In the process, we will also learn different types of shielding gases that are commonly used in TIG Welding.
A Brief Note on TIG Welding
Before looking at the TIG Welding Gas and its different types, let us take a quick overview of the TIG Welding Process. Gas Tungsten Arc Welding (GTAW), which is also known as TIG Welding, is a unique welding process that produces one of the highest quality welds among all Electric Arc Welding processes. Before TIG Welding, the ARC Welding process used carbon electrodes that doesn’t have any protection from the air. In the early 1940s, a new technique was introduced during the second world war. Here, the carbon electrodes were replaced by tungsten electrodes, and helium gas (an inert gas) was used as a shield to protect the electrode and the molten metal from the surrounding air. As a result, the quality of welds is much better. TIG Welding originated in the U.S. In the early days, helium was abundantly available there. As helium became the main shielding gas for this welding process, it was known as Heliarc Welding. A couple of years later, the TIG welding process became popular in Europe. But helium was not widely available there and hence they went with argon. As expected, they named it Argonarc Welding. Both Helium and Argon are inert gases. Hence, the name TIG Welding, which stands for Tungsten Inert Gas Welding became popular worldwide. Even though inert gases are the main choice as Shielding Gas, sometimes, other gases and a mixture of gases also became applicable for this welding process. Hence, the American Welding Society renamed it Gas Tungsten Arc Welding (GTAW).
Shielding and its Importance
We know that Arc Welding is a high-temperature process where we melt the metals to weld them. While the high temperature helps in melting the metals, it also causes an important problem that can ruin the process. What is this problem? Temperatures close to the melting point of a metal can accelerate the surrounding air and causes a reaction with the molten metal or the electrode. This can contaminate the welding process and might lead to welding deformities, welding cracks, porosity, formation of slags, making the welding spot brittle, or any other. The two main culprits in this contamination are oxygen and nitrogen. When a metal at a very high temperature reacts with oxygen, it forms oxides. This is bad for the longevity of the weld. There are two problems with nitrogen. One is as the weld cools and the molten metal solidifies, the trapped nitrogen gas in the form of bubbles escapes and this results in the formation of pores in the weld. When atmospheric nitrogen mixes with molten metal, it forms nitrides. Metal nitrides can make the weld brittle. So, what can we do to prevent this from happening? A simple and reliable approach is to shield the welding process from the surrounding atmosphere. There are two ways we can do this; Shielding Gas and Flux.
Gas Shielding
Shielding Gases form an envelope around the molten metal and prevent any contaminants to enter the welding zone and react with the metal. Gases essentially purge the surrounding gases from the metal and create a shield around the weld spot. Welding Torches or Guns are designed to direct the shielding gas around the metal and electrode to protect them. Both TIG Welding and MIG Welding use shielding gases. In the later section, we will see more details about TIG Welding Gas. In a separate guide, we will understand MIG Welding Gas.
Flux Shielding
Welding Flux is also another way to shield the molten pool of metal and the electrode. Shielded Metal Arc Welding, Submerged Arc Welding, Plasma Arc Welding, etc. use fluxes for shielding. There are a couple of ways in which you can use flux shielding. The first and simple approach is to apply a solid flux on the surface of the metal before welding. Next, you can use it with the electrode wire through a binding agent. Alternatively, some welding processes have flux as a core in the wire itself. Irrespective of how you apply it, welding flux provides shielding action in two ways. The solid (or semi-solid goop) flux will melt when it meets the heat of the arc. The liquid flux will react with the contaminants on the surface of the metal and forms solid slags on top of the molten metal. Once the metal solidifies, you have to clean the surface to remove the flux slags. The next way is quite interesting. When we start the welding process, the high-temperature arc will decompose the flux and releases carbon dioxide into the surroundings. This will push the surrounding air and prevents any contamination.
TIG Welding Gas
As we have seen in the previous section, TIG Welding, or Gas Tungsten Arc Welding uses shielding gases to protect the electrode and the molten pool of metal from contamination. So, the immediate question we get is “What gases are suitable for Shielding TIG Welding?”. In the early days of TIG Welding (early 1940s), TIG Welding used Helium as a shielding gas. Hence, before the term TIG Welding or GTAW are popular, this welding process is known as Heliarc Welding. The main reason for using Helium was its availability and cost. It was abundantly available in the U.S. and was very affordable. But when Heliarc Welding came to Europe (in the mid-1940s), the availability of Helium gas was a problem. Hence, they worked around it and started using Argon as the shielding gas. As a result, this welding process was known as Argonarc Welding in Europe. If you observe, both Helium and Argon are Inert Gases. Later, depending on the metal we are welding, the shielding gas could be any inert gas (Argon or Helium) or a mixture of inter gases. Combining this with the main electrode, which is Tungsten, the name Tungsten Inert Gas Welding or TIG Welding became popular. Nowadays, Argon is the most popular type of shielding gas for TIG Welding throughout the world. Apart from Argon, we also use Helium, a combination of Argon and Helium, a mixture of Argon and Hydrogen, and Nitrogen are the commonly used TIG Welding Gases.
Additional Features of TIG Welding Gas
Apart from protecting the molten metal and the electrode from air contaminants, Shielding Gas can also help in improving the quality of the welding with the following factors.
Involves in the ignition of Arc Responsible for the stability of the Arc Deposition of materials on top of the metal Controls the penetration depth of the arc Determines the shape of the Arc Forms guard between the molten welding pool and nearby metal
Types of TIG Welding Gases
Now that we have seen the basics of TIG Welding Gas, let us dive a little bit deeper are understand more about different types of TIG Welding Gases.
Argon
Argon (Ar) with the atomic number 18 and an atomic mass of 40, is an inert gas (which means it has no chemical reaction with other materials). It is present in the atmosphere at only 0.9%. You can extract Argon as a by-product through the separation of liquified air to produce oxygen. The density of Argon is about one and a half times that of the air. When you combine this with its low ionization potential and high thermal conductivity, it is an excellent choice for forming an envelope around the welding zone for a significantly longer duration. As a result, Argon is one of the most common and popular TIG Welding Shielding Gases throughout the world. The cost of Argon is also low and you can use it for welding most materials such as steel (mild, stainless, carbon, low-alloy), Aluminum (and its alloys), Copper (and its alloys), Titanium, and Magnesium.
Helium
Helium, with atomic number 2 and atomic mass 4, is another inert gas. Its low cost and abundance made it a popular choice of TIG Welding Gas in the U.S. One of the important properties of Helium is its high thermal conductivity. If you compare the same arc length in the case of Argon and Helium, Helium has a higher arc voltage, which in turn means it can transfer more heat to the metals. This feature is very useful when you are welding heavy metal plates with high thermal conductivity. It can also help in deeper and wider penetration of the arc. Helium is suitable for machine welding rather than manual hand welding. You can get cylinders of Helium gas stored under high pressure. For welding, you need more than 99.99% pure Helium. It is suitable for welding Aluminum and Copper. An important point to remember is Helium is lighter than air. So, for a successful weld, you need double the flow rate when compared to Argon.
Argon + Helium
The mixture of Argon and Helium is also popular as it can produce higher heat to speed up the welding process. A typical combination of 75% Argon and 25% Helium is a common gas mixture. The higher ionization potential of Helium (25 eV when compared to 16 eV for Argon) is responsible for the heat while the higher density of Argon means you need less flow rate. Argon – Helium mixture has a problem with arc initiation (which is even worse in the case of pure Helium). A mixture of Argon and Helium is suitable for low-alloy steel and alloys of Aluminum and Copper.
Argon + Hydrogen (H2)
In order to increase the heat energy of the arc, we can combine Hydrogen (H2) with Argon. Depending on the material we are working on, you can add anywhere between 1% to 5% of Hydrogen. As Hydrogen is a reducing agent, it helps in preventing oxides on the surface of the weld. Note that the Argon and Hydrogen mixture Shielding gas is suitable for mild steel and stainless steel (where it doesn’t interfere with the metallic properties of the material). By increasing the quantity of Hydrogen in the mixture, you can use this gas for welding Nickel Alloys, Nickel – Copper, etc.
Nitrogen
Nitrogen is not an inert gas but it is a diatomic gas. The advantage of Nitrogen is that it can transfer more heat than monatomic gases i.e., Argon and Helium. So, we often mix Nitrogen with Argon to increase the heat transfer capabilities of Argon. As Argon, Helium, a Mixture of Argon and Helium, and a mixture of Argon and Hydrogen are popular and are suitable for welding all common metals, the use of Nitrogen did not become very successful in TIG Welding.
TIG Welding Gases for Different Metals
Conclusion
The choice of Shielding Gas in TIG Welding is very important as it helps in protecting the molten metal and electrode from contaminants. TIG Welding Gas can also determine the process of welding i.e., manual or automatic. Argon 75 + Helium 25 Argon 70 + Helium 30 Argon 50 + Helium 50 Argon 99 + Hydrogen 1 Argon 98.5 + Hydrogen 1.5 Argon 75 + Helium 25 Argon 70 + Helium 30 Argon 50 + Helium 50 Argon 75 + Helium 25 Argon 70 + Helium 30 Argon 50 + Helium 50 Argon 70 + Helium 30 Argon 50 + Helium 50 Argon 99 + Hydrogen 1 Argon 98.5 + Hydrogen 1.5 Argon 98 + Hydrogen 2 Argon 97 + Hydrogen 3 Argon 95 + Hydrogen 5 Welding Grade Helium (99.993% Pure) Argon 75 + Helium 25 Argon 70 + Helium 30 Argon 50 + Helium 50 Welding Grade Helium (99.993% Pure) Argon 75 + Helium 25 Argon 70 + Helium 30 Argon 50 + Helium 50 Argon 98 + Nitrogen 2 Argon 70 + Helium 30 Argon 50 + Helium 50 Argon 98.5 + Hydrogen 1.5 Argon 98 + Hydrogen 2 Argon 97 + Hydrogen 3 Argon 95 + Hydrogen 5 Welding Grade Helium (99.993% Pure) Additionally, the type of Shielding Gas is also responsible for high heat transformation. In this guide, we saw the basics of TIG Welding and looked at the essentials of TIG Welding Gas. After that, we understood the importance of Shielding Gas and also saw different types of TIG Welding Shielding gases. Finally, we listed out some popular choices of Shielding Gases for different types of metals. Comment * Name * Email * Website
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