resulting thermally induced stresses and deformations of the impeller.

[0073] As mentioned, in a preferred embodiment, the semi-finished shroud 5 and the semi-finished disk are welded together as described above, so that the heat-induced deformation of the impeller is reduced due to the thickness of the semi-finished shroud 5 and the disk 3. The excess material is then removed by machining (for example, by milling) until a Fig.10 The chip removal process also removes the circumferential excess material of the impeller, thereby removing the temporary weld bead formed along the circumferential protrusion 5.3 of the shroud 5.

[0074] Although in the above description and drawings the blades 7 are formed by machining the disk 3 and the grooves 11 are machined in the outer surface 5.2 of the shroud, as described above, the reverse method can also be used, wherein the blades 7 are machined from a blank as an integral part of the shroud 5 so that the blades 7 will protrude from the inner surface 5.1 of the shroud, while the disk 3 is provided with a smooth inner surface 3.1 and with the grooves 11 machined in its outer surface 3.2.

[0075] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be appreciated by those skilled in the art that various changes, omissions and additions may be made to the specific disclosure herein without departing from the scope of the present invention as defined in the following claims.

Claims

1. A method for manufacturing a shrouded impeller, the method comprising the following steps: placing a disk and a shroud coaxially with each other, wherein one of the disk and the shroud includes a plurality of blades protruding toward the other of the disk and the shroud, each blade having a base and a tip; wherein the other of the disk and the shroud includes a plurality of grooves in an outer surface thereof opposite the blades; wherein each groove has a side surface and a bottom; and wherein the shroud and the disk are arranged to contact each other along the blades, wherein each of the plurality of grooves extends along a corresponding one of the plurality of blades; welding each blade to the other of the disk and the shroud along the corresponding groove by an oscillating laser beam applied from the exterior of the impeller and moved along the groove; wherein the step of welding each blade to the other of the disk and the shroud along the corresponding groove comprises the following steps: Scanning a laser beam at least once along each groove in an oscillating motion and causing the bottom of the groove to melt and then solidifying the melted bottom to weld the disc and the shield along the groove; The grooves are filled with a metallic filling material by producing a series of superimposed layers of metallic material, each layer being melted by the laser beam in an oscillating motion and subsequently solidified.

2. The method of claim 1 , wherein the step of welding each blade to the other of the disk and the shroud along the corresponding groove comprises the steps of: a) scanning a laser beam in a swinging motion following a first trajectory extending along the groove, and locally welding the disc and the shield along the first trajectory; b) repeating step (a) along another trajectory, parallel to the first trajectory and laterally offset from the first trajectory in the width direction of the groove, until the entire bottom of the groove is welded to the corresponding blade; c) forming a metal filling material layer in the groove by the following steps: c1. Scanning the laser beam along the first filling track extending along the groove with a swinging motion while conveying a metal filling material in the groove and melting the metal filling material with the laser beam; c2. Repeating step (c1) along another filling track until the entire width of the groove is filled with a layer of molten and solidified metal filling material, the other filling track being parallel to the first filling track and laterally offset from the first filling track in the width direction of the groove; d) Repeating step (c) for subsequent layers of metallic filler material until the height of the recess is filled with multiple layers of molten and solidified metallic filler material.

3. The method of claim 2, wherein step (c) is repeated until the groove is completely filled with the metal filling material.

4. A method according to any one of the preceding claims, wherein the vanes project from the disk and the grooves are formed in the outer surface of the shroud opposite the disk.

5. The method of any one of claims 1 to 3, wherein the vanes protrude from the shroud and the grooves are formed in the outer surface of the disk opposite the shroud.

6. A method according to any one of the preceding claims, wherein the metallic filler material is delivered into the recess in powder form and melted by the laser beam.

7. The method according to any one of claims 1 to 5, wherein the metallic filler material is melted by the laser beam in the form of a rod or a wire.

8. A method according to any preceding claim, comprising the step of machining the blades by milling one of the disk and the shroud.

9. A method according to any one of the preceding claims, comprising the step of machining the groove by milling.

10. A method according to any one of the preceding claims, further comprising the step of machining the shroud and the disk to the final shape of the impeller after filling the groove.

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