CO2 MIG Welding
When it comes to metal fusion, one of the most common welding processes is co2 mig welding. Carbon dioxide or CO2 is the most reactive gas among the gases being used in mig welding. It is also the only form of gas that can be used as a shielding gas even without a mixture of inert gas. However, if used in pure form it can cause oxidation on non-ferrous metals such as copper, magnesium, aluminum, or other exotic metal alloys that can oxidize when exposed to high-intensity heat. It is also not a good option when it comes to any soft or thin metals like metal sheets because of the high-intensity heat it gives out. 
Also called GMAW (Gas Metal Arc Welding), MIG co2 welding is the process of fusing metals by producing an arc with the electrically charged electrode and using the gas as a shield to prevent air contamination. There are other types of arc welding applications that are also common among welders like the GTAW (Gas Tungsten Arc Welding) or better known as TIG welding and the FCAW (Flux-Cored Arc Welding) that both don’t require separate shielding gas because their electrodes itself have metal powders that burn and act as arc shields. 
Why most welders usually prefer MIG welding than TIG and Flux-cored welding is because of its many advantages. MIG welding uses CO2 as a shielding gas which provides welders a wider choice for metals they want to fuse. But like any other welding gases, it also has a bit of the disadvantage on MIG welding.
CO2 Welding Advantages and
Advantages:
Big or thin wire electrodes, it doesn’t matter with mig welding co2. Because carbon dioxide can produce high-density hot arcs, the deposition of the melted electrode remains high.
The arc is more concentrated on the spot weld which offers deeper penetration of the weld pool. 
The potential of slag formation remains small when dealing with harder and thicker metals.
The generation of arc remains constant which translates to more economical welding cost including the whole welding process. 
Without contamination from the surrounding atmosphere with co2 mig welding the result is stronger mechanical properties of the weld with better resistance against cracking.
Disadvantages:
Will not work well in a windy environment or outdoor setting where there’s a lot of draft.
It requires Direct Current or DC which means the electrical current it needs should be converted into DC if home or commercial outlets are to be used which are commonly in AC. 
Not an ideal choice for welding exotic metals and thin metal sheets unless mixed with an inert gas.
How to Optimize MIG Welding CO2
Actually, there is a big misconception on the term co2 mig welding if CO2 is used in pure form. This is because CO2 being an active gas is not an inert gas. So the term Metal Inert Gas would only be appropriate if CO2 is mixed with other gases. That’s why the right term for pure CO2 welding should be MAG or Metal Active Gas welding. 
CO2 can also work well with other gases to optimize the MIG welding process so that welders can weld even the softer metals. These gases are composed of argon (Ar) Helium (He), and oxygen (O2). Argon is an inert gas and a noble gas which means it has the full capacity to prevent chemical reactions to any other gases when used as a shielding gas. But if used in pure form on steel, you may get an ugly weld which is also brittle and weak. However, if mixed with CO2 like 75%-95% argon and 5%-25% CO2, you can have a varying welding grade with different weld penetration levels on a variety of metals. 
Helium is also another noble gas fit for co2 welding mixture and excellent for fusing non-ferrous metals as well as stainless steel. Mixing 25% helium to 75% argon, the arc can provide more a protective shield and the weld penetration also becomes deeper and wider on the surface of the weld. The only downside in using helium is its cost. But if you can buy a tri-mix of argon, helium and CO2, you still get to save on welding gas while you can weld a variety of metals including non-ferrous and thin metals.
Other Benefits of Using Pure CO2
CO2 being the regular gas for MAG welding is cheaper and a good option if you don’t have the budget to buy mixed gas for a bigger project. It is also easily available while you can purchase it in a mixed form. However, the use of CO2 requires short circuit welding. This means the electrode needs to constantly touch the work metal to create the spark to feed to the gas. So the negative effect of this is a less stable arc and a lot of spatter. If you don’t mind cleaning up the weld after welding using pure CO2, this will not be a problem. But if you want an aesthetically looking weld, better consider using the mixed C25 (75% argon + 25% CO2) gas or the tri-mix. 
If you have a MIG welder at home, another problem you can experience with co2 welding if using it in pure form is you won’t be able to rely on it when repairing thin metal sheets like the body of your automobile or your sink or gutter unless you shift to its gas mixture or use argon. Yet, the good thing about having MIG welders for home use is that most of these only require 110 volts. 
When welding carbon steel, using 100 percent CO2 also brings a good result because of the globular transfer. This means that the transfer of weld 
metal is in large droplets which helps when welding even in horizontal positions. But still, spatter would normally occur in any co2 mig welding so experts have advice in minimizing this by experimenting on increasing the current for faster melting of the electrode while controlling your speed.
Most Available Sizes of CO2 Cylinders/Canisters
If you are a beginner in MIG welding and want to know how much co2 you need for your mig welding and what are the available tank or canister size for these, then you should know the following info.
For small projects or home use MIG and TIG gases are available in cylinders. Cylinders are small gas tanks made for portability. The most common sizes of co2 welding gas are the 40, 80 and the 125 cubic feet cylinders. But if you have a workshop at home and have a lot of mig welding projects at hand, better have the largest tank for commercial use which you can lease. Yet, if you are a traveling welder, you will eventually need any of these small-size canisters for easy transport or as a back-up gas. You can also purchase these in tri-mix media. 
To give you an idea on how tall these portable cylinders are, the 40 cf (29 lbs in full weight) is only 22 inches tall, 80 cf (57 lbs in full weight) is 35 inches and the 125 cf (72 lbs full in weight) is 45 inches. All of them have a 7-inch diameter size. So for the hobbyists and mig welding learners, these are ideal sizes to master your welding process. You can order them online already filled up with gases or visit your nearest gas merchandise in your area and these tanks are also easily refillable.
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MIG welding has been with us since the mid-1900s which was originally developed for welding aluminum. But with the discovery of carbon dioxide being an active but semi-inert gas in the 1950s, mig welding co2 has become common in most of our industrial settings. Today, MIG welding is the most common welding process not only for construction and building purposes but also for domestic use because of its versatility, adaptability to weld various metals, and speed and thanks to the discovery of carbon dioxide being a notable gas for GMAW (Gas Metal Arc Welding). 
CO2 mig welding is known to be the easiest welding applications to learn among the arc welding processes that even the beginners can fuse a variety of metal types in a short time learning. But as mentioned, it also has its weaknesses like not the ideal choice for non-ferrous metals unless you mix it up with an inert gas.
It is also notorious to create weld spatter when used singly. But once you get to know its strength to create a stronger and deeper bond on thick metals you will realize its versatility and usefulness even in pure form. And what else can you get when you use it in mixed form but an even more usable welding application ready for all types of metals. 
On one of our blogs, we will teach you how to have anti-splatter techniques to avoid the extra work of cleaning up your weld work when using pure CO2.
