Novel wear testing apparatus to investigate the reciprocating sliding wear in sheet metal forming at elevated temperatures

摘要

Hot stamping has gained increasing importance in the last years due to the introduction of High Strength Steels (HSS) to improve the strength-to-mass ratio of stamped components. Despite the advantages in terms of load decrease, springback reduction and increased formability, the elevated temperatures the tools are subjected to may determine severe thermal-mechanical cycling, increased oxidation and wear, which influence the tools service life and the quality of the produced parts. In addition, the frictional behaviour is also changing with temperature, thus affecting the performance of the forming operation itself. In this paper a novel experimental apparatus suitable for reciprocating sliding wear tests at elevated temperatures is presented. It consists of a linear sliding guideway connected to an electrical actuator and equipped with a heating plate to heat metal sheets. A solid frame embeds a screw device used to apply normal load. Thermocouples placed both on the plate and on sheet sample are used to control temperature during the test. The machine is also equipped with two load cells to record the normal and the tamgential loads. The 22MnB5 high strength steel was chosen as reference material for the machine testing. The results showed the capability of the new equipment and the good stability of the mechanical and thermal condition during testing.