The Effect of Thickness on Spring Back of Double Curved Sheet Metals by a New Method

Spring back is responsible for inaccuracy of press formed sheet product. Therefore, prediction of spring back is important for precise forming of stampings. To predict the amount of spring back many successful attempts have been made for simple cases such as single curved and U or V shape sheet metals. However, for more complex shapes containing double curves or double variable curved surfaces there are few research works. In order to propose a method to solve such problem, theoretical researches followed by experimental examinations have been carried out. A new formulation for prediction of spring back in a double curved sheet metal has been proposed by authors. In this formulation an improved yield criterion that have been proposed by Yoshida, has been incorporated. This yield criterion is capable to reveal the influence of transient Baushinger effect and work hardening stagnation on spring back analysis. Using proposed formulation, the effect of thickness on spring back has been calculated and compared with experimental results. Results show that by increasing of sheet thickness, spring back increases. Reveal behaviors have been explained based on the variation of neutral axis position.