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When welding with either MIG (Metal Inert Gas) or TIG (Tungsten Inert Gas) processes, consider the gas that is to be used on the material being welded. Depending on the process you choose, you are not going to want to use the same gas for both MIG and TIG welding.
Why can’t you use the same gas for MIG and TIG welding? You can’t use the same gas because:
- TIG welding mainly requires inert gas for a clean finish and no oxidation, while if an inert gas is used solely for MIG welding, it could compromise the look of the finished weld.
- MIG welding can tolerate semi-inert gas, as it helps with the welding process. However, semi-inert gas has a harmful and somewhat destructive effect on the TIG weld process.
- TIG welding tolerates very few gases, while the MIG welding process can utilize several different gases, as well as combinations of inert and semi-inert.
In welding, there is no single universal welding process that is used for all applications. The method used must vary depending on the type of material being welded and the finish that is desired. These considerations will also influence the type of gas needed.
What is the Purpose of Gas in MIG and TIG Welding?
Shielding gases are used in MIG and TIG welding to protect the weld area from oxygen and water vapor. Oxygen and water in the atmosphere can make the welding process more difficult and cause a deterioration in the quality of the weld.
The shielding gases used are typically denser than air so they can envelop the weld completely. They will also require low flow rates to distribute the gas. There are two primary categories of shielding gas used here — inert gases, also referred to as noble gases, or semi-inert gases, aka active gases.
The use of shielding gases provides several advantages to the welding process:
- Protects the welding arc.
- Allows for welding at higher temperatures without oxidation.
- Allows for very little loss of alloying elements as the metal transfers across the arc.
- Reduces complications such as burn-in and spatter.
- Adjustments to the number of gases can be made to fit the material being welded.
Effects of Shielding Gas
Shielding gases primarily protect the liquid metal pool from atmospheric contamination and allow for a clean weld. They remove the potentially reactive gases such as oxygen and nitrogen from the vicinity of the weld. They can also stabilize the arc and enhance the metal transfer mode.
Also, shielding gases can change the basic mechanical properties of the weld area through the interaction with the base metal and filler metal. This will affect the strength, hardness, and corrosion-resistance of the weldment.
What Are the Different Types of Gases Used for MIG and TIG Welding?
As we said before, inert (noble) and semi-inert (active) are the two kinds of gases. Understanding the difference between the two will help you understand why different gases are used in MIG and TIG welding.
An inert gas has no effect on, or reaction with, the welding process. It simply performs the important task of replacing the air in the atmosphere from around the weld pool, keeping it free from oxidation and contamination.
The TIG welding process requires this, as it is known for its clean, attractive finish. The shiny, rope-like or “stack-of-dimes” appearance is achieved by a well-protected gas shield. Also, since inert gas prevents oxidation, it will protect the TIG weld from oxidizing — if the weld is allowed to oxidize, it will fail.
If inert gas is used for MIG welding (except for aluminum), higher machine power output will be needed to achieve penetration and the finished weld will look too tall because the surface tension hasn’t been broken.
Semi-inert or active gases do have an effect on the welding process — which is not preferred for TIG welding. In fact, if an active gas is used for TIG welding, the raised arc voltage will increase spatter and hole blows and cause excessive burning of the tungsten electrode.
Active gas affects MIG welding more positively. When mixed with inert gas, it makes it slightly electrically conductive which, in turn, raises the arc voltage and increases the weld penetration.
Also, active gas can break down the surface tension of the molten weld pool, allowing the molten weld pool to flow better and flatten properly.
What Are the Specific Gases Used for MIG and TIG Welding?
With very little understanding of shielding gases, one might believe that any gas could be used for any job. This, however, is absolutely not the case.
Each welding job is going to require a shielding gas specific to it. This is why it’s important to understand which gases can be used to shield what materials. In this instance, however, MIG and TIG do have gases that work well for each one respectively.
There are few shielding gases that are used the most in MIG welding: Oxygen, Carbon Dioxide, Helium, and Argon. Each of these gases falls into one of those primary categories: inert or active. Oxygen is an active gas, but Argon is inert. This distinction plays a role in how each gas affects the weld.
Carbon Dioxide (CO2) is the most commonly used active gas in MIG welding. It is also the only one that can be used in its pure form without the addition of inert gas.
CO2 is also the least expensive gas, making it an attractive choice when material costs are the main priority. Pure CO2 provides intense weld penetration, which is useful for welding thicker material. However, it produces a less stable arc and more spatter.
Argon and CO2 mixed together will give a better weld quality and appearance, as well as reducing post-weld clean up.
A mixture of between 75 to 95 percent Argon and 5 to 25 percent CO2 will give better arc stability, puddle control and reduced spatter. This mixture also allows for higher productivity rates and more visually appealing welds.
Argon produces a narrower penetration profile, which is useful for fillet and butt welds. If you are MIG welding a non-ferrous metal such as aluminum, magnesium or titanium, you’ll need to use 100 percent pure Argon for the job. For most other MIG welding jobs, pure Argon is not preferred.
Oxygen can be used in low amounts, as they can improve penetration and the fluidity of the weld pool. This gas has drawbacks, however, as it is the main cause of oxidation.
This is why Oxygen is only really recommended to be used with a minority of metals, including stainless steel. Most metals, like copper or aluminum, will most likely become too oxidized.
Stainless steel, as well as non-ferrous metals, can also be shielded by Helium. This gas is usually used in a mixture with Argon with non-ferrous materials.
The amounts of each used are totally dependent on what kind of result you’re looking for. If you are trying to use Helium with stainless steel, however, the addition of CO2 is going to be necessary.
The Helium makes the arc burn more powerfully, but this usually means that you will need to use more Argon, which will cost more. This is a more productive weld than it probably would be with just Argon shielding and this mixture has the ability to work with much thicker metals. It’s important to be able to weigh the benefits of using the mixture next to the cost and see if it’s worth it.
Unlike MIG welding, there are relatively few gases that can be used for TIG welding. Although some of the gases used are the same, MIG uses more combination gases (mixing inert and active).
Argon gas is the most popular and widely used inert shielding gas for TIG welding. It can be used on every type of metal, including aluminum.
Pure Argon provides excellent arc stability and requires less cleaning action as the arc is narrow and concentrated, giving you a precise weld without a lot of bead rollover. It will also produce a completed weld with a brighter, shinier surface appearance.
Argon and Helium, as a 50-50 mix, allows for hotter welds which can create a more full heat profile and better heat conduction. It can be used for specialized applications but, because of the added heat, you’ll have to carefully monitor the weld to make sure you are not burning through the metal.
The use of pure Helium, or a 90 percent Helium to 10 percent Argon mix, is used primarily for TIG welding with direct current electrode negative (DCEN).
Hydrogen may be used in some cases because it increases the heat input while welding. It creates a hotter, wider bead that penetrates deeper into the metal. This is advantageous when working with stainless steel.
While MIG and TIG welding does share some similarities as processes, they are definitely different when it comes to shielding gas needs. Understanding each process deeply is going to help you understand which gas is best for the job that you are working. Hopefully, this article could shine some light on what the best gases are in these instances!