LAMINATED CORE AND METHOD FOR PRODUCING A LAMINATED CORE

Abstract

A method for producing a laminated core is provided in which a plurality of lamination sheets is partially or completely separated from a strip made of a soft magnetic alloy by laser sublimation cutting, the lamination sheets each having a main surface and a thickness d. The main surface of a first of the lamination sheets is stacked on the main surface of a second of the lamination sheets in a direction of stacking and the main surfaces of the first and the second lamination sheets are substance-to-substance joined at a plurality of points by laser welding, a plurality of filler-free joints being formed between the between the first and the second lamination sheets and being entirely surrounded by the main surfaces of the first and the second lamination sheets.

Claims

1. A method for producing a laminated core, comprising: partially or completely separating a plurality of lamination sheets from a strip made of a soft magnetic alloy by laser sublimation cutting, the lamination sheets each having a main surface and a thickness d, stacking the main surface of a first of the lamination sheets on the main surface of a second of the lamination sheets in a direction of stacking, substance-to-substance joining of the main surface of the first and the second lamination sheets by laser welding at a plurality of points, a plurality of filler-free joints being formed between the first and the second lamination sheets and being entirely surrounded by the main surface of the first and the second lamination sheets.

2. A method according to claim 1, wherein for the laser sublimation cutting a first pulsed laser beam from a first laser source is directed over the strip by a first guide means and a first focusing means in order to separate the plurality of lamination sheets from a strip by laser sublimation cutting.

3. (canceled)

4. A method according to claim 2, wherein for the laser welding a second laser beam from a second laser source is positioned on the main surface of the first lamination sheet in the stack by a second guide means and a second focusing means in order to form the joint by laser welding.

5. A method according to claim 2, wherein the first and second guide means and focusing means each have optics, and the optics comprises one or more movable mirrors and the mirror or mirrors being controlled in order to direct and/or focus the laser beam.

6. (canceled)

7. A method according to claim 4, wherein the first laser beam is directed laterally and/or vertically over the strip in order to separate the lamination sheet from the strip, and/or wherein the second laser beam is directed laterally and/or vertically over the strip in order to position the joint on the main surface of the first lamination sheet.

8. (canceled)

9. (canceled)

10. A method according to claim 1, wherein the lamination sheets are partially separated from the strip by laser sublimation cutting and joined substance-to-substance to one another by laser welding, while at least the topmost lamination sheet is joined to the strip.

11. A method according to claim 1, wherein the first and the second lamination sheets are aligned with and tensioned to one another with no lateral offset.

12. A method according to claim 1, wherein the first and the second lamination sheets are aligned by mechanical stops and/or templates that engage in a form fit with the lamination sheets.

13. A method according to claim 1, wherein the first lamination sheet is clamped against the second lamination sheet in the stack by a guide, this guide having openings through which the laser beam can be positioned for the laser welding.

14. A method according to claim 1, wherein the strip is provided in the form of a coil and the strip being wound off the coil and advanced step-by-step.

15. A method according to claim 1, wherein the strip comprises locator holes with which the strip and/or the lamination sheets are positioned, and wherein the strip and/or the lamination sheets are positioned by at least one locator pin that engages in the locator holes in order to position the strip and/or the lamination sheets.

16. (canceled)

17. A method according to claim 1, wherein the strip is provided in the form of a band, a lamination sheet is separated from the band by laser sublimation cutting, the band or a further band is arranged on the lamination sheet and then the band or the further band is clamped and joined to it in at least one position by laser welding, and only then a second lamination sheet is separated from the strip.

18. A method according to claim 1, wherein the strip and the lamination sheets comprise an insulating layer and the lamination sheets with the insulating layer are separated from a strip by laser sublimation and joined substance-to-substance at a plurality of points by laser welding.

19. (canceled)

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. A method according to claim 1, wherein the lamination sheets are partially separated from the strip, at least one microweb joins the lamination sheets mechanically to the strip and the microweb is severed by laser sublimation cutting, laser cutting or mechanical cutting.

25. A method according to claim 1, wherein the strip is amorphous or nanocrystalline or crystalline or as-rolled or final annealed.

26. A method according to claim 1, wherein the laminated core is subsequently annealed.

27. A method according to claim 1, wherein the soft magnetic alloy comprises an FeSi-based alloy with 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,

28. A method according to claim 1, wherein the soft magnetic alloy is a CoFe-based alloy consisting essentially of TABLE-US-00003 5 wt % .sup. ≤Co ≤25 wt % 0.3 wt % ≤V  ≤5.0 wt % 0 wt % ≤Cr ≤3.0 wt % 0 wt % ≤Si.sup.  ≤3.0 wt % 0 wt % .sup. ≤Mn ≤3.0 wt % 0 wt % ≤Al ≤3.0 wt % 0 wt % ≤Ta ≤0.5 wt % 0 wt % ≤Ni ≤0.5 wt % 0 wt % .sup. ≤Mo ≤0.5 wt % 0 wt % .sup. ≤Cu ≤0.2 wt % 0 wt %  ≤Nb ≤0.25 wt % 0 wt % ≤Ti.sup.  ≤0.05 wt % 0 wt % .sup. ≤Ce ≤0.05 wt % 0 wt % .sup. ≤Ca ≤0.05 wt % 0 wt % .sup. ≤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, where Cr+Si+Al+Mn≤3.0 wt %, and up to 0.2 wt % of other impurities.

29. (canceled)

30. A method according to claim 1, wherein the thickness d≤0.5 mm.

31. A method according to claim 2, wherein the laser beam is directed at the main surface of the first lamination sheet so as to form a punctiform j pint and 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.

32. (canceled)

33. (canceled)

34. (canceled)

35. A method according to claim 31, wherein the longitudinal direction is arranged parallel to the lines of the magnetic flux in this plane of the finished laminated cores.

36. A method according to claim 1, wherein the power of the laser beam is adjusted such that the joints each have a depth and the depth of at least one of the joints extending over a maximum of two or a maximum of three or at least three adjacent stacked lamination sheets.

37. (canceled)

38. A method according to claim 1, wherein the first lamination sheet and the second lamination sheet are aligned in relation to one another so as to form a lap joint or a parallel joint.

39. (canceled)

40. A method according to claim 1, wherein at least three lamination sheets being stacked one on top of another and joined to one another by a plurality of joints.

41. A method according to claim 1, 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 a plurality of filler-freer joints that are each entirely surrounded by the main surface of the further and the first lamination sheets.

42. 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 one on top of another in a direction of stacking and adjacent lamination sheets being joined substance-to-substance to one another by a plurality of joints, the joints being filler-free and each entirely surrounded by the main surface of the adjacent lamination sheets, the lamination sheets having edges that are free from burrs.

43. A laminated core according to claim 42, wherein the joints are formed from molten material of the soft magnetic alloy.

44. (canceled)

45. A laminated core according to claim 42, wherein the joints are distributed over the main surface of the lamination sheets.

46. A laminated core according to claim 45, wherein the joints are distributed throughout the volume of the laminated core.

47. A laminated core according to claim 42, 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 being arranged one on top of another in the direction of stacking.

48. (canceled)

49. (canceled)

50. A laminated core according to claim 42, 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.

51. A laminated core according to claim 42, wherein the joints together have a total electrical contact surface of less than 10%-preferably less than 5%, preferably less than 1% of the boundary surface of the lamination sheets.

52. (canceled)

53. (canceled)

54. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Embodiments und examples are described in greater detail below with reference to the drawings.

[0109] FIG. 1 shows a schematic illustration of a method for producing a laminated core.

[0110] FIG. 2a shows a schematic illustration of a cross section of a laminated core with joints according to a first embodiment.

[0111] FIG. 2b shows a schematic illustration of a cross section of a laminated core with joints according to a first embodiment.

[0112] FIG. 2c shows a schematic illustration of various lateral forms of joints for a laminated core.

[0113] FIG. 3 shows a top view of the end face of a laminated core indicating joints.

[0114] FIG. 4 shows a schematic illustration of strips with locator holes with which the strip is positioned by locator pins.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0115] FIG. 1 shows a schematic illustration of a method for producing a laminated core. A metallic strip 1 made of a soft magnetic alloy is provided. The metallic strip 1 may be amorphous or nanocrystalline and may be in an as-rolled or annealed state. For example, the metallic strip 1 may be made of a CoFe-based alloy. The metallic strip has a first main surface 3, a second, opposing main surface 4 and a thickness d. The thickness d may be approximately 0.1 mm. The metallic strip 1 may be provided in the form of a wound coil or a band.

[0116] A plurality of lamination sheets 2, 2′ is partially or completely separated from the strip 1 by laser sublimation cutting. For the laser sublimation cutting a first pulsed laser beam from a first laser source 6 is directed by a first guide means 7 and a first focusing means 8 over the strip 1, typically laterally in an X-direction and a Y-direction and vertically in a Z-direction, to separate the plurality of lamination sheets 2 from a strip 1. The first pulsed laser beam may have picosecond pulses or femtosecond pulses in order to ensure that the material of the strip 1 is evaporated or sublimated along the cutting line. This prevents the material from melting and so forms burr-free edges on the lamination sheets 2. The separated lamination sheets 2, 2′ have a first main surface 3, a second, opposing main surface 4 and a thickness d. The lamination sheets 2, 2′ are then stacked one on top of another to produce a laminated core. The burr-free edges allow the lamination sheets 2, 2′ to be reliably handled automatically and a small gap to be formed between adjacent lamination sheets 2 in the stack to increase the fill factor of the laminated core.

[0117] The first guide means 7 has optics comprising one or more movable mirrors 9. The mirror or mirrors 9 are controlled using a control unit 11 to direct and/or focus the laser beam 5. The first focusing means also has optics that may have a lens 10 for focusing the laser beam 5. The laser source 6 can also be controlled using the control unit 11 in order to set the power and pulse duration of the laser beam, for example.

[0118] Once the lamination sheets 2 have been separated from the strip by laser sublimation cutting, the main surface 4 of a first of the lamination sheets 2 is stacked on the main surface 3 of a second of the lamination sheets 2′ in a direction of stacking 12. The main surfaces 4, 3 of the first and the second lamination sheets 2, 2′ are then substance-to-substance joined at a plurality of points 13 by laser welding, a plurality of filler-free joints 13 being formed between the first and the second lamination sheet 2, 2′ and being entirely surrounded by the main surfaces 4, 3 of the first and the second lamination sheets 2, 2′. In this way a laser-based method is used to separate the lamination sheets 2, 2′ from the strip 1 and to join the stacked lamination sheets 2, 2′ to one another.

[0119] For the laser welding a second laser beam 14 from a second laser source 15 is positioned by a second guide means 16 and a second focusing means 16 on the main surface 3 of the top-most lamination sheet 2 in the stack in order to form the joint 13 by laser welding. The second laser beam 14 may be a continuous laser beam or a pulsed laser beam, the pulse duration typically being greater than for the laser sublimation cutting.

[0120] The second guide means and focusing means 16, 17 have optics comprising one or more movable mirrors 18 or lenses 19. The mirror or mirrors 18 are controlled using a control unit 20 to direct and/or focus the laser beam 14 in order to form the plurality of discrete joints 13.

[0121] Depending on the structure of the production line, the first and second laser sources 6, may be used at the same or at two separate manufacturing stations.

[0122] In some embodiments the lamination sheets 2, 2′ are partially separated from the strip 1 by laser sublimation cutting. For example, the lamination sheet 2, 2′ is first joined mechanically to the strip 1 by one or more microwebs. This method can facilitate the handling of the lamination sheets 2, 2′ during the following process steps including the stacking of the lamination sheets 2, 2′. In some embodiments the lamination sheets 2, 2′ are joined substance-to-substance to one another by laser welding, while at least the top-most lamination is joined to the strip.

[0123] In some embodiments the first and second lamination sheets 2, 2′ are aligned and tensioned with no lateral offset in relation to one another. The first and second lamination sheets 2, 2′ may be aligned by mechanical stops and/or templates, for example, that engage in a form fit with the lamination sheets. In some embodiments the first lamination sheet 2 is clamped against the second lamination sheet in the stack by a guide, this guide having openings through which the laser beam 14 can be positioned for laser welding.

[0124] In some embodiments the strip 1 is provided in the form of a band. A lamination sheet 2 is separated from the band by laser sublimation cutting, the band or a further band is arranged on the top-most lamination sheet in the stack and then the band or the further band is clamped and joined to it by laser welding at at least one position in order to produce a joint 13. Only then is a second lamination sheet 2′ separated from the band.

[0125] In some embodiments the strip 1 is provided in the form of a coil and the strip 1 is wound off the coil and advanced step-by-step. The strip 1 may have locator holes with which the strip is positioned, as illustrated schematically and explained in greater detail in conjunction with FIG. 4.

[0126] In some embodiments the strip 1 and so the lamination sheets 2 have an insulating layer. The lamination sheets 2 are separated with the insulating layer from a strip 1 by laser sublimation cutting and joined substance-to-substance at a plurality of points 13 by laser welding. The insulating layer may be made of MgO or ZrO.sub.2. In this way the insulating layer is separated by the laser beam 5 by laser sublimation cutting. For the laser welding, the second laser beam 14 is directed at the insulating layer on the top-most main surface, which is typically evaporated during the production of the weld spot or weld seam.

[0127] FIG. 2a shows a schematic illustration of a cross section of a laminated core 30 that can be produced using the method illustrated in FIG. 1.

[0128] The laminated core 30 has a plurality of lamination sheets 31 made of a soft magnetic alloy that have been separated by laser sublimation from a strip made of the soft magnetic alloy. For example, the soft magnetic alloy may be a CoFe alloy, e.g. 49 wt % Fe, 49 wt % Co and 2 wt % V+Nb. The lamination sheets 31 each have a main surface 32, an opposing main surface 33 and a thickness d. The thickness d may be approximately 0.2 mm. The lamination sheets 31 are stacked one on on top of another in a direction of stacking 34, the direction of stacking 34 extending perpendicular to the main surfaces 32, 33 of the lamination sheets 31. Adjacent lamination sheets, e.g. lamination sheets 31′ and 31″ in FIG. 2a, are joined to one another by at least one, preferably a plurality of, substance-to-substance joints 35. The joints 35 are filler-free and are each entirely surrounded by the main surface 12 of the lamination sheets 31′, 31″. The plurality of substance-to-substance joints 35 is distributed over the main surface 32 of the lamination sheets 31. The joints 35 may, for example, be formed by laser welding such that the joints 35 are formed of molten material of the soft magnetic alloy that has been resolidified.

[0129] The laminated core 30 may have numerous stacked lamination sheets 31, for example 100 to 500. The joints 35 have a depth t such that they are arranged in two, as illustrated in the first embodiment shown in FIG. 2a, or more than two, for example three, as illustrated in the second embodiment in FIG. 2b, lamination sheets 31 and these lamination sheets are joined at a number of points. In cross section, the laminated core has a plurality of joints 35 that are arranged in different planes 36 of the laminated core 30 such that the lamination sheets 31 are built up by the joints 35 to form a laminated core. The joints 35 are thus distributed throughout the volume of the laminated core 30.

[0130] Outside of the joints 35, adjacent lamination sheets 31 may be separated from one another and/or electrically insulated from one another. The lamination sheets 31 may have an insulating layer that covers at least the main surfaces 32, 33. This insulating layer may, for example, be made of MgO or ZrO.sub.2. The lamination sheets 31 may be coated with the insulating layer individually. In some embodiments, however, the strip is coated with the insulating layer and the lamination sheets 31 are then separated from the strip with the insulating layer on the opposing main surfaces 32, 33. 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 31 in the stack. In some embodiments the insulating layer is applied to both main surfaces 32, 33 using a dipping process, for example.

[0131] In the first embodiment illustrated in FIG. 2a the depth t of the joint is less than 2d, i.e. twice the thickness. As a result, the joint 35 does not extend as far as the lower main surface 33 of the lower lamination sheet 31. This arrangement may be used for all or only some of the joints 35, for example for the bottom-most joints, such that the underside 39 of the laminated core 30 formed by the lower main surface 33 of the bottom-most lamination sheet 38 has no joints and so has a continuous uninterrupted structure.

[0132] In the second embodiment illustrated in FIG. 2b the depth t of the joint is greater than 2d such that the joint 35 is arranged in three adjacent lamination sheets 31, 31′ and 31″. In this embodiment the bottom-most joint 35 extends as far as the underside 39 of the laminated core 30.

[0133] In some embodiments, as in the first and second embodiments shown in FIGS. 1a and 1b, the joints 35 are offset laterally in relation to one another in two adjacent planes 36 of the laminated core 30. It is, however, also possible for a plurality of joints 35 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.

[0134] The laminated cores 30, 30′ have joints 35 which, rather than running along the outer or inner contour of the stack 30, 30′, are arranged on the main surfaces 32, 33 of the individual laminations 31 and between the individual layers of the stack 30, 30′. In contrast to laminated cores in which a plurality of stacked lamination sheets 31 are joined to one another by a weld seam at one end face 37 of the laminated core 30, here the joints 35 are entirely laterally surrounded by the adjacent lamination sheets 31 in which the joint 35 is arranged such that the joint 35 is entirely and uninterruptedly surrounded laterally by the crystalline, amorphous or nanocrystalline material of the lamination sheets 31. With the joints 35 in the laminated core 30, 30′ according to the invention, however, at least the side walls of the joints 35 entirely and uninterruptedly abut the material of the lamination sheets 31. In contrast, when there is a seam on the end face 37 of the laminated core 30 at least part of the seam abuts the air.

[0135] In the top view the joints 35 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. 2c shows a schematic illustration of different lateral forms that can be used for the joints 35. 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.

[0136] FIG. 3 shows a top view of the end face of a laminated core 30 that has the form of a stators 40. The stator 40 has a plurality of teeth 41 that are evenly distributed around an outer ring 42 such that the teeth 41 point towards the centre point or centre axis 43 of the stator 40. FIG. 3 shows examples of joints 35 in schematic form. The joints 35 may be punctiform and be arranged both in the central region of the ring 42 and in the central region of the teeth 41. In other embodiments the joints 35′ have an elongated form such as a line, which can be straight as illustrated in FIG. 3, for example. An elongated joint 35 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 35 not shown in the top view are arranged between lamination sheets located in the stack of the laminated core 30 such that the joint 35 is arranged in a plurality of planes and is distributed throughout the volume of the laminated core 30 in order to join all the lamination sheets substance-to-substance at a number of points to form a laminated core 30.

[0137] The joints 35 are laterally small and distributed over the main surfaces 32, 33 such that they can be produced with a low-energy laser beam, thereby reducing the risk of damaging the lamination sheet 31 by erroneously making a hole in the lamination sheet, for example. Consequently, the sheet thickness of the individual layers of the laminated cores 30 can be very low, typically in the region of 0.1 mm or even lower.

[0138] 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.

[0139] The laminated cores 30, 30′ may also have joints 35 between the lamination sheets 31 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 31 can be adapted to the locally occurring magnetic flux density within the layers during operation of the laminated core 30. The joints 35 can be designed so as to reduce any negative influences on the magnetic properties of the layers.

[0140] FIG. 4 shows cross sections and a top view of a strip 1 with at least one locator hole 21 with which the strip 1 is positioned and/or the lamination sheets 2 are positioned. The locator hole 21 may be formed in the strip 1 by punching using a punching tool 23. The strip 1 and/or the lamination sheets 2, 2′ can be moved by at least one locator pin 22 that engages in the locator hole or holes 20 in order to position the strip 1 or the lamination sheets 2. In some embodiments the locator holes 17 are used to position the strip in a plurality of manufacturing steps. For example, the cutting contours 24, 24′ for the lamination sheets 2, 2′ can be produced one after another, as illustrated schematically in FIG. 4, the locator holes 21 being used to align the cutting contours 24′ formed in the second step more accurately that the cutting contours 24 formed in the first step.

[0141] The method for producing a laminated core can be automated in different manners.

[0142] In one embodiment individual laminations are completely separated from a sheet by laser sublimation, stacked one on top of another manually layer by layer and joined to the stack by a plurality of welded spots distributed over the main surface. A manual method of this type can be used for the production for samples, for example.

[0143] A pulsed laser source is used for the laser sublimation method. A solid-state fibre laser, for example, may be used for the laser welding. With this method a scanner optics with a plan field lens permits the rapid and accurate positioning of the focal point in the work chamber of the laser system by directing the laser beam by mirrors, thereby making it possible to produce all the joints on one layer in one tensioning operation. Furthermore, the programmable optics can, where necessary, be used to adapt the focal position to the current stack height. Depending on the design of the joint, continuous-wave or pulsed-wave laser welding can be used. This manual embodiment of the method is particularly suitable for the production of samples and prototypes in small quantities.

[0144] In one embodiment each layer is aligned by an appropriate device and clamped to the existing stack before the laser spot welding is carried out.

[0145] 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 housing.

[0146] The purpose of clamping the layers is to ensure a minimum air gap between them after welding. This clamping 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.

[0147] In a second embodiment individual method steps such as the stacking, positioning and clamping 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 way of a grabber/suction cup, slider or turntable for welding in the work chamber of the laser system, where they are automatically clamped 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.

[0148] In a third embodiment the method is further automated. In the third embodiment a sheet metal strip or a series of metal plates (both referred to below as “bands”) are fed to a system. This can be done by way of a decoiler, guide rollers and 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 band by laser sublimation. Here the separated lamination may remain joined substance-to-substance with the band by microwebs.

[0149] Loose scrap can be blown out of the band by compressed air and removed from the system by scrap chutes, for example. The first lamination is placed in a positioning device by a feed cycle. 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 band. The next feed cycle positions a second lamination above the first in the same manner.

[0150] In a manner similar to the second partially automated embodiment, the two laminations are now automatically clamped together by a guide and then joined by repeated laser welding. In a further feed cycle the scrap remaining in the band (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 band. 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.

[0151] 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 in conjunction with pin stops to position the band (ventilated infeed). This ensures the exact positioning of the cutting and welding operations carried out at the individual stations in relation to one another.

[0152] 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.

[0153] 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.

[0154] According to the invention a connection 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 connection points produces a comparatively small electrical contact surface between the layers, which minimises eddy current losses. The small connection point size also simplifies this method of positioning the connection points, which impairs the magnetic flux as little as possible.

[0155] 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 flux are advantageous. The magnetic flux is then only impaired by the width of the seam, so reducing the cross section without imperfections available for the flux. Where a seam runs parallel to the flux, its length has no influence on flux 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.

[0156] 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.