EP3727717A1

EP3727717A1 - Method for manufacturing a lamina for a laminated core for an electric machine

Info

Publication number: EP3727717A1
Application number: EP18833840.4A
Authority: EP
Inventors: Torsten Wilharm; Andre Johanning; Peter-Paul Mauritsz; Arnoldus Andreas Robert MUTSAERS; Arjen Brandsma
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2017-12-20
Filing date: 2018-12-20
Publication date: 2020-10-28
Also published as: WO2019120626A1

Abstract

The present disclosure relates to a method for manufacturing a lamina (28) comprising web-parts (24), defining a crosspiece of reduced thickness, which lamina (28) are used in a stack of such lamina (28), such as a laminated stator core (26) of an electric machine (10). According to the present disclosure, the lamina (28) is manufactured in at least three steps of: - first punching a hole in a basic material to at least one, but preferably to both sides of the crosspiece of the lamina (28) to be formed; - then compressing the basic material at each crosspiece of the lamina (28) to be formed between two press-shaping tools; and - finally forming the lamina (28) including the crosspiece thereof by cutting corresponding parts or the complete contour thereof from the basic material.

Description

METHOD FOR MANUFACTURING A LAMINA FOR A LAMINATED CORE FOR AN ELECTRIC MACHINE

The present disclosure relates to a method for manufacturing a lamina for a stack of such lamina, i.e. a laminate, such as applied as the core of a rotor or a stator of an electric machine, e.g. an electric motor. The known lamina is typically produced from electric steel and is either disc shaped (rotor core) or ring shaped (stator core) with a thickness that is small relative to its diameter. In order to optimise the electrical and magnetic properties of the lamina, in particular in relation to its application in the electric machine, it is known to locally reduce the thickness thereof, i.e. to form localized depressions therein, as part of the overall production process, as is for example described in the German patent applications DE10242404 and DE10227129. In particular, a relatively slender crosspiece or bridge can be formed between two larger parts of the lamina, such as the pole teeth thereof. In particular it becomes possible to form the crosspiece not only relatively narrow in the principal plane of the lamina, but also relatively thin in a direction perpendicular to such principal plane, i.e. in thickness direction. Such slender crosspieces favourably reduce unwanted magnetic leakage flux and/or parasitic magnetic losses. Furthermore, because the crosspieces are formed by plastic deformation their magnetic permeability is favourably reduced further.

The known lamina is typically cut and shaped out of electric steel basic material in a blanking process, such that the crosspieces are formed in thickness direction by pressing and in width direction by blanking.

The blanking process is, as such, well-known and is broadly applied in the manufacturing of metal parts. In the known blanking process and device at least the 2D contour of the lamina is cut out of a sheet or strip of basic material by pressing a correspondingly shaped blanking punch through the basic material that, at the same time, is firmly and held in place by and between a blanking die and a blank holder of the blanking device that each define a respective cavity shaped to accommodate and guide the blanking punch. It is known to further provide the blanking device with a counter punch located opposite the blanking punch, which punch thus engages the basic material from the opposite side as the blanking punch. By exerting a pressure on the basic material by and between the blanking punch and the counter punch during the cutting out of the lamina, the cut edge thereof can generally be more accurately formed than without exerting such pressure, i.e. without applying the counter punch. Additionally, by exerting such pressure the lamina can, to a certain extent, be shaped in 3D by the plastic deformation of the basic material. This particular arrangement of the blanking process is known as fine-blanking.

According to the present disclosure, the above known manufacturing method of the lamina, in particular the step of forming the localized depression therein, requires the application of an unfavourably high (pressing) force and, moreover, may easily result in a small, but notional shortcoming in the resulting shape of the lamina. By the pressing force, the basic material is locally (i.e. at the location of the crosspiece) displaced to (locally) reduce the thickness thereof. This displaced basic material will end up in another location on the lamina, where it increases the thickness thereof. Although such thickness increase may be controlled by increasingly spreading it out over a larger surface area of the lamina, an increasingly higher pressing force is disadvantageously required. Furthermore, any remaining area of increased thickness is principally undesirable and can be detrimental to the application of the lamina. In particular, because many such laminas are stacked to form the rotor or stator core, any such systematic flatness deviation accumulates over the height of the stack. Alternatively, if the crosspiece was already cut to width before being pressed, its width will inadvertently increase again by the said displacement of the basic material when being pressed to reduce its thickness. As a result, the cross sectional area of the cross piece will not be reduced by the said pressing thereof, at least not to the desired extent. Also, it becomes difficult to accurately control the (cross sectional) shape and dimensions of the crosspiece.

The present disclosure aims to improve upon the known lamina manufacturing method, in particular in terms of the resulting shape and/or dimensional accuracy of the laminas obtained therewith. In particular according to the present disclosure, each lamina is formed out of the basic material in at least three steps by:

- first punching a hole into the basic material by means of a piercing punch to at least one, but preferably to both sides of each crosspiece of the lamina to be formed;

- then compressing the basic material at each crosspiece of the lamina to be formed between two press-shaping tools; and

- finally forming the lamina including the crosspiece thereof by cutting corresponding parts or the complete contour thereof from the basic material.

Because, in accordance with the present disclosure, a hole is preformed to the side or sides of each crosspiece, the volume of basic material that is displaced to reduce the thickness of the crosspieces relative to the (nominal) thickness of the basic material can flow more easily, in particular can flow at least partly into the free space provided by the hole or holes. Therefore, the said required pressing force is reduced and/or the dimensional accuracy of the lamina is improved.

In a more detailed embodiment of the above, novel lamina manufacturing method, the piercing punches applied in the said first step and/or the press-shaping tools applied in the said second step are provided with an essentially cylindrical shape with an essentially circular cross-section. This design of the piercing punches and/or press-shaping tools is favourable, because it provides a relatively high strength and wear resistance at relatively low cost. In this case, the diameter of the cylindrical press-shaping tools corresponds to and defines a length of the crosspiece.

Preferably, the crosspiece is finally formed with either the known blanking or the known fine-blanking process with a front side of the blanking punch and/or of the counter punch applied therein, which front side engages a respective principal plane of the basic material, being provided with raised sections corresponding in location and size with the crosspieces. By this measure it is favourable prevented that the crosspieces bend excessively when these and/or other parts and/or the complete contour of the lamina are cut from the basic material in the (fine-)blanking process.

Alternatively, the same tools are used in the second and third steps of the above, novel lamina manufacturing method, i.e. preferably one of the press-shaping tools applied in the second step also serves as the blanking punch of the blanking device in the third step and the other press-shaping tool applied in the second step also serves as the counter punch of the blanking device in the third step. More in particular, the said second and third steps are carried out in short succession or even, at least partly, simultaneously, meaning that the pressure applied in the second step to compress the basic material need to necessarily be removed in the third step, but can be maintained therein.

In the following, the lamina manufacturing method to the present disclosure is explained further by way of example embodiments and with reference to the drawings, whereof:

Figure 1 schematically depicts an electrical machine in cross section;

Figure 2 is a schematic perspective view of a laminated stator core of the electric machine of figure 1 including a close-up of a detail of a single lamina thereof with a thin section or crosspiece; and

Figures 3A to 3C schematically illustrate a novel manufacturing method of the lamina of figure 2, in particular of the crosspiece thereof. In figure 1 , an electrical machine 10 is schematically shown in a simplified cross-section thereof. The electric machine 10 may be an electric motor (commutator motor, electronically commutated DC motor, AC motor, etc.), a generator, or the like. If the electric machine 10 is used as a motor, it be part of a larger drive device, for example for a window regulator in a motor vehicle.

The electric machine 10 of figure 1 comprises a rotor 12 which is arranged on a shaft 14. Furthermore, the electric machine 10 comprises a stator 16, which is arranged around the rotor 12 and in turn is mounted in a container ring or yoke 18. The stator 16 is constructed substantially annular and has circumferentially arranged, outwardly facing pole teeth 20. Around the pole teeth 20, which extend in the axial direction of the electric machine 10, copper wire windings 22 are arranged in a known manner. Successive pole teeth 20 are connected to one another via ring- segment-shaped web parts 24 of the stator 16. The web parts 24 are shown to taper starting from the pole teeth 20, until they are narrowest essentially halfway between two successive pole teeth 20.

In figure 2, it is shown in a perspective view of the stator 16 that it is composed of individual stator laminas 28 stacked on top of each other to form a laminated stator core 26. The stator laminas 28 are connected together in a known manner. Also the rotor 12 of the electric machine is typically laminated (not shown).

Figure 2 also includes a close-up a single stator lamina 28 showing only a section thereof including the web part 24. The web part 24 is shown to include a thin middle section 30, i.e. crosspiece 30, of small thickness“d”, at least relative to a nominal thickness“D” of the lamina 28 between its two principal planes 32, 34. The crosspiece 30 is preferably formed by locally compressing the material of the lamina 28, either before the lamina 28 is cut from a sheet of basic material, in particular electric steel, or thereafter. By forming the crosspiece 30 between each pair of adjacent pole teeth 20 of each of the rotor laminas 28, an unwanted magnetic leakage flux and/or parasitic magnetic losses during operation of the electric motor incorporating the laminas 28 is favourably reduced. Furthermore, because the crosspieces are formed by plastic deformation, rather than by grinding or cutting, the magnetic permeability thereof is favourably reduced further. However, at the same time, the accuracy of the overall shape lamina 28 appears to be detrimentally affected by such process step of forming the crosspieces 30 by the local compression of the lamina 28. In particular, the flatness of either one or both of the principal planes 32, 34 of the lamina 28 is less than without such local compression and/or a width of crosspieces 30 is increased, or at least is less accurately defined, than without such local compression.

For improving the accuracy with which the overall shape of the lamina 28 including crosspieces 30 is formed, the present disclosure proposes a novel manufacturing method including at least the three steps that are schematically illustrated in the figures 3A, 3B and 3C successively. Each such figure 3A, 3B, 3C shows the basic material 50 in a top elevation as well as in a cross-section A-A thereof, while being processed in a respective manufacturing method step.

In a first step of the novel manufacturing method that is illustrated in figure 3A, a pair of holes is punched into the basic material 50 on either side of each respective crosspiece 30’ of the lamina 28’ to be formed, by means of respective pairs of piercing punches 60 that locally remove portions 51 of the basic material 50. Preferably, but not necessarily, all of such holes are punched simultaneously in this first method step. Preferably also, the piercing punches 60 are shaped cylindrical. Furthermore, the circumferences of the punched holes preferably touch on the radial inner and on the radial outer contours of the lamina 28’ to be formed. However, some basic material 50, e.g. less than 50% of the width, i.e. a transverse dimension, of the crosspieces 30’ to be formed, may also be left there between.

In a second step of the novel manufacturing method that is illustrated in figure 3B, the crosspieces 30’ to be formed between each of said pairs of holes 31 is compressed between two press-shaping tools 70, 71 that are provided on either side of the basic material 50 and that are thereto forced together. In this second method step the thickness d of the basic material 50 at crosspieces 30’ to be formed is reduced by plastic deformation and the displacement of material into the free space provided by the holes 31 to either side thereof. Preferably, but not necessarily, all of the crosspieces 30’ to be formed are compressed simultaneously in this second method step. Preferably also, the dimension of the press-shaping tools 70, 71 in the transverse, i.e. width direction of the of the crosspiece 30’ to be formed, exceeds a width thereof, e.g. by more than 50% of such width, whereby the flatness of the basic material 50 at the location of such crosspiece 30’ to be formed is favourably maintained or even improved. Furthermore, at least one press-shaping tool 70 is preferably shaped cylindrical. With the novel manufacturing method, a favourably high thickness reduction ratio, quantified as d/D, can be achieved in this second method step, in particular in the range from 0.6 to 0.3, preferably around 0.5.

In the example embodiment of figure 3B, only one press-shaping tool 70 is moved relative to the basic material 50 to compress it. It is, however, entirely possible to move both press-shaping tools 70, 71 relative to the basic material 50, e.g. in essentially equal amounts such that the section 32 of reduced thickness d and thus the crosspiece 30 is formed essential in the middle of the (uncompressed) basic material 50 (not shown). Hereby, a mechanical strength of the end-product lamina 28, in particular of the web-parts 24 and crosspieces 30 thereof, is favourably high.

In a third step of the novel manufacturing method that is illustrated in figure 3C, the lamina 28 including the crosspieces 30 thereof is finally formed in a known manner, in particular in a blanking process. To this end, for example, a blanking punch 80, in particular a front side thereof, with an outer contour essentially corresponding to the contour of the lamina 28 is pushed against and cuts through the basic material 50 that is kept in place relative to the blanking punch 80 by a blanking die 81 with an inner contour essentially corresponding of the contour of the lamina 28. Commonly a blanking holder (not shown) is applied in the blanking process as well, on the opposite side of the basic material 50 from the blanking die 81 , to clamp and hold the basic material 50 in place between them, while the planking punch 80 cuts through it. Furthermore, a counter punch (not shown) may be applied, in the blanking process, on the opposite side of the basic material 50 from the blanking punch 80, to clamp and hold the lamina 28’ to be formed in place between them, while the planking punch 80 cuts through the basic material 50. In this latter arrangement of the blanking process, known as fine-blanking, the blanking punch 80 and the counter punch can also serve as the said two press-shaping tools 70, 71 in the second method step. In either case, i.e. both in blanking and in fine-blanking, the front side of the blanking punch 80, and/or possibly the counter punch in case of fine- blanking, is preferably provided with raised sections 82 corresponding in location and size with the crosspieces 30. By these raised section 82, it can be prevented that the thin and thus relatively weak crosspieces 30 bend in the blanking process.

The present disclosure, 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 by 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 a lamina (28) for a stack of lamina (26), such as applied as the core of a rotor or a stator in an electric machine (10), from basic material (50), wherein the lamina (28) comprises at least one crosspiece (30) with a thickness that is reduced relative to a nominal thickness D of the lamina (28), characterized in that the lamina (28) is manufactured from the basic material (50) in at least three process steps, in that in a first process step at least one hole (31 ) is punched in the basic material (50) to the side of the still to be formed crosspiece (30’), in that in a second process step the basic material (50) at the location of the still to be formed crosspiece (30’) is compressed in thickness direction and in a third process step a part of the overall contour of the lamina (28) including the crosspiece (30) is formed by cutting it out of the basic material (50), preferably by means of blanking.

2. The lamina (28) manufacturing method according to the claim 1 , characterized in that in the said first process step a hole is punched on either side of the still to be formed crosspiece (30’).

3. The lamina (28) manufacturing method according to the claim 1 or 2, characterized in that in the hole (31 ) or the holes (31 ) is/are punched in the said first process step by means of a predominantly cylindrical piercing punch (60).

4. The lamina (28) manufacturing method according to the claim 1 , 2 or 3, characterized in that in the said second process step the basic material (50) at the location of the still to be formed crosspiece (30’) is compressed between two press shaping tools (70, 71 ).

5. The lamina (28) manufacturing method according to the claim 4, characterized in that a dimension of the two press-shaping tools (70, 71 ) in the transverse or width direction of the still to be formed crosspiece (30’) is larger than a dimension of the crosspiece (30’) in that direction.

6. The lamina (28) manufacturing method according to the claim 4 or 5, characterized in that, in the said second process step, both press-shaping tools (70, 71 ) are moved towards each other in the thickness direction of the basic material (50), preferably such that ultimately the crosspiece (30) is formed in the middle thereof.

7. The lamina (28) manufacturing method according to a preceding claim, characterized in that, in the said second process step, the basic material (50) is compressed in thickness direction at the location of the still to be formed crosspiece (30’) to a reduced thickness d of at most six tenths and at least three tenths of the nominal thickness D of the basic material (50).

8. The lamina (28) manufacturing method according to a preceding claim, characterized in that, in the third process step, the said part of or the complete contour of the lamina (28) including the crosspiece (30) is blanked from the basic material (50) with the aid of at least a blanking punch (80) and a blanking die (81 ).

9. The lamina (28) manufacturing method according to claim 8, characterized in that a front side of the blanking punch (80) applied in the said third process step is provided with a raised section (82) that engages the lamina (28) at the location of the still to be formed crosspiece (30’).

10. The lamina (28) manufacturing method according to claim 8 or 9, characterized in that a counter punch is applied therein, located opposite the blanking punch (80) that is pressed against the other side of the basic material (50) as the blanking punch (80) for cutting the lamina (28) from the basic material (50) and in that the blanking punch (80) and the counter punch that are applied in the said third process step also serve as the two press-shaping tools (70, 71 ) that are applied for compressing the basic material in the said second process step at the location of the then still to be formed crosspiece (30’).