Concept and Classification of Gas Metal Arc Welding

The arc welding method of using the melting electrode, using the external gas as the arc medium, and protecting the metal droplets, welding the high temperature metal in the

weld pool and welding area is called the gas shielded metal arc welding. According to the different welding wire materials and shielding gases, they can be divided into the

following methods, as shown in the figure.

According to the classification of welding wires, it can be divided into solid core welding and flux core welding. Arc welding with inert gas (Ar or He) of solid wire is called metal

inert gas welding (MIG welding) for short; Metal Active Gas Arc Welding (MAG) is a kind of arc welding with solid core wire and rich argon mixed gas. CO2 gas shielded welding

using solid wire, abbreviated as CO2 welding. When flux cored wire is used, the arc welding with CO2 or CO2+Ar mixed gas as the shielding gas is called flux cored wire gas

shielded welding. It can also be used without shielding gas. This method is called self shielded arc welding.

The difference between ordinary MIG/MAG welding and CO2 welding

The characteristics of CO2 welding are: low cost and high production efficiency. However, there are drawbacks such as high splashing and poor forming, so some welding processes

use ordinary MIG/MAG welding. Ordinary MIG/MAG welding is a method of arc welding using inert gas protection or argon rich gas protection, while CO2 welding has strong oxidation

resistance, which determines the differences and characteristics between the two. The main advantages of MIG/MAG welding compared to CO2 welding are as follows:

1) Reduce splashing by more than 50%. The welding arc is stable under the protection of argon or argon rich gas. Not only is the arc stable during droplet transfer and jet transfer, but also

in the short circuit transfer of low current MAG welding, the arc has a smaller repulsion effect on the droplet, ensuring a reduction of over 50% in the spatter amount during short circuit

transfer in MIG/MAG welding.

2) The welding seam is evenly formed and aesthetically pleasing. Due to the uniform, fine, and stable droplet transfer in MIG/MAG welding, the weld formation is uniform and aesthetically pleasing.

3) It can weld many active metals and their alloys. The oxidation of the arc atmosphere is very weak, even without oxidation. MIG/MAG welding can not only weld carbon steel and high alloy steel,

but also many active metals and their alloys, such as aluminum and aluminum alloys, stainless steel and its alloys, magnesium and magnesium alloys, etc.

4) Greatly improved welding process, welding quality, and production efficiency.

The difference between pulse MIG/MAG welding and regular MIG/MAG welding

The main forms of droplet transfer in ordinary MIG/MAG welding are jet transfer at high current and short circuit transfer at low current. Therefore, low current still has the disadvantages of

large splashing and poor forming, especially some active metals such as aluminum and alloys, stainless steel, etc. cannot be welded under low current. Therefore, pulse MIG/MAG welding

has emerged, and its droplet transfer characteristic is that each current pulse transfers one droplet, which essentially belongs to droplet transfer. Compared with ordinary MIG/MAG welding,

its main characteristics are as follows:

1) The optimal droplet transfer form for pulse MIG/MAG welding is one pulse to transfer one droplet. By adjusting the pulse frequency, the number of droplets transferred per unit time can be

changed, which is the melting speed of the welding wire.

2) Due to the droplet by droplet transfer process, the droplet diameter is roughly equal to the diameter of the welding wire, resulting in lower arc heat and lower droplet temperature (compared

to jet transfer and large droplet transfer). So the melting coefficient of the welding wire is increased, which means the melting efficiency of the welding wire is improved.

3) Due to the low temperature of the droplet, there is less welding smoke. This not only reduces the burning loss of alloy elements, but also improves the construction environment.

Compared with ordinary MIG/MAG welding, its main advantages are as follows:

1) Welding spatter is small, even without spatter.

2) Good arc directionality, suitable for all position welding.

3) The weld seam is well formed, with a large fusion width, weakened finger like penetration characteristics, and small excess height.

4) Perfect welding of active metals (such as aluminum and its alloys) with low current.

Expanded the range of current used for MIG/MAG welding jet transfer. During pulse welding, the welding current can achieve stable droplet transfer from near the critical current of jet transfer to a

large current range of tens of amperes.

From the above, it can be seen that the characteristics and advantages of pulse MIG/MAG, but nothing can be perfect. Compared with ordinary MIG/MAG, its shortcomings are as follows:

1) Welding production efficiency habits have slightly lower sensitivity.

2) There is a high requirement for the quality of welding personnel.

3) Currently, the price of welding equipment is relatively high.

The main process decision for selecting pulse MIG/MAG welding

Based on the above comparison results, although pulse MIG/MAG welding has many advantages that other welding methods cannot achieve and compare, it also has problems such as high equipment prices,

slightly low production efficiency, and difficulty for welders to master. So the selection of pulse MIG/MAG welding is mainly determined by the welding process requirements. According to the current domestic

welding process standards, pulse MIG/MAG welding is basically required for the following welding.

1) Carbon steel. The occasions with high requirements for weld quality and appearance are mainly in the pressure vessel industry, such as boilers, chemical heat exchangers, central air conditioning heat exchangers,

as well as the vortex shells of water turbines in the hydropower industry.

2) Stainless steel. Use low current (referred to as low current below 200A) and occasions with high requirements for weld quality and appearance, such as locomotives, pressure vessels in the chemical industry, etc.

3) Aluminum and its alloys