"blowout" TIG welding sealed aluminum sguare tube

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I done a search and read some threads and cant seem to find the problem i am having. maybe just search overload LOL. At work i have to repair cracks and such on these little 2kw generator frames. the frame is 1"x.125 aluminum tube i am unsure of the alloy but i have found the 5356 rod works better then 4043.As you can see from the pic the tube is formed in such a way that there is no open ends or caps of any kind. The problem i am facing is there seems to be pressure building inside of the tube when i weld causing it to oxidize, burn, not wet...all kinds of funky stuff, even "pop" and sent nice molten aluminum my way.now i know that the factory puts "relief" holes in places where the tubes come together like the top bars and the little tiedown angle piece. i know this because i have had to cut out and replace those before. what i HAVE been doing is drilling my own 1/8" hole in the bottom, do my repair then attempt to weld the hole back up.as soon as i start on the hole it does the same thing. the frame comes to me bare with no engine or electronics so i know i aint getting some kind of wacked out interference. the rig i am using. Miller Syncrowave 250 DX150 Volts, foot pedal, arc control set to balanced penetration. (it doesn't have all the pulse control and stuff...i would not be able to figure it out anyway LOL) i have tried max pen. balanced cleaning and max cleaning ALL do the same to a degree. 3/32 pure (green tip) tungsten. tried larger/smaller tungstenWeldcraft® WP20 water-cooled torch100% Argon set at around 15 cfh1/16 or 3/32 5356 rod (depending on the repair)i have built sealed tube frames before and never came across this. ITS DRIVING ME NUTZ!!!! Please help o' great masters of metal.John
Reply:If you are still venting tubing from one to another then I don't know either...Maybe a bigger hole from tube to tube?...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by zapsterIf you are still venting tubing from one to another then I don't know either...Maybe a bigger hole from tube to tube?...zap!
Reply:The blowout is from the air inside getting hot and expanding.  If you heat some other part of the tube, and then let it cool off as you weld up the last little bit, it will change from a blow to a suck as the air cools off.  I don't know if heating will ruin the paint.  You might drill a little hole a few inches away from your repair.  Do the repair, and then weld up the little hole as the repair is cooling.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:Originally Posted by AndyAThe blowout is from the air inside getting hot and expanding.  If you heat some other part of the tube, and then let it cool off as you weld up the last little bit, it will change from a blow to a suck as the air cools off.  I don't know if heating will ruin the paint.  You might drill a little hole a few inches away from your repair.  Do the repair, and then weld up the little hole as the repair is cooling.
Reply:larphead,You may want to try drilling your relief hole in an existing weld bead.  That way you're only filling filler and not the base metal.Make sure your relief hole is not too close to the last weld you do.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:I've welded on similar aluminum frames used in US Army flame thrower compressors.  They are relatively thin aluminum and they look like they have been Tig welded, but it's very possible that they are using a mig with some sort of a small spool gun.  I don't think a mig weld would have any problems with the gas heating up in the tubing because the weld would be completed before the pressure had time to build.If you HAVE to Tig it, maybe wrap the section with some cool wet cloths to keep the air inside the tubing cool?Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:update on this. tried the "let it cool heat another part" trick, worked kinda sorta. i dont think i was getting enough heat from the propane torch to compete with the heat from the TIG. thought about using the oxy/acte but that would just be another hose to contend with. did not try "cool wet rag" method. while i may have to experiment with it seemed like it would make a mess. what i DID do that seemed to work better. was drill a very small hole (3/64th i think) ABOVE and in the same tube as where the repair was. do the repair and let cool completely (to bare hand touch any way) flip the frame so that the vent hole is to the bottom and quickly fill. it IS a pressure issue (i could hear the little hole whistling LOL) but since hot air and gases rise, placement of the vent and position of the frame seemed to be the key I have to TIG them. i do have a spool gun but it is a big honking thing and i suck at MIG alum. dont use it unless i absolutely have to. like boss holding a gun to my head have to. plus it is hooked up to the millermatic and i would have to hook up a bottle of pure argon. AND drag another ground cable and more hose into my way.....im just lazy LOLbut that does make me think to start another thread in the miller forum
Reply:just let it cool before you weld up the vent hole, doing short sections of chromoly we had the same problem, but eventually we just welded all the beads like 95%, then let them cool, then came back later and welded them up. just do it quick so the air doesn't have time to heat and expand while the weld is still molten, the cooler the easier.