What Type of Gas Is Best for MIG Welding in DIY Applications? | MillerWelds

What Type of Gas Is Best for MIG Welding in DIY Applications?

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Whether you’re welding mild steel, aluminum or stainless steel, choosing the right shielding gas is essential for achieving great results. Learn more about shield welding and discover the best gas options for your MIG welding project, along with tips for proper setup and troubleshooting common issues.
Welder MIG welding at table with MIG welder and gas canister in background
A finished horizontal tee joint weld completed using C25 shielding gas.

What is shielding gas for MIG welding?

Welding produces a molten puddle made up of the base metal and filler metal being fused together. Shielding gas protects that puddle from atmospheric contaminants like nitrogen and hydrogen.

Without shielding gas, the finished weld would be very weak and peppered with pinpoint holes once it solidifies — a defect known as porosity. Shielding gas acts as a blanket over the molten weld puddle, keeping atmospheric contaminants out. 

The type of gas used also has an impact on the characteristics of the weld — affecting spatter levels, arc stability, arc performance and many other factors. 

The desired welding transfer you want to achieve is also dependent on the type of shielding gas you’re using. So, if you want to do a spray transfer, globular transfer or short-circuit transfer, you need to select a certain type of shielding gas for each transfer mode in MIG welding. For example, a shielding gas high in argon makes it difficult to achieve short-circuit transfer mode but easier to achieve spray transfer.

How to choose the right type of shielding gas

Hobbyist welders most commonly use three types of filler metals to match the base material they are welding: solid steel wire to weld mild steel, aluminum wire to weld aluminum and stainless-steel wire for stainless. The shielding gas options vary based on the material being welded.

Welding gas for mild steel

  • 75% Argon/25% Carbon Dioxide (C25 Gas): This mix is very common for welding mild steel. C25 gas produces minimal spatter and provides good arc characteristics. It also has a good bead profile, allowing it to wash out well at the toes of the weld. One drawback: this mix is more expensive than other options. 
  • 100% Carbon Dioxide (C100): A cost-effective alternative to 75%/25% shielding gas mixture, C100 may produce a bit more spatter and result in a slightly erratic arc. However, modern welding machines have improved performance with C100 gas, making them more efficient than the machines of 10 or 15 years ago. 
  • 90% Argon/10% CO2 (C10 Gas): While it’s less common for the DIY user, if you’re planning to use spray transfer mode with MIG welding (e.g., when welding thicker plates), the C10 gas mixture is a good option.

The front panel of the Millermatic® 211 MIG welder where operators can choose a MIG process for C25 and C100 gases.

The front panel of the Millermatic® 211 MIG welder where operators can choose a MIG process for C25 and C100 gases. 

 

The front panel of the Multimatic® 215 multiprocess welder where operators can choose a MIG process for C25 and C100 gases.

The front panel of the Multimatic® 215 multiprocess welder where operators can choose a MIG process for C25 and C100 gases. 

Welding gas for aluminum

  • 100% Argon: The most common gas used for MIG welding aluminum is 100% argon. It allows for easy spray or pulsed spray transfer due to its low ionization value. An additional benefit of 100% argon gas is its versatility for TIG welding aluminum. If you MIG weld aluminum and also TIG weld in your shop, having this gas on hand is convenient because it supports both processes.

    Learn more in our article on Best Practices for Proper Shielding Gas in TIG Welding. 

  • Helium/Argon Blends: While effective for aluminum, these gas blends are often too costly for DIY welders due to the high price of helium. Also, because aluminum is highly sensitive to contamination, it’s best to avoid using a gas with CO2, which can introduce carbon into the weld.

Welding gas for stainless steel

There are many gas combinations available for MIG welding stainless steel. Many MIG welding power sources have traditionally been designed for short-circuit transfer mode to be used with a helium trimix shielding gas for stainless. Helium helps the puddle wash out without adding too much inductance, providing a good bead profile and good bead characteristics. But as mentioned above, the cost of helium today can be prohibitive for DIY welders.

In recent years, manufacturers have shifted to designing MIG welding power sources for use with different gas combinations for welding stainless steel.

  • 98% Argon/2% CO2: A versatile option that can be used for short-circuit transfer, spray transfer and pulsed spray transfer modes, this gas blend provides a good bead profile and wetting characteristics without the premium price point of helium. As with aluminum, it’s important to avoid introducing too much CO2 into the mix with stainless, as it can cause porosity or other weld defects.

Welding gas for silicon bronze

It’s becoming increasingly common to use a silicon bronze filler metal to join dissimilar metals or a variety of coated materials among DIY welders, specifically for applications such as automotive repair and for art and sculptural welding. Using an ERCuSI-A silicon bronze filler metal results in what is essentially a MIG brazing process.

  • 100% Argon: Typically, you want to go with a 100% argon shielding gas. This allows for a nice short-circuit transfer that helps the puddle wash out when using silicon bronze filler metal.

Shielding gas tips and best practices for quality welds

While choosing the right shielding gas is an important step, the following best practices will also help you produce better results.

Tip 1: Ensure proper setup and flow rate

Purge valve before attaching regulator: Before you hook up the shielding gas, twist open the valve on top of the canister to let a small amount of gas out and then close the valve again. This cleans out the connection, so when you attach the regulator there are no contaminants like dust that can get into the welding system. Then, make sure you attach the regulator as instructed in the owner’s manual. Typically, a regulator has two dials. The right one will control the gas cylinder, and the left one will control the gas flow rate. 

Set flow rate according to welding process: For MIG short-circuit welding it’s recommended to use a 25 to 35 cubic feet per hour (cfh) gas flow rate. TIG welding typically runs a lower flow rate, while MIG processes using other transfer modes (other than short-circuit transfer) can run slightly higher than 35 cfh.

A flow rate that is too low will introduce porosity into the weld because there isn’t enough coverage to protect the puddle. A flow rate that is too high wastes gas and can also produce an eddy current that results in turbulence, introducing atmospheric contaminants into the weld that cause porosity.

Use wind blocks for outdoor welding: Anytime you’re welding outdoors with a gas-shielded process, try to set up a wind block or tent to prevent the wind from blowing the gas away.

 

An example of porosity in a weld.

An example of porosity in a weld.


Tip 2: Check all power source connections

If you experience issues with gas coverage, the first troubleshooting step is to check all of your connections on the back of your power source. On many multiprocess welding power sources, there are two different gas ports: one for TIG and one for MIG. Be sure you are connected to the right port. Then check that your cfh is set properly.

If you’re still not getting shielding gas after taking these steps, check that the MIG gun is seated properly in the drive system. Without proper seating, the gas exits at the drive system rather than making its way through the end of the MIG gun. Also, consider using an external flow meter on the MIG gun. This will monitor the cfh rate you’re getting at the end of the gun.

Tip 3: Clean the consumables

The consumables in your MIG gun include the contact tip, diffuser and nozzle. The nozzle directs the shielding gas to cover the weld puddle. However, as you weld, spatter and debris can clog the nozzle. If there is too much spatter buildup, it can disrupt the shielding gas coverage. Be sure to occasionally remove the nozzle and use pliers or another tool to remove any excess buildup.

Tip 4: Adjust Contact-Tip-to-Work Distance (CTWD)

Another troubleshooting tip to try if you’re running into shielding gas issues is to adjust your CTWD. If you’re welding too far away from the work surface, you might be losing shielding gas before it gets to the weld puddle. Try moving the end of the gun closer to the base material. While it depends on several factors, 1/4 inch to 5/8 inch is a standard recommended CTWD.

Maximize your weld quality by choosing the right gas

Selecting the right shielding gas for your MIG welding project can help you achieve the best results and reduce issues that can cause poor weld quality. Be sure to always follow the filler metal manufacturer’s recommendations for the type and amounts of shielding gas that should be used for a given wire and base material.

If you’re looking for more insights on shielding gases to help optimize your welds, check out our article on Best Practices for Proper Shielding Gas in TIG Welding.

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