GMAW is a welding process that joins metals by heating the metals to their melting point with an electric arc. The arc is ignited between a continuous (bare) consumable wire electrode and the workpiece.
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The arc is protected from atmospheric contamination by a protective gas. Shielding is achieved by flooding the arc, the molten end of the metal electrode and the weld pool area with shielding gas. The bare wire is continuously and automatically fed from a spool through the welding gun. Figure 10 shows a schematic representation of the MSG process.
The basic concept of GMAW was introduced in the 1920s; However, the process only became commercially available in 1948; Implemented as a high current density, small diameter process that uses an inert gas to shield the arc. Therefore, the process is also referred to as inert gas welding of metals.GMAW was primarily used to weld aluminum, but later process improvements included operation at low current densities and pulsed current, application to a wider range of materials, and use of reactive gases (especially CO2) and other combinations of gas mixtures.
The process uses both inert and reactive gases as protective gases. The different metals to which GMAW is applied and the variations in the process itself have resulted in different GMAW names. When the same welding process was applied to steel, the inert gases (argon and helium) proved expensive and CO2 reactive gas was used instead; the term CO2 welding was used for this. Refinements of the GMAW process for welding steel have led to the use of gas mixtures including CO and Argon and even Oxygen and Argon.Sometimes small amounts of oxygen (up to 5%) are mixed with argon. Properly mixed compounds provide more consistent arc performance, less spatter, and better wetting (i.e., diffusion and adhesion) of the weld to the base metal. Some blends have been standardized and are commercially available in bottles.The choice of gases (and gas mixtures) depends on the metal to be welded and other factors. Inert gases are used for welding aluminum alloys and stainless steels, while CO2 or a mixture of argon and carbon dioxide is commonly used for welding low and medium carbon steels. The combination of bare wire electrodes and shielding gases prevents slag accumulation in the weld, eliminating the need for manual grinding and slag removal from the deposited weld area. The
-GMAW process is therefore ideal for producing multiple welds on the same joint and significantly higher productivity can be achieved.
GMAW is used in a variety of applications in industrial manufacturing, agriculture, construction, shipbuilding, land and marine vehicles, and mining. The process is used in building structures, welding pipes, pressure vessels, structural steel components, furniture, automotive components and many other products. All commercially important metals including carbon steel, high strength low alloy steel, stainless steel, aluminum, copper, titanium and
nickel alloys can be welded in all positions with the GMAW process by selecting the appropriate combination of shielding gas, welding electrodes and variables.
GMAW can be achieved in three different ways:
- Semi-automatic welding – the machine only controls the wire feed.The movement of the welding gun is controlled manually. It can be called manual welding.
- Machine Welding – uses a gun attached to some type of manipulator (not manual). The operator must constantly adapt and adjust the controls that move the joystick.
- Automated Welding: Uses equipment that welds without the welder or operator having to constantly adjust controls. With some devices, automatic sensors monitor the correct placement of the gun in the solder joint.
