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Over-molded net-shaped gear and manufact uring methodRelated Patent Categories: Metal Working, Method Of Mechanical Manufacture, Gear Making, Gear Shaping, Die-press ShapingOver-molded net-shaped gear and manufact uring method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060236541, Over-molded net-shaped gear and manufact uring method. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This application is a continuation of U.S. patent application Ser. No. 10/690,152 filed on Oct. 21, 2003. [0002] The present disclosure generally relates to a method for manufacturing gears and, more particularly, to differential side gears, pinion gears and hypoid gears adapted for use in vehicle differentials and a method for manufacturing the gears. BACKGROUND OF THE INVENTION [0003] As is well known in the art, the fabrication of typical differential side gears and pinion gears for an automotive differential assembly is complex and costly and as such, greatly adds to the cost of the differential assembly. A typical process for forming a differential gear includes forging, annealing, rough machining, carburizing, hardening and finish machining operations. Despite the almost universal use of such forming processes, several drawbacks have been noted. [0004] One such drawback relates to the initial forming of the differential gear through forging. As those skilled in the art will appreciate, the differential gear is typically blanked or rough-formed in a forging operation from a solid billet of steel. This forging operation is relatively inefficient because the shape of the "in-process" forging is substantially different from the final desired gear shape. Specifically, each of the differential gears contemplated for manufacture by the present invention include relatively large apertures extending through the center of the gear. As such, many machining operations are required after forging. In addition, a relatively large proportion of the forging material is machined off and wasted. [0005] Another drawback concerns the machining of the differential gear. The numerous machining operations that are performed on the differential gear typically account for more than 70% of the total cost of the gear. Furthermore, the protracted nature of the machining operations often results in an average cycle time that exceeds one or more days in length. [0006] Yet another drawback concerns the material from which the differential gear is formed. Typically, the steel billet from which the gear is formed is a low carbon steel having characteristics that are particularly well suited to both forging and machining. Such steels, however, generally lack the strength that is desired for a gear and as such, a time consuming and costly carburization process is typically employed to create a layer of relatively high carbon steel on the surface of the differential gear. Carburization usually entails the placement of semi-finished gears into a heated, high-carbon environment for an extended period of time to permit carbon to migrate into the gear material to a predetermined depth. The differential gear is subsequently heat treated so that the high carbon layer provides a level of strength and durability that is commensurate with the intended application. [0007] Accordingly, there remains a need in the art for an improved differential gear manufacturing method that permits increased flexibility in the design of the gears of the differential and the adaptation of lower cost processes for their manufacture. SUMMARY OF THE INVENTION [0008] In one form, the present teachings provide a method of manufacturing a gear. The method can include: providing a die assembly having an upper die, a lower die and a mandrel, one of the upper die and the lower die defining a plurality of gear teeth, the upper and lower dies cooperating to form a die cavity, the mandrel being received into the die cavity; providing an insert portion that is formed of a solid substantially void free metal, the insert portion having a hollow body and a flange, the hollow body having opposite axial end faces, the flange extending circumferentially about the hollow body between the opposite axial end faces of the hollow body; positioning the insert portion onto the mandrel; cutting a preform portion from a tubular billet, the tubular billet being formed of a metal; positioning the preform portion within the die cavity such that the preform portion extends circumferentially about at least a portion of the insert portion; and pressing the preform portion between the upper and lower dies to form a gear in a single stroke such that a plurality of gear teeth are formed on the preform portion, the preform portion deforming during the single stroke such that the flange is embedded into the preform portion to thereby fixedly couple the insert portion and the preform portion. [0009] In another form, the present teachings provide a method for forming a side gear of a differential. The method can include: forming a metallic insert portion having a net shaped non-circular aperture formed therethrough that is adapted to slidingly but non-rotatably engage an axle shaft; providing a die assembly having an upper die, a lower die and a mandrel, one of the upper die and the lower die defining a plurality of gear teeth, the upper and lower dies cooperating to form a die cavity, the mandrel being received into the die cavity; positioning the insert portion onto the mandrel; cutting a preform portion from a tubular billet, the tubular billet being formed of a metal; positioning the preform portion within the die cavity such that the preform portion extends circumferentially about at least a portion of the insert portion; and pressing the preform portion between the upper and lower dies to form a gear in a single stroke such that a plurality of gear teeth are formed on the preform portion, the preform portion deforming during the single stroke such that the flange is embedded into the preform portion to thereby fixedly couple the insert portion and the preform portion. [0010] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0011] Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein: [0012] FIG. 1 is a schematic illustration of a motor vehicle constructed in accordance with the teachings of the present invention; [0013] FIG. 2 is a fragmentary perspective view of a portion of the motor vehicle of FIG. 1, illustrating the rear axle in greater detail; [0014] FIG. 3 is a section view of a portion of the rear axle illustrated in FIG. 2; [0015] FIG. 4 is a perspective view of a differential side gear constructed in accordance with the teachings of the present invention; [0016] FIG. 5 is a perspective view of a tube used for constructing preforms of the present invention; [0017] FIG. 6 is a perspective view of an exemplary tubular insert used for constructing gears of the present invention; [0018] FIG. 7 is a cross-sectional side view of the tubular insert of FIG. 6; [0019] FIG. 8 is a partial cross-sectional side view of a die for forming a gear from an insert and a preform, the die being in an open condition; and [0020] FIG. 9 is a partial cross-sectional side view of the die of FIG. 6 shown in a closed position. 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