Incremental Sheet Metal Forming with Direct Resistance Heating Using Two Moving Tools

This paper describes new developments in an incremental, robot-based sheet metal forming process (‘Roboforming’) for the production of sheet metal components in small batch sizes. The dieless kinematic-based generation of a shape is implemented by means of two industrial robots which are interconnected to a cooperating robot system. Compared to other incremental sheet metal forming machines, this system offers high geometrical form flexibility without the need of any part-dependent tools. The industrial application of incremental sheet metal forming is still limited by certain constraints, e.g. the low geometrical accuracy and number of formable alloys. One approach to overcome the stated constraints is to use the advantages of metal forming at elevated temperatures. For the temperature input into the sheet metal, there are different approaches like heating with warm fluids, a laser beam or using direct resistance heating. This paper presents results of the research project ‘Local heating in robot-based incremental forming’, funded by the German Research Foundation (DFG), where the heating of the current forming zone by means of direct resistance heating is examined as a variation of the Roboforming process. In order to achieve a local limitation of the heating on the current forming zone, the electric current flows into the sheet at the electric contact of the forming tool and the sheet metal. Thus the forming tool is part of the electric circuit. In current literature Authors report about results from experiments using single-point incremental forming, where the forming tool and the clamping frame of the sheet are connected to the power source. In order to further limit the heating on the forming zone, a new approach will be presented in this paper, where a second tool is used to support the forming and heating process, as both tools can be connected to the power source, making a current flow through the rest of the sheet and the clamping frame unnecessary. With the use of two tools the current flow and thus the heated zone of the sheet can be manipulated. Additionally the advantages of the supporting tool, already shown in forming at room temperature, such as increased geometrical accuracy and maximum draw angle can be used. Starting with a description of the new process setup for steel forming at about 600 °C, results of experiments evaluating the influence of the supporting tool on the forming process at elevated temperatures and the resulting geometrical accuracy will be presented in this paper. Therefore, different process parameters as forming temperature, cooling and relative positioning of the both tools have been varied.