The concept and classification of gas metal arc welding
The arc welding method that uses a molten electrode, external gas as the arc medium, and protects the metal droplets, welding pool and high-temperature metal in the welding zone is called molten electrode gas shielded arc welding.
According to the classification of welding wire, it can be divided into solid core wire welding and flux cored wire welding. The inert gas (Ar or He) shielded arc welding method using solid core wire is called Melting Inert Gas Arc Welding (MIG Welding); the argon-rich mixed gas shielded arc welding method using solid wire is called Metal Inert Gas Arc Welding (MIG welding). MAG welding (Metal Active Gas Arc Welding). CO2 gas shielded welding using solid wire, referred to as CO2 welding. When using flux-cored wire, arc welding that can use CO2 or CO2+Ar mixed gas as the shielding gas is called flux-cored wire gas shielded welding. It is also possible to do this without adding a shielding gas. This method is called self-shielded arc welding.
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The difference between ordinary MIG/MAG welding and CO2 welding
The characteristics of CO2 welding are: low cost and high production efficiency. However, it has the disadvantages of large amount of spatter and poor molding, so some welding processes use ordinary MIG/MAG welding. Ordinary MIG/MAG welding is an arc welding method protected by inert gas or argon-rich gas, but CO2 welding has strong oxidizing properties, which determines the difference and characteristics of the two. Compared with CO2 welding, the main advantages of MIG/MAG welding are as follows:
1) The amount of splash is reduced by more than 50%. The welding arc under the protection of argon or argon-rich gas is stable. Not only is the arc stable during droplet transition and jet transition, but also in the short-circuit transition situation of low-current MAG welding, the arc has a small repulsion effect on the droplets, thus ensuring MIG / The amount of spatter caused by MAG welding short circuit transition is reduced by more than 50%.
2) The welding seam is evenly formed and beautiful. Since the transfer of MIG/MAG welding droplets is uniform, subtle, and stable, the weld is formed uniformly and beautifully.
3) Can weld many active metals and their alloys. The oxidizing property of the arc atmosphere is very weak or even non-oxidizing. 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 improve the welding processability, welding quality and production efficiency.
The difference between pulse MIG/MAG welding and ordinary MIG/MAG welding
The main droplet transfer forms of 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 amount of spatter and poor shaping, especially some active metals cannot be welded under low current. Welding such as aluminum and alloys, stainless steel, etc. Therefore, pulsed MIG/MAG welding appeared. Its droplet transfer characteristic is that each current pulse transfers one droplet. In essence, it is a droplet transfer. Compared with ordinary MIG/MAG welding, its main features are as follows:
1) The best form of droplet transfer for pulse MIG/MAG welding is to transfer one droplet per pulse. In this way, 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 transfer of one pulse and one drop, the diameter of the droplet is roughly equal to the diameter of the welding wire, so the arc heat of the droplet is lower, that is, the temperature of the droplet is low (compared to jet transfer and large droplet transfer). Therefore, the melting coefficient of the welding wire is increased, which means the melting efficiency of the welding wire is improved.
3) Because the droplet temperature is low, there is less welding smoke. This on the one hand reduces the burning loss of alloy elements and on the other hand improves the construction environment.
Compared with ordinary MIG/MAG welding, its main advantages are as follows:
1) Welding spatter is small or even no spatter.
2) The arc has good directivity and is suitable for welding in all positions.
3) The weld is well formed, the melting width is large, the finger-like penetration characteristics are weakened, and the residual height is small.
4) Small current can perfectly weld active metals (such as aluminum and its alloys, etc.).
Expanded the current range of 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 larger current range of tens of amps.
From the above, we can know 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 is habitually felt to be slightly low.
2) The quality requirements for welders are relatively high.
3) At present, the price of welding equipment is relatively high.
The main process decisions for the selection of pulse MIG/MAG welding
In view of the above comparison results, although pulse MIG/MAG welding has many advantages that cannot be achieved and compared with other welding methods, it also has the problems of high equipment prices, slightly low production efficiency, and difficulty for welders to master. Therefore, the selection of pulse MIG/MAG welding is mainly determined by the welding process requirements. According to the current domestic welding process standards, the following welding must basically use pulse MIG/MAG welding.
1) Carbon steel. The occasions with high requirements on weld quality and appearance are mainly in the pressure vessel industry, such as boilers, chemical heat exchangers, central air-conditioning heat exchangers, and turbine casings in the hydropower industry.
2) Stainless steel. Use small currents (below 200A are called small currents here, the same below) and occasions with high requirements on weld quality and appearance, such as locomotives and pressure vessels in the chemical industry.
3) Aluminum and its alloys. Use small current (below 200A is called small current here, the same below) and occasions with high requirements on weld quality and appearance, such as high-speed trains, high-voltage switches, air separation and other industries. Especially high-speed trains, including CSR Group Sifang Rolling Stock Co., Ltd., Tangshan Rolling Stock Factory, Changchun Railway Vehicles, etc., as well as small manufacturers that outsource processing for them. According to industry sources, by 2015 all provincial capitals and cities with a population of more than 500,000 in China will have bullet trains. This shows the huge demand for bullet trains, as well as the demand for welding workload and welding equipment.
4) Copper and its alloys. According to the current understanding, copper and its alloys basically use pulse MIG/MAG welding (within the scope of molten arc arc welding).
Post time: Oct-23-2023
