Technical enhancements of the rotary-draw-bending to a semi-kinematic process with reduced tool surfaces

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Rotary draw bending is a widely used method for bending profiles according to DIN 8586. The application spectrum of the process extends over a large number of geometries with a constant bending radius. These products can be used in a wide range of industrial and private applications. The rotary draw bending is a tool-bound forming process, in which the tool surfaces are determined by the cross section and the bending geometry (bending radius). A change of the semi-finished geometry (e.g. circumference respectively wall thickness) or the bending geometry (bending radius) require an adaptation and/or supplement of forming tools.In addition to bending of constant radii, free-form bending processes (e.g. the three-roll-push-bending) have the advantage to produce free bending contours without need of changing the tool geometries as they base on kinematic bending. The project has the superordinate goal to extend the tool-bound rotary draw bending process to a partial kinematic bending process, by tools with simplified geometries and additional tool axes. This gives the opportunity to serve future demands for enhanced flexibility of forming processes and the economic production of smaller quantities towards individualized products.A method for a systematic approach to reduce tool surfaces is not yet known. In the project, a method based on local and temporal variations of tool contacts for the reduction of the tool surfaces is investigated and tested. The tool contact is analyzed with FE simulations to examine the effects of the tools’ contact surfaces reductions. The generated surface elements are used as reduced tool surfaces. This method is applied to the rotary draw bending tools bending die, pressure die, clamp die and wiper die, respectively. After reducing the tools’ surfaces, it will be investigated to what extent the tools generated in this method influence the forming results compared to conventional tools.When considering contact normal stress development over the process time of forming, kinematic concepts could also be derived in which surfaces only have a temporary shaping effect.The main result is achieving a flexibilization of the rotary draw bending process. With a tool configuration based on a partly kinematic bending, it is possible to bend both, different bending radii and different tube dimensions by the suggested method.