Failure analysis of a cold work tool material slides against carbon steel in sheet metal forming process - A case study of hinges production

In general, the contact conditions between the tool and the workpiece materials in sheet metal forming process are always of high industrial importance since it permits to enhance the tool life. The present work focuses on the sliding metallic contacts taking place in the case of the manufacturing of hinges. A case study has been conducted on the cold plastic rolling (CPR) tool and the hinges in the CPR process. An expertise of CPR die active part and hinge surface was carried out in order to identify and to analyze the failure mechanisms. Several techniques were used such as profilometry, energy dispersive spectroscopy (EDS), optical and scanning electron microscopy (SEM). The failure mechanisms of the tool and the hinge were studied during various cycles of manufacturing. The failure of the CPR die active part was found to be related to the transfer of fragments from the hinge material and then their accumulation on the tool surface, generally referred to galling. The failure mechanisms of the hinge material were found to depend on the number of manufacturing cycles. At first and intermediate stages, fine and large scratchings were produced on the curved surface of the hinge, respectively. At later stages, a back transfer of sheet fragments to the hinge surface takes place by severe scratchings.