The oxygen needed to be kept away from the weld pool as it may lead to oxidation at the welding site. The shielding gas is the answer to the problem of oxidation as the shielding gas will replace the oxygen-containing air which is present all around us and weld pool as well. The shielding gases prevent from exposure to oxygen, nitrogen, and hydrogen from the atmosphere leading on to a variety of the problems like porosity in weld bead and excessive formation of spatter. There are two categories of shielding gases Inert and semi inert. The two inert gases helium and argon are cost-effective to use in the welding process of Tig welding and Mig Aluminum welding. The semi inert or active shielding gases are Co2, O2, Nitrogen, and Hydrogen. The active gases like Co2 in small and controlled quantity can improve the GMAW weld characteristics.
Difference between Inert and Active Gases; The inert gas such as Argon gas has no effect on or with the welding itself as it replaces the air or oxygen away from the weld pool. The active gases always have effects on the welding process and welding results. In the Mig welding process, the Co2 breaks down the surface tension of the molten pool of welding the same as water change to a drip by breaking the surface tension. The molten weld pool flows and flattens for the correct weld deposit. The Mig welding application generally need active gases thus called as Metal active gas or MAG or Metal Active Gas rather than Mig which is Metal Inert Gas
The Common Used Gases: The most common active gases which are being used are Co2 as 100% and a mixture of Argon and Co2. The active gases are used primarily for the Mig welding process for most of the metals except Aluminum and Mig Brazing. The Co2 is the cheapest active gas or the welding process. The shielding gas as Co2 produces a cool, coarse, better spatter arc and hard weld deposit. The Co2 at 100% may not produce desirable result on very thin material as well as thicker material for which Argon and Co2 mix produces better and superior results as arc here become softer, smoother and resulting weld deposit become slightly soft and more malleable.
The active gas in Tig welding process will raise arc voltage which will result in excessive burning of tungsten electrode and increase hole blows. Now inert gas in Mig welding needs higher machine power output to achieve the required penetration and finished weld may look tall as surface tension is not broken properly.
There are several different mixes of argon and Co2 available in the market. The 95%% argon and 5% Co2 is the ideal for the Mig welding up to 8 mm steel. The 8-25 mm steel may need 90% argon with 10% Co2 while 80% argon with 20% Co2 may be ideal for the Mig welding of 20mm or more.
Gases Towards Weld Pool: The weld pool is the place where these gases are required so the efforts should be such that gases may be supplied with all its might at the weld pool.The consumable n the Mig gun like diffuser, contact tip and nozzle needs to check properly for the quality and how properly they are fitted in to its places. The improper fitting may lead on to clogging with spatter. The bad diffuser may lead on to with turbulent , unbalanced gas flow.