GMAW Welding Defined and Explained

Key Points

• GMAW, also known as wire welding, is a common type of welding that uses an electric arc between metal and a wire electrode to melt and fuse the parts together.
• GMAW emerged in the late 1940s as a cost-effective alternative to gas tungsten arc welding (GTAW).
• GMAW can be used on both thick and thin sheets of metal, as well as aluminum and other nonferrous materials.
• There are four main types of GMAW welding techniques: short circuit, spray, globular and pulse spray.
• GMAW welding has many applications in industries such as manufacturing, automotive, construction, aerospace and more. It is versatile, easy to learn and efficient. However, it can be costly upfront and is not suitable for outdoor use.

Gas metal arc welding (GMAW), also known as wire welding, is one of the most common types of welding. As we covered in our history of welding blog, the GMAW welding process emerged in the late 1940s when a continuously fed electrode wire replaced the tungsten electrode in the gas tungsten arc welding (GTAW) process.

It quickly became popular because it was more cost-effective than GTAW. Today, GMAW is used in industries ranging from construction and manufacturing to auto racing and vehicle production. Keep reading to learn how GMAW works, GMAW welding types, applications, pros/cons and more!  

What Is Gas Metal Arc Welding (GMAW)?

In the GMAW process, an electric arc is formed between the metal and a wire electrode, applying heat to the metal pieces. This action melts and fuses the parts together to form a permanent bond.

Another term for GMAW is metal inert gas (MIG) welding. In the MIG and GMAW processes, a continuous solid wire electrode travels through the welding gun along with a shielding gas, which protects against contaminants in the air. This welding process can be used on both thick and thin sheets of metal, as well as aluminum and other nonferrous materials.

How Does GMAW Work?

Now that you understand the basics of GMAW, let’s dive a bit deeper into the process.

GMAW welding process

The GMAW welding process happens when an arc is created between a wire electrode and the workpiece, which melts them both to form a pool. As mentioned previously, the electrode is continuously fed, and a shielding gas is used. The process is considered semi-automatic since wire feed and arc length are controlled by power, but travel speed and positioning are controlled manually.

To be successful, welders must master how to properly guide and clean the gun and optimize the voltage, flow rate and wire-feed rate. The travel speed a welder employs will influence the quality and shape of the weld. GMAW welders need to judge how the weld puddle size relates to the joint thickness to determine the correct travel speed without getting out of range of the welding procedure limitations.

Gases used in GMAW welding

Shielding gases are required for GMAW welding as they are used to protect the weld pool from contaminants in the air. The most common types of gases used during the process are argon and helium, which are both inert gases. This means they will not undergo chemical reactions.

However, active gases such as carbon monoxide can also be used. This is called metal active gas welding. Some welders combine active and inert gas together.

Inert gases, active gases and a combination of the two all protect the weld pool from contamination while providing unique penetration profiles.

Power sources for GMAW welding

Constant-voltage power sources are used for the majority of GMAW welding and other semi-automatic processes. The power source provides a constant voltage to the arc length during the process. There is a self-correcting arc length feature that helps produce stable welding conditions.

GMAW welding polarity

GMAW welding processes operate with reverse welding polarity when the wire electrode is positive. This is because more heat is generated, which helps reduce the chance of defects from a lack of fusion.

Tools used

Some of the basic tools used for GMAW welding include:

• GMAW welder
• MIG welding nozzles
• Welding magnets
• Angle grinder
• Chop saw
• Soapstone
• Pliers
• Clamps
• Chipping hammer
• Band saw

Safety equipment like auto-darkening helmets, gloves and protective clothing are also used during GMAW welding.

4 Types of GMAW Welding

When it comes to GMAW welding, there are a few different techniques that can be used to transfer weld metal from the arc to the base metal. These transfer modes are:

1. Short circuit

The coldest form of GMAW welding is short circuit, which uses low voltage. The welding wire touches the metal, electricity goes through the gun and a short circuit is created. The effect is a wet metal puddle that quickly solidifies and fuses the materials together.

2. Spray

In a spray transfer mode, wire gets melted into fine droplets that get sprayed or misted into the weld joint. This is a constant voltage process that uses a high heat input and sends a constant stream of weld metal from the arc to the base material.

3. Globular

The globular transfer method is similar to the short circuit method. An electrode wire arcs and touches the base material. However, there is a higher heat input, and the wire is heated for a longer period. This creates a larger weld puddle, which collects at the tip of the gun and drips into the joint.

4. Pulse spray

The pulsed spray transfer is similar to the spray arc method but modified to remove potential disadvantages. The welder will pulse the voltage many times per second, allowing a droplet to form at the end of the wire that gets pushed across the arc into the puddle. It is the most functional and flexible transfer time but can be the most expensive as it requires a high-end MIG welding machine.

What is MIG Welding vs. MAG Welding?

MIG (Metal Inert Gas) and MAG (Metal Active Gas) are types of gas metal arc welding. Both use a consumable wire electrode and a shielding gas to protect the weld pool from atmospheric contamination. The difference is in the type of shielding gas used.  

MIG welding uses inert gases such as argon or helium, which do not react with the weld pool, making MIG welding ideal for non-ferrous metals like aluminum, copper and magnesium, where oxidation can be particularly problematic. Inert shielding gasses ensure a clean, stable arc and a high-quality weld free from contaminants. Industries where precision and weld appearance are critical, such as aerospace and automotive manufacturing, favor MIG welding.

On the other hand, MAG welding utilizes active gases like carbon dioxide or a mixture of carbon dioxide and argon. While these gases can react with the molten weld pool and introduce minor impurities, they penetrate deeper to create a more stable arc. MAG welding is most effective on ferrous metals like steel. It is often employed in heavy-duty industries like construction due to its efficiency in creating strong welds in less controlled environments.

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 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 the fluidity of a welding puddle that comes with a GMAW welder make vertical or overhead welding difficult with the spray transfer mode.

GMAW Welding FAQs

What does GMAW stand for in welding?

GMAW stands for gas metal arc welding. The term is representative of the process. During the GMAW welding process, an electric arc forms between the electrode and metal to melt metal pieces together. The process also requires a shielding gas to protect the weld pool from contaminants.

What does MIG stand for in welding?

MIG welding stands for metal inert gas welding. “Inert” defines the type of shielding gas used during the process.

Is GMAW the same as MIG welding?

GMAW and MIG welding are the same, and the terms are used interchangeably.

What is the difference between GMAW and SMAW?

The shielding agent is the primary difference between shielded metal arc welding (SMAW) and GMAW welding. As previously mentioned, GMAW requires a shielding gas.

However, SMAW, also known as stick welding, uses a flux-covered electrode connected to a power source to create a weld. As the flux around the metal electrode heats up, it melts and produces a gas shielding agent, removing the need for a separate gas source.

GMAW Welding Classes

In the Welding Technology program at Universal Technical Institute (UTI), students learn GMAW processes, equipment and applications in courses like Gas Metal Arc Welding I and II and Welding Applications I and II.¹ Students are taught skills that include:

• How to set up and use GMAW equipment and the required welding accessories
• Modes of metal transfer
• Different gases available to shield a weld
• How to produce groove-style joints and steel fillet welds in the horizontal and flat planes
• Basic maintenance of a GMAW-style welding machine, including gas hookup and wire spool replacement
• How to perform overhead and vertical welds
• How to change out whips/guns, correctly maintain a GMAW machine, set up different shielding gases and replace rollers
• How to build specific projects and perform various weld types in all positions

UTI students are also taught welding safety, blueprint basics and mathematics used in fabrication. Brian Masumoto, a welding instructor at UTI Rancho Cucamonga, says the main advantage of UTI’s program is the breadth of instructor experience.

“Our instructors have 70+ years of experience in welding and fabrication,” Masumoto says. “As instructors, we find out what type of welding career the students want to get into and apply what’s in the curriculum to that specific job.”

UTI Campuses That Offer Welding Training

• Avondale, Arizona
• Long Beach, California
• Rancho Cucamonga, California
• Sacramento, California
• Miramar, Florida
• Lisle, Illinois
• Bloomfield, New Jersey
• Mooresville, North Carolina
• Exton, Pennsylvania
• Austin, Texas
• Dallas/Fort Worth, Texas
• Houston, Texas