Investigation of the influence of reversing stroke profiles on the workpiece characteristics in deep drawing using servo press technology (ServoDrawing)

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Deep drawing is one of the most important manufacturing technologies for the production of sheet metal components with threedimensional geometry. High strength lightweight construction steels are more and more used for the deep drawing of car body parts, due to economic and ecological reasons. The higher strength allows the use of thinner sheet metals which leads to a decrease of part weight while maintaining the load capacity of the parts. In comparison to conventional deep drawing steel qualities these high strength steels possess a significantly lower formability. This leads to increased buckling and earlier occurrence of cup base fracture. Furthermore, significantly higher process forces arise. Thus, new challenges regarding the process boundaries of deep drawing arise out of the use of high strength lightweight construction steels. From this follows an economic problem, as the reduced formability of high strength steels and the higher process forces narrow down the range of workpieces producible by deep drawing processes. One possibility for a selective impact on formability of high strength steel during deep drawing is the use of innovative servo press technology. In contrast to conventional drives a very exact positioning of the ram and high torques also at low input speed as well as in stop position are possible with servo press technology. Servo presses allow the free programming of ram-displacement-process time-characteristics within the physical limits. A special ram displacement-process time characteristic is the reversing stroke profile. It is characterized by a single or multiple reversion of the ram moving direction during the forming process. First research activities reveal that the material flow during deep drawing is positively influenced by reversing stroke profiles in comparison to conventional profiles. The cause for this effect is not researched yet and thereby derives a need of action. The scientific problem consists in the explanation of the influences of reversing stroke profiles on material flow in the workpieces as well as the tribological interactions within the contact areas regarding friction effects. The aim of this project is the development of an extensive explanatory model for the cause and effect relationships between reversing stroke profiles and the resulting workpiece characteristics for the deep drawing of high strength steels. The aspired model explains the mechanical active principles on buckling effects, sheet thinning, process force reduction and tribologic relationships between tool and workpiece by empirical correlations and analytical formulations based on FEM. By the acquired fundamental process knowledge a comprehension based and target-oriented process design for the deep drawing of high strength steels with reversing stroke profiles is enabled.