How to Set Gas Pressure For MIG Welding With Charts And Explanations

Although MIG welding is one of the most straightforward methods, creating solid and uniform MIG welds takes time. The process starts with weld preparation and choosing the right consumables and accessories for the job.

One of the essential parts of MIG welding is shielding gas. But making a sound weld is more than just choosing the right shielding gas. You will also need to adjust the gas flow for the given MIG welding application.

In this article, we'll explain how to set gas pressure for MIG welding and discuss the factors that affect the recommended gas flow.

Source: https://www.youtube.com/watch?v=f41Zr_R9oO8

Can You MIG Weld Without Shielding Gas?

The short answer is no. You cannot MIG weld without a shielding gas. MIG welding, also known as Gas Metal Arc Welding (GMAW), uses an unshielded solid MIG wire.

You will need an external shielding gas to protect the molten weld puddle and wire from atmospheric contamination. MIG shielding gases , such as Argon or CO2, create a protective layer. This layer prevents atmospheric gases such as Hydrogen or Oxygen from entering the molten weld puddle and creating defects such as porosity.

Source: https://www.youtube.com/watch?v=24wiLU7JwZs&t=388s

Using and choosing the right shielding gas for the given MIG welding applications is not the only issue. You will also need to adjust the pressure or the shielding gas flow.

Shielding Gas Flow Rates (CFH or l/min)

Shielding gas flow measures the volume of shielding gas delivered through the MIG gun per unit of time. In the States and most literature and blogs, shielding gas flow is expressed in cubic feet per hour (ft3/h, or CFH). We will also use this rate to recommend the flow rates in this article.

However, keep in mind that some regulators and sources outside the US (commonly Europe) use liters per minute (l/min). Although l/min-rated regulators are also precise, you will have to use online converters or a conversion rate of 1:2,1188 (l/m:ft3/h) to follow the literature.

Source: https://www.mig-welding.co.uk/

That’s why we recommend sticking to widespread CFH gas flow regulators.

How to Set Shielding Gas Pressure For MIG Welding

To adjust the shielding gas flow, you will need a meter, such as the YesWelder QB01 Argon/CO2 Gas Flow Regulator . Install the regulator on the shielding gas cylinder and connect the hose to your MIG welder.

QB01 Argon/CO2 Welding Flow Meter Gas Regulator

The gas regulator typically has two gauges or a gauge and a square flow tube with a metal ball. The first gauge measures the cylinder's pressure in PSI, which helps you read how much shielding gas is left in the bottle. The other gauge, or, in the newer regulators, the square flow tube, measures the shielding gas flow in CFH. This vertical plastic tube has a small ball inside.

To set the pressure, open the valve on your cylinder and then the valve on your regulator. As you open the regulator valve, gas flows through a square tube. The pressure makes the ball rise, allowing you to read the current flow in CFH. You can open the valve further to increase the flow or close it to decrease it.

Set the Gas Pressure for MIG Welding
Source: https://www.youtube.com/watch?v=SRNWAzGElrA

Regulators that show the flow on the gauge are also available. However, they use needles and springs that may get stuck, so we definitely recommend the square tube regulators.

Dual-flow welding regulators, such as YesWelder WX-AR564-CGA580, allow you to attach two individual welding machines to a single-cylinder bottle. These regulators have one pressure gauge and two square flow tubes. The indicator also reads the pressure of the Argon bottle. You attach the two welders to two separate tubes and use the valves to adjust the gas flow individually.

WX-AR564-CGA580 Dual Flow Welding Regulator

What is the Recommended MIG Shielding Gas Flow?

The recommended MIG Welding gas pressure for mild steel is 15-20 CFH. However, this is just a suggested flow for the general indoor, mild steel applications. There are a series of factors that can affect the recommended MIG shielding gas flow, with the most important being the following:

• Welding conditions

• MIG gun nozzle size

• Metal type

• Shielding gas type

Each factor will tune the recommended gas flow up or down, depending on the MIG welding applications and conditions. So, let's explore the suggestions further.

Source: https://www.youtube.com/watch?v=Wc1lmkCclGs

Welding Conditions And Shielding Gas Pressure

Welding conditions can significantly impact the recommended MIG shielding gas pressure. The essential factors will depend on whether you are welding indoors or outdoors. When welding indoors, inside the garage, or in a workshop with little to no draft, you can use lower shielding gas rates. A pressure of 10-15 CFH will do just fine.

Indoors MIG Welding Process
Photo by @handf4b (TikTok)

In indoor applications, there is little to no wind or draft. Since there is no or low natural air movement, the draft won't blow away the shielding gas away from the weld. As a result, you don’t need a flow higher than 15 CFH. However, as a rule of thumb, you should never go below the minimum gas flow rate of 10 CFH, even though you are welding in suitable environmental conditions.

When there is a draft or natural air movement in your workshop, you should increase the gas flow to 20-30 CFH. By increasing the rates, you reduce the risk of draft or wind blowing the protection and supply a solid protective layer.

MIG welding outdoors is usually not recommended, as the wind blows away the shielding gas. If you have to use MIG for outdoor welding, increase the rates to 30-35 CFH or the maximum rate supported by your nozzle. But keep in mind that you won’t always get defect-free welds when MIG welding outdoors. A better solution is to use self-shielded processes such as Flux-cored arc welding or stick welding when welding in on-field applications and repairs.

Flux-cored arc welding is commonly used in field applications and repairs.
Photo by @gtbb.nick (TikTok)

MIG Gun Nozzle Size

The nozzle is an essential part of the MIG welding gun. It directs the gas into the weld puddle and protects the contact tip. Nozzles come in various shapes, material types, and sizes. There are bottle-form, conical, and cylindrical nozzles, each with its advantages and disadvantages.

Some Types of MIG Gun Nozzle
Source: https://www.superiorconsumables.com/mig-welding-nozzles/

While different nozzle types show different shielding gas coverage in various applications, the size will affect the recommended shielding gas pressure.

As a beginner or everyday welder, you are likely to use 3/8" nozzles. These are typical for small welders and household applications, and they require an average of 18 to 22 CFH gas flow.

1/2" nozzles are next in line, and they are specific for higher-rated home MIG welders. Using a 1/2" nozzle requires an average gas flow of 22 to 27 CFH. 5/8" nozzles are installed in industrial welders and MIG torches. These are cylindrical/straight nozzles that require an average of 30 to 35 CFH to provide proper shielding gas coverage.

Finally, there are large industrial nozzles sized 3/4". These operate at high heat of 400-600 amps and require an average gas flow rate of 30 to 40 CFH. If needed, maximum rates can reach up to 65 CFH to provide better gas coverage.

Source: https://www.uti.edu/blog/welding/mig-welding-nozzles

Shielding Gas Flow Based On Metal Type

You can use MIG to weld a wide variety of metals, with the most popular being mild steel, stainless steel, or aluminum. These are the most common metals you'll encounter in your home, hobby, or DIY welding. However, unlike with TIG, you cannot weld other non-ferrous metals.

MIG Welding DIY Project—A Trolley
Photo by @@zetianrongjie (IG)

Welding each type of metal requires a different approach, including the choice of shielding gas and gas flow rate. Here is how to adjust the MIG gas pressure based on the metal type.

Mild Steel MIG Gas Flow

Mild steel is one of the most forgiving metals to weld. Combined with MIG welding, you won't have too many issues during the welding. The same rules apply to choosing the gas and adjusting the gas flow.

You can successfully MIG weld mild steel using Argon, Argon/CO2 mixture, or pure CO2. Most welders recommend a C25 mixture of 75% Argon and 25% carbon dioxide (CO2). This mixture provides a good balance between arc stability, penetration, and cleanliness.

The difference between MIG welding with a 75/25 Argon mix and 100% CO2.

Pure CO2, or 100% CO2 shielding gas, is an economical choice. The mixture produces deeper penetration, which is ideal for thicker metal but somewhat worse weld aesthetics.

When using a C25 mixture or pure CO2 to MIG weld mild steel, you should start with 10-15 CFH. This is a good starting point for indoor welding with no draft, but if you notice any porosity, increase the flow to 20-25 CFH. This rate should be more than enough to finish any mild steel welding project.

8.0mm Carbon Steel MIG Welding with 100% CO2 Shielding Gas
Photo by @perfectwelders (TikTok)

MIG Welding Stainless Steel Gas Flow

Stainless steel is more tricky to weld. Some say that thin stainless steel can distort even if you look at it wrong. The reason is high thermal expansion and low thermal conductivity. Stainless steel quickly picks up and holds excessive heat, causing distortion and loss of corrosion-resistant properties.

To MIG weld stainless steel, welders use a mixture of Argon and Oxygen (98% Ar and 2% O2) or a helium-rich tri gas mixture of Helium, Argon, and CO2 (85-90% He, 10% Ar + 2-5% CO2). MIG welding stainless steel requires a recommended starting gas flow of 20-30 CFH.

MIG Welding Stainless Steel Process
Photo by @foreverfab_mn (TikTok)

Using a helium-rich tri-gas mixture requires special care and higher gas flow. Helium conducts heat better, so it can overheat the metal without proper heat control. However, Helium is lighter than Argon or CO2, which is why welders recommend higher gas flow rates.

Low flow will cause Helium to float above the weld puddle rather than provide proper protection. That's why gas pressure requires a bit of tweaking to prevent porosity and carbide precipitation.

MIG Welding Aluminum Gas Flow

Aluminum is one of the trickiest metals to weld. Welding requires proper heat control and exceptional cleanliness. To MIG weld aluminum, you will need high purity, inert, or non-reactive shielding gas such as Argon or Helium. MIG welding thin aluminum requires 100% Argon, while thicker sections often use a mixture of 75% Argon and 25% Helium.

MIG welding aluminum with 100% Argon requires higher wire feed speed and travel speed. As a result, you also need a higher shielding gas flow of 30 CFH. A higher gas flow rate is necessary in order to provide proper coverage during high-speed welding.

MIG Welding Aluminum with 100% Argon
Source: https://www.youtube.com/watch?v=kCgm3bVDsMw

When MIG welding thick aluminum with 75% Argon and 25% Helium, you will need even higher rates. Once again, Helium is lighter than Argon, so you will need approximately 50 CFH to ensure it reaches the weld puddle and stays there.

Shielding Gas Type and Gas Flow

As noted in the text, some shielding gases are lighter, denser, or heavier than others. For example, Helium is much lighter than Argon or CO2, so it requires higher rates to reach and stay in the weld puddle.

Keep in mind that you will need different regulators when using various MIG shielding gas types. In most cases, Argon and CO2 are measured equally, so you will find calibrated Argon/CO2 regulators. Using Helium with an Ar/CO2 regulator can cause inaccurate measurements.

Choose the Right Regulator
Source: https://www.youtube.com/watch?v=JL3BPU1shd4

In addition, if you MIG weld with 100% CO2, you will need a designated carbon dioxide regulator. Pure carbon dioxide reaches low temperatures as the gas expands, so it can cause frost build-up or even freeze your Argon/CO2 regulator.

Keep in mind that CO2 bottles use a CGA-320 connector, while all other cylinders and Argon/CO2 regulators use CGA-580 fittings. If you decide to plug the Ar/CO2 regulator into the CO2 bottle, make sure you have a CGA-320 to CGA-580 adapter.

How a CGA Connector is Used for Connecting any Cylinder Valve
Source: https://www.youtube.com/watch?app=desktop&v=5oZNgUa130k

Minimum and Maximum Gas Flow Rates

The final goal of setting the gas flow is to use enough MIG gas pressure to fill the nozzle and provide consistent shielding gas coverage. Using less gas than recommended causes a lack of gas and defects such as porosity, discoloration, or atmospheric air contamination.

Source: https://fractory.com/mig-welding-explained/

The minimum gas flow rate for mild steel is 10 CFH. You can use it when welding mild steel indoors without draft or natural air movement. When MIG welding aluminum or stainless steel, you shouldn't use less than 20 CFH. As a rule of thumb, you shouldn't use less than 10-15 CFH, but if you notice porosity, you should tune it up to 20-25 CFH.

On the other hand, using too much shielding gas is also not an option. Due to the venturi effect, using too high flow causes turbulence that sucks in the atmospheric contamination instead of deflecting it. Therefore, high flow rates can also cause porosity and surface contamination.

The nozzle size dictates the maximum gas flow rate. For the small 3/8 "and 1/2" nozzles, you shouldn't exceed 30-40 CFH. Meanwhile, larger nozzles can handle 55 to 65 CFH without causing contamination. If you notice porosity when using high rates, try reducing the gas pressure.

Final Thoughts

Choosing the adequate shielding gas flow is crucial for any MIG welding application. Even if you choose the right shielding gas type, the flow itself can make or break the project.

MIG welding mild steel in indoor applications typically requires low rates of 10-15 CFH, but you can tune it up to 20-25 CFH if there is a draft. MIG welding aluminum requires higher rates, as you need higher wire feed speed and welding speed to avoid distortion. Start with 25-30 CFH, and tune it up if you notice porosity.

Metal types are not the only ones responsible for the gas flow adjustments. You'll also have to consider nozzle sizes, gas types, and environmental conditions. Based on all the factors, you should adjust the valve to get the best results.

The final goal is to get consistent, solid, and uniform welds. Small holes (porosity), discoloration, or surface defects are a sign your gas coverage is wrong, so you'll have to increase or decrease the gas pressure.