An assessment of numerical parameters influencing springback in explicit finite element analysis of sheet metal forming process

Abstract

Springback is one of the key factors influencing the quality of stamped sheet metal parts in sheet metal manufacture. There have been diverse efforts to evaluate and/or decrease springback for a long time. Analytical methods have been mainly developed, at first, for analyzing parts of two-dimensional or simple three-dimensional geometry. Since it is almost impossible to apply analytical methods to fully three-dimensional parts in general, numerical methods including the finite element method (FEM) have recently been developed and applied to sheet metal parts of general shape as a result of rapid progress of computing environments. However, the results of springback simulated by FEM may vary greatly according to how numerical factors are set, for example element size, punch velocity, contact penalty constant, damping ratio, etc. Therefore, a comprehensive assessment of numerical factors influencing springback is required. In this work, numerical factors influencing springback have been evaluated quantitatively using the Taguchi method. To clarify the effect of each factor, the U-draw bending process is chosen as an evaluation problem because of its large springback. In the analysis, the explicit time integration method is used in the simulation of forming stage, whereas the implicit time integration method is applied to the springback stage in order to get the static solution readily. Numerical experimentation has been carried out under various combinations of numerical factors. From comparison of the numerical results with the experimental results, factors important for springback have been assessed. (C) 1998 Elsevier Science S.A. All rights reserved.