Method of producing a poly-V pulley

A method of producing a poly-V pulley which has a cylindrical trunk, first and second ears for preventing a V belt from being disengaged from the trunk, the ears projecting respectively from axial ends of an outer peripheral face of the trunk, and poly-V grooves formed between the first and second ears on the outer peripheral face of the trunk, the method comprising the steps of cutting a thick pipe blank into a fixed dimension to obtain the trunk;

• forming a V-shaped slot over a circumferential direction in an intermediate portion in a thickness direction of each of the axial end faces of the trunk, and forming first and second preliminary ears to project outwardly from axial ends of the outer peripheral face of the trunk by a first pressing in which the axial end faces of the trunk are clamped between upper and lower dies each having an annular wedge-like projection, and the wedge-like projections are caused to bite the axial end faces of the trunk;
• forming an annular boss portion in a radially inner side with respect to the V-shaped slot of at least one of the axial end faces of the trunk, thereby removing the V-shaped slot, and increasing the projecting amount of the first preliminary ear or the second preliminary ear by a second pressing in which annular split pieces of the axial end faces of the trunk which are outside the respective V-shaped slots are clamped between the upper and lower dies, thereby inwardly compressing in the axial direction to a depth of the V-shaped slot;
• and shaping by rolling the first and second preliminary ears into the first and second ears of a predetermined shape, forming the poly-V grooves between the first and second ears.