Measurement of Actual Load and Contact Stress in Air-Stamp Hammer Forging

Abstract

The actual punch load, contact pressure, and frictional stress on the punch surface has been measured in air-stamp hammer forging. An example of stamping where the punch is inserted into the center of a circular cylinder in a circular die with flash land has been chosen for the detection of contact stress on the punch. The punch load was detected by fitting strain gauges on the side wall of the inner hole machined on the bottom surface of the punch. Pressure and friction sensors were installed on the top flat surface of the punch, the corner of the punch, and the flash land surface. In the stamping process where the work material is only pressed by the punch top, the pressure on the punch was nearly equal to the punch load divided by the top area of the punch. When the compressed bulged material came into contact with the outer side surface and the deformed material came into contact with the bottom of the punch, the friction on the corner of the punch increased. The punch load increased rapidly when the material filled the die cavity. The pressure and friction applied on the flash land surface increased as the flash thickness and temperature decreased with the progress of stamping.