LAMINATED CORE AND METHOD FOR THE PRODUCTION OF A LAMINATED CORE

Abstract

A method for the production of a laminated core is provided. A plurality of laminations are provided that are made of a soft-magnetic CoFe alloy and that have a first main surface and a second main surface that is located opposite the first main surface. An adhesive is applied to the first main surface of a first of the laminations by means of a printing process. The adhesive is then transferred to a partially cured B-stage. A second main surface of a second of the laminations is stacked on the B-stage adhesive, which is located on the first main surface of the first lamination, thereby forming a stack of loose laminations. The stack or the adhesive in the stack is cured, the adhesive thus being transferred to the fully cured C-stage in order to bond the first and second laminations to one another and so produce the laminated core.

Claims

1. A method for producing a laminated core, the method comprising the following: providing a plurality of laminations made of a soft-magnetic CoFe alloy, each having a first main surface and a second main surface that is located opposite the first main surface; applying an adhesive to the first main surface of a first of the laminations by means of a printing process; transferring the adhesive to a partially cured B-stage; stacking a second main surface of a second of the laminations on the B-stage adhesive that is located on the first main surface of the first laminations, thereby forming a stack of loose laminations; curing the stack, the adhesive thus being transferred to the fully cured C-stage in order to bond the first and second laminations together and so produce the laminated core.

2. A method according to claim 1, wherein the printing process comprises a screen printing process, a stencil printing process, a pad printing process, or an ink-jet printing process.

3. A method according to claim 1, wherein during curing, a pressure is exerted on the stack, and the curing is carried out at between 70? C. and 250? C. for between 10 minutes and 8 hours.

4. A method according to claim 3, wherein the pressure is between 0.01 MPa und 10 MPa.

5. A method according to claim 3, wherein the pressure is exerted by means of a press.

6. A method according to claim 1, wherein the adhesive is applied to the first main surface of the first lamination in a pattern of coated and uncoated regions.

7. A method according to claim 6, wherein the coated regions of the pattern have the form of dots or lines.

8. A method according to claim 6, wherein the distance between adjacent coated regions lies between 0.01 mm and 100 mm.

9. A method according to claim 1, wherein between 1% and 90% of the first main surface is coated with the adhesive.

10. A method according to claim 1, wherein the adhesive has a layer thickness of 0.5 ?m to 50 ?m.

11. A method according to claim 1, wherein the laminations each comprise the contour of a stator or a rotor.

12. A method according to claim 1, wherein at least one of the first and second main surfaces of the laminations comprises an electrically insulating layer.

13. A method according to claim 1, further comprising: separating the laminations from a strip, at least one side of this strip being coated with an electrically insulating layer.

14. A method according to claim 13, wherein the laminations are separated from the strip by means of punching or cutting.

15. A method according to claim 1, wherein the soft-magnetic CoFe alloy has a composition of: 35 to 55 wt. % Co and up to 2.5 wt. % V, the rest being Fe and unavoidable impurities, or 45 wt. %?Co?52 wt. %, 45 wt. %?Fe?52 wt. %, 0.5 wt. %?V?2.5 wt. %, the rest being Fe and unavoidable impurities, or 35 wt. %?Co?55 wt. %, 0 wt. %?Ni?0.5 wt. %, 0.5 wt. %?V?2.5 wt. %, the rest being Fe and unavoidable impurities, or 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 being Fe and unavoidable impurities, or 5 to 25 wt. % Co, 0.3 to 5.0 wt. % V, 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. %, the rest being Fe and unavoidable impurities.

16. A method according to claim 1, wherein the adhesive further comprises an electrically insulating filler and/or a marker.

17. A method according to claim 1, wherein the laminations are further aligned in the stack.

18. A method according to claim 1, wherein the adhesive is arranged on the first main surface of the first lamination in such a thickness and pattern that no adhesive runs out between the edges of the stack during curing.

19. A method according to claim 1, wherein the curing of the stack is carried out in a furnace.

20. A method according to claim 19, wherein the furnace is a heating sleeve, an induction coil, a convection furnace or an NIR furnace.

21. A method according to claim 1, wherein the adhesive comprises an epoxy resin-based adhesive or a polyurethane resin-based adhesive or an acrylic resin-based adhesive.

22. A laminated core comprising: a plurality of laminations comprising a soft-magnetic CoFe alloy, each having a first main surface and a second main surface that is located opposite the first main surface and being arranged in a stack, wherein an adhesive is arranged between the laminations, the adhesive comprising a composition that can be transferred to a B-stage and that has a thickness of 0.1 ?m to 10 ?m.

23. A laminated core according to claim 22, wherein the adhesive further comprises an electrically insulating filler and/or one or more additives.

24. A laminated core according to claim 22, wherein at least one of the first and second main surfaces of the laminations further comprises an electrically insulating layer, and the adhesive is in contact with the electrically insulating layer.

25. A laminated core according to claim 24, wherein the electrically insulating layer comprises an oxide of Mg or Al or Zr.

26. A laminated core according to claim 22, the soft-magnetic CoFe alloy having a composition of: 35 to 55 wt. % Co and up to 2.5 wt. % V, the rest being Fe and unavoidable impurities, or 45 wt. %?Co?52 wt. %, 45 wt. %?Fe?52 wt. %, 0.5 wt. %?V?2.5 wt. %, the rest being Fe and unavoidable impurities, or 35 wt. %?Co?55 wt. %, 0 wt. %?Ni?0.5 wt. %, 0.5 wt. %?V?2.5 wt. %, the rest being Fe and unavoidable impurities, or 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 being Fe and unavoidable impurities, or 5 to 25 wt. % Co, 0.3 to 5.0 wt. % V, 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. %, the rest being Fe and unavoidable impurities.

27. An electric machine, comprising: a laminated core according to claim 22, wherein the laminated core comprises the form of a stator or a rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1A shows a schematic top view of a laminated core.

[0046] FIG. 1B shows a schematic cross section of the laminated core from FIG. 1A.

[0047] FIG. 2A shows a top view of a lamination with an adhesive pattern.

[0048] FIG. 2B shows an enlarged view of FIG. 2A.

[0049] FIG. 2C shows a profile of the adhesive pattern from FIG. 2A.

[0050] FIG. 3 shows a flow diagram of the method for the production of a laminated core.

[0051] FIG. 4 shows the measured bond strength of various adhesives.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0052] FIG. 1A shows a schematic top view and FIG. 1B shows a cross sectional view of a laminated core 10. The laminated core 10 comprises a large number of laminations 11 that are arranged in a stack 12. FIG. 1B shows four laminations 11 in cross section. However, an actual laminated core typically contains hundreds or thousands of laminations. The laminations 11 are formed of a soft-magnetic alloy such as a cobalt-iron alloy, e.g. an alloy based on 49 wt. % Co, 49 wt. % Fe and 2 wt. % V. The laminations 11 have a planar form and each have a first main surface 13 and a second main surface 14 that is located opposite the first main surface 13. The first and second main surfaces 13, 14 are approximately parallel.

[0053] In order to construct the stack in a stack direction 23 perpendicular to the first and second main surfaces 13, 14 of the laminations 11, the second main surface 14 of a first of the laminations 11 is arranged on the first main surface 13 of a second of the laminations 11 and the second main surface 14 of a third of the laminations 11 is arranged on the first main surface 13 of the first laminations 11.

[0054] The laminated core 10 also has an adhesive 18 that is arranged between the laminations 11 of the stack 12. The adhesive 18 is thus arranged between the second main surface 14 of a first lamination 11 and the first surfaces 13 of the laminations 11 below them, and these laminations 11,11 are bonded together. A layer of adhesive is arranged between adjacent laminations 11, 11 of the stack 12.

[0055] The laminated core 10 may take different forms. As shown in the top view in FIG. 1A, in this embodiment the laminations 11 have the shape of a stator and have their final contour. In the embodiment shown in FIG. 1A the laminations 11 each include an outer circular ring 15 and a large number of teeth 16 that project from the inside 17 of the ring 15 and extend in the direction of the axis 19 of the ring 15. In this embodiment the teeth 16 each have a T-shape.

[0056] The adhesive 18 has a composition that can be transferred to a B-stage. The B-stage describes an adhesive that can be dried or partially cured. In this B-stage the adhesive is no longer adhesive, i.e. it is not tacky. Epoxy resin is one example of an adhesive that can be transferred to a B-stage. Duromer resins such as polyurethane resin or acrylic resin, for example, are further adhesives that can be transferred to a B-stage. The full curing of this type of adhesive 18 is carried out in a separate second step in which the adhesive 18 is fully chemically crosslinked, in the process the laminations 11, 11 are wetted in order to produce the adhesive bond between the laminations 11, 11.

[0057] The adhesive 18 is applied in the fluid A-stage to the first surface 13 of each lamination 11 by means of a printing process. In this embodiment the adhesive was applied by means of a screen printing process. A stencil printing process, a pad printing process or an ink-jet printing process can also be used instead of a screen printing process. The adhesive 18 can be applied over a large area of each lamination 11 or in a pattern so as to produce coated regions 20 and uncoated regions 21. The screen printing process has the advantage that the thickness of the A-stage adhesive 18 applied can be adjusted. In addition, the adhesive 18 can easily be applied to the first main surface 13 of laminations 11 in a specific pattern using a mask. Furthermore, the method is suitable for large quantities.

[0058] The laminations 11 may have a thickness of between 0.1 and 1 mm. The thickness of the adhesive 18 in the finished laminated core 10 may be between 0.10 ?m und 10 ?m. The thickness of the adhesive 18 is preferably small so that the laminated core 10 has a high fill factor. In addition, the thickness of the adhesive 18 in the fluid A-stage may depend on the coated surface area. For example, the thickness may be greater if the portion of the area of the lamination 11 is smaller. This ratio can be used to prevent the adhesive 18 from running out over the edges of the laminated core 10 during the first and second curing steps.

[0059] In some embodiments at least one of the first and second main surfaces 13, 14 of the laminations 11, 11 is coated with an additional electrically insulating layer 22. This additional insulating layer 22 may be polymer-free and contain ceramic particles such as MgO, ZrO.sub.2 or Al.sub.2O.sub.3. This electrically insulating layer 22 may cover the surface completely or only partially. A partial coating can be used for some CoFe alloys to promote preferred texture growth. In this embodiment the adhesive 18 is applied to the electrically insulating layer 22 by means of the screen printing process.

[0060] FIG. 2A shows a top view of a lamination 11 according to a further embodiment in which the adhesive 18 is applied in a pattern in the fluid A-stage. As can be seen more clearly from the enlarged view in FIG. 2B, in this embodiment the pattern has coated regions 20 that are approximately stripe-shaped and narrower and broader regions that are separated from one another by uncoated regions 21 of the main surface 13. The stipe-shaped coated regions 20 run approximately parallel to one another. In other embodiments the coated regions 20 are dot-shaped or rectangular. Once applied, the adhesive 18 partially cured, e.g. at 180? C. for 1 minute for epoxy resin, to transfer the adhesive 18 to the partially crosslinked B-stage. FIG. 2C shows a profile of the adhesive pattern from FIG. 2A on the first main surface 13 of the lamination 11 in the partially crosslinked B-stage. The coated regions 20 have a thickness of less than 10 ?m in the B-stage state of the adhesive 18.

[0061] FIG. 3 shows a flow diagram 30 of various methods for producing a laminated core that can be used to produce a laminated core according to one of the embodiments described here.

[0062] In box 31 a strip (ribbon) made of a cobalt-iron alloy is provided. This strip may be produced using a metallurgical process and is provided cold rolled. The strip may, for example, be made of VACODUR 49 (an alloy based on 49 wt. % Co, 49 wt. % Fe, 2 wt. % V). Optionally, in box 32, at least one side of the strip can be coated with an electrically insulating ceramic layer such as MgO, Al.sub.2O.sub.3 or ZrO.sub.2, for example. This electrically insulating ceramic layer may be applied to the strip by means of a dipping process or a spraying process, for example. In box 33 a large number of laminations are formed from the strip by means of punching or laser cutting, for example. The laminations may have the final contour of a stator or a rotor or of a part of a stator, e.g. a stator tooth or a stator ring, or a part of a rotor. In box 34 the laminations are subjected to a heat treatment process referred to as final annealing or magnetic final annealing. During this heat treatment the magnetic properties of the laminations adjusted. For VACODUR 49 the laminations can be final annealed at 880? C. for 6 hours. In box 35 an adhesive is applied to one of the main surfaces of the laminations by means of a printing process such as screen printing. The adhesive may be contain an epoxy resin dispersion.

[0063] In box 36 the adhesive is transferred to the B-stage. The adhesive is thus dried or partially cured so as to partially cross link the polymer component of the adhesive. In this stage the adhesive is solid, and the exposed surfaces of the adhesive are no longer adhesive. In box 37, the laminations with the B-stage adhesive are stacked one on top of another so as to arrange an adhesive layer between adjacent laminations. Since the adhesive is in the B-stage and the exposed surfaces are no longer adhesive, the laminations are loose in the stack and so can be moved relative to one another and aligned relative to one another. A pressure is then exerted on the stack, e.g. the stack is pressed between two plane parallel surfaces. In one embodiment, in box 38 the adhesive is fully cured under pressure, the adhesive being transferred from the B-stage to the C-stage. This process may be carried out in a hot press, for example. For example, curing can be carried out by heat treating the stack in the hot press for 2 hours at 200? C. The pressure is them removed and the finished laminated core is provided in box 39.

[0064] Alternatively, the transfer of the adhesive from the B-stage to the C-stage can be carried out in two steps. In this embodiment, after box 37 the adhesive in the stack is firstly partially cured under pressure in box 40. The pressure is then removed in box 41, and the adhesive is fully cured without the need to exert a pressure on the stack. This method can also be termed post-curing or tempering. This method has the advantage that the mechanism used to exert the pressure on the stack need not be exposed to high temperatures. The fixed laminated core is provided in box 42.

[0065] FIG. 3 also shows two comparison methods in which the adhesive is not transferred to the B-stage before the laminations are stacked. After box 35, in box 100 the laminations are stacked on top of one another with an adhesive layer in a fluid state and a pressure is exerted on the stack. In box 101 the adhesive is fully cured under pressure and in box 102 the laminated core is finished. Alternatively, after box 100, the adhesive is partially cured under pressure in box 103, the pressure is removed, and the adhesive is fully cured in box in box 104. In box 105 the laminated core is finished.

[0066] FIG. 4 shows the measured bond strength of various adhesives for shear test samples as per DIN EN 1465 and the results of bond strength tests for adhesives HT, K01 and EB 548 on laminations of the CoFe alloy VACODUR 49, coated with DL1 (a thin methylate film), which transforms into MgO particles during the heat treatment, and finally annealed. At the chosen overlap length, the bond strength of the bonding varnish usedRemisol EB 548exceeds its material strength such that in the majority of tests the sample tears in the VACODUR 49 laminations. In contrast, the fracture behaviour of adhesives HT and K01 is exclusively adhesive, i.e. the boundary layer between the methylate film and the adhesive fails.

EXAMPLES

[0067] In one example, a method for the production of a laminated core comprises the following: [0068] laser cutting/punching of individual laminations formed of a cobalt-iron alloy, [0069] annealing of individual laminations to restore the desired soft-magnetic properties, [0070] coating one side of the individual laminations with an adhesive (A-stage adhesive), [0071] baking the adhesive contact (and setting the B-stage of the adhesive), [0072] positioning the dry individual laminations on a device, [0073] compressing the lamination stack (still on the device) between 2 parallel surfaces (parallelism from the press, not from the stack), [0074] (partial) fast curing of the adhesive under pressure and with the introduction of heat, e.g. NIR, induction, heating sleeve, etc., [0075] removal from the device (laminated core is touch-dry), [0076] full curing of the laminated core in the furnace (batch curing).

[0077] This embodiment can be used for large quantities.

[0078] In a further example, a method for the production of a laminated core comprises the following: [0079] laser cutting/punching of individual laminations formed of a cobalt-iron alloy, [0080] annealing of individual laminations to restore the desired soft-magnetic properties, [0081] coating one side of the individual laminations with adhesive (A-stage of the adhesive), [0082] baking the adhesive contact (and setting the B-stage of the adhesive), [0083] positioning the dry individual laminations on a device, [0084] compressing the stack of laminations (still on the device) between 2 parallel surfaces (parallelism from the press, not from the stack), [0085] curing the adhesive under pressure and with the introduction of heat (e.g. heating sleeve), [0086] removing the fully cured laminated core from the device.

[0087] As there is initially no adhesive on the lamination, the punched/lasered laminations can be annealed in order to set optimum magnetic properties. Optimum magnetic properties of the cobalt-iron alloy are particularly advantageous in applications in the field of aviation/motor racing. No adhesive is applied to the finally annealed laminations until this has been done since the punched/lasered and coated laminations cannot be re-annealed to achieve optimum magnetic properties as the annealing temperature is greater than the temperature resistance of the adhesive.

[0088] In some embodiments adhesive is already present over the entire area before stacking. This means that adhesive is present even in those regions subject to high layer pressure due to fluctuations in the strip thickness, for example. In other embodiments the adhesive is applied to parts of the area only and other parts are free of adhesive.

[0089] The adhesive may be enriched with fillers to achieve improved electrical insulation of the layers. Filler contents of over 50% can be used. The adhesive is distributed evenly either over the entire area or over predetermined parts of the area using the printing process such that all regions are wetted with adhesive. This results in high core strength.

[0090] In summary, the method permits the production of laminated cores in their final contour from magnetically optimally annealed laminations. The heat treatment of the laminations in their end contour may take place before bonding so as to ensure the desired magnetic properties. For a CoFe alloy in the 49% Fe, 49% Co, 2% V class this heat treatment, also known as final annealing, can be carried out at 800? C. to 880? C. for between 0.5 and 10 hours. Before bonding, each individual layer up to the last covering layer is coated on one side with adhesive. To ensure an even and reproducible application of adhesive that is also scalable in form and quantity, this is done by means of a printing process such as screen printing. The regions where the adhesive is applied, e.g. dots of adhesive, are typically less than 10 ?m high. The printed laminations bearing the adhesive in the A-stage are dried in the furnace such that the adhesive used is partially crosslinked and forms a bonded layer, i.e. the adhesive is transferred to the B-stage. Depending on the composition of the adhesive, this can be carried out at 200? C. for less than 1 minute. The laminations can then be stacked and stored for several weeks/months. The coated and dry laminations with the B-stage adhesive regions are stacked on a device that enables the laminations to be aligned precisely. The laminations are stacked such that there is a layer of adhesive between each lamination. Since the adhesive is non-sticky in the B-stage, the individual layers can be adjusted as many times as necessary until the correct position is achieved. The stacked and aligned laminations are compressed using a press in order to achieve the required packing density/fill factor. The compressed laminated core is cured under the influence of heat. During this process the adhesive softens again, thereby enabling the wetting and spreading of the adhesive dots and achieving a further increase in fill factor. After curing the adhesive is in the fully cross-linked C-stage.