1. Field of the Invention
The present invention relates to a spline forming die to be used in forming splines by forging.
2. Description of the Prior Art
Conventionally, a ring-shaped die 1 of the type shown in FIG. 6 has been used in forming splines. A multiplicity of teeth 3 each having a cross-sectional shape corresponding to that of a spline are formed around the circumferential edge of a forming land 2 inside the ring-shaped die 1, and splines having a predetermined shape are formed by inserting a metal stock, which constitutes a shaft, into the forming land 2 by forging, and drawing (extruding) the metal stock by surface pressure and shearing friction due to the teeth 3.
However, in the case of the conventional die 1, a number of problems, such as wear and galling, occur in the teeth 3 at all times owing to shearing friction which works on a spline-forming portion of the metal stock while splines are being formed on the metal stock by the teeth 3. To avoid such problems, it has been necessary to take full account of the complicated surface treatment of the teeth 3 or the surface roughness of the metal stock.
Not only does complicated frictional behavior occurs unsteadily, but also the nonuniformity of the inner portions or the dimensions of individual metal stocks causes the frictional behavior to vary further complicatedly, so that unstable characteristics or dimensional errors occur in products.
In addition, it has been difficult to form large-module splines because of the limitation of plastic deformation due to the friction of the metal stock.