Gases for MIG Welding
When it comes to gases for mig welding, we have to know which gases are to be used to avoid producing weld that is undesirable. The main role of MIG welding gases is to act as a shielding gas for the weld pool from the surrounding atmosphere. If shielding gas will be weak or not the right combination, there is likely the oxidation and nitrogen absorption right on the weld pool. There could also be excessive sputter and porous welding results. So your choice for gas for mig welding should always be right and this is the time to know more about the mig welding gases. 
There are a number of gases that can be used on MIG welding. There is argon, carbon dioxide, helium, and oxygen. But among these four, there is only one gas that can be used singly for welding stainless steel but can still produce a good weld and this is carbon dioxide (CO2). The rest can be used as mixtures for better heat and weld penetration.
Carbon dioxide is a form of active gas or a semi-inert gas that is composed of one carbon and two oxygen atoms. Using it as a shielding gas for mig welding, CO2 can displace oxygen around the arc because being a semi-inert gas, it also has low reactivity with other substances. For the home hobbyist, the use of 100% CO2 is usually preferred. CO2 is known to provide a deeper penetration profile on joints especially on corner joints where the weld should penetrate deeper into the smallest space between metals.
Characteristic of CO2
Carbon dioxide is known as the most usable gas for MIG welding because of its reactive quality while this is the only substance that can be used in MIG welding in its purest form – on ferrous metals, so to speak. Unfortunately, using it alone has its negative effect on thinner, softer and non-ferrous metals like copper, magnesium and aluminum as it can cause oxidation.
TIG welding is the most preferred welding process when it comes to welding thin and soft metals. But it needs argon with a mixture of helium which are both noble gases in dealing with these metals. If you use carbon dioxide on TIG welding as a shielding gas, this can cause burn through and metal warping as the metals would not be able to handle the heat. On the other hand, if you don’t have a TIG welder, using pure argon on your MIG welder can also produce good welding results but only on non-ferrous metals. You also need to control the amperage to manipulate the heat from the arc. 
Pure CO2, aside from giving a deeper weld penetration is also the cheapest gas you can buy for your MIG welder. But another drawback in using it singly is the arc becomes less stable with a greater probability of spattering unlike when it gets mixed with other gases. So if you don’t like cleaning up after every weld, a mixture with other gases can be a good concept.
Mixing Argon with Gas for
We have mentioned that other gases for mig welding can be possibly used with CO2 as it lacks qualities that other gases have when dealing with thicker and heavier metals. And so far, argon is the main inert gas that can produce the best mixture with CO2. Even the expert welders agree that there is a distinctive comparison when pure CO2 is used compared to mixing it with argon. 
Generally, welders prefer the 25% CO2 and 75% argon or better known as C25 as the best gases for mig welding combinations. With CO2 being used in pure form and can produce a deeper penetration but with thinner weld surface, argon and CO2 mixture can produce also a deeper penetration but the surface of the weld is wider and flatter. This is good if you want to produce a smoother weld on fillet and butt welds. So with the combination of argon, the arc becomes hotter while providing better shielding and the electrode tends to melt faster without causing much spatter unlike with pure CO2. 
Argon is an inert gas but also a noble gas which has the characteristic of zero reaction to many substances. Inert or noble gases are used to prevent unwanted chemical reactions on welding that can result in degrading the weld output. And what we are referring to as “unwanted chemical reactions” are oxidation and hydrolysis that can be caused by the mixture of oxygen and air moisture.
Other Gases for
When choosing gas for MIG welding, it is important that you have to evaluate your welding objectives so that you can choose the right gas for certain applications. You also need to consider the price of the gas, the weld result, what you need to prepare, if there is the need for post-weld clean up, the kind of base material you want to weld and your productivity goals if you want to venture on MIG welding for work or business.
So aside from argon, some welders also use helium and oxygen to mix with CO2. Oxygen is also a reactive gas just like CO2 and if combined about 9% of CO2 could enhance weld pool fluidity while improving weld penetration and helps in creating a more stable arc. However, this mixture could only be better on mild carbon steel, stainless steel and any low alloy metals. If used on exotic metals like aluminum, copper, and magnesium, these could result in metal oxidation. 
Helium is also among the common gases for mig welding that is inert and works well with CO2 for non-ferrous metals and even on stainless steel. As a protective shield, it can produce wide and deeper penetration welds on thick metals. It should also work well with argon and some experts recommend 25% to 75% helium to 75% to 25% argon mixture. If you want to experiment on the penetration and bead profile and travel speed of your welding, you can adjust the ratio slowly until you reach your goal. Helium can produce a hotter arc. However, this is an expensive gas and if you want to use this on stainless steel, you need to tri-mix it with argon and CO2.
Combination of Gases for
To give you a better understanding of the right mixture of gases for mig welding on common metals as well as the right choice for the electrode types and sizes and the polarity setting, we are giving you some tips that based on the gas chart settings we usually see on MIG welders.
- For steel – wire type should be solid wire like ER70S-6 (wire size ranges between .024mm to 035mm) on DCEP polarity. The gas mixture should be 75% argon/25% CO2.
The use of 100% CO2 on steel can also produce excellent results (wire size .024mm to .035mm) on steel. On flux core with wire type E71T-11 on DCEN, there is no shielding gas required. This is an excellent choice for outdoor and windy applications (wire size ranges between .030mm to .045mm).
- For stainless Steel – wire type should be stainless steel on DCEP polarity. Tri-Mix 90% helium/7.5 argon/2.5% CO2. Wire size ranges between .024mm to .035mm.
- For aluminum with optional spoolmate 100 on DCEP – aluminum wire 4043ER (wire size .030mm to .035mm) and requires 100% argon.
- For aluminum with optional spoolmate 150 on DCEP – aluminum wire 4043 ER and 5356 (wire size .030 to .035 mm) also requires 100% argon.
OUR
MIG welding can be your best welding process once you know the right combination of its required gas. It is also the easiest welding process to learn and master. But if you plan to buy your MIG welder for the first time, make sure you choose a unit that has a chart for the gas mixture so you know the kinds of metal you can efficiently use your MIG welder. Or if you’re buying from an actual store, you can ask the store personnel to recommend the proper gas combination to match your metals including the corresponding size of the wire, the electrode type and the polarity.
Using different gases for mig welding can help you complete your projects regardless of the metal type you need to weld. Carbon dioxide is the most usable gas in MIG welding. But as we have said, it has its downside when it deals with thinner metals. More so, if you need to weld thin metals with a MIG, you have to learn the right mixture of CO2 with inert gases, or else you should opt for the TIG welder. 
Some questions that come to us inquiring about the possibility of mig welding without gas if it could be possible. Our answer is yes, this could be possible. However, there are some considerations we have to note and we shall discuss this on our other blogs.
