Patent Publication Number: US-2022239206-A1

Title: Method and apparatus for transfer molding of electric motor cores and magnetizable inserts

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to copending applications filed concurrently herewith titled “METHOD AND SYSTEM FOR ASSEMBLING A ROTOR STACK FOR AN ELECTRIC MOTOR,” “ROTOR ASSEMBLY METHOD AND SYSTEM EMPLOYING CENTRAL MULTI-TASKING ROBOTIC SYSTEM,” and “INTEGRATED ROBOTIC END EFFECTORS HAVING END OF ARM TOOL GRIPPERS,” which are commonly assigned with the present application and the contents of which are incorporated herein by reference in their entireties. 
     FIELD 
     The present disclosure relates to the manufacture of electric motors, and more particularly to the assembly of rotor cores and magnets for such electric motors. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     With the continuing electrification trend in motor vehicles, related components such as electric motors for electric vehicle powertrains are being developed for high volume production. These electric motors are complex assemblies, typically including a stator and a rotor made up of a plurality of rotor cores with a plurality of magnets disposed in pockets of the rotor cores. Such a construction can be seen, by way of example, in U.S. Publication No. 2018/0287439, which is commonly owned with the present application and the contents of which are incorporated herein by reference in their entirety. 
     Assembly of these electric motors can be time consuming and challenging given the complexity of the design of the rotor cores and their embedded magnets. Further, providing a secure connection between the plurality of magnets within the rotor core pockets while achieving assembly efficiency for high volume production can be difficult. Adhesive materials have been used to secure the magnets within the rotor core pockets, however, precisely controlling the volume of adhesive and its curing behavior has proven to be challenging. 
     These issues related to the manufacture of electric motors, including issues with securing magnets in rotor core pockets, are addressed by the present disclosure. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, a method of securing magnetizable inserts within cores of an electric converter is provided that comprises: placing an assembly of rotor cores in a transfer molding press, the magnetizable inserts being disposed within cavities of the rotor cores and the cavities of the rotor cores being in fluid communication; placing a polymer preform proximate a central portion of the assembly of rotor cores; displacing the polymer preform such that the polymer preform changes state and flows radially and then axially through each of the cavities of the rotor cores; removing the assembly of rotor cores from the transfer molding press; and removing polymer waste from the assembly of rotor cores. 
     In variations of this method, which may be implemented individually or in any combination: the assembly of rotor cores is preheated before being placed into the transfer molding press; the polymer preform is preheated before being placed into the transfer molding press; the assembly of rotor cores is weighed before being placed into the transfer molding press and is weighed after being removed from the transfer molding press, wherein a difference in weight is compared with a predefined weight value to determine a fill volume of the cavities; the assembly of rotor cores is placed into the transfer molding press and removed from the transfer molding press by a robot; the polymer preform defines a cylindrical geometry; the polymer preform is a thermoset material; the polymer preform is displaced vertically such that the polymer flows distally, in a gravitational direction, through the cavities; the assembly of rotor cores further comprises upper and lower tooling; and the cavities of the rotor cores are radially staggered between adjacent rotor cores. 
     In another form of the present disclosure, a method of securing magnetizable inserts within cores of an electric converter is provided that comprises: weighing an assembly of rotor cores, the magnetizable inserts being disposed within cavities of the rotor cores and the cavities of the rotor cores being in fluid communication; preheating the assembly of rotor cores; placing the assembly of rotor cores in a transfer molding press; preheating a polymer preform; placing the preheated polymer preform proximate a central portion of the assembly of rotor cores; displacing the polymer preform such that the polymer preform changes state and flows radially and then axially through each of the cavities of the rotor cores to form a bonded assembly; removing the assembly of rotor cores from the transfer molding press; removing polymer waste from the assembly of rotor cores; and weighing the bonded assembly. 
     In variations of this method, which may be implemented individually or in any combination: the assembly of rotor cores further comprises upper and lower tooling, wherein the upper tooling and the polymer waste are removed before weighing the bonded assembly; the assembly of rotor cores is placed into the transfer molding press and removed from the transfer molding press by a robot; the polymer preform defines a cylindrical geometry; and the polymer preform is a thermoset material. 
     In yet another form of the present disclosure, an apparatus for securing magnetizable inserts within rotor cores of an electric converter is provided that includes an upper tool comprising a plurality of runners and gates, a plurality of stacked rotor cores disposed adjacent to the upper tool, the magnetizable inserts being disposed within cavities of the rotor cores and the cavities of the rotor cores being in fluid communication, and a lower tool disposed adjacent to the plurality of stacked rotor cores, opposite the upper tool, wherein the lower tool comprises a central mandrel extending through a center of the plurality of stacked rotors, the lower tool further comprising a plurality of ventings. The runners of the upper tool and the cavities of the rotor cores are in fluid communication to allow a polymer to flow radially through the runners and axially through the cavities of the rotor cores during a molding process to secure the magnetizable inserts to the rotor cores. 
     In variations of this apparatus, which may be implemented individually or in any combination: the upper tool further comprises a topside runnerplate and a bottomside vent plate; the lower tool comprises a plurality of ventings; the cavities of the rotor cores are radially staggered between adjacent rotor cores; and the upper tool and the lower tool define locating features to position the plurality of stacked rotor cores within the apparatus. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1A  is a perspective view of an electric converter to which the teachings of the present disclosure are applied; 
         FIG. 1B  is an exploded view of a rotor core and magnetizable inserts of the electric converter of  FIG. 1A ; 
         FIG. 2  is a schematic cross-sectional view of an apparatus for securing magnetizable inserts within rotor cores of an electric converter in accordance with the teachings of the present disclosure; 
         FIG. 3  is a perspective view of an assembly of rotor cores and tooling constructed according to the teachings of the present disclosure; 
         FIG. 4  is a perspective view of the tooling of  FIG. 3 ; 
         FIG. 5  is a perspective view of the lower tooling of  FIG. 4  constructed according to the teachings of the present disclosure; 
         FIG. 6  is a perspective cross-sectional view of the assembly of  FIG. 3 , taking along line  6 - 6 ; 
         FIG. 7  is a bottom perspective view of the assembly of  FIG. 3 ; 
         FIG. 8  is a cross-sectional view of the assembly of rotor cores and tooling illustrating flow paths for the molten polymer and heat according to the teachings of the present disclosure; 
         FIG. 9  is a flow diagram illustrating a method of securing magnetizable inserts within rotor cores of an electric converter according to the teachings of the present disclosure; 
         FIG. 10A  is a perspective view of a plurality of rotor cores having magnetizable inserts secured within their cavities after a molding process according to the teachings of the present disclosure; and 
         FIG. 10B  is an enlarged view of magnetizable inserts secured within the cavities of a rotor core after the molding process according to the teachings of the present disclosure. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring to  FIGS. 1A and 1B , an electric converter to which the teachings of the present disclosure are applied is illustrated and generally indicated by reference numeral  20 . The electric converter  20  generally includes a plurality of rotor cores  30  (only one shown in  FIG. 1B  for purposes of clarity) and a plurality of magnetizable inserts  32  disposed within cavities  34  of the rotor cores  30 . As set forth above, construction of such an electric converter  20  is described in greater detail in U.S. Publication No. 2018/0287439, which has been incorporated herein by reference in its entirety. Advantageously, the present disclosure provides an innovative and efficient method and a related apparatus for securing the magnetizable inserts  32  within the cavities  34  of the rotor cores  30 . 
     Referring to  FIG. 2 , an apparatus for securing the magnetizable inserts  34  within the rotor cores  30  is schematically illustrated and generally indicated by reference numeral  50 . The apparatus  50  generally includes an upper tool  52 , a lower tool  54 , and a plurality of stacked rotor cores  30  disposed between the upper tool  52  and the lower tool  54 . The magnetizable inserts  32  are disposed within the cavities  34  of the rotor cores  30  as shown, and the cavities  34  are in fluid communication. In other words, the cavities  34  are open to each generally other along an axial direction “Y” as shown such that an adhesive material can flow through each of the cavities  34  during molding as set forth in greater detail below. 
     The apparatus  50  is disposed within a transfer molding press  60 , which comprises a plunger  62  disposed within a housing  64 . The plunger  62  functions to displace the adhesive, which in one variation is a polymer preform  70 , during molding. The polymer preform  70  as shown generally defines a cylindrical geometry before molding, or a puck-like shape. However, it should be understood that other geometries may be employed while remaining within the scope of the present disclosure. In one form, the polymer preform  70  is a thermoset material, such as by way of example, an epoxy. It should be understood, however, that other types of thermoset materials or polymer materials (e.g., thermoplastics) may be employed while remaining within the scope of the present disclosure. 
     Referring now to  FIGS. 3-7 , the upper tool  52  and the lower tool  54  are illustrated and described in greater detail. The upper tool  52  comprises a runner cavity  72  connecting a plurality of runners  74 , along a topside runnerplate  76 . The upper tool  52  in one form also includes a bottomside runnerplate  78 . A plurality of gates  80  extend from the runners  74  to the cavities  34 . The plurality of runners  74  and gates  80  receive and direct a flow of the polymer preform  70  after it changes state (i.e. from a solid to a liquid) and becomes molten during the molding process as described in greater detail below. 
     The lower tool  54  is disposed adjacent to the plurality of stacked rotor cores  30 , opposite the upper tool  52  such that the rotor cores  30  are “sandwiched” between the upper tool  52  and the lower tool  54 . The lower tool  54  comprises a central mandrel  82 , which extends through a center of the plurality of stacked rotors  30  (best shown extending through the center in  FIG. 2 ). In one form, the mandrel  82  comprises keyways  83 , which mate with tabs  31  (shown in  FIG. 1B ) to properly locate/align the rotor cores  30  within the assembly. In another form, the mandrel  82  is also “scalloped” with a series of cutouts  77  and ridges  79  extending around its periphery. Accordingly, the ridges  79  provide reduced contact area with the rotor cores  30 , thus reducing friction when removing the rotor cores  30  from the lower tool  54  and mandrel  82  after molding. 
     The lower tool  54  further comprises a plurality of ventings  84 , which provide vents for air to escape the apparatus  50  during the molding process. The runners  74  and the gates  80  of the upper tool  52 , and the cavities  34  of the rotor cores, are in fluid communication to allow the polymer preform  70  to flow radially, in a direction indicated by arrow “X” through the runners  74 , then axially along direction “Y” through the gates  80 , and then continuing along direction “Y” through each of the cavities  34  of the rotor cores  30  during the molding process to secure the magnetizable inserts  32  to the rotor cores  30 . 
     More specifically, and with reference to  FIG. 8 , the upper tool  52 , lower tool  54 , and stacked rotor cores  30  are shown to illustrate flow paths of the molten polymer and heating channels (air flow) for the molding process. As shown, the molten polymer flows radially along the runners  74  and then axially through the gates  80 , and then through the cavities  34  of the rotor cores  30 . The lower tool  54  and the rotor cores  30  include passageways  85  disposed along an inner portion of the apparatus  50 , which provide heating channels, or a conduit for air flow, during the molding process. 
     In one form, the cavities  32  of the rotor cores  30  are radially staggered between adjacent rotor cores as shown. Further, the upper tool  52  and the lower tool  54  define locating features to position the plurality of stacked rotor cores  30  within the apparatus  50 . As best shown in  FIGS. 6 and 7 , the lower tool  54  include locating apertures  87  that interface with features/pins (not shown) of the transfer molding press  60  to locate the lower tool  54  for the molding process. Similarly, the upper tool  52  comprises locating apertures  89 . As further shown, the upper tool  52  comprises an optional notch  93  (which mates with a corresponding feature of the transfer molding press  60 , not shown) to ensure that the apparatus  50  is properly located for molding. The lower tool  54  also includes additional apertures  95 , which are used for insertion of a tool to remove or push the rotor cores  30  off of the mandrel  82 /lower tool  54 . Further, one or more flats  97  may be formed in the lower tool  54  for proper radial orientation in the transfer molding press  60 . 
     Referring now to  FIGS. 2, 8, and 9 , a method of securing the magnetizable inserts  32  within the rotor cores  30  is generally illustrated. The method comprises placing an assembly of rotor cores  30  in the transfer molding press  60 , wherein the magnetizable inserts  32  are disposed within the cavities  34  of the rotor cores  32 . (Generally, the “assembly of rotor cores” as used herein includes the rotor cores  30  and the magnetizable inserts  32 ). As previously set forth, the cavities  34  of the rotor cores  30  are in fluid communication with each other and with the runners  74  and gates  80 . 
     Before placing the assembly of rotor cores  30  in the transfer molding press  60 , the assembly of rotor cores  30  may optionally be preheated, and the polymer preform  70  may also be optionally preheated in one form of the present disclosure. In another variation, the assembly of rotor cores  30  is weighed before being placed into the transfer molding press  60 . In one form, the assembly of rotor cores  30  and the lower tool  54  are weighed together. Similarly, in one form, the assembly of rotor cores  30  with the lower tool  54 , and optionally the upper tool  52 , are preheated before being placed into the transfer molding press  60 . 
     The polymer preform  70  is placed in the housing  64 , below the plunger  62 , of the transfer molding press  60  and proximate a central portion  88  of the assembly of rotor cores  30 . Alternately, the polymer preform  70  may be placed on top of the upper tool  52 , proximate the central portion  88 , prior to molding. Within the transfer molding press  60 , heat and a transfer pressure are applied, and the plunger  62  moves downward to displace the polymer preform  70  such that the polymer preform  70  changes state and flows radially, along the direction X, and then axially, along the direction Y, through the runners  74 , the gates  80 , and subsequently the cavities  34  of the rotor cores  30 . 
     A clamping force is provided by the transfer molding press  60  to the upper tool  52  and the lower tool, which varies in magnitude depending on the number and size of rotor cores  30  and the volume of the cavities  34  being filled by the polymer preform  70 . In one form, the central mandrel  82  of the lower tool  54  is spring-loaded in order to apply additional forces when clamping. The clamping force continues to be provided within the transfer molding press  60  for a predetermined period of time, or a cure time after all of the polymer preform  70  has been pressed by the plunger  62 , which is a function of the specific material of the polymer preform  70 . In one example, the cure time is 120 seconds for an epoxy material. Further, the transfer pressure (applied by the plunger  62 ) is also a function of the volume of the cavities  34  being filled by the polymer preform  70 . 
     After the cavities  34  have been filled by the polymer preform  70 , and after the predetermined period of time for curing, the assembly of rotor cores  30  is removed from the transfer molding press  60  and any polymer waste is removed from the assembly of rotor cores  30 . Optionally, the assembly of rotor cores  30  is weighed after being removed from the transfer molding press  60 , after removing the polymer waste, and a difference in weight is compared with a predefined weight value to determine a fill volume of the cavities  34 . As set forth above, the assembly of rotor cores  30  is weighed with the lower tool  54  in one form of the present disclosure to determine the difference in weight. 
     In one variation of the present disclosure, the assembly of rotor cores  30  is placed into the transfer molding press  60  and removed from the transfer molding press  60  by a robot (not shown). Further, the polymer preform  70  may be placed into the transfer molding press  60  by a robot. 
     In the form illustrated herein, the polymer preform  70  is displaced vertically such that the polymer material of the polymer preform  70  flows distally, in a gravitational direction, through the cavities  34 . However, it should be understood that the assembly of rotor cores  30  and related tooling may be oriented differently, such as in a horizontal direction rather than the vertical direction as shown, while remaining within the scope of the present disclosure. 
     Referring now to  FIGS. 10A and 10B , the completed rotor cores  30  are illustrated, with the magnetizable inserts  32  being secured within the cavities  34  by a polymer material  71  of the polymer preform  70 . As shown, the polymer material  71  has cured around the magnetizable inserts  32 , thus forming a bond between the magnetizable inserts  32  and the rotor core  30 . 
     Before arriving at the transfer molding press  60 , the polymer preforms  70  are refrigerated and may be staged near the transfer molding press  60  for a period of time prior to being loaded into the plunger housing  64 . In another form, the polymer preforms  70  may be included in a “loaf” or bar of polymer material, and a specific volume, or width, may be cut off of the bar as a function of the weighing steps as set forth above or other quality inspection method. For example, if the cavities  34  are not being completely filled, then an increased volume of polymer preform  70  may be cut from the bar for the next molding cycles. 
     Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or “approximately” in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability. 
     As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. For example, while the disclosure is directed to electric motors, it should be understood that the teachings of the present disclosure may be applied to other electric/electricity converters such as generators. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.