Influence of lubrication on the measured thermoelectric volt-age and temperature in the forming zone when embossing S355MC

Abstract

Cold Metal Forming is one of the most frequently used sheet metal manufacturing processes because of high material efficiency, accuracy grade and surface quality as well as short cycle times of the produced parts. In order to reach the requirements for both quality of the components and process stability, minimizing tool wear is one of the main aims in this field. One of the most influential factors on wear development is the occurring process temperature. The dissipation of more than 80 % of the plastic work as well as frictional heating lead to a severe temperature rise in the forming zone, especially during processes with high tension between tool and workpiece respectively high strain rates like embossing and blanking. Beside the influence on the mechanical properties of the materials, the temperature rise causes thermoelec-tric voltages and currents. These thermoelectric phenomena in combination with the occurring temperature reinforce the wear mechanisms Adhesion and tribochemical reaction, which determine the tool wear development because they can appear right from the beginning. State of the art is the application of lubricants in order to minimize temperature and consequently wear by reducing friction, removing heat and building reaction layers due to the additives. However, in order to improve the understanding of the interactions between the surfaces of the tool and the sheet metal precise meas-urements of the temperature as well as the occurring thermoelectric voltages are essential. This report shows the measur-ing concept and the appearing thermoelectric voltage, current and temperature during blanking S355MC