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View Full Version : Does aluminum require AC or DC for welding?



rotate
05-26-2010, 09:14 PM
I know that on TIG, AC is used for aluminum because the polarity reversal is suppose to help clean the surface. I'm not very clear on the mechanism but that's what I've read.

I've noticed that Lincoln Electric MIG welders uses DC for welding aluminum.

Can someone explain why DC is used for MIG while AC is used for TIG, in the case of welding aluminum?

ADGO_Racing
05-26-2010, 09:39 PM
Mig is a completely different creature. Nothing is the same, current, gasses, etc.

I have never been a fan of aluminum Mig welding. The lower end machines will do it, but not well. I have only seen in recent years a couple high end Miller machines that do a good job with aluminum Mig, but they are $8,000 welders. They better be able to weld Aluminum, steel, the crack of dawn, and make me coffee and breakfast while they are doing it.:D

We do a lot of welding here, but Tig is king followed by Stick. Mig is for sheet metal and some other light non critical work. We only weld Aluminum with Tig.

BigMike782
05-26-2010, 11:08 PM
Aluminum is generally TIG'd with AC but can be TIG'd with DC using helium and a fair sized machine.

JRouche
05-26-2010, 11:18 PM
Yup, you can TIG (GTAW) weld aluminum with DCEN... Depends on what you are welding and with what you are welding, the consumables.. JR

MichaelP
05-27-2010, 12:01 AM
You can easily weld aluminum with MIG if you have enough power (in general, at least, a 185 Amp machine) and a spool gun. You can do it without a spool gun too, but it'll be a headache.

Doc Nickel
05-27-2010, 12:12 AM
For aluminum, as noted, with a TIG the AC "back and forth" cycle helps blow oxides off the weld pool. With a MIG, the same basic idea is produced by the "make and break" cycle as the MIG wire contacts the work, melts, breaks contact, makes contact again, melts, breaks contact, etc.

Aluminum has been MIG welded with great success for many years, and it doesn't take a particularly impressive machine to do so. It takes a somewhat specific kind of machine (constant current, I believe) but like all welding processes these days, advancements in technology have brought the "exotic" machinery- like TIG and spoolgun MIG- closer to home-shop affordable.

On the other hand, I don't recommend the little 110V "box store special" MIGs for aluminum- then again, I don't necessarily recommend them for welding steel, either, after having used them extensively for many years before finally buying a "real" MIG...

Doc.

MichaelP
05-27-2010, 12:24 AM
Aluminum has been MIG welded with great success for many years, and it doesn't take a particularly impressive machine to do so. It takes a somewhat specific kind of machine (constant current, I believe) Just a regular MIG machine (constant voltage).

macona
05-27-2010, 01:30 AM
Aluminum mig is a hot process. Usually you are in a spray arc and that dumps a lot of heat into the gun. My nozzles often turn black welding aluminum. Aluminum is one of the only processes that actually benefit from pulse mig. With a good pulse mode you can get a bead that looks like a tig weld.

Doc Nickel
05-27-2010, 01:46 AM
Just a regular MIG machine (constant voltage).

-I knew it was one of the two. :D

Doc.

oldtiffie
05-27-2010, 02:10 AM
http://www.millerwelds.com/products/mig/onephase.php

http://www.millerwelds.com/products/mig/oneandthreephase.php

http://www.millerwelds.com/products/mig/

http://www.millerwelds.com/interests/instructors/

http://www.millerwelds.com/resources/

barts
05-27-2010, 03:13 AM
Back in the mid eighties, we built a robotic cell to weld Bradley Fighting Vehicle turrets; it used 450A at about 30V DC Al wirefeed, w/ a push-pull setup. Very impressive big blue Miller welders....

- Bart

Machinist Wannabe
05-27-2010, 03:39 AM
Just a little extra input. If you use a mixture of 50%Argon and 50%Helium
instead of plain Argon for shielding gas you will get better results (better
spray transfer, also good for thicker material).

(Don,t let my user name missguide you. I may not be a machinist but I
know a thing or two on welding)

small.planes
05-27-2010, 07:25 AM
With TIG the EN portion of the AC is just like you were welding straight DC, and 2/3 of the heat goes into the workpiece. The EP portion of the cycle will be as though you were welding reverse polarity, and 2/3 of the heat goes into the tungsten. However the gas ionization on this polarity cleans the metal of tenacious oxides, which is needed for aluminium.

MIG runs EP anyway, and the electrode is consumable, so the polarity is already correct for aluminium welding. You can weld aluminium with DC TIG EP, but generally you'll overheat the (supposed to be) non consumable electrode.

There is a welding forum here (http://bbs.homeshopmachinist.net/forumdisplay.php?s=&daysprune=&f=7) and a quick search (http://bbs.homeshopmachinist.net/search.php?searchid=451478) will bring up all sorts of useful info.

Dave

JoeLee
05-27-2010, 11:40 AM
When I bought my Miller Sidekick years ago I was told it would weld alum. The manual instructs you to change the polarity tabs under the cover and also to change the work lead to a plastic lined one so the alum. wire won't shave and clog up. I did all that and it still wouldn't weld alum. Tried several different gasses as well. All I got was white smoke and a black mess. I always TIG alum and never have a problem.

JL...............

torker
05-27-2010, 07:46 PM
If you can't get your mig into spray transfer...you are in trouble.
There's a couple of clowns in town here who think they are weldor/fabricators...they have a cheap spool gun and no training.
I just had to correct one of their jobs...
They built a motor mount for a big boat...
It was for a 150 pound 4 cycle trolling engine.
They built the plate out of 1/4" alu...the guy never even made it to the lake 20 minutes away.
His $6000 engine was hanging a couple inches off the road ...hangin by the gas hoses and battery cables.
Every weld ...about 16" in total length...FAILED!!!
Not enough heat...they didn't even look that nice. And he likes to "burp" the gun so it looks like tig welding...lol!

Bill736
05-27-2010, 09:31 PM
I don't recommend it, but a few years ago I stick welded an aluminum carburetor with a coated aluminum rod. My neighbor backed his truck into his riding mower, and broke the carburetor off of the engine. A used replacement carburetor wasn't readily available at a reasonable price, so I decided we had nothing to lose. I welded the bolt flange ears back onto the carburetor body, and the carburetor is still in service today, some 6 years later. No, it wasn't a pretty job, but it has held up well. I don't recall if I used AC, DC, or what polarity.

macona
05-27-2010, 10:19 PM
I have heard mixed results with the sticks. Good if you need to fix something in a pinch.

I built the motor mount for my 10EE from 1/2" aluminum weldments. Initially I tried to tig it but even with my 300 amp inverter it just wasnt going to happen. So I migged it. Finished it a fraction of the time, including stopping to fix my wire feed issues.

Teflon/nylon liners are not really necessary. I know of production shops that run normal steel liners with no problems. Also if you can run 5356 or one of the other 5000 series wires. They are much stiffer and feed better. They do not run as smooth as 4043 but the welds are stronger and can be anodized.

http://i65.photobucket.com/albums/h228/macona/Monarch%2010EE/DSC03395.jpg

stevenpaul
05-29-2010, 09:39 AM
you can do it with a mig though you need a plastic,nylon lining that goes to the torch not the metal spring type. Drill the tip out .1 oversize the wire tends to expand and jam in the tip, i just drilled out a wornout .8 tip . Giving it some clearance works wonders
im no expert but have welded a broken crank case on a dirt bike and a boat like this. you also need to crank the wire speed up.
steve:cool:

lazlo
05-29-2010, 10:50 AM
Teflon/nylon liners are not really necessary. I know of production shops that run normal steel liners with no problems.

I've found that Teflon liners are a necessity if you don't have a spool gun. Even with 5xxx series aluminum, teflon liners, and keeping the lead straight, it still will bird-nest, but the teflon liners help a lot.