Untersuchung des Inkrementellen Rohrumformens mit dem Ziel der Erstellung eines Prozessmodells zur Vorhersage der Rückfederung
Zusammenfassung der Projektergebnisse
The increasing demands for resource-efficient products lead to the need for manufacturing methods that are suitable for the processing of high-strength materials in terms of lightweight design and the flexible and cost-effective production of complex parts. For this reason, in the field of forming technology, it is necessary to develop new technologies that are suitable for the precise shaping of high-strength steels as well as to be used flexibly to form various product geometries and variants. Incremental tube forming is a combination of free-form bending and spinning, which allows the manufacturing of curved tailored tubes under greatly reduced forming forces and high geometrical accuracy. Here, ITF was used to manufacture the bent tubes with high flexibility. The manufactured tube consists of variable cross-sections, diameters, thicknesses, as well as a 3D contour. The influence of different parameters on the forming forces were investigated. An analytical model was developed, which can predict the forming forces as well as the influence of the different process parameters. The model is based on the assumption of the proportional loading and replacing the spinning rolls with a fixed die. It is shown that the analytical model for ITF process can predict the bending moment reduction up to 77-90% in comparison to the conventional bending, where the experimental results show a reduction of 94-98%. However, the absolute value of the predicted bending moment is still three to four times higher than the experimental values. Despite the deviation in the absolute values of the bending moments, the amount of springback can be calculated with high accuracy (deviations of 5%), since the bending moments are small in ITF process. The ITF process was also investigated based on a numerical model, which was developed in ABAQUS/Explicit. In this investigation, two models with high and few degree of simplifications were applied. It was observed that the simplified FE model based on a fixed die predicts a lower reduction of bending force in comparison to the more complex FE model which is based on the real spinning process. In the model which was based on the real process, where the diameter was reduced by the spinning rolls, the results were in agreement to the experiments. The investigation of the plastic strain history shows, that the rotational speed is an important parameter. It is observed that at low rotational velocities, the cross-section of the tube shows a non-uniform distribution of the plastic strains. This non-uniformity of plastic strains is reduced at the end of the process, where bending dominates. This phenomenon is accompanied with a higher bending force. However, for higher rotational speeds the cross-section deviations are reduced. Hence, the investigation reveals the main influence parameters of the ITF process and delivers a guideline in terms of the process design. By the proper application of the tube forming technology, load paths combined with strong compressive stresses can be achieved, so that dimensional accuracy is improved by the reduced bending force. The numerical investigation of the plastic strain history reveals also that the combined bending and spinning process is first governed by the spinning operation and the bending process starts just at the last steps of forming in the end region of the spinning devices. Hence, considering the proportional loading lead to an increase in the calculated bending forces. At the end it can be concluded that due to the high flexibility, geometrical accuracy of the products and the low tooling cost, the ITF is a suitable manufacturing method, especially in a low batch production, to manufacture the load-optimized tubes.
Projektbezogene Publikationen (Auswahl)
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2012. Incremental Tube Forming and Torque Superposed Spatial Bending - A View on Process Parameters. In: Kusiak, J., Majta, J., Szeliga, D. (Hrsg.), Metal Forming 2012, Proceedings of the 14th International Conference on Metal Forming, Krakow, Poland, pp. 415–418
Becker, C., Staupendahl, D., Hermes, M., Chatti, S., Tekkaya, A.E.
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2013. Numerical Investigation of the Incremental Tube Forming Process. Key Engineering Materials, Vol. 554-557, pp. 664–670
Becker, C., Isik, K., Bayraktar, A., Chatti, S., Hermes, M., Soyarslan, C., Tekkaya, A.E.
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2013. Prediction of surface roughness due to spinning in the incremental tube forming process. Production Engineering - Research and Development, Vol. 7/2-3, pp. 153–166
Becker, C., Quintana, G., Hermes, M., Cavallini, B., Tekkaya, A.E.
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2014. Fundamentals of the incremental tube forming process. CIRP Annals - Manufacturing Technology, Vol. 63/1, pp. 253–256
Becker, C., Tekkaya, A.E., Kleiner, M.
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2014. Inkrementelles Rohrumformen von hochfesten Werkstoffen, Dissertation
Becker, C.
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2015. Incremental Tube Forming. In: Tekkaya, A.E., Homberg, W., Brosius, A. (Eds.), 60 Excellent Inventions in Metal Forming. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 351–356
Becker, C., Hermes, M., Tekkaya, A.E.
