Effects of welding velocity on the impact behavior of droplets in gas metal arc welding

The influence of welding velocity on the impact behavior of the globular metal transfer was studied by high speed video photography with a laser source during gas metal arc welding of E36 steel. The welding current and voltage were 180 A and 30 V during the welding process. The results indicated that the impact location of a droplet depended strongly on the welding velocity. There was a critical welding velocity (0.4 m/min) that when the welding velocity was lower than this value the droplet impacted inside the weld pool, while the welding velocity was higher than this value the droplet impacted outside the weld pool. The results showed that when a droplet impacted outside the weld pool it would rebound or adhere on the workpiece, which was depended on the kinetic energy of the droplet. The rebound percentage of droplets increased with increasing kinetic energy. With increasing welding velocity, the mass of droplets was not changed obviously, but the flight velocity of the droplet increased, i.e. the kinetic energy of droplets increased with increasing welding velocity. The results also showed that when a droplet impacted outside the weld pool, the droplet which rebounded away from the workpiece surface formed weld spatters, resulting in discontinuous weld appearance, while the droplet which adhered on the workpiece surface streamed to the weld pool and good weld joint would still be obtained. Molten metal decreases with increasing welding velocity. When the welding velocity increases from 0.4 m/min to 2.0 m/min, the weld width decreases from 12.9 mm to 6.3 mm and the weld penetration decreases from 5.4 mm to 2.1 mm.