The 1 mm thick tantalum thin sheet commonly used in the production of tantalum thin-walled tubes is mostly processed and manufactured by welding. In the production of tantalum pipes prepared by welding, there are gaps in the butt joints, which are prone to forming defects such as hump and burn-through during welding. The existence of butt gaps affects the arc shape and the heat dissipation conditions of the workpiece, and it is bound to affect the welding pool. 

(1) When the gap range δ≤0.108 mm, during the welding process, due to the thermal expansion of the butt workpiece itself, part of the gap is

The parts have disappeared before melting, and the formation process of the molten pool is the same as without the butt gap, forming the same molten pool from beginning to end.

(2) When the gap range is 0.108 mm <δ≤0.22 mm, there is still a small gap when the workpiece is melted, and the molten pool is formed on the two butting workpieces. As the arc input heat increases, the workpiece continues to expand toward the butting gap , The molten metals are squeezed together and naturally merge together to form the same molten pool under the action of the affinity between the liquid metals.

(3) When the gap range is 0.22 mm <δ≤0.35 mm, there is still a large gap when the workpiece is melted. Due to the uneven heating of the arc and the force of the molten pool, an inclined solid-liquid interface is formed at the butt edge. The molten metal shrinks into droplets under the action of surface tension and is adsorbed on the inclined surface. As the heat input by the arc increases, the workpiece continues to expand toward the butt gap, while the volume of the droplets continues to increase. When gravity and arc force along the inclined surface When the direction component is greater than the effect of the surface tension on the droplet, the droplet on the butt workpiece flows downward along the inclined surface to the butt gap to form a molten pool.