Untersuchungen zur konduktiven Erwärmung für Warmzugversuche an Blechen
Gerhardt, Kai; Hirt, Gerhard (Thesis advisor); Bleck, Wolfgang (Thesis advisor)
Aachen / Shaker (2015, 2016) [Book, Dissertation / PhD Thesis]
In implementation of innovative lightweight construction concepts in automotive engineering, the design of steel materials moved into the focus of the engineers which have high strength after forming. The requirements, producing sheet metal parts with complex geometry and high strength, combined with a minimum part weight, can be met by using an innovative forming process called press hardening. High-strength heat treatable steels, such as the 22MnB5, are suitable for use in this process and also for the subsequent use in automobiles. A process simulation for efficient optimization of forming processes requires precise material data in the temperature range of the used process. The possibilities to determine these material data are very limited and appropriate test facilities are cost-intensive. The aim is, to examine how it is possible to perform hot tensile tests under the process conditions of press hardening with a low cost extension of a mechanical universal testing machine. In the present work, initially a systematically elementary knowledge of hot forming of sheet metal and the determination of flow curves of sheet metal blanks is acquired. To extend the universal testing machine a heating unit is designed. The measurement of deformations and the sample temperature in the testing procedure is carried out with existing measurement systems. The usage of a thermografic camera enables a large-scale measurement on the sample surface and thus the analysis of the temperature distribution. With the knowledge gained, suitable sample geometries for the usage in conductively heated tensile test are identified. Elemental analysis methods are applied to these sample geometries for flow curve determination. This work shows that a low cost extension of a universal testing machine is feasible to realize tensile tests under the process conditions of press hardening. Finally, the conditions for an application of FEM for inverse simulation of conductively heated tensile test were tested. The simulation model created represents the sample heating and the subsequent tensile test as well. For this case, the basic conditions for a use of the FEM for inverse simulation are now given.