For any type of welding it’s important to choose the right mixture. There are different gases for each process, as well as different ratios depending on the application. Below you will find all the information you need about gases to create the perfect welds!
In order to choose the right shielding gas, it’s important to understand its role when welding. The main role of shielding the weld pool is to prevent exposure of the molten metal to oxygen, nitrogen and moisture that naturally occurs in the air. These three elements will react with the weld pool, causing porosity (creating small holes in the welded bead, making the bead porous) and excessive splatter. Gases can also aid in penetration and arc stability. Below are four different processes, along with the types of shielding gas and their application.
MIG: An abbreviation of Metal Inert Gas welding, or also known as GMAW, can mean both MIG and MAG depending on the type of gas used. MIG uses an inert shielding mixture (meaning non-reactive with metal). An example is Argon, which is used to shield the welds from Oxygen, Nitrogen, moisture and contaminants in the air. Inert means won’t help with penetration or arc stability, as it’s unreactive but ensures no contaminants can enter the weld pool.
MAG: is a similar process to MIG, with the difference in the type of gas used. MAG stands for Metal Active Gas where Carbon Dioxide or Oxygen is used alongside an inert gas. This will help arc stability and penetration, as well as reducing splatter. MAG can be useful when working with thicker metals, as the Oxygen/Carbon Dioxide will aid penetration and stability of the arc.
TIG: Tungsten Inert Gas is the process of using a tungsten electrode that delivers the current to the arc. An inert gas is delivered to the weld pool for protection and cooling. TIG is typically used for intricate work where stronger and higher quality welds are needed, however the learning curve is much greater compared to GMAW.
FCAW: Flux Cored is a versatile process, typically used with mild or low-allow steel. FCAW is mainly used in heavy fabrication such as structural welding or shipbuilding for example. Most commonly a blend of Carbon Dioxide and Argon is used, if the flux core wire isn’t self-shielding.
It’s common to find as 100% of a mixture due being inert, making it very stable due to it’s unreactive properties. You can find a pure mixture when working with aluminium, magnesium or titanium, or a large component for materials such as carbon steel. It’s common to add CO2 alongside Argon in mixtures between 75-92% Argon and 25-5% CO2. Usually these mixtures would be used in a commercial environment as CO2 added to the shielding mixture reduces splatter, lowering production costs.
CO2 is reactive meaning it will oxidize metal unlike Argon which is inert. Despite its reactive properties, it’s the only reactive gas that you will find in 100% concentrations without an inert additive. Typically pure CO2 is used in short circuit welding. Carbon Dioxide is also cheap as well as providing deeper weld penetration which is useful when working with thicker material. The downsides of a pure Carbon Dioxide is increased splatter and more unstable arc, which can be rectified by reducing the CO2 content with Argon.
Typically used with non-ferrous metals, as well as stainless steel in the mixture alongside Argon and CO2. When added to a mixture Helium will produce wide, deeply penetrating welds suitable for thicker metals. It will also create a hotter arc which will increase travel speeds and productivity when welding on a large scale. Generally helium will be between 25% and 75% of a mixture depending on application, depending on its concentration will change its effects on weld penetration, bead profile and speed of travel. A unique property of Helium is it’s extremely light atomic weight, this means you need a higher flow rate to compensate.
Used when working with nickel and stainless steel – in particular thicker material due to hydrogen’s ability to improve the pools fluidity and improve cleanliness of the materials surface. A downside of Hydrogen is embrittlement, typically when welding carbon steel and many different alloys. For this reason hydrogen use is limited to nickel and stainless steel, in a mixture alongside argon with hydrogen being up to 10% of the mixture depending on application. You may also find hydrogen in argon-CO2 blends to prevent the oxidizing effect carbon dioxide has.
Generally used in small amounts between 2-5%, oxygen is used in a mixture to increase arc stability and reduce surface tension of the weld pool. The reduction in surface tension allows the molten metal to penetrate deeper into the two metals, producing a better weld. Oxygen will oxidise the molten metal, therefore it’s not suitable when welding aluminium, magnesium and copper as well as some exotic metals. If too much oxygen is present in the gas blend, it can cause the heated area of the metal to become brittle.
Argon and CO2 blends are typically found when welding with carbon, low-alloy steels as well as stainless steel. The higher CO2 concentration present in the blend will increase weld penetration and bead wetting properties. It should be noted that higher CO2 concentrations in a mixture will increase the amount of splatter. Argon/CO2 can be used across various metal thicknesses and applications, such as structural steel, farm machinery and tools. Higher levels of CO2 (20%+) will be found when short arc welding as well as a gas of flux-cored wires, whereas lower concentrations will be found when pulse arc welding or spray arc welding.
Oxygen along with Argon are found in conventional and pulsed spray transfer. Used when working with clean Carbon and Stainless Steel. The concentration of oxygen is 5% or less, as too much oxygen can react with the weld. The addition of Oxygen with Argon reduces the amount of splatter, whilst increasing weld pool fluidity.
This mix is used for short-circuit transfer welding with Stainless Steel. The Carbon Dioxide concentration is low to reduce Carbon absorption and maintain corrosion resistance which is especially important with multi pass welds. The addition of Carbon Dioxide and Argon into the mix increase weld stability and penetration. The Helium content is kept high to increase arc temperature, ensuring deep penetration and fluidity of the Stainless Steel weld pool.
Getting the full potential from your chosen mixture is important, so you can save money as well as producing higher quality welds. Choosing the correct consumables such as a diffuser, contact tip and nozzle will determine the precision of delivery to the weld pool.
Choosing consumables with a smooth surface will avoid splatter build up that may reduce flow, therefore providing a smoother delivery. An appropriately sized nozzle for your desired application will help to avoid splatter build up. A nozzle that’s too narrow will become clogged quicker than a larger nozzle, which will also negatively impact flow.
A splatter guard can be used to prevent splatter build up. A reputable brand of splatter guard will act as a second line of defence to splatter, as well as gas diffusion. Using a splatter guard will help to deliver a consistent and smooth flow. Ensure to choose a quality diffuser by a reputable brand – off brands and poorly designed pieces of equipment could negatively impact flow, resulting in poorer welds.
Different gases respond differently when introduced to the heat of an arc. Here are three properties each possess.
Reactivity: Whether a gas reacts with the weld pool will determine its classification within two groups – either inert or active. Inert gases, also known as noble gases such as Argon are unreactive. Active gases also known as reactive gases such as CO2 or Oxygen will react or combine with other elements within the weld pool. Not all active gases are reactive all the time, for instance CO2 at room temperature is inert, but when exposed to the temperature of the arc it becomes reactive.
Thermal Conductivity: The gases ability to transfer thermal energy will affect the shape of the arc, weld penetration as well as temperature distribution within the arc. Carbon Dioxide has a higher thermal conductivity than Argon, allowing thermal energy to dissipate through the gas faster and more even compared to Argon.
Ionization: How much energy is needed to ionize the gases (Transform from its gas state to a plasma state where the ions are positively charged). The lower the ionization potential the lower input energy is needed to initiate and maintain arc stability. For example the ionization potential for Carbon Dioxide is 14.4 eV compared to 15.7 eV for Argon, meaning it’s
Depending on the type of flux-cored wire used it may not be necessary to shield the weld pool. There are two types of flux-cored wire, self-shielding and non-shielded. If you’re using a self-shielding wire, the wire itself contains deoxidizers such as Aluminium, Silicone and Manganese that will be consumed when they come into contact with Air at high temperature.
The reaction will shield the weld as the wire is consumed, mitigating the need for a shielding gas. If you’re using a wire that isn’t self-shielding, you will need to use an appropriate mixture to ensure contaminants can’t enter the weld pool, and potentially enhance characteristics of the arc depending on the metal used.
If you’re using regular self-shielding flux core wire, there is no need to use extra gas. You can affect the integrity of the joined material or change arc characteristics, which is dangerous when used in applications that require an integral weld.