Abstract: The outer side of a pair of curved parts 3d of a longitudinal annular blank is pressed and energized towards the curved part 3d of the opponent side with a molding outer die 14 of a shaping device 13 to press and widen each curved part 3d to a large curved part of large curvature radius, and a half-finished article 17 is molded, and thereafter, the half-finished article 17 is pressed and widened by cooperative operation of a finishing inner die of the shaping device and a window part of a perfect circle functioning as an outer die to manufacture a ring-shaped member. Therefore, a yield rate or a percentage of the weight of the ring-shaped member with respect to the weight of the raw material and the yield rate or the percentage of the ring-shaped member with respect to the blank can be improved, and the cost can be reduced.

Abstract: The outer side of a pair of curved parts 3d of a longitudinal annular blank is pressed and energized towards the curved part 3d of the opponent side with a molding outer die 14 of a shaping device 13 to press and widen each curved part 3d to a large curved part of large curvature radius, and a half-finished article 17 is molded, and thereafter, the half-finished article 17 is pressed and widened by cooperative operation of a finishing inner die of the shaping device and a window part of a perfect circle functioning as an outer die to manufacture a ring-shaped member. Therefore, a yield rate or a percentage of the weight of the ring-shaped member with respect to the weight of the raw material and the yield rate or the percentage of the ring-shaped member with respect to the blank can be improved, and the cost can be reduced.

Abstract: The yield rate or the percentage of the weight of the ring-shaped member with respect to the weight of the raw material and the yield rate or the percentage of the ring-shaped member with respect to the blank are improved to achieve the cost reduction. A half-finished article 18 having large curved parts 3D obtained by widening the curved parts 3d so as to have a curvature radius larger than the initial curvature radius, and bulge-out parts 3E curved to a circular arc shape at a curvature radius larger than the curvature radius of the curved parts 3d at the linear parts 3b, 3c is molded, and thereafter, the half-finished article 18 is molded into an annular shape to obtain the ring-shaped member 1.

Abstract: The yield rate or the percentage of the weight of the ring-shaped member with respect to the weight of the raw material is improved to achieve the cost reduction of the ring-shaped member. A plurality of longitudinal annular blanks 3 is punched out from a raw material 2 of a predetermined width, and the longitudinal annular blank 3 is molded into an annular ring-shaped member 1.