LAMINATED CORE, ELECTRIC MACHINE, TRANSFORMER AND METHOD FOR PRODUCING A LAMINATED CORE

Abstract

A laminated core comprising a plurality of lamination sheets made of a soft magnetic alloy is provided. The lamination sheets have a main surface and a thickness d. The main surfaces of the lamination sheets are stacked one on top of another in a direction of stacking. Adjacent lamination sheets are joined to one another by a plurality of substance-to-substance joints, the joints being filler-free and entirely surrounded by the main surfaces of the adjacent lamination sheets.

Claims

1. A laminated core, comprising: a plurality of lamination sheets made of a soft magnetic alloy that each have a main surface and a thickness d, the main surfaces of the lamination sheets being stacked on top of another in a direction of stacking and adjacent lamination sheets being joined together by a plurality of substance-to-substance joints, the joints being filler-free and entirely surrounded by the main surfaces of the adjacent lamination sheets.

2. A laminated core according to claim 1, wherein the joints are laterally entirely bordered by the crystalline material of the lamination sheets.

3. A laminated core according to claim 1, wherein the joints are made of molten material of the soft magnetic alloy.

4. (canceled)

5. (canceled)

6. (canceled)

7. A laminated core according to claim 1, wherein the joints are distributed throughout the volume of the laminated core.

8. A laminated core according to claim 1, wherein the joints are arranged in a plurality of planes of the laminated core and have a different lateral arrangement in the planes and/or are arranged one on top of another in the direction of stacking.

9. A laminated core according to claim 1, wherein the joints in the plane of the main surface are punctiform, circular, elongated, corner-shaped, annular, curved, straight, X-shaped, Y-shaped, V-shaped or U-shaped.

10. (canceled)

11. (canceled)

12. (canceled)

13. A laminated core according to claim 1, wherein d≤0.5 mm.

14. A laminated core according to claim 1, wherein the joints have a depth and the depth of at least one of the joints extends over a maximum of two or a maximum of three or at least three adjacent stacked lamination sheets.

15. (canceled)

16. (canceled)

17. A laminated core according to claim 1, wherein together the joints have a total electrical contact surface of less than 10% of the boundary surface of the lamination sheets.

18. A laminated core according to claim 1, wherein the lamination sheets are separated from a strip and each have a direction that is parallel to the direction of rolling of the strip, the lamination sheets have a thickness that varies over the area of the lamination sheet, and wherein the direction of the lamination sheets in the laminated core varies.

19. (canceled)

20. A laminated core according to claim 1, wherein the soft magnetic alloy is an Fe—Si-based alloy comprising 2 to 4.5 wt % of at least one element from the group comprising Si and Al, the rest Fe and unavoidable impurities, or a CoFe-based alloy comprising 35 to 55 wt % Co and up to 2.5 wt % V, the rest Fe and unavoidable impurities, or a CoFe-based alloy comprising 45 wt %≤Co≤52% wt %, 45 wt %≤Fe≤52% wt %, 0.5 wt %≤V≤2.5% wt %, the rest Fe and unavoidable impurities, or a CoFe-based alloy comprising 35 wt %≤Co≤55% wt %, 0 wt %≤Ni≤0.5% wt %, 0.5 wt %≤V≤2.5% wt %, the rest Fe and unavoidable impurities, or a CoFe-based alloy comprising 35 wt %≤Co≤55% wt %, 0 wt %≤V≤2.5% wt %, 0 wt %≤(Ta+2Nb)≤1% wt %, 0 wt %≤Zr≤1.5% wt %, 0 wt %≤Ni≤5% wt %, 0 wt %≤C≤0.5% wt %, 0 wt %≤Cr≤1% wt %, 0 wt %≤Mn≤1% wt %, 0 wt %≤Si≤1% wt %, 0 wt %≤Al≤1% wt %, 0 wt %≤B≤0.01% wt %, the rest Fe and unavoidable impurities, or a CoFe-based alloy comprising 5 to 25 wt % Co, 0.3 to 5.0 wt % V, the rest Fe and unavoidable impurities.

21. A laminated core according to claim 1, wherein the soft magnetic alloy being a CoFe-based alloy consists essentially of TABLE-US-00002   5% wt % ≤ Co ≤ 25% wt % 0.3% wt % ≤ V ≤ 5.0% wt % 0% wt % ≤ Cr ≤ 3.0% wt % 0% wt % ≤ Si ≤ 3.0% wt % 0% wt % ≤ Mn ≤ 3.0% wt % 0% wt % ≤ Al ≤ 3.0% wt % 0% wt % ≤ Ta ≤ 0.5% wt % 0% wt % ≤ Ni ≤ 0.5% wt % 0% wt % ≤ Mo ≤ 0.5% wt % 0% wt % ≤ Cu ≤ 0.2% wt % 0% wt % ≤ Nb ≤ 0.25% wt % 0% wt % ≤ Ti ≤ 0.05% wt % 0% wt % ≤ Ce ≤ 0.05% wt % 0% wt % ≤ Ca ≤ 0.05% wt % 0% wt % ≤ Mg ≤ 0.05% wt % 0% wt % ≤ C ≤ 0.02% wt % 0% wt % ≤ Zr ≤ 0.1% wt % 0% wt % ≤ O ≤ 0.025% wt % 0% wt % ≤ S ≤ 0.015% wt % the rest iron, Cr+Si+Al+Mn being≤3.0% wt %, and up to 0.2 wt % other impurities.

22. A laminated core according to claim 21, wherein 10 wt %≤Co≤20% wt %, or 0.5 wt %≤V≤4.0% wt %, or 0.1 wt %≤Cr≤2.0% wt %, or 0.1 wt %≤Si≤2.0% wt %, and/or the sum formula being 0.1 wt %≤Cr+Si+Al+Mn≤1.5% wt %.

23. An electric machine comprising a rotor and a stator or having an armature and a stator, the stator comprising a laminated core according to claim 1.

24. (canceled)

25. A transformer having a laminated core according to claim 1.

26. (canceled)

27. A method for producing a laminated core, comprising: providing a plurality of lamination sheets made of a soft magnetic alloy and having a main surface and a thickness d, stacking the main surface of a first lamination sheet on the main surface of a second lamination sheet in a direction of stacking, substance-to-substance joining of the first and the second lamination sheets by means of a plurality of filler-free joints that are entirely surrounded by the main surfaces of the first and second lamination sheets.

28. A method according to claim 27, wherein the first lamination sheet is substance-to-substance joined to the second lamination sheet by means of laser welding or laser spot welding to form a joint.

29. A method according to claim 27, wherein a laser beam is directed in one or both of a lateral direction in order to position the joint on a first lamination sheet and a vertical direction.

30. (canceled)

31. A method according to claim 29, wherein the laser beam is directed at the main surface of the first lamination sheet so as to form a punctiform joint.

32. A method according to claim 29, wherein the laser beam is directed over the main surface of the first lamination sheet so as to form an elongated joint with a longitudinal direction.

33. (canceled)

34. (canceled)

35. A method according to claim 32, wherein the longitudinal direction is arranged parallel to the lines of the magnetic flow in this plane of the finished laminated core.

36. (canceled)

37. (canceled)

38. A method according to claim 27, wherein the first lamination sheet and the second lamination sheet are aligned in relation to one another to form a lap joint or a parallel joint.

39. (canceled)

40. A method according to claim 27, wherein at least three lamination sheets are stacked one on top of another and joined to one another by means of a plurality of joints.

41. A method according to claim 27, further comprising: stacking at least one further lamination sheet on the second lamination sheet and then substance-to-substance joining the further lamination sheet and the first lamination sheet by means of a plurality of filler-free joints that are entirely surrounded by the main surface of the further and the first lamination sheets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Embodiments und examples are described in greater detail below with reference to the drawings.

[0057] FIG. 1a shows a schematic illustration of a cross section of a laminated core with joints according to a first embodiment.

[0058] FIG. 1b shows a schematic illustration of a cross section of a laminated core with joints according to a first embodiment.

[0059] FIG. 1c shows a schematic illustration of various lateral forms of joints for a laminated core.

[0060] FIG. 2 shows a top view of the end face of a laminated core indicating joints.

[0061] FIG. 3 shows a scanning electronic microscope image of a top view of a punctiform joint.

[0062] FIG. 4 shows a metallographic section of a cross section of a joint that extends over three lamination sheets.

[0063] FIG. 5 shows an optical microscope image of a top view of an elongated joint.

[0064] FIG. 6 shows a metallographic cross section of a cross section of an elongated joint.

[0065] FIG. 7 shows a side view of a laminated core.

[0066] FIG. 8a shows a static measurement of the initial magnetisation curve of a laminated core.

[0067] FIG. 8b shows a static measurement of the permeability of a laminated core.

DETAILED DESCRIPTION

[0068] FIG. 1a shows a schematic representation of a cross section of a laminated core 10. The laminated core 10 has a plurality of lamination sheets 11 made of a soft magnetic alloy. The soft magnetic alloy may, for example, be a CoFe-alloy, e.g. 49 wt % Fe, 49 wt % Co und 2 wt % V+Nb. The lamination sheets 11 each have a main surface 12, an opposing main surface 13 and a thickness d. The thickness d may be approximately 0.1 mm. The lamination sheets 11 are stacked one on top of another in a direction of stacking 14, this direction of stacking 14 extending perpendicular to the main surfaces 12, 13 of the lamination sheets 11. Adjacent lamination sheets, e.g. lamination sheets 11′ and 11″ in FIG. 1a, are joined to one another by at least one at least, preferably a plurality of, substance-to-substance joints 15. The joints 15 are filler-free and are each entirely surrounded by the main surface 12 of the lamination sheets 11′, 11″. The plurality of substance-to-substance joints 15 are distributed over the main surface 12 of the lamination sheets 11. The joints 15 may be made by laser welding, for example, such that the joints 15 are formed of molten material of the soft magnetic alloy that has resolidified.

[0069] The laminated core 10 may comprise numerous stacked lamination sheets 11, e.g. 100 to 500. The joints 15 have a depth t such that they are arranged in two, as illustrated in the first embodiment shown in FIG. 1a, or more than two, e.g. three as illustrated in the second embodiment shown in FIG. 1b, lamination sheets 11, and these lamination sheets are joined to one another at certain points. In cross section, the laminated core 10 has a plurality of joints 15 that are arranged in different planes 16 of the laminated core 10 such that the lamination sheets 11 are built up by the joints 15 to form a laminated core. As a result, the joints 15 are distributed throughout the volume of the laminated core 10.

[0070] Outside of the joints 15, adjacent lamination sheets 11 may be separated from one another and/or electrically insulated from one another. The lamination sheets 11 may have an insulating layer that covers at least the main surfaces 12, 13. This insulating layer may, for example, be made of MgO or ZrO.sub.2. The lamination sheets 11 may be coated with the insulating layer individually. In some embodiments, however, the strip is coated with the insulating layer and the lamination sheets 11 are then separated from the strip with the insulating layer on the opposing main surfaces 12, 13. It is possible to coat only one of the main surfaces with the insulating layer and to arrange the insulating layer between adjacent lamination sheets 11 in the stack. In some embodiments the insulating layer is applied to both main surfaces 12, 13 using a dipping process, for example.

[0071] In the first embodiment illustrated in FIG. 1a the depth t of the joint is less than 2d, i.e. twice the thickness. As a result, the joint 15 does not extend as far as the lower main surface 13 of the lower lamination sheet 11. This arrangement may be used for all or only some of the joints 15, for example for the bottom-most joints, such that the underside 19 of the laminated core 10 formed by the lower main surface 13 of the bottom-most lamination sheet 18 has no joints and so has a continuous uninterrupted structure.

[0072] In the second embodiment illustrated in FIG. 1b the depth t of the joint is greater than 2d such that the joint 15 is arranged in three adjacent lamination sheets 11, 11′ and 11″. In this embodiment the bottom-most joint 15 extends as far as the underside 19 of the laminated core 10.

[0073] In some embodiments, as in the first and second embodiments shown in FIGS. 1a and 1b, the joints 15 are offset laterally in relation to one another in two adjacent planes 16 of the laminated core 10. It is, however, also possible for a plurality of joints 15 to be arranged vertically one on top of another. Depending on the depth of the joints, the vertically aligned joints may overlap vertically or abut one another vertically so as to form a column of re-solidified molten material of the soft magnetic alloy.

[0074] The laminated cores 10, 10′ have joints 15 which, rather than extending along the outer or inner contour of the stack 10, 10′, are arranged on the main surfaces 12, 13 of the individual laminations 11 and between the individual layers of the stack 10, 10′. In contrast to laminated cores in which a plurality of stacked lamination sheets 11 are joined to one another by a weld seam at one end face 17 of the laminated core 10, here the joints 15 are entirely laterally surrounded by the adjacent lamination sheets 11 in which the joint 15 is arranged such that the joint 15 is entirely and uninterruptedly surrounded laterally by the crystalline, amorphous or nanocrystalline material of the lamination sheets 11. With the joints 15 in the laminated core 10, 10′ according to the invention, however, at least the side walls of the joints 15 entirely and uninterruptedly abut the material of the lamination sheets 11. In contrast, when there is a seam on the end face 17 of the laminated core 10 at least part of the seam abuts the air.

[0075] In the top view the joints 15 can have different lateral forms. It is also possible to use joints of different lateral form and/or different depth in the same laminated core. FIG. 1c shows a schematic representation of different lateral forms that can be used for the joints 15. For example, the joints may be a circle, an ellipse, part of a circle, a straight or curved line, a polygon or oscillate about a given path in the form of a ring or a straight line.

[0076] FIG. 2 shows a top view of the end face of a laminated core 10 that has the form of a stators 20. The stator 20 has a plurality of teeth 21 that are evenly distributed around an outer ring 22 such that the teeth 21 point towards the centre point or centre axis 23 of the stator 20. FIG. 2 shows examples of joints 15 in schematic form. The joints 15 may be punctiform and be arranged both in the central region of the ring 22 and in the central region of the teeth 21. In other embodiments the joints 15′ have an elongated form such as a line, which can be straight as illustrated in FIG. 2, for example. An elongated joint 15 may also have other forms, e.g. a curved shape or the shape of a circular ring, or be X-shaped, V-shaped, etc. Other joints 15 not shown in the top view are arranged between lamination sheets located in the stack of the laminated core 10 such that the joint 15 is arranged in a plurality of planes and is distributed throughout the volume of the laminated core 10 in order to join all the lamination sheets substance-to-substance joint at certain points to form a laminated core 10.

[0077] The joints 15 are laterally small and distributed over the main surfaces 12, 13 such that they can be produced with a low-energy laser beam, thereby reducing the risk of damaging the lamination sheet 11 by erroneously making a hole in the lamination sheet, for example. Consequently, the sheet thickness of the individual layers of the laminated cores 10 can be very low, typically in the region of 0.1 mm or even lower.

[0078] As a result of the laser welding process the laminated cores may have very small joints. In the case of spot welding, weld spot diameters in the region of 10 μm to 1000 μm, 10 μm to 500 μm or 20 μm to 60 μm can be achieved. In the case of linear seams, the joints may have seams of the same width, i.e. a width of 10 μm to 1000 μm, 10 μm to 500 μm or 20 μm to 60 μm, and a length L, where L>B. The electrical contact surface between the layers can be reduced to a maximum of 10% or 5% or 1% of the boundary surface, for example. This increases the electrical resistance between the individual layers and so reduces eddy current losses.

[0079] The laminated cores 10, 10′ may also have joints 15 between the lamination sheets 11 that can vary in form, size, number and position on the cross section from lamination sheet to lamination sheet. Moreover, the form, size, number and position of the lamination sheets 11 can be adapted to the locally occurring magnetic flow density within the layers during operation of the laminated core 10. The joints 15 can be designed so as to reduce any negative influences on the magnetic properties of the layers.

[0080] The laminated core according to the invention can be produced by means of various methods.

[0081] In one embodiment individual laminations are completely separated from a sheet, stacked manually layer by layer one on top of the other and joined to the stack by means of a plurality of welded points distributed over the main surface.

[0082] In one embodiment each layer is aligned using an appropriate device and clamped to the existing stack before laser spot welding is carried out.

[0083] The purpose of this alignment is to ensure the complete overlapping of the layers with no lateral offset and no undesirable relative rotation about the longitudinal axis of the stack. Mechanical stops and template elements that engage in a form fit with geometrical elements of the individual layers, for example, can be used to perform this alignment. External and internal diameters, tooth flanks and locating elements fitted by the stack manufacturer, for example, are suitable for positioning the finished stacks on the motor/generator shaft or in a house.

[0084] The purpose of tensioning the layers is to ensure a minimum air gap between them after welding. This tensioning can be carried out using a guide, for example, that presses an individual lamination flat against the top-most lamination of the already joined stack and contains local openings to permit welding. Here either the guide may be pressed against the stack or the stack pressed against the guide. The option of a fixed guide offers the advantage of providing a fixed focal point location for the laser welding operation.

[0085] For the laser welding a solid-state fibre laser, for example, may be used. With this method a scanner objective permits the rapid and accurate positioning of the focal point in the work chamber of the laser system by directing the laser beam by means of mirrors, thereby making it possible to produce all the joints on one layer in one tensioning operation. Furthermore, the programmable objective can, where necessary, be used to adapt the focal position to a given stack height. Depending on the design of the joint, continuous-wave or pulsed-wave laser welding can be used. A scanner objective with a plane field lens, for example, can be used to position the laser beam perpendicularly on the surface, while the laser beam is guided over the surface to position the joint exactly.

[0086] This manual embodiment of the method is particularly suitable for the production of samples and prototypes in small quantities.

[0087] In a second embodiment individual method steps such as the stacking, positioning and tensioning of the laminations are automated such that the entire method is partially automated. To this end, ready cut laminations are fed in a magazine or connected by microwebs in a metal strip, for example, to the automatic system, which then transfers them by means of a grabber/suction cup, slider or turntable for welding in the work chamber of the laser system, where they are automatically tensioned and joined substance-to-substance at a plurality of points to the lamination sheet or sheets below. Once the desired stack height is reached, the partially automated process comes to an end and the finished stack can be removed. The stack height can be determined by an integrated height measurement device or by a layer-counting function in the automated system.

[0088] In a third embodiment the method if further automated. In the third embodiment a sheet metal band or a series of metal plates (both referred to below as “strips”) are fed to a system. This can be done by means of a decoiler, guide rollers or a feeder device, as used in punching technology. With small sheet thicknesses there is no need for straightening to remove any coil set that may be present. The contour of a first lamination is cut from the strip using an integrated cutting tool. Once cut out, the lamination remains substance-to-substance joined to the strip either along the entire outer contour or by microwebs.

[0089] The cutting of the lamination contour can be divided between a plurality of stations and carried out separately in one or more feed cycles. At the first stations the parts of the cut that produce loose scrap are carried out. This scrap falls from the strip under the effect of gravity and in some cases assisted by being blown out using compressed air, for example, and is removed from the system by means of scrap chutes, for example. A feed cycle places the first lamination in a positioning device. Here the microwebs are either severed perpendicular to the infeed by remote laser cutting or by a further tool movement and the lamination thus removed from the strip. The next feed cycle positions a second lamination above the first in the same manner.

[0090] In a manner similar to the second partially automated embodiment, the two laminations are now automatically tensioned together by a guide and then joined by repeated laser welding. In a further feed cycle the scrap remaining in the strip (the “scrap lattice”) is transported out of the work chamber and the next lamination is positioned above the stack already joined. The stack grows layer by layer as the process is repeated, the already joined laminations being removed as a growing stack in a second cycle direction perpendicular to the strip. The second cycle direction may, for example, take the form of a vertical movement of the lamination positioning device. Alternatively, the focal position can be adjusted by moving the laser vertically.

[0091] If the individual operations are separated as in this third embodiment, pilot holes can be cut at the first station and then used at subsequent stations pin stops to position the strip (ventilated infeed). This ensures the exact positioning in relation to one another of the cutting and welding operations carried out at the individual stations.

[0092] In all the preferred embodiments described below the term “joint” is always used to refer to a joint produced by laser welding in the form of a lap joint according to the third embodiment.

[0093] In a third embodiment of a laminated core the laminated core has a plurality of punctiform joints with a diameter of not more than 20-200 μm that are distributed over the contact surface of at least two layers to be joined, i.e. over the main surfaces of adjacent lamination sheets. This type of distribution, which ensures a joint between layers that is sufficiently strong for the further processing and subsequent use of the stack and at the same time has no more than a minimal adverse effect on the desired electromagnetic properties of the stack, is advantageous. Laminated cores according to the invention have a large number and fine distribution of joints. As a consequence, external loads in individual joints cause comparatively low stresses since the mechanical stresses are distributed over a plurality of joints and the lever arms between the load application points and the joints are shortened. Such external loads are created by punctiform and linear contact surfaces and relative movements when joining the stacks to shafts and housings, for example.

[0094] According to the invention a tying point can be located at any point on the lamination without requiring any change to the design of the system. In this way it is possible to effectively prevent local or complete delamination and the splitting of the laminations in the region of delicate structures (such as teeth), for example. Despite their plurality, the small size of the tying points produces a comparatively small electrical contact surface between the layers, which minimises eddy current losses. The small tying point size also simplifies this method of positioning the tying points, which impairs the magnetic flow as little as possible.

[0095] In a fourth embodiment other forms of joints, which can be freely selected by setting the path of the laser dot, are used alongside punctiform joints. The forms may, for example, be straight lines, circles, polygons or other curved lines. Linear seam courses that run parallel to the lines of the magnetic flow are advantageous. The magnetic flow is then only impaired by the width of the seam, so reducing the cross section without imperfections available for the flow. Where a seam runs parallel to the flow, its length has no influence on flow impairment and can be optimised with regard to joint strength and electrical contact surface. This shifts the comprise between electrical contact, magnetic influence and joint strength towards higher joint strengths.

[0096] In a fifth embodiment the position of the joints is varied from layer to layer in order to lengthen the eddy current paths created by the electrical contact. Here the laser is set such that as few layers as possible (ideally only two) are joined at each joint. Here the bottom-most layer should not be fused over the entire thickness. This arrangement can be used in the third and fourth embodiments, i.e. with punctiform and elongated joints.

[0097] In a series of tests sample ring stacks of VACODUR 49 (VD49) were produced by means of laser spot welding. The stacks produced were subjected to metallographic examination and measurement.

[0098] Laser-cut sample rings of VACODUR 49 were fed manually and individually to a clamping device and positioned using a mandrel. Once a sample ring had been fed in, the lid was closed and clamped by screwing to the lower part of the device. The device was positioned in the work chamber of a laser machining centre using stops. The clamped and tensioned layer was laser welded to the already joined sample ring stack below it at a plurality of points on the main surface through the openings in the lid. Following the welding operation, the device was removed, the lid taken off and the next layer or the next sample ring was clamped as described above. The process was repeated until 50 layers of sample rings had been welded to form a ring stack. Four ring stacks were produced in total, varying the laser technology parameters and the form (point and line) and position (always at the same point or alternating from layer to layer) of the joint.

[0099] FIG. 3 shows a scanning electron microscope image of a top view of an example of a punctiform joint and FIG. 4 shows a metallographic section through a punctiform joint in a laminated core. A substance-to-substance joint, in this case comprising three layers, can be seen in cross section. In this embodiment the joints are produced by the repeated welding of two layers at the same point.

[0100] FIG. 5 shows an optical microscope image of a top view of an example of a linear joint.

[0101] FIG. 6 shows a metallographic crosssection through a linear joint. The section cut was not parallel to the course of the seam as a result of which the substance-to-substance joint is visible in the right-hand part of the image only (the crosssection extends out of the seam at the left).

[0102] FIG. 7 shows a microscope image of a side view of a ring stack produced in the tests in which the stacked lamination sheets can be seen. It also shows a very good fill factor since the distances between the lamination sheets are small.

[0103] FIGS. 8a and 8b show static measurements of the initial magnetisation curve (FIG. 8a) and the permeability (FIG. 8b) of the ring stacks produced. The ring stacks were subjected to annealing following stacking. Rings 2-4 were laser spot welded with various parameters and compared with a reference stack of loosely stacked rings in the measurement. The lack of any significant difference to the comparison stack indicates that there is no irreversible influence of the stacking process including laser spot welding on the static soft magnetic properties of the material processed.