PSI - Issue 38

Martin Killmann et al. / Procedia Structural Integrity 38 (2022) 212–219 Killmann / Structural Integrity Procedia00 (2021) 000 – 000

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revealed that the angle describing the gaps circumferenti al size should lie between 2α = 40 and 2α = 60 for the highest increase in local prestresses. When using large interference fits, gaps also induce high tensile stresses at the outer die wall. In this case, low angles should be used to decrease the lever distance and bending effect. Generally, the effect of gaps is more pronounced for a low number of functional elements. Since each critical element requires a local prestress, the number of gaps necessary equals the number of functional elements. When distributing many gaps along the die, the lever arm responsible for the bending effect decreases. That is why gaps are best suited for use in geometries with two critical areas opposite each other. A decrease in tensile stresses of about 100 MPa is still possible for four functional elements. For more critical areas stresses do not decrease significantly. In future investigations, solutions for the local prestressing of dies with more than four critical areas should be researched. Furthermore, fatigue tests should be conducted in order to verify the effect of the improved stress state on the tool life. Acknowledgements The authors would like to offer their sincere thanks to the Bavarian Research Foundation (BFS) for supporting the research project “Reinforcement systems for dies with non-circular-symmetrical cross- sections” (BFS AZ 1306_17) as well as to the supporting industrial partners RIBE Verbindungstechnik GmbH & Co. KG, ZF Friedrichshafen AG and PENKERT Metallbearbeitungs GmbH. Further thanks goes to ZWEZ-Chemie GmbH for the application of the lubricant and to the laboratory assistants and students supporting the execution of this work. References Duflou, J. R., J. W. Sutherland, D. Dornfeld, C. Herrmann, J. Jeswiet, S. Kara, M. Hauschild and K. Kellens, 2012. Towards energy and resource efficient manufacturing: A processes and systems approach. CIRP annals 61(2), 587-609. Engel, U., J. Groenbaek, C. Hinsel, T. Kroiß, M. Meidert, R. Neher, F. Räuchle and T. Schrader, 2011. Tooling solutions for challenges in cold forging. In: Eder, W. K. (Ed.). UTF Science III, Meisenbach, Bamberg. Groenbaek, J., 1996. Forming tool. United States Patent US5577406A. Groenbaek, J. and E. B. Nielsen, 1997. Stripwound containers for combined radial and axial prestressing. Journal of Materials Processing Technology 71(1), 30-35. Hexagon, 2020. Simufact Forming – Software Solution for Forming Processes. Hirschvogel, M. and H. Dommelen, 1992. Some applications of cold and warm forging. Journal of materials processing technology 35(3-4), 343 356. Hsia, S.-Y. and P.-Y. Shih, 2015. Wear improvement of tools in the cold forging process for long hex flange nuts. Materials 8(10), 6640-6657. International Cold Forging Group, 1992. Calculation methods for cold forging tools. In: Engel, U. (Ed.): International Cold Forging Group 1967 1992 - Objectives, History Published Documents, Meisenbach, 1992, 33-58 International Cold Forging Group, 2002. Tool Life & Tool Quality in Cold Forging Part 1: General Aspects of Tool Life. ICFG Document No. 14/02. Meisenbach, Bamberg. Jafarzadeh, H., G. Faraji and A. Dizaji, 2012. Analysis of lateral extrusion of gear-like form parts. Journal of mechanical science and technology 26(10): 3243-3252. Killmann, M. and M. Merklein, 2020. Analysis of stress pins for the local prestressing of cold forging tools. Production Engineering, 1-13. Körner, E. and F. Pingel, 2015. Produktanalysen und Perspektiven der Kaltpresstechnik - Praxiseinsatz moderner Entwicklungswerkzeuge. In: Liewald, M. (Ed.). Neuere Entwicklungen in der Massivumformung, Stuttgart Ku, T.-W., 2018. A study on two-stage cold forging for a drive shaft with internal spline and spur gear geometries. Metals 8(11), 953. Lange, K., 1984. Umformtechnik 1: Grundlagen. Springer, Berlin. Tekkaya, A., J. Allwood, P. Bariani, S. Bruschi, J. Cao, S. Gramlich, P. Groche, G. Hirt, T. Ishikawa and C. Löbbe, 2015, Metal forming beyond shaping: Predicting and setting product properties. CIRP Annals 64(2), 629-653. Tekkaya, A. and A. Sonsöz, 1996. Life Estimation of Extrusion Dies. International Journal of Mechanical Sciences 38(5): 527-538.