Laser beam welding and formability of tailored banks

Abstract

Laser beam welding of sheet steel for tailored blanks is increasingly being used in the automotive industry as high-quality laser welded blanks can be produced having good formability and corrosion resistance. As part of an experimental formability analysis, complete penetration welds in square-butt joints were produced at different laser power levels and multiple travel speeds on a drawing-quality special-killed steel sheet having different sulfur contents. In the unwelded condition, no differences in formability were observed between the two steels. However, for a given heat input, differences in formability were observed between the welded steel blanks because of a reduction in the weld fusion zone ductility due to the presence of sulfide inclusions. It was also found that the weld, heat-affected zone and base metal composite yield strength, as measured on tension specimens with the weld in the middle and parallel to the loading axis, decreased with increasing travel speed. Since travel speeds at a given power directly affected the weld mechanical properties and weld geometry, the results showed that work hardening efficiency was enhanced with welding speed. It was concluded that both impurity level in the steel and the weld geometry are important factors governing the formability of laser-welded blanks.