A Measurement of Contact-Pressure Distributions in the Upsetting of Cylindrical Billets

The contact-pressure distribution in upsetting is estimated by measuring the elastic-strain distribution in the loading platen. The strains in the platen are measured by pipe-type strain gages, and are converted into contact pressure by a finite-element analysis. Compensation for the strains due to the friction on the contact surface is possible to some extent. The estimated pressure distributions almost agreed with those measured by the pressure-pin method. The pressure was distributed uniformly over the contact surface in the well-lubricated specimens regardless of the diameter-to height ratio of the specimen, d0/h0. Friction hills were observed in the unlubricated specimens with d0/h0=4 and 2. A concave pressure distribution was obtained for the specimen with d0/h0=1, where the pressure increased from the center to the periphery of the contact surface. The present method can be applied to measure die-pressure distributions in practical metalworking processes.