Evaluation of the shear stresses on surface structured workpieces in dry forming using a novel pin-on-cylinder tribometer with axial feed

In production engineering cold forging processes are of great importance due to the high material utilization and the associated energy and resource efficiency. In order to successfully perform cold forging processes, liquid and solid lubricants are used, which are often questionable due to ecological, economic and legislative reasons. For these reasons, dry forming exhibits an increased research potential. The absence of lubricants in dry forming significantly contributes to the waste reduction in manufacturing processes and to the goal of a lubricant-free factory. However, this goes along with the requirement that the dry tribological system has to incur the functions of absent lubricants. In this work, it is proposed to reduce friction by surface structures on workpieces. Positive effects of surface structures were already observed in dry sheet metal forming. However, sheet metal forming significantly differs from cold forging due to lower contact pressures and a lower surface expansion of the workpiece. In order to enable dry forming in cold forging for the first time, friction-optimized surface structures on workpieces are explored. Using a newly developed Pin-On-Cylinder tribometer, experiments present the influence of selected surface structures and surface layer states on the frictional shear stresses in dry contacts.