| 摘要 |
PURPOSE:To improve the accuracy in the cylindricity in the cylindrical part of the outside diameter after working in the stage of sizing of thin-walled sintered parts having large level differences by forming a projection on the circumferential surface of a punch to be press fitted to the inner side surfaces of the sintered parts. CONSTITUTION:In the stage of sizing a sintered part 6 as a rough material by means of a punch 4 and a die 5, an annular projecting part 4b is provided in the secified height position from an end surface 4a to the punch 4, and said part 4b is formed to have the diameter which is 0.4-0.5% the diameter of the punch 4 or is larger by 0.3-0.7mm. therefrom. The axial length thereof is set at 3-7mm.. The punch 4 enters the inside side surface 6C of the part 6 and the end part on the side of the surface 6C where the punch is press fitted is expanded by the part 4b, whereby an expanded part 6d is formed. In this state the part 6 is press fitted and pressurized into the die 5 and since the part 6d is fitted onto and restrained by the part 4b, the surface 6C does not fall toward the inner side of the sintered part and sufficient cylindricity is assured. |
