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Whether you're welding mild steel, aluminum or stainless steel, choosing the right shielding gas is important to getting good results.
The Best MIG Welding Gas
Do you have questions about choosing the right welding gas for yourDIY Welding Projects? Whether you're MIG welding mild steel, aluminum, or stainless steel, choosing the right shielding gas for your base material is an important first step to achieving good results.
Learn more about shielding gas options for MIG welding, and get tips for proper setup and troubleshooting.
What is shielding gas used for?mig welding?
Welding creates a molten pool consisting of the base metal and filler metal being fused together. The shielding gas protects this puddle from atmospheric contaminants such as nitrogen and hydrogen.
Without shielding gas, the finished weld would be very weak and riddled with small holes after solidification, a defect known as porosity. The shielding gas acts like a blanket over the molten weld pool, preventing the entry of atmospheric contaminants.
The type of gas used also affects the properties of the weld. Your choice of gas can affect spatter levels, arc stability and arc performance, among many other factors.
Also, the desired weld transfer depends on the type of shielding gas used. So, whether you want to do a spray, ball, or short transfer, MIG welding requires you to select a specific type of shielding gas for each transfer mode. For example, a high argon shielding gas makes it difficult to achieve short circuit transmission mode but easier to achieve spray transmission.
Common shielding gases for MIG welding
Hobbyist welders typically use three types of filler metals to match the base material they are welding: solid steel wire for welding mild steel, aluminum wire for welding aluminum, and stainless steel wire for stainless steel. Shielding gas options vary depending on the material being welded.
Welding Gas for Structural Steel
A mixture of 75% argon and 25% carbon dioxide (sometimes referred to as "C25 gas") is widely used for welding mild steel. It generates minimal spatter and offers good arc properties. It also has a good bead profile that allows it to wash well into the tip of the weld. One drawback: this mixture is more expensive than other options.
Another gas used for mild steel is 100% carbon dioxide, sometimes referred to as C100. It is a good alternative that is less expensive than a 75%/25% shielding gas mix, but can generate a little more spatter and result in a slightly erratic arc. However, as the technology of DIY welding power sources improves, 100% CO2 gas machines are performing better than machines from 10 to 15 years ago.
While it is less common for the DIYer to switch to a spray transfer mode when MIG welding (for example, if welding a thicker panel), a 90% Argon/10% CO2 gas or C10 gas is a good option.
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| The front panel of the Millermatic® 211 MIG welder where operators can select a MIG process for C25 and C100 gases. |
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| The front panel of the Multimatic® 215 multi-process welder, where the operator can select a MIG process for C25 and C100 gases. |
Welding gas for aluminum.
The most widely used gas for MIG welding aluminum is 100% Argon. With this gas, you can easily switch to a spray transfer or pulsed spray transfer mode for aluminum due to its low ionization value.
Another advantage of 100% argon gas is that it can also be used for TIG welding aluminum. So if you MIG and also TIG weld aluminum in your shop, this is a useful gas to have on hand as it covers both processes.
Read about best practices forcorrect shielding gas for TIG welding
Although there are many helium/argon gas mixtures that are suitable for aluminum, the high cost of helium makes these gases not a good choice for most home welders. Furthermore, aluminum is very sensitive to contamination. Therefore, avoid using a CO2 gas, which can introduce carbon into the weld.
Welding Gas for Stainless Steel
There are many gas combinations available for MIG welding of stainless steel. Many MIG welding power sources have traditionally been designed for the short circuit transfer mode for use with a helium trimix shielding gas for stainless steel. The helium helps eliminate the puddle without adding too much inductance, providing a good profile and beading properties. But as mentioned above, today's helium costs can be prohibitive for DIY welders.
There has been a shift in recent years as manufacturers develop MIG welding power sources that are used with various gas combinations to weld stainless steel.
A mixture of 98% argon and 2% CO2 is a good choice for stainless steel. As with aluminum, it is important to avoid introducing too much CO2 into the mix with stainless steel, as this can cause porosity or other weld defects. An argon/CO2 gas mix is a versatile option. It can be used for short circuit transmission, spray transmission and pulsed spray transmission. It still offers a good bead profile with decent wetting properties and is much more affordable than a helium gas mix.
Welding gas for silicon bronze
The use of a silicon bronze filler metal to join dissimilar metals or a variety of clad materials is becoming more common among home welders for applications such as automotive repair and art and sculpture welding. The use of an ERCUSI-A silicon bronze filler metal essentially results in a MIG brazing process.
Typically, you want to use a 100% argon shielding gas. This allows for good short circuit transfer which helps eliminate puddling when using silicon bronze filler metal.
Shielding Gas Best Practices
While selecting the correct shielding gas is an important step, follow these best practices for best results.
Tip 1 – Make sure you have the correct flow and settings
Before connecting the shielding gas, open the valve at the top of the container to release a small amount of gas, then close the valve again. This cleans the connection so contaminants such as dust cannot enter the welding system when the regulator is connected. Then be sure to connect the controller as directed in the owner's manual. Usually a controller has two dials. The right controls the gas cylinder and the left controls the gas flow.
The welding process used determines the correct flow rate. A gas flow rate of 25 to 35 cubic feet per hour (cfh) is recommended for short circuit MIG welding. TIG welding generally has a lower flow rate, while MIG processes with other transfer modes (except short circuit transfer) can run just over 35 cfh.
Too low a flow rate will result in weld porosity because there is not enough coverage to protect the puddle. Too high a flow rate wastes gas and can also create an eddy current that creates turbulence and introduces atmospheric contaminants into the weld that cause porosity.
Any time you weld outdoors with a gas shielded process, try to put up a windbreak or tent to keep the gas from being blown away by the wind.
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| An example of porosity in a weld. |
Tip 2: Check all connections
If you are having problems with the gas cover, the first step in troubleshooting is to check all the connections on the back of the power supply. On many multi-process welding power sources there are two different gas connections: one for TIG and one for MIG. Make sure you are connected to the correct port. Then check if your cfh is set correctly.
If you still do not get shielding gas after these steps, verify that the MIG gun is properly seated in the drive system. Without a proper adjustment, gas will exit the drive system instead of flowing out the end of the MIG gun.
Consider using an external flow meter on the MIG gun. This will control the cfh rate you get at the end of the weapon.
Tip 3: Clean consumables
Consumables on your MIG welding torch include contact tip, diffuser, and nozzle. The nozzle directs the shielding gas into the weld pool. However, when welding, spatter and dirt can clog the nozzle. If too much splash builds up, it can disrupt the shielding gas shield.
Be sure to remove the nozzle from time to time and use tweezers or another tool to remove excess debris.
Tip 4: Set the contact tip to working distance (CTWD).
Another troubleshooting tip to try if you encounter shielding gas issues is to adjust your CTWD.
If you weld too far from the work surface, you may lose shielding gas before it reaches the weld puddle. Try to get the end of the gun closer to the base material. Although this depends on several factors, 1/4" to 5/8" is a recommended standard CTWD.
Shielding Gas Nozzles for MIG Welding
Choosing the right shielding gas for your MIG welding project can help you get the best results and reduce problems that can lead to a poor quality weld. Always follow the filler metal manufacturer's recommendations for the type and amount of shielding gas to use for a particular wire and base material.