Development of a robot-based die-less incremental sheet metal forming process

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For a cost efficient production of prototypes and small batch sizes, current research projects are developing incremental sheet metal forming processes, which use tools with a small or even no work piece dependency. The final sheet geometry is achieved by repeated localized forming with a simple hemispherical tool. To increase the geometrical accuracy, the sheet can be supported on its backside. Different forming methods have been developed which use work piece dependent or independent supporting tools. The first range from simple backing plates to complex full dies. The latter either use no support at all or a kinematically controlled work piece independent supporting tool. Roboforming belongs to the last group, which is the most flexible and cost efficient, only requiring a CAD model. Roboforming is a method developed at the LPS, where two cooperating industrial robots incrementally form a sheet with a forming and a supporting tool. It currently offers two forming strategies: a circumferentially acting supporting tool and a local supporting tool. Due to the kinematically controlled forming process particularly in combination with subsequent forming of shaped elements Roboforming is able to form a large part scope with a high flexibility. For the industrial application, however, a very high level of geometrical complexity and geometrical accuracy is necessary. Currently, especially the subsequent deformation as a consequence of the interaction of differently shaped elements causes geometrical deviations, which are limiting the increase of the part scope.Thus the project aims for an increased geometrical complexity and increased geometrical accuracy in kinematically controlled incremental sheet metal forming in the so called Roboforming. This shall be achieved by creating a procedure for an optimal design of each forming step, their sequence and their forming strategies in Roboforming. During the course of planning, taking into account the part orientation every shaped element must be analyzed according to its stabilizing or subsequently deforming effect. Additionally research has to be done in order to determine at which point in the forming process each element should be directly or subsequently formed in order to get complex parts with a very good accuracy. This requires a detailed analysis of the direct and subsequent forming of elements. The latter allows a significant increase of the draw angle and supports the adjacent areas by using the peripheral supporting tool which prevents their deformation. The full potential of the two moving tools shall be used by optimizing the forming strategies and by combining and tuning them for each part. The necessary development of an approach to optimal design of individual forming steps and their sequence, as is required in the incremental sheet metal forming, represents a particular challenge.