In CO2 gas shielded welding, due to the different forms of droplet transfer, different welding process parameters are required

Process parameters during short-circuit transfer. Short-circuit transfer welding adopts fine wire welding. The diameter of the commonly used welding wire is Φ0.6～1.2. As the diameter of the welding wire increases, the spatter particles increase accordingly. In short-circuit transfer welding, the main welding process parameters are arc voltage, welding current, welding speed, gas flow and purity, and the welding wire depth.

1) Arc voltage and welding current

Arc voltage is the key parameter during short-circuit transition, and the characteristic of short-circuit transition is the use of low voltage. The arc voltage matches the welding current, and a stable welding process with small spatter and good weld formation can be obtained. The general parameter of Φ1.2 is voltage 19V; current 120～135.

2) Welding speed

With the increase of welding speed, the weld width, penetration depth and reinforcement are all reduced. If the welding speed is too high, defects such as undercut and incomplete penetration are likely to occur. At the same time, the gas protection effect is deteriorated and air holes are likely to occur. If the welding speed is too low, it is easy to produce defects such as burn-through, coarse structure, and increase deformation and reduce production efficiency. Therefore, the welding speed should be correctly selected according to production practice. Usually the speed of semi-automatic welding does not exceed 0.5m/min, and the speed of automatic welding does not exceed 1.5m/min.

3) Gas flow and purity

If the gas flow is too small, the stiffness of the shielding gas is insufficient, and the weld is prone to defects such as pores; when the gas flow is too large, not only the gas is wasted, but also the oxidation is enhanced, and a dark gray oxide scale will be formed on the surface of the weld. The quality of the weld is degraded. In order to ensure that the welding area is free from air pollution, when the welding current is high or the welding speed is high, the welding wire has a long extension and the outdoor welding, the gas flow should be increased. Generally, the gas flow rate is between 15 and 25L/min for filament welding. The purity of CO2 gas shall not be lower than 99.5%. At the same time, when the pressure in the cylinder is lower than 1Mpa, stop using it to avoid pores. This is because when the pressure in the cylinder decreases, the vaporized amount of water dissolved in liquid CO2 also increases, so that more water vapor is mixed into the CO2 gas.

4) Extension length of welding wire

Since thin welding wires are used for short-circuit transfer, the resistance heat generated on the extended length of the welding wire has a great influence. The extension length increases, the resistance heat on the welding wire increases, the welding wire melts faster, and the productivity increases. But when the extension length is too large, the welding wire is prone to overheating and fusing in sections, causing serious spatter and unstable welding process. At the same time, as the extension increases, the distance between the nozzle and the weldment also increases, so the gas protection effect becomes worse. However, if the protruding length is too small, the distance between the nozzle and the weldment will be shortened, and splash metal will easily block the nozzle. The proper extension length should be 10-12 times the diameter of the welding wire, and 8-15mm is suitable for fine wire welding.