GAS TUNGSTEN ARC WELDING (GTAW)

GAS TUNGSTEN ARC WELDING (GTAW) GTAW – (also referred to at TIG –

Tungsten Inert gas or Heli-arc). An electric arc produced between a metal electrode and the metal being welded. Completely shielded by a gas blanket to protect the weld, the arc and the electrode from contamination from atmospheric gases such as oxygen, hydrogen and nitrogen.

Advantages of GTAW

Weld non-ferrous and exotic metals.

Deep penetration. Weld in all positions. Clean weld – no slag. Weld light to heavy gage metals. Excellent appearance.

Disadvantages

More user skill is required. Cost of equipment may be

higher than other processes. Prone to wind drafts. Metal must be clean.

Non-consumable Electrodes

Electrodes are not consumed in the weld puddle.

Inert gas provides a shield to protect the electrode.

Usually 7” in length – common diameters are 1/16”, 3/32” & 1/8”.

If electrode turns blue, it’s getting to hot. Check gas, water & amps.

Shielding Gases

Argon and helium are the most commonly used. They can be mixed or added to other inert gasses as well.

Both gases are inert (do not change chemically under any circumstances).

The gas flow requirements depend on: a) size of electrode, b) size of the molten puddle, c) type of inert gas used, d) position, speed of travel, if a draft is present, is a gap is present, electrode extension, etc.

Types of Electrodes

Pure Tungsten – Green band-Use A.C. with high frequency on continuos.

Ball electrode for best results (put machine on DCEP. Depress foot pedal slowly until arc starts and continue until a ball 1-1/2 times the diameter of the electrode is formed. Put machine back to AC.

Melting temperature of approx. 6098 F. Highest of all metals.

Do not touch to filler or base metal. Will contaminate immediately.

If this happens, break off contaminated area and ball the electrode.

pure tungsten is for use on Aluminum.

Thoriated Tungsten –

Red band is 2% thorium, yellow band is 1% thorium.

Used on all steels with DCEN polarity. Does not contaminate as easily as

pure tungsten. Better arc stability and runs better at

low amps. A 60 centerless grind on the

electrode is required.

Electrode size

Depends on the size of the puddle required. (metal thickness)

Electricity should run at the capacity of the electrode. Example; Do not try to run too many amps through a small electrode or too few amps through a large diameter electrode.

High Frequency

Developed so that the welder does not have to scratch start to arc.

Not always built into a machine. You may have to purchase a high frequency unit for your power source.

Stabilizes the arc – eliminates most of the dead zone in the AC cycle. The newer machines allows you to control the frequency modes.

METAL PREPARATION

Prepare all metals to be welded to insure a high quality weld.

“V” metal if possible to insure deep penetration.

Clean metals using the following methods: Mechanical – grinder, file, emery cloth, any

abrasives, etc. Chemical – They make acids to clean

metals. If you choose to use one, read the instructions, as there are safety precautions you must follow!

Contaminated Electrodes

If a thoriated electrode becomes contaminated, break off the area and regrind using a centerless grind technique.

If a pure tungsten electrode contaminates, break off area to produce a square end. A ball will appear after several minutes of welding.

EQUIPMENT

All of our GTAW machines will serve as SMAW machines as well.

Set switches to remote (2 of them). Set switch to GTAW / TIG step 4 when using the

foot rheostat. Set high frequency to “Start Only” for DC welding

on steels. Set high frequency to “Continuous” for AC welding

on Aluminum. Set current control to the maximum you can run

on the electrode. Post surge is the amount of time that the gas and

water continue to flow after the weld has stopped. This protects the electrode and weld puddle.

Rule of thumb is 1 second for every 10 amps you weld with.

Regulator

Single stage or flow gages are the types used.

Gas pressure depends on the type of gas being used, the size of the weld puddle, position, type of metal, etc.

Cylinders are high pressure. Treat them as you would an oxygen cylinder.

Types of torches

Air-cooled – used for light duty or when water is not possible. Heavier gage wire is used which make the torch heavier.

Water cooled – Can carry more amperage through a smaller gage wire (lighter) than air-cooled. Requires a cooling radiator or fresh water and a drain. Make sure water is turned on first before starting to weld.

GTAW Leads

Power cable, water in and water out, and the gas hose make up the water-cooled torch. The air-cooled has a power and gas line only.

DO NOT walk on leads, roll them up too tight, expose them to heat, spatter or hot metal as they are easily destroyed.

We use a leather or nylon cover on out leads to protect them.

Parts to the Torch Head

Torch body Collet (chuck) Collet body Electrode cap Ceramic nozzle – the size of the nozzle will

depend on the size of the electrode used, the size of the weld puddle, and the amount of gas needed.

Cups are graduated in 1/16th “ increments. A #5 nozzle has an inside diameter of 5/16”. They also come in clear Pyrex, which allows for a better view of the weld puddle.

SAFETY

Make sure “ALL” skin is covered. Light will burn your skin if exposed.

Use proper eye protection (#11 or 12 lens). Turn off power to set-up or take the torch head

apart. You can get shocked if you accidentally push the foot rheostat.

High Frequency wounds are the result of a poor ground or wet gloves. Electricity follows the least path of resistance. You are a better conductor of electricity than metal is. Turn the machine off the make changes on it.

Follow the common safety rules from SMAW and GMAW as they apply.

Use Common Sense!

Problems

Arc will not start – check to see that the machine is set-up for GTAW.

Check to see if the ground is properly attached. Move electrode closer to base metal or depress the foot rheostat more.

Contamination of electrodes – if the tungsten has come in contact with the base metal or the filler, it may be contaminated. If the arc wanders, changes color or is too hard to control, it’s probably contaminated. Break off the contaminated area and prep it according to the electrode.

Holds in the weld – use less foot rheostat (amps) or move faster.

Porosity in the weld – inadequate gas coverage, too hot of a weld or contaminates in the metal (or filler) may be the cause.

STARTING THE ARC

Be seated, position the foot rheostat and get the torch positioned.

Extend the electrode ¼” from the nozzle. This may vary depending on the situation.

Angle the torch about 20 from perpendicular in the direction of travel.

The arc gap will be about 1/8th “. Slowly depress the foot rheostat until the arc

stabilizes. Remain until the metal has heated to the point it becomes liquid.

Once the bead is completed, let the foot rheostat off but do not move the torch away from the puddle. The gas is continuing to flow and protect the weld.