Effects of the gap on molten pool dynamics and weld formation in laser lap welding of thin 316L stainless steel plates

Large thin-walled structures will inevitably generate gaps during laser welding owing to the deformation caused by thermal stress, which could alter the molten pool dynamics and dramatically affect the weld formation. In this work, the 316L stainless steel plates with 0.8 mm and 2.0 mm thickness is selected as the upper plate and the lower plate, respectively, for the laser welding. The effects of the gap on molten pool dynamics and weld formation are investigated combining the numerical modeling and experimental testing. The accuracy of the numerical model was verified through the combination of experiment and numerical simulation. The results showed that the weld morphology exhibits gradually destabilization with the increase in the gap. Furthermore, a chasm was formed when the molten metal on the upper and lower plates under the conditions of 0.2 mm and 0.4 mm gap was separated by the gap. Increasing with the keyhole opening area of upper plate, in particular, liquid metal gradually accumulated in the middle of the keyhole until the metal on both sides fused to generate a weld breakpoint under 0.4 mm clearance.