Experimental Study on Micro Forming of Structured Surfaces for High Static Friction Connection Elements

Abstract Bolt connections are the most prevalent technical solution to join several devices. To meet high requirements on lightweight constructions and safety-relevant technologies bolt connections require additional security elements or surface modifications to increase static friction without damaging the workpiece surface significantly. One possible solution is the micro structuring of the connection element surface within the conventional forming process chain. For the manufacturing of micro structured connection elements a micro structured forming tool is needed. Therefore, the forming tool has to feature a negative geometry of the connection element surface micro geometry. Requirements on forming tool materials are high hardness in combination with high wear resistance and good toughness. Suitable technologies to manufacture such micro structured metal dies are laser beam machining (LBM), electrochemical machining (ECM) and electrical discharge machining (EDM), respectively. In this study the micro forming process of high static friction connection elements is investigated. The manufactured connection element surfaces are analyzed after the forming experiments and the results are associated with the surfaces of the metal dies. Therefore the surfaces of the utilized metals dies are compared with each other and with a grinded reference surface and characteristic parameters are analyzed. The comparison is based on the resulting surface roughness parameters and surface conditions before and after lubricated forming experiments. At least wear of the metal dies after multiple forming operations is analyzed. As one result, ECM manufactured metal dies have shown a high degree of replication in combination with high wear resistance.