Selecting the right welding gas - Shielding gas guide for MIG and TIG welding
Selecting the right welding gas for your MIG and TIG application can make or break your project.
The reason for this is simple - different metals have different properties.
Metals therefore react differently to the elements in the oxygen in the air once they begin to melt during a welding process.
A welding gas, or shielding gas, is designed to protect your metal from contamination once it begins melting and thus protect the integrity of your weld.
Without the appropriate welding gas your metal can contaminate and your welding join can become frail overtime.
So, with that in mind, lets talk about welding gas or shielding gas.
The appropriate welding gas for welding a particular metal will differ depending on whether you’re MIG or TIG welding.
The thickness of the metal must also be taken into account.
Before we talk about the different welding gas combinations that are appropriate for different metals, it is worth getting to know some basic information about the different gases themselves.
The most commonly used welding gas for MIG and TIG applications. Can be used pure or mixed with other gases. Argon is colourless, odorless and non-toxic gas. It composes 93% of the earths atmosphere but it can create an oxygen and nitrogen free inert shield, making it appropriate for welding a wide range of metals and alloys. It is frequently mixed with Hydrogen (H2), Carbon Dioxide (CO2), Helium (He) and Oxygen (O2) to optimise the quality of a weld depending on the thickness and characteristics of the metal.
Helium is an extremely light and non-flammable gas. In fact it is the second lightest gas behind hydrogen. It is odorless, non-toxic and tasteless. Its primary function as a welding gas is to provide an inert shield and prevent contamination through oxidisation for a wide range of metals. These include stainless steel, aluminum, copper and magnesium alloys.
CARBON DIOXIDE (CO2)
Carbon Dioxide is an odorless, tasteless, and nonflammable gas which is found in the earth’s atmosphere. As a welding gas it is commonly combined with argon (Ar) as an inert shield for low alloy steels, mild steels and carbon steels.
Once again it is non-toxic, odorless, colorless and tasteless. It is the lightest of welding gases. As a welding gas, hydrogen is commonly combined with Argon for high temperature metals, especially stainless steel. It is commonly used in plasma cutting processes.
Occasionally used as a welding gas, usually in combination with argon for use on duplex stainless steels. Nitrogen is again colorless, odorless, and non-toxic. It is non-flammable at normal atmospheric temperatures. Propane
OK, Now that you now the basic about the main gases used in welding, lets talk about which ones and which combinations, are appropriate for the metal you want to weld. Let’s start with MIG welding
MIG welding of Mild Steel
If you’re looking for an all-purpose Mild Steel welding gas an Argon-Co2 combination is your best option. Argon-CO2 blends produce minimal spatter, a nice bead appearance is forgiving on thinner mild steels meaning it is less likely to burn through. eWelders sells an 86% Argon-14% Mild Steel welding gas from Ross Welders which we recommend as an all purpose mild steel gas. We sell these in 12 x 1120g cylinder bulk packs at an extremely competitive price and include free shipping to save you money. Click here to view this product. As an alternative you can use a pure Co2 mix. This will provide a deeper weld penetration but will result in a rougher weld than if you use a Argon-Co2 mix. It is therefore worth keeping in mind depending on the project. eWelders sell a pure Co2 welding gas bulk pack here.
If you’re looking for an optimum welding gas combination depending the thickness of the mild steel, different Argon-Co2 combinations are available from specialist gas dealers.
Here is our is recommendation:
0-4mm Mild Steel: 93% Argon, 5% Co2, 2 % Oygen (O2)
4-12mm Mild Steel: 84-86% Argon, 14-16% Co2 (Click here)
12mm+ Mild Steel: 78%Argon, 20% Co2, 2% O2
MIG welding of Aluminium
Argon is generally the go to gas for aluminium welding, whether you’re TIG welding, or MIG welding. We recommend you use a pure argon shield when welding aluminium base metals less the 15mm thick. eWelders provide free shipping on 12x1120g cylinders bulk packs of pure argon for $379. This represents super value for welders who regularly weld aluminium.
For welding thicker metals a helium mix can be added to increase the penetration. Start at about 20-25% helium for 15mm thick and then increase the helium content as the aluminium gets thicker. Helium mixes will increase the price of the welding gas shield, in comparison to argon.
DO NOT use a welding gas containing any Carbon Dioxide or Oxygen when welding aluminium, regardless of whether you’re using MIG or TIG process at it will contaminate the metal and affect the weld quality.
MIG welding of Stainless Steel
Stainless steel does have different properties to mild steel.
These need to be taken into account when selecting your welding gas shield. However, it is far less fickle than aluminium and the welder has various shielding gas options.
An Argon-Co2 blend will provide good results on common stainless steels.
But stainless does contain a higher level of chromium which increases its resistance to corrosion. This contributes to a slightly higher melting point than mild, carbon-based steels.
For this reason many welders opt to use a helium combination as helium conducts more heat and increases the weld penetration. Helium will increase weld speed but won’t necessarily translate to cost saving because it is more expensive than Argon and creates higher consumption rates.
For high quality welds consider an argon-helium-Co2 blend with about 25-33% helium and 1 Co2. This will create a high travel speed, better control of distortion in thin material, and superior bead shape.
Mig welding of stainless steel to Mild Steel
Consider a Argon-Co2-helium blend contain 25-33% helium and 1% Co2.
Pure argon is generally the welding gas of choice for use as a shield when using the TIG process. TIG welding is generally suited to welding stainless steels and aluminium. When welding aluminium, a pure argon gas such as this one can be effectively used for metals up 18mm thick.
Once the aluminium base metal exceeds this width it is worth adding a helium blend to increase weld penetration. We recommend a 75% Argon 25% helium blend for aluminium welds thicker than 18mm.
A similar principal applied when choosing a welding gas shield for TIG welding of stainless steel. Pure argon can effectively be used for a width of up to 8mm. Once the stainless steel exceeds this width add switch to an argon-helium blend.