Everything to Know About MIG/MAG Welding

MIG/MAG welding, also known as gas-shielded arc metal welding, is a widely used welding technique in various industries. In this article, we will delve into the details of this welding process and explore why MIG/MAG welding is such a popular method.

MIG/MAG Welding Definition

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MIG/MAG welding is a type of arc welding that’s also known as GMAW, which stands for Gas Metal Arc Welding. It’s basically a process during which an electric arc is produced between a metal welding wire fed through a torch to a welding piece.

The electric power strategically melts both the piece of metal and the tip of the welding wire, creating a molten pool. To ensure the quality of the weld, a gas supply is used to shield the electrical arc from any airborne contaminants (oxygen, nitrogen, moisture) present at the worksite.

Fundamentals

Two gases are used: 

• Inert gas, for MIG (Metal Inert Gas)

• Active gas, for MAG (Metal Active Gas)

MIG welding is suitable for fusing delicate materials like aluminum or alloys that are sensitive to oxygen and nitrogen. MIG welding employs inert gases such as argon, which is a mixture of argon and helium.

As for MAG welding, this method employs oxidants found on the surface of molten pools. The oxidation process is done through the presence of oxygen or carbon dioxide. However, these gases aren’t used in their pure state but mixed with shielding gases. They're active gases. 

How does MIG/MAG welding work?

MIG/MAG welding has three different metal transfer methods. This type of welding uses the following modes:

• Short circuit (GMAW-S): Direct contact between the welding wire and the molten pool;

• Pulsed MIG: A droplet forms with each peak of the electrical output; 

• Axial spray: Includes globular transfer (glob by glob), axial spraying (spattering), and a combo of the two.

Furthermore, there are four types of welds classified according to their position:

• Flat weld

• Horizontal weld

• Vertical weld

• Overhead weld

Different gas mixtures are available depending on the welding mode used, the type of weld being made, and the materials being worked on. They’re mostly made of argon, which benefits from being denser than air. Therefore, it can shield the molten pool better than helium since the latter is lighter than air.

Adding oxygen (O2) or carbon dioxide (CO2) to argon basically yields the same result: 

• Stabilizes the electric arc.

• Improves the look of the weld.

The benefit of oxygen and carbon dioxide is that they don’t need as much force to be expelled from the torch as helium since they’re much denser than air.

As for helium, it has a better thermal conductivity compared to argon. Therefore, it ensures better uniformity with the electric arc.

What’s a MIG/MAG welding machine?

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A MIG/MAG welding machine essentially houses a transformer that adjusts a high voltage (575 V or 220 V) to a low amperage (20 to 50 amps) and a low voltage (16 V to 40V) to a high amperage (80 to 500 amps). 

Aside from the transformer’s purpose, a MIG/MAG welding machine also includes a current rectifier, which converts alternating current (AC) into direct current (DC). Why? To ensure the welding arc is stable and reaches the very high heat required for welding.

Polarity is also inverted during this welding process.

To adjust a welding machine’s current output, the welder can use either of these settings:

• Amperage

• Voltage 

The welding machine’s current output can be set by adjusting the welding wire feed speed, while the voltage can be adjusted directly on the machine. Changes in voltage will directly impact the length of the electrical arc.

Some MIG/MAG welding machines also have a slope and inductance setting. The inductance is what controls the speed at which the current reaches amperage and voltage parameters set by the welder.

MIG/MAG welding machines that lack a slope control feature come preset from the factory at 2 volts for 100 amps. However, increasing the slope allows for better control over low amperage in a short circuit mode. This mode is essential for two reasons:

• It won’t cut through thin material.

• It reduces spattering when starting the arc.

Regarding inductance, it serves to prevent overheating or electrode explosions. In certain modes, such as axial spray transfer, it’s essential to have, low inductance settings to ensure proper and controlled metal transfer.

Pros and Cons

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The MIG/MAG welding process has eight advantages: 

• It allows for welding in various positions, including underwater, using submerged arc welding (SAW).

• Has a continuous electrode wire feed.

• No length restrictions for electrode wire.

• Suitable for welding all metals and alloys retailed in stores;

• Lack of slag;

• High metal deposition rate, higher than those of SMAW (shielded metal arc welding).

• The welding speed is very fast, also related to deposition rates.

• Deep welding penetration can be achieved using axial spray mode.

However, this welding process also has a few downsides:

• The equipment can be complex to set up and relatively expensive. 

• The system is very vulnerable to drafts that disrupt the shielding gas.

• Generates intense heat and a powerful electric arc.