Abstract:
An apparatus and method for forming cylindrical magnetic assemblies for rotating electrical machines. The apparatus and method pre-bends and finally bends a flange of the supporting shell to lock the permanent magnets in place. This is done in a single station and in two steps by way of an apparatus that permits handling of cylindrical bodies of considerably different diameters and lengths.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to an apparatus and method for forming cylindrical magnet assemblies for rotating electrical machines.  
           [0002]    In many forms of rotating electrical machines, there is provided a cylindrical shell that contains a plurality of circumferentially spaced permanent magnets. Generally these magnets are retained within the shell by a magnet case that is complimentary to the shell. However, recently the use of high energy neodymium based magnets has replaced ferrite based magnets. By using these high energy neodymium based magnets, it is possible to increase the magnetic intensity while at the same time, reducing the size of the components. However, because of their high magnetic strength, it is necessary to insure that the magnets are rigidly held within the cylindrical shell.  
           [0003]    One way it is proposed to maintain the magnets in position is to deform or fold the edge of the shell into engagement with the magnets so that they are trapped between two flanges thus formed on the shell. However, the previous methods for forming this have resulted in a cumbersome operation which has been difficult to obtain automatically and required two separate forming steps in different stations.  
           [0004]    It is, therefore, a principle object to this invention to provide an improved and simplified apparatus and method for assembling the permanent magnets of a rotating electrical machine.  
           [0005]    It is a further object to this invention to provide an improved method and apparatus for retaining the permanent magnets in position within a cylindrical shell, which is versatile and can be adapted for use with various sized shells.  
         SUMMARY OF INVENTION  
         [0006]    A first feature of the invention is adapted to be embodied in a machine for folding over a peripheral flange of a cylindrical shell. The apparatus comprises a support for the shell, a forming tool having a pre-bending section and a final bending section angularly related to each other about a plane extending parallel to the support and a drive. The drive is effective to cause relative axial movement of the support and the forming tool to bring the forming tool into engagement with a peripheral flange of a shell positioned on the support. The drive also effects relative radial movement of the support and the forming tool for determining which of section of the forming tool engages the peripheral flange of the shell positioned on the support. In addition, the drive effects relative rotation of the support and the forming tool to deform a circumferential portion of the peripheral flange of the shell positioned on the support. A control operates the drive for first partially bending the peripheral flange of the shell positioned on the support around a circumferential area by the pre-bending section of the forming tool and then completes the bending thereof by the final bending section of the forming tool.  
           [0007]    Another feature of the invention is embodied in a method of forming a magnet assembly for a rotating electrical machine. The method comprises the steps of forming a shell having a cylindrical section open at one end and at least partially closed at its other end by a radially extending end wall extending radially inwardly from the cylindrical section and an extending section thereof at the open end of said shell. A plurality of magnetic sections are placed within the shell with their outer periphery in engagement with the inner surface of the cylindrical section and one end thereof in engagement with the end wall The extending section of the shell is initially bent toward the magnetic sections by bringing a first section of a forming tool into axial contact therewith and then continuing to bend a circumferential extent of the extending section by effecting relative rotation between the shell and the forming tool around the axis of the cylindrical section. Then the extending section is finally bent of into locking engagement with the magnetic sections by bringing a second section of the forming tool into contact with the extending section and effecting relative rotation between the shell and the forming tool around the axis of the cylindrical section. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a front elevational view of an apparatus constructed in accordance with the invention and capable of performing the method of the invention.  
         [0009]    [0009]FIG. 2 is a side elevational view of the apparatus.  
         [0010]    [0010]FIG. 3 is an enlarged view looking in the same direction as FIG. 1 with portions shown broken away and in section.  
         [0011]    [0011]FIG. 4 is a perspective view, with a portion broken away, of a cylindrical shell which forms the magnet carrier.  
         [0012]    FIGS.  5 - 7  are is a cross sectional view looking in the same general direction as FIG. 3 and show the steps in the forming operation.  
         [0013]    [0013]FIG. 5 shows the forming tools before engagement with the work piece.  
         [0014]    [0014]FIG. 6 shows the initial pre-bending forming operation.  
         [0015]    [0015]FIG. 7 shows the final bending operation. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Referring now in detail to the drawings and initially to FIGS. 1 through 3, an apparatus for performing the method of the invention and embodying the invention is indicated generally by the reference numeral  11 . The apparatus  11  includes four corner pillars  12 , which are adapted to be supported on the floor. The pillars  12  are connected to each other at their upper ends by cross pieces  13  and at their lower ends by cross pieces  14  to form a rigid frame for the apparatus  11 .  
         [0017]    A support plate  15  is affixed to the pillars  12  at an appropriate height and is adapted to support a work piece in the form of a cylindrical ferrous material having a shape best shown in FIG. 4 and identified generally by the reference numeral  16 . Referring now to FIG. 5, the workpiece  16  includes a cylindrical shell portion  17  that is at least partially closed at one end thereof by a radially inwardly extending end wall  18 . The end wall  18  forms an opening  19  to pass a shaft in the completed rotating electrical machine.  
         [0018]    A cylindrical inner surface  21  of the shell  17  is adapted to receive a plurality of circumferentially spaced permanent magnets, which may be carried in a magnet carrier of any suitable type. These magnets and carrier are positioned to engage the cylindrical surface  21  with their lower ends being supported on the end wall  18 .  
         [0019]    A ledge  22  is formed at the upper end of the surface  21  and is coextensive with the upper ends of the magnets and their carrier. A thinner peripheral flange  23  is formed on the shell and in the illustrated embodiment forms a continuation of the cylindrical section  17 . This peripheral edge  23  has a length that is greater than the radial dimension of the end surface  22  for a reason which will become apparent shortly.  
         [0020]    Referring again to the apparatus  11  and specifically FIGS. 1 through 3, the support plate  15  has mounted on it a fixture  24  that is adapted to receive the shell  16  and hold it against transverse movement. This fixture  24  is rotatably connected to a drive shaft  25  that is driven by a rotary motor  26  which may be hydraulically operated.  
         [0021]    A moveable forming tool apparatus, indicated generally by the reference numeral  27 , is supported for vertical movement in the directions indicated by the arrow A on guide rails  28  formed on the pillars  12 . This moveable forming tool apparatus  27  has a base portion  29  that is connected to the piston rod of a reciprocating hydraulic cylinder assembly  31 . The cylinder housing of this assembly  31  is fixed to the upper cross pieces  13  by a fastener arrangement  32 .  
         [0022]    A feed screw, indicated generally by the reference numeral  33 , is rotatably journalled on the underside of the base portion  29  and has a pair of axially spaced threaded portions  34  and  35  which are of opposite hand. This feed screw  33  is journalled in a pair of spaced bearing assemblies  36  and is driven by the shaft  37  of a further rotary hydraulic motor  38 .  
         [0023]    Referring now primarily to FIG. 3, a pair of forming tool assemblies, each indicated generally by the reference numeral  39 , are associated with the feed screw portions  34  and  35 . These assemblies  39  include recirculating ball nuts  41  each of which cooperates with a respective one of the feed screw portions  34  and  35 , so that when the feed screw  33  is rotated in one direction or the other, the assemblies  39  will move toward each other or away from each other in the directions indicated by the arrow B.  
         [0024]    Each nut  41  has a supporting brackets  42 , each of which journals a pair of shafts  43 . Rotatably supported on the shafts  43  are forming tools  44 . Each forming tool  44  has an angularly inclined surface  45 , which forms a pre-bending section and a generally cylindrical portion  46  which forms the final bending operation. These operations will be described shortly in more detail.  
         [0025]    Referring now back primarily to FIGS. 1 and 2, the apparatus further includes a control panel  47  that controls the operation of the reciprocating hydraulic motor  31  and the rotating hydraulic motors  26  and  38 . The hydraulic system for these operations is shown schematically at  48  and is contained within a hydraulic circuit assembly.  
         [0026]    An operator start switch  49  is conveniently positioned on the machine so that the operator can initiate the forming operation, which will now be described by primary reference to FIGS. 5 through 7. As may be best seen in FIGS. 5 through 7, the forming tool forming sections  45  and  46  are disposed at an angle to each other. In the illustrated embodiment, the section  45  is a cone of revolution and thus has a planar configuration in cross section. It is also to be understood that this shape could be of a concave curve and in any event terminates at the section  46 , which extends parallel to the work piece face  18  and surface  22 .  
         [0027]    In operation, a work piece  16  with the permanent magnets and the magnet carrier in place is positioned on the support  24  and specifically in confronting relationship to the forming tools  39 . It should be noted that the permanent magnets may magnetized before being inserted into the shell or may be magnetized thereafter.  
         [0028]    Initially, the feed screw  33  is rotated in a direction to cause the forming tools  39  to be positioned so that their pre-forming sections  45  are disposed immediately above the extending flange  23  of the shell  16 . Then, the device is lowered by actuation of a hydraulic cylinder  31  so as to bring the sections  45  of the forming tools into engagement with the flange  23  as shown in FIG. 6 so as to partially deflect it. The workpiece  16  is rotated so that the entire circumferential extent of the flange  23  is pre-bent.  
         [0029]    Then, the feed screw is rotated so as to move the forming tools  39  away from each other and to bring the final forming sections  46  into registry above the top of the bent flange  23 . Then, the device is further lowered and rotated so as to complete the forming operation.  
         [0030]    Thus, it should be readily apparent that the apparatus prevents both the preforming and final bending to be accomplished in the same station and in successive steps. Also, because of this construction the apparatus is capable of affixing magnet carriers having widely different diameters. Of course, the foregoing description is that of preferred embodiment of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.