A new grid method to analyze the formability of sheet metals by concentric circles printed on surface of the material

The production of automotive bodies for most vehicle models is carried out through sheet metal forming, a process capable of meeting the enormous demand in this segment. However, manufacturers face many challenges in terms of productivity, design, performance and safety, in addition to the process of electrifying cars, which also requires adaptation of models. To meet these needs, several studies have been carried out focused on modernizing car bodies, in terms of materials, processes and innovative projects. Within this context, however, with a focus on improving stamping processes, the Concentric Circles Method (CCM) was created in this study. The objective of the method is to improve investigative techniques regarding the effect of process and design variables in the stamping process on the behavior of plastic deformations. The model consisted of printing concentric circles on the surface of the test specimens used in the Modified Nakazima tests, which defined twelve regions on the sample, from the flange to the punch pole. Therefore, after stamping the DP600 steel until its rupture, the true deformations and Vickers microhardness in these regions were measured and calculated, from which representative graphs of the deformation and hardness profiles along the stamped sheet were obtained. These graphs allowed the precise interpretation of the effect of the sheet press forces (785 kN and 1157 kN) and the drawbead geometries (flat, circular and square) used in the tests, to explain the performance result obtained with the forming limit curves (FLC). Through the FLCs, a better formability of the DP600 steel was achieved with the circular drawbead, in both blank holder forces (BHF), and a worse formability performance with the flat drawbead (without the tooth), also with both BHF. As main conclusions, it was seen that the CCM method was effective and capable of explaining the stamping performance of DP600 steel obtained with FLCs, allowing a more sophisticated understanding of the material behavior during stamping, in addition to providing data for the improvement of numerical stamping simulation models.