Tig Aluminum AC, Electrode + or -?

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Hi,New to TIG welding aluminum and was wondering if I have something setup incorrectly.  When I was welding steel, I used DCEN and everything worked fine.  I have a Syncrowave 250DX and thought I would try out aluminum.  I switch the control to AC, put in a pure tungsten and tried to weld.  The arc started and it made a lot of noise but the pool never formed.  I did notice that the tungsten turned red hot.  I have the torch on the negative side, does the torch have to be on the positive side of the machine?Thanks for helping out a newbie,Craig
Reply:When you are in DC the current travels from (+ to -) or (- to +) depending on if you are in DC+ or DC-.  When you are in AC the current spends it cycle alternating between DC+ and DC-.   So in other words it should not make a difference which side you have your torch on in AC.   AC Tig is alot louder than DC as you noticed.  Then tungsten also gets hotter in AC than DC, and sometimes it takes a little longer to form a pool in aluminum than in steel depending on what thickness and alloy etc...   Keep at it and goodluck  ~JacksonI'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:Aluminum will also take more heat input than steel, since it conducts heat so well and the rest of the workpiece will drain that pool of its heat darn near as fast as you can heat it up.  Don't be afraid to stomp on the pedal to get'er started, but dial it back to prevent burnthrough as you go along - the thermal conductivity is a double-edged sword insofar as it makes things hard to START, but once you've been running a bit of a bead the rest of the workpiece is essentially becoming very much preheated (much more than steel, anyway).MR
Reply:Try to preheat the metal with the torch first. That should make it easier to start. Also try a bit larger tungsten ie: if you started with 3/32 go to 1/8. And don't be afraid to give it alot of heat to start.Brett B & B Fabrication and Welding Inc.Spalding, MI.
Reply:Originally Posted by Hammack_WeldingWhen you are in AC the current spends it cycle alternating between DC+ and DC-.   So in other words it should not make a difference which side you have your torch on in AC.
Reply:Thanks guys for all the great advice.  I'm going to pretty much try all of the ideas.  After reading the posts, I think my biggest problem was that I'm starting with too thick of a peice.  I had a peice of 1/2" 6061 lying around and thought I'd just try and run a bead.  Obviously, I was mistaken.So, this is what I'm going to try, get a peice of 1/8", increase my 3/32" pure tunsten to 1/8", preheat the peice first and up the amps I'm using, 200amps should be enough right?  The setup for aluminum is totally different than steel but I really want to learn to do aluminum so I'm gonna give it a go.  Thanks again for all the input, I'll let you know how it goes and possibly take some pics if I can figure out the digital camera.Craig
Reply:Cluna is correct.  That never crossed my mind,  If you have a machine capable of manipulaing the AC wave, it could make a difference.  However after seeing that you are starting with 1/2 inch T-6 I would suggest going to something a bit thinner to start running some beads before you start adjusting things.  also with an 1/8 inch piece you will not need to preheat it.  Normally speaking I do not preheat anything less than a 1/4 in.  Keep at it and you will get the hang of it in no time. ~JacksonI'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:Well, I FINALLY ran my first bead in aluminum.  It wasn't a very good bead, by the end of the bead I was burning through the material because I guess it was getting too hot.  All in all though, I'm happy with it.  It's odd, I can actually see the contaminates getting into the bead, kind of a black color.I still have TONS to learn and lot's of scrap material to practice on but I couldn't have done it without everyones help.Thanks again to everyone,Craig
Reply:Craig, you will find that the further you weld on aluminum that you will have to start easing up on heat a bit.  Aluminum transfers heat fast.  good to hear things are working out for you.  ~jacksonI'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:You should not have to preheat aluminum with the Syncrowave 250.  It should have more than enough power to get a chunk of 1/2 hot enough to lay a bead.And like Cluna said, if you have the cables reversed, and you are going for more penetration, and you will get more cleaning which will put heat into the tungsten.
Reply:Well, thanks to everyones help here, I've ran a couple of beads.  Please don't slam me too hard, this is only the second set of beads that I've ran on aluminum so I know I have a lot of room for improvement.  I particularly have trouble starting and ending the weld.  Then, as I'm moving along, my hand will get stuck and the middle of the bead starts to look funny.Here is the setup I used in case it can help others some way.1/4" 6061-T6 Aluminum PlateSynchrowave 250DX250Amps3/32" Ceriated (Orange) Tunsten Ball End1/8" Filler Material20 CFM ArgonBalance set to Green line between 6 and 8Here are the beads, any constructive criticism is greatly appreciated.Thanks to all,Craig
Reply:If those are actually your second set of beads, then you're doing PHENOMENALLY well.  Your filler addition looks to be on-par, the welds are clean and contamination-free (from their outward appearance anyway), and the only thing you'll want to do is let off the amperage controller a LITTLE bit slower at the end of some of those welds to allow that crater to fill properly instead of forming a divot.  That's such a minor suggestion when taken in the context of how beautiful those beads really are - ESPECIALLY for a relative newbie to aluminum!Absolutely phenomenal.MR
Reply:Dude, if thats really your second set of beads your doin hella good!! I'm no tig weldor but I can pretty much tell when someone has the knack. Guess what?
Reply:TEK - I AM a TIG welder by hobby, and I'll absolutely agree with your statement!  This guy's got it in his BLOOD!MR
Reply:Thanks guys for all the encouragement.  I still have a ways to go, running beads I think is easier than actually welding two pieces together.  I was going to post my first set of beads but they are really bad compared to the picture I posted.  I think my welder might be making me look better than I am.  I really love the Synchrowave 250DX, it's a joy to work with.  I just bought the pulser option too, I'm hoping it will help with my welding.I was wondering if anybody could lend some advice on starting the weld.  As you can see from the picture, the starting position on the right gets kind of globbed up.  I'm having trouble knowing when to start moving the pool.  With steel, the pool is very obvious but with aluminum I have a hard time telling.Thanks again for all the kind words, next I'm going to try and weld something together, wish me luck :-).Craig
Reply:Yep, a natural.  I been doing it for a long time and mine arent that good.Smithboy...if it ain't broke, you ain't tryin'.