Page 38 - MetalForming-Mar-2018-issue

Welding Well
AC GTA welding, use hearing protection.
Independent Amplitude
A few advanced GTA inverters also enable operators to adjust amperage independently during the EN and EP portions of the AC cycle. Doing so enables them to direct more heat where they want it—into the work—and reduce heat on the tungsten.
For example, when welding 1⁄4-in.- thick aluminum, an operator could set EN at 200 A and EP at 70 A and subse- quently increase penetration and/or travel faster, add more filler rod, reduce or eliminate the need to pre-heat the weldment and use 100-percent argon instead of a higher-energy (and more costly) argon/helium blend.
Increasing the EN-to-EP ratio con- stricts the arc cone, which in turn enables the operator to narrow the weld puddle and better direct weld bead placement. The ability to reduce EP values may also permit the use of a smaller-diameter electrode. With these benefits, independent amplitude con- trol may be of value for welding thinner section or when extreme precision counts.
For testing EN and EP values, one way to start is by using standard EN setting recommendations (e.g., 1 A per 0.001 in.) and by reducing EP values to about one-third of EN values. If the weld shows signs of insufficient clean- ing action, increase EP values.
Total Recall
At the start of the article, we noted that optimum settings depend on the actual application. For that reason, experiment on scrap and practice parts. Conduct nondestructive and destruc- tive tests as necessary, and document parameters and the results. Note that just about all advanced GTA welders enable users to store and recall weld parameter settings with the push of a few buttons. After finding ideal settings, you can quickly call up a saved pro- gram for the next time you encounter the same application. MF
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