Abstract
In the automotive industry, sheet metal forming simulation using finite-element methods (FEM) has been widely used for the formability evaluation. On the other hand, lighter weight vehicles with increasing use of high strength steel or aluminum alloys have become more and more important in order to reduce the environmental impact. However, prediction technologies for complex and subtle defects such as springback and surface distortion that are typically observed in above-mentioned materials are not yet established. There is, therefore, a strong necessity for the establishment of accurate simulation strategies to deal with these problems. In this study, in order to realize accurate and robust springback analyses, several improvements have been made in the static explicit elastoplastic FEM code "STAMP3D". First proposal in this study is a new algorithm to deal with non-equilibrated forces that are caused by several non-linear factors occurring in the deformation process, which are inevitable in the numerical analyses by using explicit scheme. In this method, neither supplementary calculations nor iterative processes are required, resulting in reasonable computation time, numerically stable calculation and better springback accuracy for the analysis of a part with a complicated geometry. Secondly, an algorithm to deal with contact between the sheet and elastic tools is proposed, which aims at more accurate simulations taking into account non-uniform draw-in caused by the flexure of the blank-holder and the die. A method for coupling analysis is newly proposed in this paper. This method is discussed in terms of computational accuracy and efficiency. All these newly proposed algorithms have proven to be capable of enhancing the accuracy and reliability of sheet forming simulations, through several comparisons between experimental and numerical results of drawing process including those of real automotive parts with complex geometries and subtle surface defects.
Keywords: Sheet metal forming, FEM simulation, elastoplastic, springback, static explicit.