What Should the Gas Pressure Be When MIG Welding?

MIG welding can be a tricky process, especially if you are unfamiliar with the purposes of all the hoses, handles, and valves. Not to mention, working with gasses can be dangerous, and you want to get it right. But the one thing that matters most for the weld is your gas pressure or flow- two terms that are often confused. 

Typical gas flow when MIG welding varies for different inside nozzle diameters. For ½ inch nozzles, your typical flow setting should be around 22-27 CFH. For ⅝ inch nozzles, the types often used in industrial settings, you should use around 30-35 CFH. For ¾ inch, 30-40 CFH should be enough.

But what is CFH? Isn’t gas pressure usually measured in PSI? And what is the difference between flow and pressure? Which one should you be adjusting, and how? In this article, we will answer all of these questions. 

What Gas Pressure Should I Use When Welding?

Gas flow should be adjusted depending on the inside diameter of the welder’s nozzle. For each diameter, there is a different minimum and maximum and a typical flow rate. For this article, we will be using this chart

Gas flow is measured in CFH, not PSI. PSI is used to measure pressure, which, as stated above, usually cannot be changed and will be set at anywhere from 3-8 PSI. On quality machines, there will be an apparatus that does this automatically to compensate for spattering. 

CFH stands for Cubic Feet per Hour, and it measures how much gas is going to be making its way through your nozzle. Maintaining the correct CFH is critical to ensure a smooth weld. Without sufficient CFH your weld pool can be infected by outside chemicals like particulate matter floating in the air or unwanted gasses.  

Nozzle Size

CFH for a ½ inch nozzle should be around 18 CFH at minimum. Typically, this flow is set at around 18-22 CFH, depending on the conditions of your welding environment. You shouldn’t go beyond around 40 CFH. ½ inch nozzles are common on small welding machines owned by private individuals and hobbyists.

For ⅝ inch nozzles, CFH should be set at around a 22 minimum. Typically, 30-35 CFH is used for these types of nozzles. CFH should never go beyond approximately 55 for these nozzles. These nozzle diameters are common for welders working in industrial settings. 

For ¾ inch nozzles, you should have a minimum of 30 CFH. For these nozzle diameters, welders will tend to use around 30-40 CFH. Don’t go beyond approximately 65 CFH. These nozzle diameters are common when using large size core wire. 

Environmental Exposure

One thing to remember is that the large range of recommended CFH is there to allow welders to adjust for various environmental factors. Wind, for example, can be blocked out by adjusting CFH, resulting in a better weld with less exposure to the outside air. Make sure to examine your welds for porosity before applying them to a project.   

If you are following these guidelines and still getting porous or otherwise poor-looking welds, you might try setting up a weld-shield. This can be as simple as placing your body between the flow of the air and your weld surface.

How Do You Adjust the Pressure on a MIG Welder?

To properly adjust the flow on a MIG welder, a few steps must first be accomplished.

First, you should turn on the MIG welder. Adjusting the valves on the welder before turning on the MIG machine will not change the flow pressure because the gas valve will not be activated. 

To activate the gas valve on the MIG machine, you will have to press the trigger on your handle. After this, read the CFH on your regulator gauge. For a given nozzle diameter, proper CFH can be determined from the sections above.

CFH Gauge

Above the tank, you will notice two regulator gauges. One gauge measures PSI, which is controlled by the machine, and the other measures CFH. The gauge you want to watch is the one on the left, which measures CFH. 

Turn the valve below the left gauge until you reach the desired CFH. Again, the desired CFH should be decided based on the conditions in your welding environment and the inside diameter of your nozzle. 

At this point, you can release the trigger. By now, you should notice a long string of wire coming from the tip of your welding gun. This is normal, and it means that your MIG welder is functioning properly. 

Start Welding

To start welding, you should trim the excess wire that came from the gun while you were adjusting your CFH. 

Remember that CFH should be adjusted based on the environment you are welding in. If there is a fan or a draft is coming in from anywhere in the room, you will need to increase the CFH on your machine to adequately shield the weld pool. 

If you are adjusting your CFH all over the place and can’t seem to make a good weld, you might need to set up a weld-shield, as stated before. To do this, you can put something between your weld and the air source- like your body.

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Something to Look Out for

MIG welding stands for Metal Inert Gas welding, and this name isn’t chosen at random. You might notice that when you MIG weld, you are mixing gasses and an electric arc, just like you do with a gas oven. So, why doesn’t anything blow up or light aflame?

The inert part of Metal Inert Gas is important here. For gas to be inert means that it does not undergo chemical reactions under certain conditions. In this case, those conditions are high temperature and the presence of an electric arc. 

So, you’re not going to blow yourself up. But one thing you should watch out for is asphyxiation or suffocation. 

If you’ve chosen to use your garage door as a weld-shield, you might be trapping yourself in an enclosed space with gases building up. Just like with a running car in a small garage, this might suffocate you. 

To prevent this, stay away from enclosed spaces while welding, and keep air flowing. Also, check around the gas regulator for leaks or other irregularities. It’s a small thing, but it could save your life. Leakage results in extra gas loss and can result in unbreathable air in a confined space.

In Conclusion

In conclusion, flow rate, or what is sometimes confused for pressure, should be adjusted for your welding environment and nozzle size. A greater gas flow can be used to get better welds by shielding out unwanted reactions. 

Depending on what kind of welder you are using, you might need to adjust your welder’s flow to anywhere between 22 and 40 CFH. Nozzle size is key, and if you don’t know your nozzle size you might be able to guess depending on where you weld.  

Also, welders should remember that shielding flow is not the only way to prevent unwanted reactions in the weld pool. Weld shields like garage doors can be used, but standing between your weld pool and an air source is also a good way to do it. 

Lastly, welders should remember to take the necessary safety precautions to avoid such dangers as asphyxiation. Asphyxiation can be avoided by providing ample ventilation in the working environment. Checking your equipment for leaks can also increase workplace safety and save you money by preventing the loss of valuable gas 

Sources:
http://www.netwelding.com/MIG_Flow%20Rate-Chart.htm#:~:text=MIG%20shielding%20gas%20flow%20is,from%203%20to%208%20psi.

https://itstillruns.com/set-gas-mig-welder-5653314.html

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If you liked this article, have a look at my other articles I wrote about the topic!

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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