Concept and classification of MIG arc welding
The arc welding method using molten electrode, with the external gas as the arc medium, and protecting the metal droplet, welding the molten pool and the high temperature metal in the welding zone is called the MIG arc welding. According to the different welding wire materials and protective gases, it can be divided into the following methods, as shown in the figure.
According to the classification of welding wire can be divided into solid wire welding and flux-cored wire welding. Inert Gas (Ar or He) Arc Welding with solid core wire is called MIG arc welding (Metal Inert Gas Arc Welding); Argon rich Gas Arc Welding with solid cored wire, referred to as MAG (Metal Active Gas Arc Welding). CO2 gas welding with solid cored wire is referred to as CO2 welding. In the case of flux-cored wire, the arc welding that can use CO2 or CO2+Ar mixture as the shielding gas is called flux-cored wire gas shielding welding. It can also be done without protective gas, which is called self-protective arc welding.
Difference between common MIG/MAG welding and CO2 welding
The characteristics of CO2 welding are: low cost and high production efficiency. However, there are shortcomings of large splash amount and poor forming, 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 a strong oxidation, which determines the difference and characteristics of the two. The main advantages of MIG/MAG welding compared to CO2 welding are as follows:
1) The amount of spatter is reduced by more than 50%. The welding arc under the protection of argon or argon rich gas body is stable, not only the arc is stable during the droplet transition and the jet transition, but also the arc has less repulsive effect on the droplet in the short circuit transition of the small current MAG welding, thus ensuring that the splash amount of the short circuit transition of MIG/MAG welding is reduced by more than 50%.
2) The weld formation is uniform and beautiful. Because MIG/MAG welding droplet transition is uniform, fine, stable, so the weld formation is uniform and beautiful.
3) Can weld many active metals and their alloys. The oxidation of the arc atmosphere is very weak, even no oxidation, MIG/MAG welding can not only weld carbon steel, high alloy steel, but also can weld many active metals and their alloys, such as: aluminum and aluminum alloys, stainless steel and its alloys, magnesium and magnesium alloys.
4) Greatly improve the welding process, welding quality and production efficiency.
Difference between pulsed MIG/MAG welding and ordinary MIG/MAG welding
The main droplet transition form of ordinary MIG/MAG welding is the jet transition at high current and the short circuit transition at low current, so the small current still has the shortcomings of large splash and poor forming, especially some active metals can not be welded at low current, such as aluminum and alloys, stainless steel and so on. Therefore, pulsed MIG/MAG welding is developed, and its droplet transition is characterized by a droplet transition for each current pulse, which belongs to the droplet transition in essence. Compared with ordinary MIG/MAG welding, its main features are as follows:
1) The best droplet transition form of pulsed MIG/MAG welding is one pulse transition to one droplet. In this way, by adjusting the pulse frequency, the number of drops in the melt drop transition per unit time can be changed, that is, the melting speed of the welding wire.
2) Due to the drop of a pulse of the droplet transition, the droplet diameter is roughly equal to the diameter of the welding wire, then the droplet arc heat is low, that is, the droplet temperature is low (compared with the jet transition and the large drop transition). Therefore, the melting coefficient of the welding wire is improved, that is, the melting efficiency of the welding wire is improved.
3) Because of the low drop temperature, the welding smoke is less. In this way, the burning loss of alloying elements is reduced on the one hand, and the construction environment is improved on the other hand.
Compared with ordinary MIG/MAG welding its main advantages are as follows:
1) Welding splash is small, or even no splash.
2) Good arc directivity, suitable for all-position welding.
3) The weld is well formed, the melting width is large, the finger-like melting depth characteristics are weakened, and the residual height is small.
4) Small current perfect welding of active metals (such as aluminum and its alloys).
The current range of MIG/MAG welding jet transition is expanded. In pulsed welding, the welding current can be stable from the critical current of the jet transition to the larger current range of tens of amperes.
From the above we can see the characteristics and advantages of pulsed MIG/MAG, but nothing can be perfect. The disadvantages compared with ordinary MIG/MAG are as follows:
1) The welding production efficiency habitually feels slightly low.
2) High quality requirements for welders.
3) At present, the price of welding equipment is higher.
The selection of pulsed MIG/MAG welding is mainly determined by the process
According to the above comparison results, although pulsed MIG/MAG welding has many advantages that other welding can not be realized and compared, it also has problems such as high equipment price, slightly low production efficiency and difficult for welders to master. Therefore, the selection of pulsed 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 pulsed MIG/MAG 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, and turbine turboshells in the hydropower industry.
2) Stainless steel. The use of small current (200A below is called small current, the same below) and the weld quality, appearance requirements are higher occasions, such as locomotives, chemical industry pressure vessels, etc.
3) Aluminum and its alloys. The use of small current (200A below is called small current, the same below) and the weld quality, appearance requirements of higher occasions, such as high-speed cars, high-voltage switches, air separation and other industries. In particular, high-speed cars, including CSR Group Sifang vehicles, Tangshan Vehicles Factory and Changke and other small manufacturers for their outsourcing processing. According to industry news, by 2015, all provincial capitals and cities with a population of more than 500,000 have realized bullet trains, which shows the large demand for bullet trains and the large demand for welding workload and welding equipment.
4) Copper and its alloys. According to the current understanding, copper and its alloys are basically pulsed MIG/MAG welding (in the range of MIG gas protection welding).
