Abstract:
A method of preparing a plurality of bar-wound stator conductors for electrical interconnection includes inserting the plurality of conductors into a stator, twisting a conductor such that a first conductor of a first row is adjacent to a second conductor of a second row; trimming the adjacent first and second conductors to a common length using a trimming device; and grinding the trimmed first and second conductors to a pre-determined surface profile using a rotary cutting tool.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under DOE/NETL grant number DE-EE0002629. The invention described herein may be manufactured and used by or for the U.S. Government for U.S. Government (i.e., non-commercial) purposes without the payment of royalties thereon or therefore. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to methods of shaping the ends of bar-wound stator conductors. 
     BACKGROUND 
     Electric devices such as motors and generators having a stator secured within a housing of the motor/generator are well known. A rotor mounted on a shaft is coaxially positioned within the stator and is rotatable relative to the stator about the longitudinal axis of the shaft to transmit the force capacity of the motor. The passage of current through the stator creates a magnetic field tending to rotate the rotor and shaft. 
     Some stators are generally configured as an annular ring and are formed by stacking thin plates, or laminations, of highly magnetic steel. A copper winding of a specific pattern is configured, typically in slots of the lamination stack, through which current is flowed to magnetize sections of the stator assembly and to create a force reaction that causes the rotation of the rotor. 
     Bar pin stators are a particular type of stator that include a winding formed from a plurality of bar pins, or bar pin wires. The bar pin wires are formed from a heavy gauge copper wire with a rectangular cross section and generally configured in a hairpin shape having a curved section and typically terminating in two wire ends. The bar pins are accurately formed into a predetermined shape for insertion into specific rectangular slots in the stator, and are typically coated with an insulating material prior to insertion, such that the adjacent surfaces of the pins within the slots are electrically insulated from each other. 
     Typically, the curved ends of the bar pins protrude from one end of the lamination stack and the wire ends of the bar pins protrude from the opposite end of the lamination stack. After insertion, the portions of the wire protruding from the lamination stack are bent to form a complex weave from wire to wire, creating a plurality of wire end pairs. Adjacent paired wire ends are typically joined to form an electrical connection, such as through a welding operation. The resultant weave pattern and plurality of joints determines the flow of current through the motor, and thus the motive force of the rotor. 
     SUMMARY 
     A method of preparing a plurality of bar-wound stator conductors for electrical interconnection includes inserting the plurality of conductors into a stator, twisting the plurality of conductors such that a first conductor of a first row is adjacent to a second conductor of a second row; trimming the adjacent first and second conductors to a common length using a trimming device; and grinding the trimmed first and second conductors to a pre-determined surface profile using a rotary cutting tool. The pre-determined surface profile may include, for example, an internal chamfer or plurality of grooves. 
     Each of the plurality of conductors may include an insulation layer disposed about the surface of the conductor, where the method further includes the step of removing the insulation layer in an area that is proximate to an end of each of the respective first and second conductors. 
     The stator may include a plurality of slots, and inserting the plurality of conductors into the stator may include inserting four of the plurality of conductors into each of the plurality of slots. Each of the first row and the second row may then comprise four conductors disposed in a respective slot. 
     The method is particularly adapted for automated processing techniques, where it may further include sensing an angular position of the stator and controllably rotating the stator to align a row of conductors with the trimming device. Likewise the controller may transition the trimming device from an operational position to a docked position prior to controllably rotating the stator. As may be appreciated, the docked position may be more removed from the stator than the operational position. 
     In once configuration, trimming the adjacent first and second conductors to a common length may include removing a portion of each of the respective first and second conductors through shearing. Trimming of the first and second conductors in this manner may form a burr that protrudes from each respective conductor. As such, grinding the trimmed first and second conductors to a pre-determined surface profile may include removing the burr. 
     In one configuration, the method may further include stabilizing the plurality of conductors using a ring fixture, where the ring fixture defines a plurality of holes that extend through the fixture and are configured to receive the conductors. As may be appreciated, the ring fixture may include a stator-side facing the stator and a non-stator side facing away from the stator. To facilitate locating of the conductors in the fixture, each of the plurality of holes may have a larger cross-sectional area at the stator side than at the non-stator side. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a stator assembly prior to joining the wire ends of the stator winding. 
         FIG. 2  is a partial schematic perspective view of the wire end portion of the stator assembly of  FIG. 1 . 
         FIG. 3  is partial schematic perspective view of a wire end portion of a stator assembly, illustrating uncut wire ends, trimmed wire ends, and surfaced wire ends. 
         FIG. 4  is a partial schematic perspective view of the wire end portion of the stator assembly of  FIG. 3  in communication with a trimming device and a surfacing device. 
         FIG. 5A  is a schematic cross-sectional view of a plurality of wire end pairs adjacent a rotary cutting tool that is configured to cut a flat surface profile. 
         FIG. 5B  is a schematic cross-sectional view of a plurality of wire end pairs adjacent a rotary cutting tool that is configured to cut a surface profile having an internal chamfer. 
         FIG. 5C  is a schematic cross-sectional view of a plurality of wire end pairs adjacent a rotary cutting tool that is configured to cut a surface profile having external chamfers. 
         FIG. 5D  is a schematic cross-sectional view of a plurality of wire end pairs adjacent a rotary cutting tool that is configured to cut a surface profile having a plurality of grooves. 
         FIG. 6  is a partial schematic perspective view of a ring fixture adjacent to a wire end portion of a stator assembly. 
         FIG. 7  is a partial schematic cross-sectional view of a plurality of conductors extending through a ring fixture. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numerals are used to identify like or identical components in the various views,  FIG. 1  schematically illustrates a stator assembly  10  of an electric machine having a plurality of bar-wound electrical conductor windings (generally at  12 ). The stator  10  may generally be configured as an annular ring and may be formed from a lamination stack  16  (i.e., a plurality of individual laminations stacked in an ordered manner) (also referred to as the “stator body  16 ”). Each lamination may include a plurality of radially distributed slots which may be oriented during assembly of the lamination stack  16  to define a plurality of generally rectangular slots  18  through the stator  10 . Each slot  18  may be particularly adapted to receive one or more of the conductor windings  12 . 
     As generally illustrated in  FIG. 1 , the stator  10  may be configured as a bar pin stator, wherein the conductor windings  12  are formed from a plurality of bar pins  24  (also referred to as “bar pin wires  24 ”). The conductor windings  12  may further include terminals or connections  20   a ,  20   b  and  20   c , for connecting the various phases of the windings  12  to an electrical controller such as a power inverter module. The bar pin wires  24  are typically formed from a heavy gauge, high conductivity copper wire with a rectangular cross section. Each bar pin wire  24  may generally be configured in a hairpin-type shape, which has a curved section  22  at one end, and may terminate in two wire ends  28  at the opposing end. Prior to insertion, the bar pins  24  may be accurately formed into a predetermined shape to construct a predetermined weave pattern after insertion into the slots  18 . In one configuration, the bar pins  24  may be coated with an insulating material  26  prior to insertion, such that the adjacent surfaces of the bar pins  24  within the slots  18  are electrically insulated from each other. To facilitate joining of the wire ends  28  to form an electrical connection, the wire ends  28  of the bar pins  24  may be stripped of the insulating layer  26  prior to insertion into the slots  18  of the lamination stack  16  and prior to bending to form a weave pattern such as the weave pattern shown in  FIG. 1  and in additional detail in  FIG. 2 . Each slot  18  may be lined with a slot liner, to insulate the bar pins  24  from the lamination stack  16 , and to prevent damage to the insulating layer  26  during insertion of the bar pins  24  in the slots  18 . 
       FIG. 1  shows the curved ends  22  of the bar pins  24  protruding from one end of the lamination stack  16  and the wire ends  28  of the bar pins  24  protruding from the opposite end of the lamination stack  16  (i.e., the wire end portion  14  of the stator  10 ). As mentioned above, after insertion, the wire ends  28  protruding from the lamination stack  16  may be bent to form a complex weave of bar pins  24  on the wire end portion  14  of the stator  10 . In this weave, each respective wire end  28  may be paired with and joined to a different wire end  28  according to the connection requirements of the winding  12 . 
       FIG. 2  shows, by way of non-limiting example, a perspective view of the wire end portion  14  of stator  10 . As illustrated, the collective wire ends  28  of the bar pins  24  may be arranged in four layers, with each layer being disposed radially outward of the previous layer. For example, the outermost layer may include a plurality of wire ends  28  closest to the outer diameter of the lamination pack  16 , and the innermost layer may include a plurality of wire ends  28  closest to the inner diameter of the lamination stack  16 . Additionally, the wire ends  28  may be aligned in a plurality of rows  30  that each extend radially outward from the center of the stator  10 . As shown in  FIG. 2 , the plurality of wire ends forming the innermost or first layer of the winding  12  are identified as wire ends  34 . The second layer of the winding  12 , which is proximate to the first layer, is formed of a plurality of wire ends identified as wire ends  36 . The third layer of the winding  12  is formed of a plurality of wire ends identified as wire ends  44 . The outermost or fourth layer is formed of a plurality of wire ends identified as wire ends  46 . 
       FIG. 2  shows each of the wire ends  34  in the first layer being bent such that it is proximate to and paired with a wire end  36  in the second layer, (i.e., forming a first, or inner wire end pair  32 ). Once suitably prepared, such as will be described below, the wire ends  34 ,  36  of the inner wire end pair  32  may be fused together, such as through an electric welding process (e.g., gas tungsten arc welding (GTAW or TIG welding), plasma arc welding (PAW), or electric resistance welding (ERW)), soldering, or through other similar processes that may create a mechanical and electrical bond between the wires  34 ,  36 . 
     Similar to the inner wire pair  32 , the wire ends  44  of the third layer may be bent such that they are each proximate to, and paired with a wire end  46  in the fourth layer, (i.e., forming a second, or outer wire end pair  42 ). The wire ends  44 ,  46  of the outer wire end pair  44  may be fused together through a process that may be similar to the one used to form the inner wire end pair  32 . 
     Prior to fusing the wire pairs  32 ,  44  together, it may be desirable to prepare the wires to better receive the fusing means (e.g., weld or solder).  FIG. 3  schematically illustrates three wire end groupings  60 ,  62 ,  64 , where each grouping respectively represents the conductors at a various manufacturing stage prior to fusing the wire ends together. 
     The first grouping  60  schematically illustrates the wires  28  following insertion into the stator  10  and twisting to form the weave. These wires may be purposely longer than required by the final design to account for manufacturing variation in the pre-insertion bending process and to reduce the amount of strain on the wires as they are woven together into the rotor slots for insertion. As such, the wires of the first grouping  60  have a length that is substantially unchanged from the original insertion. 
     The second wire end grouping  62  schematically illustrates a plurality of wires  28  that have been sheared from their initial length (i.e., group  60 ) by a trimming device. The trimming operation may ensure that the wire ends are all disposed at a substantially common length relative to the stator and/or each other. While such a trimming operation may provide a substantially uniform plane of trimmed wire ends  28 , due to the malleability of copper, it may also produce a protruding nip/burr that may be difficult to weld (depending on the process used) and/or may be non-uniform from wire to wire. 
     The third wire end grouping  64  schematically illustrates a plurality of wires  28  that have been profiled/surfaced to remove the protruding nip/bur created via the trimming process. As such the profiling/surfacing may result in a plurality of wire ends that are substantially aligned along a plane that is normal to the central axis of the stator body  16  and at a controlled distance relative to the stator body  16 . These profiled ends (e.g. grouping  64 ) may be particularly adapted to receive the fusing means (e.g., weld or solder) such as during an automated welding/soldering processes. 
       FIG. 4  schematically illustrates the stator  10  provided in  FIG. 3 , in communication with a manufacturing apparatus  68  that includes a trimming device  70  and a surfacing device  72 . The trimming device  70  may generally be configured to cut the wire ends (i.e., resulting in wire end grouping  62 ), while the surfacing device  72  may generally be configured to grind/shape the trimmed ends to result in accurately profiled ends (i.e., generally illustrated as grouping  64 ). In one embodiment, the trimming  70  and surfacing  72  devices may be disposed underneath the stator assembly  10  such that the force of gravity may aid in removing all errant particles produced by the operations away from the stator. The manufacturing apparatus  68  may further include a vacuum system  74  that may draw air away from the stator to further prevent trimming and surfacing artifacts from falling into the stator  10 . These precautions may aid in reducing the likelihood of a subsequent electrical short that may be caused by damaged/nicked wire insulation or debris trapped within the stator. 
     As shown in  FIG. 4 , in one configuration the trimming device  70  and the surfacing device  72  may each selectively transition between a respective operational position (generally at  80 ,  82 ) and a docked position (shown in phantom generally at  84 ,  86 ). While the trimming and surfacing devices  70 ,  72  are in their respective docked positions  84 ,  86 , the stator assembly  10  may be permitted to more freely rotate relative to the manufacturing apparatus  68  and/or may be easily loaded and/or unloaded from the manufacturing apparatus  68 . 
     During operation, the stator body  16  may be placed on an indexing turntable or clamped into a similar controllably rotatable fixture adjacent to the manufacturing apparatus  68 . Initially, both the trimming device  70  and surfacing device  72  may be in their respective docked positions  84 ,  86 . A sensing device  90  may monitor the angular position of the stator  10  relative to the manufacturing assembly  68 , and may be in communication with a manufacturing controller  92  to control the indexing of the turntable. The controller  92  may initially align the stator  10  such that the first wire to be trimmed is bought into the proper position for trimming (i.e., disposed vertically above the trimming device  70 ). Once in position, the trimming device  70  may be raised up into the operational position  80  to trim the four wire ends of the two wire pairs  32 ,  42  with the trim head  94 . 
     In one configuration, as generally shown in  FIG. 4 , the trim head  94  may include two shearing blades that are hinged to each other on one end of the blade. Likewise, other blade configurations and/or shearing mechanisms may be used to effectuate the trimming of the wire ends. As may be appreciated, the trim head may be hydraulically, pneumatically, or electrically actuated in a manner that causes the two shearing blades to act in cooperation to cut the wire ends. 
     Once the trim head  94  clips the wire ends, the wire trimming device  70  may return to the docked position  84  to allow the controller  92  to rotate the turntable in a direction  95 , to bring an adjacent wire pair sets into position above the trimming device  70 . Again, once the adjacent wire pair set is in proper position, the trimming device  70  may be raised into the operational position  80  to repeat the trimming process. This indexing and trimming may continue until all of the wires are cut. 
     The surfacing device  72  may use a rotating cutting tool  96  to accurately plane or profile the trimmed wire ends. Unlike the trimming device  70  which may toggle between the operational and docked positions  80 ,  84  for each row, in one configuration, the surfacing device  72  may remain in the operational position  82  for the entirety of the manufacturing process. As the stator  10  is rotated to bring the next set of wire pairs into the trimming position, the rotation feeds the next set of trimmed wire pairs across the surfacing mechanism&#39;s rotating cutting tool  96 . 
     The rotating tool  96  may generally be in the form of a cylindrical cutting head such as an end mill, and/or may include an abrasive surface such as a grinding stone. When the stator&#39;s final set of wire pairs have been trimmed, the stator assembly  10  may continue to index until the final set of trimmed wire pairs is surfaced, even though no trimming is required in these last few indexes. When all of the wire pair sets have been trimmed and surfaced, the trimming and surfacing devices  70 ,  72  may return to their docked positions  84 ,  86  and the completed stator  10  may be removed from the manufacturing apparatus  68 . 
     In one configuration, the rotating cutting tool  96  may be configured to shape the wire ends in a manner to more easily receive a weld or solder coupling. For example, and without limitation, as shown in  FIGS. 5A-5D  the rotating cutting tool  96  may plane the wire ends ( FIG. 5A ), cut internal chamfers ( FIG. 5B ), cut external chamfers ( FIG. 5C ), and/or cut a plurality of grooves ( FIG. 5D ) into the wire ends. Additionally, multiple profiles may be combined into a single tool  96 . 
     More specifically,  FIG. 5A  illustrates a flat surface profile  100  that may plane the wire pair ends as the ends are indexed across the surface of a cutting tool  96 . In this embodiment, the rotating cutting tool  96  may have a purely cylindrical profile. The flat surface profile  100  of the wires may provide a well controlled and predictable surface for the mechanized placement of a weld bead. 
       FIG. 5B  illustrates a wire surface profile with an internal chamfer  102  that is machined via a protuberance  104  extending from the cutting tool  96 . As shown, the protuberance  104  may align with the joined edge faces of the wire pairs to create the chamfer at the wire interface. The chamfer may aid in confining the flow of molten weld material and/or promoting deeper weld penetration at the mating faces of the joined wire pairs. 
       FIG. 5C  illustrates a surface profile with an external chamfer  106  that is machined by a cutting tool  96  with shaped recesses  108  designed to chamfer the outer edges of the wire pairs while also surfacing the wire ends. Such an external chamfer may ensure that the weld bead is deposited near the mating faces of the joined wire pairs, and may further reduce the size of the weld area to decrease the overall packaging size of the stator assembly  10  in the welded wire pair area. 
     Finally,  FIG. 5D  generally illustrates a serrated or grooved surface profile  110  that is cut by a similarly designed cutting tool  96 . The serrated profile  110  may offer the advantages of the internal chamfer  102  and the external chamfer  106 , while also increasing the surface area of the wire ends for improved heat transfer during the welding process. The grooves of the serration may also limit the flow of the molten weld bead material to contain the weld bead on the wire ends. 
     As generally illustrated in  FIGS. 6 and 7 , in one configuration, a ring fixture  120  may be used to stabilize the wire ends during the trimming, shaping, and welding processes described above.  FIG. 6  generally illustrates a partial section of the ring fixture  120  below the stator assembly  10  prior to its installation. In one configuration, the ring fixture  120  may include two concentric rings of rectangular holes  122 ,  124  (respectively) that may align with the intended position of each of the wire pairs. 
       FIG. 7  is a partial cross section of the stator assembly  10  with the ring fixture  120  disposed about the wires. The section has cut through several un-labeled wires that are on their helical path to meet their particular wire pair partner, and through the wires that populate the particular stator slot  18  that is cut by the section. 
     The rectangular holes  122 ,  124  of the ring fixture  120  may have a tapered cross section with a larger cross-sectional opening on the stator-side  126  of the fixture  120  than on the non-stator-side  128 . The tapered holes may be advantageous for many reasons. As may be appreciated, the taper may generally reduce the effort required to insert the ring fixture by effectively funneling the wire ends into the hole. In this manner, the fixture may align the wire pairs into proper position as the ring is being forced on the stator assembly  10 . Finally, the taper may also urge the mating surfaces of the wire pairs into close contact for trimming, surfacing and optionally, welding. 
     The ring fixture  120  may serve multiple purposes for the stator preparation and assembly. As mentioned, when the fixture  120  is installed, it may ensure proper positioning of the wire pairs, as well as the alignment of mating surfaces of the wire pairs. The ring fixture  120  may also stiffen the wire pairs for the trimming and surfacing operations.  FIG. 6  shows wire pairs  32 ,  42  as they have emerged through their respective holes  122 ,  124  in the ring fixture  120 . After the ring fixture  120  is installed, the wire pairs  32 ,  42  may be trimmed from the original wire length  130  to the trimmed length  132  and finally surfaced to a weld ready length and surface condition  134 . Both the trimming and surfacing operations are aided by the force reaction capability of the ring fixture  120 , since it imparts the stiffness of the full set of the wire pairs on the particular wire pair(s) that are being trimmed or surfaced (i.e., strength in numbers). The ring fixture  120  also may act as a shield to prevent particles and dust generated in the trimming and surfacing operations from being propelled toward the stator laminate stack  16 . 
     In one configuration, the ring fixture  120  may be removed and reused in subsequent stator assemblies  10 . Alternately, the ring fixture  120  may be left in place during the welding of the wire pairs  32 ,  34  to ensure precise location of the surfaced wire pairs (i.e., an aid for mechanized welding). During the welding process, the ring fixture may further serve as a shield to keep weld particles from dripping/splattering toward the stator laminate stack  16 . Additionally, the ring fixture  120  may act as a heat shield to reduce the weld induced damage to the insulation of the unstripped portions of the bar pin wires. 
     Finally, in one configuration, the ring fixture  120  may be left on the stator  10  as a permanent component. As a permanent component of the stator assembly  10 , the ring fixture  120  could be manufactured from an insulating material, such that it may act as an insulting brace to isolate the wires from each other. The controlled wire pair position, via the ring fixture, would also ensure that the complex weave of wires would not shift over time between the stator laminate stack  16  and the pair-welded ends. 
     The structural stiffness and positional precision of the wire pairs  32 ,  42  in the ring fixture  120  may further enable other, non-welding, methods of wire pair joining to be used. For example, with the wire pair joint integrity reinforced by the ring fixture  120 , a crimp ring could be used to join the wires. Likewise, the use of a solder bath may also be used to electrically couple the wire pairs (without regard for the structural stability of the solder joint due to the added stiffness of the ring fixture  120 ). 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.