The Numerical Simulation & Experimental Validation Of Distortional Springback Advanced High-strength Dual Phase Steel Sheet Metal Forming

Low carbon steels are being replaced by advanced high strength steels (AHSS) due to high demand of the future lighter weight vehicle, while still maintaining good or even better crash performance. However, wide application of AHSS in many potential automobile structure parts is still limited due to challenges in terms of springback. And for complicated structural parts, distortion springback is a big problem. Although a lot of research work has been done to improve the springback prediction accuracy, improvements are still called for. Besides, there are no mature evaluating indicators to describe the distortion, and the investigation in processing parameters'effects to distortion is little.In order to study the characteristic of advanced high-strength steel (AHSS) distortional springback, DP780 provided by Bao-Steel is chosen, and two kinds of S-Rail (one open forming S-Rail and one semi-open one) are designed, which are stamped using the same draw die and checked using the same measuring tool. The Z-direction springback of flange outer edge in eight important cross-sections is measured. Based on the experiments results, the whole springback condition of S-Rail is investigated. In order to study the distortional springback, which appeared in S-Rail drawing experiments, a new method to evaluate the distortional springback is proposed, and the impacts of blank holding force, frictional coefficient and material rolling directions to distortional springback are investigated. The results are of help to control the industrial distortional springback.Meanwhile, the springback predictions of DP780 under several process conditions are finished using LS-Dyna and validated by experiment. It is shown that, the numerical Z-direction springback value is a little higher than the experimental one, but the variation trend along the eight measuring sections demonstrates good agreement with experiment one.Also, the springback control technique using draw beads is tried out in paper. The geometry draw bead is chosen for simulation, and a creative different-height-section draw bead is designed. An obvious decrease in distortion is obtained. The results show a new approach for the future springback control research.