What is Tig welding?- Tungsten Inert Gas welding

What is A Tig Welding?

Tungsten inert gas (TIG) welding, also known as gas tungsten arc welding (GTAW) and occasionally referred to as Heli-Arc, a name derived from early applications that utilized helium as the shielding gas, is a welding technique that creates an arc between a non-consumable tungsten electrode and the workpiece.

During the process, a shielding gas safeguards both the electrode and the weld area, while the use of filler metal remains optional. What sets TIG welding apart from other arc welding methods is its reliance on a non-consumable electrode that does not serve as filler material.

In terms of skill, TIG welding closely resembles oxyacetylene welding, as it demands the ability to handle a torch in one hand and a filler rod in the other. Additionally, the process requires further coordination, since many TIG machines incorporate a foot pedal to control amperage.

Similar to MIG welding, TIG is considered a clean welding method because the shielding gas removes the need for flux and eliminates slag formation.

Safety

Because TIG welding is a notably clean process, some welders may feel inclined to work without gloves or wear short-sleeved shirts. However, this practice is strongly discouraged.

Given that TIG is an arc welding method, it generates ultraviolet (UV) light at higher intensities compared to other welding techniques. Unlike processes that produce smoke or fumes, which can help filter UV rays, TIG welding leaves these rays unfiltered, posing a significant risk of severe skin burns. Therefore, it is essential to ensure all exposed skin is adequately covered to protect against UV damage.

Regarding eye protection, a minimum filter shade of #10 is required. Additionally, if using an auto-darkening helmet, it is important to verify that it is specifically rated for TIG welding, as some entry-level models are not suitable for this process.

Equipment

The fundamental equipment required for TIG welding includes a constant current welding machine, a cable with an attached torch, a work cable paired with a clamp, an electrode, and an inert gas cylinder equipped with a regulator and flow meter. Additional, optional items may consist of a remote amperage control and a water-cooled torch.

While it is possible to use a midrange shielded metal arc welding machine to supply the current for TIG, a dedicated, high-quality TIG machine offers several advantages. These machines can deliver current as either AC or DC and typically feature an optional high-frequency output that enables arc initiation without contact. They also often provide a remote control option, commonly a foot pedal and a solenoid for managing the shielding gas.

The ability to combine AC current with high-frequency output is particularly beneficial for welding aluminum, yielding strong and reliable results. Recently, inverter-based TIG machines have emerged with enhanced current control capabilities. These advanced units are becoming increasingly affordable, making them accessible for use in home or hobbyist workshops.

Torch & cables.

The TIG torch is designed to hold the electrode securely while supplying the shielding gas necessary for welding. It may be either air-cooled or water-cooled, depending on the amperage requirements.

The key components of the torch include the cup (or nozzle), collet body, collet, end cap, and torch body. The collet and collet body work together to firmly grip the electrode, ensuring a stable electrical connection that facilitates the creation of the welding arc.

Electrodes commonly come in diameters of 1/16″, 3/32″, or 1/8″. It is essential that both the collet and collet body correspond to the electrode’s size to guarantee a tight fit, preventing unintended arcing within the collet.

The cup, also referred to as the nozzle, directs the shielding gas flow to protect the electrode, weld puddle, and filler metal from contamination by atmospheric air, thereby promoting a clean, high-quality weld. Typically, air-cooled torches are suitable for operations involving less than 200 amps, while applications exceeding this amperage require the use of water-cooled torches to manage heat effectively.

Nozzles regulate the amount of shielding gas delivered over the weld pool, with their coverage area dependent on size—ranging from 1/4″ to 3/4″ in diameter. Smaller nozzles provide less coverage, while larger ones extend the shielded area. Additionally, nozzles vary in length, from short to extra-long, with differences in price and performance characteristics.

For lower amperage work, nozzles made from 90 to 95 percent alumina oxide are often the most cost-effective choice. However, these materials are less resistant to thermal shock and may degrade, crack, or detach when exposed to higher amperages.

Lava nozzles, though more expensive than alumina oxide, offer greater resistance to cracking and are better suited for medium amperage applications. One drawback is that their internal wall thickness varies, which can result in uneven gas coverage.

For effective TIG welding, tools such as welpers, locking pliers, and a stainless-steel wire brush prove useful accessories.

Tig Welding Gas

Argon

Argon, being an inert gas, does not engage in reactions with other elements or compounds. It is approximately 1.4 times denser than air.

These inert qualities make argon particularly effective as a protective shield against atmospheric contamination, which explains its widespread use in various welding techniques. Additionally, its low ionization potential contributes to reliable arc initiation and stable arc performance during welding.

Helium

Helium is an effective shielding gas due to its high thermal conductivity and capacity for increased ionization. It is particularly suitable when higher heat input is required and when minimizing exposure to oxidizing elements is critical, as is often the case in welding materials like aluminum and magnesium.

Gas Flow Rate

Gas flow rates in welding can vary significantly, typically ranging from 10 cubic feet per hour (CFH) to over 60 CFH. This variation depends on several factors, including the welding current, torch size, the composition of the shielding gas, the welding position, and the surrounding work environment.

Generally, higher operating currents necessitate the use of larger torch nozzles and increased gas flow rates. When currents exceed 150 amps, it becomes essential to employ a water-cooled TIG torch.

This approach helps manage heat buildup effectively and allows for the use of a smaller tungsten electrode, which can reduce operator fatigue.

Another important consideration is gas density, which affects the minimum flow rate required to adequately shield the weld. For instance, argon, being approximately 1.4 times denser than air and ten times heavier than helium, demands higher flow rates, especially when welding in vertical or overhead positions, to maintain weld quality.

Conversely, helium tends to be more advantageous in overhead welding because of its lower density, which allows it to rise and provide effective shielding.

In flat welding positions, when helium-enhanced gas blends are used, it is necessary to increase the gas flow rate compared to using pure argon. In fact, flow rates may need to be 50 percent higher or more to achieve comparable weld quality.

Tig Welding Rod (Electrodes)

Selecting the appropriate tungsten electrode is a fundamental initial step in TIG welding, with six commonly used types available. Equally important is the preparation of the electrode tip, which can significantly influence welding performance.

The options for tungsten electrodes include pure tungsten, 2% thoriated, 2% ceriated, 1.5% lanthanated, zirconiated, and rare earth variants. The tips are typically prepared in three forms: balled, pointed, or truncated.

Tungsten, a rare metallic element, is essential in manufacturing TIG electrodes due to its exceptional hardness and resistance to high temperatures, which enable efficient transfer of welding current to the arc. Notably, tungsten has the highest melting point among metals, at 3,410 degrees Celsius.

These non-consumable electrodes, whether composed of pure tungsten or tungsten alloys combined with rare-earth elements and oxides, are available in various sizes and lengths. The selection of the correct electrode depends largely on the type and thickness of the base material, as well as whether the welding process employs AC or DC current.

Moreover, the choice between balled, pointed, or truncated tip preparations plays a critical role in achieving optimal welding outcomes. To assist in proper identification, electrodes are color-coded at their tips, helping to avoid confusion among different types.

Preparing The Electrode

Before use, the cut end of the electrode should be either sharpened to a point or melted into a ball. This can be achieved by grinding the tip to a point or by chemical sharpening. Typically, the electrodes are supplied in 7-inch lengths.

To increase the number of usable points, the electrode can be scored with a file or cut-off wheel and then snapped in half. Although tungsten is very hard, it is also brittle, making it easy to break by holding each end with pliers and snapping it over a sharp edge, such as a table corner.

Since tungsten electrodes look and feel identical regardless of their composition, it is crucial to keep them separated by type. The color-coded markings may wear off over time or be removed if the electrode tips are ground. Therefore, using clearly labeled containers for each electrode type is recommended to avoid confusion.

Two essential aspects when grinding electrodes are the choice of grinding wheel and the direction of grinding. It is important to use a hard, fine-grit grinding wheel specifically reserved for tungsten.

If the wheel has residual metal particles from grinding aluminum or steel, these contaminants can transfer to the tungsten, leading to unstable arc performance and reduced weld quality.

Because tungsten is a very hard material, it heats up during grinding. The electrode tip should be sharpened so that the grinding marks align lengthwise along the tip, rather than forming circular or crosswise patterns.

Lengthwise grinding directs the electron flow toward the electrode tip, whereas circular grinding results in an unfocused arc that may jump sideways from the electrode instead of emanating from the tip.

Alternatively, tungsten can be sharpened chemically by dipping a heated tungsten rod into a suitable chemical solution. The taper on the tungsten tip should ideally measure two to three times the tungsten’s diameter.

How To Set Up a Tig Machine?

Dedicated TIG machines, such as this one, have many advanced features. The basic setup, however, is the same.

• The positive and negative output receptacles serve as connection points for the torch and work clamp.
• The gas outlet is designed to connect with the torch’s gas hose.
• The remote-control socket accommodates either foot or finger controls, enabling the welder to adjust the current during welding for greater precision.
• The operating mode selector allows the user to choose between high-frequency start and scratch start options.
• The process mode button or reset switch is used to select the welding current type, either alternating current (AC) or direct current (DC).
• The AC balance control, operated via the settings button and encoder knob, permits adjustment of the AC power to be more positive or more negative. This adjustment influences the cleaning action and penetration depth. While standard AC power balances at 50%, advanced machines can shift this balance up to 90% in either direction.
• The start current control regulates the current level required to initiate the arc.
• The welding current setting defines the operating current range, within which the foot or finger control modulates the current.
• Slope downtime gradually decreases the arc power without extinguishing it, allowing the weld crater to fill smoothly before the arc ends.
• The gas post-flow control determines the duration for which shielding gas continues to flow after the arc is extinguished.

Pre welding Checklist

• If using a water-cooled torch, check for leaks.
• Check all cables for wear and damage.
• Clean and fit up parts to be welded.

Striking An Arc

If you do not have a high-frequency option, initiating the arc requires physically striking it, a method known as a scratch start. To do this, position the cup against the workpiece at a sharp angle. Move the tip until it briefly touches the surface, then quickly angle it away to ignite the arc.

Once the arc is established, lift the cup away from the workpiece and adjust to the correct torch angle. In contrast, high-frequency systems enable the arc to jump the gap without the electrode making physical contact with the workpiece.

How To Tig Weld?

Step 1: Begin by adjusting the machine settings according to the manufacturer’s guidelines for the specific material you intend to weld. Power on the welding unit, and if your setup includes a water pump, switch it on as well. Secure the work clamp to either the welding table or directly to the workpiece.

Lower your helmet, then activate the foot pedal or finger control if your equipment uses one. To initiate the arc, gently touch the tungsten electrode to the base metal and drag it lightly to create the arc. For welders equipped with a high-frequency start feature, this scratch-start method is unnecessary.

Next, apply a tack weld at both ends of the joint. Depending on the material and setup, you might be able to fuse the pieces together using only the torch’s heat, or you may need to introduce a filler rod to secure the tack welds.

Step 2: Position yourself for welding from right to left if you are right-handed. Hold the torch at approximately a 15° angle to the right of center. Keep the filler rod in your left hand, ensuring you are comfortably situated to maintain control of both the torch and rod throughout the weld.

Step 3: Once a molten puddle has formed, carefully dip the tip of the filler rod into the center of the puddle. Maintain a low angle with the rod to avoid disturbing the shielding gas. It is important to keep the rod tip near the puddle but avoid placing it directly inside. Continue moving the electrode to the left, repeating the melting and dipping process to add material.

Step 4: As you near the weld’s end, be mindful that the accumulated heat causes the molten puddle to develop faster than at the start. This may require you to slow your travel speed to maintain control. Additionally, you might need to adjust the torch angle to a shallower position, reducing heat concentration on the base metal and promoting a smoother finish.

Post welding Sequence:

• Turn off the cylinder valve.
• Purge gas from the gas line.
• Turn off the flow meter or gauge.
• Turn off the machine.
• Coil hoses and cables off the floor.

TIG Welding Troubleshooting

TIG filler metal is supplied in rod form, typically ranging from 1/16 to 3/16 inch in diameter. These rods come in a wide variety of alloys, such as aluminum, chromium and chromium-nickel, copper, nickel and its alloys, magnesium, titanium, and zirconium.

Different alloy compositions are tailored to produce specific types of welds on particular base metals. While these filler metals largely mirror those used in oxyfuel welding, one notable difference is that carbon steel rods for TIG welding are not copper-coated, unlike their oxyfuel counterparts.

Becoming proficient in TIG welding takes practice, and identifying problem welds is an important step.

• Weld A exhibits excessive heat input. To address this, it is advisable to either increase the travel speed or reduce the amperage.
• Weld B appears insufficiently heated, merely resting on the surface of the base metal without adequate penetration. Corrective measures include decreasing the travel speed or raising the amperage.
• Weld C was executed too rapidly, indicating the need for a controlled and consistent travel speed to ensure proper weld quality.
• Weld D represents a well-executed weld characterized by uniform ripples, appropriate penetration, and a moderate crown, indicative of good overall quality.

TIG Welding Problem

Weld Looks Porous or Sooty

Solutions:

• Make sure the shielding gas is on and is the correct type.
• Make sure the shielding gas cylinder is not empty.
• Eliminate drafts.
• Make sure the base metal is totally dry.
• Clean base metal thoroughly.
• Increase gas flow rate.

Base Metal Distorts

Solutions:

• Tack weld parts before welding.
• Clamp parts down to the rigid surface.
• Scatter welds to diminish heat buildup.

Unstable Arc

Solutions:

• Adjust the electrode to the work angle.
• Clean base metal thoroughly.
• Clean electrode.
• Connect the work clamp to a workpiece.
• Bring the arc closer to work.

Electrode Is Rapidly Consumed.

Solutions:

• Make sure polarity and current settings are correct.
• Increase electrode size.
• Increase gas flow.
• Decrease current.
• Increase gas post-flow time.
• Use proper shielding gas.

A well-done TIG welding on aluminum has even ripples and good penetration. This sample weld shows two passes to create a fillet weld on 1 ⁄4″ stock.

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