Simulation sowie experimentelle Untersuchung von Materialschädigungen bei Umformprozessen

Threads that are typically produced on flat thread rolling machines often have seams, cracks, closes wrinkles and hollow spaces leading to customer complaints, productivity losses and scrap costs. So far, the fundamental understanding of the thread rolling process is missing, so that in this work systematic experimental and simulation-based investigations were carried out. For the description of the material flow behavior of the steel 23MnB4, a material model of tensile and compression tests was developed. In a next step, a suitable friction model was created, which was calibrated by a slide upsetting test. The focus of damage modeling was on a macro-mechanical model proposed by Cockcroft and Latham and a micro-mechanical model was based on Lemaitre. Employing the findings of material, friction and damage modeling, the simulations could be set up with the software SIMUFACT.FORMING. For the first time, it was possible to simulate such a complex thread rolling process in a 3D setting. The application of this simulation model to similar tool geometries was successfully tested on two examples that are relevant in practice. Finally, the fatigue behavior of screws with strong and less pronounced material damage was investigated. The work is completed with TEM investigations of all individual steps in a life cycle of a screw, starting from the cut-off, over the press and rolling blank up to screws subject to fatigue tests.