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Welding covers a vast list of applications. We use it in industrial and agricultural practices, as well as everywhere we need two or more components fused. We typically use welding with metals and thermoplastics.
Because of the different materials, we can fuse through welding, there are also varying welding equipment to make these welding processes easier. Additionally, these machines utilize fuels and consumables to make the fabrication process successful.
Gas Metal Arc Welding (GMAW)
Gas metal arc welding is a process that uses the heat generated from an electric arc between a consumable electrode and a workpiece or pieces of a workpiece. The generated heat melts the metals in a weld pool that fuses as it cools.
In GMAW, the consumable electrode comes in the form of a long, thin wire rolled or wound in a spool. During the welding process, the welder feeds this wire into the welding zone to provide the required welding filler metal to fill the welding gap. The electrode typically has the same material as the workpiece.
A GMAW device uses a nozzle that simultaneously feeds both the electrode and the gas into a weld pool. The gas functions as a shielding gas while the nozzle releases it around the melting electrode.
What Is Shielding Gas?
As its name suggests, a shielding gas protects the molten metal from oxidation and contamination. Welders have used shielding gases to maintain the quality of their work since the 1920s. As World War II raged on, shielding gases evolved into a commercial standard from being a vocational practice.
If you want to become a successful welder, you have to understand the importance of shielding gases. You have to know that substances in the atmosphere can ruin the quality of every weld bead you make, among several other factors.
The primary intent of using a shielding gas is to avoid the exposure of the molten weld pool to hydrogen, nitrogen, and oxygen in the surrounding air. If the weld pool becomes exposed to these gases, it will have excessive spatter and holes in the weld bead, resulting in weaker welds.
Additionally, choosing the right shielding gas can impact the whole welding process. After using different shielding gases, you will notice the difference in arc and metal transfer characteristics, welding speed, weld penetration, and undercut tendencies. You will also see the variations in fusion zone widths and surface shape patterns.
MIG Welding Vs. MAG Welding
MIG welding stands for metal inert gas welding, while MAG welding stands for metal active gas welding. Both are types of GMAW processes using consumable electrodes and shielding gas.
The primary differences between MIG and MAG welding include the types of gases used and the type of base metals that use them. As its name suggests, MIG welding uses inert gases during the welding process. It is the preferred procedure for joining non-ferrous metals like aluminum, magnesium, or titanium.
On the other hand, MAG welding uses a mixture of active and inert gases. Technically speaking, if you add active gases to the shielding gas mixture, MIG welding becomes MAG welding. Welders use MAG welding for ferrous metals.
Unlike in MAG welding, the shielding gas in MIG welding does not disintegrate during the welding process. Since the shielding gas remains intact, the welding process does not induce any external chemical elements that may damage or contaminate the weld beads.
However, the downsides to MIG welding are its higher costs and limited shielding gas options. Industrial-grade inert gases are more expensive than active gases, making MAG welding the more economical choice. Moreover, MAG welding gives you the option to make variegated gas mixtures to alter welding outputs.
TIG stands for tungsten inert gas. Unlike MIG and MAG welding, TIG welding uses a fixed, non-consumable tungsten electrode. It also uses the same inert gases used in MIG welding.
What Gas Does A MIG Welder Use?
Since MIG stands for metal inert gas, it is fairly obvious that it only uses inert gases. The common characteristics of inert gases include being odorless, colorless, and monatomic. They are also chemically unreactive.
The naturally occurring inert gases include helium, neon, argon, krypton, xenon, and radon. Radon is radioactive and scarce, and it has better uses in the medical field. Likewise, neon, krypton, and xenon come in relatively small quantities and have better uses in other applications.
One percent of the air around us is argon. It comes as a pure by-product in the production of pure oxygen, and it is the best shielding gas a welder could use for aluminum welding. If you are looking to weld non-ferrous metals, you can choose between TIG or MIG welding, but be sure to use 100 percent argon for your shielding gas.
If you are looking to make fillet and butt welds, you will need a shielding gas that can deliver narrower penetration. With argon, you can produce quality fillet and butt welds using a relatively fluid and smooth arc. Moreover, using argon as a shielding gas results in minimal post-weld cleanups compared to highly reactive gases.
Many welders also often mix small amounts of helium, hydrogen, or oxygen with argon to intensify arc characteristics and improve metal transfer rates. Using such mixtures, you can change output results, as each type of gas will have a different effect on the weld pool.
Like argon, helium is also generally used by welders for non-ferrous metals. However, welders also use it on stainless steel.
Helium as shielding gas produces wide and deep penetrations on a workpiece, making it an excellent option for thick metals. It can create a hotter arc than argon, which means it travels faster and, in effect, increases productivity.
The problem is, the cost of helium is sometimes higher than its welding productivity rate, which is why it is rarely used as a shielding gas in its pure form. Instead, seasoned welders mix it with argon in variable ratios to keep the MIG application for non-ferrous metals. By adjusting the ratios between argon and helium, you can modify the bead profile and penetration.
If you plan to use helium with ferrous metals, such as stainless steel, you will have to add carbon dioxide to the argon-helium mixture. Helium is an excellent shielding gas against the oxidation of stainless steel, copper alloys, aluminum, and magnesium.
In its pure form, carbon dioxide is the most commonly used gas for welding that does not require the addition of inert gases, such as helium or argon. It is the most economical option, especially when aesthetics is not important.
However, using pure carbon dioxide changes the process from MIG to MAG welding. Pure carbon dioxide can produce deep weld penetration that makes welding thick materials highly productive.
Nevertheless, using pure carbon dioxide limits the welding to a short circuit process, which causes arc instability and more spatters when mixed with other gases. More spatters equate to a more thorough post-weld cleanup.
Since oxygen is a highly reactive gas, it also converts MIG welding to MAG welding. It is only added in small amounts to the shielding gas mixture.
In small quantities, oxygen can improve the fluidity of the weld pool, the stability of the arc, and penetration in mild carbon, stainless steel, and low alloy metals.
Oxygen is not a recommended additive to shielding gases for non-ferrous metals or other metals that can develop further damage due to oxidation. Such metals include aluminum, copper, and magnesium.
In many other applications, additives to argon include hydrogen and nitrogen. Hydrogen, in its pure form, can serve as a shielding gas for high-temperature applications.
On the other hand, nitrogen can serve as a purging gas for steel pipes or tubes. If mixed with argon, nitrogen also works as a shielding gas for stainless steel.
High-grade applications, such as those in the aerospace industry, have also used xenon as a shielding gas for welding. It is very expensive, and therefore not economical for industrial welding applications.
Factors Affecting the Welding Technique
Since MIG welding covers a wide application range, you should learn to choose your shielding gas accordingly. Evaluate your goals and set your expectations so that you can come up with the output you need.
The workpiece material, the cost of shielding gas and consumables, the desired outcome, and the post-weld cleanup requirements dictate MIG and MAG welding considerations.
Consider the main material of your workpiece. If it is prone to oxidation, stick with MIG welding and choose argon as your primary shielding gas. If oxidation, spatters, and post-weld cleanup are not a problem, carbon dioxide is the most economical option.
If you are looking for high weld quality, a good overall appearance, and minimal post-weld cleanup, stick with MIG welding. At the same time, reduce the infusion of highly reactive gases into your shielding gas mixture.
What gas does a MIG welder use? If you strictly stick with the inert gases used in MIG welding, then argon and helium are your top-of-the-line options.
Argon is the cheaper choice for having the best results. If you have more cash to spend and want to speed up the process, helium does the trick well.
Shift to MAG welding if you think the cost for MIG is not very economical. Create a shielding gas mixture that can maximize your budget for argon, add carbon dioxide into the mix, or use pure carbon dioxide and reduce the cost to a minimum.
Keep in mind that if oxidation will ruin your non-ferrous material, it is better to stick with MIG welding. Lastly, always get the best welding equipment for your welding tasks, and remember the practice safety welding protocols from AWS and ASME.
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