Determination of forming limit diagrams for pulsating loading

It is difficult and expensive to find the optimum process parameters to form sheet metal parts without any geometric defects by trial and error, and it is not even possible in some cases. The design of the process and its parameters are usually estimated using the finite element method. The first and most important step in making these analyses is to determine the material properties of the workpiece. The most important of these parameters are the flow curve from the tensile test and forming limit curves (FLC) obtained using the Nakajima test, which is an out-of-plane forming test. In today's technology, the limits of formability are increased by applying forming forces in pulsating form. The FLC's available in the literature are produced under monotonous loading conditions. In this study, FLC's were developed under pulsating loading conditions as well as monotonous ones. In this thesis, the FLC of AA5754-O, which is widely used in the automotive industry, was obtained at room temperature using the Nakajima test. Monotonous and pulsating loading parameters were applied on test specimens in possible ranges under a Taguchi experimental design scheme. The tests were performed under optimum parameters with three repetitions for each test sample. The strains on formed parts were measured using the Asame 4.1 system. FLC's were generated based on the measured strains according to the ISO-12004-2(2008) standard. Consequently, based on the FLC's, a meaningful increase in overall formability was obtained by pulsating forces as compared to monotonous tests. Keywords: AA5754-O, variable loading, sheet forming, Nakajima test, forming limit curve