Tech Talk: Best TIG Welding Performance Depends on Proper Tungsten Choice
(As seen in Applied Welding, Issue 2, 2003)
Q: What type of tungsten should I use for AC and DC TIG welding?
A: Today’s “universal” electrode is a tungsten with 2 percent cerium or tungsten with 1 to 2 percent of lanthanum.
Q: What about thoriated tungstens?
A: They remain the most common tungsten used in DC applications, but many people are starting to shy away because of the element’s radioactivity.
Q: What about weld performance?
A: Ceriated and lanthanated electrodes are equal to other electrodes in terms of their welding properties and even surpass them in some respects.
Q: Shouldn’t I use a pure tungsten for AC welding?
A: If welding codes demand it, yes. Otherwise the main advantages of a ceriated or lanthanated electrode include:
* Excellent ignition and re-ignition performance.
* Long service life.
* Better current carrying capacity.
* Outstanding in the low current range.
* Maintains a point instead of balling
Q: Why should I AC weld with a pointed tungsten?
A: Pure tungsten balls up, producing a wider arc cone and arc wandering. A rare earth tungsten used in combination with advanced squarewave technology maintains a point and lets you use smaller tungsten. This provides a more focused arc so you can more precisely control heat input and weld bead profile. For a pointed electrode, experts recommend a truncated point because an over heated needlepoint can fall into the weld (see fig. 1).
Fig. 1: A needlepoint, truncated and balled tungsten.
Q: Does AC welding with a TIG inverter offer benefits?
A: Yes, but you need to use rare earth tungsten to achieve the full benefits of a machine like the Dynasty® 200 (shown below). Through its extended balance control (up to 90 percent EN) and adjustable output frequency (20 to 250 Hz) you can take more heat off the tungsten and direct it at the workpiece. This allows you to:
* Improve control over weld depth-to-width ratios.
* Establish the weld puddle much faster.
* Increase travel speeds.
* Reduce welding and post-welding finishing time.
* Cut tungsten and gas consumption.
* Eliminate arc wandering.
Q: What tungsten size should I use with the Dynasty?
A: Through frequency and extended balance control, you should be able to weld up to 200 amps with 3/32-in. ceriated tungsten. For thinner material, use a 1/16-in. tungsten to better focus the heat.