Some observations on contact stress measurement by pin load cell in bulk metal forming

Abstract The information on the intensity and distribution of the contact stresses in bulk metal forming operations is essential both for the die design and for the process analyst. As the theoretical and numerical methods for the contact stress determination have some analytical constraints a number of experimental methods have been developed. One of them is the pin load cell technique which has been applied in different metal forming operations. In this paper some problems related to the measurement of normal contact stress are presented. The focus is placed on the problem of initial pin position relative to the die surface. Experimental investigations were carried out in order to determine the influence of the axial pin position on the measured contact stress values. The process studied was that of simple upsetting of cylindrical specimens. It has been shown that the axial pin position 0.15mm above the die surface prior to the defonnation gives the most realistic results.