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The tubular hydroforming process has been used to reduce the weight of body-in-white (BIW) components by consolidating parts and eliminating weld flanges. Electric resistance welding (ERW) is the primary joining method for hydroformed tubes made of mild steels and some conventional high strength steels. Due to recently introduced Advanced High Strength Steels (AHSS), such as dual phase and TRIP steels, laser welded (LW) tubes have also been considered for hydroforming applications, particularly for thin-wall, large-diameter tubes. In this study, LW and ERW tubes are evaluated in a free-expansion hydroforming process using various strength steels including AHSS. The LW tubes made from both DP590 and TRIP590 steels were successfully hydroformed to a 64% expansion ratio(the maximum for the die cavity), an improved performance over the ERW TRIP590 tubes. The ERW tubes made from C-Mn440 and lower strength grades were also free-expansion hydroformed successfully to the maximum die cavity.

Advanced high strength steels (AHSS), such as dual phase (DP) and transformation induced plasticity (TRIP) steels, have been used successfully for making light weight vehicles and their usage is growing. Now, the automotive industry is expanding the use of AHSS to higher strength levels for further mass reduction. In a 2003 SAE paper, the material and formability characteristics for such steels were presented for steel grades of DP980, high yield type DP780 (780YM), low yield type DP780 (780YL), TRIP780, and TRIP590. In this study, experiments were conducted to assess the formability of these high strength steels using a T-channel, which incorporates several different forming modes in automotive stamping. The feasibility of computer simulation technology for the formability analyses of AHSS is also addressed.