Modelling of the Forming Limit Band -A new Method to Increase the Robustness in the Simulation of Sheet Metal Forming Processes

Forming Limit Curves are valid for one particular material alloy, temper and gauge combination. However material properties vary from batch to batch due to variation in the production process. For there a single Forming Limit Curve can not be an exact description of the forming limit. Several researchers have proposed a more general concept, namely the Forming Limit Band (FLB) as a region covering the entire dispersion of the Forming Limit Curves. A Forming Limit Band can successfully be predicted using the normal statistical distribution found in different production lots, of the yield stresses. Until now, the study of the dispersion was only experimental. Using the FORM-CERT software the influence of the different material parameters on the FLC has been studied. Using the normal distribution of mechanical properties the plus and minus 3-Sigma limits are used to determine the Upper- and the Lower FLC. The region between these two curves represents the Forming Limit Band. The paper presents for the first time the numeric modelling of the FLB concept. This method is illustrated on the AA 6111-T43 aluminum alloy.