EP2349625A1

EP2349625A1 - Manufacturing method for closed impellers

Info

Publication number: EP2349625A1
Application number: EP09756271A
Authority: EP
Inventors: Werner Jahnen
Original assignee: Sulzer Markets and Technology AG
Current assignee: Sulzer Markets and Technology AG
Priority date: 2008-10-20
Filing date: 2009-10-20
Publication date: 2011-08-03
Also published as: EP2177298A1; US20110255976A1; WO2010046353A1

Abstract

In a manufacturing method for closed impellers comprising vanes (2, 2a) with vane channels (3) disposed therebetween, said vane channels having a predefined shape, machined openings for the vane channels are made in a blank using a programmably controlled machining device. In the manufacturing method, electrodes (11) of a device for electric discharge machining or for electrochemical stripping are introduced into the openings in another work step and a portion of the predetermined shape of the vane channels (3) is produced through electric discharge machining or through electrochemical stripping.

Description

P.7795 / St / Li

Sulzer Markets and Technology AG, CH-8401 Winterthur (Switzerland)

Production method for closed wheels

The invention relates to a manufacturing method for closed wheels according to the preamble of claim 1 and a closed impeller made with such a method.

Closed impellers are used in turbomachinery such as pumps or turbines to transfer energy to a fluid such as gas, vapor, or liquid, or vice versa, energy from a fluid to the impeller. A closed impeller for this purpose contains one or more blades, between a front and a rear cover plate, as a top plate and bottom plate or cover and

Floor are arranged, are arranged, wherein the rear cover plate and / or the blades are normally connected to a hub which may be designed to receive a shaft. Blade channels are formed between the blades, which are closed as a result of the arrangement of the blades between the front and rear cover plate.

The technical production of closed wheels has a long tradition. For this purpose, molds with cores are used, which define the shape of the blade channels. Closed wheels, which are produced by casting, have the disadvantage that faulty points in the interior of the impeller can hardly be repaired, and that in particular in comparatively thin blades or thin-walled cover the quality control is critical. In addition, also the limited accuracy of the cast wheels and the roughness of the cast surfaces, a problem depending on the application.

It has therefore begun to produce closed wheels for demanding applications by means of machining. For this purpose, the shape of the blade channels is machined out of a blank, which is usually made of solid material. In addition, the outer shape of the impeller can be machined. The machining has proven to be particularly useful if the material of the impeller is easy to machine and the geometry is comparatively simple, so that all areas to be machined in the impeller can be easily achieved with a cutting tool.

Depending on the application of the wheels they are highly loaded during operation, in which they are exposed to considerable centrifugal forces at peripheral speeds of up to 400 m / s. Such impellers are therefore made of solid material using high strength steels, stainless steels, superalloys, and other suitable materials. A disadvantage is that some of these materials make special demands on the machining due to their toughness and / or hardness.

In addition, the geometry of the impeller to be produced can give rise to difficulties in machining. A close staggering of the blades at the inlet of the impeller and / or a strong curvature of the blades may, for example, lead to the geometry that the entire blade can not be machined, or only part of the blade channel can be machined, and that The blades remain areas that are usually wedge-shaped and protrude into the blade channel. Similarly, a comparatively strong curvature of the front cover plate can lead to the geometry of the entire cover surface of the blade channel can not be machined, and remain on the top surface areas that are usually wedge-shaped and project into the blade channel. In machining, however, difficulties can also arise if the area to be machined can be achieved by geometry with a cutting tool, but the machining conditions are unfavorable, for example because the area to be machined is located far inside the blade channel and long tools are required, which can absorb or exert only low lateral forces. The feed rate must be reduced in this case, whereby the processing times and costs are increased accordingly. The unfavorable machining conditions also require that, for reasons of geometry, it is necessary to deviate from the optimum angle of attack of the cutting tool, which can lead to unacceptable machining results. These difficulties are exacerbated when the material to be machined makes special demands on the machining. For the reasons mentioned above, the machining can be uneconomical, even if the geometry of a machining would be possible in principle.

One known solution to the machining problems encountered with machined closed impellers is to make the impeller from multiple prefabricated parts which are joined together by welding. For example, first the hub, the rear cover plate and the blades can be milled from the solid one piece and then the separately prepared front cover plate are welded to the blades. It is also possible, for example, to mill the hub, the rear cover disk and the outer part of the front cover disk as well as the blades in one piece from the solid and then to weld the separately produced inner part of the front cover disk to the blades. Disadvantages of such welded wheels are the weld seams and the distortion caused by the welding, as well as the considerable expense for the fixation and possibly for the protective gas, which is required for materials that are weldable only in a protective atmosphere. The cost of quality assurance welded wheels is usually also relatively high and certification of the process difficult. In addition, the achievable strength is limited and can only be increased with additional effort.

It is also known to produce wheels by means of spark erosion. For this purpose, from a blank, which is usually made of solid material, the blade channels completely eroded by means of formula electrodes. However, this method is comparatively slow and expensive. Thus, the production of an impeller by spark erosion take several weeks to complete. In addition, the available EDM machines are equipped with only three-axis control by default, which complicates the control of EDM processing. If higher demands are placed on the accuracy, then the effort increases since the formula electrodes in this case have to be replaced comparatively frequently. Because of the great expense, the production of wheels by means of spark erosion is used only in isolated cases and in materials in which other manufacturing processes fail.

The object of the present invention is to provide a manufacturing method, by means of which closed wheels can be made in one piece, and which allows the production of comparatively complicated geometries, their production not possible with machining methods of the prior art or comparatively less economical is. Another object of the present invention is to provide a closed impeller made by such a manufacturing method.

This object is achieved according to the invention by the defined in claim 1 manufacturing method for closed wheels and by the defined in claim 15 closed impeller.

In the inventive production method for closed impellers with blades, between which blade channels are formed, which have a predetermined shape, openings for the blade channels are created in a blank by means of a program-controlled cutting device in a blank. By doing Manufacturing processes are additionally introduced in a further step electrodes of a device for EDM or electrochemical ablation in the openings and made part of the predetermined shape of the blade channels by spark erosion or by electrochemical machining. For example, the machined openings for the blade channels may be a raw form of the blade channels, and / or the machined openings for the blade channels may be continuous.

In an advantageous embodiment, in addition to the openings, a part of the predetermined shape of the blade channels is produced by machining. Advantageously, in addition to the openings, the largest part, in particular at least 75% or at least 90%, of the predetermined shape of the blade channels is produced by machining. The machining production of part or most of the predetermined shape of the blade channels can, for example, take place before the spark erosion, so that the part of the predetermined shape to be eroded is kept small or reduced to a minimum.

In a further advantageous embodiment, the impeller comprises a front cover plate and a rear cover plate, wherein the blade channels and / or the blades and / or one or both cover plates may have a curvature.

In an advantageous embodiment of the production method, a machining method is used, in which in each case curved guide surfaces for the machining by means of a cutting tool are provided in the openings to be created for the blade channels and / or in the blade channels to be created, the thus to the shape and spatial position the blade channels are adapted so that the cutting tool is not brought into contact with a blade channels limiting edge surface in the Zerspan process the cutting tool each guided along a guide surface and machined by the respective guide surface machining area is machined to an opening and / or to create parts of a blade channel, wherein the Cutting tool has a guide axis and is guided in relation to the guide axis at a constant guide angle along the respective guide surface.

Advantageously, within a blade channel, the guide surfaces do not become an edge surface and / or an end surface

Parallel surface and / or offset surface arranged. Further, if necessary, a tool coordinate and / or a tool vector of the cutting tool can be adapted to the guide surface. Advantageously, at least two guide surfaces of an opening and / or a blade channel are not parallel.

In an advantageous embodiment, the guide angle is not changed during the production of an opening and / or a part of a blade channel. In a further advantageous embodiment variant, the guide angle is varied during the production of an opening and / or a part of a blade channel during a change from one guide surface to the next guide surface according to a predetermined scheme.

Depending on the application, the change of the cutting tool from a guide surface to a next guide surface is carried out discontinuously and / or to change from a guide surface to a next guide surface a bore in the region of the two

Guide surfaces or provided in the region of all guide surfaces of an opening and / or a portion of a blade channel. However, the change of the cutting tool from a guide surface to a next guide surface can also be carried out continuously, for example helically in the form of a helix.

Regardless of the embodiments described above, the guide angle is usually set to a value between 70 ° and 120 ° or between 85 ° and 95 ° or between 88 ° and 92 ° and advantageously to a value of substantially 90 °. Furthermore, the invention comprises a closed impeller manufactured by means of a manufacturing method according to one of the above-described embodiments and variants.

The inventive manufacturing method has the advantage that thus closed wheels can be made in one piece, the blade channels can not be generated purely machined due to the geometry and / or their production would be uneconomical in purely machining the blade channels. Thanks to the fact that a part and usually the largest part of the blade channel shape can be machined and only a smaller part is produced by means of spark erosion, a cost optimization is possible.

The above description of embodiments and variants is merely an example. Further advantageous embodiments will become apparent from the dependent claims and the drawings. In addition, in the context of the present invention, individual features from the described or shown embodiments and variants can be combined with one another in order to form new embodiments.

In the following the invention will be explained in more detail with reference to the embodiments and with reference to the drawing. Show it:

1 shows a closed impeller, in the production of which, during purely machining of the blade channels difficulties may occur

2 shows the impeller according to FIG. 1 with a cutting tool inserted into a blade channel, the front cover disk being omitted in order to make the blades visible, FIG.

3 shows an embodiment of a closed impeller according to the present invention,

3A is a detailed view of a variant of the impeller according to FIG. 3 with a blade on which, on one side after the machining a wedge-shaped area has stopped

3B shows a detailed view of a variant embodiment of the impeller according to FIGS. 3 and 3A with a blade channel, on the front cover surface of which after the cutting

Processing in addition a wedge-shaped area has stopped

Fig. 4A-4C, the wedge-shaped portions of the embodiment according to

3B during processing by means of a spark erosion method according to an exemplary embodiment of the production method according to the invention,

Fig. 5A shows the embodiment according to Fig. 3B seen from the front of the impeller, wherein the front cover plate is omitted in the drawing to make the blades visible,

Fig. 5B, the embodiment of FIG. 3B seen obliquely from the outside, wherein the front cover plate is omitted in the drawing to make the blades visible, and

6 shows a section of an impeller during machining by means of a machining process according to a further exemplary embodiment of the production method according to the invention.

Fig. 1 shows a closed impeller, in the production of which in one piece with purely machining machining of the blade channels difficulties may occur. The impeller 1 may include one or more blades 2.1, 2.2 disposed between a front shroud 5 and a rear shroud 6, the rear shroud and / or vanes normally being connected to a hub 4 adapted to receive a shaft can be. Between the blades 2.1, 2.2 are a or a plurality of blade channels 3.1, 3.2 are formed, which have a predetermined shape, and which are closed due to the arrangement of the blades between the front and rear cover plate.

Fig. 2 shows the above-described impeller according to Fig. 1 with a cutting tool 10 inserted into a blade channel 3.1 with the front cover disc omitted in the drawing to make the blades visible in full length. The impellers shown in Figures 1 and 2 are the same regardless of the different representation. Due to the length of the blades, a comparatively long cutting tool is required for the machining of the blade channels 3.2, 3.2 of the impeller shown, for example, as shown in Fig. 2, a cutting tool with a long shaft. The curvature and staggering of the blades 2.1, 2.2 of the impeller shown is such that a purely chip-generating production of the blade channels still seems almost possible. Due to the length and the tapered shank of the cutting tool but is expected to have a low feed rate and thus with increased processing costs. Problems in the machining process also arise when a comparatively small radius of curvature is required at the transition between blades and shrouds.

Fig. 3 shows an embodiment of a closed impeller, which was manufactured by a manufacturing method according to the present invention. The impeller 1 may include one or more blades 2, 2a arranged between a front cover disk 5 and a rear cover disk 6. Between the blades 2, 2a are one or more

Blade channels 3 are formed, which have a predetermined shape, and which are closed due to the arrangement of the blades between the front and rear cover plate. The individual blades may have different lengths, for example, by, as shown in Fig. 3, blades 2 a shortened in length between blades 2, also called "splinter vanes", are arranged.

In a further advantageous embodiment, the impeller comprises a front cover plate and a rear cover plate, wherein the Blade channels 3 and / or the blades 2, 2a and / or one or both cover plates 5, 6 may have a curvature.

In the production method according to the invention, openings for the blade channels 3 are produced in a blank by means of a program-controlled cutting device by milling the openings, for example, in a known manner with a multi-axis CNC milling machine. For example, the machined openings for the blade channels may be a raw form of the blade channels, and / or the machined openings for the blade channels may be continuous. In an advantageous embodiment variant, in addition to the openings, part or most of the predetermined shape of the blade channels, for example at least 75% or at least 90%, is produced by machining.

FIG. 3A shows a detailed view of a variant of the embodiment of the impeller according to FIG. 3 with a blade 2 on which a wedge-shaped region 8, which projects into the blade channel 3, has remained on one side after the machining. Such wedge-shaped areas can arise, for example, if due to the curvature and / or staggering of the blades 2, 2 a, a purely chip-removing production of the

Blade channels 3 is not possible or not economical. Fig. 3B shows a detailed view of a variant of the embodiment of the impeller according to FIG. 3 with a blade channel 3, on whose front cover surface after the machining, a wedge-shaped region 9 has additionally stopped, which protrudes into the blade channel 3. Such wedge-shaped regions 9 may arise, for example, if due to the curvature of the front cover plate a purely machined production of the blade channels 3 is not possible or not economical.

In the manufacturing method according to the present invention, electrodes of a device for spark eroding or electrochemical ablation are additionally introduced into the openings or blade channels in a further working step and a part of the predetermined shape of the blade channels by means of spark erosion or by means of electrochemical Abtragens made. FIGS. 4A-4C show the wedge-shaped regions 8, 9 from the exemplary embodiment according to FIG. 3B during processing by means of a spark erosion electrode 11 according to an exemplary embodiment of the production method according to the invention. In FIG. 4A, the spark erosion electrode 11 is inserted into the blade channel 3. Fig. 4B shows the spark erosion electrode 11 in processing the wedge-shaped portion 8 formed on the blade 2, and in Fig. 4C, the spark erosion electrode 11 abuts against the blade 2 and front deck surface of the blade channel 3 with portions of the wedge-shaped ones Areas 8, 9 are already wegerodiert.

Fig. 5A shows the embodiment according to Fig. 3B seen from the front of the impeller, wherein the front cover plate has been omitted in the drawing to make the blades visible. The impeller shown includes a plurality of blades 2.1, 2.2, 2.1 a, 2.2 a, which are arranged between a front cover plate and a rear cover plate. Blade channels 3 are formed between the blades, which have a predetermined shape and which are closed as a result of the arrangement of the blades between the front and rear cover disk. The individual blades may be of different lengths, for example by having blades shortened 2.1a, 2.2a, also called "splinter vanes", between the blades of full length, as shown in Figure 5A, on the blade 2.1 and on the front The top surface of the blade channel 3 after cutting has stopped in each case a wedge-shaped region 8, 9, both of which project into the blade channel 3. Fig. 5A additionally shows a spark erosion electrode 11 which is inserted into the blade channel 3 for processing the wedge-shaped regions 8, 9 is.

Fig. 5B shows the same embodiment as Fig. 5A seen obliquely from the outside, wherein the front cover plate has been omitted in the drawing to make the blades visible. With regard to details of Fig. 5B, reference is made to the above description to Fig. 5A.

The spark erosion electrode used in the production method according to the invention is advantageously designed as a shaped electrode, which is adapted to the shape of the blade channels. Normally, several formula electrodes are needed, for example three or four, since usually different areas of the blade channels have to be processed. In addition, the formula electrodes wear out and must be replaced depending on the desired accuracy of processing. Advantageously, the shape of the blade channels is produced by machining, as far as this is possible and / or economical, and subsequently in the unfinished areas, the shape of the blade channels is produced by means of spark erosion or by means of electrochemical removal. For spark erosion or electrochemical ablation, a program-controlled spark erosion machine or machine for electrochemical ablation with four or more controlled axes is advantageously used.

A blade channel of an inventive impeller has a length of typically 30 mm to 300 mm and a width and / or height of typically 10 mm to 200 mm. In individual cases, however, the dimensions mentioned may differ significantly from the stated values.

As a material for the closed impeller, a metal or a metal alloy is advantageously used in the inventive manufacturing method, for example aluminum, titanium, steel, nickel, an aluminum or magnesium alloy, a nickel or cobalt base alloy, forging or casting material, a non-ferrous metal, but also another material that can be machined and additionally optionally eroded or electrochemically removed.

In an advantageous embodiment of the inventive

Manufacturing method, a Zerspanverfahren is used, which will be explained below with reference to FIG. 6, and in which in the openings to be created for the blade channels 13 and / or in the blade channels 3 to be created respectively curved guide surfaces 14 for machining by means of a cutting tool 10 are provided, which are adapted to the shape and spatial position of the blade channels, that the cutting tool 10 during machining not with the blade channels limiting edge surface 2 in In the machining process, the cutting tool 10 is guided along a guide surface 14 and a machining area 12 predetermined by the respective guide surface is machined to produce an opening 13 and / or parts of a blade channel 3, the cutting tool 10 being a guide axis 10a and is guided in relation to the guide axis at a constant guide angle α along the respective guide surface 14. The said guide angle is often referred to as the angle of attack.

Fig. 6 shows a section of a closed impeller 1 in section. The impeller includes an opening to be created 13, which is advantageously designed as a blade channel 3, and curved guide surfaces 14. A cutting tool 10 with a guide axis 10 a is not shown in FIG. 6 manipulator of a cutting device, such as a multi-axis CNC milling machine such as a five-axis CNC milling machine, chipping along a guide surface 14 out. 6, a part of the opening 13 to be created or of the blade channel 3 to be created is already finished in an initial region 15, while in an adjoining region 16 the opening or the blade channel has not yet been completed. Expediently, all guide surfaces 14 are calculated before the beginning of the machining operation for producing the opening 13 or the blade channel 3. In Fig. 6, the guide surfaces in the processing area 12 are shown schematically as curved dashed lines. According to the invention, the cutting tool 10 is guided with respect to its guide axis 10a at a constant angle α to the respective guide surface. The guide surfaces 14 are advantageously determined so that the tool can mill out the entire opening 13 or the entire blade channel 3, without the guide tool comes into contact with one of the edge surfaces 2, which limit the opening or the blade channel.

The guide surfaces 14 are advantageously calculated so that the cutting tool 10 at least with respect to certain guide surfaces and possibly with respect to all calculated guide surfaces in Machining at the same angle α, namely substantially below the specified by the manufacturer for the cutting tool optimum guide angle is performed. Certain deviations of, for example, +/- 5 ° or +/- 1 ° or less from the optimum guide angle are generally tolerable if the quality of the machined impeller does not suffer and the cutting tool is essentially still working optimally.

Advantageously, in the above-described machining process within an opening 13 to be produced or within a blade channel 3, the guide surfaces 14 are arranged to no edge surface 2 and / or no end surface as a parallel surface and / or offset surface. For the purposes of this application, the term "offset surface" refers to surfaces which, although not strictly parallel in the strict sense, nevertheless have the same distance from each other everywhere. An example of this is e.g. two concentric spherical shells with different diameters, which are at a fixed distance over the entire surface, but still have different radii of curvature.

Further, if necessary, a tool coordinate and / or a tool vector of the cutting tool 10 can be adapted to the guide surface 14. Advantageously, in each case at least two guide surfaces of an opening and / or a blade channel are not parallel and form no offset surfaces to each other.

In an advantageous embodiment, the guide angle α is not changed during the production of an opening 13 and / or a part of a blade channel 3. In a further advantageous embodiment variant, the guide angle α is varied during the production of an opening 13 and / or a part of a blade channel 3 in a change from one guide surface to the next guide surface according to a predetermined scheme, the guide angle advantageously for all guide surfaces only slightly, for example Deviates +/- 5 ° or +/- 1 ° from the optimum guide angle.

Depending on the requirements of the material to be machined or the geometry to be produced or depending on other parameters The change of the cutting tool from a guide surface to a next guide surface can be carried out discontinuously and / or it can for changing from a guide surface to a next guide surface a bore in the region of the two guide surfaces or in the region of all guide surfaces of an opening and / or a portion of a blade channel be provided. However, the change of the cutting tool from a guide surface to a next guide surface can also be carried out continuously, for example spirally in the form of a ramp or helix. That is, for example, that the cutting tool more or less continuously in a direction of advancement of the

Zerspanwerkzeuges, for example, is driven substantially perpendicular to a guide surface 14, so that the transition from a guide surface is not discontinuous but gradually, so that the cutting tool in the advancing direction, for. performs a spiral or helical movement.

Regardless of the embodiments and variants described above, the guide angle α is normally set optimally to the cutting tool, for example to a value between 70 ° and 120 ° or between 85 ° and 95 ° or between 88 ° and 92 ° and advantageously to a value of essentially 90 °.

The machining method described above allows to work completely on a workpiece having a more or less constant optimum guide angle, even if it has a very complicated geometric structure and the material is difficult to machine, because e.g. has a high hardness and / or high strength and / or other properties that make the machining difficult.

With the Zerspanverfahren described above, it is also possible in particular to provide undercuts in the generation of the blade channels by the guide surfaces 14, on or along which the cutting tool 10 is guided at a constant guide angle α, suitably chosen, that is calculated, in particular Also, a conical cutting tool can be used, with which even undercuts can be realized, while maintaining a constant guide angle to the guide surface.

Furthermore, the invention comprises a closed impeller manufactured by means of a manufacturing method according to one of the above-described embodiments and variants. Such closed wheels have the advantage that they are made in one piece, and that comparatively short lead times for prototypes and a comparatively high accuracy of the geometric shape can be achieved compared to cast wheels.

Claims

Claims P.7795

1. Manufacturing process for closed impellers with blades (2, 2.1, 2.2, 2a, 2.1a, 2.2a), between which blade channels (3, 3.1, 3.2) are formed, which have a predetermined shape, using a program-controlled cutting device in one Openings for the blade channels are created by cutting the blank, characterized in that in a further step, electrodes (11) of a device for spark erosion or electrochemical removal are introduced into the openings and a part of the predetermined shape of the blade channels (3, 3.1, 3.2) by means of

Spark eroding or using electrochemical removal.

2. Manufacturing method according to claim 1, wherein the openings for the blade channels created by machining are one

Raw shape of the blade channels, and / or the openings for the blade channels created by machining are continuous.

3. Manufacturing method according to claim 1 or 2, wherein in addition to the openings a part of the predetermined shape of the blade channels (3, 3.1,

3.2) is produced by machining.

4. Manufacturing method according to claim 3, wherein in addition to the openings, the majority, in particular at least 75% or at least 90%, of the predetermined shape of the blade channels (3, 3.1,

3.2) is produced by machining.

5. Manufacturing method according to one of claims 1 to 4, wherein the

Impeller comprises a front cover disk (5) and a rear cover disk (6), and in particular the blade channels (3, 3.1, 3.2) and/or the blades (2, 2.1, 2.2, 2a, 2.1a, 2.2a) and/or one or both cover disks (5, 6) have a curvature.

6. Manufacturing method according to one of claims 1 to 5, wherein a machining process is used in which in the openings to be created for the blade channels and / or in the

Blade channels (3, 3.1, 3.2) are each provided with curved guide surfaces (14) for machining by means of a cutting tool (10), which are adapted to the shape and spatial position of the blade channels in such a way that the cutting tool does not come into contact with one of the blade channels during machining delimiting edge surface is brought into contact, and in the cutting process the cutting tool (10) is guided along a guide surface (14) and a machining area (12) specified by the respective guide surface is machined in order to create an opening and / or parts of a blade channel , characterized in that the cutting tool (10) has a guide axis (10a) and is guided along the respective guide surface at a constant guide angle (α) with respect to the guide axis.

7. Manufacturing method according to claim 6, wherein within a blade channel (3, 3.1, 3.2) the guide surfaces (14) are arranged as a parallel surface and/or offset surface to no edge surface and/or no end surface.

8. Manufacturing method according to claim 6 or 7, wherein a tool coordinate and / or a tool vector of the cutting tool (10) are adapted to the guide surface (14).

9. Manufacturing method according to one of claims 6 to 8, wherein at least two guide surfaces (14) of an opening and / or one

Blade channel are not parallel and no offset surfaces to each other form.

10. Manufacturing method according to one of claims 6 to 9, wherein the guide angle (α) is not changed during the manufacture of an opening and / or a part of a blade channel.

11. Manufacturing method according to one of claims 6 to 9, wherein the guide angle (α) during the production of an opening and / or part of a blade channel when changing from one guide surface to the next guide surface according to a predetermined

Scheme is varied.

12. Manufacturing method according to one of claims 6 to 11, wherein the change of the cutting tool (10) from one guide surface to a next guide surface is carried out discontinuously and / or in which a hole is required in the area of the two guide surfaces to change from one guide surface to a next guide surface, is provided in particular in the area of all guide surfaces of an opening and / or part of a blade channel.

13. Manufacturing method according to one of claims 6 to 12, wherein the change of the cutting tool (10) from one guide surface to a next guide surface is carried out continuously, in particular spirally in the form of a helical line.

14. Manufacturing method according to one of claims 6 to 13, wherein the guide angle (α) is set to a value between 70° and 120°, in particular to a value between 85° and 95° or between 88° and 92° and preferably to a value of essentially 90° is set.

15. Closed impeller manufactured using a manufacturing method according to one of claims 1 to 14.