Improved Tool Surfaces for Incremental Bulk Forming Processes of Sheet Metals

Abstract

Sheet-bulk metal forming is a process used to manufacture load-adapted parts with high precision. However, bulk forming of sheet metals requires high forces, and thus tools applied for the operational demand have to withstand very high contact pressures, which lead to high wear and abrasion. The usage of conventional techniques like hardening and coating in order to reinforce the surface resistance are not sufficient enough in this case. In this paper, the tool resistance is improved by applying filigree bionic structures, especially structures adapted from the Scarabaeus beetle to the tool’s surface. The structures are realized by micromilling. Despite the high hardness of the tool material, very precise patterns are machined successfully using commercially available ball-end milling cutters. The nature-adapted surface patterns are combined with techniques like plasma nitriding and PVD coating, leading to a multilayer coating system. The effect of process parameters on the resistance of the tools is analyzed experimentally and compared to a conventional, unstructured, uncoated, only plasma nitrided forming tool. Therefore, the tools are used for an incremental bulk forming process on 2 mm thick metal sheets made of aluminum. The results show that the developed methodology is feasible to reduce the process forces and to improve the durability of the tools.