Before we take a closer look at the different welding processes, it may be beneficial to become familiar with a few key words and concepts in the welding world:
MIG and MAG welding (welding process number 131/135) are both variations of the gas metal arc welding (GMAW) process, as they are often referred to in some countries. In MIG and MAG welding, the arc burns between the workpiece and a melting electrode, which is fed continuously.
The heat created from the arc forms a molten pool, which fuses the materials together and forms a joint.
The arc and the molten pool are protected by a gas, which can be argon or helium (MIG welding) or carbon dioxide (MAG welding), or a mixture of these.
A variation of these welding methods is flux cored welding, which uses a small electrode filled with a powder that protects the weld pool or contains metal particles to increase the amount of material added.
Another method is TIG welding, where the electrode is made of non-melting tungsten, and the gas is argon (read more about TIG further down in the article).
The main difference between MIG welding and MAG welding is the gas used in the welding process.
The gases in MIG welding are classified as inert gases (non-reacting gases). The process is suitable for welding aluminum, copper, and magnesium, among other materials.
The composition of the shielding gas is important, as it has a major effect on the stability of the arc, metal transfer, weld profile, penetration ability and the degree of spatter.
The development of MIG/MAG/TIG power supplies has been driven by the need to control the droplet transition, from the electrode to the weld pool. There are various ways to control the droplet transition.
For example, you can vary the current in pulses, or specify when and how the drop should be transferred.
MIG welding was first patented in the United States, in 1949, by the Battelle Memorial Institute, for welding aluminum, using a power source with a falling characteristic.
In 1952, MIG became a popular process in the UK, for welding aluminium using argon (noble gas) as the shielding gas, and for carbon steel using CO2 (active gas).
CO2 and argon-CO2 mixtures are known as MAG (metal active gas) welding.
In the late 1950s, short-arc techniques were in use, which made it possible to weld thin materials, using smaller diameter electrode wires and more advanced power supplies.
Further development led to the discovery of the spray-arc technique in the mid-1960s. Small amounts of oxygen were added to the shielding gas, which formed a fine droplet transfer from the electrode into the molten pool.
In the last 30 years, new electronics have emerged, which have developed synergic power sources, which have led to increased use of pulse welding.
Welding with these power sources reduces the risk of welding defects, especially in thicker materials.
Metal Inert Gas welding is a process for joining metals. It can be automated or semi-automated. MIG welding is popular in manufacturing and industry, and can be used for the fabrication and repair of products.
In MIG welding, a continuous wire is used as the electrode and filler material, together with a gas that protects and shields the molten pool from the environment and contaminants.
The process involves the power source, which creates an electric arc between the electrode and the metal, which melts both parts, forming a solid joint when it cools.
MIG welding is often used because the process is fast and versatile. The flexibility of the process makes it possible to weld different metals and thicknesses.
Most often, argon gas, or a mixture of helium and argon, is used to protect the welding zone from oxygen and nitrogen in the air. This prevents spatter and ensures that the weld is strong and fine.
MAG welding uses reactive gases such as oxygen or carbon dioxide. Mixing the gases with argon ensures arc stability and an optimized appearance of the weld seam.
Gas selection has an impact on productivity, quality, and which material you should weld.
The MAG process is used for unalloyed, low-alloyed and high-alloyed materials.
Steel is the most commonly used material in MIG/MAG welding.
Electrodes for process 131/135 (MIG/MAG) are solid wires. The choice of wire type is based on the composition of the materials to be welded. It is also possible to use metal cored and flux cored wires, which can increase the deposition rate, but then the process falls under process numbers 138 and 136 (FCAW).
As previously mentioned, Tungsten Inert Gas welding (welding process number 141) is an arc welding process that produces the weld with a non-consumable tungsten electrode, and argon gas. In this welding process, the filler material is fed as a wire. TIG welding is also known as Gas Tungsten Arc Welding (GTAW).
TIG welding's original name is Heliarc, and became a popular process in the 1940s, for joining magnesium and aluminum, and stainless materials.
Instead of slag, an inert gas shield is used to protect the molten pool, making the welding process an attractive alternative to gas and manual metal arc welding.
The arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium.
A hallmark of TIG welding is the small, powerful arc from the pointed electrode, which is ideal for high-quality and precision welding.
The metal is applied by the melting electrode. This means that TIG welders do not need to balance the heat input from the arc, because the electrode is not consumed/melted during welding.
If filler material is required, it must be added separately to the molten pool. This can be added manually or mechanized, using an external wire feeder.
The electrode used in TIG welding is made of tungsten or a tungsten alloy. Pure tungsten has a melting point of around 3422 degrees Celsius. When welding, when connected, the pole is at around 3200 degrees Celsius.
Modern power sources are often both direct current and alternating current sources, and have a high frequency for easy ignition of the arc.
The constant current power source has a falling characteristic, producing electrical energy, which is conducted across the arc through a column of highly ionized gas, which is known as plasma.
The polarity of TIG depends on the material to be welded.
Direct current with a negatively charged electrode is often used when welding steel, nickel and titanium.
Alternating current is used in aluminum welding, where the direction of the current alternates between positive and negative charges between the electrode and the base material. This causes the electron flow to constantly change direction, preventing the tungsten electrode from overheating, while retaining heat in the base material.
Surface oxides are removed during the electrode-positive portion of the cycle, and the base material is heated more deeply during the negative portion of the cycle.
Because tungsten has the highest melting point of pure metals in the periodic table, the electrode does not melt while producing the arc that heats the material, liquefying the material.
TIG welding is suitable for, among other things, rust-resistant steels, aluminum and nickel alloys, as well as thin sheets of aluminum or stainless steel.
Manual TIG requires a lot of skill from the welder, but produces few welding defects if used correctly. Newer variations of this method include keyhole TIG, where the electrode is heated to near melting temperature before being added to the arc.
In manual metal arc welding (MMA), the small arc is effective for thin plates, or for controlled penetration (in the bottom weld on pipe welds).
Because the deposition rate can be low (using separate filler material), MMA or MIG may be the preferred welding processes for thicker materials, and for filling in thick-walled pipe welds.
TIG welding is also widely used in mechanized systems, either autogenous or with filler wire.
Not sure which gas to use? Which shielding gas to use depends on the material you are welding:
In addition to general shielding of the arc and weld pool, the shielding gas contributes to a number of important functions:
The shielding gas has a significant impact on the stability of the metal transfer and the behavior of the weld pool. Especially in the case of weld penetration. As mentioned above, general shielding gases for MIG welding are mixtures of argon, oxygen and CO2. In special gas mixtures, the shielding gas may also contain helium.
Do you have any questions, or would you like more information about welding?
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Sources: Western Australia Department of Training and Workforce Development, The Welding Institute Ltd., Store norske leksikon.
