Iron core and method for manufacturing an iron core for an electric machine

Abstract

A method for producing an iron core (1) for an electric machine (2) comprises: providing (S3) several sheet metal strips (10A-10H) of different lengths, each comprising or consisting of iron; arranging (S4) the sheet metal strips (10A-10H) into a stack (11); and forming (S5) the stack (11) by means of a tool (4) and fixing (S6) the sheet metal strips (10A-10H) of the stack (11) together to obtain the iron core (1) with at least one curvature (K1-K4).

Description

[0001] The present disclosure relates in particular to a method for manufacturing an iron core for an electric machine, to a method for manufacturing an electric machine, to an iron core, an electric machine and a vehicle.

[0002] Vehicles, especially aircraft, are powered by a wide variety of propulsion systems. Internal combustion engines, such as piston engines or gas turbine engines, enable long ranges and high speeds. Electric drive units, on the other hand, allow the use of sustainably generated energy and are often particularly low-maintenance and quiet. Advances in battery and fuel cell technology are constantly expanding the applications of electric drive units.

[0003] For electric motors and other electrical machines, especially electric drive units, continuous improvement of various target parameters can be pursued, such as energy efficiency, power-to-weight ratio, or service life. At the same time, it may be desirable to manufacture electrical machines in the simplest and most reliable way possible. However, such objectives can conflict with one another. Manufacturing iron cores for electrical machines with high precision can be particularly challenging.

[0004] The task is to improve the production of an iron core for an electric machine.

[0005] According to one aspect, a method for manufacturing an iron core for an electric machine is described. The method comprises providing several sheet metal strips of varying lengths, each sheet metal strip comprising or consisting of iron, and arranging the sheet metal strips into a stack. Furthermore, the method comprises forming the stack of sheet metal strips using a tool and, simultaneously or subsequently, fixing the sheet metal strips of the stack together to obtain the iron core, the iron core being produced with at least one curvature.

[0006] In this way, the individual sheet metal strips can be produced separately and thus with exceptionally high precision. This makes it possible to produce an iron core with a precise geometry in a simple and reliable manner. Another approach, in which a single long sheet metal strip is wound multiple times around a body and the resulting multi-layered ring is cut to obtain one or more iron cores, has proven to be very costly in order to achieve the desired precision during cutting. The solution proposed here eliminates the need for such cutting of a wound ring.

[0007] The reshaping can be carried out in such a way that the iron core is formed into a C-shape. This allows the iron core to surround an electrical coil of the electric machine, thus effectively guiding the magnetic flux of the coil.

[0008] During the fixing process, adjacent metal strips can be glued together across their entire surface. This allows for high stability.

[0009] The process may further include, prior to the provisioning step, the following steps: specifying a shape for the iron core and / or calculating the lengths of the individual sheet metal strips based on the specified shape. For example, with a C-shaped iron core, the innermost sheet metal strip has the shortest length, and the outermost one the longest.

[0010] It can be provided that each of the sheet metal strips has a different length than one or more, in particular all, of the other sheet metal strips. The sheet metal strips can have successively increasing lengths (and be arranged accordingly in the stack). This allows the specified shape to be reproduced exactly. For example, three, four, five, or more than five sheet metal strips are provided.

[0011] Providing the sheet metal strips of varying lengths can involve cutting and / or punching the strips from a sheet. These steps can be performed at high speed yet with precision.

[0012] Each of the sheet metal strips extends from one end to the other. It can be arranged that, after forming and fixing, the first ends together describe a first end face of the iron core, and the second ends together describe a second end face of the iron core. The two end faces can lie in the same plane. This allows for particularly good guidance of the magnetic field lines.

[0013] The sheet metal strips can be manufactured to suit the required dimensions (thickness, width, length).

[0014] The tool can comprise a first tool half and a second tool half. The first tool half has, for example, a C-shaped contact surface for the stack of sheet metal strips. The second tool half can have a complementary contact surface. This enables a fast and precise forming process.

[0015] The tool and / or the sheet metal strips can each include one or more positioning elements for positioning the sheet metal strips on the tool. This prevents slippage. The positioning element(s) of the sheet metal strips and the positioning elements of the tool work together (e.g., interlock) to position the sheet metal strips on the tool.

[0016] It can be stipulated that all the sheet metal strips are flat before the forming step. This makes it particularly easy to produce the sheet metal strips with a precise shape.

[0017] According to one aspect, a method for manufacturing an electric machine is described, comprising the production of several iron cores according to any embodiment described herein. The method further includes mounting the iron cores and at least one coil onto at least one support to form a stator, and rotatably mounting, for example, a permanent magnet rotor on the stator. Since a large number of iron cores can be used in such an electric machine, the advantages described above can be particularly beneficial.

[0018] According to one aspect, an iron core for an electric machine is specified, extending from a first end face to a second end face and having at least one curvature in between, wherein the first end face is oriented perpendicular to an adjacent section of the iron core, and the second end face is oriented perpendicular to an adjacent section of the iron core, wherein the iron core comprises several sheet metal strips of different lengths fixed to one another, each comprising or consisting of iron and each extending from the first end face to the second end face. Regarding the advantages, reference is made to the above specifications.

[0019] According to one aspect, an iron core for an electrical machine is specified, manufacturable and / or produced by the method according to any of the embodiments described herein.

[0020] The iron core can be C-shaped. The sheet metal strips can each be C-shaped. An innermost sheet metal strip can be surrounded by another sheet metal strip, which in turn is surrounded by another sheet metal strip, and so on.

[0021] The two end faces of the iron core can lie in the same plane.

[0022] The iron core can, for example, have two, three, or four curves.

[0023] According to one aspect, an electric machine is specified, comprising a stator with one or more iron cores according to any of the embodiments described herein. Regarding the advantages, reference is made to the information above.

[0024] According to one aspect, a vehicle, in particular an aircraft, is specified, comprising the electric machine according to any of the configurations described herein and / or an electric drive unit with the electric machine according to any of the configurations described herein and, for example, a propeller. The advantages described above can be particularly relevant for vehicles, especially aircraft.

[0025] Exemplary embodiments are now described with reference to the figures; the figures show: Fig. 1 an aircraft with several electric machines to drive several propellers; Fig. 2 a cutaway view of one of the aircraft's electrical machines according to Fig. 1 with a stator and a rotor; Fig. 3 a module of the stator of the electric machine according to Fig. 2 with a coil and several iron cores; Fig. 4 an iron core of the module according to Fig. 3; Fig. 5 several curved sheet metal strips; of the iron core according to Fig. 4 Fig. 6 the sheet metal strips according to Fig. 5 in an as yet unbent, flat state; Fig. 7 a sheet of metal from which one of the sheet metal strips according to Fig. 6 is cut out; Fig. 8 a tool for bending the sheet metal strips according to Fig. 6 into the form according to Fig. 5; Fig. 9 one tool half of the tool according to Fig. 8 in a top view; Fig. 10 and Fig. 11 one tool half of the tool according to Fig. 8 in a sectional view and a top view; and Fig. 12 a method for producing an iron core for an electric machine and for producing an electric machine.

[0026] Fig. Figure 1 shows an aircraft 3, exemplified as an air taxi. The aircraft 3 comprises a cabin 30 and several electric drive units, four in this example. Each electric drive unit includes an electric machine 2, in the form of an electric motor, and one or more propellers 32. Each electric machine 2 drives its respective propeller(s) 32. For this purpose, each propeller 32 is operatively connected to a rotor of the respective electric machine 2 (e.g., rigidly connected to it, for example, via a shaft and / or a gearbox). A battery system 31 with one or more electric batteries supplies electrical current for operating the electric machines 2. In this example, the electric machines 2 are direct drives.

[0027] Aircraft 3 is shown here as an example of a vertically launching and landing aircraft, although a design as a fixed-wing aircraft is also possible.

[0028] Fig. 2 illustrates the basic structure of one of the examples shown. Fig. 1 electrical machines of identical construction 2.

[0029] The electric machine 2 comprises a stator 20 and a rotor 21 rotatable about an axis of rotation relative to the stator 20. The rotor 21 is rotatably mounted on the stator 20 by means of bearings 22, here in the form of ball bearings, or alternatively, for example, plain bearings. The electric machine 2 is shown here as an example of an external rotor. The rotor 21 surrounds the stator 20. The stator 20 is arranged inside the rotor 21. The stator 20 can be mounted to a supporting structure of the aircraft 3 by means of a mounting area, here in the form of a flange 202, and is in the state according to Fig. 1 assembled.

[0030] The rotor 21 comprises a shaft flange 210, on which a shaft can be mounted and in the state according to Fig. 1 is mounted. The rotor 21 then drives the propeller 32 via the shaft.

[0031] The stator 20 also has a base. The base has brackets on which supports for the coils and iron cores of the stator 20 are mounted (these components are in Fig. 2 is not shown for the sake of simplicity, but instead shown separately, e.g. in Fig. 3 illustrated.

[0032] Fig. Figure 3 shows a module of the stator 20. The stator 20 comprises several such modules, e.g., three or, as in the present example, six. Such a module can also be called a phase module. The module has a coil 200. As in Fig. As can be seen in Figure 3, the module of the stator 20 of the electric machine 2 comprises two supports 201, each in the form of a plate. The supports 201 are spaced apart from each other and aligned parallel to each other. The electric coil 200 runs between the two supports 201. The coil 200 is positioned between the two supports 201 of the module. When the coil 200 is energized, a magnetic field is generated, which interacts with the permanent magnets 211 of the rotor 21 and thus causes the rotor 21 to rotate relative to the stator 20.

[0033] In this process, for example, each of the multiple modules is supplied with one phase of an alternating voltage, e.g., a three-phase alternating voltage. This is provided by one or more inverters, which convert a direct current voltage from the battery system 31 into the alternating current voltage.

[0034] The stator module 20 further comprises several iron cores 1. The iron cores 1 each extend from one support 201 to the other support 201. The iron cores 1 are each rigidly connected to both the one support 201 and the other support 201. In this case, the iron cores 1 are engaged with both the one support 201 and the other support 201. The iron cores 1 are each inserted into a receptacle of one support 201 and into a receptacle of the other support 201.

[0035] The iron cores 1 comprise or consist of iron. The iron cores 1 may comprise or consist of a ferromagnetic metal alloy. In this case, the iron cores 1, together with the coil 200, form an inductor. The iron cores 1 conduct the magnetic flux of the coil 200. Furthermore, the iron cores 1 fix the coil 200 to the supports 201. The iron cores 1 serve as a support for the coil 200. Thus, the iron cores 1 have two functions, an electromagnetic and a mechanical one, namely the guiding of the magnetic field lines and the support of the coil 200. The iron cores 1 are each C-shaped.

[0036] The coil 200 has several turns. The turns of the coil 200 (or at least some of the turns of the coil 200) run concentrically along a circular segment around the axis of rotation of the rotor 21 (radially closer to the axis of rotation of the rotor 21 relative to the stator 20), are then wound radially outwards and continue radially further away from the axis of rotation along a circular segment concentrically around the axis of rotation. The turns (or at least some of the turns of the coil 200) are then wound radially inwards and connect to a correspondingly adjacent turn. The coil 200 is formed by an insulated electrical conductor.

[0037] The radially inner winding portion of the coil 200 is enclosed by several pairs of the described iron cores 1. Here, by way of example, the electrical conductor of the coil 200 is sectionally encased in a potting compound, which is in contact with the iron cores 1. The radially outer winding portion of the coil 200 is also enclosed by several pairs of the described iron cores 1. Here too, the electrical conductor of the coil 200 is sectionally encased in a potting compound, which is in contact with the corresponding iron cores 1.

[0038] The stator 20 is designed for multiphase, in this case three-phase, operation and is connected to a three-phase alternating voltage with phases U, V, W. During normal operation of the electrical machine 2, the coils 200 are accordingly energized with the alternating voltage.

[0039] The electric machine 2 is designed in the form of a transverse flux machine. The coil 200 of the in Fig. The coils of the module shown in section 3, and correspondingly the coils of the other modules, run section by section in the circumferential direction around the axis of rotation. As shown in Fig. As can be seen in Figure 3, the electrical conductor is bent several times to describe the windings of the coil 200. In this case, the coil 200 is arc-shaped and can also be described as banana-shaped.

[0040] The present design provides that the electric machine 2 serves as a drive motor for the respective propeller 32. It may also be provided that the electric machine 2 can be operated in generator mode.

[0041] Fig. Figure 4 shows one of the iron cores 1. As already mentioned, the iron core 1 is C-shaped. The iron core 1 has a shape F, which describes a convex side and a (opposite) concave side. The iron core 1 forms (with its concave side) a recess in which at least part of the coil 200 can be received. In the assembled state, the iron core 1 surrounds a section of the coil 200.

[0042] The iron core 1 is curved and elongated. The iron core 1 extends from a first end face 12 to a second end face 13. The end faces 12 and 13 form end surfaces. Between the first end face 12 and the second end face 13, the iron core 1 has at least one curvature K1-K4; in the example shown, four curvatures K1-K4.

[0043] The first end face 12 is oriented perpendicularly to an adjacent section A1 of the iron core 1. The second end face 13 is oriented perpendicularly to an adjacent section A5 of the iron core 1.

[0044] Starting from the first end face 12, the iron core 1 extends with the adjacent section A1 to a first curvature K1. The section A1 between the first end face 12 and the first curvature K1 is straight. The first curvature K1 is connected to a second curvature K2 via a straight section A2. A third curvature K3 is connected to the second curvature K2 via another straight section A3. A fourth curvature K4 is connected to the third curvature K3 via another straight section A4. The straight section A5 adjacent to the second end face 13 connects the fourth curvature K4 to the second end face 13. The shape F of the iron core 1 is curved at the curvatures K1-K4. The curvatures K1-K4 can be acute or rounded. Sections A1 and A5 at end faces 12 and 13 run parallel to each other.The adjacent sections A2 and A4 run diagonally to it, and the middle section A3 runs perpendicular to the two sections A1 and A5 at the end faces 12 and 13.

[0045] While Fig. Figure 4 illustrates the outer shape F of the iron core 1, showing Fig. 5 the structure of the iron core 1. This illustrates that the iron core 1 comprises several adjacent sheet metal strips 10A-10H, each extending from the first end face 12 to the second end face 13.

[0046] The metal strips 10A-10H are fixed together to form a bundle. The metal strips 10A-10H are of different lengths. The metal strips 10A-10H each contain or are made of iron. In this case, the metal strips are made of an iron alloy.

[0047] Each of the sheet metal strips 10A-10H extends from a first end 100 to a second end 101. The sheet metal strips 10A-10H are each elongated and follow the C-shape of the outer form F. The first ends 100 of the sheet metal strips 10A-10H together form the first end face 12 of the iron core, and the second ends 101 of the sheet metal strips 10A-10H together form the second end face 13 of the iron core 1. The two end faces 12, 13 lie in the same plane E (or alternatively, are parallel but offset from each other). The sections A1, A5 adjacent to the end faces 12, 13 run perpendicular to the plane E.

[0048] As already mentioned, the sheet metal strips 10A-10H are each C-shaped. An innermost sheet metal strip 10A is surrounded by a next sheet metal strip 10B, which in turn is surrounded by a next sheet metal strip 10C, and so on, up to an outer sheet metal strip 10H, which encompasses the remaining sheet metal strips 10A-10G.

[0049] The metal strips 10A-10H are bonded together over their entire surface using an adhesive 14. The two outer metal strips 10A, 10H are bonded to the next metal strip 10B, 10G, respectively, while the inner metal strips 10B-10G are bonded to the two adjacent metal strips 10A-10H. The adhesive 14 and / or an optional surface coating electrically insulates the individual metal strips 10A-10H from one another to reduce eddy currents.

[0050] Fig. Figure 6 illustrates the individual sheet metal strips 10A-10H before a forming process. In this state, the sheet metal strips 10A-10H are flat. In this example, the sheet metal strips 10A-10H each have the same thickness. They also each have the same width (perpendicular to the thickness). However, in this example, all sheet metal strips 10A-10H have different lengths L (perpendicular to both the width and the thickness). The innermost sheet metal strip 10A in the finished iron core 1 has the shortest length L, while the outermost sheet metal strip 10H in the finished iron core 1 has the longest. As shown in Fig. As shown in Figure 6, the respective difference in length between a sheet metal strip 10A-10G and the next larger one is always the same.

[0051] Fig. Figure 7 illustrates a top view of a sheet metal strip 10H cut from a piece of sheet metal B. The sheet metal strips 10A-10H can be cut or punched from the same piece of sheet metal B or from other pieces.

[0052] Fig. Figure 8 shows a tool 4 with which an iron core 1 can be formed from a stack of 11 sheet metal strips 10A-10H.

[0053] The tool 4 comprises a first tool half 40 and a second tool half 41. The first tool half 40 has a C-shaped contact surface 400. The second tool half 41 has a C-shaped contact surface 410, which is complementary to the contact surface 400 of the first tool half 40. The contact surface 400 of the first tool half 40 is convex, and the contact surface 410 of the second tool half is concave.

[0054] The tool 4 is configured as a press. When the stack 11 is positioned between the tool halves 40 and 41, and the tool halves 40 and 41 are closed (i.e., the second tool half 41 is placed onto the first), the stack 11 is pressed into a C-shape. The second tool half 41 rests on a base 401 of the first tool half 40. A control unit 42 controls the movement of the tool halves 40 and 41 relative to each other.

[0055] Fig. Figure 9 illustrates the first tool half 40 in a top view. It can be seen that the first tool half 40 has several (here, for example, four) contact surfaces 400 arranged side by side. The contact surfaces 400 are connected to each other via the base 401. Similarly, the second tool half 41 has several (here again, four) contact surfaces 410. This allows several iron cores 1 to be produced simultaneously.

[0056] For example, a stack 11 with adhesive already in between is placed into the tool 4 and the tool is closed until the adhesive has hardened.

[0057] As shown by the Fig. 10 and Fig. As can be seen in Figure 11, the tool 4 includes several positioning elements, here by way of example in the form of grooves 411 (alternatively or additionally e.g. in the form of pins), for positioning the sheet metal strips 10A-10H on the tool 4. Fig. Figure 10 shows a cross-section along the in Fig. 11. Section plane AA is shown.

[0058] In the example shown, several grooves 411 are provided, namely six by way of example. These extend according to Fig. 10 parallel to each other. The grooves 411 are formed in the side walls of the receptacle formed by the second tool half 41. In this example, several, namely three, grooves 411 are arranged on each of the two longitudinal sides of the receptacle. In this specific example, one of the grooves 411 is arranged on each of the longitudinal sides at the location of the contact surface 410, which has a kink and on which one of the curvatures K2, K3 is formed. Furthermore, one of the grooves 411 is arranged centrally along each longitudinal side.

[0059] The sheet metal strips 10A-10H also have positioning elements, exemplified here by projections 102. In this example, the projections 102 each have the form of a protruding nose. The projections 102 extend laterally from the sheet metal strips 10A-10H, specifically along both longitudinal sides in the example shown.

[0060] The positioning elements of the sheet metal strips 10A-10H engage with the positioning elements of the second tool half 41 in the tool 4. This prevents the sheet metal strips 10A-10H from slipping during the forming process, particularly in the direction of the longitudinal axis x, which extends along the length of the receptacle and perpendicular to the (smaller) width of the receptacle in the direction of the width axis y and perpendicular to the depth of the receptacle in the direction of the height axis z. During the bending process, the projections 102 slide along the grooves 411 into the receptacle of the second tool half.

[0061] After the sheet metal strips 10A-10H have been formed and fixed together to form the respective iron core 1, the protrusions 102 can be removed, e.g. by milling or cutting.

[0062] With reference to Fig. Section 12 will now describe a method S10 for manufacturing an iron core 1 for an electric machine 2. The method comprises the following steps.

[0063] Step S1: Specifying a shape F for the iron core 1, e.g., the one in Fig. 5 shown form.

[0064] Step S2: Calculate the lengths L of the individual sheet metal strips 10A-10H according to the given shape F, for example the one in Fig. 6 lengths L shown. It can be provided that each of the sheet metal strips 10A-10H has a predetermined length L different from all the other sheet metal strips 10A-10H.

[0065] Step S3: Providing several sheet metal strips 10A-10H of varying lengths, each containing or consisting of iron. Each sheet metal strip 10A-10H can have a different length L than all the other sheet metal strips 10A-10H. Providing the sheet metal strips 10A-10H of varying lengths may involve cutting and / or punching the sheet metal strips 10A-10H.

[0066] Step S4: Arrange the sheet metal strips 10A-10H into a stack 11.

[0067] Step S5: plastic deformation of the stack 11 using tool 4. The deformation is carried out, for example, in such a way that the iron core 1 is formed in a C-shape.

[0068] Step S6: Fixing the sheet metal strips 10A-10H of the stack 11 together. During fixing, adjacent sheet metal strips 10A-10H can be bonded together over their entire surface. Fixing takes place, for example, in the closed tool 4. The adhesive 14 cures there.

[0069] This is how iron core 1 is obtained. Iron core 1 has one or more curvatures K1-K4.

[0070] The result is a C-shaped iron core 1 with perpendicular end faces 12, 13. This leads to reduced costs through improved material utilization, less waste, improved tolerances, and a shorter manufacturing time.

[0071] A method for manufacturing an electrical machine 2 comprises the following steps: Step S10: Produce several iron cores 1 as described above. Step S11: Mounting the iron cores 1 and at least one coil 200 on at least one support 201 to produce a stator 20. Step S12: Mounting a permanent magnet rotor 21 rotatably on the stator 20.

[0072] It is understood that the disclosure is not limited to the embodiments described above and that various modifications and improvements may be made without deviating from the concepts described herein. Any of the features may be used separately or in combination with any other features, provided they are not mutually exclusive, and the disclosure extends to and encompasses all combinations and subcombinations of one or more features described herein. Reference symbol list 1 iron core 10A-10H sheet metal strips 100, 101 first, second end 102 Positioning element (projection) 11 stacks 12, 13 first, second end surface 14 Adhesive 2 electric machine 20 Stator 200 coil 201 carriers 202 Flange 21 Rotor 210 wave flange 211 Permanent magnet 22 warehouses 3 aircraft 30 cabin 31 Battery system 32 propellers 4 tools 40 first tool half 400 square meters of installation area 401 Base 41 second tool half 410 m² of installation area 411 Positioning element (groove) 42 Control unit Section A1-A5 B sheet metal Level E F shape K1-K4 curvature Length L

Claims

[1] Method for producing an iron core (1) for an electric machine (2), comprising: - Providing (S3) several strips of sheet metal of different lengths (10A-10H), each containing or consisting of iron; - Arrange (S4) the metal strips (10A-10H) into a stack (11); and - Forming (S5) the stack (11) using a tool (4) and fixing (S6) the sheet metal strips (10A-10H) of the stack (11) together to obtain the iron core (1) with at least one curvature (K1-K4). [2] Method according to claim 1, wherein the forming (S5) is carried out such that the iron core (1) is formed in a C-shape. [3] Method according to claim 1 or 2, wherein during fixing (S6) adjacent sheet metal strips (10A-10H) are bonded together over a surface area. [4] Method according to any of the preceding claims, further comprising, prior to the provisioning step (S3): - Specifying (S1) a shape (F) for the iron core (1); and - Calculate (S2) the lengths (L) of the individual sheet metal strips (10A-10H) according to the given shape (F). [5] Method according to any of the preceding claims, wherein each of the sheet metal strips (10A-10H) has a length (L) different from all of the other sheet metal strips (10A-10H). [6] Method according to any of the preceding claims, wherein the provision (S3) of the sheet metal strips (10A-10H) of different lengths comprises cutting and / or punching the sheet metal strips (10A-10H). [7] Method according to any of the preceding claims, wherein each of the sheet metal strips (10A-10H) extends from a first end (100) to a second end (101), wherein after forming (S5) and fixing (S6) the first ends (100) jointly describe a first end surface (12) of the iron core (1) and the second ends (101) jointly describe a second end surface (13) of the iron core (1) and wherein the two end surfaces (12, 13) lie in the same plane (E). [8] Method according to any of the preceding claims, wherein the sheet metal strips (10A-10H) have the same thickness and width as each other. [9] Method according to one of the preceding claims, wherein the tool (4) comprises a first tool half (40) with a C-shaped contact surface (400) and a second tool half (41) with a contact surface (410) designed to complement the first tool half. [10] Method according to one of the preceding claims, wherein the tool (4) and / or the sheet metal strips (10A-10H) comprise / comprise at least one positioning element (102, 411) for positioning the sheet metal strips (10A-10H) on the tool (4). [11] Method according to one of the preceding claims, wherein the sheet metal strips (10A-10H) are each flat before the forming step (S5). [12] Method for manufacturing an electric machine (2), comprising: - Manufacturing (S10) several iron cores (1) according to the method according to one of the preceding claims; - Mounting (S11) the iron cores (1) and at least one coil (200) on at least one support (201) to produce a stator (20); and - Mounting (S12) a permanent excitation rotor (21) rotatably on the stator (20). [13] Iron core (1) for an electric machine (2) extending from a first end face (12) to a second end face (13) and having at least one curvature (K1-K4) in between, wherein the first end face (12) is oriented perpendicular to an adjacent section (A1) of the iron core (1) and the second end face (13) is oriented perpendicular to an adjacent section (A5) of the iron core (1), wherein the iron core (1) comprises several sheet metal strips (10A-10H) of different lengths fixed to one another, each comprising or consisting of iron and each extending from the first end face (12) to the second end face (13). [14] Iron core (1) according to claim 13, wherein the iron core (1) is C-shaped, wherein the sheet metal strips (10A-10H) are each C-shaped and an innermost sheet metal strip (10A) is surrounded by a next sheet metal strip (10B), which in turn is surrounded by a next sheet metal strip (10C). [15] Iron core (1) according to claim 13 or 14, wherein the two end faces (12, 13) lie in the same plane (E). [16] Iron core (1) according to any one of claims 13 to 15, wherein the iron core (1) has two, three or four curvatures (K1-K4). [17] Electric machine (2) comprising a stator (20) with one or more iron cores (1) according to any one of claims 13 to 16. [18] Vehicle, in particular aircraft (3), comprising the electric machine (1) according to claim 17.

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