Welding gas is an important component of MIG and TIG welding. While you can attempt to MIG weld without it, the quality of the resulting weld is just not as good. And in the case of TIG welding, gasless welding is not at all possible.
Unbeknownst to many, choosing what welding gas to use is not limited to selecting which one is suitable for your chosen workpiece. You also need to consider other aspects, such as the right settings when using for MIG and TIG welding and the cylinder sizes suitable for your workshop.
At a loss about all these? You don’t have to. You just need to keep reading to find out more, as well as learn some tips that can prove handy for all your welding projects.
Types of Welding Gas
When we talk about gases in welding, most people would immediately think of the shielding gas. What they don’t realize is that there are actually different types of welding gases used. There are also gases used to clean the welds formed or protect the materials after welding.
Some metals or filler rods require preheating before welding to ensure a quality weld or brazing. For this purpose, you need to use heating gas. This type of gas is typically a mix of fuel gas with some oxygen added and when it is lit up, it gets warm enough to heat, but not melt, the materials.
To prevent the contamination of the molten pool when MIG or TIG welding, which results in an ugly weld, you need to use a shielding gas. This type of gas is important because it not only affects the appearance of the weld but also the bead shape and penetration, alloy content, fumes produced, and many others.
Shielding gases are often inert gases and can either be pure, which is made up of a single type of gas, or a mix of different gases. The pure gases are argon, carbon dioxide, and helium, while the mixtures used as shielding gases can include different combinations of pure gases or adding oxygen, nitrogen, or hydrogen to them.
Among all the pure gases, argon is the most widely used shielding gas because it is inert and will not cause a reaction to the metals being welded. Because of this, it is suitable for aluminum welding, as well as for other metals that are refractory or reactive. You can use this gas with all types of materials in TIG welding, while its use in MIG welding is limited to nonferrous materials.
Argon also causes a low heat transfer because both its ionization potential and thermal conductivity are low, creating the deep and narrow penetration it is known for. Not only that, but you also get a very stable arc that allows you to have better control over the weld pool. Also, argon aids in the breaking down of any oxides present in the workpiece.
In contrast, helium is known for having high ionization potential and thermal conductivity that results in a deep but wider weld and increased heat. Unfortunately, it also makes starting the arc much more difficult, especially if you do not use the correct settings of your MIG or TIG welder. This gas is not commonly used in MIG welding and is only suitable for nonferrous metals when using it for TIG welding.
Carbon dioxide is normally only used for MIG welding, as well as the highly-similar flux core welding, because it has complex interactions with different metals. With this gas, you get a balanced weld ratio in terms of depth and width due to its wide penetration and high heat. This increased heat is also because of its low thermal conductivity and ionization potential.
Using different shielding gas mixtures is a common practice. In fact, these mixtures even work better with certain metals compared to using pure gases. Found below are the different metals and recommended mixtures of shielding gases to be used when welding:
- Carbon steel – argon and carbon dioxide, argon and oxygen, argon, carbon dioxide, and oxygen
- Stainless steel – argon and carbon dioxide, argon, carbon dioxide, and helium (aka tri-mix), nitrogen and hydrogen (only for austenitic stainless steel)
- Aluminum – argon and helium, tri-mix
- Light gauge steel – argon and oxygen
- Nickel – argon and helium
- Copper – argon and helium
A common issue is that welders take strides to ensure a neat weld on the surface but neglect the underside of the weld. Because of this, the underside looks different and can even be contaminated because it is unprotected by any shielding gas.
To address all these, doing a back purge is necessary for a clean weld on both the surface and its underside. When back purging, a purging gas that acts like a shielding gas is used for the underside. This process is usually done when welding stainless steel, as well as nickel and titanium alloys.
Carbon dioxide and nitrogen are often used as purging gases, but you can also use other inert gases like helium and argon.
In instances where you need to ensure that your finished weld must be completely flaw-free, a shielding gas may not be enough to prevent contamination. As the weld cools, it can still be stained or damaged by any contaminants present in the atmosphere. Using a blanketing gas, often nitrogen, will protect your workpiece from these contaminants.
Shielding gases are the welding gases used most often, but it is also important to familiarize yourself with the other types you can use for your projects.
Welding Gas Cylinder Sizes
A welding gas is typically not flammable but it still poses some health risks, that is why you need to choose the right cylinder size for your workshop. Not only that, but it will also provide convenience for you because you don’t have to keep getting a new one when you run out of gas while welding.
High-pressure gases, namely oxygen, helium, nitrogen, hydrogen, and carbon dioxide, use cylinders with uniform sizes. A high-pressure gas cylinder, also called a bottle or tank, typically has volumes ranging from 20 to 300 cubic feet. Bottle sizes are indicated either by their volume or represented by letters, such as:
- R = 20 standard cubic foot or scf
- V = 40 scf
- Q = 80 scf
- D = 125 scf
- S = 150 scf
- K = 200 scf
- T = 300 scf
Note that the welding gas bottle sizes above apply for those encased in steel cylinders. There are also aluminum cylinders available, but they have much more limited sizes.
Low-pressure gases, on the other hand, have more varied sizes.
Gas Tanks for Welding
When it comes to welding, argon is arguably considered as the most important gas. Different welding types use different amounts of argon, as well as other gases, so you need to know which gas tanks to use for your welding project.
The problem lies in the fact that, with the exception of high-pressure gas bottles, many of the gas tanks used in welding come in different sizes depending on the manufacturer. This is purposely done by manufacturers so that they can easily identify which tanks are theirs.
Despite this, they also make gas tanks in sizes that can be considered common to different manufacturers. Argon, for example, has the following common sizes that are represented either by a letter or number:
- R or 20 = 21 cubic feet
- RR or 40 = 44 cubic feet
- Q1 or 60 = 65 cubic feet
- Q or 80 = 83 cubic feet
- S or 125 = 125 cubic feet
- S or 150 = 155 cubic feet
- K or 250 = 251 cubic feet
- T or 330 = 335 cubic feet
Note that the S-sized gas tanks have two types available, that is why it is important for you to check the actual volume when purchasing this type of tank. And in most cases, the smallest-sized gas tank allows you to weld continuously for an average of 1 hour to 1 hour and a half.
Gas Settings for MIG and TIG Welding
Aside from choosing which welding gas to use and the right bottle size you need, you also need to determine the right gas settings for MIG and TIG welding.
Using welding gases is not as simple as letting them flow freely as you weld. You need to make sure that just the right amount is being released because this will also affect weld quality. Both MIG and TIG welding have uniform gas settings regardless of the type of shielding gas.
When it comes to MIG welding, the flow rate typically ranges from 25 to 30 cubic foot hours (CFH) and its matching pressure should be between 3 to 7 psi. Most welders consider 20 CFH as an ideal flow rate, since setting it higher increases spattering and also makes the weld porous. Note that bigger nozzle diameters, as well as drafty conditions, will require higher gas flows.
The gas flow rate of TIG welding, on the other hand, is typically lower than that of MIG welding and ranges from 15 to 25 CFH on average. However, it can also go up to 50 CFH if you use larger cup sizes. If your flow rate is between 35 to 50 CFH, the pressure should be between 20 to 30 psi to match it. But if you have a lower flow rate, you also need to lower the psi.
MIG and TIG welding both require the flow rate and pressure to be directly proportional. That is, the higher the flow rate, the higher the required pressure. They only differ in the actual numbers.
Gas Welding Tips
These different gases are extremely helpful when welding, but using them is not as straightforward as some would think. Whether it’s your first time to use gas when welding or you have already tried it but have yet to get satisfactory results, these tips are sure to help you out.
- Use a gas lens if you want the flow of shielding gas to be evenly distributed and lessen weld defects caused by contamination
- If you want a laminar flow, opt for a converging nozzle with the longest length and largest diameter suitable for your welding project
- To get the best results, you should do a pre-flow and post-flow of the shielding gas
- Don’t ignore any gas leaks. Not only will it contaminate your work, but you also end up wasting gas and money because of it
- Back purging is the best way to prevent sugaring or oxidation on the underside of your workpiece
- For aluminum welding, lessen the gas if you are welding on A/C
- When working on sheet metal, opt for a shielding gas with a higher argon content for less spatter
- Use tri-mix gas consisting of 90% helium, 8% argon, and 2% carbon dioxide when MIG welding 304 and 316L stainless steel
- Test if your gas flow is appropriate by placing your hand around 3 inches from the nozzle tip and allow the gas to flow. If you feel the gas at this distance, it means you have an adequate gas flow that will prevent a porous weld
- Refer to manufacturer recommendations in terms of which shielding gas to use with your welder and workpiece. Your shielding gas should also match your welding wire.
- Ensure that the shielding gas flowing out sufficiently protects the molten pool to reduce spatter
More is not necessarily good in terms of using welding gases. For both MIG and TIG welding, you need to use the right amount of gas for your welding projects. If you use more than what is necessary, it will be easier for your workpiece to be contaminated.