WO2023126074A1

WO2023126074A1 - Method for manufacturing lamellas for a lamination

Info

Publication number: WO2023126074A1
Application number: PCT/EP2022/025599
Authority: WO
Inventors: Robert Van Den Heuvel; Peter NOUWS; Gert Jansen; Arjen Brandsma; Oleg Alexandrov
Original assignee: Robert Bosch Gmbh
Priority date: 2021-12-30
Filing date: 2022-12-27
Publication date: 2023-07-06
Also published as: NL2030372B1

Abstract

The present invention relates to a method for manufacturing lamellas (20) from sheet metal (30) for a stack of such lamellas (20), i.e. a lamination, such as the core of a transformer or of a rotor or a stator of an electric machine. According to the present invention, in a first manufacturing step (A), the individual lamellas (20) are only partially cut loose from the sheet material (30), while connecting tabs (32) are left between the lamellas (20) and a remaining frame part (31) of the sheet material (30). Subsequently, in a second step (B) of the novel manufacturing method, the individual lamellas (20) are processed while still connected to the frame part (31) of the sheet material (30). Finally, in a third step (C) of the novel manufacturing method, the lamellas (20) are successively completely cut loose from the sheet material (30) by cutting the connecting tabs (32).

Description

METHOD FOR MANUFACTURING LAMELLAS FOR A LAMINATION

The present invention relates to a method for manufacturing lamellas from sheet material, in particular metal such as electrical steel, for a stack of such lamellas, i.e. a lamination, such as the core of a transformer or of a rotor or a stator of an electric machine. In the latter case, the lamellas are typically (but not necessarily) either disc shaped (rotor core) or ring shaped (stator core). At least in these latter, electrical applications of the lamination stack, the individual lamellas thereof typically have a thickness that is small compared to their other dimensions, often having an absolute value in the thickness range between 0.05 to 0.5 mm. The present invention in particular relates to lamellas having a largest dimension that amounts to at least 500 up to 2500 times their thickness dimension.

The lamellas of the lamination stack are individually obtained from sheet material by means of stamping, i.e. blanking. This process step of lamella blanking is typically preceded by one of more successive punching, i.e. piercing steps, wherein holes for accommodating shafts, bolts, magnets or wire windings and/or weight reduction or cooling holes are formed in the sheet material. These individually blanked lamellas are mutually stacked in a desired amount to form the stack thereof. In this latter respect, it is a well-known practice to form the lamination stack, i.e. to mutually stack the lamellas thereof as part of the process step lamella blanking. That is to say that the lamellas are successively blanked from a continuously supplied strip of sheet material with a later blanked lamella being stacked on top of earlier blanked lamellas by the same action of the blanking punch, as whereby this is cut from the sheet material. JP 2005-191031 A provides an example of such well-known practice that has the advantage that the blanked lamellas need not be individually (and delicately) handled.

Depending on the intended application of the lamination stack, it is known to provide the sheet material with an electrically insulating and/or a bonding coating (such as a heat-activated varnish or “Back-lack”), before the process steps of lamella blanking and stacking. Such coating is applied to the sheet material before blanking, since after blanking and stacking the processing of the main faces of the lamellas is no longer possible, or at least is highly unpractical and/or inefficient. Thus the problem arises that such coating may be damaged in blanking in particular at the edges of the cut surfaces thereof.

After blanking, stacking and possibly welding, it is known to perform an annealing heat treatment on the lamination stack for improving the mechanical and/or electromagnetic properties, in particular the magnetic permeability, thereof. For example, a work hardening effect of the blanking process that is detrimental to the said electromagnetic properties, can be removed in annealing. The intensity of such annealing heat treatment in terms of the temperature and duration can be optimized according to need, as for instance described in relation to rotor and stator cores in US- 10199910 B2 and J P-5228379 B. In this respect it is known that the annealing at relatively low temperature (<«600°C) results predominantly in stress relief (so-called recovery), whereas at intermediates temperatures («650-750°C) also recrystallisation and grain growth occurs and at even higher temperatures (>«800°C) grainsize refinement and homogenization is obtained as a result of the phase transformation from ferrite to austenite at such higher temperatures and back again during the gradual cooling to ambient (so-called normalizing). When annealing the lamination stack, the problem arises that it takes a long time to heat up such stack, since its surface area is small compared to its volume and mass, at least relative to the lamellas thereof separately.

Against the above known technical background, the present invention aims to provide a method for manufacturing the lamination stack that mitigates several of the problems and/or limitation associated with the known manufacturing method.

According to the invention, in a first step of the novel manufacturing method, the individual lamellas are only partially cut loose from the sheet material, while connecting tabs, i.e. bridges are left between the lamellas and a remaining frame part of the sheet material (or between two directly adjacent lamellas, i.e. without any sheet material remaining between such directly adjacent lamellas). By these bridges, the lamellas thus remain connected to, in particular remain integral with such frame part. Subsequently, in a second step of the novel manufacturing method, the individual lamellas are processed while connected to the said frame part of the sheet material via the said bridges. Subsequently, in a third step of the novel manufacturing method, the lamellas are completely cut loose from the sheet material, i.e. are separated from the frame part thereof, by shearing-off or otherwise cutting the said bridges. Thus successively separated lamellas, can be conveniently stacked on top of one another in accordance with the above-discussed, known practice.

This novel manufacturing method favorably enables a subsequent processing of the lamellas, in particular of the main faces thereof, without requiring the direct and delicate handling of individual lamellas. Instead, the lamellas are favorably handled indirectly via the said frame part of the sheet material, i.e. are handled “in-frame”. For example, the frame part can be conveniently pulled (or pushed and pulled simultaneously to favorably minimize stress) to transport the lamellas to, from or in subsequent process steps. Furthermore, also the cut surfaces of the lamellas can thus be subsequently processed.

In particular according to the present invention, the said second step of the novel manufacturing method, i.e. the said subsequent processing entails one or more of: the in-frame annealing of the (partially cut) lamellas; the in-frame surface (heat) treatment of the (partially cut) lamellas, including the cleaning and/or the de-oxidation in an atmosphere composed of a mixture of hydrogen and nitrogen gas, the oxidation, the (carbo-)nitriding, the surface alloy element enrichment thereof, etc.; the (chemical or physical) deposition of a coating of the (partially cut) lamellas inframe; or the (physical) application of an adhesive or a varnish (e.g. Back-lack) or component thereof on one or both of the main faces of the (partially cut) lamellas in-frame.

More in particular in the above respect, the partially cut lamellas are preferably first annealed and then oxidized during their cooling down from the annealing temperature. This has the advantage that the lamellas need to be heated only once while both annealing and oxidizing these. Alternatively, the partially cut lamellas are preferably first annealed and then a coating or an adhesive is applied to one or both of the main faces of the annealed lamellas. This has the advantage that the coating or the adhesive is not subjected to the (high) annealing temperature, such that most known coating compounds and (metal) adhesives can be applied.

According to a further aspect of the invention, the in-frame annealing of the lamellas comes with the surprising advantage vis-a-vis lamination stack annealing that the lamellas can be differentially annealed, meaning that different annealing intensities are applied in different areas of the lamella. For example, the sourced sheet material is typically normalized to start with, such that the lamellas only need to be annealed near the cut surface thereof (e.g. up to between 0.1 to 0.5 mm below such surfaces). More in particular, those areas of the lamellas that are exposed to the highest stress levels in the application of the lamination stack are recrystallized, but not normalized, whereas those areas that are that are exposed to the strongest magnetic fields in the said application are normalized. Differential annealing requires the localized heating of the lamellas by a means of, for example, a laser (beam), an electron-beam or induction.

According to a still further aspect of the invention, the frame part with the partially cut lamellas is reeled-up into a coil. Hereby, the transport and/or subsequent processing of the partially cut lamellas can be facilitated and/or economized. For example, the coil can be conveniently annealed in a batch oven, whereas the uncoiled strip of sheet material would require continuous oven. Moreover, such coil enables the favorable storage and/or buffering of the partially cut lamellas in between the three steps of the novel manufacturing method, or even in between the processes of the said subsequent processing. Preferably a spacer is applied between the windings of the coil to facilitate the penetration of the oven atmosphere between the windings. The spacer can be a covering layer of porous or permeable material.

According to a yet further aspect of the invention, the partially cut lamellas are separated from the frame part of the sheet material in the said third step of the novel manufacturing method by means of a (physical) contactless cutting process, such as laser cutting. Such contactless cutting process is conventionally not feasible, because it is slow compared to blanking and therefore uneconomical. However, presently only the bridges between the lamellas and the frame part of the sheet material need to be cut in the said third step of the novel manufacturing method.

According to a yet further aspect of the invention, 4 or more bridges are left between each lamella and the frame part of the sheet material that are preferably essentially equally spaced along the outer contour thereof. Moreover, at least 4 of the bridges are preferably at least partly oriented between the lamella and the said frame part (or a directly adjacent lamella) in a direction wherein the sheet material is supplied, with 2 bridges located on either side of the lamella as seen in such supply direction. By these features, a deformation of the lamellas -that might otherwise occur when the frame part is pulled and/or pushed to transport these in the said supply direction- can be favorably avoided. The number is bridges per lamella is preferably limited to facilitate the removal thereof in a later process step of the process lamination stack manufacturing method. In this latter respect, it has been determined that applying more than 20 bridges per lamella does typically not add benefit.

In the following, the lamination stack manufacturing method according to the present invention is explained further and in more detail by way of example embodiments and with reference to the drawings, whereof:

Figure 1 provides two typical examples of known lamellas, namely a stator ring for a stator core lamination stack and a rotor disc for rotor core lamination stack of an electric motor;

Figure 2 schematically illustrates the basic setup of the presently relevant part of a known lamination stack manufacturing method;

Figure 3 schematically illustrates a first elaboration of a novel lamination stack manufacturing method according to the present invention;

Figure 4 schematically illustrates a first possible embodiment of the novel lamination stack manufacturing method according to the present invention; and Figure 5 schematically illustrates a second possible embodiment of the novel lamination stack manufacturing method according to the present invention.

Figure 1 provides two examples of lamellas 1 that can be suitably produced with the method for manufacturing a stack of metal lamellas discussed herein.

In the example depicted on the left side of figure 1 , the lamella 1 takes the form of a stator ring 10 for an electric motor. In the electric motor a number of such stator rings 10 are stacked in axial direction to form a stator core lamination stack. In the presently illustrated, non-limiting, example of the stator ring 10, it is shown to include several holes 11 inside its circularly-shaped outer contour that are equally spaced along its circumference, which holes 11 for example serve to accommodate assembly bolts or to channel cooling liquid. Moreover, the inner contour of the stator ring 10 is shaped by a large number of radial inwardly extending pole teeth 12 with an equal number of radial slots 13 therebetween, which slots 13 serve to accommodate windings of electric wire in the electric motor.

In the other example of figure 1 that is depicted on the right side thereof, the lamella 1 takes the form of a rotor disc 20 of an electric motor. In the electric motor a number of such rotor discs 20 are stacked to form a rotor core lamination stack. In the presently illustrated, non-limiting, example of the rotor disc 20, it is shown to include a central hole 21 that defines the inner contour of the rotor disc 20 and that serves to accommodate a rotor shaft, extending in axial direction through the whole of the rotor core lamination stack while being fixed thereto in the electric motor. Moreover, within its circularly-shaped outer contour the rotor disc 20 is provided with eight sets of four holes 22 that serve to accommodate permanent magnets in the electric motor. These sets of four magnet holes 22 each, are equally spaced along the circumference of the rotor disc 20, i.e. with two adjacent such sets being arranged at a 45 degree angle relative to one another.

In figure 2 the basic setup of the presently relevant part of a known lamination stack manufacturing method is schematically illustrated in relation to the rotor disc 20 illustrated in figure 1 and in a plan view of a strip of sheet material 30. In this figure 2, as well as in the following drawing figures, the part or parts of the sheet material 30 that is or that are being cut and removed from the sheet material 30 in a respective process step, i.e. that are currently being pierced or blanked, are shaded. The sheet material 30 is supplied to a so-called progressive stamping device (not illustrated) in the direction of the arrow S, i.e. from the left to the right in figure 2, in the form of a (length of a) continuous strip that is typically reeled-off from a coil.

In a first step I of the known method, a set of pilot holes 40 are pierced through the sheet material 30 on either side thereof by means of piercing punch-and-die-pairs of the progressive stamping device. These pilot holes 40 are used to receive locating pins (not illustrated) later on in the progressive stamping device (i.e. towards to right in figure 2) that serve to align the sheet material 30 inside the device. In a second step II of the known method, further (sets of) holes 21 , 22 are pierced through the sheet material 30 by means of further piercing punch-and-die-pairs, which further holes 21 , 22 correspond to the shaft hole 21 and the magnet holes 22 of the -still to be cut- rotor disc 20. It is noted that, typically depending on the geometric complexity of the lamella 1 , the said first and second steps I and II of the known lamination stack manufacturing method can be integrated into a single process step, subdivided into multiple process steps, or otherwise combined. For example in this respect, the piercing of the pilot holes 40 can be combined with the piercing of the shaft hole 21 in a first step, with the magnet holes 22 being pierced in a second step.

In a third step III of known method, the rotor disc 20 is cut from the sheet material 30 in a well-known manner by means of a blanking punch-and-die-pair of the progressive stamping device. The blanked rotor disc 20 is ejected from the progressive stamping device, as schematically indicated by the arrow E, and thereby either is placed directly on top of the rotor disc lamination stack or is transported individually for subsequent processing before such lamination stacking is carried out. In a fourth step IV of the known method, the remaining frame part 31 of the sheet material 30 exits the progressive stamping device.

It is further known to provide the lamination stack with a weld seam along its height after lamination stacking, in order to hold the lamellas 1; 10; 20 thereof together and thus to facilitate the handling of the lamination stack. In this case, and if lamella’s 1 ; 10; 20 have been individually annealed in accordance with the present invention, this weld seam can be differentially annealed by heating the lamination stack only locally, favorably rather than completely. In particular, the weld seam, preferably including its so-called heat-affected-zone, is stress-relieved but not normalized annealed, in particular not recrystallized. Alternative or in addition to such lamination welding, the adjacent lamellas 1; 10; 20 in the lamination stack can also be glued or baked together (such as in case of the said Back-lack coating), or can be mechanically interlocked (such as by an interference fit). In this case, and if lamella’s 1; 10; 20 have been individually annealed in accordance with the present invention, the lamination stack favorably need not be annealed at all.

The present invention seeks to improve upon the known lamination stack manufacturing method. According to the invention such improvement is achieved with the novel lamination stack manufacturing method that is schematically illustrated in figure 3.

The first and second steps II illustrated in figure 3 correspond to those illustrated in figure 2 and can, likewise, be carried out by means of a (progressive) stamping device 50 (illustrated in figure 4). However, thereafter, in a first step A of the novel method, multiple, mutually spaced elongated holes 23 are pierced through the sheet material 30, following the outer contour of the rotor disc 20, such that the rotor disc 20 remains an integral part of the sheet material 30. In other words, in this first novel step A connecting bridges 32 remain between the rotor disc 20 and a frame part 31 of the sheet material 30, which connecting bridges 32 are defined by and between the said elongated holes 23.

It is noted that such first step A of the novel manufacturing method can in principle be caried out simultaneous with the said one of more successive piercing steps for forming the holes 21, 22 in the body of the lamellas 20 (i.e. inside the outer contour thereof). Nevertheless, these latter piercing steps are preferably completed before the said first novel step A is carried out. Moreover, the said first novel step A can itself be carried out in multiple, i.e. separate and subsequent piercing (sub-)steps.

After such first novel step A and as indicated in figure 3 by the letter X, the rotor disc 20 exits the stamping device while still connected to the frame part 31 sheet material 30 via the said bridges 32, for the convenient subsequent processing thereof in a second step B of the novel method. Thus in such second novel step B, the rotor discs 20 are processed in-frame in accordance with the present invention.

In an advantageous realization of the said second step B according to the present invention, the said subsequent processing therein entails first annealing the rotor discs 20, preferably differential-annealing these, for (locally) optimizing their mechanical strength and magnetic properties, and then oxidizing or coating these for their mutual electrical insulation. A coating with adhesive properties may be preferred in this respect for improving the handling of the rotor disc lamination stack and/or to avoid the said welding thereof. Alternative to such oxidizing or coating, a (metal) glue may be applied to one or both of the main surfaces of the rotor discs 20.

Thereafter, in a third step C of the novel manufacturing method the rotor disc 20 is completely cut loose from the sheet material 30, i.e. is separated from the frame part 31 thereof by shearing-off the said bridges 32 by means of a cutting device 70 (illustrated in figure 4). In the illustrated embodiment, the rotor disc 20 is cut loose, i.e. the bridges 32 are severed from the outer contour of the rotor disc 20, by means of blanking. After being cut loose, the rotor disc 20 is ejected from the cutting device, as schematically indicated by the arrow E, and preferably placed directly on top of the rotor disc lamination stack. Also after the rotor disc 20 has been cut loose, the remaining frame part 31 of the sheet material 30 exits the cutting device corresponding to the said fourth step IV of the known method.

As schematically illustrated in figure 4, the said three steps A, B and C of the novel manufacturing method can be embodied as a continuous processing line, typically preceded by the reeling-off RO of a coil 33 (containing an initial length) of the sheet material 30. The first step A of the novel manufacturing method is carried out by the progressive stamping device 50 that also takes care of the first and second steps I and II of the known method. The thus partially cut loose rotor discs 20 are transported through handling the frame part 31 of the sheet material 30 to a device 60 for the subsequent processing of the rotor discs 20 in the second step B of the novel manufacturing method, such as a (continuous) heat treatment oven, or a coating or adhesive applicator. Thereafter, the thus partially cut loose and subsequently processed rotor discs 20 are transported from the subsequent processing device 60 to a cutting device 70 for separating the rotor discs 20 from the said frame part 31 in the third step C of the novel manufacturing method.

Such in-line embodiment of the novel manufacturing method is mostly suited for a relatively short subsequent processing of the rotor discs 20 in the said second step B. In particular a subsequent processing that can keep up with a rate of the partial cutting of the rotor discs 20 in the said first step A. For example, an adhesive can be applied, in particular sprayed, relatively quickly on one or both of the main faces of the rotor discs 20. In case of a more elaborate subsequent processing in the said second step B and/or to favorable decouple the production rates between the said three steps A, B and C of the novel manufacturing method, the frame material 31 with multiple rotor discs 20 connected thereto, can be reeled-up Rll into a coil 51 , 61 in between two of the said three steps A, B and/or C. This latter embodiment of the novel manufacturing method is schematically illustrated in figure 5.

As schematically illustrated in figure 5, the said three steps A, B and C of the novel manufacturing method can be embodied as a batch processing line. In this case after the first step A of the novel manufacturing method is completed, the thus partially cut loose rotor discs 20 are reeled-up Rll together with the said frame part 31 into an initially-processed coil 51 (containing a certain length of the sheet material 30). Such initially-processed coil 51 can then be subsequently processed, in the second step B of the novel manufacturing method, such as by annealing in a batch oven 61. Alternatively, the initially-processed coil 51 can be reeled-off RO, before being supplied to the subsequent processing device 60, such as the afore-mentioned continuous heat treatment oven 60. In this case, the thus partially cut loose and subsequently processed rotor discs 20 and the surrounding frame part 31 of the sheet material 30 either can be directly supplied to the cutting device 70 (as illustrated in figure 4), or can be reeled-up Rll again into an subsequently-processed coil 61 , as illustrated in figure 5. Such subsequently-processed coil 61 is reeled-off RO before being supplied to the cutting device 70 for separating the rotor discs 20 from the said frame part 31 in the third step C of the novel manufacturing method.

The present invention, in addition to the entirety of the preceding description and all details of the accompanying figures, also concerns and includes all the features of the appended set of claims. Bracketed references in the claims do not limit the scope thereof, but are merely provided as non-binding examples of the respective features. The claimed features can be applied separately in a given product or a given process, as the case may be, but it is also possible to apply any combination of two or more of such features therein.

The invention(s) represented in the present disclosure is (are) not limited to the embodiments and/or the examples that are explicitly mentioned herein, but also encompasses amendments, modifications and practical applications thereof, in particular those that lie within reach of the person skilled in the relevant art.

Claims

1. A method for manufacturing lamellas (1 ; 10; 20) from sheet material (30) for a lamination stack thereof, such as a transformer core or a stator or rotor laminate of an electric motor, wherein the lamellas (1 ; 10; 20) are partially cut loose from the sheet material (30) in a first process step (A), wherein the lamellas (1 ; 10; 20) are subsequently processed and/or treated as part of the sheet material (30) in a second process step (B) and wherein the lamellas (1; 10; 20; 50) are finally completely cut loose from the sheet material (30) in a third process step (C).

2. The method for manufacturing lamellas (1 ; 10; 20) according to claim 1, characterized in that, in the first process step (A), a respective lamella (1; 10; 20) is partially cut loose by piercing a number of elongated holes (23; 15; 25) along the outer contour thereof, while leaving a corresponding number of connecting bridges (32) between that respective lamella (1 ; 10; 20) and a frame part (31) of the sheet material (30) or an adjacent lamella (1 ; 10; 20), and in that in the third process step (C) that respective lamella (1; 10; 20) is completely cut loose by severing the said bridges (32) along its outer contour.

3. The method for manufacturing lamellas (1 ; 10; 20) according to claim 2, characterized in that, in the first process step (A) and as seen in a long direction of the sheet material (30), at least two of the said bridges (32) are provided on either side of a respective lamella (1 ; 10; 20) that partly extend also in the said long direction between that respective lamella (1; 10; 20) and the said frame part (31) and that are preferably essentially equally spaced along the circumference of that respective lamella (1; 10; 20).

4. The method for manufacturing lamellas (1; 10; 20) according to claim 2 or 3, characterized in that, in the third process step (C), the said bridges (32) are severed by means of a contactless cutting process, such as laser cutting.

5. The method for manufacturing lamellas (1; 10; 20) according to any of the preceding claims, characterized in that, after completing the first process step (A) and prior to the second process step (B) and/or after completing of the second process step (B) and prior to the third process step (C), the sheet material (30) is reeled-up.

6. The method for manufacturing lamellas (1 ; 10; 20) according to claim 5, characterized in that, in the second process step (B), the sheet material (30) is processed or treated in a reeled-up state, i.e. as a coil, in particular is subjected to an annealing heat treatment.

7. The method for manufacturing lamellas (1 ; 10; 20) according to claim 6, characterized in that, a spacer is applied between subsequent windings of the reeled- up sheet material (30), i.e. the sheet material coil.

8. The method for manufacturing lamellas (1; 10; 20) according to any of the preceding claims, characterized in that, in the second process step (B), the lamellas are at least party subjected to:

- an annealing heat treatment for improving the mechanical and/or electromagnetic properties thereof,

- a surface (heat) treatment, such as the cleaning and/or the de-oxidation thereof in an atmosphere composed of a mixture of hydrogen and nitrogen gas, and/or the oxidation, (carbo-)nitriding, surface alloying, etc. thereof,

- a coating deposition for the electrical insulation thereof and/or for adding corrosion resistance thereto, and/or

- an application of an adhesive or a varnish or component thereof on one or both of the main faces thereof.

9. The method for manufacturing lamellas (1; 10; 20) according to any of the preceding claims, characterized in that, in the second process step (B), the lamellas (1; 10; 20) are firstly and at least partly subjected to an annealing heat treatment and, subsequently, are either oxidized or provided with a coating or an adhesive when cooling down from the annealing heat treatment.

10. The method for manufacturing lamellas (1; 10; 20) according to any of the preceding claims, characterized in that, in the second process step (B), the lamellas (1; 10; 20) are subjected to an annealing heat treatment at the location of, at least, the surfaces that were cut in the first process step (A).

11. The method for manufacturing lamellas (1; 10; 20) according to any of the preceding claims, characterized in that, the lamination stack is assembled by mutually stacking the lamellas (1; 10; 20) obtained therein and by subsequently welding these together, and in that, the lamination stack is annealed exclusively at the location of the weld, in particular is stress relief annealed and not normalized or recrystallized annealed.

12. The method for manufacturing lamellas (1; 10; 20) according to any of the preceding claims, characterized in that, the lamellas (1; 10; 20) have a thickness in the range from 0.05 mm to 0.5 mm and, more in particular, in that a largest or a main dimension of the lamellas (1; 10; 20) amounts to between 500 and 2500 times their thickness.