Effect of laser beam wobbling on the overlap joint strength of hot-press-forming steel over 2.0 GPa tensile strength

Abstract

High-strength hot-press-forming (HPF) steel is extensively utilized in the automotive industry to lower the weights of car bodies. Resistance spot welding is commonly used when assembling car bodies; however, laser overlap welding is gradually replacing resistance spot welding owing to its high productivity and quality. The joint strength of laser overlap-welded HPF steel with a tensile strength of 2.0 GPa was investigated in the present study. Laser wobble welding was employed to increase the interface-bead width and the resultant joint strength. In laser overlap welding without wobbling, all the specimens were fractured at the interface during the tensile-shear test where the maximum load was 8.2 kN. An increase in the wobbling width not only induced an increase in the interface-bead width but also splitting of the weld bead. The interface-bead width (6.7 mm) was much higher than the base metal thickness (1.2 mm), with a wobble width of 1.6 mm. The wide interface-bead width resulted in a fracture load of 10.7 kN, and the fracture location moved from the interface to the upper plate. Laser wobble welding was confirmed to be an effective approach for increasing the joint strength in laser overlap welding.