Design of High Strength Differential TWB to Enhance Drawability: FE Study and Optimization

Abstract

In this study cylindrical cup deep drawing of the high strength differential Tailor Welded Blank (TWB) consisting of Twinning-Induced Plasticity (TWIP) steel and low carbon steel (mild steel) was investigated using a finite element (FE) analysis. The strength ratio of TWIP to mild steel was about 4, which has not been investigated in previous researches. The formability of the TWB sheet was correlated to the weld-line movement and the thinning in the softer part of the TWB. From this virtual FE experiment, the inferior drawability of TWB when compared to monolithic blanks resulted from uncontrolled material flow A modified tool design was proposed by adding the counter-punch concept to control the material flow near the weld-line. Then, the process parameters such as blank holding force, counter-punch force, friction conditions of punch-to-blank and counter-punch-to-blank were optimized using the Taguchi method An improved tool design in combination with optimized process parameters improved the drawability of the TWB significantly.