Abstract

A method of and apparatus for punching a hole in sheet material is provided using pressurized fluid as the female die together with a modified male punch. The slug of material to be sheared from the material is during and after shearing continuously held against the face of the punch by the difference in pressure between the fluid and the punch face. In addition the area adjacent the perimeter of the hole may be deformed and drawn away from the die block face as the punch advances through the material. As the punch is withdrawn, the slug remains held against the punch face. The mechanical force withdrawing the punch together with the fluid pressure bearing on the slug and deformed area forces the slug and deformed area of material toward the die block face, inelastically retracting the deformed area. The deformed area may be fully retracted to a substantially flat form or partially retracted to a countersunk form.