Development of GMAW

While electric arc welding, in general, started in the 1800s which contributed to all arc welding processes, gas metal arc welding (GMAW) in its infancy didn’t make it on to the welding scene until 1920s. This early version was based on the concept of using a continuous feeding bare electrode. It wasn’t until Battelle Memorial Institute picked up the development of the process in 1948 that we began to see the wire feeding process that we are more familiar with today. Gas metal arc welding continuously had advancements and improvements since its conception.

The early idea that started it all began in the 1920s by General Electric. GMAW was designed under similar constructs of GTAW (Gas Tungsten Arc Welding). But unlike GTAW, the electrode would be a consumable, continuously fed electrode operating on a constant voltage circuit (CV).

GMAW was used for joining non-ferrous metals until 1953, when the use of Carbon Dioxide (CO2) was introduced as an atmospheric shielding gas. This change in gas mixtures allowed for ferrous and nonferrous welding applications. However, spray transfer mode, which we will explore in detail in this chapter, was the only transfer mode developed at the time and used a larger diameter electrode wire. The addition of CO2 to the shielding gas in steel applications meant higher heat, which inturn discouraged its use by some welders and limited the versatility it now holds in the present day.

In 1958-1959 Short-Circuit transfer mode was developed, which allowed for a smaller diameter electrode wire to be utilized, took a more advanced power supply, but required lower heat levels making it popular with the growing sheet metal industries. Its smaller wire is also where this process got the slang term “micro-wire” and the behavior of short circuit mode the term “dip-transfer.” More advancements were made in the 1960s and 1970s to the original spray transfer process, introducing what is called “spray transfer pulse,” which assisted in lowering overall heavy heat input into the work pieces, among other benefits. GMAW and other welding processes are continuously updated and advanced as equipment manufacturers and technology advance. This is by no means a fully encompassing history of GMAW, and the welding technology will only advance in our lifetimes.

Basics of the process

Gas Metal Arc Welding is what is referred to as a “semi-automatic” process. This means that while the welder/operator controls the gun and the travel speed, travel angle, work angle, and electrode stick out, the wire-feed speed (wfs), current, voltage, and gas flow rate (typically in cubic feet per hour (CFH) is preset at the welding machine before start. Additionally, GMAW can be set up as a fully automatic welding process when used in conjunction with a CNC or robotic type system.

Gas Metal Arc Welding uses a solid wire electrode that is continuously heated and fed from the welding machine and into the weld pool. Along with its shielding gas, the wire runs through the gun conduit cable, sometimes referred to as a “whip,” which contains a liner sheath inside, runs through a contact tip, and on to the surface to be welded. The shielding gas comes out of holes along the contact tip, fills the nozzle, and protects the wire and molten weld puddle directly in front of the arc.

The process is incredibly versatile allowing for the weldability of both ferrous and non-ferrous metals and for the use of different shielding gasses. Both inert gas is called metal inert gas (mig), and reactive gasses are metal active gas (mag). The thickness of wire ranges from about .023” to ⅛” in diameter, making this process available for a wide range of metal thicknesses and needs.

Gas metal arc welding typically uses direct current electrode positive (DCEP/DCRP), commonly referred to as reverse polarity. DCEP is ideal for GMAW because it allows for deeper penetration of weld, the least amount of spatter, and more predictable metal transfer, all while allowing for the best cleaning of the oxide layer, which is found on most metals.

GMAW uses a constant voltage (CV) power source such as a transformer-rectifier or inverter. Constant Voltage machines maintain the set voltage at the panel during the welding process even as the welder changes stick out distance. Changing the stick out distance does increase or decrease the resistance in the wire, and therefore, the machine will adjust the current appropriately. Because the wire is continuously fed, the arc length does not change, and therefore the voltage will remain the same. Section 10.2 goes over more detail about setting up the welding machine for use.

Uses of GMAW in industry today

Gas type, filler metal, base metal, and transfer mode all play a factor in what and how to weld in the GMAW process. Today, Gas Metal Arc Welding is used all over the world and in a large array of applications. Most notably, the sheet metal, and by extension, the automobile industry, as well as pipe fitting, robotic welding, railway, construction trades, and manufacturing. Because the equipment for GMAW isn’t as portable as other processes, welders utilizing this process will more often than not, find themselves working in fabrication shops. But considering how diverse GMAW can be regarding its applications for ferrous and nonferrous metals alike, the possibilities feel almost limitless. This process is also popular amongst hobbyist welders and artists due to its general ease of use and low maintenance of the equipment.

Attributions

1. Figure 10.1: RK WL GMAW by Weldscientist is released under CC BY-SA 4.0
2. Figure 10.2: GMAW diagram en by Curkuma Putz is released under CC BY-SA 3.0
3. Figure 10.3: A MIG welder at work by Stephanie Oostman, for WA Open ProfTech, © SBCTC, CC BY 4.0