Hydroforming Formability of Electric Resistance Welded Tubes for Automobiles

From the viewpoint of applying ERW (Electric Resistance Welded) steel tubes for automotive structural parts by means of hydroforming technology, a series of free-bulge experiments is carried out. Four kinds of mild and high tensile strength steel tubes are provided. Initial stress ratio, α_m that represents an axial force level is adopted as an experimental parameter. Expansion limit increases with decrease of α_m. The bulge shape and the expansion limit are also affected by the mechanical properties of tubes. The strain hardening property in bulge deformation is approximated by a parabolic equation.