What is Tungsten Inert Gas (GTAW or TIG) Welding?

What is A Tig Welding?

TIG (tungsten inert gas) welding, commonly called Gas tungsten arc welding (GTAW), and sometimes referred to as Heli-Arc (the L-TECH trade name) because early uses of TIG welding used helium as a shielding gas, is a process that generates an arc between a non-consumable tungsten electrode and the workpiece.

A shielding gas protects the electrode and the weld, and filler metal may or may not be used. Tig welding differs from other arc processes because the electrode is non-consumable and not used as a filler material.

TIG is more like oxyacetylene welding in terms of the skills needed to manipulate a torch with one hand and a filler rod with the other.

TIG requires another layer of coordination because most machines also use a foot-activated amperage control. Like MIG, TIG is a clean process, because the shielding gas eliminates the need for flux and resultant slag.

Safety

Because TIG is such a clean process, welders are often tempted to weld without gloves or in a short-sleeve shirt. This is not recommended.

As it is an arc process, the arc produces ultraviolet light at a higher level than other processes, and because there are no fumes or smoke, those light rays are unfiltered and can cause severe burns. It is critical to cover all exposed skin to prevent UV burns.

Filter requirements for eye protection are a minimum of a shade #10, and if you have an auto-darkening hood, be sure it is rated for TIG. Some entry-level auto-darkening helmets are not designed for TIG.

Equipment

The basic equipment needed for TIG is a constant current welding machine, cable with a torch, work cable and clamp, electrode, and inert gas cylinder with regulator and flow meter. Optional equipment includes a remote amperage control and a water-cooled torch.

Although a midrange shielded metal arc welding machine can be used to deliver the current for TIG, a dedicated good-quality TIG machine delivering the current as AC or DC provides an optional high-frequency output for no-touch arc starting, has a remote-control option for a foot-pedal control, and has a solenoid for shielding gas control.

The combination of AC and high frequency makes it possible to weld aluminum with good results. The newest inverter-based TIG machines have advanced current control capabilities and are becoming more affordable for the home or hobby shop.

Torch & cables.

The TIG torch holds the electrode and delivers the shielding gas. It can be air- or water-cooled. The torch parts include a cup or nozzle, collet body, collet, end cap, and torch body. The collet and collet body hold the electrode firmly in place to allow for the transfer of electricity to generate the arc.

The electrode diameter is typically 1 ⁄16″, 3 ⁄32″, or 1 ⁄8″, and the collet body and collet must match this size to ensure a tight connection so the electrode cannot arc in the collet.

The cup or nozzle directs the shielding gas to protect the electrode, puddle, and filler metal from atmospheric air to ensure a clean, quality weld. Air-cooled torches typically come in sizes for use with less than 200 amps—more than 200 amps will require the use of a water-cooled torch.

Nozzles, or cups, provide a controlled amount of shielding gas to cover the weld pool, determined by their size, which can range from 1 ⁄4″ to 3 ⁄4″ in diameter. A smaller nozzle provides less coverage than a larger nozzle. Nozzles also vary in length, short to extra-long, and in their price and performance.

The most cost-effective nozzles are 90 or 95 percent alumina oxide— these are adequate for lower amperage applications. On higher amperage applications, however, they do not resist thermal shock very well, and in this use, they may deteriorate, crack, and fall off.

Lava nozzles cost more than alumina oxide, but they are also more resistant to cracking. They work well for medium amperage applications, but because they have varying wall thicknesses around the inside diameter, gas coverage may be unequal.

Welpers, locking pliers, and a stainless-steel wire brush are handy for TIG.

Tig Welding Gas

Argon

Because it is an inert gas, argon does not react with other compounds or elements. It is about 1.4 times heavier than air.

The inert properties of argon make it ideal as a shield against atmospheric contamination, which is why it is used in many welding processes. Because its potential for ionization is low, argon promotes good arc-starting characteristics and arc stability.

Helium

Because of its high thermal conductivity and potential for high ionization, helium is a good choice for a shielding gas when increased heat input is sought and when there is a low tolerance for oxidizing elements, such as when welding aluminum and magnesium.

Gas Flow Rate

Gas flow rate can range from 10 cubic feet per hour (CFH) to more than 60 CFH, depending on the current developed, torch size, shielding gas composition, welding position, and operating current—not to mention the surrounding work environment.

As a rule, a higher operating current requires a larger torch nozzle and higher gas flow rates. Operating currents greater than 150 amps also require that you use a water-cooled TIG torch.

This not only controls the heat buildup but also can allow you to use a smaller tungsten diameter, thereby reducing user fatigue. Gas density—the weight of the gas relative to air—influences the minimum flow rate required to shield the weld adequately.

Because argon is about 1.4 times as heavy as air and 10 times as heavy as helium, the gas flow rates must be increased to maintain quality when working in vertical or overhead positions. On the other hand, helium can be more effective than argon when working overhead, because it floats.

When working in the flat position with helium-enhanced blends, maintaining weld quality requires that you increase gas flow when compared to using argon alone. Flow can be 50 percent or more than with pure argon.

Tig Welding Rod (Electrodes)

There are six common tungsten electrodes available for use in TIG, and choosing the right one is a crucial first step. Tip preparation is also critical.

The electrode choices are the following: pure tungsten, 2 percent thoriated, 2 percent ceriated, 1.5 percent lanthanated, zirconiated, and rare earth. The end preparations include balled, pointed, and truncated.

Tungsten is a rare metallic element used in the creation of TIG electrodes. Tungsten’s hardness and high-temperature resistance facilitate the transfer of the welding current to the arc. Tungsten has the highest melting point compared to other metals, at 3,410 degrees Celsius.

Whether pure tungsten or an alloy of tungsten and other rare-earth elements and oxides, these non-consumable electrodes come in a variety of sizes and lengths. The proper electrode choice depends on the base material type and thickness and on whether you are using an AC or DC welding process.

Choosing between balled, pointed, or truncated end preparations also is crucial in optimizing your results. Color coding eliminates confusion over electrode types. The color appears at the tip of the electrode.

Preparing The Electrode

Prior to use, the cut end of the electrode must be sharpened to a point or melted to a ball. The tip may be ground to a point or chemically sharpened. The electrodes come in 7-inch lengths.

To increase the number of points available, score the electrode with a file or cut-off wheel, and snap it in half. Tungsten is very hard but brittle, so it is easy to grasp each end of the electrode with pliers and snap it in half over a sharp table edge.

Because all tungsten electrodes look and feel the same regardless of their composition, it is important to keep them clearly separated by type. The color codes will wear off, or, if you point each end of your electrode, be ground off. It is helpful to have clearly labeled containers for each type of electrode.

Two critical factors in grinding the electrodes are the grinding wheel and the grinding direction. You must use a hard, fine grinding wheel dedicated exclusively to tungsten.

Metal particles left on the wheel from grinding aluminum or steel would contaminate the tungsten, which causes erratic arc behavior and poor weld quality.

An extremely hard material, tungsten will become hot as it is ground. Sharpen the electrode tip so that grinding marks run lengthwise down the tip, not in a circular or crosswise pattern.

Lengthwise grinding focuses the electron flow toward the tip; circular grinding causes the arc to be unfocused and possibly jump sidewise from the electrode rather than off the tip point.

Chemical means also can be used to sharpen tungsten by dipping a hot tungsten rod into a chemical agent. The length of the taper on the tungsten tip should be two to three times the diameter of the tungsten.

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 are for the torch and work clamp connections.
• The gas outlet connects to the torch gas hose.
• The remote-control socket is for the foot or finger control. Using a remote control allows the welder to control the amount of current while welding.
• The operating mode selects high-frequency or scratch starts.
• The process mode button/reset selects either AC or DC.
• AC balance control using the settings button and the encoder knob allows for adjusting AC power to be more positive or more negative to create either more cleaning action or deeper penetration. Advanced machines can adjust the AC power to be as much as 90% positive or negative, rather than the 50% for standard AC power.
• Start current controls the current for arc starting.
• Welding current sets the range for welding. The foot or finger control then operates within this range.
• Slope downtime gradually reduces power to the arc without extinguishing the arc. This allows for the weld crater to fill before the arc is extinguished.
• Gas post flow controls how long the shielding gas will 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

Unless you have a high-frequency option, you will need to physically strike an arc—called a scratch start. Rest the cup on the workpiece at a sharp angle. Move the tip until it briefly contacts the work, then angle it back again to start the arc.

After the arc is started, lift the cup off the workpiece and establish the proper torch angle. High frequency allows the arc to jump the gap without needing to create physical contact between the electrode and the workpiece.

How To Tig Weld?

Step 1. Set the controls based on the manufacturer’s recommendations for the material to be welded. Turn on the machine, and turn on the water pump, if available. Attach the work clamp to the welding table or workpiece.

Flip down your helmet, activate the foot or finger control if using one, and strike an arc by scratching the tip of the tungsten against the base metal. If your welder has a high-frequency option, you do not need to scratch start the arc.

Place a tack weld at each end of the joint to be welded. You may be able to tack the joint by simply fusing the two pieces with the heat of the torch, or you may have to use a filler rod.

Step 2. Position yourself to weld from right to left (if you are right-handed) with the torch at a 15° angle to the right of the center. Hold the filler rod in your left hand. Position yourself so you can comfortably hold the torch and filler rod for the duration of the weld.

Step 3. When a molten puddle has formed, dip the tip of the filler rod into the middle of the molten puddle. Keep the filler rod at a low angle to prevent disturbing the shielding gas. Keep the tip of the filler rod near—but not in—the puddle. Move the electrode to the left and continue the melting and dipping process.

Step 4. As you approach the end of your weld, you may need to adjust your travel speed, because the buildup of heat in the material makes the molten puddle form more quickly at the end of the weld than at the beginning. You may also need to adjust the torch angle to be shallower (not shown here) so that less heat is directed into the base metal.

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

Filler metal for TIG comes in rod form and ranges from 1 ⁄16 to 3 ⁄16 inch in size. Rods are available in a variety of alloys, including aluminum, chromium and chromium nickel, copper, nickel and nickel alloys, magnesium, titanium, and zirconium.

Specific alloy compositions are available for creating specific weld types on specific base metals. These filler metals are similar to those used in oxyfuel welding, with the exception of the carbon steel rods, which are not copper coated as they are for oxyfuel.

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

• Weld A is too hot. Increase the travel speed or decrease the amperage.
• Weld B is too cold and is simply sitting on top of the base metal rather than penetrating it. Decrease the travel speed or increase the amperage.
• Weld C was done too quickly. Travel speed needs to be controlled and consistent.
• Weld D is a good-quality weld with even ripples, good penetration, and a moderate crown.

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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