Sheet metal for forming a laminated core for a rotor of an electrical machine

Abstract

Sheet (100) for forming a laminated core for a rotor (200) of an electrical machine, namely an asynchronous machine, wherein the sheet (100) has radially extending grooves (10) for receiving short-circuit bars (15), wherein at least one groove (10) has a first, radially inner end (10a) and a second, radially outer end (10b), wherein the sheet (100) has a recess (14) in a region (100a) which is radially further outward than the second end (10b) of the groove (10), wherein the recess (14) is closed at least on one side in the radial direction, wherein the sheet (100) comprises a first web (12), wherein the first web (12) is designed such that the first web (12) closes the recess (14) on one side in the radial direction, that the first web (12) is arranged in the radially outer direction directly adjacent to the second end (10b) of the groove (10), that the sheet (100) has a flat outer surface (100b) at least in a circular segment of the sheet (100) associated with the groove (10), wherein the sheet (100) comprises a second web (13), and wherein the second web (13) is arranged such that a radially outer surface (13c) of the second web (13) forms part of the outer surface (100b), characterized in that the first web (12) is designed with a substantially greater width (12d) in relation to the width (13d) of the second web (13).

Description

The invention relates to a sheet metal for forming a laminated core for a rotor of an electric machine, in particular of an asynchronous machine, and to a method for producing a rotor of an electric machine.Prior ArtIt is known from the prior art that losses arise in the rotor of an electric machine, in particular of an asynchronous machine, during operation, which lead to heating and, as a result of temperature limits which must thus be maintained, to thermal limitation of the continuous power of the electric machine for durability. The removal of this heat from the rotor is technically difficult and in the prior art is typically effected via the rotor shaft and the thermally sensitive bearings. Although alternative cooling concepts, such as, for example, by internal cooling of the rotor shaft or forced cooling by fan wheels, are described in the prior art, they are always associated with high production-related outlay or additional losses. For the operation and the economic efficiency of an electric machine, in particular an asynchronous machine, it is therefore of great importance to keep the rotor losses as low as possible overall.One type of loss is the electrical heat loss, especially in the conductive areas of the grooves or on the short-circuiting ring of the squirrel cage. These current heat losses in the rotor cage are produced by the rotor currents flowing therein within individual short-circuiting rods and the short-circuiting rings. From various publications and measurements it is known that additionally current heat losses occur in the rotor, which cannot be explained solely by the current flowing in the rotor and the direct current resistance of the rotor cage. According to the prior art, the additional losses are taken into account overall by an addition factor which naturally does not provide any information about the actual output and distribution in the rotor. These additional losses are evident as a result of an increase in the effective resistance of the rotor as a result of current displacement effects and additionally occurring eddy currents due to alternating magnetic fields scattering into the rotor.DE 10 2010 043 384 A1, for example, attempts to reduce the electrical losses by a special geometry of a cage rotor. In this case, a leakage slot is provided, which forms a groove open radially outwards, so that this groove is connected to the air gap between the rotor and the stator. However, the problem arises with such an arrangement that the outer circumferential surface of the rotor has depressions which, at high rotational speeds, can lead to noise excitations and additional losses as a result of additional friction losses of the air flow in the gap.US 2010 0 253 174 A1 relates to the provision of a rotor of a motor which is capable of improving the motor output under magnetic saturation conditions of the rotor teeth. The rotor of an induction motor of this invention may have slots formed approximately in the shape of a T. The slits may be formed such that the upper slits are disposed at an outer circumferential portion of the rotor core and the lower slits are disposed on an inner side of the upper slits. The width in the circumferential direction of the upper slot is wider than the width in the circumferential direction of the lower slot, and the width in the circumferential direction of a rotor tooth between adjacent upper slots is narrower than the width in the circumferential direction of the rotor tooth between adjacent lower slots.US 6 058 596 A relates to a method of manufacturing an induction motor rotor comprising: stacking a plurality of rotor laminations, each of the rotor laminations having a plurality of closed rotor slots with substantially similar shapes, some of the closed rotor slots being disposed further from a center of rotation than the others of the closed rotor slots; filling the rotor slots with rotor cage material; machining an outer surface of the stacked rotor laminations to cause some of the rotor slots to become open rotor slots.DE 689 11 929 T2 shows a cage rotor induction motor for frequency converter operation, having a rotor whose rotor core has a plurality of substantially axially extending rotor grooves in which rotor conductors are arranged, each rotor groove having a main part in which a rotor conductor is arranged and a groove opening lying between the main part and that surface of the rotor which delimits the air gap of the motor, a magnetic bridge being present for separating the groove opening from the main part of the groove, the ends of the bridge adjoining the rest of the rotor core on both sides of the groove opening and that surface of the bridge which points towards the interior of the rotor conductor having a curved shape towards the interior of the rotor conductor.DD 91 694 A1 shows a double cage rotor for three-phase asynchronous motors, in which, in order to achieve the greatest possible variation of the slot between upper and lower bars of the double groove, the intermediate variation slots are arranged asymmetrically with respect to the groove centre line and the metal sheets are layered in a side-rotated manner, so that the effective variation slot width is correspondingly reduced. It is provided that the slot slots on the rotor circumference are arranged asymmetrically with respect to the slot center line and the metal sheets are layered in a side-rotated manner.Japanese Patent Application Laid-Open No. 08-140,319 A proposes that two rotor grooves are arranged as inner circumferential rotor grooves and outer circumferential rotor grooves in the radial direction of a rotor core, respectively, to eliminate eddy current losses of a rotor in which short-circuiting rods are provided in a rotor groove. The outer side rotor slots are formed as voids filled with nothing, and a substance whose electric resistance is low does not exist near the surface of a rotor. As a result, no eddy current is generated, and the loss by pulse width modulation (PWM) can be greatly reduced. This improves the efficiency, particularly low load efficiency, of a PWM controlled induction motor.CN 1 05 449 944 A relates to a cage rotor for an electric induction machine, comprising a rotor body comprising a laminated array of steel sheets axially stacked with respect to an intended axis of rotation of the rotor. A plurality of rotor slots extend substantially axially through the rotor body and are each filled with a cast rotor conductor. Another slot is located radially outward of each rotor conductor in the circumferential surface of the rotor body and extends parallel to the rotor conductor forming an air gap separating the peripheral steel sheet portions of the rotor body. Each further slot extends radially to the respective rotor conductor to lengthen the air gap to this point.Presentation of the Invention: Object, Solution, AdvantagesIt is an object of the present invention to further develop a sheet metal for forming a laminated core for a rotor in such a way that current heat losses are reduced.The above-mentioned object is achieved by a sheet metal for forming a laminated core for a rotor of an electric machine, in particular of an asynchronous machine, which has radially extending grooves for receiving short-circuit bars. At least one of these grooves has a first and a second end, wherein the first end is arranged further inward than the second end, as seen radially. The sheet metal further comprises a recess which is arranged in a region of the sheet metal lying further outwards compared to the second end of the groove. The recess is formed closed at least on one side in the radial direction.The present invention is based on the finding that the losses due to electromagnetic influences are distributed inhomogeneously. In particular, the power loss density in the vicinity of the air gap between the rotor and the stator of an electric machine is considerably greater than in the regions oriented radially further inward relative to the rotor shaft.By providing a recess in a region which is located further outward in the radial direction than the radially outer, second end of the groove, wherein the recess is formed so as to be closed at least on one side, conductive material is removed in the vicinity of the air gap in order to counteract the losses occurring there. Overall, the recess results in both less material of the metal sheet being present in the vicinity of the air gap and the short-circuit bars being displaced radially further inward in the grooves. This leads to a reduction of the current heat losses in the rotor by up to 60% at high rotational speeds.Due to the fact that the recess is formed closed at least on one side in the radial direction, a connection between the groove and the air gap is avoided. This prevents an undesirable depression in an otherwise planar outer surface of the sheet metal, which brings with it advantages both with regard to acoustics and efficiency. Excessively strong depressions, as proposed, for example, by the abovementioned German patent application, lead at high rotational speeds to noise excitations and additional losses, triggered by additional friction losses of the air flow in the depressions. Furthermore, the sheets produced in this way, or the electric machines equipped therewith, cannot be operated in an oil bath in order to cool them. These disadvantages do not occur in the above-mentioned solution according to the invention, since the recess is formed so as to be closed at least on one side in the radial direction.A sheet metal in the sense of the invention is in particular shaped in the form of a disk. It has above all a cylindrical shape with a very small thickness or height compared to the radius. In particular, the sheet metal has a lateral surface which forms the radially outermost surface.A groove is formed in particular as an elongate recess in the sheet metal. The groove is to be understood as an opening through the sheet metal in the thickness direction. The groove serves to receive a short-circuiting rod. Rotor teeth are formed between the grooves of a metal sheet.The term "recess" is to be understood as meaning an air pocket. In particular, the recess is to be understood as an aperture in the sheet metal in the thickness direction. The recess is formed closed at least on one side in the radial direction. This means that the recess is bounded by the metal sheet in the radial direction of the metal sheet at least on one side of the recess. The recess is preferably formed closed on both sides in the radial direction. The recess is characterized in particular in that it is not filled with an electrically conductive material, in particular a short-circuit rod.In particular, the recess is arranged between the second end of the groove and the air gap between the rotor and the stator. The air gap is formed in particular between the inner circumferential surface of the stator and the outer circumferential surface of the rotor. The rotor is primarily a short-circuiting rotor of an asynchronous machine. Due to the fact that the recess is closed at least on one side in the radial direction, there is no connection between the groove and the air gap. The recess thus does not connect the groove and the air gap between the rotor and a stator of the electric machine to one another. Thus, the groove remains closed off from the air gap despite the recess which is located between the groove and the air gap.The sheet metal comprises in particular a first web which is formed in such a way that it closes the recess on one side in the radial direction. The first web is thus arranged primarily between the groove and the recess and / or between the recess and the air gap. The first web connects in particular adjacent rotor teeth, between which the groove lies, to one another. The first web is primarily a so-called scattering web. This name benefits the web because it provides undesirable magnetic flux leakage between the rotor teeth. The obvious solution, based on the above-mentioned finding of making a part of the sheet metal connecting the rotor teeth thicker in order to displace the conductive material radially inward, is disadvantageous for electromagnetic reasons because the static magnetic leakage flux would greatly reduce torque and power of the electric machine. By means of an embodiment according to the invention, the electrically conductive material is offset radially inward, wherein at the same time an undesired magnetic leakage flux is avoided.According to the invention, the first web is arranged directly adjoining the second end of the groove in the radially outer direction. In other words, the first web forms the termination of the groove in the radially outer direction and thus defines the second end thereof. In particular, the first web has a first radially inner end and a second radially outer end. The first, radially inner end determines in particular the second end of the groove.In particular, the recess is formed exclusively closed on one side in the radial direction.In a position of the first web directly adjoining the second end of the groove, the recess is thus formed to be radially inwardly closed. The recess is in particular not closed radially outwards, so that the recess is in direct connection with the air gap. In other words, in such a case, a radially outer surface of the web forms a depression in the lateral surface of the metal sheet.According to the invention, the metal sheet has a planar, in particular closed, lateral surface at least in a circle segment assigned to the groove, preferably along the entire circumference of the metal sheet. In other words, the lateral surface of the metal sheet has a constant radius in this region. This means that the lateral surface does not have any depressions or elevations. The first web is preferably arranged in such a way that a radially outer surface of the web, which is arranged at its second end, forms part of this planar lateral surface, so that friction and noise excitations are minimized. This makes the sheet metal suitable for use in a vehicle, in particular a passenger car, since in particular there the requirements for acoustics and efficiency are particularly high as a result of the high rotational speeds.In particular, the entire lateral surface of the metal sheet is of planar design and therefore has no elevations or depressions. This has the advantage above all that at high rotational speeds no noise excitations or additional losses occur as a result of additional friction losses in the unevennesses.In particular, the recess is substantially rectangular in an axial plan view of the metal sheet. The recess has in particular a width in the radial direction of the sheet and a length formed perpendicular thereto. The length of the recess corresponds in particular to 30% to 100%, preferably 40% to 80%, of the maximum width of the groove.Furthermore, the recess can be substantially triangular in an axial plan view of the metal sheet. In particular, the recess narrows from the second, radially outer end in the direction of the first, radially inner end. In other words, the extension of the groove in a direction perpendicular to the radial direction decreases in a radially inward direction. In particular, the recess narrows largely conically. Above all, an extent of the recess at the first end corresponds to at most 60%, further preferably at most 50%, further preferably at most 30%, of the extent of the recess at the first end.Furthermore, the metal sheet has both a first web which directly adjoins the second end of the groove and a second web which is arranged in such a way that a radially outer surface of the second web forms part of the lateral surface of the metal sheet, wherein the lateral surface is of planar configuration at least in a circle segment of the metal sheet assigned to the groove. In other words, the recess is closed on both sides in the radial direction. While the first web closes off the recess radially inward, the second web delimits the recess radially outward. In detail, the second web has a first, radially inner end and a second, radially outer end. The first radially inner end delimits the recess and forms the second, radially outer end thereof.In particular, the embodiment described above produces a planar lateral surface of the metal sheet which does not have any elevations or depressions, with the result that friction and noise excitations are minimized, wherein at the same time the space, that is to say the recess, between the first web and the second web remains open, in order thus to avoid undesired magnetic leakage flux between the individual rotor teeth.In particular, the metal sheet has at least three wall sections which delimit the recess and thus define it. It is primarily a first wall section and / or a second wall section which are formed by a first or a second web, and two further wall sections, a third wall section and a fourth wall section which are at an angle, primarily at right angles, to the first and / or the second wall section.Advantageously, the sheet metal comprises four wall sections, wherein the second wall section is opposite the first wall section and the third wall section is opposite the fourth wall section.Adjacent wall sections merge into one another in transition regions. In particular, the transition regions between adjacent wall sections are rounded, in particular the radially inner transition regions, which are preferably located between the first wall section and the third wall section and between the first wall section and the fourth wall section. Rounded transition regions mean, in particular, that they do not have corners or edges. In particular, all transition regions between all adjacent wall sections are rounded.At high speeds, the material arranged in the rotor grooves is pressed outwards due to centrifugal forces and exerts mechanical pressure on the sheet metal, in particular on the region in which the recess is arranged. In the case of non-rounded transition regions, increased mechanical stresses arise in the corner regions of an inner web as a result of notch action, which can lead to structural mechanical failure. By a rounded configuration of the transition regions between the wall sections, the mechanical stresses are significantly reduced and the aforementioned disadvantages can be avoided.In an arrangement of only a first web, namely in such a way that its radially outer surface forms part of a planar lateral surface of the metal sheet, the recess is formed to be closed radially outwards, but not radially inwards. Such an arrangement is advantageous above all from an electromagnetic point of view, wherein a planar lateral surface is nevertheless ensured. Nevertheless, the short-circuiting rods must still be held in their position at high rotational speed. This is particularly suited for a geometry of the recess in which it narrows from radially outside to radially inside. This ensures that the material located in the grooves is adequately supported by the sheet metal by the centrifugal forces.Advantageously, the metal sheet has a recess as described above in each case in a radially outer region of all grooves. Furthermore, in particular all the sheets of the laminated core are configured as described above. In particular, the invention relates to a laminated core for a rotor, in particular to a rotor, and furthermore preferably to an electric machine, in particular an asynchronous machine.In a further aspect, the invention relates to a method for producing a rotor of an electric machine, in particular of an asynchronous machine, which is characterized by the lamination of a plurality of the above-described sheets, their axial alignment for forming a laminated core and the insertion of short-circuiting bars into the grooves of the sheets or the casting of a material for forming short-circuiting bars. When multiple sheets are stacked, they are stacked one on top of the other in particular in the axial direction, wherein these are arranged such that their grooves lie one above the other. The radially extending grooves seen with respect to a metal sheet thus form, in conjunction with a plurality of metal sheets, a longitudinal perforation of the laminated core formed in this way, into which already produced short-circuit bars, in particular made of conductive material, such as, for example, copper or aluminum, can be inserted, or into which liquid copper material can be cast in order to form short-circuit bars. When casting in copper material, it is advantageous that the first web directly adjoins the second end of the groove, so that the material is prevented from flowing out.Brief Description of the DrawingsThey show schematically: FIG. 1 is an axial top view of a sheet metal according to the invention; FIG. 2 is an axial top view of a further sheet metal according to the invention; FIG. 3 is an axial top view of a further sheet metal according to the invention; and FIG. 4 is an axial top view of a further sheet metal according to the invention.FIG. 1 shows an axial plan view of a sheet (100) according to the invention, which is part of a rotor (200) of an electric machine, in particular of an asynchronous machine. Furthermore, FIG. 1 shows a part of the stator ( 300) of the electric machine in a sectional illustration. The rotor (200) is arranged in the interior of the stator (300), wherein an air gap (400) is located between the rotor (200) and the stator (300).The sheet (100) is of cylindrical design and has a lateral surface (100b) on its radially outer surface. The lateral surface ( 100 b) faces the stator ( 300) and thus the air gap ( 400). The sheet (100) has a plurality of grooves (10) extending in the radial direction. The grooves (10) have a first end (10a) and a second end (10b), wherein the first end (10a) is located radially further inward compared to the second end (10b). Furthermore, the grooves (10) have a third end (10c) and a fourth end (10d). The grooves (10) are each located between two rotor teeth (11) of the metal sheet (100) or of the rotor (200). A short-circuiting rod (15) is arranged in the interior of the groove (10).A recess (14) is arranged in a region (100a) of the metal sheet (100) which lies radially further outwards than the second end (10b) of the groove (10) but which lies radially further inwards than the air gap (400) between the rotor (200) and the stator (300). The recess (14) is formed as an opening in the thickness direction of the sheet (100), wherein the thickness direction extends into the plane of the drawing of FIG. 1.In the radial direction, the recess ( 14) is formed closed on one side, namely towards the groove ( 10). Between the groove (10) and the recess (14), a first web (12) of the metal sheet (100) is formed, which web separates the groove (10) and the recess (14) from one another. The first web ( 12) has a first end ( 12 a) which simultaneously delimits the groove ( 10) at its second end ( 10 b). Furthermore, the first web ( 12) has a second end ( 12 b), wherein the second end ( 12 b) is located radially further outwards than the first end ( 12 a). The second end ( 12 b) of the first web ( 12) delimits the recess ( 14).To form the recess ( 14), the sheet metal ( 100) has a plurality of wall sections ( 100 c, 100 e, 100 f). A first wall section ( 100 c) forms both the second end ( 12 b) of the first web ( 12) and a first, radially inner end ( 14 a) of the recess ( 14). A third wall portion (100e) and a fourth wall portion (100f) are disposed adjacent to and extend perpendicular to the first wall portion (100c). The third wall section (100e) forms a third end (14c) of the recess (14), while the fourth wall section (100f) forms a fourth end (14d) of the recess (14).The recess (14) is in direct contact with the air gap (400). The recess ( 14) thus has a second, radially outer end ( 14 b) before the air gap ( 400) adjoins, but this is not structurally limited. The lateral surface ( 100 b) of the metal sheet ( 100) is not planar because of the recesses ( 14).The transition regions ( 100 g) between adjacent wall sections, i.e. between the third wall section ( 100 e) and the first wall section ( 100 c), and between the fourth wall section ( 100 f) and the second wall section ( 100 c), are formed in an angular manner. In particular, the wall sections are arranged in such a way that a right angle is formed in the transition regions ( 100 g). Furthermore, the transition regions ( 100 g) can be rounded in the embodiment illustrated in FIG. 1.FIG. 2 shows an axial plan view of a further sheet (100) according to the invention. The embodiment of FIG. 2 is similar in many aspects to the embodiment shown in FIG. 1. As a difference, however, the sheet metal has a second web ( 13) in addition to a first web ( 12). The second web ( 13) is in particular formed thinner than the first web ( 12). The second web (13) comprises a first end (13a) facing the recess (14) and forming the second end (14b) of the recess (14) and a second end (13b) facing the air gap (400). At the second end ( 13 b), the second web ( 13) has a radially outer surface ( 13 c). The radially outer surface ( 13 c) forms part of the lateral surface ( 100 b) of the metal sheet ( 100). The second web (13) is arranged such that the lateral surface (100b) comprising the radially outer surface (13c) of the second web (13) has a constant radius. This applies at least in a segment of a circle in which the groove ( 10) is arranged, in particular along the entire circumference of the metal sheet ( 100).By providing the second web ( 13), the recess ( 14) is formed closed on both sides in the radial direction. In particular, the recess (14) is delimited by the first web (12) in the direction of the groove (10), while the recess (14) is delimited by the second web (13) in the direction of the air gap (400). More specifically, in the radial direction, a first wall portion (100c) forming the second end (12b) of the first web delimits the recess (14), while a second wall portion (100d) forming the first end (13a) of the second web (13) delimits the recess (14) radially outwards.In a direction transverse to the radial direction, a third wall section ( 100 e) and a fourth wall section ( 100 f) delimit the recess ( 14). The transition regions between adjacent wall sections ( 100 c, 100 d, 100 e, 100 f) are formed angularly, such that the recess ( 14) has a rectangular shape in the plan view of FIG. 2. The recess (14) has a rectangular shape, the width extending in the radial direction and the length perpendicular thereto.FIG. 3 shows an axial plan view of a further embodiment of a sheet (100) according to the invention. FIG. 3 shows only the sheet metal ( 100) or a part of the rotor ( 200) of an electric machine. The sheet (100) of FIG. 3 is formed analogously to the sheet (100) of FIG. 2. As the only difference, the transition regions ( 100 g) between some adjacent wall sections are rounded. More specifically, the radially inner transition regions ( 100 g), in other words the transition regions ( 100 g), are formed rounded off from the first wall section ( 100 c). In detail, the transition region ( 100 g) between the third wall section ( 100 e) and the first wall section ( 100 c) and the transition region ( 100 g) between the fourth wall section ( 100 f) and the first wall section ( 100 c) are rounded. Furthermore, the substantially greater width ( 12 d) of the first web ( 12) compared to the width ( 13 d) of the second web ( 13) can be seen in FIG. 3.FIG. 4 shows an axial top view of a further sheet (100) according to the invention. In many aspects, the sheet (100) is formed analogously to the embodiment of FIG. 2. In particular, the sheet metal ( 100) has a first web ( 12), which is designed analogously to the second web ( 13) of FIG. 2. In contrast to the embodiment of FIG. 2, however, the sheet (100) shown in FIG. 4 does not have an inner web. The recess ( 14) is thus formed closed only on one side in the radial direction. Namely, the first web (12) closes off the recess (14) radially outwards, while the recess (14) is not closed off at its first end (14a), but directly adjoins the groove (10).The recess ( 14) tapers from its second end ( 14 b) in the direction of the first end ( 14 a). The third wall section ( 100 e) and the fourth wall section ( 100 f) are thus arranged at an angle to the second wall section ( 100 d) which deviates from 90°. In particular, the angles are selected such that the recess ( 14) is substantially triangular in shape in the plan view of FIG. 4.List of reference characters100 Sheet metal 100 a Bereich of the sheet metal 100 b Mantelfläche surface 100 cFirst wall section 100 dSecond wall section 100 eThird wall section 100 f Vierter wall section 100 gÜbergangsbereich region between wall sections 10 Nut 10 aFirst end of the groove 10 bSecond end of the groove 10 cThird end of the groove 11 Rotor teeth 12First web 12 aFirst end 12 bSecond end 12 cRadially outer surface 12 d Breite 13Second web 13 aFirst end 13 bSecond end 13 cRadially outer surface 13 d Breite 14 Ausnehmung 14 aFirst end 14 bSecond end 14 c Drittes end 14 d Viertes end 15 Short-circuiting rod 200 Rotor 300 Stator 400 Air gap

Claims

Sheet (100) for forming a laminated core for a rotor (200) of an electric machine, namely an asynchronous machine, wherein the sheet (100) has radially extending grooves (10) for receiving short-circuit bars (15), wherein at least one groove (10) has a first, radially inner end (10a) and a second, radially outer end (10b), wherein the sheet (100) has a recess (14) in a region (100a) lying radially further outward compared to the second end (10b) of the groove (10), wherein the recess (14) is formed so as to be closed at least on one side in the radial direction, wherein the sheet (100) comprises a first web (12), wherein the first web (12) is formed such that the first web (12) closes the recess (14) on one side in the radial direction, the first web (12) being arranged directly adjacent to the second end (10b) of the groove (10) in the radially outer direction, the metal sheet (100) having a planar lateral surface (100b) at least in a circular segment of the metal sheet (100) assigned to the groove (10), the metal sheet (100) comprising a second web (13), and the second web (13) being arranged in such a way that a radially outer surface (13c) of the second web (13) forms part of the lateral surface (100b), characterized in that the first web (12) is formed with a substantially greater width (12d) in relation to the width (13d) of the second web (13).Sheet (100) according to Claim 1, characterized in that the recess (14) has a first, radially inner end (14a) and a second, radially outer end (14b), the recess (14) tapering radially inward in the direction of the first end (14a) starting from the second end (14b).Sheet (100) according to either of Claims 1 and 2, in that the recess (14) has a first, radially inner end (14a) and a second, radially outer end (14b), the sheet (100) having a first wall section (100c), a second wall section (100d), a third wall section (100e) and a fourth wall section (100f), the wall section (100c, 100e, 100f) delimiting the recess (14), the third wall section (100e) and the fourth wall section (100f) being arranged in each case adjacent to the first wall section (100c), a transition region (100g) between the third wall section (100e) and the first wall section (100c) and a transition region (100g) between the fourth wall section (100f) and the first wall section (100c) being formed in a rounded manner.Method for producing a rotor (200) of an electric machine, in particular an asynchronous machine, characterized bythe following steps: • stacking a plurality of sheets (100) according to one of Claims 1 to 3, • axial alignment of the sheets (100) in order to form a laminated stack, • insertion of short-circuiting bars (15) into grooves (10) of the sheets (100) or casting in of a material in order to form short-circuiting bars (15).

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