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In freeform bending the desired geometry is created by defined movements of the die while a continuous feed takes place. To compensate the differences and variations in properties of the semi-finished product, the motion profile has to be adjusted. Currently, this calibration is done once before the manufacturing process of a certain profile. Therefore, numerous iterations consisting of bending and measuring certain radii based on a default motion profile are performed. The measured data is subjected to a curve fit, which is not sufficiently suitable for all profiles and materials setups due to the fixed predefined function that is used. Furthermore, the tool setup is not taken in account. This results in wrong kinematics and production rejects. In this work, an enhanced geometrical model is introduced which incorporates tool parameters - such as distances, clearances and positioning aspects - as a starting point for further calculations. Furthermore, different calibration methods are tested and compared to each other using FEM simulations to fit the calculated curve to the actually used specimen. This work establishes the basis for further compensation and calibration strategies in order to improve the handling of varying properties of semi-finished products within the freeform bending process.

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The optimal design of the tools in bulk metal forming is a crucial task in the early design phase and greatly affects the final accuracy of the parts. The process of tool geometry assessment is resource- and time-consuming, as it consists of experience-based procedures. In this paper, a compensation method is developed with the aim to reduce geometrical deviations in hot forged parts. In order to simplify the transition process between the discrete finite-element (FE) mesh and the computer-aided-design (CAD) geometry, a strategy featuring an equivalent surrogate model is proposed. The deviations are evaluated on a reduced set of reference points on the nominal geometry and transferred to the FE nodes. The compensation approach represents a modification of the displacement-compatible spring-forward method (DC-SF), which consists of two elastic FE analyses. The compatible stress originating the deviations is estimated and subsequently applied to the original nominal geometry. After stress relaxation, an updated nominal geometry of the part is obtained, whose surfaces represent the compensated tools. The compensation method is verified by means of finite element simulations and the robustness of the algorithm is demonstrated with an additional test geometry. Finally, the compensation strategy is validated experimentally.

Freeform bending offers a wide range of possibilities in terms of component geometries, material grades and profile cross-sections. In the field of circular solid and hollow profiles, the design of the tool is determined by the circular shape of the profile used. When using rectangular profiles, the cross-section of the tool cannot be easily obtained by an offset of the profile cross-section. The large tolerance ranges of the profile standards require compromises with regard to the shape and tolerances of the tool. Tests have shown that the design of the tool has a great influence on the quality of the component. Furthermore, the trade-off in the tool design can lead to unsuitable tool shapes leading to defects and damages on the profile. These are mainly wrinkling, cross-sectional deformations and strongly deformed profile corners, which in some cases form cracks in the material. In this paper, the influences of the tool design on the bending result and the defects of the profiles are investigated. For this purpose, several tool designs with different variants and combinations of the movable die and the fixed die are compared with each other.