Influence of stiffness on contact-time and temperature at dies surface in hot and warm forging: an experimental approach

In hot and warm forging, the surface layers of dies at the tool-workpiece interface are exposed to high mechanical stress cycles and severe temperatures caused by process operating conditions (such as the forging temperature, cooling policy and lubricating tool surfaces) and characteristics of the forging system. Among these characteristics, the elasticity of the forming machine and the contact-time are particularly important for their impact on the service life of the dies. This paper presents an experimental approach to evaluate the influence that the press characteristics, such as the total stiffness and contact-time under pressure, have on temperature distribution at the die surface during hot forging cycles. The experimental apparatus is presented together with the procedure and results of forging experiments that were carried out to validate the approach when applied to a forging system based on a screw press.