Gas Tungsten Arc Welding, commonly known as Tungsten Inert Gas (TIG) welding, is a precision welding process widely used in Kenyan fabrication workshops and manufacturing industries that require high-quality welds with minimal spatter and superior control. This chapter delves into the specialized equipment and accessories essential for TIG welding, highlighting their specific roles and maintenance to ensure optimal performance. Additionally, it covers the proper handling and care of consumables such as filler rods, which are critical to producing strong, defect-free joints in various metals. Mastery of these elements is crucial for welding professionals engaged in sectors like automotive repair, metal fabrication, and infrastructure maintenance across Kenya.

4.1 TIG welding equipment and accessories

TIG welding requires a distinct set of equipment and accessories designed to give precise control over the welding arc and the shielding gas flow. The equipment must be kept in excellent condition to prevent weld defects and to protect the operator. Understanding the types, use and care of each item helps a workshop get consistent weld quality and a long service life from its equipment.

4.1.1 Types

The TIG process depends on several specialised components that work together to produce a stable arc and protect the weld pool from atmospheric contamination. The three items the welder handles most directly are the torch, the non-consumable tungsten electrode and the filler wire. The choice among them depends on the metal, its thickness, the current type and the welding position. Example: a workshop repairing thin stainless steel trolleys would use a small air-cooled torch, a fine tungsten electrode and a stainless steel filler wire, while a heavy aluminium fabrication would need a larger torch and a thicker electrode.

4.1.1.1 TIG torch

The TIG torch holds the tungsten electrode, carries the welding current to it and delivers the shielding gas around the arc. Its design determines how much current it can carry safely, how well the gas covers the weld pool and how comfortably the welder can reach the joint.

Torches are classified by how they are cooled:

• Air-cooled torches: Cooled by the shielding gas and the surrounding air. They are lighter and more flexible, and suit low to medium current work and short welds, as in small fabrication shops and repair work.
• Water-cooled torches: Cooled by a circulating water supply from a cooler unit, which also cools the power cable. They carry higher current for long periods without overheating, so they suit thick sections and production welding.

Torches are also made in different head angles and sizes, including flexible-neck types for restricted access. Pipe and tight-corner work often needs a short or flexible head.

The main torch components are shown below.

4.1.1.2 Tungsten electrode

The tungsten electrode produces the arc but does not melt into the weld, because tungsten has the highest melting point of all metals. It is made in different compositions, each suited to a particular current type and metal. Diameters commonly range from about 1.0 mm to 4.0 mm, and the diameter must suit the current being used and the collet fitted.

The main types are identified by the colour band on the end of the electrode.

Thoriated electrodes contain a weakly radioactive material, so grinding dust must be controlled with good extraction and the electrodes must be stored and handled with care. Many workshops prefer ceriated or lanthanated electrodes for this reason.

The tip shape matters:

• For DC welding: Grind the tip to a point, with the taper length about two to three times the electrode diameter, to give a narrow, stable, focused arc.
• For AC welding: Use a slightly rounded or truncated tip, because a sharp point melts away on the AC cycle.

4.1.1.3 Filler wire

Filler wire is the metal added to the weld pool to fill the joint, build up the weld and give the required strength. In TIG welding it is added by hand, or by a wire feeder in mechanised work, and it is fed into the leading edge of the pool without touching the tungsten. Filler wire must be compatible with the base metal. Example: a contractor welding stainless steel handrails would choose a stainless steel filler, whereas aluminium tanks need an aluminium alloy filler.

The wire is supplied in different forms and diameters:

• Cut straight lengths (rods): Usually about 1 m long and used for manual welding. Diameters commonly range from 1.6 mm to 3.2 mm, chosen to suit the joint thickness and the current.
• Spooled wire: Used with automatic or mechanised wire feeders for long or repeated welds.
• Type by base metal: Mild steel, stainless steel, aluminium, copper and titanium each use a matching filler. Typical classifications are ER70S-2 for mild steel, ER308L for 304-type stainless steel, ER4043 or ER5356 for aluminium, ERCu for copper and ERTi-2 for commercially pure titanium.
• Identification: The classification is printed or stamped on the rod or its packaging and must be checked before use to avoid mixing fillers.
• Cleanliness: The wire must be free of grease, oil and oxide, because contamination carried into the pool causes porosity and weak welds.

The selection, storage and handling of filler rods are treated in detail under the use and care of materials.

TIG power sources and controls

The power source supplies the welding current and determines how stable the arc is and which metals can be welded. Example: a workshop that welds both aluminium window frames and stainless steel counters needs a machine with AC and DC output and fine current control.

• Constant current output: The current stays almost steady even when the arc length changes slightly, giving precise control of heat input. This is vital for thin material.
• AC and DC capability: AC is used for aluminium and magnesium, because it breaks up the surface oxide. DC, with the electrode negative, is preferred for steel, stainless steel and copper.
• High frequency start: A high frequency spark starts the arc without the tungsten touching the work, which reduces tungsten contamination and wear. Lift-arc starting is an alternative on some machines.
• Current slope and pulse controls: Gradual current rise and fall reduce crater cracking and help control heat on thin sections.
• Duty cycle: The rating shows how long the machine can run at a given current in a ten-minute period without overheating, and the welder should not exceed it.

Shielding gas delivery system

The gas delivery system carries inert gas from the cylinder to the weld area at a steady, controlled rate. The gases themselves are covered under shielding gases. Example: a leaking hose fitting in a fabrication bay lets air into the stream and shows up as a dull, porous weld.

• Cylinder: Holds the gas under high pressure and must be fixed upright and protected from knocks.
• Regulator: Reduces the cylinder pressure to a safe, steady working pressure.
• Flowmeter: Shows and sets the flow in litres per minute, so the welder can match flow to the nozzle and joint.
• Gas hose and fittings: Carry gas to the torch, and must be free of leaks and kept separate from oil and grease.
• Nozzles and gas lenses: Shape the gas flow around the weld. Larger nozzles give wider coverage, which is helpful on aluminium and titanium.

Ancillary accessories

These items improve control, accuracy and weld quality. Example: a welder joining thin stainless steel sheet in a food-equipment workshop uses a foot pedal to ease the current down at the end of each weld.

• Foot pedal control: Lets the welder vary the current smoothly while welding, giving fine heat control on thin or heat-sensitive material.
• Torch-mounted controls: A thumb or finger control on the torch gives current adjustment where a pedal cannot be used, such as in awkward positions.
• Tungsten grinder: A dedicated grinder or wheel prepares the electrode tip cleanly and repeatably.
• Earth (work) clamp and cable: Gives a good electrical return path, and must grip clean metal.
• Dedicated stainless steel brushes: Clean joints and welds without transferring carbon steel particles to stainless steel or aluminium.
• Purging equipment: Fills the back of pipes and enclosed joints with inert gas to protect the root of the weld from oxidation, which is important for stainless steel and titanium.

4.1.2 Use and care

Correct use and regular maintenance extend equipment life and give consistent weld quality. Neglected equipment leads to gas leaks, unstable arcs, contaminated welds and costly downtime. Example: a farm workshop that welds irrigation fittings can avoid many repeat repairs by checking hoses and nozzles before each job.

Proper use of equipment

• Correct setup: Set the power source to match the material, thickness and electrode type. A wrong polarity or current setting causes tungsten contamination and an unstable arc.
• Gas flow adjustment: Set the argon flow on the flowmeter, typically within 8 to 15 litres per minute depending on nozzle size and joint, so that the pool is protected without turbulence that draws in air.
• Electrode preparation: Grind the tungsten lengthwise on a wheel kept for tungsten only, so that grinding marks run along the electrode and the arc stays steady.
• Electrode stick-out: Let the electrode extend a short distance beyond the nozzle, about the diameter of the nozzle bore for standard cups, and more only when a gas lens is fitted.
• Matching the collet: Fit a collet and collet body of the same size as the electrode, so that the electrode is gripped firmly and current passes well.
• Post-flow: Keep the gas flowing after the arc stops so that the hot tungsten and the cooling weld stay shielded.

Maintenance practices

• Regular inspection: Check cables, connectors, hoses and torch parts for wear, cracks or loose fittings that could cause electrical faults or gas leaks.
• Cleaning nozzles and diffusers: Remove spatter and deposits so that gas flow stays smooth, and replace cracked or chipped ceramic cups.
• Electrode replacement: Replace or regrind electrodes that are contaminated, split or worn, to keep arc quality.
• Checking O-rings and seals: Replace worn O-rings on the torch body and back cap to prevent air from being drawn into the gas stream.
• Water-cooled systems: Keep coolant at the correct level and clean, and check hoses for leaks.
• Storage: Keep accessories in a clean, dry place to prevent corrosion, and coil cables loosely without kinks.

Safety considerations

• Handling gas cylinders: Secure cylinders upright with a chain or stand, and check connections for leaks with soapy water to prevent hazardous gas release.
• Electrical safety: Inspect cable insulation, make sure the earth clamp is firmly attached to clean metal and work in dry conditions to avoid electric shock.
• Personal protective equipment: Wear a welding helmet with the correct filter lens, gloves and flame-resistant clothing to protect against ultraviolet radiation, heat and fumes.
• Ventilation: Weld where fumes can be extracted or dispersed, particularly when working with coated metals or in enclosed spaces.
• Grinding precautions: Use eye protection and dust extraction when grinding tungsten.

Chapter Summary

This chapter explored the essential components and accessories of Tungsten Inert Gas (TIG) welding equipment, including the TIG torch, tungsten electrode, and filler wire, emphasizing their types, uses, and proper care to ensure optimal performance. It highlighted the importance of maintaining filler rods through correct handling and storage to preserve their integrity during welding. The chapter also examined the role of shielding gases, focusing on argon and helium, which protect the weld area from atmospheric contamination and influence weld quality. A detailed explanation of the TIG welding process for metals up to 16 mm thickness was provided, outlining the step-by-step procedure necessary to achieve strong, clean welds. Practical applications were demonstrated through welding steel, aluminium, copper, and titanium plates and pipes within the 4-16 mm range, particularly in the overhead position where skillful technique is crucial. The comprehensive coverage of equipment, materials, shielding gases, and procedural steps equips learners with the knowledge to perform TIG welding effectively across various metals and challenging positions.