(1) Splash during the free transition of the droplet. The main form of splash during the free transition of the droplet. In a CO2 atmosphere, the droplet will bend up under the action of the spot pressure, and it is easy to form large splashes. This situation often occurs when welding with relatively large currents, such as using a 1.6mm diameter welding wire with a current of 300-350A, which occurs when the arc voltage is relatively high. If the current is increased again, the transition of fine particles will be produced. At this time, the spatter is reduced, mainly at the neck between the droplet and the welding wire. The large current density at this place causes the metal to overheat and explode, forming fine particle spatter. In the process of fine particle transition welding, it may be splashed by droplets or droplets thrown from the molten pool. This is due to improper cleaning of the welding wire or workpiece or the high carbon content of the welding wire. A large amount of CO and other gases are generated in the molten metal. These gases accumulate to a certain volume, and the pressure increases and separates out of the liquid metal, causing droplets to splash. When the large droplet transitions, if the droplet stays at the end of the welding wire for a long time and the heating temperature is high, a strong metallurgical reaction or evaporation occurs inside the droplet, and gas is violently precipitated, causing the droplet to explode and generate splashes. In addition, spattering may occasionally occur during the transition of large droplets, because the droplets fall off the welding wire and enter the arc, and a series arc appears on the droplets. Under the action of the arc force, the droplets sometimes fall into the molten pool. Is thrown out of the molten pool to form splashes.
(2) Splash during droplet short-circuit transfer There are many forms of splash during short-circuit transfer. Splash always occurs at the moment when the short-circuit bridge breaks. The size of the spatter depends on the welding conditions, and it often changes in a wide range. There are currently two views on the cause of the splash. One view is that the splash is the result of an electrical explosion on a short-circuit bridge. When the molten droplet contacts the molten pool, the molten droplet becomes a bridge connecting the welding wire and the molten pool, so it is called a small liquid bridge, and the circuit is short-circuited through the small bridge. After the short circuit, the current gradually increases, and the liquid metal at the small bridge shrinks sharply under the action of the electromagnetic contraction force, forming a very thin neck. As the current increases and the necking decreases, the current density at the small bridge increases rapidly, heating the small bridge sharply, resulting in the accumulation of excess energy, and finally causing the small bridge to vaporize and explode, and at the same time cause metal splashing. Another view is that the short-circuit splash is caused by the decomposition and volume expansion of the gas caused by the heating of the CO2 gas when the arc is re-ignited after the small bridge burst, resulting in a strong aerodynamic impact, which acts on the molten pool and the end of the welding wire On the molten droplets, they are thrown out under the action of pneumatic impact and splash. Experiments show that the former view is more correct. The amount of splashing is related to the energy of the electric explosion. This energy is mainly accumulated within 100-150μs before the small bridge is completely destroyed, and is mainly determined by the short-circuit current (ie short-circuit peak current) and the diameter of the small bridge at this time.