TWI Industrial Member Report Summary 882/2007
By S Lockyer and G Verhaeghe
Background
In the automotive industry, the body-in-white structure is fabricated from zinc coated steel sheet conventionally joined by resistance spot welding, although laser welding is becoming more common. The advantages of laser welding over resistance spot welding are single-sided access, reduced flange widths, increased torsional stiffness, less thermal distortion, high speed automated processing and design flexibility. However, when welded in a lap joint configuration, zinc coated steels tend to produce spatter and can give rise to relatively high levels of porosity due to the vaporisation of the zinc. This usually occurs if the sheets are clamped tightly together and when the coating thickness on the sheets is in excess of 5µm. A common solution is to create a gap at the joint interface enabling the zinc vapour to escape. At the same time, the joint gap can result in the formation of other weld imperfections and little information exists on the effect of those weld imperfections on the in-service performance of joints of this type.
Objective
Quantify the effect of influence and root concavity on the fatigue performance of laser welded lap joints in thin gauge zinc coated automotive sheet steel.