"Method for the construction of rotor and stator elements of

turbomachinery"

Field of the invention

The present invention relates to a method for the construction of rotor and stator elements of turbomachinery.

Rotor and stator elements are typically vaned elements with more or less complex geometries that are realised from a blank through the removal of a high percentage of material with respect to the volume of the starting part, up to 80%- 90% of the volume of the starting part.

The present invention is applied both to drive turbomachines (turbines) and work turbomachines (compressors).

Preferably but not exclusively, the present invention relates to the turbomachinery used in the aeronautic/aerospace sector and/or the energy field and/or the motoring field and/or the shipbuilding field.

Such elements are, for example and not exclusively, open or closed impellers, rotor and stator vaned rings or discs, preferably for radial turbines, inlet/outlet guides, diaphragms, etc..

Preferably but not exclusively, the present invention relates to expansion turbines used in apparatuses for the production of electrical energy which, preferably, exploit geothermal sources through, for example, the Rankine water-steam cycle or through the Organic Rankine Cycle (ORC).

Background of the invention

As is known, the realisation from the blank of the stator and rotor elements is actuated by means of mechanical processing on a solid starting part (which can also be a molten or 3D printed part) through operations that remove material gradually and a little at a time. Known technologies used include, for example, the removal of chips through mechanical and even robotized or abrasive water jet (AWJ) milling machines and the electrical discharge machining through EDM (electrical discharge machining) or ECM (electrochemical machining) machines. In the production of complex rotor and stator elements of the present invention, these processes can reach removal speeds of a few tens or a few hundreds of cubic centimetres per minute. For example, the removal of rough machining with a 40 mm cutter can be performed at a removal speed of about 80-100 cm3/min. The removal of rough machining with one or more AWJ heads can reach 300 - 350 cm3/min.

Methods are also known that envisage the removal of material in blocks through an abrasive water jet (AWJ). For example, the public document US2013/0171915 illustrates a process for realising a vaned disc that envisages cutting out a block of material from a solid starting part by means of an abrasive water jet. The abrasive water jet passes through the thickness of the solid starting part, so that the cutout block can slide out from said part by gravity.

The public documents US2013/0167359, US201 1/041334, US201 1/023300, US201 1/016716, US201 1/016714, US201 1/016712 also illustrate similar methods. Summary

In this field, the Applicant has perceived the need to improve the known constructive methods for the realisation of complex rotor and stator elements of turbomachinery, so as to ensure high construction quality in order to guarantee the reliability and efficiency of the turbomachinery in which they are installed and, at the same time, to speed up their production and reduce the related costs.

In fact, the Applicant has noted that traditional techniques for the gradual removal of material imply long realisation times.

The Applicant has also noted that the quickest methods such as those described in the documents mentioned above allow, in some cases, only approximate rough machining to be performed and, in other cases, for rotor and stator elements with complex shapes, they cannot even be used as the through cut would end up intersecting the geometries (typically the vanes) of the rotor or stator elements to be realised.

"Complex geometry" typically means a geometry with (very curved) action vanes or a high number of vanes (therefore with not much space between one and another) or with very twisted vanes between the inlet and the outlet (used for compressors, for example). Conversely, "simple geometry" typically means with a higher reaction geometry, either with fewer vanes or with untwisted vanes.

In this context, the Applicant pursues the following objectives: ^■ providing a method for the construction of rotor and stator elements of turbomachinery that is quick and relatively simple, so as to reduce production costs, but at the same time allow complex geometries to be realised;

■ providing a method for the construction of rotor and stator elements of turbomachinery which however enables the quality and constructive precision thereof to be improved and therefore the reliability and efficiency of the turbomachinery in which they are installed.

More specifically, the Applicant pursues the following objectives:

■ reducing the processing times necessary for obtaining the finished geometries of the vanes;

^■ reducing the processing costs by reducing the processing times;

^■ reducing the processing costs using machines with lower costs per hour and using fewer tools for processing and/or machines that allow various grooves to be processed in parallel;

^■ allowing any type of material to be processed more economically;

^■ reducing the investment costs for machinery to be used;

^■ allowing the removed waste material to be resold and/or reused.

The Applicant has found that the above indicated and other objectives can be reached by performing interrupted, or non-through, cuts in the thickness of the starting solid/single block (of preferably metal material) so as to define and remove entire blocks of material from said solid/single block, generating respective blind cavities. Preferably, second whole blocks are removed on an opposite side of the solid so as to open the blind cavities and form through openings. Said blind cavities or said through openings define the passages between the vanes of the rotors/stators and are preferably finished with subsequent processing.

In particular, the stated and other objectives are substantially attained by a method for the construction of rotor and stator elements of turbomachinery according to one or more of the appended claims and/or according to one or more of the following aspects.

More specifically, according to one aspect, the present invention relates to a method for the construction of rotor and stator elements of turbomachinery.

The method envisages: preparing a solid of material to be machined; performing cuts in the solid so as to delimit blocks of material interposed between portions of material intended to form vanes of the rotor or stator element; removing said blocks to clear passages between the portions of material; optionally, finishing said portions of material to confer the final shape to said vanes and to said passages. For the formation of each of the passages, the step of performing cuts comprises: performing interrupted cuts in the solid; wherein at least some of said interrupted cuts are mutually incident in respective terminal points within the solid to delimit in said solid at least one block and, after the removal of said at least one block, a respective blind cavity.

Preferably, for the formation of each of the passages, the step of performing cuts comprises: first performing first interrupted cuts on a first side of the solid to delimit in said solid at least a first block and, after the removal of said at least a first block, a respective first blind cavity; performing, preferably later, second interrupted cuts, preferably on a second side of the solid opposite the first side, to delimit in said solid and at the first blind cavity at least a second block and, after the removal of said at least a second block, a respective second cavity.

Preferably, for the formation of each of the passages, the step of performing cuts comprises: first performing first interrupted cuts on a first side of the solid to delimit in said solid at least a first block; performing, preferably later, second interrupted cuts, preferably on a second side of the solid opposite the first side, to delimit in said solid and at the first block at least a second block joined to the first; performing third interrupted cuts, preferably on a third side of the solid, to divide the first block from the second block. Interrupted or non-through cuts means rectilinear or substantially rectilinear cuts that finish inside the solid, i.e. do not cross the entire thickness of the solid, and that, were they to continue beyond the respective endpoints, would intersect the final geometric shapes of the rotor or stator element to be obtained, i.e. they would ruin the rotor or stator element during the construction step.

Blind cavity means that said cavity has a blind bottom defined by the zone/line/plane of intersection/incidence (set of endpoints) of the interrupted cuts. In one aspect, first interrupted cuts and/or straight lines that continue beyond the respective endpoints intersect the second interrupted cuts and/or straight lines that continue beyond the respective endpoints. In other words, the first interrupted cuts and/or straight lines that continue beyond the respective endpoints are inclined with respect to the second interrupted cuts and/or straight lines that continue beyond the respective endpoints.

The Applicant has verified that the method according to the invention allows, first of all, complex rotor and stator elements to be realised (which cannot be realised with the AWJ prior art with through cuts) such as to allow greater design freedom. The intersecting interrupted cuts allow the ratio between the total volume removed after removing the block(s) and the volume of material removed during the execution of the cuts or between the total volume removed after removing the block(s) and the total volume to be removed to be maximised in order to have the final vaned geometry. Thanks to this characteristic, the intersecting interrupted cuts allow larger blocks to be removed and to get closer straight away to the final geometric shape required, even in the event that such geometry is very complex. The Applicant has also verified that the method according to the invention allows the processing times and costs necessary for obtaining such complex geometries to be considerably reduced (particularly in relation to the prior art that envisage the gradual removal of material), precisely due to the fact that the material is removed in blocks.

The Applicant has also verified that the material removed in blocks can be resold at a higher cost with respect to the chips deriving from traditional processes, or reused as a starting material (e.g. for constructing single vanes).

Larger thicknesses of material can also be cut (intersecting cuts from the outside and from the inside) increasing the field of application of the AWJ cut (which is currently only used for through cuts below a certain limited thickness).

Preferably, after the removal of the blocks, the volume of the generated passage is comprised between about 85% and about 95% of the finished passage volume between the vanes, i.e. of the volume obtained after finishing.

The method according to the invention makes it possible to get close to the definitive shape of the rotor/stator element already after the sole removal of the blocks.

In one aspect, the second cavities open into the first cavities.

In other words, after performing the first blind cavity, the second interrupted cuts cut out the second block which borders onto the first cavity and that, once removed, leaves the second cavity free which is in communication with the first cavity so as to define one of the mentioned passages. In one aspect, the method envisages performing further cuts to place each first cavity in communication with a respective second cavity.

In one aspect, said further cuts delimit further blocks, the first cavities being placed in communication with the second cavities through the removal of said further blocks.

In other words, after the removal of the first block and of the second block, the first blind cavity is not yet in communication with the second cavity (which is therefore also blind) and the further cuts are performed to place in communication said first and second cavities and to perform one of the mentioned passages.

In one aspect, the blocks have a tapered shape. In one aspect, the blocks have a prismatic, conical, pyramidal, wedge, trapezoidal shape, etc. Such shapes allow the blocks to be easily removed once cut out.

In one aspect, the blocks are removed by letting them fall by gravity. In one aspect, the blocks are removed through ejector devices, for example comprising magnets. In one aspect, the blocks are removed manually.

In one aspect, said cuts are performed through a very high pressure water jet (e.g. 2000 - 8000 bar), preferably with abrasive water jet (AWJ), preferably through a water-jet device.

This type of technology allows the production cycles subsequent to rough machining to be reduced, since there are no heat deformations during AWJ processing. There are no microstructural/metallurgic alterations or alterations to the processed material or to the surface of the component. The rough machining step is less influenced by the type of material to be processed with respect to the processing performed using cutters or EDM or ECM. There are no mechanical tools with the related costs and problems (e.g.: vibrations, problems relating to the size of the cutters). Any material can be processed without the cutting process being excessively influenced. It is also possible to use different nozzles simultaneously, which makes the rough machining even faster.

In one aspect, said cuts are performed through the mechanical removal of chips, preferably through milling, preferably with a milling machine. In one aspect, said cuts are performed through laser, preferably through a laser device. In one aspect, said cuts are performed through electrical discharge machining EDM. In one aspect, said cuts are performed through plasma jet, preferably through a plasma torch. In one aspect, said cuts are performed through a combination of two or more of the aforementioned techniques (water jet, mechanical removal of chips, laser, electrical discharge machining, plasma jet) or others.

In one aspect, the depth of the interrupted cuts is checked.

In one aspect, the depth of the interrupted cuts is controlled through a feedback control. In one aspect, the method envisages detecting the depth of the cut through at least one sensor and controlling a cutting tool (e.g. the water jet device, the milling machine, the laser device, the EDM machine, the plasma torch) according to the detected depth. In one aspect, the operating parameters of the cutting tool are adjusted according to the detected depth. In one aspect, said at least one sensor may be, for example, of the optical, capacitive, X-ray type.

In one aspect, the depth of the interrupted cuts is controlled through a predictive control (in feedforward/regression analysis). In one aspect, the method envisages performing a plurality of tests on a determined material, with different contingent conditions and with a determined cutting tool and creating a mathematical model. In one aspect, the operating parameters of the cutting tool are set according to the depth to be obtained and through said mathematical model.

In one aspect, the operating parameters of a water jet device are selected from the group comprising: pressure and speed of the jet, quantity of abrasive, type of abrasive, translation speed of the device head, rotation of the head.

In one aspect, the cuts are performed by moving the head of the device and/or the solid.

In one aspect, the cuts are performed using a plurality of water jet devices.

In one aspect, the operating parameters of an EDM machine are selected from the group comprising: work/peak currents, axial speed, axial resolution.

In one aspect, the blocks have a volume "Vbl", wherein the performance of the cuts involves the removal of a volume of removed material "Vt", wherein the finishing performed after the removal of the blocks involves the removal of a finishing volume "Vfin". A volume "Vb" of material removed after the removal of the blocks is therefore equal to "Vb = Vbl +Vt". A total volume of material "Vtot" removed from the solid to obtain the final geometry/shape of the vanes (after the finishing) is therefore equal to "Vtot = Vb + Vfin = Vbl + Vt + Vfin".

In one aspect, a "Vb/Vtot" ratio is greater than about 0.45, preferably comprised between about 0.60 and about 0.95. In one aspect, a "Vt/Vbl" ratio is less than about 0.3, preferably comprised between about 0.005 and about 0.05.

In one aspect, the finishing is performed through conventional milling and/or EDM

(electrical discharge machining) and/or ECM (electrochemical machining).

In one aspect, the starting solid is obtained by forging or by melting or by 3D printing.

In one aspect, said rotor or stator element is selected from the group comprising: open and closed impellers, inlet/outlet guides, diaphragms, diffusers. Preferably, said rotor or stator element is selected from the group comprising: open and closed vaned rings and discs, discs with radial vanes, open and closed impellers. In one aspect, the present invention also relates to a rotor or stator element obtained by means of the method claimed and/or described in one or more of the preceding aspects.

Further characteristics and advantages will become more apparent from the detailed description of methods for the construction of rotor and stator elements of turbomachinery according to the present invention.

Description of the drawings

This description will be set out below with reference to the attached drawings, provided solely for indicative and therefore non-limiting purposes, in which:

^■ figure 1 illustrates a three-dimensional view of a portion of a vaned ring for radial turbines according to the method of the present invention;

^■ figure 2 illustrates a three-dimensional view of a portion of a vaned disc for radial turbines according to the method of the present invention;

^■ figures 3A - 6A illustrate three-dimensional views of a portion of the ring of figure 1 or of the disc of figure 2 in subsequent processing steps of the method according to the invention;

^■ figures 3B - 6B illustrate top and sectional views corresponding to the three-dimensional views of figures 3A - 6A;

^■ figures 7 and 8 illustrate top and sectional views of further processing steps of the ring of figure 1 or of the disc of figure 2;

^■ figures 9A - 1 1 A illustrate three-dimensional views of a portion of the ring of figure 1 or of the disc of figure 2 in subsequent processing steps in accordance with a variant of the method according to the invention; ^■ figures 9B - 1 1 B illustrate top and sectional views corresponding to the three-dimensional views of figures 9A - 1 1 ;

^■ figure 12 illustrates a step of a variant of the method according to the invention;

■ figure 13 illustrates a step of a further variant of the method according to the invention.

Detailed description

With reference to the mentioned figures, reference numeral 1 overall indicates a rotor vaned ring of an expansion turbine of the radial centrifugal type, not illustrated as a whole in the appended drawings. For example, such turbine is used in the sector of plants for generation of electrical energy of the Rankine cycle type, either Organic Rankine Cycle (ORC) or water vapour, which exploit geothermal resources as sources. The turbine comprises a fixed casing in which a rotor is housed so as to be able to rotate. For this purpose, the rotor is rigidly connected to a shaft which extends along a central axis "X-X" (which coincides with a rotation axis of the shaft and of the rotor) and is supported in the fixed casing by appropriate bearings. The rotor comprises a rotor disc directly connected to the mentioned shaft and provided with a front face and an opposite rear face. The front face projectingly bears a plurality of rotor vaned rings 1 that are concentric and coaxial to the central axis "X-X". The fixed casing comprises a front wall that projectingly bears a plurality of stator vaned rings that are concentric and coaxial to the central axis "X-X". The stator vaned rings extend within the casing towards the rotor disc and are radially alternated with the rotor vaned rings 1 to define a radial path of expansion of the work fluid which enters through an axial inlet and expands moving radially away towards the periphery of the rotor disc up to entering into a transit volute and then exiting from the fixed casing through an appropriate outlet.

The rotor vaned rings 1 and the stator vaned rings are structurally similar to one another. In the following therefore a description will be made of the rotor vaned rings 1 .

With reference to figure 1 , the vaned ring 1 comprises a first support ring 2 or base ring intended to be anchored to the front face of the rotor disc. Figure 1 illustrates only one portion of said ring, which extends along the whole circumference indicated with the letter "C".

The base ring 2 has a first annular central body 3, which in the above-mentioned section is rectangular or square, from which an annular anchoring appendage 4 extends axially on one side and comprises an elastically yielding ring 5 which terminates with a connecting foot 6. The elastically yielding ring 5 is directly connected to the base ring 2 and the connecting foot 6 is positioned at an end of the elastically yielding ring 5 opposite the first annular central body 3. The elastically yielding ring 5 enables a radial deformation thereof when subjected to loads (centrifugal force, temperature) of the turbomachine when operating. The connecting foot 6 is configured for stably engaging in an appropriate seating, not illustrated, fashioned in the rotor.

The vaned ring 9 comprises a second support ring 7 or reinforcement ring. The second support ring 7 has a second annular body 8, which in the above-mentioned section is rectangular or square.

The vaned ring 1 comprises a plurality of vanes 9 with an airfoil that extend between the base ring and the reinforcement ring 2, 7. The base ring and the reinforcement ring 2, 7 are coaxial and axially spaced from one another. Each vane 9 has a leading edge 10 and a trailing edge 1 1 parallel to the central axis "X- X" of the vaned ring 1 . As the turbomachine is a centrifugal radial turbine in which the work fluid moves radially outwards, the leading edge 10 of each vane 9 radially faces inwards, i.e. towards said central axis "X-X", and the trailing edge 1 1 radially faces outwards. The vanes 9 are arranged equally spaced from the central axis "X-X" and circumferentially spaced by a constant pitch from one another.

Figure 2 illustrates a portion of a variant of the aforementioned rotor disc 12 which, in this case, comprises a support disc 13 and integrates the rotor rings 1 . In other words, the support disc 13, the base rings 2, the reinforcement rings 7 and the rotor vanes 9 are obtained as one part from a single full disc. The aforementioned rotor ring 1 and rotor disc 12 are, for example, made of stainless steel, for example: AISI 410, AISI 420, AISI 630 (17-4 PH), 13-4 PH.

Figures 3A - 1 1 B refer to the realisation of the vaned ring 1 but, as can be immediately noted, similar methods may be used for the realisation of the rotor disc 12. A steel solid defined by a full ring obtained by forging or melting or through 3D printing is first subjected to rough machining turning which has the function of removing much of the stock present on the forged ring itself (Step 1 - rough turning).

The rough machined full ring is preferably subjected to a stabilisation step (Step 2 - component stabilisation). The stabilisation of the material (also through possible distension in the oven) is performed to remove any stress and deformation connected with the rough turning. In this way, any deformations during subsequent processing can be prevented.

Subsequently, the full ring is preferably subjected (Step 3 - Semi-finish turning) to semi-finish turning in order to prepare the component for the subsequent vane processing step. Such turning is performed based on the grips to be used and to leave as little stock as possible in the area to be processed for obtaining the vanes, so as to reduce the quantity of material to be removed and therefore the times and costs.

There follows the actual production of the vanes (Step 4 - Vane production) realised according to the method of the present invention. Such processing of the vanes, which will be later explained in more detail with reference to the appended figures, preferably comprises hybrid processing that consists of a rough machining step (Step 4.1 ) and a finishing step (Step 4.2). The rough machining step is used to remove most of the material to be removed without precise tolerances (typical tolerance of +/- 2 mm), while the finishing step is preferably used to achieve required tolerances, geometries and roughness (typical shape tolerance +/- 0.05 mm with roughness of Ra= 0.8 pm).

After this, the vaned ring is preferably subjected to a post-vane production stabilisation step (Step 5 - Component stabilisation), which is performed to remove internal stress from the material, caused by the processing of the vanes and the consequent breaking of the fibres of the starting material.

A finish turning step (Step 6 - Finish turning) allows the dimensions of the ring to be brought to the finished values required by the drawing, with the related characteristics of dimensional tolerances, concentricity, parallelisms, shape tolerances and roughness. Finally, preferably, a polishing step (Step 7 - Vane polishing) reduces the roughness of the vanes to lower values than those that can be obtained through machine tools.

The vane production (Step 4 - Vane production) can be performed in accordance with a first embodiment of the method of the invention illustrated in Figures 3A - 8. First a vane rough machining step is performed (Step 4.1 ). A turned full ring 14 coming from Step 3 (Semi-finish turning) is positioned in a water jet device configured to perform cuts with a very high pressure abrasive water jet (AWJ). For example, the water jet is emitted at a pressure of 5000 bar and the abrasive comprises particle sizes of 400 pm and a mesh of 60 pm.

In the appended figures 3A - 8, for simplicity purposes, only a portion (arch) of the full ring and of the vaned ring 1 is shown. Such arch is repeated the same way throughout the circumferential extension of the ring. The turned full ring 14 constitutes a solid of material to be processed.

Figures 3A and 3B represent the mentioned portion of the full ring 14. Figure 3A shows the parts that will define the elastically yielding ring 5 and the connecting foot 6 of the vaned ring 1.

Four first interrupted/blind cuts 15', 15", 15"', 15"" are performed on a first side 16 of the portion of the full ring 14 through the abrasive water jet 17 emitted by a head 18 of the water jet device. A first cut 15' of the four is substantially orthogonal to the first side 16, a second cut 15" of the four is inclined with respect to the previous one and intersects it at a terminal line 19 lying within the thickness of the full ring 14 (Figure 4A). A third 15"' and a fourth cut 15"" connect the first one to the second one 15', 15" along orthogonal planes thereto. For example, for performing the first cut 15', the jet 17 penetrates into the material along an orthogonal direction to the first side 16 and then the head 18 is moved vertically to generate said first cut 15'. The head 18 is then repositioned (in broken lines in figure 3A) and then it performs the subsequent cuts 15", 15"', 15"" or proceeds with the cut by cutting 15"', then cuts 15" and then 15"" (in this case the jet stays always on and performs the whole cycle in series). In a not illustrated variant, numerous heads 18 could be used to simultaneously perform the first cuts 15', 15", 15"', 15"".

The first cuts 15', 15", 15"', 15"" delimit a first wedge-shaped entire block 20 (visible in Figure 4B) that is removed by gravity and/or manually and/or using extractor devices, e.g. equipped with magnets, not illustrated. The removal of the first block 20 generates in the first side 16 of the full ring 14 a respective first blind cavity 21 counter-shaped to the first block 20 removed. As can be seen in Figures 4A and 4B, the terminal line 19 defines the blind bottom of the cavity 21 .

Second interrupted/blind cuts 22', 22", 22'", 22"" are performed on a second side 23 of the portion of the full ring 14 through the abrasive water jet 17 emitted by the head 18 (Figures 5A, 5B). The second interrupted cuts 22', 22", 22'", 22"" terminate at the first cavity 21 and delimit a second substantially parallelepiped- shaped entire block 24. A face 25 of such second block 24, when the second block 24 is still in position within the solid, faces the inside of the first blind cavity 21 . The removal of the second block 24 generates in the second side 23 of the full ring 14 a respective second cavity 26 counter-shaped to the second block 24 removed. Such second cavity 26 is further in communication with the first cavity 21 so as to define a passage 27 through the wall of the ring.

In the illustrated example, further cuts are also performed, this time through cuts, one of which is indicated in figures 6A and 6B with the line "T", which smooth off an edge inside the passage by removing a further block 28 of a triangular section. As can be noted, after the removal of such further block 28, the passage afforded through the ring already has a shape close to the passage 27 between two vanes 9. The passage 27 separates portions of material intended to form the vanes 9 of the vaned ring 1 .

Subsequently, the finishing (step 4.2) of the passage previously rough machined, is performed through CNC milling or EDM or ECM until the final shape of the passage 27 is obtained, corresponding to the lower surface and the upper surface of the vanes 9 that delimit it (Figure 7).

The volume of the passage 27 generated after the rough machining (cuts and removal of blocks, Step 4.1 ) is comprised, for example, between about 85% and about 95% of the volume of the finished passage between the vanes, i.e. of the volume obtained after finishing (Step 4.2). Furthermore, after rough machining (cuts and removal of blocks, Step 4.1 ).

Repeating the work steps described above along the whole circumferential extension of the vaned ring 1 , the plurality of vanes 9 separated by the passages 27 is obtained, i.e. the final vanes (Figure 8). A variant of the embodiment described above is illustrated in Figures 9A - 1 1 B. As can be noted, the operation illustrated in figures 9A and 9B corresponds to that of figures 5A and 5B but in this case the second block 24 removed is triangular and its removal does not place in communication the second cavity 26 (which is therefore blind) with the first cavity 21 .

Then further cuts (third set of interrupted cuts, lines "T1 ") are performed to generate and remove a further (third) triangular block 28 and a fourth set of cuts (lines "T2") to remove a fourth block 29. The removal of the fourth block 29 places in communication the first cavity 21 with the second cavity 26 generating the passage 27.

The cuts described above can be performed by moving the head of the device and/or the ring.

The water jet 17 of the abrasive water jet is managed so as to control the depth of the interrupted cuts inside the material of the ring.

In one embodiment, the water jet device comprises a sensor connected to a control unit that governs the operating parameters of the water jet device itself.

The operating parameters of the water jet are adjusted according to the detected depth so as to perform the cuts until the desired depth. By way of example, such operating parameters are: pressure and speed of the jet, quantity of abrasive, type of abrasive, translation speed of the device head, rotation of the head, geometry of the nozzle. By way of example, the sensor may be of the optical, capacitive or X- ray type. This type of control is in feedback.

In a different embodiment, the depth of the interrupted cuts is controlled through a predictive control (in feedforward/regression analysis). For this purpose, a plurality of cutting tests are performed with the water jet device on a determined material and with different contingent conditions. Such tests allow a mathematical model to be created that connects the operating parameters of the water jet (which may be those mentioned above) with the cutting depths. When it is necessary to perform actual vane production (Step 4 - Vane production), the operating parameters of the water jet device are set according to the depth to be obtained and through the previously built mathematical model.

The following table reports the characteristic values of the percentage ratio "Vb/Vtot" between the volume removed after the removal of the blocks "Vb" (Vb = Vbl + Vt) and the total volume "Vtot" (Vtot = Vbl + Vt + Vfin) of material removed from the solid after the finish obtained with the process according to the invention (for different types of rotor and stator elements) compared with the same ratios obtained through the removal of blocks with through cuts.

The same table also reports the values of the ratio "Vt/Vbl" between the volume of material removed by the cuts "Vt" and the volume "Vbl" of the blocks cut out in the method according to the invention.

The closed vaned rings are of the type illustrated in Figure 1 . The open vaned rings are like the one in Figure 1 but without the reinforcement ring. The vaned discs are of the type illustrated in Figure 2.

It is to be remembered that "complex geometry" typically means a geometry with (very curved) action vanes or a high number of vanes (therefore with not much space between one and another) or with very twisted vanes between inlet and outlet (used for compressors, for example). "Simple geometry" instead typically means with a higher reaction geometry, either with fewer vanes or with untwisted vanes.

Table

Vb/Vtot Vb/Vtot Vt/Vtot

Through cuts Interrupted Interrupted Prior art cuts Invention cuts Invention

Closed vaned rings Complex geometry n.a. 85% 2%

Simple geometry 85% 95% 2%

Open vaned rings Complex geometry n.a. 85% 2%

Simple geometry 85% 95% 2%

Vaned discs Complex geometry n.a. 75% 2%

Simple geometry n.a. 85% 2%

Radial vaned discs Complex geometry n.a. 85% 2%

Simple geometry 85% 95% 2%

Closed impellers Complex geometry n.a. 85% 5%

Simple geometry 75% 95% 5%

Open impellers Complex geometry n.a. 85% 5%

Simple geometry 10% 95% 5%

Diaphragms Complex geometry n.a. 85% 5%

Simple geometry 85% 95% 5%

Diffusers Complex geometry n.a. 85% 5%

Simple geometry 85% 95% 5% As can be noted, some geometries, the complex ones, cannot be obtained (indicated in the Table with "n.a.") with through cuts whereas they can be obtained with the interrupted cuts according to the invention. Other geometries can also be obtained with the through cuts but the percentage of material removed after the removal of the blocks is decisively lower than that obtainable with the interrupted cuts according to the invention. This means that the method according to the invention allows both simple and complex geometries to be performed in an easier and quicker manner and therefore with time and cost savings. Furthermore, as can be noted from the third column, it is sufficient to remove a little material through the cuts to remove blocks of significant volume.

Figure 12 illustrates another variant of the method of the invention. In this case the method is applied for the realisation of a rotor vaned disc 30 with vanes 9 that extend radially from a central body 31 of said vaned disc 30. Figure 12 illustrates a full starting disc and two of the vanes 9 are further represented in broken lines during the realisation step.

Figure 12 represents a moment of the rough machining step (Step 4.1 ) performed through interrupted cuts 15', 15" that generate a block 32 of prismatic material which, once removed, leaves in the full starting disc a blind cavity 33 counter- shaped thereto. The interrupted cuts terminate and join up at a terminal bottom line 34 located at the central body 31 but are distanced from the bases 9a of the vanes 9. As can be noted, the blind cavity 33 in fact only partly corresponds to the shape of the vanes 9 (indicated in broken lines).

The final rough geometry of the vanes 9 may be obtained by performing further cuts and removing further blocks and/or in the subsequent finishing step (Step 4.2) by removing the material located between the blind cavity 33 and the broken lines indicated in figure 12.

Figure 13 represents a further variant similar to the method of figure 3A-6B. Unlike what is illustrated in such figures, the vaned ring realised according to the method of figure 13 is open, i.e. the vanes, once realised, have a free end. The first four interrupted/blind cuts 15', 15", 15"', 15"" are parallel to one another, delimiting four sides of a parallelepiped-shaped block. The second interrupted/blind cuts 22', 22", 22"', 22"" are also parallel to one another, delimiting four sides of a parallelepiped-shaped block. These two blocks are separated by realising a further third interrupted cut 35 from above through the abrasive water jet 17 emitted by the head 18. The abrasive water jet 17 penetrates through an upper surface 36 of the full ring 14. The third cut 35 is incident with respect to the first 15', 15", 15"', 15"" and the second cuts 22', 22", 22"', 22"".

In other embodiments, not illustrated in detail, the interrupted cuts according to the method of the invention may be realised with methodologies different from AWJ. For example, in one embodiment the cuts are performed through electrical discharge machining through EDM machines using a feedback or feedforward control of the operating parameters such as: work/peak currents, axial speed, axial resolution.

In other embodiments, the cuts may be performed through the mechanical removal of chips through milling or through a laser device or through a plasma torch. It is also possible to use hybrid processing obtained through the combination of two or more of the techniques mentioned above.

List of elements

1 rotor vaned ring

2 first support ring/base ring

3 first annular central body

4 annular anchoring appendage

5 elastically yielding ring

6 connecting foot

7 second support ring/reinforcement ring

8 second annular body

9 vanes

9a bases of the vanes

10 leading edge

1 1 trailing edge

12 rotor disc

13 disc

14 turned full ring

15', 15", 15"', 15"" first cuts

16 first side

17 abrasive water jet head

terminal line

first enitre block

first blind cavity

", 22'", 22"" second cuts second side

second entire block face of the second block second cavity

passage

further third block fourth block

rotor vaned disc central body

prismatic block of material blind cavity

terminal line

third cut

upper surface