what does gmaw stand for in welding
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1. What is gmaw welding
Gas metal arc welding (GMAW for short) is a welding method that uses an arc that is continuously fed at a constant speed between a meltable welding wire and the workpiece to be welded as a heat source to melt the welding wire and base metal to form a molten pool and weld. In order to obtain a good weld, external gas should be used as the arc medium and protect the molten droplets, molten pool metal and high-temperature metal in the welding zone from the harmful effects of the surrounding air.
2. Gmaw welding definition
Gas metal arc welding, referred to as gas shielded arc welding or gas shielded welding, can refer to molten extremely inert gas shielded arc welding and molten extremely active gas shielded arc welding. Refers to a type of arc welding that uses external gas as the arc medium and protects the arc and welding zone. It is an automatic or semi-automatic process in which automatic welding requires continuous feeding of welding wire and argon or helium gas for protection from the nozzle of the welding torch. Welding power sources can be either DC or AC. According to the arc, it can be divided into spherical arc, jet arc, pulse jet arc and short circuit arc welding.
At the beginning of its development, gmaw welding was mainly used for welding aluminum and non-ferrous metals, and then its high welding efficiency made it develop in the steel field since the 1940s.
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3. Features of gmaw welding
Since different types of shielding gases and welding wires have different effects on the arc state, electrical characteristics, thermal effects, metallurgical reactions, and weld formation, they are divided into different welding methods according to the type of shielding gas and welding wire type.
The welding method in which a small amount of oxidizing gas (O2, CO2 or their mixed gases) is added to argon as a protective gas is called melting active gas arc welding (MAG welding in English). Usually this method is applied to ferrous metals. Under normal circumstances, the active gas contains 2%~5% O2 or 5%~20% CO2. Its function is to improve arc stability and improve weld formation.
The welding method that uses pure CO2 gas as the shielding gas is called CO2 gas shielded welding (CO2 welding for short). CO2+O2 mixed gas is also used as a protective gas. Due to its low cost and high efficiency, CO2 welding has become the main welding method for ferrous metals.
It can be seen from the above that if the properties of the protective gas are different, the arc shape, droplet transfer and weld bead shape will be different. It has an important influence on the welding results. Therefore, gas metal arc welding is mainly classified according to shielding gas. On the other hand, according to the droplet transfer form at the welding wire end, in addition to the typical spray transfer arc welding, there are also short-circuit transfer arc welding methods and pulse arc welding methods. These welding methods have different power requirements. Both spray transfer and short-circuit transfer arc welding methods use a DC constant voltage source, and the latter has special requirements for DC power. The pulse arc welding method uses a power source with DC pulse output characteristics.
The various methods of gmaw welding have different characteristics. Most low carbon steel uses CO2 welding method. Using MAG welding can achieve a stable welding process and beautiful weld beads. But it is not as economical as CO2 welding. Pulse MAG welding can achieve stable spray transition in the low current range below the critical current, with small welding spatter and beautiful weld formation.
4. Gmaw welding process
The gmaw welding process uses continuous wire feeding and high current density, so the welding wire deposition rate is very high. At the same time, the welding deformation is relatively small and the slag is minimal, making it easy to clean. Therefore, this process is an efficient and energy-saving welding method.
5. Scope of application of gmaw welding
MIG welding is suitable for welding stainless steel and non-ferrous metals such as aluminum and copper. And for mild steel it is an expensive welding method.
Pulse MIG welding is similar to pulse MAG welding and can achieve stable spray transfer in the low current range.
The short-circuit transition welding method is suitable for all-position welding and is mainly used for welding of medium and thin plates and root passes. The spatter is large and the shape is not good. At present, measures have been taken from the aspects of welding power source and protective gas, which have been greatly improved.
