WO2008033175A2

WO2008033175A2 - Fabrication of heat-treated laminations for high-speed rotors in electrical machines

Info

Publication number: WO2008033175A2
Application number: PCT/US2007/014005
Authority: WO
Inventors: Michael C. Lewis; Raymond C. Zowarka, Jr.; Michael D. Werst
Original assignee: Board Of Regents, The University Of Texas System
Priority date: 2006-06-14
Filing date: 2007-06-13
Publication date: 2008-03-20
Also published as: WO2008033175A3

Abstract

Embodiments of the present invention include methods and an apparatus to fabricate heat treated laminations (61) such as for high-speed rotors of electrical machines. A method, for example, includes heat treating a steel material, cutting a lamination pattern in the steel material to define a plurality of laminations (61), and bonding sets (31) of the plurality of steel laminations (61).

Description

FABRICATION OF HEAT-TREATED LAMINATIONS FOR HIGH-SPEED ROTORS IN ELECTRICAL MACHINES

BACKGROUND OF THE INVENTION

1. Related Applications

[0001] This non-provisional application claims priority to and the benefit of U.S. Patent Application No. 60/813,680, by Lewis et al. titled "Fabrication of Heat-Treated Laminations for High-Speed Rotors in Electrical Machines," filed June 14, 2006, incorporated herein by reference in its entirety.

2. Government License Rights

[0002] This invention was made with government support under Contract No. 26-3912- 03xx awarded by the United States Navy/General Atomics Division. The government has certain rights in the invention.

3. Field of the Invention

[0003] The present invention relates to the power industry and, more particularly by the field of electrical machines.

4. Description of Related Art

[0004] Conventional electric machines such as, for example, electric motors and electric generators, are typically in the form of a rotor connected to a rotatable shaft which rotates within the confines of a stator. These machines use electromagnetic principles to convert mechanical energy into electricity or vice a versa. On relatively small machines, the magnetic field may be provided by one or more permanent magnets. On relatively large machines, the magnetic field is created using electromagnets.

[0005] One phenomenon inherent with such electric machines, which utilize changing magnetic fields, is the production of eddy currents, which transform useful kinetic energy into heat. Such eddy currents generally reduce the efficiency of such electric machines. In order to minimize such currents, various methodologies have been employed including the use of magnetic core materials that have low electrical conductivity, such as, for example, iron alloyed with silicone, and/or the use of thin insulated sheets of magnetic or magnetically receptive material, typically referred to as laminations. Larger electric machines generally favor the use of thin sheets of laminations having an insulating material or paint inserted therebetween to aid in inhibiting the circulation of electrons, thereby suppressing the flow of eddy currents, with the greater the number of laminations per unit area, i.e., the thinner the laminations, the greater the suppression of eddy currents. It is standard practice in the industry to use electrical grade steels for laminations.

[0006] The most efficient means of increasing energy storage/energy densities in the electrical machines is to increase the rotor tip speed. Increases in rotor tip speed, however, also increase mechanical stresses within the laminations. Current commercially available materials, i.e., electrical grade steels, are limited in mechanical strength and size availability. Recognized by the Applicants is that certain alloy steels, such as, for example, AISI 4000 series steels, do not possess the limitations of the typical electrical steels. Since these steels can be hardened and heat-treated, their mechanical strength can be increased substantially, up to four times greater in some cases. Recognized by the Applicants, is that the increased mechanical strength of such alloy steels, if used to make the laminations, can allow for a significant increase in rotor tip speed and stored energy.

[0007] Although such heat-treated alloy steel laminations possess great strength, conventional electrical machines do not use such heat-treated alloy steel because the heat- treating process performed on the laminations results in significant fabrication and assembly issues. As a result of the heating and the severe quenching cycle, during which the thin laminations are cooled rapidly in a bath of water or oil, thermal stresses are induced that cause the laminations to warp significantly. The warped laminations create a significant issue with laser cutting or stamping, and provide difficulties in assembling or stacking the laminations to form the rotor core. Recognized by the Applicants is the need for a method of forming the rotor core using heat-treated alloy steel laminations, which can overcome the problems caused by warping of the laminations, which occur when the laminations are heat- treated. SUMMARY OF THE INVENTION

[0008] In view of the foregoing, embodiments of the present invention address the warping issue and allow alloy steel laminations to be used in the fabrication of high-speed rotors. Embodiments of the present invention also include a process for manufacturing and assembling heat-treated alloy steel laminations for high speed rotors in electric machines. Embodiments of the present invention solve problems associated with the heat-treating of thin alloy steel laminations. Embodiments of the present invention address the warping issue and allow the alloy steel laminations to be used in the fabrication of high-speed rotors. Advantageously, the processes, outlined here, address these issues and produce laminations that can be used in fabricating rotor cores for electrical machines.

[0009] More specifically, embodiments of the present invention provide a method of producing heat-treated steel lamination stack sections for rotor cores for high-speed electrical machines. For example, a method of producing such lamination stack sections can first include the steps of cutting a plurality of annuli from one or more sheets of alloy material, and heat treating the plurality of annuli. The step of heat treating the annuli results in obtaining a high strength value for the alloy but results in warping. When the thin annuli material is subjected to extreme heat, e.g., ~1600°F, and then quickly cooled by quenching it in oil or water, internal thermal stresses are induced, which cause the annuli or laminate to warp. Not much can be done to prevent warping at this stage because any clamping or holding fixture would tend to interfere with the heat-treatment of the material. Clamping the parts, however, is possible in a final tempering step of the heat-treatment, where the annuli is held at a much lower temperature, e.g., ~750°F, for a number of hours. In producing the annuli (laminations), it was recognized or found that clamping the laminates during the tempering stage greatly reduces the warping seen in the laminations.

[00010] The method also includes cutting a lamination pattern in each of the plurality of heat-treated annuli. There still remains, however, some warping after tampering. As such, the step of cutting also includes locally flattening a portion of each heat-treated annuli along the cutting pattern, for example, using a foot tool (similar to a sewing machine guide) positioned immediately in front of the, e.g., laser cutter, and cutting the pattern as the material is being flattened. Advantageously, according to this step, there is no need to try to completely flatten the entire body of the annuli, only the portion along the cutting pattern.

[00011] The method also includes bonding a plurality of the cut laminations to form a small stack of laminations defining a bonded section of a core lamination stack, which is, in turn, formed of a plurality of such bonded sections. The step of bonding advantageously includes applying a bonding material, e.g., epoxy resin, between each of a small stack of cut laminations, bonding the laminations to each other in order to build a small stack of bonded laminations equaling approximately 1". This step also includes use of a specially designed clamping fixture capable of aligning the laminations and maintaining pressure on them while the bonding epoxy is allowed to cure in a heating device, e.g., oven, at an elevated temperature of, e.g., ~300°F. Once fully cured and the fixture removed, a flat approximately 1" stack of laminations is ready for final core assembly.

[00012] Finally, the method includes the step of forming a sufficient number of these "small stacks" or bonded sections and assembling a rotor core by stacking the sections on an assembling core fixture until the core lamination stack reaches a preselected or desired axial thickness.

[00013] An advantage of this process is that it allows the use of high-strength alloy steel laminations in the rotors of electrical machines. The heat-treated alloy steel laminations, for example, possess yield strengths three to four times greater than those of standard electrical grade steels. Laminations made from heat-treated alloy steel produce a rotor core that is capable of much higher stresses, which equates to higher energy densities and less weight. Applicants recognize, however, that a disadvantage of this method is that tolerances are more difficult to control since the laminate is not perfectly flat. This problem, however, is advantageously manageable and can be overcome by clamping the laminations during tempering, locally flattening the part of the laminations to be cut during final cutting or stamping, rather than the entire laminations, and bonding the laminations into small stacks or sections before final core assembly. Because it requires an additional heat-treatment step, this process can be more time consuming than normal lamination production, but the benefits significantly outweigh the extra processing time. [00014] Another advantage of this process, for example, is that the bonding of the laminations can be beneficial in allowing the laminations to handle much higher interference fits onto the rotor shaft without buckling. High-speed rotors require higher radial interferences where buckling of the laminations may be a problem. The bonding serves two purposes in not only keeping the laminations flat, but also in helping to prevent buckling during fabrication of a high-speed rotor. Further, the bonding is advantageous because the bonding material, e.g., epoxy provides an electrical insulation/isolation between laminations, negating a requirement for core painting or other insulating means.

BRIEF DESCRIPTION OF THE DRAWINGS

[00015] So that the manner in which the features and advantages of the invention, as well as others which will become apparent, may be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it may include other effective embodiments as well.

[00016] FIG. 1 is a perspective view of a rotor core of an electrical machine having heat treated laminates according to an embodiment of present invention;

[00017] FIG. 2 is a perspective view of an annuli used to form a lamination according to an embodiment of the present invention;

[00018] FIG. 3 is a perspective view of a heating tray individually and separately carrying a plurality of annuli according to an embodiment of the present invention;

[00019] FIG. 4 is a perspective view of a heating device applying high heat to a tray of annuli according to embodiment of the present invention;

[00020] FIG. 5 is a perspective view of a fluid bath quenching a tray of annuli according to an embodiment of the present invention; [00021] FIG. 6 is a perspective view of a clamp or clamping fixture clamping a plurality of annuli according to an embodiment of the present invention;

[00022] FIG. 7 is a perspective view of a clamp or clamping fixture clamping a plurality of annuli according to an embodiment of the present invention;

[00023] FIG. 8 is a perspective view of a heating device applying low heat to a plurality of annuli clamped by a clamp or clamp fixture according to an embodiment of the of the present invention;

[00024] FIG. 9 is a schematic view of an annuli being cut to form a laminate according to an embodiment of the present invention;

[00025] FIG. 10 is a perspective view of a plurality of cut laminations being mounted on a fixture according to an embodiment of the present invention;

[00026] FIG. 11 is a perspective view of a heating device applying low heat to a small bonded stack section of laminations according to an embodiment of the present invention;

[00027] FIG. 12 is a perspective view of a stack of a plurality of bonded lamination stack sections awaiting final core assembly according to an embodiment of the present invention;

[00028] FIG. 13 is a perspective view of a plurality of bonded lamination stack sections forming a lamination stack according to an embodiment of the present invention;

[00029] FIG. 14 is a perspective view of an assembling core fixture for assembling a core from a plurality of bonded lamination stack sections according to an embodiment of the present invention;

[00030] FIG. 15 is a table providing a comparative analysis of different materials with respect to yield strength and tensile strength;

[00031] FIG. 16 is a graph illustrating qualities of a certain alloy steel;

[00032] FIG. 17 is a graph illustrating stored energy and rotor tip speed versus material yield strength; [00033] FIG. 18 is a schematic flow diagram illustrating a method of producing heat- treated steel lamination stack sections for assembling a rotor core according to an embodiment of the present invention;

[00034] FIG. 19 is a schematic flow diagram illustrating a method of heat treating a plurality of annuli according to an embodiment of the present invention; and

[00035] FIG. 20 is a schematic flow diagram illustrating a method of bonding a plurality of cut laminations to form a bonded section of a core lamination stack according to an embodiment of the present invention.

DETAILED DESCRIPTION

[00036] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. Prime notation, if used, indicates similar elements in alternative embodiments.

[00037] It is perhaps best shown in FIGS. 15 and 16, heat-treated alloy steel, such as, for example, those from the AISI 4000 series, possess great strength over that of conventional electrical steels in both yield strength and the ultimate tensile strength. Conventional electrical machines, however, do not use such heat-treated alloy steel in forming laminations for rotors because the heat-treating processes performed on the laminations has resulted in significant fabrication and assembly issues. As perhaps best shown in FIG. 17, increased strength of the laminations, however, can lead to increased energy (power density capability) and an ability to obtain and maintain an increased rotor tip speed (higher RPMs). FIGS. 1-20 illustrate embodiments of a method or process of producing heat-treated steel laminations for rotor cores for high-speed electrical machines, which solve, or at least mitigate, such issues faced in the industry. [00038] As shown in FIGS. 1-20, in general, embodiments of such a method can involve three key steps, namely heat-treating steel material including clamping during tempering, locally flattening laminations material when cutting a lamination pattern to form a plurality of laminations, and bonding small stacks or sets of the plurality of laminations before final core assembly. These steps beneficially overcome manufacturing issues that have prevented the use of heat-treated alloy steel laminations in a rotor core, while obtaining/maintaining high material strength, allowing for the achievement of much greater tip speeds and power densities.

[00039] FIG. 18 illustrates a high level flowchart of a method of producing heat-treated bonded lamination stack sections 31 (see, e.g., FIGS. 12-13) for rotor cores 33 (see, e.g., FIG. 1) that are capable of being used in high-speed, high power density, electrical machines. The method, according to an embodiment of the present invention, typically first includes cutting a plurality of donut shaped annuli 35 (see, e.g., FIG. 2) from one or more sheets or roles of alloy material (not shown) such as, for example, various alloy steels including AISI 4000 alloy series steels (block 111). Next, a plurality of the cut annuli 35 are positioned in a heating tray 37 such as, for example, that shown in FIG. 3 (block 121). In a preferred configuration, the heating tray 37 has a plurality of separate bins or sections 39 to individually hold each of the annuli 35 to allow air and/or fluid to readily circulate between upper and lower surfaces of the annuli 35 when positioned in the heating tray 37, to allow processing multiple annuli 35, simultaneously, while still providing a substantially uniform heating and cooling ability. The heating tray 37, in the exemplary configuration, can hold enough annuli 35 to form a between 0.5" and 1.5" thick bonded lamination stack section 31. As described below, this plurality of annuli 35 positioned in the heating tray 37 is then heat- treated (block 130) which results in a significant increase in strength, with generally, an acceptable reduction in magnetic properties.

[00040] FIG. 19 illustrates a high level flowchart describing the heat treatment process of block 130. The plurality of annuli 35 carried in the heating tray 37 are together first positioned in a heating device 41, e.g., such as that illustrated in FIG. 4, to be, for example, solutionized. Solutionization of an alloy involves the heating of the alloy to dissolve and uniformly distribute alloying elements. According to an embodiment of the present invention, the annuli 35 are heated in the heating device 41 to a temperature of approximately between 1500° to 1700⁰F, with 1600⁰F being the norm, at atmospheric pressure, for approximately 8 hours (block 131). As also illustrated in FIG. 5, following the heat treatment, the annuli 35 carried by the tray 37 are then quenched in a liquid fluid bath 43, e.g., oil or water, to rapidly cool the annuli 35 at a rate of cooling sufficient to, for example, prevent the alloying elements from falling out of solution (block 133). According to a preferred configuration, there is sufficient fluid in the fluid bath 43 to allow for a simultaneous cooling of each annuli 35 held by the tray 37 from 1600⁰F down to 900⁰F in under approximately 5 seconds, for example, depending upon the specific alloy used.

[00041] This heat-treating/quenching process, for example, can be the primary source of the warping problems. That is, when the thin laminate material forming each annuli 35 is subjected to such extreme heat (see, e.g., FIG. 4), and then quickly cooled by quenching it in oil or water (see, e.g., FIG. 5), internal thermal stresses are induced, which cause the alloy material forming the annuli 35 to warp. Not much can be done to prevent warping at this stage because any clamping or holding fixture would tend to negatively affect the heat- treatment of the material. As will be described in more detail below, clamping the material, however, is possible in the final tempering step of the heat-treatment, where the annuli 35 is held at a much lower heat value, e.g., ~750°F or so, for a number of hours.

[00042] After the solutionization process is complete, the annuli 35 are removed from the heating tray 37 and clamped (block 135), for example, between a pair of endplates of a clamping fixture 45 (FIG. 6) to substantially flattened each of the annuli 35. FIGS. 6 and 7, illustrate examples of a clamping fixture 45, 45', which can be used to flattened the annuli 35. As perhaps best shown in FIG. 8, the clamped annuli 35 are then tempered (block 137). Particularly, the clamped annuli 35 along with the clamping fixture 45, 45', are positioned together in, and heated in, a heating device 51 to a temperature sufficient to flatten the stack of annuli 35 to reduce the warping, but below the solutionizing temperature e.g., at a temperature between approximately 500°-1000°F, with 750⁰F being the norm, for, e.g., two to three hours, depending upon the type of alloy used. In producing the bonded lamination stack sections 31, it was recognized or found that clamping the laminates during this tempering stage greatly reduced the warping seen in the laminations. Note, according to the illustrated embodiment, prior to heat-treating, the lamination alloy was first cut into oversized annuli 35 from which the final pattern can be cut. Heat-treating annuli 35, rather than whole sheets, were found to be beneficial in reducing the warping during the quench cycle. The heat-treated annuli 35 still showed a degree of warping upon heat-treating, but this warping was manageable in the final cutting steps, as described below.

[00043] As shown in FIG. 18, once the material has been heat-treated, the pattern of the lamination may be cut from the lamination annuli (block 141). As shown in FIG. 9, rather than attempt to completely flatten the annuli 35, at this stage, efficient cutting can be obtained by using a foot tool 53 positioned in front of a cutter 55, e.g., laser, configured to flattened the portion of the annuli 35 to be cut. That is, the entire area of the annuli 35 need not be flattened, just the area, e.g., 2" x 2" or so, along the pathway of the cutting pattern.

[00044] As shown in FIGS. 18 and 20, the warped cut laminations are stacked and bonded to one another, e.g., to each adjacent lamination, to form a small stack section, between 0.5" inches to 3.0", preferably between 0.5" inches to 1.5", and more preferably approximately 1" when completed. This bonding process is a key step to making the laminations usable. More specifically, as perhaps best shown in. FIG. 20, the cut laminations 61 are positioned atop a base of a clamping fixture 63 such as, for example, that shown in FIG. 10 for bonding the laminations 61 (block 151). Bonding material 65, such as, for example, resin or epoxy, is then deposited, for example, on the upper surface of each lamination 61 prior to stacking the next lamination 61 (block 153) until the stack section 31 reaches the desired height (block 155). According to the preferred configuration, the bonding resin or resin 65 selected was 3M Scotch Cast Electrical Resin 265.

[00045] Once the stack has reached the desired height, e.g., 1", the clamping fixture 63 is set to maintain the clamp at, for example, approximately 75 to 125 psi (block 157), and clamping fixture 63, along with the bonded stack section 31, is positioned in a heating chamber 71, e.g. oven, such as that shown in FIG. 11, for curing the bonding material 65 at an elevated temperature of, for example, between approximately 100⁰F to 325°F for one to three hours (block 159), depending upon the type of resin or epoxy used. When 3M Scotch Cast Electrical Resin 265 was used, preferred clamping pressure/force was maintained at 100 psi during curing, at a temperature of 300⁰F for approximately one hour. Note, the clamping fixture 63, such as, for example, that shown is FIG. 10, was designed to align the laminations 61 and maintain applied pressure while the bonding epoxy/resin 65 was allowed to cure in the heating chamber 71 at the elevated temperature. Once fully cured and the fixture 63 removed, a substantially flat 1" stack section 31 of laminations 61 is ready for final core assembly (see, e.g., FIGS. 12-14).

[00046] From this point, as would be understood by those skilled in the art, there are numerous variations of obtaining enough bonded stack sections 31 to form the core 33. For example, as perhaps best shown in FIG. 12, a plurality of bonded sections 31 can be produced. As identified in FIGS. 18 and as illustrated in FIG. 13, the bonded stack sections 31 of the lamination stack 73 (FIGS. 13-14) can be can be stacked on an assembling core fixture 81 (FIG. 14) (block 161) until the core 33 is completed (block 171).

[00047] Notably, the epoxy resin 65 was found to provide sufficient internal laminate insulation so as to negate a need for separate insulating laminations or core painting to reduce eddy currents. Nevertheless, in an alternate embodiment of the method, a separate installation lamination or laminations (not shown) can be intermittently interleaved between the bonded sections as the core 33 is being assembled on the assembling core fixture 81.

[00048] Regardless, as indicated in FIG. 18, once the core 33 is completed, a bird cage-type or other clamping device (not shown) can be used to securely hold the stack sections 31 together and the inner border of the core lamination stack 73 can be machined to size the inner bore as necessary to fit a rotatable shaft (block 181).

[00049] This Application is related to U.S. Patent Application No. 60/813,680, by Lewis et al. titled "Fabrication of Heat-Treated Laminations for High-Speed Rotors in Electrical

Machines," filed June 14, 2006, U.S. Patent Application No. by Werst et al. titled

"Rotor Assembly and Method of Assembling a Rotor of a High Speed Electric Machine" filed June 13, 2007, U.S. Patent Application No. 60/813,067, by Werst et al. titled "Apparatus and Method for Clamp Laminations in a High Speed in Electric Motors" filed June 13, 2006;

U.S. Patent Application No. , by Kitzmiller et al. titled "Rotor Assembly and Method of Assembling a Rotor of a High Speed Electric Machine", filed June 13, 2007; U.S. Patent Application No. 60/813,735, by Kitzmiller et al. titled "High Performance Rotating Rectifier for AC Generator Exciters", filed June 14, 2006; and U.S. Patent Application No. 60/814,017, by Jordan et al. titled "Electric Machinery Laminated Cores With Insulating Laminations", filed June 15, 2006, each incorporated by reference in their entireties. [00050] In the drawings and specification, there have been disclosed a typical preferred embodiment of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification. For example, the method was primarily directed to producing heat-treated steel lamination stacks for rotor cores in high-speed electrical machines. The process, however, is equally applicable to low to moderate-speed electrical machines and to stators.

Claims

THAT CLAIMED IS:

1. A method of producing heat-treated steel lamination stack sections (31) for rotor cores (33) for high-speed electrical machines, characterized by the steps of: heat treating a plurality of annuli (35) from one or more sheets of alloy material; cutting a lamination pattern in each of the plurality of heat-treated annuli (35); and bonding a plurality of the cut laminations (61) to form a bonded section (31) of a core lamination stack (73), a plurality of bonded sections (31) forming the core lamination stack

(73).

2. A method as defined in Claim 1 , further characterized by the steps of: positioning the bonded section (31) of the core lamination stack (73) on an assembling core fixture (81); and iteratively performing one or more of the steps of cutting the plurality of annuli (35), heat treating the plurality of annuli (35), cutting a lamination pattern in each of the plurality of heat-treated annuli (35), bonding the plurality of cut laminations (61), and positioning the bonded section (31) of the core lamination stack (73) on the assembling core fixture (81) until the core lamination stack (73) reaches a preselected axial thickness.

3. A method as defined in Claim 1, wherein the annuli (35) are ring-shaped, having an outer diameter larger than that required of a cut lamination (61) and an inner central aperture diameter smaller than that required of a finished lamination (61), the method being further characterized by the step of positioning an insulating lamination between at least one of the plurality of bonded sections (31) of the core lamination stack (73).

4. A method as defined in Claim 1, being further characterized by the step of: positioning the plurality of annuli (35) in a heating tray (37) providing an air gap between each of the plurality of annuli (35) prior to the step of heat treating the plurality of annuli (35) to thereby provide substantially uniform heating and cooling of each of the plurality of annuli (35) when heated simultaneously.

5. A method as defined in Claim 1, wherein the step of heat treating the plurality of annuli (35) includes the steps of: solutionizing the plurality of annuli (35); quenching the plurality of annuli (35) simultaneously in a liquid fluid to cool the plurality of annuli (35) at a rate of cooling sufficient to prevent the alloying elements from falling out of solution; clamping a subset of the plurality of annuli (35) between a pair of endplates to substantially flatten each of the plurality of annuli (35); and tempering the clamped subset of the plurality of annuli (35).

6. A method as defined in Claim 5, wherein the step of solutionizing the plurality of annuli (35) includes the step of applying heat to the plurality of annuli (35) at a temperature 'sufficient to substantially dissolve and substantially uniformly distribute alloying elements thereof defining a solutionizing temperature for a preselected solutionizing time period.

7. A method as defined in Claim 6, wherein the solutionizing temperature is between 1500 degrees Fahrenheit and 1700 degrees Fahrenheit, and wherein the solutionizing time period is between seven and nine hours.

8. A method as defined in Claim 5, wherein the step of tempering the clamped subset of the plurality of annuli (35) includes the step of applying heat to the clamped subset of the plurality of annuli (35) at a temperature below the solutionizing temperature defining a tempering temperature for a preselected tempering time period at a preselected pressure to thereby reduce the warping caused by the quenching step.

9. A method as defined in Claim 8, wherein the tempering temperature is between 500 degrees Fahrenheit and 1000 degrees Fahrenheit, and wherein the tempering time period is between two and three hours.

10. A method as defined in Claim 1, wherein the step of cutting a lamination pattern in each of the plurality of heat-treated annuli (35) includes the steps of: flattening a portion of the heat-treated annuli (35) according to the lamination pattern to be cut using a foot tool (53) positioned immediately in front of a laser cutter (55); and cutting the flattened portion according to the lamination pattern.

11. A method as defined in Claim 1, wherein the step of bonding a plurality of the cut laminations (61) to form a section of a core lamination stack (73) includes the steps of: stacking one of the plurality of cut laminations (61) atop a base of a clamping fixture (65); inserting bonding material (65) on a surface of the one of the plurality of cut laminations (61); and iteratively performing the steps of stacking and inserting bonding material (65) until the stack (73) reaches a preselected thickness, the stack (31) having preselected thickness defining a single one of the plurality of bonded sections (31) of the core lamination stack (73).

12. A method as defined in Claim 11, wherein the inserted bonding material (65) is epoxy or resin, and wherein the preselected thickness of the stack (31) is approximately between 0.5 in. and 1.5 in.

13. A method as defined in Claim 11, wherein the step of bonding a plurality of the cut laminations (61) to form a section (31) of a core lamination stack (73) includes the steps of: applying a preselected clamping pressure on the stack (31 ); and curing the bonding material (65) in the compressed stack (31) in an oven (71) at a preselected curing temperature.

14. A method as defined in Claim 13, wherein the step of curing the bonding material (65) in the compressed stack (31) in an oven includes the steps of: positioning the compressed stack (31) in the oven (71); and maintaining the applied a clamping pressure on the stack (31) while the bonding material (65) is allowed to cure.

15. A method as defined in Claim 13, wherein the applied clamping pressure is in a range of between 75 psi and 125 psi; and wherein the elevated curing temperature is in a range between 100 degrees Fahrenheit and 325 degrees Fahrenheit.

16. A method of producing heat-treated steel lamination stack sections (31) for electric machines, characterized by the steps of: heat treating a plurality of annuli (35) cut from alloy material; cutting a lamination pattern in each of the plurality of heat-treated annuli (35); and bonding the plurality of cut laminations (61) to form a bonded section (31) of a core lamination stack (73), a plurality of bonded sections (31) forming the core lamination stack

(73).

17. A method as defined in Claim 16, further characterized by the steps of: positioning the bonded section (31) of the core lamination stack (73) on an assembling core fixture (81); positioning an insulating lamination atop the bonded section (31) of the core lamination stack (73); and iteratively performing one or more of the steps of cutting the plurality of annuli (35), heat treating the plurality of annuli (35), cutting a lamination pattern in each of the plurality of heat-treated annuli (35), bonding the plurality of cut laminations (61), and positioning the bonded section (31) of the core lamination stack (73) on the assembling core fixture (81) until the core lamination stack (73) reaches a preselected axial thickness.

18. A method as defined in Claim 16, wherein the annuli (35) is ring-shaped, having an outer diameter larger than that required of a cut lamination (61) and an inner central aperture diameter smaller than that required of a finished lamination (61).

19. A method as defined in Claim 16, being further characterized by the step of: positioning the plurality of annuli (35) in a heating tray (37) providing an air gap between each of the plurality of annuli (35) prior to the step of heat treating the plurality of annuli (35) to thereby enhance heating and cooling uniformity of each of the plurality of annuli (35).

20. A method as defined in Claim 16, wherein the step of heat treating the plurality of annuli (35) includes the steps of: clamping a subset of the plurality of annuli (35) between a pair of endplates to substantially flatten each of the plurality of annuli (35); and tempering the clamped subset of the plurality of annuli (35).

21. A method as defined in Claim 20, being further characterized by the steps of: solutionizing the plurality of annuli (35) by applying heat to the plurality of annuli (35) at temperature sufficient to substantially dissolve and substantially uniformly distribute alloying elements thereof defining a solutionizing temperature for a preselected solutionizing time period; and quenching the plurality of annuli (35) simultaneously in a liquid fluid to cool the plurality of annuli (35) at a rate of cooling sufficient to prevent the alloying elements from falling out of solution.

22. A method as defined in Claim 21, wherein the solutionizing temperature is between 1500 degrees Fahrenheit and 1700 degrees Fahrenheit, and wherein the solutionizing time period is between seven and nine hours.

23. A method as defined in Claim 20, wherein the step of tempering the clamped subset of the plurality of annuli (35) includes the step of applying heat to the clamped subset of the plurality of annuli (35) at a temperature below the solutionizing temperature defining a tempering temperature for a preselected tempering time period at a preselected pressure to thereby reduce the warping caused by the quenching step.

24. A method as defined in Claim 23, wherein the tempering temperature is between 500 degrees Fahrenheit and 1000 degrees Fahrenheit, and wherein the tempering time period is between two and three hours.

25. A method as defined in Claim 16, wherein the step of cutting a lamination pattern in each of the plurality of heat-treated annuli (35) includes the steps of: flattening a portion of the heat-treated annuli (35) according to the lamination pattern to be cut using a foot tool (53) positioned in front of a cutter (55); and cutting the flattened portion according to the lamination pattern.

26. A method as defined in Claim 16, wherein the step of bonding a plurality of the cut laminations (61) to form a section of a core lamination stack (73) includes the steps of: stacking one of the plurality of cut laminations (61) atop a base of a clamping fixture (65); inserting bonding material (65) on a surface of the one of the plurality of cut laminations (61); and iteratively performing the steps of stacking and inserting bonding material (65) until the stack (31) reaches a preselected thickness, the stack (31) having preselected thickness defining a single one of the plurality of bonded sections (31) of the core lamination stack (73).

27. A method as defined in Claim 26, wherein the inserted bonding material (65) is epoxy or resin, and wherein the preselected thickness of the stack (31) is approximately between 0.5 in. and 1.5 in.

28. A method as defined in Claim 26, wherein the step of bonding a plurality of the cut laminations (61) to form a section of a core lamination stack (73) includes the steps of: applying a preselected clamping pressure on the stack (31); and curing the bonding material (65) in the compressed stack (31) in an oven (71) at a preselected curing temperature.

29. A method as defined in Claim 28, wherein the step of curing the bonding material (65) in the compressed stack (31) in an oven (71) includes the steps of: positioning the compressed stack (31) in the oven (71); and maintaining the applied clamping pressure on the stack (31) while the bonding material (65) is allowed to cure.

30. A method as defined in Claim 28, wherein the applied pressure is in a range of between 75 psi and 125 psi; and wherein the preselected curing temperature is in a range between 100 degrees Fahrenheit and 325 degrees Fahrenheit.