Studies on Testing and Modelling of Formability in Aluminium Alloy Sheet Forming

In this paper, the influence of tensile and formability parameters on the forming limit diagram is reported and a model is created to predict the forming limit strains of various grades of aluminium sheet metals. Aluminium alloys of grades AA5052, AA6061 and AA8011 with a thickness 0.8 mm, 1.0 mm and 1.2 mm have been selected for the study. Experiments are conducted to construct the forming limit diagram (FLD) for the above mentioned sheet metals. Tensile tests were conducted to evaluate strain hardening index, strength coefficient, ductility, yield strength, ultimate tensile strength, normal anisotropy, planar anisotropy and strain rate sensitivity. The fractured surfaces of the specimens were viewed with a scanning electron microscope. Using Design of Experiments (DOE), regression modelling was done by taking the tensile properties and formability parameters as input variables and the forming limit strain as response. Regression equations were created to predict the limiting strain values at the tension-tension, plane strain and tension-compression strain states. The experimentally evaluated strain values were compared with the predicted strain values and the comparison shows good agreement of the values. The Taguchi method of optimization was used to find the optimum values for the input variables and using these optimum values, the optimum forming limit strains were found. It is found that the so created regression model predicts the FLD of various grades of sheet metals by which the tedious job of experimental determination of the FLD can be avoided