HOW DOES AC WELDING DIFFER FROM DC WELDING

[bikerdib]

You have probably noticed a trend; an AC/DC machine gives you a better weld in most cases and also give you more versitility. One point, make sure your supply circuit is heavy enough to handle the welder. Running DC draws a little more input current than AC.

[Soundguy]

You can also weld thinner metal.

i weld sheet metal ( car / tractor body / hood panel thickness ) with a 30/70a ac arc welder. any thinner and you could put the metal on a barn roof.

dc welds thinner than this? like what? aluminum foil maybee?

[Rock knocker]

If I recall correctly, 7018 used to only be available for use on DC but now they have 7018 that will burn pretty well on either

7018 has always been a AC/DC rod. In the last several years, some 7018 has been manufactured which is certainly better on AC than in past years. But the AWS has always considered 7018 as AC/DC.

How the numbers work (short version):
70xx The first two digits is the tensile strength X 1000 psi
xx1x The third digit: 1 is all position, 2 is a position rod
xxx8 Even numbers are AC/DC, odd is AC

[joshuabardwell]

xxx8 Even numbers are AC/DC, odd is AC

I'm not sure that's right. Here's what the Internet says.

EXX10 DC+ (DC reverse or DCRP) electrode positive.
EXX11 AC or DC- (DC straight or DCSP) electrode negative.
EXX12 AC or DC-
EXX13 AC, DC- or DC+
EXX14 AC, DC- or DC+
EXX15 DC+
EXX16 AC or DC+
EXX18 AC, DC- or DC+
EXX20 AC ,DC- or DC+
EXX24 AC, DC- or DC+
EXX27 AC, DC- or DC+
EXX28 AC or DC+

The "default" seems to be that everything can be run on DC, and some rods have stabilizers in their flux that also allow them to be run on AC. That's my understanding.

[CNC Dan]

The "default" seems to be that everything can be run on DC, and some rods have stabilizers in their flux that also allow them to be run on AC. That's my understanding.

That's the way I've understood it.

[Gary Fowler]

While 7018 could be ran many years ago with AC, it was definetely not an AC rod. Very hard to start and arced out a lot with AC. It took a steady hand and lots of patience to weld AC with 7018 back before the made an AC version. AC welding takes a very long arc length compared to DC rods and since all low hydrogen rods need to be keep to a short arc length, it made them very hard to weld with.

[LD1]

cant really add anything other than the differences that are mentioned, are very subtle. Like it being quieter. It sure is, but unless you either weld everyday, or do it side by side, you probabally wont "notice".

And if you were experienced and pretty good with the AC, again, DC is a little smoother and easier, but you may not "notice". IE: if you havent used your AC welder in a month, and bring this thing home and start burning rod, you may not "notice" these differences.

[Shield Arc]

Wonder if you could talk these guys into using an AC welder?

[joshuabardwell]

Wonder if you could talk these guys into using an AC welder?

Shield Arc: For the n00bs out here, tell me why DC is safer in that circumstance than AC?

[joshuabardwell]

And if you were experienced and pretty good with the AC, again, DC is a little smoother and easier, but you may not "notice". IE: if you havent used your AC welder in a month, and bring this thing home and start burning rod, you may not "notice" these differences.

I can kind of attest to this. I'm very new to welding. When I first got my welder, a diode in the rectifier bridge was bad and the DC output didn't work, so I started learning on AC. After a few weeks, I replaced the diodes and now practice pretty much 100% on DC. I can tell that the arc is a little easier to start, and I can see that there is less "buckshot" spatter, but as far as the "more stable arc," "easier to control," "nicer bead appearance," and so forth... well, my arc control and bead appearance is so bad to begin with that any difference the DC might be making is invisible.