Aluminium Tig welds

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After laying a weld in ally does going over the top of the weld with the tig torch just to remelt the weld and not to add filler damage the weld?Ive done it a few times where I wasnt overly concerned about strength just as a cosmetic thing so you have a smooth top to your weld rather than a series of half moons. Yes, a welder would rather see a nice even set of pools but the public at times have other veiws.
Reply:Well I believe as long as you let the metal cool down to room temperature before smoothing it over it wouldn't hurt the integrity of the weld too much.  I'd turn it down a little though.
Reply:But it depends on how critical the application is.  You would be sacrificing strength for an asthetic weld.  You might be better off leaving it the way it is.
Reply:I agree with metal mafia. How critical is the weld? Asthetics are not really as important as fit, form and function.Tony
Reply:i was taught NEVER "go over" your welds..better get it right the first time...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 zapsteri was taught NEVER "go over" your welds..better get it right the first time...zap!
Reply:we have a company here in town that does that when they weld the ends back in truck fuel tanks it may look pretty but you never know most of the time its done to hide a bad weld  we don't do it at workI agree with what zap said Creative metal Creative metal Facebook
Reply:Thanks for all the replies.Let me stress this is not a load bearing weld , it is joining two pieces of aluminium capping on balustrading.It is as an alternative to grinding some of the weld off. Yes, if you have a nice even "stack of dimes" it seems a pity but the public as I said often see things differently.I was more interested in how running over the top would affect the weld itself, I don't suppose if you are only remelting the filler and not the parent material it would affect your penetration ?? But I was concerned how it would affect the material your using as reinforcement and the HAZ.It is all 6060 and 6061 alloy aluminium.Why would letting the weld cool to room temperature help?
Reply:Going back over WILL decrease the quality of the weld.  You will create porosity along the sides of the weld in the parent metal as well as extra stress to the parent metal.  Even though it is not a load bearing piece, if your weld is no good, cut it out and re-weld it.
Reply:My bad. I didn't understand the post correctly. I thought the question was about grinding doon the weld. Definately not go over the weld to get it to look good. Like Zapster said, get it right the first time.
Reply:I don't buy the argument that washing compromises the weld. If it did, multipass welds wouldn't be an option. Here is an article that should be peeked at in reference to the topic. Considering the stresses on their welds, the practice cannot be very harmful to the products strength http://www.manufacturingcenter.com/t...602welding.aspScroll down to breaking all the rules.Last edited by cluna; 06-25-2006 at 11:12 PM.
Reply:going over it only means you screwed it up the first time...you'll never hide a bad weld from me no matter what you do  You Had Better Get It Right The First Timesome places will see right thru a bad weld and the part will be rejectedand thats that.. ...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:I worked in a shop that did mold repair. Any weld that was gone over without adding filler rod cracked. Maybe it was due ot the hardness of the material (RC50), but I still wouldn't do it. Just the fact that it happened every time to this one guy is proof enough for me that it is not a good practice. I don't do it just because  when I was learning, the instructor said not to do it. A bad looking weld might be strong and not pretty, but a pretty weld isn't necessarily gonna be strong. Try it and then check the weld under a loupe or microscope and see if it hasn't cracked. If it has to be pretty, practice on a scrap piece before doing the actual part. Just a few words from experience, ultimately you will do what you think is right and if you're ok with that, that's fine. That's what I like about this forum, so much experience and everyone is willing to give their opinion from experiences.Tony
Reply:Hey Cluna!I for one happen to agree with you also because, in my thirty+ years of welding and fabricating experience, I've welded more times than I can remember - Aluminum joints whereby more than one pass was required in order to complete the weldments...  The same can be said with all other materials because many joints need to be welded with more than one pass to bring the weld deposit up to flush at minimum with the surface of the base material... I weld 316L & Ti ,1/2" to 3", schedule 10 to 40 pipe & tube all day long no both butt and fillet joints using GTAW. i have three other welders that also are welding these assemblies together also, and not once has any of the weldments that I had to repair because of not meeting acceptance criteria, fail for the reason of me having to "Touch up" the welds (with just a slight amount of filler added) so that appearance wise they would be acceptable ... Not only that ,these welds would then be again subject to NDT (both X-ray and Hydro-testing as per ASME B31.1) and occasional random destructive testing also... All have passed with flying colors!!!   The reason why these never fail is because we use a repair welding procedure specification that has been Proven thru TESTING time and again to work!!!So I have to agree with Cluna on this discussion! Respectfully,SSBN727Last edited by SSBN727; 06-26-2006 at 12:51 AM."Run Silent...  Run Deep!!!
Reply:Washing a weld in for appearance purpose may be fine for some applications, but in my line of work, it is not.  I would not hesitate to say that my welds are more scrutinized than most, if not all, on this board.  My welds are x-rayed and even placed under electron microscopes to check for grain structure and miniscule cracking.  With all this equipment, we have played with differing techniques.  Washing a weld ALWAYS produces an inferior end product.  The multipass that you referred to is comparing apples to oranges.  With a multipass, you are laying a good weld WHILE ADDING FILLER. SSBN727 said he has had no problems, but he also is adding filler.  The problems occur when filler is not added. As I said, on some applications, washing a weld for appearance may be fine and there would never be a problem with it.  But, if you know that it produces an inferior weld, then why do it?
Reply:Well thanks for the replies gave me a bit to think about.Found it amusing the presumption of poor welding though.Maybe I should have posted some before and after shots....just to show I was not lying?
Reply:Originally Posted by XwelderWith a multipass, you are laying a good weld WHILE ADDING FILLER. SSBN727 said he has had no problems, but he also is adding filler.  The problems occur when filler is not added. As I said, on some applications, washing a weld for appearance may be fine and there would never be a problem with it.  But, if you know that it produces an inferior weld, then why do it?
Reply:Here is a follow-up question to consider about washing...would it make a difference if you were welding a pure metal versus an alloy?  I guess I was just thinking that the metals I have always heard had problems with washing were alloys that tend to lose thier goodies when heated beyond a certian point.  For example, stainless.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Originally Posted by clunaCannodale washes  the bead on the front forks *on purpose* for strength, then you might reconsidered the premise that 'washing is bad' That is about as critical a weld as you will find and the consequence of failure can be death. Washing is costly though and that is the biggest reason to not do it.
Reply:Originally Posted by XwelderI weld commercial airliners, slightly more critical than a bicycle.  I don't need to reconsider my "premise"  I know it to be fact.
Reply:If you choose to believe that a bike is more critical than any thing on an aircraft, then there is no point continuing this conversation with you.
Reply:i believe on a airplane most stressed parts that have actual meaning are riveted to each other ...correct? you need flex yaknow i'm no plane builder by a long shot but stuff that has to flex that much on a plane can not possibly be welded together...crack break snap...maybe you weld the seat back railings and stuff like that but the chassis of a plane is not welded ummmmm have a nice day...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:I would say the use of welding on aircraft is rather dependant on application.   TIG was originally developed for welding aircraft in WWII.  Though there are conditions and reasons for and against.IF it Catches...Let it Burn
Reply:How many people know that the first tig was with helium only, before they discovered argon, hence linde's  trade name " Heli-Arc ".
Reply:If you go back to the article Cluna cited, you can see that Cannondale DOES NOT autogenously weld the second pass of the forks.Per the Article:"We then make a second pass that smoothes the weld bead to the point where the joint looks like it was molded.” Because the cosmetic second takes the crown off the weld, operators continue to add filler wire to maintain throat thickness." Case closed, bad technique now debunked.-dsemanOriginally Posted by XwelderIf you choose to believe that a bike is more critical than any thing on an aircraft, then there is no point continuing this conversation with you.
Reply:My welds are not on the airframe, or chassis as Zap called it.  He is correct in that those parts of a plane are not welded.  However, There are many components of a commercial airliner that do require welding.  I work on the engines.  Even there, weld is only allowed on non-rotating parts.  These are generally called cases.  These cases are the frames for the engine.  They can made from Al, stainless, Ti, Inconel, or any number of alloys. They are under tremendous pressure and heat.   As scary as it may sound, these cases crack.  I repair the cracks.  I don't know if you would classify that as structural, but they are very critical.
Reply:Originally Posted by Xwelder As scary as it may sound, these cases crack.  I repair the cracks.  I don't know if you would classify that as structural, but they are very critical.
Reply:Originally Posted by clunaI consider just about everything critical on a vessel that travels in the pressurized strata. Even a door handle. I'm a proponent of not welding aluminum if at all possible as I noted earlier in the thread. It is hard to beat the strength of a rivet/expoxy combination on a material with a low strength like that of aluminum (let alone the hassle of reheatreating after the weld)I was curious since I know that the newer technologies are starting to make to the field that actually make Al weld viable for structures.
Reply:Structural welding is pretty common on general aviation airplanes.  However, it's limited to 4130 tubular frame structures.  There is an AWS spec for the procedure and the material is usually not heat-treated afterwards.  Preferred filler metals have a lower carbon content than 4130 itself providing some dilution of the parent material with the resulting alloy having better elongation properties, but reduced tensile strength.  The HAZ should be as small as possible and as such, in that particular application I suspect that washing, or even a second pass would make the joint prone to cracking.I'd like to add that there is a significant difference between a weldor and a welding engineer.  Experience as a weldor doesn't imply any specific knowledge or understanding about a given process or material.-Heath
Reply:Originally Posted by halbrittHowever, it's limited to 4130 tubular frame structures.  There is an AWS spec for the procedure and the material is usually not heat-treated afterwards.  ...cut...  The HAZ should be as small as possible and as such, in that particular application I suspect that washing, or even a second pass would make the joint prone to cracking.
Reply:Remember that in 6061, autogenous welding is impossible due to the presence of mag silicide and iron silicide interstitially, which migrate to the grain boundaries while the weld puddle is freezing, and cause "hot short" cracking.  This is why 4043 filler metal is used on 6061.  It contains silicon, which forms a lower melting eutectic phase that normalizes the stresses during this freezing cycle.  As long as the rewelding of the joint does not pull in an appreciable amount of base metal that would cause the silicon in the weld metal to drop below about 1 1/2%, rewelding causes no harm to the weld.  My company welds over 6000 tons of aluminum a year, into the tens of thousands of linear inches of weld, and our customers demand perfectly smooth welds because they are vacuum critical applications.  Our welders frequently do the "stack of dimes", and then re-flow the weld to give it a more aestheically pleasing appearance for our customer.I r 2 a perfessional