Gas Tungsten Arc Welding, commonly known as Tungsten Inert Gas (TIG) welding, is a precision welding process widely used in Kenya's fabrication workshops, automotive repairs, and manufacturing industries. Its ability to produce high-quality, clean welds on a variety of metals makes it indispensable for professional welders aiming for superior joints. This chapter delves into the essential TIG welding equipment and accessories, as well as the proper handling and care of materials such as filler rods, which are critical to achieving optimal weld quality.

4.1 TIG welding equipment and accessories

Tungsten inert gas (TIG) welding makes the weld with an arc between a tungsten electrode and the work. The tungsten does not melt away into the weld, which is why it is called a non-consumable electrode, and the welder adds filler metal by hand as a separate rod or wire when the joint needs it. An inert gas, usually argon, flows around the electrode and over the weld pool to keep out the air. The process gives clean, precise welds on thin metals and on stainless steel, aluminium and other metals that are difficult to weld by other methods, and it is slower than MIG welding.

A TIG welding set is made up of a power source, a torch, a tungsten electrode, filler metal, a gas supply and a control. The power source gives a constant current: it holds the current steady while the arc length changes slightly with the movement of the hand. It supplies direct current for steel and stainless steel, and alternating current for aluminium, where the reversal of the current breaks up the oxide skin on the surface. An arc starting circuit begins the arc without touching the tungsten to the work, either with a high-frequency spark or by lifting the tungsten from the work, so that the tungsten is not contaminated. The current is varied by a foot pedal or a finger control on the torch, which lets the welder reduce the current at the end of the weld to fill the crater.

The torch, the tungsten and the filler metal are the items that the welder handles all the time, and they are studied in this topic with their use and care.

4.1.1 Types

The table gives an overview of the three items that are studied in this section.

4.1.1.1 TIG torch

The TIG torch holds the tungsten, passes the welding current to it and delivers the shielding gas around it. Unlike a MIG torch, it does not feed any wire, so it is lighter and the welder can hold it like a pencil.

The parts of the torch are:

• Body and handle: the main part that is held, with the connections for the cable and the gas inside it.
• Back cap: closes the back of the body and holds the tungsten in place. A short cap is used where access is limited.
• Collet: a small split sleeve that grips the tungsten. It is made for one diameter of tungsten, so it must match.
• Collet body: holds the collet and spreads the gas around the tungsten.
• Gas nozzle (cup): a ceramic cup that shapes the flow of gas over the weld pool. Nozzles are made in several sizes, and a larger nozzle gives a wider gas cover. A gas lens is a fine mesh behind the nozzle that makes the flow smoother, so that the welder can use a longer tungsten stick-out for access.
• Switch or pedal connection: starts the gas and the current. Some torches have a gas valve in the handle.
• Cable and hose: carry the current and the gas, and, on a water-cooled torch, the cooling water in and out.

Torches are cooled by air or by water. An air-cooled torch is lighter and simpler and is used for light and medium work, at lower currents. A water-cooled torch has a circuit of water through the head and the cable, so it can carry a higher current for longer without overheating, and it is used for heavy or continuous welding. The rating of a torch is marked on it, and it must not be run above that rating.

Torch heads are made straight, angled or flexible. An angled head, for example, lets the welder reach a joint inside a frame or a corner, and a flexible head can be bent to the shape that the job needs.

4.1.1.2 Tungsten electrode

Tungsten melts at a very high temperature, about 3 400 °C, so it can carry the arc without being used up. The electrode is made of pure tungsten or of tungsten with a small amount of an oxide added, which improves arc starting, arc stability and the life of the tip. The colour code on the end of the rod identifies the type.

The colour codes vary slightly between standards, so the label on the packet is read before use.

The size and the shape of the tungsten matter:

• Diameter: chosen to suit the current. A larger diameter carries a higher current, and a diameter that is too small for the current melts at the tip and contaminates the weld.
• Tip for direct current: ground to a point, with the grinding marks running along the length of the electrode and not round it, so that the arc is steady and does not wander. A tip that is ground to a length of about two to three times the diameter focuses the arc.
• Tip for alternating current: a small rounded or balled end, formed by the arc when the current is started, because a sharp point melts away on alternating current.
• Stick-out: the length that projects from the nozzle is kept short, about 3 mm to 6 mm for a flat joint, so that the gas covers the tungsten and the weld.

Example: a welder prepares to weld a stainless steel pipe with direct current. A 2.4 mm lanthanated electrode is ground to a point on a dedicated grinding wheel, with the grinding lines along the rod, and fitted in a collet of 2.4 mm with 5 mm of stick-out.

If the tungsten touches the weld pool or the filler wire, it is contaminated and the arc becomes unsteady. The welder stops, breaks off the damaged end and grinds a new tip.

4.1.1.3 Filler wire

Filler wire is the metal that is added to the weld pool by hand to fill the joint. It is supplied as straight rods, usually about 1 m long, and as a coil for automatic machines. It is bare and carries no flux, because the shielding gas protects the pool, so its surface must be kept clean.

The filler wire is chosen to match the base metal:

• Mild steel: a carbon steel rod made for TIG, for example a rod of the ER70S-2 class, which has deoxidisers that clean the pool.
• Stainless steel: a wire of the same grade as the parent metal, for example ER308L for the common 304 grade, labelled on the packet.
• Aluminium: a wire of the aluminium alloy that is suited to the base metal, such as ER4043 or ER5356, which are chosen with the base metal's alloy in mind.

The diameter is matched to the thickness of the metal and the size of the weld: a thin wire for thin sheet and a thicker rod for heavy sections. Diameters of 1.6 mm, 2.4 mm and 3.2 mm are common. A rod that is too thick chills the pool, and a rod that is too thin is used up too quickly and makes the welder's hand movements too fast.

The wire is kept in its packet with its label showing the type until it is used, because a mixed-up rod is not easily identified and gives a weld of the wrong composition. The handling and storage of the rod are set out under Filler rod.

4.1.2 Use and care

TIG equipment is delicate compared with MIG equipment, and its results depend on the cleanliness of the electrode, the nozzle and the gas. Care of the equipment is therefore part of the welding.

Setting up the equipment:

1. Check that the machine is off, and fit the torch, the earth lead and the gas hose.
2. Choose the tungsten for the metal and the current, and fit a collet and a nozzle that suit its diameter and the joint.
3. Prepare the tip of the tungsten on a clean grinding wheel kept for tungsten only, and fit it with the correct stick-out.
4. Connect the gas, open the cylinder valve slowly and set the flow with the gas running, and test the joints for leaks.
5. Set the polarity and the current, direct current for steel and alternating current for aluminium, and the pedal or finger control.
6. Fix the earth clamp to clean bare metal on the work, close to the joint.
7. Make a trial weld on scrap of the same metal and check the arc before starting the job.

Use of the equipment:

• Keep the tungsten clean: do not touch it to the pool or the filler rod. Regrind it when it is contaminated.
• Use the gas properly: use the pre-flow and the post-flow of the gas, so that the tungsten and the weld cool in the gas and do not oxidise.
• Do not overload: stay within the current rating of the torch and the diameter of the tungsten.
• Protect against the arc: the TIG arc is bright, even at low current, and gives off strong ultraviolet light. A helmet with the lens shade that the current requires, gloves and covering clothing are always worn. The high-frequency starting spark can interfere with nearby electronic equipment, so the equipment is kept away from it.

Care and storage:

• Torch: inspect the cables, the connections and the nozzle before each use. Replace a cracked ceramic nozzle, a worn collet and perished seals.
• Tungsten: store it in a labelled tube, and keep each type apart. Handle thoriated rods with care, and use dust extraction when grinding.
• Water-cooled torch: check the level and the flow of the coolant, and look for leaks around the connections.
• Regulator and hoses: keep them clean and dry and free of oil, and replace a worn hose.
• Filler wire: keep it dry and clean, wrapped in its packet, with its label.
• After work: close the cylinder valve, release the gas from the line, switch off the machine and hang the torch so that the cable is not kinked.

Chapter Summary

This chapter covered the essential equipment and accessories used in Tungsten Inert Gas (TIG) welding, including the TIG torch, tungsten electrode, and filler wire, emphasizing their types and proper care to ensure optimal performance. It detailed the use and maintenance of materials, particularly focusing on the filler rod, which plays a crucial role in achieving strong welds. The chapter explored the shielding gases commonly used in TIG welding, with a focus on argon and helium, explaining their properties and how they protect the weld area from contamination. The TIG welding process for metals up to 16 mm thick was presented step-by-step, highlighting the precise procedure required for effective welding. Practical applications were discussed, demonstrating how TIG welding is performed on steel, aluminium, copper, and titanium plates and pipes, especially in the overhead position. The integration of equipment handling, material care, appropriate gas selection, and correct welding techniques equips students with the skills needed to carry out TIG welding proficiently across various metals and positions.