Patent ID: 7765906
Filing Date: 2010-08-03
Classification: B21D,Y10T

Abstract:
1. A method of forming a through-hole in a circumferential wall of a tubular part of a metal work piece, comprising the steps of: setting the metal work piece at a die; inserting a punch, which is fixed to and projected from a cantilever rod-shaped metal core whose front part is thinner than a rear part thereof so as to allow the punch to move toward the die in the tubular part and the step-shaped border between the front part and the rear part is rounded, and the length of the punch projected from the metal core is shorter than a thickness of the circumferential wall; moving the punch into contact with the interior of said metal work piece by a force from an elevating block which receives the metal core and is movable in a punching direction, simultaneously cutting part of the way through the work piece and causing the metal core of the punch to become elastically bent; moving the punch further to fracture the remainder of the through-hole, wherein the elastic bend of the metal core is relieved causing the scrap to be forced out of the through-hole and be removed in conjunction with a sucking in a discharge hole.