CA1183568A - Laminated core for electrical apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A laminated core for an electrical machine is disclosed which comprises a plurality of annular lamina-tions. Each lamination is edge rolled from straight strips of magnetic material with teeth punched into one edge. Each lamination is slightly less than 360° in arcuate length, leaving a slight gap between its ends to allow the finished core to be accurately sized by com-pressing its outer surface. By punching the straight strips from sheet metal in such a way as to orient the grain structure in the direction of tooth extension and edge rolling the opposite edge, a selective grain orienta-tion can be achieved which is magnetically advantageous throughout the core.

Description

3~

1 49,921 LAMINATED CORE FOR ELECTRICAL APPARATUS

BACKGROUND OE TH~ INVENTION
Stator cores of dynamoelectric machines are con-ventionally produced by sta.~ping a plurality of annularly shaped pieces from sheet met21 and stacking them together S to form a cylindrical core with a coaxial bore there-through. Typically, the punchings have teet~ extending radially inward which are aligned w-t~ similar teeth of other punchings to form axially running slots in the bore of the cylindrical core. At a la~er stage of manufacture, conductors are disposed in these slots to form the stator wlnding of a dynamoelectric machine.
This process is inherently wasteIul since the stamping of circular components from sheet metal creates scrap between adjacent circular punchings and between the teeth of each punching. In most situations this scrap is useles~ for any alternate purpose and, thereIore, adverse-ly affects the manufacturing costs of the stator cores.
A means to avoid this high percentage of waste-ul scrap has been developed and consists o~ edge rolling a band of material into a helical shape. This process is described in U.S. Patent No. 1,920,354 issued to Carpenter on August 1, 1933i U.S. Patent No. 3,845,647 issued to Cockin on November S, 1974; U.S. Patent Mo. 3,464,10l issued to Zubal on September 2, 1969; U.S. Patent No.
3,062,267 issued to Hart et al on November 6, 1962; and U.S. Patent No. 3,152,629 issued to Rediger on October 13, 35~

2 49,921 1964. These patents all wind helica~ cores from a contin-uous strip of material by rolling the strip on its edge.
Some of these devices, such as Carpenter, Zubal, Rediger, and Hart, utilize a shaping means that exerts a radially inward force on the strip to bend it into a circular shape while others, such as Cockin, use forming rolls to cause the outer edge of the helical winding to be rolled to a thinner cross-section than the inner edge. This thinning operation causes the strip to curl into a generally circu-lar shape.
U.S. Patent No. 4,116,033 issued to Iwaki et al.describes an apparatus and method for forming a wound core which does not result in an outer lamination edge which is thinner than its inner portion. This patent also des-cribes a tooth-slot nesting arrangement for punching its straight strip to minimize scrap material. An apparatus for continuously winding helical cores is described in U.S. Patent No. 3,283,399 issued to Hart et al. on Novcm-ber 8, 1966. This device, like the other edge winding devices described above, can be used to produce the cores made in accordance with the present invention.
Due to the resilience of the strip material, the wound helices made on these devices t-r.d~ to spring back to a shape other than that which was intended. Also, due to variations in the strip's thickness, the outer edge can be~ro~lled to va~ying degrees of deformation which results in varying degrees of circular curling. Because of these problems, various corrective measures have been employed.
U.S. Patent No~ 4,202,196 issued to Asai on May 13, 1980 discloses a method of forminy a core with a precise inner core diameter. This method is in response to the inherent instabiLity of heLicaLly wound cores made in the manner described above. Another aLternative to this problem is described in U.S. Patent No. 3,436,812 issued to Aoki on April 8, 1969 which punches teeth in the strip ater it is formed into a helical shape. This ~jraJ
method winds an unslotted strip into a continuous ~c~

~ ~35~

3 49,921 and then cuts the spiral into a plurality of annularly shaped rings by severing the spiral with a single axial cut. The indivldual rings are then stamped to form a plurality of teeth on their inside edge. This process is intended to avoid the typical misregistration of the teeth that occurs if they are punched in the strip prior ~o the helical winding operation described above.
Another m~thod, responsive to the ~imensional accuracy problems discussed above, is disclosed in U.S.
lOPatent No. 2,058,362 issued to Smally on October 20, 1936.
This patent uses curved laminations which are each approx-imately 91 arcuate degrees in length. By assembling them with their ends abutting each other, a core is progres-sively built.
15Individual laminations are discussed in U.S.
Patent No. 4,102,040 issued to Rich on ~ul~ 25, 1978 which describes a laminated core produced by arranging a plural-ity of straight strips in a stack and then bending t~e stack to form a cylindrical core with an axial parting line formed by its plurality OI aligned s~rip ends.
As should be apparent, helical winding of spiral cores is a means of effectively minimizing scrap in the manufacture of stator cores for dynamoelectric machines, but significant production problems are inherent in the known methods of winding them. These problems have in-duced several corrective techniques which, themselves, increase the cost of manufacture.
It is the object of the present invention to correct the assembly problems of typical edge winding methods with minimal increase in their cost and to also improve the operating characteristics of the finished core.
SUMMARY OF THE INVENTION
~he present invention relates to the production of stator cores for dynamoelectric machines and, more particularly, to the manuacture of edge wound laminated cores that are dimensionally accurate and have improved operating characteristics.

4 49,921 In accordance with the present invention, pre-punched strip material is wound into a helical shape by any suitable method such as the those described above.
Instead of a continuous helix, however, the strip can be wound into segments that are each slightly less than 360 in arcuate length. This can be accomplished by beginning with straight strips of the proper predetermined length or, in the alternative, by severing the circular helix at the proper angular position to result in the generally circular shapes which comprise approximately 359 of a complete annular ring.
Rings made in this manner are then stacked to-gether to form a cylindrical core. Since each individual ring has prepunched teeth on its inner edge, the teeth can lS be aligned to form axially running ~roov~s, or slots.
This registration ca~ be accomplished by stacking the individual laminations on a mandrel which its inside each ring and has radially extending splines which fit into the slots between the teeth of the rings.
Since each ring is less than 360 of a circle, it can easily be deformed to form a dimensionally accurate cylindrical core when associated with other similarly made rings. When a core is thus fo~med, the rings can be ~astened together in any suitab~e way to produce a stator core which is dimensionally accurate and has proper slot registration.
As a further improvement, the electrical proper-ties of a core made in zccordance with the present inven-tion can be significantly improved by producing the straight strips by stamping them rom rolled sheet metal in such a way as to have the direction of rolling run in a parallel direction to the extension of the teeth from the strip or, in other words, perpendicular to the strip's length~ As the strip is edge rolled, the outer edge of the circularly shaped ring is worked so as to orient the grain structure of this outer edge in a circumferential direction or generally parallel to the strip's length while the grain structure of the teeth remains unchanged.

3~;i6~ -49,921 A core made in accordance with the present in-vention can thus comprise a tooth section with radially oriented grain structure and an outer, or yoke, section with circumferentially oriented grain structure. ~his S grain structure orientation results in superior permea-bility and lower iron losses in the îinished cores.
Since cores made in accordance with the present invention are made from straight strip material, two strips can be punched from a thin sheet of metal in such a way as to further minimize scrap.
The teeth of one strip can be arranged to fit in the slots of an adjacent strip on a sheet o~ Imaterial prior to the stamping operation. The strips, by facing in opposite directions in a nested fashion, minimize the scrap produced by eliminating the wasted materia1 that would otherwise be lost from between the teeth. Instead, this material becomes the teeth of the cooperatively associated strip.
For many years motor designers have used graded-slots for single-phase motors. This design principle has often, but not always, been coupled with the use of some-what more nearly rectangular laminations to achieve a general reduction in stamping scrap. Some slots are graded or varied to achieve greater depth in the radial direction. Since constant tooth width is used, it is apparent from the geometry that greater slot width is also achieved. ~he main, or running, winding of the single-phase motor is inserted into these deeper and wider slots.
Conversely, the auxiliary, or starter winding operates only during the starting of the motor and may have signi~icantly less thermal mass. It is inserted into slots which have been graded in ~he opposite manner, that is, shallower and narrower. In the typicaL graded-slot design, tooth pitch is not altered. Both main and starter teeth have identical and constant tooth pitch.
With study of the geometry, it becomes apparent that graded-slots, as just described above, are physically 6 49,921 impo~sible to produce while using the tooth/slot nesting principle to yield minimum scrap. However, in accordance with the present invention, if the grading is done in the opposite manner, using variable tooth and slot pitch, a variable slot and tooth width is obtained and the advan-tages of graded-slots can be maintained. In order to allow the straight strips to be stamped in a nested man-ner, each tooth of a specific straight strip is matched by a slot in the same strip with a generally equal width.
This allows the teeth to be associated in a nested manner . in ~ generally equal slot in another straight strip . . ~
which can be punched simultaneously. According to the present invention, graded slots can therefore be produced in continuous strips of material in a way to minimize scrap and make possible them being edge wound to form helical cores.
It is therefore an object of the present inven-tion to provide a laminated core which can be manufactu~ed with a minimal amount of scrap but which has superior magnetic characteristics to conventionally produced cores.
It is a further object of the present invention to provide a core which can be manufactured with dimensional accur-acy.
BRIEF DESCRIPTION OF THE DRAWINGS
. __ The present invention will be better understood from a reading of the description of the preferred embodi-ment in conjunc:tion with the figures, in which:
Figure 1 is an isometric view of a core made in accordance with the present invention;
Figure 2 is a view of a single laminatlon of the present invention;
Figure 3 illustrates the way the strips of the present invention may be nested during a stamping opera-tion in which they are punched from a continuous sheet of magnetic material;
Figures aA and 4B further illustrate the nested relationship of two straps of magnetic material along with their grain structure orientation;

S6~
7 49,921 Figure 5 demonstrates a straight strip as it is edge rolled to form an annular lamination; showing the resultant changes in its grain structure orientation;
Figu.res 6A and 6B illustrate two straight strips of magnetic material which have been punched with an graded-slot ~ooth configuration; and Figure 7 depicts a graded-slot lamination made in accordance with presently known stamping techniques.
DESCRIPTION OF T~E PR~FERRED EMBODIMENT
A laminated stator core, made in accordance with the present invention, is shown in Figure 1. The core 10 comprises a plurality of generally annular laminations 1~
with each of these laminations 12 comprising a plurality of teeth 14 which extend radially inward ~rom a yoke portion 16 thereof. Each circular lamination 12 extends circumferentially around the cylindrical core 10 for an arcuate distance which is slightly less than 360. It has been determined that a lamination which comprises from 355~ to 359 of a circle can satisfactorily produce a core 10 made in accordance with the present invention. The remaining arcuate distance that is not traversed by the lamination 12 forms a slight gap 18 between the two adja-cent ends of each lamination. As shown in figure 1, the laminations 12 are stacked in such a way as to randomly distribute their gaps 18 around the periphery of the core 10 .
After the laminations 12 are s.acked with their teeth 14 and slots 20 aligned to form axially running grooves, the outside diameter of the core 10 can be formed to a preselected dimension by compressing it radially inwardly while the laminations are mounted on a mandrel to produce the desired dimensions of the inside diameter of the core. Any deformation in an individual lamination 1 will be compensated by an associated change in its gap 18.
Therefore, it should be understood that the core can be formed in such a way as to correct for any individual variation in laminations.

3~
8 49,921 This ability to form the outside diameter of the core enables dimensionally oversized or ~mdersized lamin-ations to be corrected during assembly. It has been found that conventional edge winding equipment does no-t produce circular laminations 12 to precise tolerances and a cer-tain amount of resiliency in the shaped lamina~ion is to be expected.
By stacking the individual laminations 12, as shown in Figure 1, they can also be aligned over a splined mandrel which fits into the inside diameter of the lamina-tions 12. This allows proper tooth 14 registration to be maintained during ~he forming process.
When the diameters are ~ormed with dimensional accuracy and the teeth 14 are properly aligned, the lamina-tions 12 can then be fastened together by any suitablemeans such as welding or potting.
Figure 2 shows a single lamination 12 with its teeth 14, slots 20 and gap 18. The teeth 14 extend radi-ally inward from the lamination's yoke portion 16. Be-tween each adjacent pair of teeth 14, a slot 20 is formedwhich is sized to accept a stator conductor after the lam-ination is stacked with others to form a core. It should be apparent that the gap 18 allows the lamination 12 shown in Figure 2 to be radially compressed to a smaller diameter than illustrated in Figure 2, limited only by the size of the gap 18.
The armular lamination 12, or ring, shown in Figure 2 can be manufactured by any of the edge winding techniques described above. It can be severed from a con-tinuous helical coil or rolled from a precisely measuredstraight strip whose length has been determined to result in the proper circumferential dimension required to pro-duce a lamination which has a predetermined gap and is of a preselected circular configuration. A representative apparatus on which the rlng 12 can be produced is des-cribed in copending Canadian application Serial Number 410,253 filed August 26, 1~81 assigned to the assignee of the present application.

35~j~
9 49,921 When each of the laminations are rolled from in-dividual straight strips of material, as discussed above, additional advantages can be realized in the magnetic characteristics of each lamination and therefore of the completed core. Figure 3 shows a sheet 30 of rolled sheet material from which laminations are to be made. Sheet material of this type is normally rolled in the direction ,~t shown by the arrow R1. This rolling, which is inherent in the manufacture of rolled sheet material of this~e~sults in a grain orientation of the material which is in the direction of the arrow R1.
Also shown in Figure 3 are four typical straight strips 32a, 32b, 32c and 32d, which are to be eventually edge-wound into circular laminations. The strips are stamped from the sheet in such a way that their individual lengths are perpendicular to the direction of grain orien-tation Rl. Figure 3 also demonstrates the cooperative association of strip 32a with 32b and of strip 32c with 32d. Each of these pairs comprises two nested strips wherein the teeth of one strip ~ disposed in the slot of its associated strip to minimize scrap. It should be understood that, for teeth which are not rectangular, total eliminatlon of scrap is not possible. However, the nesting of associated strips, as shown in Figure 3, mini-.25 mizes the amount of scrap produced for any particulartooth design.
It should be understood that many tooth designs are not rectangular as shown in Figure 3. Instead, some are shaped with rounded bottoms as shown ln Figure 2.
However, since the present invention is not dependent on a particular tooth configuration, rectangular tooth shapes will be illustratively used herein.
Using straight strips 32a and 32b from Figure 3, Figures 4A and 4B further show their nested relationship as the two are parted. Arrows R1 illustrate the original direction of grain orientation, as described in conjunc tion with Figure 3 and the discussion above. As Figures 3~i68 49,921 4A and 4B clearly show, the grain orientation is the same throughout both straight s~rips and is consistent in both the tooth 14 and yoke 16 portions of the strips. It should be understood that this particular orientation of grain structure in the straight strips is due to both the rolling direction by which the roll of sheet metal (ref-erence numeral 30 of Figure 3) was produced and the orien tation of the straight strips on that sheet metal. As Figure 3 illustrates, the straight strips 32a, 32~, 32c and 32d were punched from the sheet 30 so that their lengths were perpendicular to the direction of rolling R.
Figure 5 illustrates a strip 32b of material as it is being formed into a circular, edge wound shape. It should be understood that, although no winding e~uipment lS is shown in Figure 5, any device that is capable of edge winding a straight strip, such as 32b, of prepunched material into an annular shape can be utilized.
~ s the strip is rolled into a circle, i~s outer edge is elongated and becomes thinner. This elongation is a physical necessity because of the greater circumferen-tial distance around which the outer edge extends. When a prepunched strip is edge-rolled, it typically experiences elongation from its outer edge S0 to a point 52 just below the root of the slot 20. Betwesn this point 52 and the root of the slot 20, the strip experiences a slight com-pression and, in the tooth 14 region, no material deforma-tion occurs.
Tha elonbgation of the outer portion, or yoke 16, of the strip ~ causes the grain structure in that por-tion of the strip to become oriented in the direction ofelongation of the strip. Arrows R2 show this new direc-tion of grain orientation in Eigure 5. It should be apparent that, since the yoke 16 is elongated and the tooth 14 portion is not deformed, the result of the edge rolling operation is to orient the grain structure of the yoke 16 in a circumferential direction R2 whiLe leaving the grain structure of the teeth 14 unchanged and oriented 3~
11 49,921 in a radial direction in the annular lamination that is produced by the edge rolling operation. It should further be apparent tc one skilled in the art that this selective grain orientation of the tooth 14 and yoke 16 portions of each lamination improve the magnetic characteristics, increasing permeability and reducing iron losses.
Figures 6A and 6B illustrate a variation of the present invention in which the slots 20 and the teeth 14 do not comprise a uniform pitch. This type of construc-tion, referred to herein as a graded-slot design, selec tively provides larger slots for the main wi~ding and smaller slots for the auxiliary winding of a single phase motor. It should be apparent from a viewing of Figures 6 and 6B together that the elements and methods of the present invention are equally applicable in graded-slot designs. Of course, in order to permlt the eco~omical nesting described above, the tooth widths and slot widths must be coordinated so that the teeth 14 of one strip 6~a are cooperatively associated wi~h ~he slots 20 of another strip 60b, and vice versa. It sho~ld be apparent from these figures that, even in graded-slot designs, the material saving nesting techniques described above and shown in Figures 3, 4A and 4B are appl cable. It should further be apparent that the selective grain orientation, also describecl above, can be achieved in an graded-slot design.
Figure 7 depicts a graded-slot lamination de-signed for manufacture by presently used stamping tech~
niques. It ccnsists of slots of variable depth in order to provide slots with variable area. .~s e~plained above, the purpose of this variability is to provide large slots for the maln windings and small slots for the auxiliary winding. The auxiliary winding slot 71 is clearly smaller than the main winding slot 72 with gradations therebe-tween. It should be obvious, by studying the geometry involved, that a pattern of varying slot depths, as shown in Fig. 7, is not physically possible to manufacture while 12 ~g,~21 achieving the maximum savings obtained in a double width strip having full slot to tooth meshing as shown in Fig ures 3, 4a and 4b. The graded-slot design of the present invention, as shown in Figs. 6A and 6B, in contrast, utilizes slots which have a constant depth and is thus manufacturable. This geometric advantage, which results in reduced material usage, accrues irrespective of the method used for edge winding or forming the strip and irrespective of the usage of the grain orientation advan-tage illustrated in Figures 3, ~a and 4b.
The present invention provides a laminatedstator core that utilizes edge rolled laminations which result in significant material savings. It further pro-vides a means of correcting typical malformations expari-enced in most conventional roll-forming methods by employ-ing single laminated rings ~ith a gap within each lamina-tion. Also, ~he present invention makes possi~le a selec-tive grain orientation within each lamination which si~g-nificantly improves the magnetic characteristics of the core and the electrical performance of ~he resulting dynamoelectric machine. Furthermore, it is applicable to both uniform and graded-slot designs.
It should be apparent to one skilled in the art that the present invention provides a stator core that reduces manufacturing costs and improves the electrical characteristics of a dynamoelectric machine comprising it.
It should also be understood that, although the present invention has been described in considerable detail and with particularity, it should not be considered to be so limited.

Claims (2)

What I claim is:

1. A core for a dynamoelectric machine, comprising:
a plurality of annular laminations, each of said laminations comprising a sheet metal arcuate section of less than 360°, each of said plurality of annular laminations having its ends spaced apart to describe a gap therebetween, each of the plurality of gaps being disposed at differing annular positions around said core, each of said plurality of annular laminations having a plurality of teeth extending in a radially inward direction, each of said plurality of laminations being formed by edge-rolling a straight strip of material into a generally circular shape, said straight strip of material having a length which is predetermined to result in said annular lamination of less than 360 arcuate degrees, said length of said straight strip being substantially greater than the width of said straight strip, each of said plurality of teeth having a grain structure orientation which is generally parallel to the diameter of said core, each of said plurality of laminations being a single piece of said material having a grain structure orientation in its radially outward portion which is generally circumferential and which is generally concentric with said core.

2. A core for a dynamoelectric machine, comprising:
a plurality of annular laminations, each of said annular laminations comprising a sheet metal arcuate section of less than 360°, each of said plurality of laminations hav-ing its ends spaced apart to describe a gap therebetween with the plurality of gaps being disposed at differing angular positions around said core, each of said plurality of lamina-tions having a plurality of teeth extending in a radially in-ward direction, each of said plurality of laminations being formed by edge-rolling a straight strip of material into a generally circular shape, said straight strip of material having a length which is predetermined to result in an annular lamination comprising less than 360 arcuate degrees, said length of said strip of material being substantially greater than its width, said plurality of teeth describing a plurality of slots therebetween with each of said plurality of slots be-ing disposed between an adjacent pair of said teeth, each of said plurality of slots having a radial dimension which is gen-erally equal to the radial dimension of each other slot, each of said plurality of teeth varying significantly in its circum-ferential dimension than others of said plurality of teeth, each of said plurality of slots varying significantly in circumfer-ential dimension than others of said plurality of slots, said variations in the circumferential dimensions of said teeth and said slots resulting in a nonuniformity of tooth pitch in each of said plurality of laminations.