Welding is a form of metalwork that helps make things like fences and gates. It is essential in many industries like automotive and construction. In this fabrication process, two or more parts of metal or thermoplastics are joined using heat, pressure and filler material. A slag-free and clean weld is obtained when the process uses MIG shielding gas. The gas prevents the exposure of the molten weld material to Hydrogen, Oxygen and Nitrogen in the atmosphere, and exposure can lead to holes in the weld and excessive spatter. The mechanical properties of the finished weld depend upon the shielding gas.
Welders consider the project goals before choosing a suitable gas for welding. The common gases used are Carbon dioxide, Argon, Oxygen and Helium. The gas used needs to match the connecting wire.
Carbon dioxide is the most common gas used for welding because it is cost-effective and doesn’t require the addition of inert gas. It creates a harsher and less stable arc, provides a deep weld penetration and forms a stronger bead. The gas is used in its pure form because it causes more spatter when combined with other gases and requires more cleanup. Pure CO2 welds suit projects where the aesthetics of the weld is unimportant.
Pure Oxygen is not suitable for welding metals like iron. Only a small amount of Oxygen is blended into CO2 or Argon, and it enhances arc stability. It also improves the weld pool fluidity and penetration when it is used to weld mild steel and stainless steel. The maximum amount of Oxygen added to the shielding gas is 9%. Oxygen causes metal oxidation and is not used to weld aluminium, copper and magnesium.
Argon allows narrow penetration and creates a smooth and fluid arc. Pure Argon is used to weld non-ferrous materials like aluminium and titanium but not used to weld steel. In most cases, welders blend Argon with CO2 or O2. The mixture produces less spatter than 100% CO2. Since Argon is denser than air, it settles over the welded area and protects the molten pool from gas contamination. Generally, it is mixed with other gases for deeper penetration into the metal.
Helium is lighter than Argon with higher ionisation potential. As it is light, it quickly floats away from the weld pool. Therefore the shielding rate gas flow must be doubled, and using helium for welding becomes expensive. Mixing helium with argon makes it more affordable. Helium produces a hotter arc which improves weld penetration and is suitable for connecting thick metals. Moreover, it reduces the porosity of the weld.
Welding projects with a more significant percentage of Argon in the shielding gas mixture provide better results. Pure Argon is not used for welding because it creates an inconsistent and ugly weld. A 75 – 25 mixture of Argon and CO2 gives a cleaner look and is preferred for delicate projects with thin metals.
Things to consider while choosing a shielding gas
- The price of the gas
- Required characteristics of the finished weld
- Cleaning after welding
- Parent metal
- Productivity requirements
MIG shielding gas plays an essential role in welding, and smooth connecting depends on the selection of gas. The heat produced by the arc and the appearance of the weld bead depends on the gas used. When welders use the wrong shielding gas, it results in irregular and flawed welds. And welding is vital in many industries because it provides strong joints by fusing two materials.