Abstract: A method of manufacturing a spline shaft, comprising ironing a hollow stock by cold forging and forming splines in a desired portion of said hollow stock by cold forging by using its work harden state. This method makes it possible to reduce the weight of a product by using a hollow stock, and to prevent buckling of the material of the hollow stock during the formation of splines owing to work-hardening caused by the ironing. Further, a predetermined root strength can be ensured without requiring induction hardening. Accordingly, a reduction in weight is achieved, and the production speed and yield are improved.

Abstract: A spline forming die is made up of: upper and lower ring-shaped holders; and rollers vertically rotatably retained between the upper and lower holders and projected from a circumferential end of a holder. Using this spline forming die, splines having a stable precision in a spline-forming direction are formed by a press load due to the rotation of the rollers without the metal stock being subject to shearing friction. Further, a large module of splines can also be formed by setting the diameter of each of the rollers to a large size.

Abstract: A method of forming an internal spline shaft, comprising forming splines on an inner circumferential portion of a hollow stock by cold forging in such a way that a clearance "a" between an inner diameter of the hollow stock and an outer diameter of a tool guide portion, a difference "b" between a reduced diameter of a forming land and the inner diameter of the hollow stock, and a forming-land approach angle .theta. satisfy respectively specific relationships. By this method, products having internal long splines can be obtained in a high yield by cold forging method.