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The use of advanced high strength steels (AHSS) such as dual phase (DP), transformation induced plasticity (TRIP) and stretch flanging (SF) steels of the tensile strength of 600 MPa range are well established in automotive components production. This is due to their superior crash energy absorption ability and vehicle weight reduction potential. Recent trends show rapid growth in applications of even higher strength grades such as 800 MPa and 1000 MPa tensile strength and above. They are mostly used for fabrication of crash sensitive components to meet much higher safety requirements in side impact and roll-over accidents. One of the few concerns during the fabrication of AHSS components is the formability limit in flanging and hole expansion operations. Questions have been raised about the applicability of existing manufacturing experience with conventional high strength low alloy steels (HSLA) to new generations of AHSS.

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.

Experimental procedures and results of a benchmark test for springback are reported and a complete suite of obtained data is provided for the validation of forming and springback simulation software. The test is usually referred as the Slit-Ring test where a cylindrical cup is first formed by deep drawing and then a ring is cut from the mid-section of the cup. The opening of the ring upon slitting releases the residual stresses in the formed cup and provides a valuable set of easy-to-measure, easy-to-characterize springback data. The test represents a realistic deep draw stamping operation with stretching and bending deformation, and is highly repeatable in a laboratory environment. In this study, six different automotive materials are evaluated.