DC aluminum TIG- ok for inverter? what gas?

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I'm thinking of trying my Thermal Arc 185 AC/DC tig machine in DC mode on aluminum.   I understand this is done with the torch on the positive side, right?  Is there any reason not to try it with this machine?  I don't want to damage it.  Also, I forget what gas is used for this.  Can I do it with regular pure argon?   I'm not trying to weld anything super thick, just want to try it to see how it is.  I'll probly use 1/8" plate for the experiment.Thanks for all replies.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Right outa Da book:DCEP GTAW...  30% heat into work, 70% at electrode Long arc, 3/16" to 1/4"Best Cleaning action, least penetration.  Argon for the gasElectrode Large, up to 1/4" max amps 125Welds thin sheet up to .050"DCEN  Helium gas, deep penetration Small electrode, 1/16" for 125 amps  Can go up to 600 amps or moreCleaning: None1/4" to 3/4" full penetration  Short arc (1/16")Real world weldin.  When I grow up I want to be a tig weldor.
Reply:Post pics of the weld if you can. I wanted to try this myself.
Reply:Thanks David.It looks like I will try it DCEP with a 1/8" red tungsten (largest size I have) and argon gas.   I hope that will be thick enough tungsten.So 1/8" material is too thick for DCEP?Turbo, if I have any success worth posting, I'll take pics, other wise I'll be reporting how much I suck at DC aluminum tig.   MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Just post pics of the electrode dripping I have never tired to weld aluminum with DC, but sure have had the polarity wrong with tig.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Ok, I experimented a little trying to run beads with DC just now on the aluminum.   It was 'different', to say the least.   I can't claim any success.   First I tried it in electrode positive.  At 60 amps on 1/8" material with a 1/8" tungsten, the tungsten quickly balled up, no puddle was created to add filler into, the arc was eratic, blowing every which way.  As soon as I got just a little close to the work, the tungsten vaporized in a poof and blew a hole in the material.  I tried it a few more times at that setting with same result.  At 120 amps, a half inch of tungsten vaporized the instant I hit the pedal.  Fortunately it didn't melt all the way into the gas lens.   No setting in between produced any kind of weld.  No change in arc length had any noticeable effect on the erratic arc, except to vaporize the tungsten if I got closer than about 1/8 inch.  At 1/4" arc length the arc acted like a tornado blowing all over the plate.   I don't think I'll do any more experimenting in electrode positive.Then I tried it in electrode negative, same tungsten size, same 60-120 amp range, same argon gas (I dont have any helium).   The arc was extremely focused and the tungsten kept a perfect point and barely heated up, just a slight glow at the very tip.  At 60 amps it made a very narrow bead (without filler) all the way down the plate, but no puddle, just melting along like plastic, grey at the toes with a black stripe down the middle.  At 100 amps it pierced a keyhole the size of a pin through the 1/8" material at the start, then the whole thing turned to a plastic-ish mush.  Attempting to add filler made it more black, grey and turned the plastic mush into a big ball of plastic mush.  All amperages in between made similar results, to a lesser degree.   I think I will try more with electrode negative when I have time to see if I can get to do anything worth talking about.   I don't foresee it working very well though.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:David stopped short on us.  The book (Lincoln's Procedures Handbook of Arc Welding) also says argon is sometimes used on automated DCSP Tig.  It list Straight polarity as an automated application.
Reply:DCEN with  helium argon mix or just helium but it will be hard to keep the arc goingChuckASME Pressure Vessel welder
Reply:yes you need 100% helium
Reply:You also need to do everything you can to clean the oxide off the surface of the base metal and filler wire immediately before welding.  At a minimum, wire brush the base metal aggressively and then immediately begin welding.  This will remove much of the oxide layer on the aluminum surface.  The longer it takes you to start welding, the more the oxide layer on the base metal will spontaneously repair itself.
Reply:Originally Posted by A_DAB_will_doYou also need to do everything you can to clean the oxide off the surface of the base metal and filler wire immediately before welding.  At a minimum, wire brush the base metal aggressively and then immediately begin welding.  This will remove much of the oxide layer on the aluminum surface.  The longer it takes you to start welding, the more the oxide layer on the base metal will spontaneously repair itself.
Reply:Don't worry about the acetone.  You're wasting precious time.  I wasn't kidding when I said weld immediately after wire brushing.  The oxide coating on aluminum begins to reform instantaeously.  You can TIG weld aluminum with DCEN, but without a cabinet filled with Argon, you've got to hussle.  Keep trying and let us know how it goes.
Reply:In my world of tool and die welding Tig welding aluminum with DC straight(electrode negitive) polarity with pure and I mean 99%pure helium works great if the base is thick .250 or greater. I like welding this way. Most aluminum I weld is done this way.The puddle is different than with A.C. The travel speeds are faster. I use a 3/32 tungsten and about 250 amps adjusted with the foot peedal of course. The filler meatal needs to be added and with drawn fto the puddle quickly or it will ball up. Cleaning is important as you can see the oxides floating on the puddle. Sound welds can be made with this process. If you try to weld thin material it will get way to hot and make a mess of the work. I have never tryed it with argon I don't belive it would be effective.
Reply:Thanks welderman and everyone.  I think since I dont have the helium and I don't have a need to weld aluminum of 1/4" or more thickness, I think I'll leave the DCEN AL TIG alone for now.  I was only trying it for the sake of experimentation and learning.  For my purposes, AC works better.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by turboblownPost pics of the weld if you can. I wanted to try this myself.
Reply:Wow, that's really nice work William .MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I wouldn't want to walk on those steps when they are wet. Treadplate is one of the most slipperly surfaces when wet.
Reply:When you are welding with TIG the torch is NEGATIVE and the ground is positive. If you change polarity you DO NOT change the cables you use the switch or handle on the machine ONLY to change polarity.To weld Aluminum the machine needs to have AC capability. If it does not have AC it will not work on aluminum, and the reason is that  the sinewave is not correct. You will be able to make a puddle but then black oxides will form on the surface (with DC) and it will prevent proper welding. Aluminum needs that cleaning action of the AC sine wave to weld properly.For aluminum you would only use helium gas to weld sections thicker that 1/4 inch and your 185 machine would not be large enough. Helium in the gas mix is to increase penetration.Your machine would be at its best with a WP-20 weldcraft torch or simular brand and size. That size torch would be good up to 150 amps.Argon gas is the shielding gas and pure tungsten (green stripe) for AC on aluminum.
Reply:[QUOTE=Donald Branscom;169064]To weld Aluminum the machine needs to have AC capability. If it does not have AC it will not work on aluminum QUOTE]You ceratinly can weld aluminum with DC. It's done by many shops. Although somtimes from another planet, Billy Mac just showed us pics of DC welded aluminum that he did.
Reply:Originally Posted by DesertRider33I'm thinking of trying my Thermal Arc 185 AC/DC tig machine in DC mode on aluminum.   I understand this is done with the torch on the positive side, right?  Is there any reason not to try it with this machine?  I don't want to damage it.  Also, I forget what gas is used for this.  Can I do it with regular pure argon?   I'm not trying to weld anything super thick, just want to try it to see how it is.  I'll probly use 1/8" plate for the experiment.Thanks for all replies.
Reply:Donald, my Thermal Arc machine does have AC and wave control, etc.  It doesn't have a DC polarity switch on the machine, so I swapped cables at the output terminals.   The torch is a CK20, watercooled, 250 amps if I remember right.  I don't have helium, only argon and various argon mixes for mig that do not contain helium.   It took very little power on DCEN to heat up the material.  120 amps was too much for the 1/8" aluminum.   I think the potential exists to weld alot thicker aluminum on DCEN than AC.Worldsgreatestwelder, I did it for the sake of experimentation.  I like to experiment and try new things.  Sometimes they work, sometimes they don't, but I always end up learning something, which is the main idea.   In this case, it didn't work for crap on DCEP and only kinda sorta showed some glimmer of hope for working on DCEN.  If I had the right gas and thicker material, it might have worked better on DCEN.  Maybe next time....Thanks everyone for all your comments, info and suggestions.   Discussions like these are one benefit about being here on the forum.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Originally Posted by turboblownI wouldn't want to walk on those steps when they are wet. Treadplate is one of the most slipperly surfaces when wet.
Reply:Originally Posted by DesertRider33Wow, that's really nice work William .
Reply:Just be careful with those aluminum steps if it's storming, Bill. You know how they attract lightning.
Reply:Originally Posted by turboblownJust be careful with those aluminum steps if it's storming, Bill. You know how they attract lightning.