Safe mechanical joining processes by digital manufacturing supervision in steel coil productions

Mechanical joining processes, in particular joining by forming like self-pierce riveting or clinching, require homogenous material characteristics for reliable joint properties. Joining processes in production are called safe, when the estimated properties for each manufactured joint, e.g. strength, remain in predefined narrow boundaries. Thus, an automated process monitoring is possible. A key reliability factor in automated production are varying joining materials properties. In case of steel, the knowledge of mutually dependent manufacturing steps at the coil build-up are crucial: First, milling conditions, such as dressing grade, predetermine the mechanical strength and fracture strain of the later joint. Second, the structure of corrosion protection layer by electrolytic or hot-dip galvanizing combined with forming and corrosion protection lubricants define the gliding abilities at later joining processes. It was found that a high dependency exists between solidification behaviour as well as surface friction level of the joining material and the stability of the joining process and the load capacity of the joint. To achieve safe mechanical joining results, these mentioned material properties must be guaranteed precisely by production monitoring techniques at the coil manufacturing. These include among others, methods for the non-destructive testing of mechanical properties at different coil areas, as well as systems for monitoring surface conditions and layers. As the material properties are build up over several production steps, production data are digitally collected today, analysed under quality aspects and if necessary corrective measurements are set online in the production.