Heavy Aluminum Welding

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Hi guys (and gals),  I'm not by any means a beginning welder but I have a question regarding welding a heavy piece of aluminum.  I am trying to weld a nipple flange to a SCUBA tank.  The tank is around 0.6" in wall thickness and the flange is comparable.  Both are 6061.  Problem is that my Miller Dynasty 300 doesn't have enough punch to accomplish it.  My torch (Weldcraft I think) is water cooled but rated for 250 A.  The 300 Amps could probably do it except the Dynasty has a 10% duty cycle at that high of an Amperage.  I tried preheating with a rosebud until it was almost too hot to get close to but the welder was still over-taxed.  I could only get about 1/2" of bead before the fan kicks on.  I also have a decent Hobart MIG but I have never tried MIG welding Al.  Which would you guys try next given my equipment, MIG, stick, or farming it out to a shop with a 500 A welder?
Reply:.6" thick welded to flange thats about the same thickness? I run a syncro 250 (it goes to 300, but Lord knows what the duty cycle on that is) I would do the exact same setup, preheat to 700-900 and then set the machine to kill, I do a fair amount of 1/2" 6061 weldments and thats the best method I've foundIs the dynasty's fan just kicking on or does it straight up stop you from weldingMiller Spoolmate 200 w/t S-52 WirefeederMM 211'09 Miller Trailblazer 302
Reply:What are you using this for? Scuba cylinders are considered junk after temps exceed 300 deg F. If you preheated one with a rose bud, I'd be very leery of using it for any sort of pressures above that of a standard 175 psi air compressor and even then I'd want to hydro test it..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:You forgot to add helium to the equation. Problem solved.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Originally Posted by DSWWhat are you using this for? Scuba cylinders are considered junk after temps exceed 300 deg F. If you preheated one with a rose bud, I'd be very leery of using it for any sort of pressures above that of a standard 175 psi air compressor and even then I'd want to hydro test it.
Reply:Originally Posted by shovelonYou forgot to add helium to the equation. Problem solved.
Reply:So what if the fan kicks on. I go full bore all the time with my Dynasty 300DX. Yes I do wait once in a while but you should be able to do that at 300 amps without having to wait. You still have to stop and reposition  the part.www.tjsperformance.comDynasty 300 DXHTP 240HTP Microcut 380Hyperthem 85JD2 Hyd Bender and HF Hyd Ring Roller all in one =(Frankenbender)Bpt. Mill/DRO4' x 8' CNC Plasma TableInstagram: tjsperformanceYT: TJS Welding and Fabrication
Reply:Originally Posted by TJSSo what if the fan kicks on. I go full bore all the time with my Dynasty 300DX. Yes I do wait once in a while but you should be able to do that at 300 amps without having to wait. You still have to stop and reposition  the part.
Reply:Originally Posted by MoonRise+999 on the preheat of aluminum and use for any sort of pressure usage.  Those aluminum parts are pretty much scrap for any sort of pressure vessel use now, as is.The 6061, after that preheat and/or after welding, is about 1/2 the strength of the T4 or T6 heat treated 6061.For anything critical, the weldment would most likely have to be completely heat treated.What is the usage of that weldment?
Reply:Originally Posted by DSWWe had a guy learn that the hard way when I worked at the dive shop. He was an independent instructor and got a really good deal on about 20 alum scuba cylinders from a shop out of state that was closing. So he brings them all home and decides he'll clean them up and paint them all so his students stand out from the crowd at the lake and do a bit of free advertizing in the process. The paint shop bead blasts them all down, then the paint guy convinces the instructor that powder coating will out last plain paint and be less expensive than the custom wraps they sell for  scuba cylinders. After that the instructor brings them in to us to get them hydro'd and inspected and then filled. Every single cylinder failed hydro. That's when we found out the story behind all of this and that the paint shop baked the cylinders to cure the powder coat.
Reply:I could imagine the heat dissipation but with some preheat to 250 degrees and 300 amps, I would think it could be done no problem. You could put some heat fence around it to trap the heat in.
Reply:Originally Posted by motolife313I could imagine the heat dissipation but with some preheat to 250 degrees and 300 amps, I would think it could be done no problem. You could put some heat fence around it to trap the heat in.
Reply:That welder should have more than enough power. You might need a bigger torch though, that 1/8" tungsten might not be able to handle the power. Have you been melting the tungsten?Ian TannerKawasaki KX450 and many other fine tools
Reply:I've learned to be somewhat patient whith AL give that a try.
Reply:Originally Posted by Ian DuffinYeah my thought was it shouldnt be to difficult, but the points raised about the structural integrity of the tank are worrisomeIt can be done, but probably shouldn't haha
Reply:Here is a 1/4-inch thick lap joint I made with my Dynasty 300. Way less than half throttle. As shovelon says, helium is the trick.  Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Originally Posted by motolife313Can't he heat treat it? Not sure the cost myself
Reply:Ya I heard about stress risers. I think if you set everything up right and penetrated right it could be real strong. Would be tough with Al tho
Reply:It's not just the penetration im worried about, its the fact that he has to puncture the tank this to, work and it looks like the bung is on the long flat sides, I.e. The weakest. Google scuba tank failure/rupture/blows up and see if you can see a common denominatorI pulled this from the internet just to give you an idea, I mean they form it in one piece, and look how thick it is near the valve!  Originally Posted by motolife313Ya I heard about stress risers. I think if you set everything up right and penetrated right it could be real strong. Would be tough with Al tho
Reply:Originally Posted by DSWWhat are you using this for? Scuba cylinders are considered junk after temps exceed 300 deg F. If you preheated one with a rose bud, I'd be very leery of using it for any sort of pressures above that of a standard 175 psi air compressor and even then I'd want to hydro test it.
Reply:Originally Posted by shovelonYou forgot to add helium to the equation. Problem solved.
Reply:Originally Posted by Ian DuffinI completely forgot that, good call! And If I remember correctly this is probably for a large pneumatic beer can launcherAmiright?
Reply:Originally Posted by CEPHere is a 1/4-inch thick lap joint I made with my Dynasty 300. Way less than half throttle. As shovelon says, helium is the trick.
Reply:Originally Posted by Ian DuffinI'm sure you could, but the way those bottles are designed there are no "tear points" for it to fail, same with the tanks we have for our argon and what not. If you notice the almost extrude/punch the whole bottle, form the neck after the piston is retracted, then put a round deal for the valve stem...not sure how they secure it but it's tough.Introducing a sharp line in the form of a bung, could have issues.At low pressure (0-200) he'd probably be alright, anything after that I wouldnt want to be around it
Reply:Originally Posted by eanaumanWhat percentage Helium.  Any tricks to welding with Helium?Originally Posted by motolife313In Jodie's last video he had a tank of 100% helium and mix it with 100% argon and used only 5 cfh of each gas with a number 5 cup and it worked really good. He could travel about twice as fast with 50% helium vs 100% argon with the same amps. I think he used 100 amps
Reply:Originally Posted by motolife313I could imagine the heat dissipation but with some preheat to 250 degrees and 300 amps, I would think it could be done no problem. You could put some heat fence around it to trap the heat in.
Reply:Originally Posted by eanaumanWhat percentage Helium.  Any tricks to welding with Helium?
Reply:Originally Posted by MinnesotaDaveHeat fence on heavy aluminum?  This thinking makes no sense to me - please explain how this surface treatment will stop the heat from traveling.
Reply:Originally Posted by eanaumanThe big difference is the thermal mass of the tank is huge compared to those plates.  It acts as a giant heat sink...
Reply:Originally Posted by MinnesotaDaveHeat fence on pre-heated heavy aluminum?  This thinking makes no sense to me - please explain how this surface treatment will stop the heat from traveling.
Reply:Originally Posted by shovelonNo tricks at all. Just watch the pretty light.25% helium added will really boost the heat in the arc. You can buy it as a 75%argon/25%helium blend at just about any weld gas supplier. Some people go 50/50 like B_C, but he likes to haul azz when he is production welding. I can weld 1" alum quite easily with my Dynasty200 using 75/25. Even did it with the yellow chinese machine before the torch spewed dragon breath on me.
Reply:If it's going to be surrounded by a steel shell anyway, why not just make the whole thing out of steel pipe or 516-70 boiler plate and be done with it?
Reply:Originally Posted by Ian DuffinI'm sure you could, but the way those bottles are designed there are no "tear points" for it to fail, same with the tanks we have for our argon and what not. If you notice the almost extrude/punch the whole bottle, form the neck after the piston is retracted, then put a round deal for the valve stem...not sure how they secure it but it's tough.
Reply:Originally Posted by MikeGyverThe neck ring you're (possibly) talking about is just attached for stamping/branding, etc. ... and the threads for the cap are just pressed on to the tank itself, which is formed entirely from one single piece of metal.
Reply:Originally Posted by EcondronGeez... 1" TIG aluminum?? You must be wearing a space suit or something to protect yourself from the heat! That aluminum weldment you helped me out with for MIG aluminum got pretty frickin' hot. I would definitely not want to be TIGing that. I can't say I've ever heard anyone recommend TIG welding aluminum even over 3/8". At that point I think MIG aluminum is so much more efficient. Just my $0.02 but what do I know! I don't even really know how to TIG weld.
Reply:Originally Posted by shovelonInverter tigs are much more capable of producing an intense stable AC arc to melt the base material. Couple that with helium and the base glazes right off for adding filler. I found that current maxed out and equal amplitude creates maximum heat in the arc, but cleans to break the oxide layer. Clean material helps greatly as well. 5356 has some exothermic properties provided by the magnesium as well. When reducing the EP, the overall amp output average drops which I hate. Good tungstens don't degrade so I can rule that out. One time a few years ago I welded a thick fillet with my Dyn200Dx plugged into a housecurrent plug of 120volts on a 20 amp circuit, 120 amps weld current, 100% weld grade helium and 4043 filler. DC straight for the root pass, then flipped to AC for the cover pass. No rectification of the AC arc and put a nice weave on it.
Reply:Originally Posted by TJSWhat are your starting parameters set at when using all helium. I tried all helium a long time ago with my Dynasty 300DX and could not even get an arc to start (a/c).
Reply:Perhaps if you bought some rockwool insulation at home depot or lowes and wrapped the cylinder in it it would keep the heat in better and allow you to use less amps? maybe it's a waste of time or insignificant, I've done it with brazing, and it helped.
Reply:FWIW, low frequencies of the AC arc are supposed to give you a boost with thicker aluminum.  It's counterintuitive.  One would think that the focus of a high frequency AC arc cone would concentrate the heat more, but lower frequency puts more heat in.  I guess more time in EN or something....TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:Yes this is correct and Terry can attest to it using his Dynasty 700. discovered by trial and error too I believe.    Also my thought for the OP is that the initial weld in the first pic needs to be completely removed as it is probably a cold weld and may not have good penetration.   Here is the "practice on scrap so you don't ruin your actual workpiece".Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:Originally Posted by Drf255FWIW, low frequencies of the AC arc are supposed to give you a boost with thicker aluminum.  It's counterintuitive.  One would think that the focus of a high frequency AC arc cone would concentrate the heat more, but lower frequency puts more heat in.  I guess more time in EN or something....
Reply:Originally Posted by MinnesotaDaveIt's my belief that it's because higher frequency increases the number of times the machine switches through the zero crossing point per second - the more times it is crossed, the lower the average amperage.I know inverters make this crossing much faster than a transformer machine, but it is still not instantaneous.
Reply:Originally Posted by EcondronGeez... 1" TIG aluminum?? You must be wearing a space suit or something to protect yourself from the heat! That aluminum weldment you helped me out with for MIG aluminum got pretty frickin' hot. I would definitely not want to be TIGing that. I can't say I've ever heard anyone recommend TIG welding aluminum even over 3/8". At that point I think MIG aluminum is so much more efficient. Just my $0.02 but what do I know! I don't even really know how to TIG weld.
Reply:Originally Posted by MoonRise+999 on the preheat of aluminum and use for any sort of pressure usage.  Those aluminum parts are pretty much scrap for any sort of pressure vessel use now, as is.The 6061, after that preheat and/or after welding, is about 1/2 the strength of the T4 or T6 heat treated 6061.For anything critical, the weldment would most likely have to be completely heat treated.What is the usage of that weldment?
Reply:Originally Posted by shovelonWelding 1" and greater is common practice. It just takes grunt to melt the root, and helium speeds up the process. The size of the puddle is dependant on the amps you have at your disposal. At some point the amount of amps is inconsequential as too many amps just gouges  the root. Changing the arc profiles help greatly to reel in the gouging but at some point it is fruitless.I can form a tiny puddle in the root of a 1" thick bar at lets say 200 amps and 90% helium and 10% argon. Then run a root pass into that root. I can do the same at 350 amps and 25% helium and 75% argon. I can do the same at 600 amps and no helium. The standard I go with is 50% helium, 50% argon and I can run root and stringer passes on unlimited thickness at 350 amps. I mentioned B_C  prefers a 50/50 blend for speed. That is one reason his welds are so consistent. Most of his stands are 3/8ths thick and he cranks them out like cookies. Up the thickness and he slows down, but no thickness will prevent him from laying down filler. And 4943 flows like water. Bam, right to the root and toes, then plump to your heart's desire!
Reply:Originally Posted by eanaumanI will pick up some helium and practice a little bit.  Good skill to know in any event.  Do you use much preheat when doing this type of weld with Helium.  The tank is a huge heat sink.  If you recommend preheat, how much is enough?  I plan on having it heat treated back to T6 if it is possible to do without too much distortion.  The heat treat guys suggest that it be done vertically.  I thought I would suspend it from the top valve opening and support it with a platform under the base to try and prevent it from stretching.
Reply:On second thought you better use 4943 and heat treat.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Originally Posted by OscarMy thoughts exactly. Even with high-frequency switching of the inverter (not to be confused with that of the AC arc)  in the 20kHz range or higher, the slope of the edges of the squarewave is just that-a slope, and not a vertical instantaneous transition. Fourier lives on, even in the welding world.
Reply:Originally Posted by shovelonOn second thought you better use 4943 and heat treat.