MIG welding allows for continuous welding and produces cleaner, neater welds. This process uses a continuous wire to create a weld. Unlike other welding methods, there is no need for a filler material here.
But, does MIG welding require gas? What gas should you use, though? Is there one gas that works in all welding applications, or is each gas application-specific? In this article, I’ll answer all questions you might have about MIG welding gas.
Do You Need Gas for MIG Welding?
MIG is short for inert metal gas and refers to a specific welding method. By definition, MIG welding requires gas to function correctly. Here, an inert gas shields the molten metal pool that forms from interacting with the surrounding atmosphere during welding.
Some specialist MIG welding applications use a “gasless” method, although this only refers to external gas used. Here, the flux used is self-shielding, converting to gas as the wire melts. This gas acts as the shield instead of external gas, as in typical MIG welding applications.
In MIG welding, a solid wire is continuously fed to the welding point. This eliminates the need to stop welding from replacing an electrode, as in stick welding. The shielding gas protects the molten metal from exposure to atmospheric oxygen, hydrogen, and nitrogen, which could cause excessive spatter and a porous weld bead. This also reduces the need to clean up during welding.
These factors combine to produce a neat, clean weld joint and save time in the welding process.
Best Gas for MIG Welding
Choosing the correct shielding gas is essential for successful MIG welding. The gas chosen affects the arc stability, weld penetration profile, transfer process, and mechanical properties of the finished product, among other factors. This gas is also application-specific, so no one gas will work equally well in all applications. Often, various gases would work well in one application, making a choice slightly more complex. Some factors to consider in this choice include
- Gas costs can vary wildly.
- Desired properties. The gas affects the finished product.
- Preparation and cleanup.
- Base material.
- Weld transfer process.
- Productivity goals. Gas affects the welding process speed.
Pure argon is a good choice when welding non-ferrous metals, such as magnesium, titanium, and aluminum. Argon allows for very shallow weld penetration, ideal for butt and fillet welds. However, for this reason, it’s not well suited to welding thick elements.
Argon CO2 Mix
Mixing argon and carbon dioxide at a ratio of 75 – 95% argon and 5 – 25% carbon dioxide produces extremely high weld quality. This mixture also reduces post-weld cleanup, reducing the time spent working on a single weld and improving the finished weld’s appearance.
Other advantages of this gas mixture include greater arc stability, puddle control, and reduced spatter. Since this process is compatible with the spray transfer process, it improves productivity.
Carbon dioxide (CO2) is the most commonly used reactive gas used in MIG welding. This is also the only gas that can be used pure, without adding an inert gas to the process. Another factor counting in its favor is that carbon dioxide is generally the least expensive MIG welding option. When using carbon dioxide, you can achieve very deep weld penetration, essential when welding thick material.
Carbon dioxide has some limiting factors, though. The welding arc it produces is less stable than that of other gases. This can be remedied by mixing carbon dioxide with other inert gases, which drives up the cost. Carbon dioxide causes more significant weld spatter and is limited exclusively to the short circuit process.
Helium is generally used when welding non-ferrous metals, similar to pure argon. However, it is also suitable for welding stainless steel. Its weld penetration profile is deep and wide, rendering it ideal for welding thick elements. It is often mixed with argon in a ratio of 25 – 75% helium and 75 – 25% argon. Adjusting these ratios allows you to control the bead profile, penetration depth, and travel speed.
Helium’s arc is hotter than when using other gases. This allows for greater travel speeds, resulting in higher productivity rates.
The limiting factor here is cost since helium is far more expensive than argon and requires a higher flow rate. This means that you will use more helium, further driving up costs. In some cases, this cost increase is balanced by the increased productivity rate – a factor that depends on the application.
Shielding Gas for Different Material
Gas for MIG Welding Aluminum
Pure argon is most commonly used for welding aluminum. A mixture of argon and helium would be used in some cases, although this is not as common.
MIG Welding Gas for Steel
When welding mild steel, pure carbon dioxide is the most commonly used gas. The most common mixture for DIY applications is 25% carbon dioxide and 75% argon due to the improved arc stability.
Shielding Gas for Stainless Steel
When welding stainless steel, a tri-mix of helium, argon, and carbon dioxide is often used. This mixture reduces cost since helium and argon are expensive. It also produces a robust and deep weld that is spread evenly across the entire area. You could also use pure argon.
Gas Pressure for MIG Welding
What is the correct Argon pressure for MIG welding? In MIG welding, we measure the gas flow, not the gas pressure. The pressure provided by the gas canister is constant, usually set between 3 and 8 PSI (20 – 55 kPa). The resultant gas flow depends on the diameter of the nozzle used in each application, which could vary widely. As mentioned earlier, some gases also require a greater flow rate than others, further complicating matters. Since this factor is crucial to successful MIG welding, it is essential to know the required flow rate.
The correct gas flow depends on the nozzle diameter. When using a half-inch (12mm) nozzle, you need a flow setting or 22 – 27 CFH (cubic feet per hour) (623 – 765 LPH or Liters per hour). Industrial applications generally use 5/8 inch (16mm) nozzles, requiring a 30 – 35 CFH (850 – 991 LPH) flow. Alternatively, you could use ¾ inch nozzle with a gas flow of 30 – 40 CFH (850 – 1133 LPH).
Maintaining the correct gas flow rate ensures a smooth weld, which is essential. The insufficient gas flow would create an inefficient shield, allowing atmosphere access to the fresh weld. This contamination would allow harmful chemicals, particulate matter, and other unwanted gases into the weld, negatively affecting its quality. The excessive gas flow would waste gas and potentially create an arc that is too hot. This could also negatively affect the weld’s quality.
When working outside, wind and other environmental factors could affect your weld. Here, you could increase the gas flow rate to block out the wind. This allows for successful MIG welding even in foul weather. Note that this option tends to be more expensive since you would use more gas in this application. If practical, a better option would be to move the part to be welded indoors or set up a windshield around the work area.