MIG Welding Gas Selection: Your COMPLETE GUIDE [2021] (2023)

MIG Shield Gas Selectionit is extremely critical to the quality of all your soldering.

Understanding this importance led us to produce this EXCLUSIVE guide on selecting MIG Shield Gas for your projects.

After reading this guide you will understand:

• Why do we need shielding gas for MIG welding.
• A list of 10 factors that influence your choice of MIG Welding Gas.
• 03 Fundamental properties of MIG welding gas.
• 04 Basic Types of Gas MIG Welding

Ready for new knowledge? Let's go!

Why do we need shielding gas for MIG welding?

The main purpose of using shielding gas tosunny day meIt is to protect the welding area from gases in the air, such as oxygen, nitrogen, hydrogen, propane, etc.

Without the application of shielding gas, your weld pool will be exposed to gases and contaminants from the atmosphere.

This exposure causes some welding defects, such as: fusion defects, porosity (holes inside the weld bead), metal embrittlement and excessive spatter.

In contrast, using a suitable shielding gas produces cleaner and faster MIG welds:

• Cleaner welds are due to protection from atmospheric contaminants as mentioned above.
• Faster welds are possible thanks to the absence of interruptions between weld runs to replace contaminated electrodes (as in the case of stick welding).

TEN FACTORS THAT INFLUENCE YOUR SELECTION OF MIG WELDING GAS

The use of shielding gas in MIG welding has proven to be extremely effective.

However, the proper choice of MIG welding gas is influenced by many different factors.

We've researched and compiled the following list of 10 factors that all manufacturers should carefully consider before selecting shielding gas for their MIG projects.

Here is the list:

• Factor 1: TheMIG welding wire selection.
• Factor 2: The mechanical characteristics of the deposited weld metal.
• Factor 3: The thickness and type of joint on your workpiece.
• Factor 4: The condition of your workpiece (whether mill scale, oil or corrosion).
• Factor 5: TheMIG metal transfer modes.
• Factor 6: The welding position.
• Factor 7: The mounting conditions.
• Factor 8: The desired penetration profile.
• Factor 9: The desired appearance of your weld bead.
• Factor 10: The total cost (perhaps the most important factor of all).

A shortcut to optimal shielding gas selection is to consult your MIG wire supplier.

Give your supplier a good idea of ​​the details of your MIG welding project so they can offer you some suitable options, taking into account many of the above factors.

Also, be sure to check out the MIG welder recommendation guide found atindoor panel welder.

THREE Fundamental Properties of MIG Welding Gas

In this part you will learn about 03 fundamental properties of MIG Welding Gas, which are:

• Ionization potential.
• Thermal conductivity.
• Chemical reactivity with the molten solder puddle.

1. Shielding gas ionization potential

The ionization potential refers to the amount of energy required to ionize the shielding gas.

Energy is measured in eV (electronvolt).

You may ask, why do we need to ionize the gas?

Well, ionization helps make the shielding gas conductive (a conductor of heat and electricity).

When the shielding gas is conductive (i.e. a plasma), it can transfer heat and electricity to your workpiece and make your MIG welding project possible.

That is all! So, in short, to do MIG welding, we need to ionize the shielding gas, for power.

Each type of gas has a different ionization potential.

• HIGH ionization potentialmeans that the gas requiresbut energybe ionized.
• LOW ionization potentialmeans that the gas requiresless energybe ionized.

One example is argon and helium, the two most common shielding gases for MIG welding.

If you notice, argon can start the arc faster than helium.

This is because it is easier to ionize argon than helium.

Argon has a lower ionization potential (15.7 eV), while helium has a higher ionization potential (24.5 eV).

2. Shielding gas thermal conductivity

Thermal conductivity refers to the ability of the shielding gas to deliver thermal energy or heat to your workpiece.

It is considered the most important consideration when you are selecting a shielding gas for your welding projects.

As with ionization potential, different shielding gases have unique levels of thermal conductivity.

This property affects the arc shape and depth of penetration.

• HIGH thermal conductivity(from helium, for example) creates awider arc zoneswindlershallower penetration.
• LOW thermal conductivity(of argon, for example) produces aminor arc area, but onedeeper penetration pattern.

3. Chemical reactivity between shielding gas and molten pool

Well, the title pretty much says it all.

Chemical reactivity here refers to the most fundamental property of the shielding gas, whether it is inert or reactive with the weld pool.

Unlike TIG welding, in MIG operations you have more usable options for shielding gas, including inert gases (argon, helium) and reactive gases (oxygen, CO₂, etc.)

The main consideration here is that reactive gases are much more accessible (cheaper) than inert gases.

So if you're on a budget, you might want to use reactive gases.

FOUR basic types for your MIG welding gas mix

As mentioned above, there are two groups of MIG welding gases: inert and reactive.

The four most common types of shielding gas for MIG operations are: Carbon dioxide (CO₂), Argon, Helium and Oxygen.

Each option offers unique enhancements, as well as drawbacks, to your MIG's performance.

In this part, you'll learn about each one and how to mix them together to produce the most effective shielding gas for your MIG projects.

So don't blink and make sure you follow it all the way.

1. Inert MIG shielding gas

There are many factors that go into choosing a shielding gas, especially for the MIG welding process, as you have a wider range of options.

One factor is the material type of your weld metal (Remember Factor 2 mentioned above?)

If the metal being welded isnon-ferrous(meaning it doesn't contain iron), so congratulations, becausePure inert shielding gas is your best choice.

With inert shielding gas for MIG welding, you can chooseargon or helium.

(a) argon

Argon is probably the most widely used inert shielding gas.

As we discussed, Argon hasLOW ionization potential, like thisLOW thermal conductivity.

This produces a deep, narrow penetration pattern that looks like a finger, which is excellent for both butt and fillet joint types.

It is also easier to start an arc using argon as the shielding gas.

Argon is widely used in MIG welding of non-ferrous metals such as titanium, copper, nickel, aluminum and magnesium.

Argon is also a basic component to mix with other gases to create binary (two-gas mixture) or ternary (three-gas mixture) in MIG welding, which will be discussed later in this article.

(b) helium

Everything about Hélio is loud:HIGH thermal conductivity,HIGH ionization potential, and HIGH price too.

Due to its high price, helium is often added to a mixture of gases and not used in its pure form.

In addition to non-ferrous metals, helium is also applied for MIG welding of stainless steel and aluminum, especially for parts thicker than 1 inch (25 mm).

When you use helium it can produce a wider penetration profile but not as deep as argon.

One special thing about Helium is that it can increase your productivity.

This is possible because the helium creates a hotter arc, forcing you to move your MIG gun faster (increased traverse speed) and eventually finishing your MIG welds faster.

2. Reactive MIG shielding gas

Reactive shielding gases used for MIG operations include: Carbon dioxide (CO₂), Oxygen, Nitrogen, Hydrogen, etc.

Reactive gases can chemically react with the weld pool to create a desirable characteristic.

(a) Carbon dioxide (CO₂)

CO₂it's the only reactive gas you can use in its pure form (without any inert gas mixtures).

Thanks to this, CO₂is considered the most affordable option.

CO use₂As a MIG shielding gas, it provides a wide and deep penetration pattern (discussed in more detail later).

This feature makes CO₂the ideal choice for MIG welding of thick materials.

However, of the 4 metal transfer modes,pure CO₂it is only suitable with short circuit mode.

Furthermore, the use of pure CO₂creates more spatter than when mixed with other gases.

Therefore, its use is recommended for projects with low aesthetic requirements, such as a car body.

This is the basics for CO₂!

The following content goes a little deeper into why CO₂provides a wide and deep penetration pattern.

CO₂it only becomes reactive with the molten solder puddle after being ionized.

Such a penetration pattern is possible thanks to two processes called “dissociation"eu"recombination”.

• Dissociation: In the anode region (DC+), the CO₂molecule breaks down into free carbon, oxygen and carbon monoxide (CO).
• recombination: In the cathode region (DC-), which is the workpiece itself, the components released from CO₂molecule recombines to form CO₂. This creates a high level of energy, which leads to a wide and deep penetration pattern.

the amount of CO₂used as a shielding gas can seriously affect the appearance of your finished weld.

*** HIGH level of CO₂

A high level of CO₂will release more free oxygen after going through dissociation and recombination processes.

This free oxygen will react with your metal alloys (silicon, manganese, iron, etc.) to form an oxide layer.

The oxide layer then floats to the surface of the weld pool and solidifies there, creating slag.

*** LOW level of CO₂

On the other hand, a low level of CO₂it will release less free oxygen and therefore will not create an oxide layer for the final slag to form.

Therefore, perform MIG with low CO₂you can preserve all the alloying elements in your workpiece and improve the maximum tensile strength of your finished MIG welds.

(b) Oxygen (O₂)

Oxygen (O₂) will certainly react with your melt pool to form oxides.

Therefore, it should be kept at low levels (1-9%) and should be mixed with an inert gas.

OU app₂Helps improve weld pool flow, arc stability, and weld appearance.

O₂It's good forMIG Welding Stainless SteelyMild Steel MIG Welding.

Esprohibiteduse the₂with non-ferrous metals such as copper, aluminum, magnesium, as it may cause oxidation.

(c) Hydrogen (H₂)

Hydrogen (H)₂) is also used in small amounts (1-5%) and is mixed with an inert gas (probably argon).

It has HIGH thermal conductivity which helps create a smoother puddle and allows for faster travel speeds.

Hydrogen can be applied in high temperature design for austenitic stainless steels.

(d) Nitrogen (N₂)

Nitrogen (N)₂) is often used for MIG welding of stainless steel pipes, primarily as a return gas.

It can also be mixed with Argon and used as a shielding gas for MIG projects on stainless steels.

3. Two-part MIG shielding gas mixtures (binary mixtures)

Two-part MIG shielding gas mixtures, also known as binary mixtures, are typically the combination of: argon + helium; Argon + CO2; or Argon + O2.

(a) Argon + Helium

The mixture of Argon and Helium is normally applied toAluminum MIG Welding, nickel and stainless steel.

Axial sputtering and pulsed sputtering transfer are the preferred metal transfer modes for this mixture.

The addition of helium to these binary gas mixtures improves the fluidity of the molten pool and therefore increases the displacement velocity.

Helium also reduces the finger pattern found when applying pure argon, especially on aluminum.

In summary, while argon facilitates the arc and helps with the cleaning action (on aluminum), helium increases travel speed and reduces the finger-like penetration pattern.

There are two common binary mixtures for argon and helium:

• In the first place, It is75% Argon + 25% Helium. Compared to pure argon, this mixture improves the pool flow and penetration profile for aluminum, nickel and copper MIG welding.
• In second place, It is25% Argon + 75% Helium. Higher levels of helium further increase thermal conductivity, pool fluidity and broaden the penetration profile. Finally, it provides a higher scrolling speed.

(b) Argon + CO₂

A mixture of argon and carbon dioxide (CO₂) is good for stainless steel and mild steel MIG welding.

All metal transfer modes can be used with this gas mixture.

However, it depends on the level of CO₂, the proper metal transfer mode is different

• you are CO₂the content isless than 4%,pulsed spray modemust be used, especially for stainless steel.
• you are CO₂the content isless than 18%,axial spray modeIs a good choice.
• you are CO₂the content reachesmore than 18%,short circuit modeit is more effective

Normally, CO₂the level ranges from 5% to 25% in the mix.

The addition of CO₂provides better arc stability and reduces spatter than Pure CO₂could cause.

But be careful, higher levels of CO₂increases the possibility of splashes and burns.

Here are some common combinations for this gas mixture:

(c) Argon + O₂

The use of the mixture of Argon and Oxygen allows to increase the displacement speed in thin materials.

This mixture is popular in stainless steel and mild steel MIG welding.

However, the level of O₂used shall not exceed 5%.

Here are the 3 best mixtures of argon and oxygen:

• 99% Argon + 1% Oxygen: This mainly applies to MIG stainless steel projects. However, it produces a grayish appearance on your stainless steel.
• 98% Argon + 2% Oxygen: this can be used for both mild and stainless steel MIG applications. But this mixture creates a dull gray look on your stainless steel parts.
• 95% Argon + 5% Oxygen: This is usually used with axial spray or pulsed metal transfer spray mode. It is good for thicker mild steel parts. However, due to high oxygen levels, the base metal must be free of contaminants to prevent oxidation.

4. Three-part MIG shielding gas mixture (ternary gas mixture)

The three-part MIG shielding gas mixture, also known as a ternary gas mixture, comprises at least 3 different gases, one of which is inert (eg argon).

Ternary gas mixtures are very popular for MIG welding of stainless steel, carbon steel and even nickel alloys.

Here are the 4 best ternary gas mixtures that you can find in many stores:

• 90% helium + 7.5% argon + 2.5% CO₂: This mixture is perfect for short circuit transfer mode in stainless steel MIG welding projects. The high level of helium provides excellent fusion and travel speed. In addition to short circuit mode, it is also used in pulsed spray mode for stainless steel and nickel materials thicker than 1.6mm.
• 55% helium + 42.5% argon + 2.5% CO₂: this mixture provides a cooler arc, suitable for pulsed spray transfer mode. It can also be used for axial and short circuit spray transfer mode.
• 38% Helium + 65% Argon + 7% CO₂: this mix allows for a wider penetration pattern and is a good choice for short circuit transfer in mild steel MIG welding.
• 90% Argon + 8% CO₂+ 2% O₂: This mix greatly reduces splashing (due to the high inert gas content). Works well with short circuit, pulsed spray and axial spray transfer modes for MIG welding on mild steel projects.

Optimal flow rate for your MIG welding gas

The ideal flow rate for MIG welding gas depends on 4 main factors:

• Weld geometry:Flat surfaces will require a higher gas flow than rough materials as the gas spreads out more.
• Travel speed:Higher speed MIG welding simply requires more gas to shield the weld pool.
• Electric current setting:Higher current settings require more volume of shielding gas, especially helium, to completely cover the weld pool.
• Metal transfer mode for MIG welding:The 4 main variations of MIG welding have different requirements for shielding gas flow.Short circuitypulsed spraythe modes need about20 pies 3/hr.globular transferdemands on30 pies 3/hr, whilespray transferworks well with more40 pies 3/hr.

Basic MIG Shield Gas Selection Guide

As mentioned above, the choice of MIG shielding gas depends on up to 10 different factors.

Shielding gas selection is also a crucial step in setup.Correct MIG welding parameters.

So this is an important but difficult decision to make.

We've compiled a table below, which we hope will reduce complexity and help you make a decision faster.

Conclusion

That's the end of all the fundamentals about MIG Shield Gas and how to choose the right one for your project.

After reading this article, we hope you understand the factors that influence MIG gas selection, key shielding gas properties, and certain types of gas/gas mixtures.

Reference

1. Welding Principles and Practices (Fifth Edition) – McGraw Hill Education. Edward R. Bohnart. [2017]
2. Gas Metal Arc Welding: Product and Procedure Selection – Lincoln Electric. [2014]
3. gas metal arc welding. . . . Wikipedia, the free encyclopedia. Retrieved on September 28,
4. How to weld with wire feed. Welding seat. Accessed September 28, 2020.
5. Fundamentals of Shielding Gas for MIG Welding. Bernardo. Accessed September 28, 2020.
6. The fundamentals of MIG welding fumes. Tip of the American Torch. Accessed September 28, 2020.
7. MIG welding gases. GoWelding. Accessed September 28, 2020.
   

Frequently Asked Questions About Selecting MIG Welding Gas