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.

Abstract: A method of manufacturing precise sheet metal made poly-V pulleys with poly-V grooves, being uniform in thickness of peripheral wall and free of reduction of mechanical strength, by a step of preliminarily forming a lug in the peripheral wall of a cup-shaped blank and thickening the peripheral wall, a step of forming a plurality of V-grooves in a multiple arrangement on this thickened peripheral wall by pressing from both sides with a V-groove preliminary forming roller possessing a plurality of V-grooves forming ridges and a rotary inner die possessing a plurality of V-grooves while rotating the cup-shaped blank, and a step of pressing this peripheral wall with a plurality of V-grooves with a finishing roller. Furthermore, a method of manufacturing sheet metal made poly-V pulleys having advanced precision, by a step of preliminarily forming lugs and first grooves in the peripheral wall of a cup-shaped blank, and a step of thickening the peripheral wall.

Abstract: An improvement in a method of manufacturing poly-V pulleys made of sheet metal, which is performed by subjecting a preformed cupshaped blank to working by a corrugating roller, an auxiliary forming roller and a finish forming roller. Prior to corrugation of the blank by the corrugating roller, a connecting portion between the peripheral wall and the bottom wall of the blank is pressed in a manner that the inside surface of the peripheral wall and the inside surface of the bottom wall are pressed into contact with each other, thereby to preform a lug which provides a side wall for grooves adjacent to the connecting portion.