Improvement on CAE model considering surface deformations of tools in contact with blank sheet for accurate torsional springback prediction in high strength steel part forming

摘要

It is difficult to predict springback, particularly in torsion, with high accuracy by FE simulation. Generally, more accurate springback prediction has been achieved mainly by the improvement of material modeling such as Bauschinger effect and plastic anisotropy models. It is also proved that tool deformations can greatly influence on the accuracy of torsional springback prediction as shown in the authors' study. The study shows that FE simulation by using elastic tool model has 30％ more accuracy in predicting torsional spring back in a curved hat shape than that by using rigid tool model. But full elastic tool modeling is tedious work and FE calculation with the elastic tool model needs enormous time. There are two kinds of tool deformation during a press forming: tool deflection as a whole, and surface deformations where the tool is in contact with the steel sheet. Three forming experiments were carried out with an insert block of different stiffness which touched steel sheets directly, in this paper. The results revealed that surface deformations of a tool have great influence on torsional springback of a curved hat shape. Based on the results, a new tool modeling is proposed in this papar. In the model, the part of a tool in direct contact with a blank sheet is elastic and the other part is rigid. That means the model deals with only surface deformations of tools in FE simulation. The newly developed surface deformation tool model has more accurate in springback prediction than rigid tool model and has less calculation time than fully elastic tool model with almost the same accuracy.