Shielding Gases for TIG & MIG Welding: which gas is best?

Welding is a process of joining metals by melting them with an electric arc and a filler material. However, the arc and the molten metal are vulnerable to contamination from the air, which can cause defects and reduce the quality of the weld. To prevent this, welders use shielding gases to create a protective atmosphere around the arc and the weld pool.

But not all shielding gases are the same. Depending on the type of welding, the metal being welded, and the desired outcome, different gases or gas mixtures may be more suitable than others. In this article, we will explore the most common shielding gases for TIG and MIG welding, and how to choose the best gas for your project.

I. What is TIG Welding?

TIG welding, short for Tungsten Inert Gas welding, is an arc welding process that produces the weld with a non-consumable tungsten electrode. This type of welding is versatile, allowing professionals to join a large range of materials. However, it is a much slower process compared to MIG welding, resulting in greater costs and longer lead times. It is important to note that this form of welding requires highly specialized training to ensure a precise and accurate outcome.

II. What is MIG Welding?

MIG welding, also known as Metal Inert Gas welding, is a welding method in which the filler metal supplies the electric current to maintain the arc. Generally used for thicker materials, MIG welding is quick and cost-effective. Although this method is easier to learn, its welds are not as precise as those done by TIG.

III. What are the Best Shielding Gases for TIG Welding?

The most commonly used shielding gases for TIG welding are argon and helium or a mixture of the two. Occasionally, other gases like hydrogen, nitrogen, oxygen, and carbon dioxide are added. However, these additions are rarely justified and can impair the weld quality if not properly used.

1) Argon

Argon is a noble inert shielding gas, so it doesn’t chemically interact with the weld metal, tungsten electrode, or filler wire. An “inert” gas means it doesn’t react with the metal or negatively affects the completed joint properties. Since it’s denser than air, argon settles over the weld pool and protects the molten metal from air contaminants. But, it only works well in a flat welding position where gravity helps keep the heavy argon in place. The high argon density hinders the coverage if you make out-of-position welds (overhead). A simple way to solve the overhead issue is to use a higher gas flow rate, increasing costs. Argon is easy to ionize, which helps arc starting characteristics and keeping a stable arc, even if you use an extended arc length. Additionally, argon permits cathodic cleaning action, making welding aluminum possible with alternating current.

Using 100% argon gets the job done 90% of the time. Argon is a suitable shielding gas choice for TIG welding mild steel, stainless steel, aluminum, magnesium, etc. It’s also cheaper than other gases and more readily available. So, unless you benefit from helium or other gases listed below, a pure argon gas bottle will be your best friend for TIG welds.

2) Helium

Helium, like argon, is an inert gas. However, it impacts the weld differently than argon since helium has a higher thermal conductivity. Thus, it increases heat input into the joint. As a result, penetration and welding speed improve, and the resulting bead has a higher depth-to-width ratio. However, welding with a 100% helium shielding gas is usually employed with automated TIG operations rather than manual welds. Helium has a lower ionization potential, making a long arc challenging to keep. Therefore, it’s difficult to manually dab the filler wire into the molten weld pool because the tungsten tip is too close to the liquid puddle. Pure helium is not the best choice for manual TIG welding. Also, helium is more expensive than argon and lighter than air. To keep the weld protected in the flat welding position, you must use twice the gas flow as compared to argon.

A common solution is to use a mixture of helium and argon, which combines the benefits of both gases. The most commonly used mixture is 75% He and 25% Ar. This blend provides better penetration, faster welding speed, and wider coverage than pure argon. It also reduces the cost and the gas flow rate compared to pure helium. This mixture is ideal for welding thick sections of aluminum, copper, nickel, and titanium alloys.

3) Hydrogen

Hydrogen is not an inert gas, but it can be added to argon in small amounts (up to 5%) to improve the weld quality. Hydrogen stabilizes the arc, increases the heat input, and cleans the surface oxides. This results in better penetration, faster welding speed, and a smoother weld appearance. However, hydrogen can also cause porosity, cracking, and embrittlement if used excessively or on unsuitable metals. Hydrogen should never be used on carbon steels, low alloy steels, or copper alloys, as it can cause hydrogen-induced cracking. Hydrogen is mainly used for welding austenitic stainless steels, duplex and super duplex stainless steels, and nickel alloys.

4) Nitrogen

Nitrogen is another gas that can be added to argon in small amounts (up to 2%) to enhance the weld properties. Nitrogen increases the strength, hardness, and corrosion resistance of the weld metal, especially for duplex and super duplex stainless steel. However, nitrogen can also cause porosity, cracking, and loss of ductility if used excessively or on incompatible metals. Nitrogen should never be used on carbon steels, low alloy steels, or aluminum alloys, as it can cause nitrogen-induced cracking. Nitrogen is mainly used for welding duplex, super duplex, austenitic stainless steels, and copper.

IV. What are the Best Shielding Gases for MIG Welding?

The most commonly used shielding gases for MIG welding are carbon dioxide, oxygen, helium, and argon or a mixture of these gases. The choice of gas depends on the type of metal, the thickness of the material, the welding position, and the desired weld appearance.

1) Carbon Dioxide

Carbon dioxide is the cheapest and most widely available shielding gas for MIG welding. It is not an inert gas, but an active gas that reacts with the molten metal and creates carbon monoxide and carbon dioxide. This reaction helps to stabilize the arc and increase the penetration. However, it also produces more spatter, fumes, and a rougher weld appearance. Carbon dioxide also causes more arc instability and a narrower weld bead. Carbon dioxide is mainly used for welding carbon steels and low alloy steels, especially in short-circuit transfer mode.

2) Oxygen

Oxygen is another active gas that can be added to argon in small amounts (2-5%) to improve the weld quality. Oxygen enhances the arc stability, the penetration, and the wetting action of the weld pool. This results in a smoother weld appearance, less spatter, and a wider weld bead. However, oxygen can also cause oxidation, porosity, and loss of corrosion resistance if used excessively or on unsuitable metals. Oxygen should never be used on aluminum, magnesium, copper, or titanium alloys, as it can cause severe oxidation and burning. Oxygen is mainly used for welding carbon steels, low alloy steels, and stainless steels, especially in spray transfer mode.

3) Helium

Helium, as mentioned before, is an inert gas that increases the heat input and the penetration of the weld. It also produces a smoother and flatter weld appearance, less spatter, and a wider weld bead. However, helium is more expensive than argon and requires a higher gas flow rate. Helium is mainly used for welding aluminum, copper, and nickel alloys, especially in spray transfer mode.

4) Argon

Argon, as mentioned before, is an inert gas that provides a stable arc and a good weld appearance. It also produces less spatter, fumes, and oxidation than carbon dioxide or oxygen. However, argon has a lower heat input and penetration than helium or carbon dioxide. Argon is mainly used for welding aluminum, magnesium, stainless steel, and titanium alloys, especially in pulsed spray transfer mode.

V. Conclusion

Choosing the best shielding gas for TIG and MIG welding is not a simple task. It requires careful consideration of the factors that affect the weld quality, such as the type of metal, the thickness of the material, the welding position, and the desired weld appearance. The most common shielding gases are argon, helium, carbon dioxide, oxygen, hydrogen, and nitrogen, or a mixture of these gases. Each gas has its advantages and disadvantages, and some gases are more suitable for certain metals than others. The table below summarizes the main characteristics and applications of each gas.

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