Stator cores and methods for fabricating stator cores are provided. An exemplary stator core includes a stack of laminations. Each lamination in the stack of laminations comprises a yoke and a plurality of tooth segments fixed to the yoke.

INTRODUCTION

The technical field generally relates to electric machines, and more particularly relates to stators for electric machines.

An electric motor uses electric potential energy to produce mechanical energy through the interaction of magnetic fields and current-carrying conductors. The reverse process, using mechanical energy to produce electrical energy, is accomplished by a generator or dynamo. Other electric machines, such as motor/generators, combine various features of both motors and generators.

Electric machines may include an element rotatable about a central axis. The rotatable element, which may be referred to as a rotor, may be coaxial with a static element, which may be referred to as a stator. The electric machine uses relative rotation between the rotor and stator to produce mechanical energy or electrical energy.

Typically, the stator is made from hundreds of laminations. Use of stator laminations rather than a single unitary stator provides a number of advantages including the reduction of eddy current. Specifically, the electromagnetic field of a stator core generates a voltage, called an eddy current, that may result in power loss and diminished performance. Stator laminations reduce eddy current by insulating the stator core. Specifically, thin silicon steel plates that are stacked on top of one another around the center prevent eddy current flow. Further, the use of laminations cools the stator core. A solid unitary stator core would heat up with the eddy current. Therefore, reduction of the eddy current also prevents overheating of the stator core. Also, the use of laminations reduces hysteresis loss. Specifically, lamination plates have narrow hysteresis loops, requiring less energy to magnetize and demagnetize the core, thereby making the motor more efficient.

While the use of laminations in stators provides several benefits, the production of laminations can be wasteful and may not provide for optimized performance. It would be desirable to develop methods of fabricating stator cores that reduces material waste and provides for improved electrical performance. Also, it would be desirable to provide stator cores with improved electrical performance. Furthermore, other desirable features and characteristics of embodiments herein will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

SUMMARY

In an exemplary embodiment, a stator core is provided and includes a stack of laminations. Each lamination in the stack of laminations comprises a yoke and a plurality of tooth segments fixed to the yoke.

In exemplary embodiments of the stator core, each lamination in the stack of laminations is centered about a central axis, each tooth segment in the plurality of tooth segments comprises grain oriented electrical steel (GOES) material, and each tooth segment in the plurality of tooth segments has a tooth grain orientation in a radial direction from the central axis. In further exemplary embodiments, the yoke in each lamination in the stack of laminations comprises yoke segments, each yoke segment comprises GOES material, and each yoke segment has a yoke grain orientation perpendicular to the radial direction from the central axis. In further embodiments, the yoke in each lamination in the stack of laminations comprises yoke segments, and each yoke segment comprises non grain oriented electrical steel (NGOES). In further embodiments, the yoke in each lamination in the stack of laminations is non-segmented and comprises non grain oriented electrical steel (NGOES).

In exemplary embodiments of the stator core, each tooth segment in the plurality of tooth segments is fixed to a respective yoke by an interlock structure selected from at least a first interlock structure and a second interlock structure different from the first interlock structure. In further embodiments, the stack of laminations includes a middle lamination having a middle yoke, an upper lamination over and contacting the middle lamination and having an upper yoke, and a lower lamination under and contacting the middle lamination and having a lower yoke; the plurality of tooth segments includes middle tooth segments fixed to the middle yoke, lower tooth segments fixed to the lower yoke, and upper tooth segments fixed to the upper yoke; a selected middle tooth segment fixed to the middle lamination by a selected first interlock structure is located under a selected upper tooth segment and over a selected lower tooth segment; and neither the selected upper tooth segment nor the selected lower tooth segment is fixed to the upper lamination or the lower lamination, respectively, by the first interlock structure. In further embodiments, the stack of laminations includes a middle lamination having a middle yoke, an upper lamination over and contacting the middle lamination and having an upper yoke, and a lower lamination under and contacting the middle lamination and having a lower yoke; the plurality of tooth segments includes middle tooth segments fixed to the middle yoke, lower tooth segments fixed to the lower yoke, and upper tooth segments fixed to the upper yoke; and interlock structures in adjacent laminations are staggered such that a selected middle tooth segment fixed to the middle yoke by a first interlock structure does not lie directly under an upper tooth segment fixed to the upper yoke by a first interlock structure and does not lie directly over a lower tooth segment fixed to the lower yoke by a first interlock structure.

In exemplary embodiments of the stator core, the yoke in each lamination in the stack of laminations comprises yoke segments; each pair of adjacent yoke segments is interconnected at a yoke interface; the stack of laminations includes a middle lamination, an upper lamination over and contacting the middle lamination, and a lower lamination under and contacting the middle lamination; and yoke interfaces in adjacent laminations are staggered such that a selected yoke interface in the middle lamination does not lie directly under any yoke interface in the upper lamination and does not lie directly over any yoke interface in the lower lamination.

In another exemplary embodiment, a stator core is provided and includes a middle lamination; an upper lamination over and contacting the middle lamination; and a lower lamination under and contacting the middle lamination. Each lamination comprises yoke segments, and within each lamination each adjacent pair of yoke segments is interlocked at a yoke interface. Further, yoke interfaces in adjacent laminations are staggered such that a selected yoke interface in the middle lamination does not lie directly under a yoke interface in the upper lamination and does not lie directly over a yoke interface in the lower lamination. In an exemplary embodiment of the stator core, each yoke segment comprises non grain oriented electrical steel (NGOES).

In yet another exemplary embodiment, a method for fabricating a stator core is provided. The method includes aligning an expandable arbor within an expandable sleeve, and adjusting an outer edge of the expandable arbor to a desired inner diameter for the stator core. Further, the method includes forming a lower lamination between the expandable arbor and expandable sleeve, forming a middle lamination between the expandable arbor and expandable sleeve, and forming an upper lamination between the expandable arbor and expandable sleeve. Also, the method includes contracting an inner edge of the expandable sleeve to a desired outer diameter for the stator core, and connecting the lower lamination, the middle lamination and the upper lamination to one another to form the stator core.

Exemplary embodiments of the method further include punching yokes and tooth segments from sheets of material. In such embodiments, forming the lower lamination, forming the middle lamination, and forming the upper lamination comprise interconnecting the yokes and the tooth segments.

Exemplary embodiments of the method further include punching yoke segments and tooth segments from sheets of material. In such embodiments, forming the lower lamination, forming the middle lamination, and forming the upper lamination comprise interconnecting the yoke segments and the tooth segments.

Exemplary embodiments of the method further include punching yoke segments including teeth from sheets of material. In such embodiments, forming the lower lamination between the expandable arbor and expandable sleeve comprises positioning lower yoke segments between the expandable arbor and expandable sleeve and interconnecting the lower yoke segments to form the lower lamination, forming the middle lamination between the expandable arbor and expandable sleeve comprises positioning middle yoke segments between the expandable arbor and expandable sleeve and interconnecting the middle yoke segments to form the middle lamination, and forming the upper lamination between the expandable arbor and expandable sleeve comprises positioning upper yoke segments between the expandable arbor and expandable sleeve and interconnecting the upper yoke segments to form the upper lamination. Further exemplary embodiments include contracting and removing the expandable arbor after forming the stator core.

In exemplary embodiments of the method, lower yoke segments are interconnected at lower yoke interfaces, middle yoke segments are interconnected at middle yoke interfaces, and upper yoke segments are interconnected at upper yoke interfaces, and positioning the lower yoke segments, positioning the middle yoke segments, and positioning the upper yoke segments comprises staggering the middle yoke interfaces from the lower yoke interfaces and the upper yoke interfaces.

Exemplary embodiments of the method include punching tooth segments and the lower, middle and upper yoke segments from sheets of material, and interconnecting the tooth segments and the lower, middle and upper yoke segments before positioning the lower, middle and upper yoke segments between the expandable arbor and expandable sleeve.

In exemplary embodiments of the method, punching the tooth segments comprises forming the tooth segments from grain oriented electrical steel (GOES) material. In such embodiments, after forming the stator core, each yoke segment has a yoke grain orientation perpendicular to the radial direction from a central axis of the stator core.

In exemplary embodiments, interconnecting the tooth segments and the lower, middle and upper yoke segments comprises interconnecting the tooth segments and the lower, middle and upper yoke segments with interlock structures selected from at least a first interlock structure and a second interlock structure. In such embodiments, positioning the lower, middle and upper yoke segments comprises staggering the interlock structures such that a selected first interlock structure in the middle lamination is not located directly over a first interlock structure in the lower lamination and is not located directly under a first interlock structure in the upper lamination.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

As used herein, the word “exemplary” means “serving as an example, instance, or illustration”. As used herein, “a,” “an,” or “the” means one or more unless otherwise specified. The term “or” can be conjunctive or disjunctive. Open terms such as “include,” “including,” “contain,” “containing” and the like mean “comprising.” In certain embodiments, numbers in this description indicating amounts, ratios of materials, physical properties of materials, and/or use are may be understood as being modified by the word “about”. The term “about” as used in connection with a numerical value and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. In general, such interval of accuracy is ±10%. All numbers in this description indicating amounts, ratios of materials, physical properties of materials, and/or use may be understood as modified by the word “about,” except as otherwise explicitly indicated. As used herein, the “%” or “percent” described in the present disclosure refers to the weight percentage unless otherwise indicated. Further, terms such as “above,” “over,” “below,” “under,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the subject matter, as defined by the appended claims. Any numerical designations, such as “first” or “second” are illustrative only and are not intended to limit the scope of the subject matter in any way. It is noted that while embodiments may be described herein with respect to automotive applications, those skilled in the art will recognize their broader applicability.

Embodiments herein are related to motor, specifically stator, design. Certain embodiments provide for portions of the stator to be fabricated separately from other portions of the stator before being assembled and connected together. Specifically, tooth segments and yoke segments may be fabricated separately, such as by punching or stamping from sheets of material. As a result, each segment may be optimized for stator magnetic flux and for creating minimum material scrap, particularly of expensive material, from the stamping process. The segmentation design of the laminations and the selection of the material for the segmented sections of the lamination may enhance the magnetic flux and/or manufacturing process depending on the application.

Referring to the drawings, wherein like reference numbers correspond to like or similar components whenever possible throughout the several figures, there is shown inFIG.1an isometric view of a stator core10. Features and components shown in other figures may be incorporated and used with those shown inFIG.1.

The stator core10is shown partially assembled inFIG.1, and may be used to construct a stator (not shown). The stator core10may be one component of an electric machine (not shown), such as an electric motor, generator, or motor/generator. The stator core10may be configured to interface with a housing or support (not shown) of an electric machine into which the stator core10is incorporated, or with a transmission housing (not shown) when the stator core10is part of a transmission or hybrid transmission (not shown).

As shown inFIG.1, the stator core10defines a central axis15. Further, the stator core10has an annular yoke20and teeth30located on the interior side of the annular yoke and extending toward the central axis15, such that the stator core10will cooperate with an interior rotor (not shown). However, the elements and components described herein and illustrated with respect to the stator core10may also be used to construct an electric machine having an exterior rotor and interior stator, such that the stator teeth30may be located on the exterior of the yoke20and extend outwardly from the yoke20. In either case, the stator teeth30may be used to support and align stator windings (not shown) in winding slots formed between the stator teeth30. The stator windings are conductive wires or cables through which current may flow during operation of the electric machine.

The stator core10comprises a plurality of layers or laminations40. In certain embodiments, the stator core10may include a hundred laminations or more.FIG.2illustrates for reasons of clarity only three laminations40that may be used in a stator core10, i.e., a lower lamination41, a middle lamination42, and an upper lamination43.FIG.3provides a top view of a single lamination40fromFIG.2.

Embodiments herein provide for laminations40that include a non-segmented unitary yoke20, such as a yoke20that is punched from a sheet of material in one piece, or a yoke20that comprises segmented yoke segments that are fabricated separately and connected or fixed together. Further, embodiments herein provide for laminations40including teeth30comprising a plurality of tooth segments that are fabricated separately from, and connected or fixed to, the yoke20(or yoke segments), or that are fabricated with and integral with the yoke20(or yoke segments), such as teeth30that are punched from a sheet of material in one piece with a unitary yoke or with a yoke segment.

In the illustrated embodiment of the laminations40inFIGS.2-3, for each lamination40, the yoke20is segmented and includes yoke segments22. Each yoke segment22includes a connection feature24at each end, such that each pair of adjacent yoke segments is interconnected or fixed to one another at a yoke interface26therebetween. For example, each yoke segment22may have a male connection feature24at one end and a reciprocal female connection feature24at an opposite end. In an exemplary embodiment, the connection features24are universal such that any pair of yoke segments22may be interconnected at a yoke interface26therebetween.

In the illustrated embodiment, the connection features24comprise a dovetail structure. The central portion of the each dovetail connection feature24extends perpendicular to the radial direction19of the central axis15, i.e., in a tangential direction relative to the central axis15. The dovetail size may be designed as a function of the yoke width (back iron) and the core assembly stress requirements for the motor. While a sixty degree dovetail is contemplated, any suitable included angle may be used and can be reduced as necessary as a function of the yoke width. In an exemplary embodiment, the opening of the dovetail may be about 25% of the yoke width (12 mm) and may be located about 40% of the yoke width from the outside radius of the yoke segment. For example, a dovetail opening for the segment may be 3 mm and may be located 5 mm from the outer diameter of the yoke segment. The dovetail may be designed with a selected radius at the four corners for the male and female sections of the features24to reduce stresses and improve the assembly automation.

As illustrated, exemplary laminations40comprise a plurality of yoke segments22. The yoke segments22cooperate to define the laminations40as individual layers of the stator core10ofFIG.1. In the embodiments ofFIGS.2-3, the yoke20of each lamination40includes eight yoke segments22such that each yoke segment22comprises forty-five degrees of the annular yoke20; however, it may be desirable to utilize fewer or more yoke segments22in the yoke20of each lamination40, such as from one to seventy-two segments or more depending on the stator diameter and the number of teeth around the stator. For example, the stator illustrated inFIGS.1-3has seventy-two teeth and in an exemplary case, the number of yoke segments may be two, three, four, six, eight, nine, twelve, eighteen, twenty-four, thirty-six, or seventy-two and the corresponding teeth per segment will be thirty-two, twenty-four, eighteen, twelve, nine, eight, six, four, three, two or one so that the product of the number of yoke segments and the number of teeth per yoke segment is equal to seventy-two. This indicates that a larger diameter stator can be split into more yoke segments assuming the number of teeth increases with diameter. In an exemplary embodiment, each lamination40in the stator core includes a same amount of yoke segments22; however, it is contemplated that laminations40in a stator core10may be provided with different numbers of yoke segments22.

Cross-referencingFIGS.1and2, it may be seen that the stator core10may include laminations40that are arranged or stacked in alternating layers. The laminations40are aligned about the central axis15, and are rotated relative to each other about the central axis15such that each lamination40is offset relative to the respective adjacent or adjoining laminations40. With this alignment and offset, a bricklayer type pattern results.

InFIG.2, each lamination40, i.e., lower lamination41, middle lamination42, and upper lamination43, is rotated about the central axis15at a selected angle relative to each other. While illustrated as being five degrees, the angle of rotation between adjacent laminations40may be any suitable angle and the minimum rotation is determined by the angle of a single tooth. As shown, each lamination40is offset relative to the respective adjacent laminations40by the selected angle such that the yoke interfaces26, i.e., joints between yoke segments22are not aligned, i.e., are not located directly over or under one another. When viewed from the side or an isometric view the yoke interfaces26between yoke segments22are staggered from lamination41or42to adjacent lamination42or43. This is indicated clearly inFIG.2and inFIG.5, which provides an exploded top isometric view of a portion of the three laminations41,42and43ofFIG.2. InFIGS.2and5, yoke segments22are identified in the lower lamination41as lower yoke segments221and are connected at lower yoke interfaces261, yoke segments22are identified in the middle lamination42as middle yoke segments222and are connected at middle yoke interfaces262, and yoke segments22are identified in the upper lamination43as upper yoke segments223and are connected at upper yoke interfaces263. As shown, the middle yoke interfaces262are not aligned with the lower yoke interfaces261or the upper yoke interfaces263. Further, the lower yoke interfaces261are not aligned with the upper yoke interfaces263. As a result, no connection feature24in a lamination40, such as middle lamination42, is aligned with, i.e., located directly over or under (in the perspective illustrated), a connection feature24in the adjacent laminations40, such as laminations41and43.

InFIG.5, the yoke interfaces of the lower, middle, and upper laminations are illustrated as being staggered by rotating each lamination by the distance of about the width of one tooth segment. However, adjacent laminations may be rotated relative to one another by any desired distance, such as distances of about the width of two, three, four, five, or other desired number of tooth segments.

Referring back toFIGS.2-3, for each lamination40, the teeth30are a plurality of tooth segments32. InFIGS.2-3, nine tooth segments32are connected to each yoke segment22. However, any suitable number of teeth per segment may be determined as a function of the stator inside diameter, the yoke width (back iron), and the lamination material (grain oriented electrical steel (GOES) or non-grain oriented electrical steel (NGOES) as described below).

Stator tooth design may be based on the motor optimization characteristics, such that an optimum number of tooth segments or teeth30per yoke segment22can be estimated based on the percentage flux loss.

In an exemplary embodiment, each tooth segment32is I-shaped, with a narrow midsection and wider ends. As shown, each tooth segment32has a proximal end33that includes an interlock structure34provided for connecting or fixing the tooth segment32to the yoke20, resulting in a tooth interface36therebetween. At the proximal end33, each tooth segment32includes an interlock structure34or a portion of an interlock structure34. The interlock structure34of each tooth segment32is provided to connect or fix the tooth segment32to the yoke20.

Referring now toFIG.4, it may be seen that embodiments herein provide for the use of at least two different interlock structures34. Specifically, inFIG.4, a first interlock structure341is provided to connect or fix a selected middle tooth segment322to the yoke segment22while a second interlock structure342is provided to connect or fix an adjacent middle tooth segment322to the yoke segment22.

As shown, first interlock structure341has a first width indicated by arrow96and a first depth indicated by arrow97, while second interlock structure342has a second width indicated by arrow98and a second depth indicated by arrow99. While first interlock structure341and second interlock structure342share a common dovetail shape, second interlock structure342differs from first interlock structure341in size, such that second width98is greater than first width96and second depth99is greater than first depth97. While first interlock structure341and second interlock structure342share a common shape inFIGS.2-4, the interlock structures341and342may differ by having different shapes and common sizes, or by having different shapes and different sizes. Generally, the dovetail size is a function of the tooth segment width and lamination design. For example for an exemplary lamination including seventy-two tooth segments and having an internal diameter of about 240 mm, the larger interlock structure342may have a width97of about 5.5 mm. The dovetail opening width is determined by the tooth segment width and slot opening between tooth segments.

As shown inFIG.5, in the middle lamination42, a selected middle tooth segment322is fixed to the yoke20by a second interlock structure342. In the lower lamination41, a selected lower tooth segment321, lying directly under the selected middle tooth segment322, is fixed to the yoke20by a first interlock structure341. In the upper lamination43, a selected lower tooth segment323, lying directly over the selected middle tooth segment322, is fixed to the yoke20by a first interlock structure341. Accordingly, in an exemplary embodiment, no first interlock structure341lies directly over or directly under, i.e., vertically adjacent to, another first interlock structure341, and no second interlock structure342lies directly over or directly under, i.e., vertically adjacent to, another second interlock structure342when stacked in the stator core10ofFIG.1.

While only first and second interlock structures341and342are expressly illustrated inFIGS.4and5, it is contemplated that more than two interlock structures34may be used in, and staggered throughout, the stator core10such that no selected interlock structure type lies directly over or directly under, i.e., vertically adjacent to, another same interlock structure type. For manufacturing simplicity, the upper lamination41may use only one structure341around the yoke, while the middle lamination42uses only the different structure342around the yoke, and the lower lamination43may use the same structure341as the upper lamination41. This pattern may alternate among adjacent laminations so that two identical structures do not overlap.

Referring back toFIGS.2and3, exemplary embodiments provide for the formation of tooth segments32from a selected material. For example, each tooth segment32may comprise or consist of grain oriented electrical steel (GOES) material. As shown inFIG.3, when comprised of GOES material, each tooth segment32may be fabricated and assembled such to have a tooth grain orientation indicated by arrow39in a radial direction from the central axis15, i.e., the direction of the grain orientation is along the length of the tooth segment32. Such an orientation may provide for improved electrical performance. Specifically, the GOES material has better magnetic flux density in the direction of the grain orientation compared to NGOES material. Further, during design, the length of the tooth segments may be adjusted to optimize electrical performance. Tooth segments32may comprises or consist of NGOES material, for example when a higher flux density is not required and when reducing the scrap rate of the material is important to reduce the motor cost.

In certain embodiments, the yoke segments22may comprise or consist of GOES material and have a yoke grain orientation indicated by the arrows29perpendicular to the radial direction from the central axis15. Such an orientation may provide for improved electrical performance. In other embodiments, the yoke segments comprise or consist of non grain oriented electrical steel (NGOES).

Thus, it is contemplated that a stator core10may be fabricated from laminations40having: tooth segments comprised of GOES material and yoke segments comprised of GOES material; tooth segments comprised of GOES material and yoke segments comprised of NGOES material; tooth segments comprised of NGOES material and yoke segments comprised of GOES material; or tooth segments comprised of NGOES material and yoke segments comprised of NGOES material. Generally, maximum performance of an electric machine comprising the stator core may be achieved by utilizing GOES material in either or both of the yoke and teeth such that the grain direction is in the same direction that flux is expected to flow.

Referring now toFIG.6, a portion of a lamination40used in a stator core10is shown. Similar to the embodiment ofFIG.1, inFIG.6, the lamination40is comprised of a yoke20comprising yoke segments22, and the yoke segments22include integral teeth30, i.e., tooth segments32are not segmented from the yoke segments22, but are unitary with and included in the yoke segment22when fabricated, such as by stamping from a sheet of material. Such an embodiment may be desirable particularly when both the yoke segments22and teeth30may be comprised of NGOES material. The lamination40ofFIG.5may be arranged as described above to provide staggered yoke interfaces46in the stator core.

In another embodiment, each yoke20may be a single-piece, unitary member. In other words, each yoke may be comprised of a single endless yoke segment22. Such an embodiment may be desirable particularly when the yoke20or yoke segment22may be comprised of NGOES material and the tooth segments32connected thereto may be comprised of GOES material.

Referring now toFIG.7, a method for fabricating a stator core may include punching yoke segments with integral teeth or punching, separately, yokes or yoke segments and tooth segments from sheets of material. For embodiments with tooth segments, the method includes interconnecting the tooth segments and the yoke segments. The method may include bonding the tooth segments to the yoke. The fabrication method may include welding the stacked laminations at several locations around the outer diameter of the stack or by chemically bonding the individual laminations to one another. For either process, stacking the laminations may be performed with a special fixture to make sure the laminations are aligned properly in a perfect circle with minimum variation due to the tolerances at the wedge interlocks. Specifically, the method further includes aligning an expandable arbor70about central axis15and within an expandable sleeve80and adjusting an outer edge71of the arbor70to a desired inner diameter for the stator core. A bottom plastic dielectric ring plate (not shown) may be placed between the arbor70and sleeve80to support the laminations to be formed.

Thereafter, the method includes positioning lower yoke segments between the arbor70and sleeve80and interconnecting the lower yoke segments to form a lower lamination, positioning middle yoke segments between the arbor70and sleeve80and interconnecting the middle yoke segments to form a middle lamination; and positioning upper yoke segments between the arbor70and sleeve80and interconnecting the upper yoke segments to form an upper lamination. Positioning the yoke segments may comprise staggering the middle yoke interfaces from the lower yoke interfaces and the upper yoke interfaces as described above. Also, positioning the yoke segments may comprise staggering the interlock structures such that a selected first interlock structure in the middle lamination is not located directly over a first interlock structure in the lower lamination and is not located directly under a first interlock structure in the upper lamination as described above. As described above, the number of laminations formed between the arbor70and sleeve80may be one hundred or more.

The method may include positioning a top plastic dielectric ring plate90over the top of the uppermost lamination in the stack of laminations to control the stacking factor and hold the tooth segments to prevent any movement during the insertion of hairpins. After the laminations are assembled together to form the stator, the hairpins are inserted in the slots between the teeth. A hairpin has the shape of a Greek pi and one leg is inserted in one of the slots and the second leg in a different slot to form the wiring diagram. The hairpin's legs will fill-up the slots between the teeth. The current flowing through the hairpin generates the magnetic field around the stator.

After the laminations are positioned as desired, the method includes contracting an inner edge81of the expandable sleeve80to a desired outer diameter for the stator core. Further, the method includes connecting the stack of laminations to one another to form the stator core. For example, the method may include bonding the laminations together or welding the laminations together. After forming the stator core, the method may include retracting and removing the expandable arbor.

As described herein, embodiments provide for stator cores having improved electrical performance. Further, embodiments provide for improved methods for fabricating stator cores that may reduce material waste, and specifically reduce waste of expensive materials through the optimization of design and processing.