How to Secure Most Benefits from TIG Welding

Article From welding-advisers.com

Brief Summary:

The Gas Tungsten Arc Welding (GTAW), also called TIG Welding, has the following a dvantages:

High quality welds, low distortion
Easy to mechanize and automate
Flexibility and ease of heat control
All metals, all positions

Limitations

Lower deposition rates
Good skills required
Sensitive to cleanliness and contamination
Arc blow sensitive

The Tungsten Electrode in Gas Tungsten Arc Welding (GTAW or TIG) can make contact with a Direct Current (DC) power supply either at the positive (+) or at the negative (-) terminal.
Due to the electrode limited current carrying capacity, DCEP is used only for welding thin sheet metal where low current is sufficient. For most other applications welded with higher currents, DCEN is selected if welding other materials than aluminum or magnesium.
One of the factors of the DC Electrode Negative staying cooler is the evaporation of the emitted electrons, actively contributing to electrode tip cooling.
Advances in electronic controls of power supplies permitted to introduce new wave forms, generally with electrode negative, characterized by current pulsed between a low maintenance or background value, that keeps the arc but allows the weld to cool somewhat, and a high peak value capable of melting metal in a controlled way while ensuring the required penetration.
GTAW-P where P stands for Pulsed.
The result is better control of the weld puddle without unduly high heat input. Adjustments include both current levels and pulse duration time for each level.
Welding of thin metals or joints of dissimilar thicknesses or dissimilar alloys for manual, mechanized or automatic setups are common applications.
A variant of this process, involving high frequency switching, is useful for precision mechanized and automatic applications where directional properties (stiffness) and stability of the arc are important, the current is varied between the two levels as before, but at a selectable fixed high frequency, permitting the resulting low average current.
Grinding dust might be dangerous if inhaled or ingested, and attention should be paid to other safety issues as explained in the above specification. For AC welding with pure tungsten electrodes a ball or emispherical shape is often selected.
Tip shape is a parameter that should be kept constant once determined that the results are acceptable for a given job.
Manual GTAW is often performed without added filler metal when the joint requires only fusion of the abutting ends. Filler material can be added manually when needed from the side, right in the weld puddle, by alternatively introducing the wire tip into the arc and withdrawing it.
For mechanized or automatic welding, in order to provide a higher weld deposition rate, filler wire is fed by a mechanical feeder, drawing wire continuously from a spool.
The feeder may be similar to those used for G Metal Arc Welding with an adjustable feed speed control and wire guide. Normally the wire is fed at ambient temperature in what is known as cold wire feeding.
For special requirements, when exceptionally elevated deposition rate is needed, hot wire can be provided.
The process is similar to that described above, except that the wire is resistance heated between a contact tube and the workpiece by an AC supplied by an additional power supply, independent from the DCEN power supplied to the welding arc.
The shielding gas is provided continuously through the torch to protect the molten weld metal, the tungsten electrode and the filler wire tip, if used, from air contamination. Backup shielding gas may be provided if necessary on the underside of the weld to purge and displace surrounding air.
Shielding is always needed but it may be critical especially for highly reactive metals like titanium that would be promptly oxidized and ruined if heated in air.
The gases uses are mostly Argon and Helium or mixtures of the two.
Argon is the standard shielding gas.
Helium, which is lighter than air, must be supplied with a higher flow than argon because it tends to rise. It transfers more heat than argon for the same current and voltage. It may be needed to join metals of higher conductivity or heavy plates.
When extinguishing the arc at the end of the weld, it is important to let the gas flow for a certain time to shield the hot metal from air.
Equipment provides a delay before shutting off the gas flow, but the welder must linger with the torch upon the weld as long as needed.
Most weldable metals can be welded by the GTAW process.
It is adaptable to thin and delicate joints but also to thick and demanding applications, always of good quality although possibly not the most fast and economic process.
Aluminum alloys of the weldable kinds are among those for which GTAW is most suited. One should always remember that not all aluminum alloys can be welded successfully or with the same ease.
Joining is made difficult by the surface formation of tenacious refractory aluminum oxides of melting point much higher than that of aluminum metal.
Magnesium alloys present welding problems similar to those of aluminum. These are dealt with by the same procedures.
Stainless steels are often GTAW welded because of the cleanliness of the process and quality of results, especially for food or pharmaceutical applications.
Mechanized and orbital welding is widely used as good results are repeatable. Argon is used.
Heat resisting alloys, nickel and cobalt alloys are welded by this process that permits the use of similar or different filler metal as required and usually minimizes heat input, a parameter required to control distortion.

To read the original article please click:

http://www.welding-advisers.com/Tig-welding-tips.html