[lil'bones]

Hey guys,

Here's a technical question for ya. With SMAW and GMAW, DCEP results in 70% of the arc energy into the work piece where as with GTAW, DCEP results in 70% of the arc energy into the tungsten electrode. Why is that?
Particularly with a machine that is capable of both SMAW and GTAW.
Interested to see what some of your thoughts are.

Thanks,

[Drifta-X]

U got it wrong there buddy.
Ep will always put more heat to the electrode then the work piece, and this is required on mig and stick (but not always) as it is required to melt the stick or wire.

[lil'bones]

So how is it that with SMAW set on DCEP there is deeper penetration than with DCEN. With GTAW you get more penetration set on DCEN, on DCEP there is so much energy (heat) in the electrode that we need about 1/4" electrode at only 125amps with minimal penetration.
I suspect it has to do with the non-consumable tungsten electrode, but why?

[Rick_H]

Are you sure?
Any other opinions?

He's spot on...dcep = more heat to the electrode.

[lil'bones]

"The preferred polarity of the GTAW system depends largely on the type of metal being welded. Direct current with a negatively charged electrode (DCEN) is often employed when welding steels, nickel, titanium, and other metals. It can also be used in automatic GTAW of aluminum or magnesium when helium is used as a shielding gas.[22] The negatively charged electrode generates heat by emitting electrons which travel across the arc, causing thermal ionization of the shielding gas and increasing the temperature of the base material. The ionized shielding gas flows toward the electrode, not the base material, and this can allow oxides to build on the surface of the weld.[22] Direct current with a positively charged electrode (DCEP) is less common, and is used primarily for shallow welds since less heat is generated in the base material. Instead of flowing from the electrode to the base material, as in DCEN, electrons go the other direction, causing the electrode to reach very high temperatures.[22] To help it maintain its shape and prevent softening, a larger electrode is often used. As the electrons flow toward the electrode, ionized shielding gas flows back toward the base material, cleaning the weld by removing oxides and other impurities and thereby improving its quality and appearance.[2"

I found this on wikipedia, this makes sense.

[Otto Nobedder]

DCEP in MMA/SMAW (and GMAW) carries heat into the metal largely through conduction. The droplet of steel is well above the melting point, and carries that heat into the base metal. This is, in part, why stick and MIG are prone to cold-starts.

You are also NOT trying to conserve the electrode, but rather intentionally consume it, so the heat differential to the electrode is desireable.

I may be better able to explain this tomorrow, when I'm not 70.7% through a twelve-pack... (the square-root of brew )

Steve S

[motox]

steve
beer theory is studies generally do not suffer from content but sometimes spelling and punctuation.
craig