Welded plastic bearing cage and method of making same

The method of making a bearing retainer which comprises the steps of providing a pair of molded thermoplastic annular side rails having a plurality of circumferentially spaced axially extending ribs affixed at one of their ends to one of the side rails, providing the exposed end of each rib and the opposed surface of the adjacent side rail with a cooperating aperture and projection adapted to be disposed in axial aligned relationship, forming said aperture with a first portion to slidably receive an end portion of said projection and a second inward portion of reduced cross sectional area forming a shoulder at its intersection with said first portion, preliminarily assembling said rails by positioning said projections in partial telescopic relationship within said apertures with the peripheral end portion of said projection disposed in abutting relationship against said shoulder, ultrasonically vibrating the assembly and applying an axial force in a direction urging the side rails together, continuing the vibration of the assembly and maintaining said axial force for a period of time sufficient to effect a heat softening of the material adjacent to the abutting surfaces of said projections and said apertures to permit a deformation and flow of the material and a further telescopic movement of the projections into the apertures until the side rails move together to the desired spaced substantially parallel relationship, venting the interior of said apertures to the atmosphere to enable escape of entrapped gases from the interior thereof during the telescopic movement of the projections into the apertures, and thereafter discontinuing the vibration and permitting the heat softened material to cool and harden into a welded connection forming an integral bearing retainer.