MIG welding uses a hand-held gun that contains a spool-fed wire electrode, along with a gas nozzle that delivers a stream of gas to the weld site. This gas prevents the contact of oxygen, nitrogen, and other environmental gases with the weld bead – which helps ensure consistent, strong results.
Contamination can lead to a low-quality weld on your workpiece, so choosing the right gas is absolutely essential for the best results. But what’s the best gas for MIG welding? Unfortunately, the answer is not that simple.
Different metals require different types of gases for the best results, although in most cases, a 75/25 argon and CO2 mix will let you get good results on most metals. But let’s take a look at some of your options now, and discuss how you can choose the right MIG welding gas for your job.
MIG Welding Gas – Choosing The Right Gas
Many MIG welding applications lend themselves to a variety of shielding gas choices. You need to evaluate your welding goals and your welding applications in order to choose the correct one for your specific application. Consider the following as you make your selection:
- The cost of the gas
- The finished weld properties
- Preparation and post-weld clean up
- The base material
- The weld transfer process
- Your productivity goals.
The four most common shielding gases used in MIG welding are Argon, Helium, Carbon Dioxide, and Oxygen. Each provides unique benefits and drawbacks in any given application.
Carbon Dioxide (CO2)
CO2 is, by far, the most common and is one of the only gases that can be used in its pure form without needing the addition of inert gas, such as argon or helium. Because of this, CO2 is the most cost-effective option and a good choice if project costs are a priority.
Pure CO2, also known as 100% CO2, provides a deep weld penetration, making it handy when needing to weld thick materials. That being said, pure CO2 is limited to only the short circuit welding process and produces a less than stable arc as well as more spatter than when it is combined with other gases (also known as ‘mixed gases’).
Pure CO2 is good for projects where the aesthetics of the weld are either not important, or the weld cannot be seen, such as on the underside of a car. Post weld cleanup is also a little more involved.
Argon allows for narrower penetration, which is handy for butt and fillet welds. It also boasts a smooth and relatively fluid arc. If you are going to be welding non-ferrous metals, like titanium, aluminum, or magnesium, you’ll need to use pure argon. Argon is also often mixed with hydrogen, helium, or oxygen. This helps intensify arc characteristics and aid in metal transfer.
If weld quality and aesthetics are important, mixed gases are good to use. You have several options that vary from between 75-95% argon to 5-25% CO2. They produce better arc stability and reduce spatter compared to 100% CO2.
Mixed gases can also be used in the spray transfer process that, in turn, provide more visually appealing welds as well as increased productivity. Argon/CO2 mixtures are good for welding low-alloy, some stainless steel, and carbon metals. Be aware, however, that higher CO2 levels may cause increased spatter.
A reactive gas, oxygen is typically used in small amounts when added to shielding gases, usually between 1-9%. This improves weld pool fluidity, as well as arc stability and penetration in stainless steel, mild carbon, and low alloy metals. It is not recommended to use oxygen with aluminum, copper, magnesium, or other exotic metals since it can cause oxidation.
Oxygen/argon blends are typically used on stainless steel and plain carbon metals. It produces a stable arc with limited spatter. Higher levels of oxygen, however, may make out-of-position welding hard due to the fact that it will increase puddle fluidity.
Generally used on non-ferrous metals, helium can also be used on stainless steel. It works well with thick metals due to its wide and deep penetration abilities. It is usually used in ratios of 25-75% helium to 75-25% argon.
By adjusting these ratios, you can alter the penetration and bead profile. When using stainless steel, helium is usually used in a tri-mix gas combination with CO2 and argon. Helium is also used to prevent oxidation during the welding of metals like stainless steel, aluminum, magnesium, and copper alloys.
Helium does create a hotter arc, which provides faster travel speeds and, thus, increased productivity. That being said, helium is more expensive and does require a higher flow rate than argon does. Weighing out the value of the cost of the gas against productivity rates is important to keep in mind when considering using helium.
Hydrogen serves as a shielding gas in high-temperature applications, such as for stainless steel. It is often mixed with argon for use on austenitic stainless steel.
Nitrogen is used as a purging gas for welding stainless steel tubes. Added to argon in small amounts, it can also be used as a shielding gas for stainless steel.
Propane is typically used in scrap yards for cutting carbon steel where cut quality is not important. If your application does not require high cut quality, propane is a rather cost-effective option.
What’s the Best Gas for MIG Welding Different Metals?
The basic gas for MIG/MAG welding is argon (Ar). Helium (He) can be added to increase penetration and fluidity of the weld pool. Argon or argon/helium mixtures can be used for welding all grades.
If you want a “one-size-fits-all” option, a MIG welding shielding gas with a 75/25 mix of argon and CO2 is likely going to be your best bet. We carry a high-quality 75/25 argon and CO2 mix at Vern Lewis Welding Supply, which is an ideal, cost-effective option that can be used to weld most metals, including mild steel and nonferrous metals.
Getting the Shielding Gas to the Weld Pool
All of your efforts selecting the right shielding gas will be wasted if your equipment isn’t getting the gas to the weld. The MIG gun consumables (diffuser, contact tip, and nozzle) play a crucial role in ensuring that the weld pool is properly protected.
If you choose a nozzle that is too narrow or if the diffuser becomes clogged with spatter, for example, there might be too little shielding gas getting to the weld pool. Likewise, a poorly designed diffuser might not channel the shielding gas properly, resulting in turbulent, unbalanced gas flow. Both scenarios can allow pockets of air into the shielding gas and lead to excessive spatter porosity and weld contamination.
When selecting MIG gun consumables, choose ones that resist spattering build-up and provide a wide enough nozzle bore for adequate shielding gas coverage. Some companies offer nozzles with a built-in spatter guard that also adds a second phase of shielding gas diffusion. This results in an even smoother, more consistent shielding gas flow.
Choosing the right shielding gas for your specific application will require a careful analysis of the type of welding you’re doing as well as your operational priorities. Using the guidelines above should provide a good start to the learning process. Be sure to consult your local welding supply distributor prior to making a final decision.