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What Is MIG (GMAW) Welding?

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Gas metal arc welding (GMAW), also known as wire welding, is one of the most common welding processes. 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.

As we covered in our history of welding blog, the GMAW 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 car racing and vehicle production.

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.


Types of MIG Welding​

When it comes to MIG 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:

Short Circuit

The coldest form of MIG 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.

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.

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.

Pulse

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 Used For?​

MIG 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 MIG welding makes it a popular choice, from small repair shops and businesses to large industrial facilities.

Advantages of MIG Welding​

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

  • Easy to learn: Compared with other welding processes, MIG welding is considered simple to learn and is a one-hand operation.
  • Versatile: MIG welding can be used to weld a range of metals and alloys, and there are 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 MIG welding machines that allow users to control the polarity, wire speed and amperage.
  • Efficient: Not only is MIG welding efficient when it comes to cleanup, the one-hand operation helps improve control, which increases welding speed and automation, making it easier for the welder.

Disadvantages of MIG Welding​

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

  • Cost: The cost of a MIG welding machine is relatively high upfront, with the need for proper maintenance and replacement of parts.
  • Indoor-only use: MIG welding machines are not built to be portable, and 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 it 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 MIG welder makes vertical or overhead welding difficult.

How Does MIG Welding Work?​

Now that you know some of the uses and types of MIG welding techniques, here are more details about the process.

MIG Welding Process​

The MIG process happens when an arc is created between a wire electrode and the work piece, which melts them both to form a pool. 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. MIG welders need to judge how the weld puddle size relates to the joint thickness in order to determine the correct travel speed.

What Gas Is Used for MIG Welding?​

Shielding gases are required for MIG 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.

MIG Welding Temperature​

During the MIG welding process, base metal melts and fuses with filler metal at around 3,000 degrees Fahrenheit.

Power Sources for MIG Welding​

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

MIG Welding Polarity​

MIG welding processes operate with reverse polarity, where 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 MIG welding include:

  • MIG welding machine
  • 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 MIG welding.

MIG Welding FAQs​

Now that you’ve gotten an in-depth explanation of what MIG welding is and how it’s used, here are some answers to common questions:

What Does MIG Stand for in Welding?​

MIG stands for “metal inert gas,” meaning only inert (non-reactive) gases are used for the shielding gas.

What Does GMAW Stand for in Welding?​

GMAW stands for “gas metal arc welding.”

Is GMAW the Same as MIG Welding?​

GMAW and MIG welding are the same and are terms that can be used interchangeably.

What Is the Difference Between GMAW and SMAW?​

Shielded metal arc welding (SMAW) has a flux-covered electrode that produces a gas shield when heated. GMAW has no flux and relies on a shield from external gases. SMAW welders also require a fresh electrode periodically, whereas with GMAW the wire electrode is fed automatically.

What Is the Difference Between MIG and MAG Welding?​

MAG welding stands for “metal active gas,” so the only difference between MIG and MAG is the type of shielding gas that is used.

MIG Welding Classes

In the Welding Technology program at Universal Technical Institute (UTI), students learn GMAW processes, equipment and applications1 in courses like Gas Metal Arc Welding I and II and Welding Applications. Students learn skills like:

  • 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.”

Learn more about the welding programs offered at UTI, and request more information online.

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