Process for manufacturing outer ring member for constant-velocity joint
First shaped item with shaft part is produced by forward extrusion forming of work, and further, upset forming thereof is carried out to thereby obtain second shaped item with large-diameter part. Subsequently, backward extrusion forming of the second shaped item is carried out to thereby obtain third shaped item having not only cup part provided with ball rolling grooves but also circular diameter expansion portion provided at the mouth area of the inside wall of the cup part along the circumferential direction in such a fashion that the diameter is gradually expanded from the bottom side toward the opening side. Outer ring member for constant-velocity joint is obtained by further subjecting the third shaped item to low-temperature annealing treatment, shot blast treatment and lubricating chemical coating treatment, and thereafter to ironing forming.
1. A method of manufacturing an outer ring member for a constant velocity universal joint having a shank and a cup which are formed integrally with each other, comprising the steps of:
forming a cup having an annular large-diameter portion which is circumferentially formed in a mouth of an inner wall surface of the cup and progressively spreads from a bottom toward an opening thereof, when the cup with grooves is formed by a backward extrusion process; and
performing an ironing process on the cup, wherein before the cup is ironed, an annular ridge is formed as a mark in the mouth of the cup by a shot blasting process performed on a form.
2. A method according to claim 1 , wherein the annular large-diameter portion comprises an annular tapered surface which progressively spreads toward the mouth of the cup, the tapered surface having a terminal end contiguous to an edge of the mouth of the cup.
3. A method according to claim 1 , wherein the annular ridge having an inside diameter greater than the maximum outside diameter of a forming portion of an ironing punch.
4. A method according to claim 1 , wherein the backward extrusion process and the ironing process are carried out by a cold forging process or a warm forging process.
5. A method according to claim 1 , wherein the outer ring member comprises an outer ring member for a Birfield constant velocity universal joint or an outer ring member for a tripod constant velocity universal joint.