| 摘要 |
PURPOSE:To exceedingly reduce the abrasion at the edge surface of a piston by forming a tapered part, simultaneously with a piston body, through cold forging, onto the edge surface on a piston-rod side of the piston body. CONSTITUTION:A piston body 14 is formed through cold forging from a die 15a, spherical head punch 16, ring-shaped punch 17 and a main punch 18. In this case, a tapered step difference 19 is formed midway in the penetration hole 15 of the die 15a, and the upper part of the step difference 19 is formed as large-diameter side, and the lower part is formed as small-diameter side. The spherical head punch 16 is constituted of a cylindrical part 20 and a spherical head part 21 having a small diameter which is connected coaxially with the upper edge part of the cylindrical part 20. A slit is formed between the punch 17 and the spherical head part 21. Thus, a disc-shaped material is put into cold forging, and a tapered part 25 is formed onto the edge surface 24 which forms the counter top surface of the piston body 14 by the step difference 19 of the die 16. Therefore, the tapered part 25 can be formed simply and at a low cost, and a prescribed purpose can be achieved. |
