Method of manufacturing a rotor assembly

A method of manufacturing a rotor assembly for an electric motor, said rotor assembly having a central longitudinal axis of rotation about which said assembly is rotated when installed in said motor, said assembly including a rotor core including a stack of annular laminations of suitable ferro-magnetic materials with an inner peripheral wall formed by said stack of annular laminations defining a central opening therethrough about said central longitudinal axis, a rotor shaft extending along said central longitudinal axis, a rotor hub between said core and shaft and an oil return tube extending coaxially with said central longitudinal axis comprising the steps of:

• forming said rotor core by punching a plurality of annular laminations from a sheet of suitable ferro-magnetic material with each lamination having a central opening and a plurality of outer peripheral satellite slots;
• assembling said annular laminations in a stack so that the central openings are coaxial to define an inner peripheral wall and the outer peripheral satellite slots are skewed to provide skewed passages;
• die casting said skewed passages to form the conductor bars of said rotor and simultaneously die casting a pair of annular rings along opposed faces of said stack of laminations to form said rotor core, said pair of end rings being die cast from aluminum material and being sized and geometrically shaped in preselected trapezoidal cross-section to provide a controlled resistance for said rotor core;
• grinding said rotor core to desired tolerance and to remove burrs and edges thereon;
• cutting a rotor shaft from selected bar stock to include an undercut midsection and rough grinding the same;
• rolling said shaft to include a helical oil groove extending from one end thereof to said undercut midsection and to further include a rolled threaded section at the opposite end thereof;
• inserting said rolled shaft through the central opening defined by said stack of annular laminations and supporting said shaft in concentrically spaced relation from said inner peripheral wall defined by said annular laminations so that the longitudinal axis of said shaft extends along said central axis of rotation of said rotor;
• die casting a rotor hub from zinc material to extend between said inner peripheral wall of said stack of annular laminations and said concentrically supported rotor shaft with said rolled threaded end of said shaft extending externally from said die cast material to provide a fan mount, said die cast rotor hub including a cup-like opening at one end thereof to nestingly receive a portion of an oil return tube therein;
• forming a non-porous plastic oil return tube to include an outwardly flanged mouth portion and a cylindrical body portion terminating in an apertured base portion, said oil return tube portions being preselectively sized along their lengths and cross-sections in accordance with said cup-like opening in said rotor hub;
• and,
• press-fitting said oil return tube into sealed relation with said cup-like opening of said rotor hub and said rotor shaft so that said cylindrical body portion snugly and sealingly nests in said cup-like opening of said rotor hub with said base portion of said cylindrical portion of said oil return tube abutting the base of said cup-like opening and with said rotor shaft extending in sealed relation through said apertured base portion to be in spaced concentric relation with said cylindrical body portion and said flanged mouth portion with said flanged mouth portion concentrically surrounding said rolled helical oil groove and undercut intermediate section of said rotor shaft.