What Is “GMAW” - Gas Metal ARC Welding?

There are many different types of welding and different modes within each type. One such type is MIG arc welding which is a form of arc welding that uses protective gases to shield the welding pool from contaminates.

Going broader, GMAW encompasses two main types of arc welding. To fully understand it, it is best to first get a better understanding of arc welding.

What is ARC Welding?

The GMAW or “Gas Metal Arc Welding” is comprised of two main types of arc welding—Metal Inert Gas Welding (MIG) and Metal Active Gas Welding (MAG).

Generally speaking, arc welding is a fusion welding process where an electrical arc is used to join two metals. This electrical arc is created via a power supply and forms between an electrode and whatever you are welding.

Metal Inert Gas (MIG) vs. Metal Active Gas (MAG)

Both MIG and MAG welding use gasses as a shield to help stabilize the arch and to protect the welding pool from any air pollutants.

They differ in the type of shielding gasses used. MIG welding typically uses a mixture of helium and argon, whereas MAG welding typically uses a mixture of carbon dioxide, argon, and oxygen.

The insert gasses in MIG welding do not react with the weld pool or filler material. However, the active gasses in MAG welding are designed to affect the weld pool and change its chemistry.

So, depending on the type of material that needs to be welded together, welders can determine whether they need active or insert gas to effectively weld the two pieces together.

Types of MIG Welding

There are four main types or modes of MIG welding:

1. Spray Transfer—A spray transfer uses a thin electrode wire that is continuously fed and melted/deposited on the base material. Unlike other modes, a spray transfer drops small and even droplets of molten metal at a continuous rate—producing a nice and even-looking weld.
2. Pulsed Spray Conveyance—Similar to the spray transfer mode, an electrode wire is continuously fed and deposited on the base material. However, instead of having a steady current, the pulse mode uses pulses of voltage to melt the electrode. It is a more refined welding process that produces quality and precise welds.
3. Short Circuit—The short circuit mode has a lower heat input where the welding cable must make contact with the base material. This contact will produce repeated short circuits that transfer the metal and produce a weld. The short circuit mode tends to be less expensive as it requires less shielding gas.
4. Globular Conveyance—The globular conveyance mode is similar to the short circuit mode but uses high voltage to produce large and irregular droplets and the welding cable does not need to be in contact with the base material or welding pool. While this mode does result in spatter, it is less expensive and allows for fast welds to be made.

What is GMAW Welding Used For?

GMAW welding has many applications in some of the world’s biggest industries and can be used for:

• Manufacturing
• Automotive maintenance and production
• Construction
• Aerospace
• Pipe welding/pipe joints
• Shipbuilding
• Custom fabrication
• Railroad track repair and construction
• Underwater welding

The versatility of GMAW welding makes it a popular choice among locations ranging from small repair shops and businesses to large industrial facilities.

Advantages of GMAW Welding

A number of advantages exist for those using GMAW welding, making it one of the most widely used welding processes:

• Easy to learn: Compared with other welding processes, GMAW welding is considered simple to learn and is a one-hand operation.
• Versatile: GMAW welding can be used to weld a range of metals and alloys. There is a range of filler wire electrode materials, allowing for a range of welds.
• Less cleanup: A shielding gas protects the arc during the welding process, meaning there is minimum spatter and slag production and less cleanup after the job is done.
• Control: There are a number of settings on GMAW welding machines that allow users to control the polarity, wire speed and amperage.
• Efficient: Not only is GMAW welding efficient when it comes to cleanup but also the one-hand operation helps improve control, which increases welding speed and automation while making it easier for the welder.

Disadvantages of GMAW Welding

While there are many pros to GMAW welding, it’s also important to know what some of the cons might be:

• Cost: The cost of a GMAW welding machine is relatively high upfront with the need for proper maintenance and replacement of parts.
• Indoor-only use: GMAW welding machines are not built to be portable. Wind can blow away the shielding gas that is necessary to protect the arc, making it an unsuitable process for the outdoors.
• Burn-through: There is the potential to burn through materials that are less than 0.5 mm thick, making the process a less suitable choice for use with certain thin metals.
• Limited welding positions: High heat input and fluidity of a welding puddle that comes with a GMAW welder makes vertical or overhead welding difficult with the spray transfer mode.

GMAW WELDING PROCEDURE SPECIFICATIONS

A well developed GMAW WPS will guide welders through the trusted and accepted procedures they need to create a weld to standard. It is developed for the specific materials and welding techniques being used. With so many variables in the GMAW process, it is always best to follow a specific GMAW procedure, written by an expert welder.

Final Thoughts

All in all, MIG welding uses an electrical arc to fuse two metals. A protective gas is also used to create an atmosphere around the weld without contaminates. MIG welding also implants a continuously fed cable that can act as a filler to help fuse the base material.