METHOD FOR HYDRAULICALLY PIERCING CYLINDRICAL MEMBER

摘要

PROBLEM TO BE SOLVED: To provide a hydraulically piercing method for a cylindrical member in which the accuracy of a bore diameter and worked surface is high and a hole having reduced shear droop is formed even when the internal hydraulic pressure is low. SOLUTION: In the working method for piercing the cylindrical member 14 with a piercing punch 11 as loading the internal hydraulic pressure P on the inside of the cylindrical member 14, after forming a reduced wall-thickness part by once forming a projection 15 having a convex shape and an external size approximately equal to a dimension to be pierced in the reverse direction of the final piercing direction, the piercing are executed by pressurizing the piercing punch 11 from the tip side of the projection 15.