New methodology of springback compensation for Advanced High Strength Steels based on geometrical modifications

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Nowadays, the automotive industry is challenged by increasing environmental regulations as well as continuously enhancement of the standard requirements regarding to passengers safety. Such tendencies lead to increased use of advanced high strength steels (AHSS) for manufacturing of car body components which are placed in many areas within car body structure. However, the potential application of high strength steels is still limited since many issues have to be investigated related to formability and springback.There are various strategies to minimize springback by means of process parameter variation during the press stroke or by use of additional retention forces by the blank holder. These strategies were already applied successfully in the forming of high-strength steel alloys up to 600 MPa tensile strength, and have proven successfully in practice. When using these techniques for forming of more stronger steel materials (tensile strength higher than 600 MPa), results achieved and knowledge applied with respect to component accuracy are not satisfactory due to the increased tendency towards springback and twisting. For cold forming of such steel grades until now a defined and valid strategy or method that can be used for springback and twisting compensation is missing.The motivation of the research work basically stands for lack of such methodology to reduce springback and torsion observed in load carrying components of passenger cars, as well as to find a sophisticating compensation strategy for manufacturing such steel grades. The methodology for springback compensation will be dependent on local stress-strain state as well as on magnitude of sidewall curl and torsion moment of the component. The method to be developed first will be based on optimization of binder shapes, on global and/or local application of hardening functions, on special indentations in identified areas of component as well as on details in shape for counter striking objectives of component radii.