Application of Cold Stamping Process with 1500 MPa Ultra-High-Strength Steel for Aftermarket Bumper

With the advancement of lightweight vehicle structure design, the demand for hot-stamped steel in the aftermarket (AM) sector has steadily increased. However, Taiwan's production capacity has been limited to two hot stamping lines, insufficient to meet the growing demand for hot-stamped AM body panels. To address this issue, cold stamping processes using 1500 MPa ultra-high-strength steel have been investigated as an alternative to enhance production capacity. In this study, the Yoshida-Uemori (Y-U) model was developed for 1500 MPa steel through tensile-compression tests to characterize its Bauschinger effect and work hardening behaviour. The model's accuracy in predicting springback was validated via U-shaped panel stamping tests. The feasibility of converting a hot-stamped AM bumper to one manufactured with 1500 MPa steel was evaluated through numerical simulations incorporating the validated Y-U model, followed by experimental trials. The results demonstrated that the cold-stamped bumper met dimensional accuracy and performance standards, as verified through CAPA certification, confirming the potential of cold stamping as a viable alternative to traditional hot stamping for AM bumper production.