You can choose from a variety of different shielding gases and blends when you’re welding.
There are a few things you must understand before you’re able to make an informed decision on the type of shielding gas you need.
These are the questions you should ask yourself before you choose a shielding gas.
- Do you care about the “look” of the weld?
- Does spatter matter to you?
- Does the weld require a deep penetration, or do you want to minimize weld penetration as much as possible?
- Are you concerned about how many fumes your weld generates?
There are a few other questions you should ask yourself but, these are the base questions.
The following process can help you select the correct gas blend for your welds.
- What kind of materials are you welding?
- How thick is the material and what kind of condition is it in?
- What kind of welding position do you want to use? Also understand that the process you use is also hindered by the equipment you have available as well as your skills and productivity levels you desire.
- What are the requirements of the job? The chart below will give you a solid understanding of what you should be looking for.
What’s the function of shielding gas?
The main function of shielding gas is to reduce the weld’s exposure to outside contaminants such as oxygen, hydrogen, nitrogen, etc. When a weld is introduced to these elements it can cause imperfections to occur such as:
Types of Shielding Gasses
Argon: Color-less, odor-less, and non-toxic noble gas that makes up about .93% of the earth’s atmosphere. Argon helps provide a clean and inert environment that’s rid of oxygen and nitrogen. For metal fabrication Argon is used to create an inert gas shield during welding. It’s also occasionally mixed with oxygen, helium, hydrogen, or carbon dioxide to facilitate metal transfer in MIG welding.
Argon has low conductivity and ionization potential, which are properties that result in a transfer of heat to the arc’s outer regions.
Helium: Color-less, odor-less, taste-less, chemically inert, and non-toxic, helium is non-flammabe while also having a high thermal conductivity. Helium usually helps increase travel speed and weld pool fluidity. Helium has a high ionization potential and conductivity, which yields opposite effects of Argon.
Carbon Dioxide: Co2 is an odor-less, taste-less, color-less, non-flammable. It’s typically used alongside Argon during welding or in its pure vapor state. Doing so prevents contaminants from the atmosphere to enter the weld. At the temperatures created in the arc Co2 tends to disassociate and turn into Co and O2. This results in oxidizing of the base metal as well as dealloying of the bead.
Oxygen: 21% of the earth’s atmosphere is made up of oxygen. It’s also a taste-less, odor-less, color-less gas and is used to support oxyfuel in curring operations. Oxygen creates a shallow penetration profile with high heat input at the surface of the work.
Propane: A color-less, liquified, and flammable gas that naturally smells like gas. The flame temperature of an oxy-propane flame is lower than that of propylene or acetylene.
Propylene: A liquified, flammable, color-less gas that smells slightly sweet. Propylene has the qualities of an acetylene flame and the secondary heating capacity of propane.
Nitrogen: Nitrogen that makes up about 78% of the earth’s atmosphere. It’s a non-toxic, taste-less, color-less, and is non-flammable at atmospheric temperatures / pressures.
Each of these gasses can be used separately or they can be mixed with one another to yield different effects. When gasses are blended with one another they’re mixtures are expressed in percentages.
Examples: Argon 95% – 5% Co2 (This means the blend is 95% Argon and the remaining 5% is Carbon Dioxide) or Argon 90% – 10% Co2 (This means the blend is 90% Argon and 10% Co2)
How to choose a shielding gas for MIG welding
When you MIG weld with a shielding gas (and the correct solid wire electrode) you produce a decent looking, clean weld and eliminate the need to constantly change your welding electrode. This means that using a shielding gas will make the welding process more efficient and much cleaner of a process.
The term “MIG” stands for Metal Inert Gas (it’s also called Gas Metal Arc Welding or Metal Active Gas) which means that welders typically use an inert gas to shield their welds with. Inert gasses typically used in MIG welding are Argon and Helium.
When you’re choosing a shielding gas it’s still a great idea to consult a professional at a welding store as they’ll be able to give you input designed to fit your needs.
Typically, you’ll see mixed shielding gasses being used for MIG welding (with some of these gasses being active gasses).
Shielding gasses for MIG welding
A thing to keep in mind when you’re MIG welding is that there are a number of shielding gasses / mixes you can choose. Knowing that, there are a few considerations you’ll want to take before you choose your gas:
- How much does the shielding gas cost?
- How do you want the weld to look?
- The material you’re weld
- How the weld was prepped
- The post-weld clean up
- Weld transfer process
- How productive do you want to be?
A few of the commonly used mixes for MIG (MAG / GMAW) welding are:
- 2% Carbon Dioxide and 98% Argon: Is great for stainless steel.
- 25% Carbon Dioxide and 75% Argon
- 100% Carbon Dioxide: Is great for Carbon Steel and produces the deepest penetration, roughest weld, and smoke.
- 100% Argon: Typically used for Aluminum, Copper, Copper Alloys, Magnesium, Nickel, Nickel Alloys, and Titanium.
Video credits to Lincolnelectrictv. It has a great explanation for choosing a shielding gas and goes over the costs of each kind.
How to choose a shielding gas for TIG Welding
The typical gas used for TIG welding is Argon while Helium can also be added to create a mixture that increases the fluidity and penetration of the weld pool.
A few of the commonly used mixes for TIG (GTAW) welding are:
- Ar + Hea
- Ar + (2-5)% H2a,b
- Ar + (1-2)% N2
- Ar + 30% He + (1-2)% N2
*a means that it improves flow when compared to Pure Argon
*b means that it’s preferable for Automatic welding, has a high welding speed, and runs the risk of porosity in multi-run welds.
Video credits to Weldingtipsandtricks. It explains the process of choosing a shielding gas for TIG welding.
What is optimal gas flow?
The flow rates for shielding gas are determined by the welding process, operating parameters, and welding position. With GTAW, the flow rate is typically between 10 and 20 CFH or cubic feet per hour. For GTAW when you use a torch alongside a gas lens you’ll ensure a laminar flow, something that contributes to high weld quality, as well as lower than 10 percent gas consumption rates.
With FCAW and GMAW, the flow rate that’s recommended will vary – between 30 and 45 CFH – varying with the welding position, shielding gas composition, and operating current. When it comes to flat position welding, the helium enhanced mixtures require a slightly higher flow rate than weld that’s argon based. The gas flow rates will likely be reduced if the work to nozzle distance is as close as possible. In a few instances, the production site surveys will determine that the shielding gas flow rates are typically set in excess of 50 CFH. This may contribute to a poor weld quality as the atmospheric gases will be drawn into the arc zone because of too much gas turbulence. An optimized flow will enhance the quality and will reduce shielding gas usage.
Cost effective joining and shielding gasses
The selection of a shielding gas is highly important to get cost-effective joining of aluminum, carbon steel, and stainless steel. One can select a gas, like argon when doing aluminum welding, to achieve a suitable bead shape, minimum spatter, and suitable arc stability.
2-part blends such as carbon dioxide/argon mixtures, could perform well in a number of stainless steel and carbon steel applications where one would use pulsed spray or conventional transfer.
A lower carbon dioxide content will lower the amount of welding fumes that are generated. When you need less post weld cleanup, enhanced bead appearance, and low spatter, 3 part gas blends will provide solid results and also improve upon the welding productivity.
The base metal thickness, operator skill level, production demands, and welding position will need to be carefully considered when one is optimizing and selecting a joining process. When you have an understanding of shielding gasses, you’ll be able to optimize the welding process so as to improve quality and lower cost.
