Abstract
The reduction of springback for a U-shaped channel using a double drawing process was investigated. In this test, the punch strokes of the 1st and 2nd stamping steps were controlled and each followed by unloading. The simulations were conducted using kinematic and distortional hardening models, which were implemented into a finite element (FE) code to describe the Bauschinger effect and its associated anisotropic hardening effects during strain path change. In addition to the usual mechanical characterization tests, in-plane compression- tension experiments were conducted on DP980 and TWIP980 to determine the constitutive parameters pertaining to load reversal. Experimental and FE simulated results of the channel shape were compared for both materials in order to understand the effect of anisotropic hardening under non-proportional loading on springback.
Highlights
Advanced high strength steels (AHSS) have replaced conventional steels for automotive parts to reduce the body weight and improve the crash performance
The U-draw double stamping process was investigated for two different AHSS sheets with various blank holding force (BHF) and strokes
Two advanced hardening models lead to better predictions of the experiments compared to the results using isotropic hardening
Summary
Advanced high strength steels (AHSS) have replaced conventional steels for automotive parts to reduce the body weight and improve the crash performance. The Yoshida-Uemori (YU) constitutive model has been extensively used for springback simulation It is based on a two-surface kinematic hardening approach and can predict most of the complex hardening behaviors under load reversal [1]. Automotive parts are generally produced using multi-stage forming processes in industry In this case, since blanks undergo strain path change several times, it is difficult to simulate accurate predictions of springback with conventional constitutive descriptions. The U-draw double stamping process was investigated for two different AHSS sheets with various blank holding force (BHF) and strokes. 2. Experiment To evaluate the performance of U-draw double stamping predictions, two AHSS sheet samples provided by POSCO were investigated; i.e., a dual-phase steel (DP 980) and a twinning-induced plasticity steel (TWIP 980), both of which with a nominal ultimate tensile strength of 980 MPa. The size of the sheet specimen was 350 (length), 45 (width) and 1.2 mm (thickness). A non-quadratic yield function, Yld2000-2d [4], was employed to describe the plastic anisotropy of the sheet metals during forming
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