Gas Metal Arc Welding

There are a number of different industrial welding processes but the most common is Gas Metal Arc Welding (GMAW). This style of welding is often referred to as Metal Inert Gas (MIG) welding, but also encompasses Metal Active Gas (MAG) welding. GMAW uses a gas along a wire electrode to heat up two metals to be joined together, then creates a joint to connect them. In this description, we’ll explain how Gas Metal Arc Welding works, the difference between MIG and MAG, the four methods of metal transfer and what you need to get started.

What is Gas Metal Arc Welding?

Gas Metal Arc Welding (GMAW) refers to the process of forming a DC electric arc between a wire electrode and a piece of metal (often called the workpiece). This heats up the metal and allows it to be joined to another piece of metal. The wire electrode is a consumable piece of material that is fed through a wire feeding spool gun (or simply, welding gun) by an operator pulling a trigger to release it. The electrode melts when heated and forms what is called a weld bead which is filler metal that fuses to the workpiece and joins it.

When joining metals with this electric arc, gas is fed through the welding gun. This shields the weld from contaminants like oxygen, nitrogen or hydrogen that can make it porous (holes in it) or create excess spatter. This creates a cleaner weld pool and allows for a quick and continuous process. The type of gas used is the difference between the types of GMAW welding, MIG and MAG.

What is MIG Welding?

Metal Inert Gas (MIG) welding is a GMAW process that uses inert (meaning not moving) gases such as argon or helium as shielding gas. MIG welding is typically used for non-ferrous (not containing iron) metals like aluminum, magnesium, stainless steel, carbon steel, copper, nickel, bronze, and other alloy metals. There are some pros and cons of MIG Welding that you should know about before deciding between MIG or other methods.

What is MAG Welding?

Metal Active Gas (MAG) welding is also a GMAW process that is similar to MIG welding, but uses active gas mixtures such as a mixture of carbon dioxide (CO2), argon and oxygen. The difference in shielding gas affects the metal transfer, arc stability and the amount of spatter from the weld. The main use for MAG welding is for welding steel, as opposed to the multiple metals that MIG is used for.

Four GMAW welding transfer types

Within GMAW welding, both MIG and MAG, there are four main transfer types.

  • Short Circuit Transfer – In this method, the welding wire comes into contact with the metal and creates a short circuit from the electricity that the welding gun is providing. This melts the wire and it drips onto the workpiece and creates a pool of melted metal that becomes the joint to combine the two pieces of metal. This is most common method and uses low voltage and a minimal amount of shielding gas. This method is sometimes called “drip transfer.”
  • Globular Transfer – This is a high voltage method using argon shielding gas. The wire melts and forms a glob at the tip of the welding gun then you drip it onto the workpiece to form the joint. The drip process is slower, but can create more spatter, which makes this method slightly less popular.
  • Spray Transfer – This is also used only with high currents or voltage and the welding wire does not make contact with the pool. Metal is melted and forms at the tip of the wire, then sprays very small drops to the weld pool. The higher voltage is key to ensure that droplets do not become too large so that they can be “sprayed” over the arc.
  • Pulsed Spray Transfer – This uses lower current levels but does not use short-circuiting. Instead, it “pulses” the current to detach alternating droplets and spray into the weld pool. This can be thought of as a sort of hybrid of spray transfer and short-circuit transfer. It requires a higher end welder, but gives better versatility and performance for different types of jobs.

Uses of Gas Metal Arc Welding

Gas Metal Arc Welding has a lot of applications and is one of the most popular welding methods on industrial projects. The two industries that are most dominated by GMAW are the automotive and steel industries. Since GMAW is the easiest welding method for automated machines, many welding tasks on automobiles are performed by robots. Because of the need for shielding gas, you typically see GMAW mostly in industries where welding is done indoors, as opposed to flux cored, gas tungsten arc welding, or shielded metal arc welding.

Some of the most common projects or industries for Gas Metal Arc Welding include:

  • Manufacturing
  • Automotive Manufacturing and Repair
  • Construction
  • Transportation
  • Pipeline Welding
  • Shipbuilding
  • Home/DIY Welding
  • Heating and Air Conditioning

GMAW/MIG Welding Supplies and Equipment

To get started with Gas Metal Arc Welding (both MIG and MAG), there is some basic equipment that you need to weld:

Welding Gun – MIG and MAG welding guns typically range from $50-$150 and are widely available for purchase.

Power Source – Either a DC or alternating current power supply to create the electric arc.

Metal Wire Electrodes – You will need to find the right size (diameter) for the metal for your project. This is typically inexpensive, but will need to be replenished for future jobs.

Shielding Gas – Either active gas for MAG or inert gas for MIG, you will buy these in tanks that typically cost around $100 per tank.

Wire Feed Drive Roller – This feeds the wire electrode into the weld pool.

Other Accessories – Other accessories like a guide tube, reel stand and gas hoses may be necessary for your initial setup or to replace parts, depending on what is included when you buy your other equipment.

Those are the basics for what you need to know about Gas Metal Arc Welding. It may sound complex for the beginner, but once you understand the basic terminology and how it works, you will be ready to weld in no time. To put things in context, it may help to get a broader understanding of other welding methods, but you should have what you need to get started with GMAW welding.