Neex AC/DC Explained

[mcd176]

Can someone give me a rundown on the differences in ac and dc welding, meaning when would u use ac or dc and neg or pos, I've welded with a stick welder Years ago on DC but honestly never did have a complete understanding of it!

I use a Mig or Tig for pretty much everything but was looking into a stick welder for heavier metals

Thank in advance

Mike

 

[deereman75]

I have only worked with AC, but from what I hear DC gives you better welds, less spatter, and better out of position welds. It also lets you have more choice of rods. When I get the cash I am getting a DC inverter, and I will see just how much better it really is.

 

[Soundguy]

try these.. some take a bit of reading. but the info is collectively there.

AC vs. DC

What Is the Difference Between AC & DC Welding? | eHow.com

Stick Welding..........AC Vs. DC ???

ac versus dc welding - WeldingWeb™ - Welding forum for pros and enthusiasts

ARC Welding: AC/DC vs AC?

 

[k0ua]

Pretty much what deerman said, I have the DC inverter and it is quieter, less spatter, cleaner looking welds, and more rod selection (like 7018 for instance). I instantly went up about 3 pay grades of welder when I switched to DC.. Not that I am really any better but the welds look better:laughing:. As for DC+ or DC- it depends on what the manufacture of the rod calls for, for that rod, and will make a difference in some rods as to penetration depth. Some rods run fine either way. That is my understanding of it, but I am still a baby welder, and there are old hands on here that might be able to explain it better. I havent struck an arc with my AC machine since I got my DC machine. It is that much better, at least in my opinion. If I wanted to run a carbon arc torch or thaw a plumbing pipe, then I would use my AC machine of course.

James K0UA

 

[Gary Fowler]

AC machines have a less stable arc as the current is constantly 60 times per second switching polarity at the arc from + to -. DC has a constant polarity, thus more stable arc. Many of the rods available are for DC machines only with only a few listed for AC only. I havent tried it, but I think the DC machines will run the AC rods but the AC wont burn the DC rods well and I have tried that (arc blow, arc out, rods freeze (stick) in the puddle. AC machines require that you maintain a long arc length which causes much more weld splatter that the shorter arc DC. All in all, DC provides a much better weld that is easier to weld with than AC. Thats my opinion for what it is worth.
Almost all DC stick rods run with reverse polarity with the exception of some hardsurfacing rods that I know of that run straight polarity. . Straight polarity allows for shallow penetration so the metal basically just lays of top of the weldment which is what you want for hardsurfacing. Straight polarity is used for TIG welding also

 

[Shield Arc]

Sometimes I'll run 7018 on DCEN for open root welding. Starting to see it more and more for new hire testing with 7018 open root pipe. Guess the employers want to separate the men from the boys right off. I like DCEN more so just for the root, then switch to DCEP for hot, fill, and cap.
Here's a picture of the inside of a pipe welded from the outside with 7018.

 

[Gary Fowler]

I have seen that also and always thought that the folks specifying that must be the most stupid person in the world when it comes to welding. My thought were always, let me see the sucker who spec'ed this out come and make a test on it. Although it can be done, 7018 is not an open butt rod. Just because one can make a weld with it doesnt mean it should be done. If the engineer wants 70K tensile on the root, there are open butt rods that will do that or the best option, use TIG with ER 70S wire. You get a more uniform root pass and no slag inside the pipe and best chance to make it pass 100% xray. You have to have a perfect fitup to make a open root 7018 weld and getting that in the field under actual conditions is nearly impossible or would take so many manhours as to be impractical.

 

[Shield Arc]

Gary, why don't you tell us what you really think?


I'm more comfortable putting in an open root with Tig, I'm too inconsistent with stick, but getting better, maybe if I had a steady diet of pipe I'd be better.