| 摘要 |
PURPOSE:To pierce the central part of a billet with the guide of a cooled outside peripheral part and to improve yield by jetting a cooling fluid to the outside circumference on the rear end of the billet which is held heated to cool the same then piercing the billet. CONSTITUTION:The central part on the front end side of a billet 1 is pierced under the guide of a plug by the working part of a centering punch device 13, and the central part on the rear end side thereof is pierced with the guide of the outside peripheral part having the deformation resistance increased by the cooling in accordance with the operation of a cooling ring 16. Therefore the central part of the billet 1 is surely pierced in the rear end of the billet 1 as well which is not subjected to centering punching, thereby decreasing the circumferential thickness deviation generated at the rear end and the ruggedness in the axial direction. |
