TIG Welding Explained

TIG welding is a stable arc welding process that uses a non-consumable tungsten electrode and an inert gas in the welding arc to create high-quality welds. It became a groundbreaking success during the 1940s when it was first used for welding together aluminium and magnesium alloys in the aerospace industry.

While it started out as a solution to manufacture aircrafts, TIG welding eventually became an accelerator in different industries offering unmatched quality. A lot of advancements and innovations in technology have been made since and this process has become irreplaceable in many instances.

What Is TIG Welding?

Tungsten inert gas welding, also known as gas tungsten arc welding (GTAW), is a welding process that joins pieces of metal together through a welding current. An inert gas is supplied to the welding torch that flows along the welding arc to protect the metals from oxidation and from forming small circular gaps. A tungsten electrode is assembled within the welding torch, which has a higher melting point than most metals.

TIG welding is sometimes confused with MIG welding. Although they have their similarities, there are some key differences that need to be pointed out.

Difference Between TIG and MIG Welding

The main difference between MIG and TIG welding processes is that TIG welding uses a non-consumable electrode and separate filler material (optional). While MIG uses a continuous, consumable wire electrode that is automatically fed to the welding gun.

TIG welding is most often performed when joining pipes and thin materials. This is thanks to its low heat input, which preserves the microstructure of the metals. When it comes to thicker materials, MIG (metal inert gas) welding is preferred. Given its lower cost versus other welding processes and its ability for high weld speeds, many resort to using MIG or spot welding for mass production.

TIG rarely creates spatter and typically requires only light polishing to remove any discoloration. It holds an edge over MIG welds when it comes to looks and thus it’s preferred when the workpiece is not coated or painted, as is often the case when welding stainless steel and aluminium. This does not mean that MIG welds can’t be aesthetically pleasing but it is rather common for MIG welds to be painted.

Depending on the project, the use of filler metal is optional for TIG welding. When feeding filler rods to the weld pool, TIG welders have to use both hands and control the heat input with the pedal at the same time. All this makes TIG welding a far more challenging process than MIG, where the filler wire is automatically fed from the torch. Most welders generally start out as MIG operators and then transition later into TIG welding.

TIG welding is not simply a plug-and-play process. The primary difference that sets the TIG welder machine apart from the others is its many adjustable features, such as the amperage flow, pulse amount, AC/DC output and inert gas flow. With all these customisable functions available, the process of TIG welding is quite versatile.

TIG Welding Process

The first step in the TIG welding process is to adjust the machine to the right settings, such as the current and voltage, through the rotating knobs on the machine. Next, the correct pressure for the inert gas in the supply tank must be set through a flowmeter regulator. The TIG torch should also be modified according to the project requirements by choosing an electrode with the correct diameter, TIG collet, and other parts. Above everything else, prioritise having clean protective gear to have a clear vision while doing welds.

After all the prep work is done, it’s time to weld the metals together. Several things should be considered to ensure a smooth flow of operation: the arc length, travel speed, torch angle, and other precautionary measures. TIG welds can run weld beads without filler material, only melting the base metals, but you can use it with filler rods or metal coils if the project requires it to.

Although the internet is filled with so-called TIG cold welding videos and pictures, this method has nothing to do with the actual cold welding process. It focuses on the appearance of the welds but it actually lacks fusion due to significantly reduced heat input and is rather ineffective in creating strong, permanent joints.

TIG Welding Aluminium

Important Details While Working

1. A proper forward angle is necessary when using the torch to prevent air pocket buildup that creates porosity in the bead.

2. A short arc length should be maintained for optimal control. The electric arc will widen as the arc length is increased.

3. Consistent travel speed is the key to keeping a consistent bead. Increasing the speed will cause a narrowing of the weld bead.

4. Avoid touching the weld pool with the tungsten electrode.

5. The size of the filler metal should be correct and the process of feeding it to the weld must be executed with proper control.

6. The shape of the tungsten electrode’s tip should always be consistent. It can be resharpened on a grinding wheel.

Materials in Gas Tungsten Arc Welding

TIG welders can utilise an array of materials. Some of the base materials listed for tungsten inert gas arc welding are:

• Aluminium

• Brass

• Bronze

• Carbon steel

• Copper

• Gold

• Magnesium

• Mild Steel

• Nickel

• Stainless steel

• Titanium steel

• Different alloys

You need to keep in mind that the process of TIG welding for each material is slightly different. Modifications can range from the size of the electrode diameter down to the electric arc applied in the materials. It is vital that the electrode has the correct diameter and that the amperage applied is correct. The lower the current, the smaller the tip angle and the diameter of the electrode. 

Non-Consumable Tungsten Electrode

Tungsten is used in this process since this rare, metallic element intrinsically has a high melting temperature (3422°C) when compared to other metals (e.g. stainless steel has a melting point from 1400 to 1530°C). Tungsten offers excellent electrical conductivity without being consumed. However, erosion can still occur on the tip during the shielded metal arc welding procedure.

Tungsten electrodes can also be alloyed to improve their properties depending on the weld type. Here are some common examples:

• Pure tungsten electrodes (green) – They offer good arc stability when using AC current. Used for light metals since they keep a clean, balled end. These are also the cheapest and applied for general-purpose work.

• Thoriated electrodes (1% thorium yellow; 2% red; 3% purple) – Quite common in the welding scene as they were the first to beat pure tungsten electrodes in DC welding arc performance. They have a high current carrying capacity and they maintain the shape of the tip longer. However, thorium emits alpha radiation, which can harm the respiratory system. A dust extraction system is required for collecting the dust during tip grinding.

• Lanthaned electrodes (1% lanthanium black, 1.5% gold, 2% blue) – Non-radioactive electrode alloyed with lanthanum oxide. Characterised by excellent arc stability properties with low erosion rate. A bit less efficient than thoriated electrodes.

• Ceriated electrodes (2% cerium grey) – Non-radioactive electrode alloyed with cerium oxide. These electrodes have great arc starting but less current capacity than lanthaned electrodes.

• Zirconiated electrodes (0.7-0.9% zirconium white, 0.15-0.5% brown) – These electrodes combine tungsten with zirconium oxide. This alloy has a high resistance to contamination and longer electrode life. Produces an extremely stable arc, thus it is used when the highest quality is needed.

• Cerium lanthanium electrodes (pink) – A combination of ceriated and lanthaned electrodes offering simplified arc ignition with a long life span.

Inert Gas

Inert shielding gas is fed to the TIG torch to keep the weld pool free from contamination while the current is supplied to the welding arc. The shielding gas flow is essential in protecting the weld puddle from oxidation and impurities from the atmosphere while the metals are melted and fused along with the filler rod.

The most common shielding gas used for this process is argon. Other combinations of hydrogen and argon and a mixture of helium and argon are used when other factors are considered (e.g. metals to be welded, welding speed, material penetration, etc).

Welding Torch

A welding torch is a mechanical tool specialised in melting and fusing metals. It has several types depending on its use:

• Air-cooled TIG torches only have one gas input and are more prone to overheating, unlike water-cooled TIG torches. The primary use of these torches is for thin-walled metals and minor projects.

• Water-cooled TIG torches have a gas input while having an input and output for water lines. This is an advantage for larger projects that need rapid cooling. This comes with its price though, as a water cooler system has to be installed.

Power Source

The source of the current in gas tungsten arc welding should be drooping and constant. This allows for stable and consistent heat input. You can also switch between alternating current (AC) to direct current (DC) power source depending on the material type and weld output you desire.

AC vs DC power

There are three options available for the welding current along with its own respective uses:

• AC welding uses an alternating current between the positive and negative polarities, maintaining the heat without overheating the base material. Commonly used materials are aluminium and magnesium.

• DC power electrode negative uses the negative polarity on the torch to pinpoint the energy flow to the material, much like a hose spraying water on a targeted area. This makes it more appealing to all metals, excluding aluminium and magnesium.

• DC power electrode positive is hardly used in TIG welding since the current is flowing towards the electrode, making it ball up from the rapid heat input. The only plus side in DCEP is the presence of a “cleaning action” wherein the oxides in the weld pool’s surface give off a shiny appearance.

Another factor to keep in mind is the applied frequency Hz. Lower frequencies create a wider bead with decent penetration, whereas higher frequencies allow for more control and penetration in the weld area.

Advantages of TIG Welding

1. TIG welding can be performed on a wide array of different metals and alloys.

2. A TIG welder has many customisable functions, perfect for specific operations.

3. Applicable to varying types of metal thicknesses and complex metal welding. Although, for really thick metals, MIG or stick welding is preferred.

4. A non-consumable electrode and a stable arc allow for greater control and create high-quality TIG welds.

5. Safe gases are used in this gas metal arc welding process, as a result, it has fewer weld defects.

6. TIG welding can be performed at awkward angles. An example would be its application in welding overhangs, where the welding torch has to be in a unique position.

7. It is easy to view the workpiece since the shielding gas is colourless with minimal smoke formed.

Disadvantages of TIG Welding

1. TIG welding requires a lot of skill from the operator.

2. Welding time is noticeably longer compared to other welding techniques.

3. Using the wrong polarity can easily contaminate the weld bead.

4. The overall weld strength diminishes when exhibiting a lack of control over the heat input. This also negatively affects the microstructure of the metals.

5. Without a controlled environment, mainly a wind-free environment, it might be difficult to keep a constant gas flow over the weld area.

6. Compared to other welding techniques, the equipment and inert gases are more pricey.

Important Points To Remember

TIG welding offers accurate and good-looking weld beads with good penetration. It is the preferred method for welding aluminium and magnesium alloys, along with many other metals including stainless steel. It is a bit more expensive and slower method when compared to some other types of welding but it is irreplaceable when creating higher quality welds.

Its consistency and versatility allow it to be highly attractive across almost all industries, from professionals to hobbyists alike. Although TIG process can be automated with the use of welding robots, the manual welding process still has quite a steep learning curve and to achieve the best results, it is most often performed by experienced welders.

Fractory’s welding services are carried out by our manufacturing partners whose processes have been audited by us to guarantee high-quality welds.