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dsmabe
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    Sat Sep 20, 2014 5:50 pm

Not exactly sure how the arc pig is setup, but the only downside I see with trying to use it for tig welding aluminum is most machines this will be used on would be sine wave by nature. Possibly could compensate some by running slightly higher amperage.
Unless it smoothes the voltage/ current to resemble something closer to square wave.
Arc Pig
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    Thu Sep 18, 2014 11:12 pm
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Regarding sine wave versus square wave versus HF, the theory is that a square wave can substitute for continuous-fire HF. Either will help prevent arc extinction (or rectification, which is just extinction of the electrode-positive half-cycles.)

Note that weld current flows through a conductive path of ionized air. The weld current maintains its own ionized path by stripping electrons out of air molecules. When the weld current shuts off, the ionized air dissipates quickly. In fact it dissipates so quickly that the voltage required to re-establish the arc will double in a time on the order of a hundred microseconds (a tenth of a millisecond.) This is why it is so hard to weld in the wind; your conductive path is constantly drifting out of the weld gap.

The problem is worse with a sine wave, because each half-cycle of a sine wave ramps up slowly.

AC current is a series of half-cycles: a heating half-cycle (EN) followed by a cleaning half-cycle (EP), repeat forever. Each half-cycle of a sine wave ramps up slowly, so the arc is "off" for several milliseconds, more than long enough for its conductive path to dissipate. This problem is worse for the cleaning (EP) half of the cycle, I think because it is harder for electrons to jump off a flat surface (the workpiece.) Cleaning cycles are particularly important with aluminum, so aluminum has a particular problem with rectification (extinction of the cleaning cycles.)

Extinction/rectification is less a problem with a square wave, because square-wave voltage ramps up quickly, so the arc is "off" for less time between half-cycles, giving less time for the conductive path to dissipate.

This has been a bit long-winded, but here is the punchline: A continuous-fire HF box like the Arc Pig substitutes for a square wave. Every half-cycle, the Pig watches weld voltage ramp up, and if the voltage gets close to its maximum (Ie., if voltage approaches your welder's OCV) without re-establishing the arc, the Pig fires a flurry of high-voltage sparks to ionize the air and re-establish the conductive path.

Other continuous-fire HF boxes like the Miller HF251 do the same thing, except that the HF251 in continuous-fire mode does not monitor weld voltage, it just fires periodically on the up and down slopes of mains voltage.

Of course even with a square wave you might still want HF for no-touch ignition. Especially if your welder starts hot and melts your tungsten.

gordon
95GTSpeedDemon
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    Mon Oct 06, 2014 8:13 pm

after reading last night I tried holding down the ignition button on my pig. I noticed the weld puddle to be more distinct and was actually able to add filler metal. without holding it, it did nothing more than etch the surface.
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