MIG welding is a form of arc welding involving metal and inactive gases used to join two separate steel or aluminum pieces together using the transfer of heat. MIG stands for Metal Inert Gas. The process is sometimes referred to as GMAW in some circles, which stands for Gas Metal Arc Welding.
There are three things that need to be present for a weld to be considered MIG:
- An electrode to fill the joint between the two pieces of steel or aluminum to be connected.
- A source of power, typically a relatively stable and high-voltage power source to run a welding device.
- A shielding gas that works to protect the welds from getting into contact with airborne contaminants and dust.
Let’s take a deeper look into how MIG welders work, to better understand the mechanisms being manipulated and modified to join two pieces of metal into one uniform weld.
How MIG Welders Work
The processes of MIG welding is regarded as a semi-automatic process, as the outcome of a weld relies partially on the skillset of the operator to regulate the amount of welding being performed. This doesn’t mean that an unskilled welder is incapable of operating a MIG welder. After all, the process is relatively simple as far as ensuring the right settings: Set the voltage and use the right electrode. The skill level truly comes in with the quality of the weld. This is where the professionals are separated from the amateurs.
A MIG welder works by transferring the metal wire being used to the joint between the two pieces of metal (aluminum or steel). There are four ways to accomplish this process: globular, pulsed spray, short circuit, and spray:
- In globular transfers, the welding material transfers across the arc weld in larger droplets. Generally, these droplets are larger than the diameter of the electrode being used in the MIG welding process.
- In pulsed spray transfers, the power supply cycles between high spray transfer currents and lower background currents. This allows for super-cooling of weld pools in the background cycle.
- In short circuit transfers, the electrode touches the metal and short circuits. This causes the metal to transfer as a result of the short. This typically occurs between 20 and 200 times per second.
- In spray transfers, tiny molten droplets of super heated metal are sprayed across the arc. This works similar to the spray that comes out of a garden hose when the opening has been restricted.
Let’s dive a little bit deeper into the three requirements necessary to form a MIG weld as outlined above:
MIG Welding: The Electrode Wire
Electrode wires used in MIG welding depend on the types of materials to join. While some welds come with the wire and flux fused together, others require feeding of the wires through a nozzle as you pull the trigger through the process. This is basically how a MIG welder spits molten metal out to weld two pieces of steel or aluminum together.
Setting up this electrode requires that the user begins an arc by clamping it to the welding project, though. The metal is then held inside the welder itself, as MIG welding is classified as wire-feed type welding. Then, MIG welders allow users to adjust feed rates of wires. For this reason, users should first perform a test bead on a scrap piece of metal. This allows fine tuning of feed rates for the strongest results in the final weld. The most common electrode thicknesses for MIG welding work ranges between 0.023″ and 0.045″. However, some are thicker than this, especially if being utilized for heavy-duty or industrial applications.
MIG Welding: The Shielding Gas
There are two possible shielding gas sources in MIG welding:
- The shielding gas can originate from chemical reactions in flux, or
- The gas could come from a tank connected to the welder
The main source of the shielding gas in a MIG welder is the connected gas tank, which also contains mixtures of two inert gases: argon and carbon dioxide. This gases come from manufacturers. Yet, the main reason for using inert gases is so the gas doesn’t react with the metal, causing contaminants to compromise the structure and integrity of the weld.
When a user pulls the trigger on their welder, the gases are pumped through the welding cable, coming out the same nozzle where the welding wire is actively fed. Nevertheless, with this, the inert gas combination creates a type of shield, protecting the arc weld.
MIG Welding: The Power Source
MIG welders use DC (direct current) power sources to produce heat. However, how MIG welders work is dependent on the heat settings chosen. Yet, several voltage selections exist for users to select the option that will produce the best weld based on their needs. If a user selects a heat setting that is too high, they might find themselves with a burnt or unusable weld. This shouldn’t discourage these users, though. Even the most seasoned welding professionals make mistakes. Finally, these adjustments in heat rates for MIG welding power sources are made through modification of voltage rates to meet specific welding needs.
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