LASER-BEAM WELDING AND FORMABILITY OF TAILORED BLANKS

Laser beam welding of sheet steel for tailored blanks is increasingly being used in the automotive industry as high-quality laser welded bla nks 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 lev els and multiple travel speeds on a drawing-quality special-killed ste el sheet having different sulfur contents. In the unwelded condition, no differences in formability were observed between the two steels. Ho wever, for a given heat input, differences in formability were observe d between the welded steel blanks because of a reduction in the weld f usion zone ductility due to the presence of sulfide inclusions. It was also found that the weld, heal-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 tr avel speed. Since travel speeds al a given power directly affected the weld mechanical propel ties and weld geometry, the results showed tha t work hardening efficiency was enhanced with welding speed. It was co ncluded that both impurity level in the steel and the weld geometry ar e important factors governing the formability of laser-welded blanks.