Method for producing a hollow rotor shaft

Abstract

The present invention relates to a method for producing a hollow rotor shaft (R).

Description

The invention relates to a method for producing a hollow rotor shaft.According to the current state of the art, hollow rotor shafts are designed as two- or also three-part variants, wherein the end sections are forged or worked out of the full. The cylindrical part of the hollow rotor shaft consists of a precision tube. The individual elements are orbital welded and then machined, wherein in part an annealing of surface regions can also be added.An alternative to this manufacturing process is press rolling, wherein a tube or also a forged preform can be formed into a one-piece hollow rotor shaft. The advantage of this method is an extended geometric design possibility of the hollow rotor shaft, cf. DE 10 2020 215 933 A1, DE 100 05 578 A1, DE 197 25 453 A1, DE 10 2014 105 400 A1 and also DE 10 2023 121 770 B3. For example, cooling ribbings up to variable wall thickness profiles can be integrated directly into the production process. This saves welding seams. Furthermore, lightweight construction and functional integrations are possible.The problem with, for example, a press-rolled variant made of a tube is a thin wall thickness which results in regions of, for example, free cuts or overflows, caused by a contour of the press-rolling rollers, which can only allow correspondingly soft profiles. The tube wall thickness during the pressure rolling can also not be increased as desired, so that costs would increase by providing starting tubes with a higher wall thickness and the processing times would also increase.The object of this invention is to provide a method in which a hollow rotor shaft can be produced cost-effectively and to specify a hollow rotor shaft which is light and sufficiently dimensioned.This object is achieved by a method having the features of claim 1.The first teaching of the invention relates to a method for producing a hollow rotor shaft, comprising the following steps: - providing a tube or a forged tubular preform; - pressure rolling the tube or the forged tubular preform in one step or a plurality of steps to form a green compact using a pressure rolling core; - machining the green compact in at least one of its end sections to produce a hollow rotor shaft; wherein, in at least one step of the press rolling, a radial material stock is pushed in a section of the end section in such a way that the press rolling core has a radial thickening in the section of the material stock to be produced, wherein this thickening is defined in the longitudinal extent starting from the smaller to the larger cross section of the press rolling core by a concave section with a first radius between 2 mm and 20 mm followed by a convex section with a second radius between 2 mm and 25 mm, wherein subsequently by machining the final geometry of the hollow rotor shaft is produced and at least a part of the material stock is removed in the process.The inventors have found that a cost-effective way of manufacturing a hollow rotor shaft could be found by eliminating an over-dimensioning of the (starting) tube or the forged tubular preform, i.e. with a greater wall thickness than required. Thus, according to the invention, in at least one step of the flow forming, a radial material stock is pushed in a section of the end section in such a way that a flow forming core with a radial thickening is used in the section of the material stock to be produced, and thereby locally critical wall thicknesses as a result of machining can be ruled out. This means in particular that the radial thickening of the flow-forming core defines a contour change which provides a defined free space in order, for example, to partially thicken the wall thickness over the region length by pushing after the tapering of the tube or preform cross sections in this region.Final geometry is understood to mean a state in which the shape of the hollow rotor shaft produced is no longer influenced, in particular by shaping and / or machining. The at least one end section can define a functional section in particular as a bearing seat for receiving a bearing, as a seat for receiving a seal and / or as a toothing. The functional section can be machined and / or heat treated, for example, if necessary.The tube provided or forged tubular preform may have a starting wall thickness of between 4.0 and 12.0 mm. The starting wall thickness can be in particular at least 5.0 mm, preferably at least 6.0 mm and in particular at most 10.0 mm, preferably at most 8.0 mm, depending on the dimension of the hollow rotor shaft to be produced. The tube may be drawn, welded into a tube from a blank, or a forged preform may be used.A forged tubular preform is a hollow forged profile with an aforementioned initial wall thickness, which can comprise, for example, a wall thickness that varies or even is constant in the longitudinal extension within the aforementioned limits.According to one configuration, the concave section of the flow mandrel can have an extension between 2 mm and 20 mm, in particular between 3 mm and 18 mm, preferably between 4 mm and 15 mm, and the convex section of the flow mandrel can have an extension between 2 mm and 25 mm, in particular between 3 mm and 23 mm, preferably between 4 mm and 20 mm. This makes it possible to effectively locally push a targeted and / or desired radial material storage on a green compact.During the flow forming, the material of the (starting) tube provided is formed on a flow forming core inserted into the tube, so that the inner contour of the green compact and thus also, if no further processing of the inner contour is intended, the inner contour of the hollow rotor shaft adapts or conforms to the outer contour of the flow forming core. This forming can take place in one or also in several steps of the pressure rolling, in particular depending on the wall thickness of a green compact is to have.By means of pressure rollers, a geometry close to the final contour of a hollow rotor shaft to be produced can be produced at least in sections, so that machining can be carried out at least in sections, in particular in at least one end section, in order to achieve the final geometry while maintaining a predefined tolerance.Machining or else machining removes excess material by machining or generating chips (in a targeted manner). Machining is also intended to be understood as grinding.Thus, the convex section of the inner contour of the hollow rotor shaft can have an extension between 2 mm and 20 mm, in particular between 3 mm and 18 mm, preferably between 4 mm and 15 mm, and the concave section of the inner contour of the hollow rotor shaft can have an extension between 2 mm and 25 mm, in particular between 3 mm and 23 mm, preferably between 4 mm and 20 mm.According to one embodiment, a bearing seat portion can be provided in the at least one end portion at the outer end, the surface of which seat portion is contoured for receiving a bearing. Contouring is preferably effected by means of machining, since tight tolerances must be maintained, in particular, in order to accommodate a bearing.According to one configuration, the at least one end section can be directly adjoined by a main section of the green compact or of the hollow rotor shaft, the surface of which is contoured for receiving laminated cores. The rotor shaft is designed specifically in its main section for receiving so-called laminated cores comprising or consisting of individual configured electric sheets, grain-oriented and non-grain-oriented, wherein an insulating layer is provided in each case between the individual sheets. The hollow rotor shaft, equipped with corresponding components, is thus used in electrical systems, preferably in electrical machines, particularly preferably in traction motors or electric motors for vehicles.According to a preferred embodiment, the radial material storage can be pushed between a bearing seat section and a main section in a section of the end section. As a result, a seat for receiving a bearing and / or a seal can be produced by machining without falling below a critical wall thickness which is required for receiving bending and / or torsional loads. According to one embodiment, the complete end section of the green compact can be machined, preferably on its outer circumference.According to one embodiment, the complete main section of the green compact can be machined, preferably on its outer circumference.According to an alternative embodiment, the green compact can be machined over its entire extent, preferably on its outer periphery. In this way, in particular a hollow rotor shaft with an application-oriented tolerance, i.e. a tolerance required for the application and necessary for the function, can be provided.The invention is explained in more detail on the basis of the following exemplary embodiments in conjunction with the drawing.The drawing shows in FIG. 1 ) shows a cross section of a subsection of a spin-rolled green compact and the corresponding outer contour of the hollow rotor shaft according to the prior art machined at least in one of the end sections, right illustration, and a cross section of a subsection of an associated spin-rolling core, left illustration, and FIG. 2 ) shows a cross section of a subsection of a press-rolled green compact according to a method according to the invention, right illustration, and a cross section of a subsection of an associated press-rolled core for carrying out the method according to the invention, left illustration.The invention proposes a method for producing a hollow rotor shaft (R). First, a pipe (1) is provided which may have an initial wall thickness of between 4.0 and 12.0 mm and may be welded as drawn from a sheet metal blank to form a pipe. Alternatively, a forged tubular preform may also be provided.The tube (1) or the forged tubular preform is press-rolled into a green compact (G) using a press-rolling core (K) in an apparatus not shown, preferably in a press-rolling apparatus, in one step or multiple steps. The green compact (G) is machined in at least one of its end sections (E) to produce a hollow rotor shaft (R). The green compact (G) is press-rolled from the tube into the desired shape by means of one or more press-rolling roller(s), not shown, wherein an inner contour (I) is thus impressed or shaped on the inserted press-rolling core (K) with a predefined outer contour in the green compact (G) and resulting therefrom if no machining machining is provided in the interior of the green compact (G), even in the hollow rotor shaft (R) to be produced).When press rolling a tube or a forged tubular preform to produce a green compact (G), a preform having soft transitions is formed on the surface. These form the geometry of the non-illustrated pressure roller(s), see, for example, the right-hand illustration of FIG. 1. In order to obtain a dimensionally stable hollow rotor shaft (R), machining is carried out in at least one end section (E) of a green compact (G). In particular, the complete end section (E) of the green compact (G) can be machined. The superposition of a cutting contour (s) is shown in the right-hand illustration of FIG. 1, so that the hatched wall thickness (w) remains. In this embodiment, the reduction in wall thickness after machining is clearly visible in the region of, for example, free cuts caused by a smoothly contoured press-rolled green compact (G). Spin-rolled hollow rotor shafts (R) according to the prior art, which are finished at least in one end section (E), have a critical wall thickness (k) in cross section. The left-hand illustration in FIG. 1 shows a subsection of a corresponding deep-rolling core (K) having an outer contour, by means of which an inner contour (I) of the green compact (G) and, if appropriate, of the hollow rotor shaft (R) is produced.FIG. 2 shows an embodiment according to the invention. By pushing on a radial material supply (m) in a section of the end section (E) in at least one step of pressure rolling, the wall thickness can be locally increased without having to increase the wall thickness of the (starting) tube or the forged tubular preform. For this purpose, a flow-forming core (K) is modified in such a way that the flow-forming core (K) has a thickening (S) or a thickness increase / increase in the section of the material storage (m) to be produced, wherein this thickening (S) is defined in the longitudinal extent, starting from the smaller to the larger cross section of the flow-forming core (K), by a concave section (1) having a first radius (R1) between 2 mm and 20 mm, followed by a convex section (2) having a second radius (R2) between 2 mm and 25 mm, cf. the left illustration in FIG. 2. the final geometry of the hollow rotor shaft (R) is then produced by machining and at least a part of the material storage (m) is removed in the process.The concave section (1) of the flow mandrel (K) has an extension between 2 mm and 20 mm and the convex section (2) of the flow mandrel (K) has an extension between 2 mm and 25 mm.In the at least one end section (E) at the outer end, a bearing seat section (L) is preferably provided, the surface of which is contoured, in particular machined, to receive a bearing, not shown.The at least one end section (E) is preferably directly adjoined by a main section (H) of the green compact (G) or of the hollow rotor shaft (R), the surface of which is contoured, in particular machined, to accommodate laminated cores.Particularly preferably, the radial material storage (m) is pushed between a bearing seat section (L) and a main section (H) in a section of the end section (E), cf. right illustration in FIG. 2.For tolerance and possibly weight reasons, the green compact (G) can be machined over its entire extent.A spin-rolled hollow rotor shaft (R) machined at least in an end section (E) can thus be provided, in particular for electric machines, preferably for electric motors, preferably traction motors in the vehicle.

Claims

Method for producing a hollow rotor shaft (R) comprising the following steps: - providing a tube or a forged tubular preform; - press rolling the tube or the forged tubular preform in one step or a plurality of steps to form a green compact (G) using a press rolling core (K); - machining the green compact (G) in at least one of its end sections (E) to produce a hollow rotor shaft (R); characterized in that, in at least one step of press rolling, a radial material storage (m) is pushed in a section of the end section (E) in such a way that the press rolling core (K) has a radial thickening (S) in the section of the material storage (m) to be produced, wherein this thickening (S) in the longitudinal extension starting from the smaller to the larger cross section of the flow mandrel (K) is defined by a concave section (1) with a first radius (R1) between 2 mm and 20 mm followed by a convex section (2) with a second radius (R2) between 2 mm and 25 mm, wherein subsequently by machining the final geometry of the hollow rotor shaft (R) is produced and at least a part of the material reservoir (m) is removed in the process.Method according to claim 1, wherein the concave portion (1) of the flow mandrel (K) has an extension between 2 mm and 20 mm and the convex portion (2) of the flow mandrel (K) has an extension between 2 mm and 25 mm.Method according to any of the preceding claims, wherein in the at least one end portion (E) at the outer end a bearing seat portion (L) is provided, the surface of which is contoured to receive a bearing.Method according to one of the preceding claims, wherein the at least one end section (E) is directly adjoined by a main section (H) of the green compact (G) or of the hollow rotor shaft (R), the surface of which is contoured for receiving laminated cores.Method according to any of the preceding claims, wherein the radial material storage (m) is pushed between a bearing seat portion (L) and a main portion (H) in a portion of the end portion (E).Method according to one of the preceding claims, wherein the complete end section (E) of the green compact (G) is machined.Method according to one of the preceding claims, wherein the complete main section (H) of the green compact (G) is machined.Method according to one of the preceding claims, wherein the green compact (G) is machined over its entire extent.

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