Welding Aluminum

Discussion in 'Maintenance Bay' started by timwinters, Apr 21, 2015.

  1. timwinters

    timwinters Ejection Handle Pulled PoA Supporter

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    Just a data point:

    I need to replace the "gasket" on my carb heat "butterfly" so I just called Dynamic Propeller and ordered one. This got me to thinking about:

    A dozen or so years ago, when I first bought my 182, the pre-buy revealed that the carb heat box had seen better days and had a numerous cracks. The worst were around the "neck flare" that attaches to the carb.

    I bought a Dynamic Propeller reinforcing kit and pondered my options.

    The price for both replacement and overhaul of the box were pretty salty. I don't remember exact prices as it's been a dozen years but it seems like it was $1,000 to $1,500 or so.

    So, I stopped by a reputable local steel fabricating shop and asked if they welded aluminum. "Sure" they said, we have one guy who is our aluminum specialist. He practices on beer cans. Hmmm. Do I want to spend $50 or $1500? (or whatever it was)

    I was active in CPA at the time and posted my dilemma. The prevailing opinion was that I had lost my mind, that the type of aluminum the box was constructed of couldn't be welded, that it would set up stresses and re-crack, etc.

    I took the box into the local shop, had their aluminum guru look at it, and he assured me that "this was no hill for a stepper."

    So I decided to give it a try.

    The stiffening kit from Dynamic Propeller was installed when the box was re-installed on the airplane.

    12 years later, at last month's annual, it's still whole and no cracks have redeveloped.

    Like I said above, just a data point.
     
  2. rbridges

    rbridges En-Route

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    I dunno. If you didn't throw a mountain of money at it, I don't see how it could be fixed.
     
  3. Alexb2000

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    Cast aluminum and cast iron don't have the same characteristics IME. Quality cast aluminum, like in aircraft parts welds very well as long as you can get it really clean. Racing, R&D, etc. regularly weld on cast aluminum engine blocks that are put into service.

    For example I welded up a cast aluminum piece on a gas powered quickie saw several years ago. The vibration and abuse that part takes is about as bad as it gets and no problems.

    Cast iron is much more challenging, but can also be done.
     
  4. BiffJ

    BiffJ Pre-takeoff checklist

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    Most aluminum can be welded but some require special preparation to do so. 7075 is a tough one because the zinc in the alloy causes issues. 2024 has some problems along those lines as well but can still be welded. Chances are that your carb air box isn't one of the special alloys and is readily weldable. My guess is 5052 or something along those lines. It can be welded with an oxy acetylene rig where the 2024 and 7075 can't. One problem with welding alloys is that you change the property of the alloy where its welded and if it required high strength in those areas you will have more cracking along the weld lines. . .


    Frank
     
  5. timwinters

    timwinters Ejection Handle Pulled PoA Supporter

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    A cessna carb heat box isn't cast, it's built from sheet material and is beefed up at various mounting spots. Very light weight...hence the issue with cracking over time and the reason Dynamic Propeller developed the reinforcing kit.
     
  6. Tom-D

    Tom-D Taxi to Parking

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    The carb air box on a 182 is a work hardened and heat treated part. it can't be welded. unless you have a method of annealing and then re-heat treating the assembly.

    I have one customer that has gone thru what you are seeing, he had it weld repaired, it only took 5 hours flying until the whole assembly came apart.
     
  7. Tom-D

    Tom-D Taxi to Parking

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    There cheapest way out of this is a new part.

    When you repair it, and repair it, pretty soon you'll have a repair on a repair, with a crack in it.
     
  8. tehmightypirate

    tehmightypirate Line Up and Wait

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    Came here to second what Tom-D said.

    Welding most aluminum alloys reduces their strength which can only be recovered by re-heat-treating the final part. In addition, it can change the fatigue properties drastically.

    For reference I'm a structural engineer and not an A&P.
     
  9. timwinters

    timwinters Ejection Handle Pulled PoA Supporter

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    Tom & Mr. Pirate,

    Did you guys miss the part where I said it has lasted 12 years without issue?

    Thus far and still going strong.

    I don't know exactly what process this shop's "aluminum guru" used, all it know is that it's worked for twelve years without any add'l cracking.

    Edit: I prolly knew what process was used 12 years ago but have long forgotten since I'm not a welder.
     
    Last edited: Apr 21, 2015
  10. steingar

    steingar Taxi to Parking

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    The aluminum frame on my dearly departed fire-breathing race bike had honking big welds. The lasted for 12 years, thousands of miles and lots of tomfoolery. They'll probably last quite a few more.
     
  11. tehmightypirate

    tehmightypirate Line Up and Wait

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    I'm not saying that it can't be repaired by welding, nor that it needed all of it's original strength (though if I'm reading correctly you stiffened it as well). Welds are obviously superior to cracks so it's an improvement. I simply wanted you to be aware that welding aluminum is not the same as welding steel. Steel doesn't generally get weaker after welding, aluminum does. So, while this worked for you people need to be aware that welding aluminum reduces the strength of the part unless re-heat-treated otherwise it may not turn out well if they try something similar.

    As for the other people's mention of built in stresses and sudden recracking, maybe. Without seeing the parts geometry and the weld I can't say. This sort of a failure is possible for sure, as is my comment about fatigue strength. After 12 years I would guess that it isn't going to be an issue. However, this doesn't mean that everyone should go around welding their aluminum frames and hoping for the same results.

    If it were mine I would see about getting it heat-treated again. This isn't too expensive and would result in a better repair IMO. That said, after 12 years it's likely not worth it.
     
    Last edited: Apr 21, 2015
  12. tehmightypirate

    tehmightypirate Line Up and Wait

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    I'm going to make a guess that it was designed for the reduced strength. Obviously this doesn't mean it has no strength.

    The problem is when people take an existing aluminum part that wasn't welded and put a weld on it. Unless it was designed for the reduced strength at the weld I wouldn't attempt it without understanding the forces involved.
     
  13. airdale

    airdale Pattern Altitude

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    Very true for structural parts, but the OP's air box is not structural. It wasn't made out of dead soft aluminum because dead soft aluminum is, well, soft, and rarely used for constructing objects from sheet. But whatever stiffness is lost in the dead soft (aka locally annealed) sheet next to the weld is probably made up for by the additional stiffness that the thick weld bead provides.

    Twelve years is pretty good, though, because in my experience usually a crack that is welded will just re-develop, usually following along one side or the other of the repair weld. Maybe that stiffener kit was the silver bullet.
     
  14. Alexb2000

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    OK, you can tell I'm obviously no A&P. Sheet should be even better for welding depending on the alloy. I know the engineers cringe, but I weld aluminum all the time and rarely have any issues with cracking despite no post weld treatment. I focus more on the fit-up and minimizing welding induced stresses. For non-structural applications its also pretty easy to anneal most of the alloys just to make sure you don't have cracking issues.

    Point is I'm not surprised you haven't had any issues people make weld repairs all the time that don't fail.
     
  15. tehmightypirate

    tehmightypirate Line Up and Wait

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    Agreed, it's not really a structural part but it was obviously under some stress or it wouldn't have cracked it the first place.

    However the problem that most people don't understand is the area that losses strength extends beyond the weld, so while the welded area will have increased thickness the area around the weld will have reduced strength and the original thickness. The end result is a weaker joint than the original metal.

    I also have had the same experience with cracks unless they are repaired very precisely by drilling the ends and grinding the crack to a nice U-shaped profile for the weld. I would put money in the newer stiffeners being the key here.
     
  16. tehmightypirate

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    It's not a crack issue so much a strength issue. The yield and fracture strengths for aluminum drop in the heat affected zone of the weld. Apart from weld shrinkage and local stresses due to the welding, I bet most competent welders can weld aluminum. The key is to understand that the metal will bend and break easier now at the weld.
     
  17. ChemGuy

    ChemGuy Cleared for Takeoff

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    Sounds like the stiffening kit is doing its job.

    And your welder did a good job. Congrats on saving gas money.
     
  18. Alexb2000

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    I understand. Not knowing the alloy in question let's say 6061-t6 was used. . So we've gone from ~40Kpsi tensile to ~10-11Kpsi in the HAZ. Does it matter is the question I ask myself? On a wing spar, sure, on an air box shouldn't be a problem. Raises an interesting question whether the weld repair or an owner produced part would be a better answer?
     
  19. Subsea

    Subsea Pre-takeoff checklist

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    Objects like this are easily tempered and stress reliever back to -t6 after welding. Can't remember the procedure for 6061, but I think it's heating it to ~400 degrees F, and specified cooling for aging.
     
  20. N801BH

    N801BH Touchdown! Greaser! Gone West

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    Prove it.......:rolleyes:
     
  21. tehmightypirate

    tehmightypirate Line Up and Wait

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    Alright! Someone who speaks my language. I take it you're a fabricator?

    Given that it's lasted 12 years I agree, shouldn't be a problem and clearly wasn't in this case. My point was that unless you know that it will be fine with a 60% strength loss then you should avoid welding if other options are present; or reinforce the part so that the reduced strength isn't an issue, in this case the stiffeners are probably doing that.
     
  22. tehmightypirate

    tehmightypirate Line Up and Wait

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    Oh, I forgot to mention that my understanding is motorcycle and bike frames are typically made out of 7020 aluminum which has the nice quality of recovering most of it's strength after welding. This isn't typical of most other aluminum alloys.

    It's also worth pointing out to the class that there are many aluminum alloys that are unweldable (or at least very difficult to achieve fusion). I believe most airframe aluminum is in this category.

    As best I can tell the box is likely made from 5052 and/or 6061 aluminum alloy. 6061 is almost always heat-treated in my experience and the 5052 could be heat-treated or not. I suspect it is heat-treated otherwise why would most carb heat boxes have riveted construction and not be welded?
     
  23. N801BH

    N801BH Touchdown! Greaser! Gone West

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    I have been a fabricator for 45 years....

    You have probably seen my "toys"....

    I buy most of what you say....

    My beef was Tom's comment about " work hardening"..:goofy::goofy::goofy::goofy:
     
  24. Alexb2000

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    I do a lot of fabrication and machine work: see a problem, fix a problem, no powerpoint required, good for the soul.:)

    The other thing about this scenario is that it is also easily inspected, so we also have the "why not" factor. If it starts to crack, no biggie, pursue plan B.
     
  25. tehmightypirate

    tehmightypirate Line Up and Wait

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    True, the consequences of failure here do seem to be fairly low.
     
  26. Tom-D

    Tom-D Taxi to Parking

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    Do you know what work hardening is ?
     
  27. timwinters

    timwinters Ejection Handle Pulled PoA Supporter

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    This?

    [​IMG]

    :yesnod:

    ;)
     
  28. Tom-D

    Tom-D Taxi to Parking

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  29. Tom-D

    Tom-D Taxi to Parking

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    That would depend upon if you were flying, and the carb heat doesn't work. Remember the 182, / O-470 is a known ice maker. so, a well working carb heat box is pretty important.

    Also, you can repair anything if you can find an A&P stupid enough to sign it off.
     
  30. Alexb2000

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    Tom-

    Are you saying you would never weld aluminum to do a repair?
     
  31. Tom-D

    Tom-D Taxi to Parking

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    Never said that, I just wouldn't weld the 182 air box. I do not have the equipment to do that properly, and I don't know any Field mechanic that does.
     
  32. timwinters

    timwinters Ejection Handle Pulled PoA Supporter

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    I'll remind you that it's been 12 years without any hint of add'l issues and I fully expect it to go a dozen more. Just because you don't have the expertise, skills, equipment or practical knowledge to pull it off doesn't mean it can't be done.

    That's a pretty high horse you're riding these days, Tom. Hope you don't fall as I doubt you'd survive the long drop. :rolleyes:
     
  33. Checkout_my_Six

    Checkout_my_Six Touchdown! Greaser!

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    You may want to re-think changing IAs in the future....cause the next one just might not sign off those welds.:yikes::no:

    Those aluminum sheet metal welds may have worked just fine.....but I bet it's not in compliance with neither the manufacture's recommended maintenance nor the other recognized gold standard....AC 43.13 1B or 2B.
     
    Last edited: Apr 22, 2015
  34. timwinters

    timwinters Ejection Handle Pulled PoA Supporter

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    It's been signed off by at least five different IAs. None have said a word, likely none have even noticed until I point it out to them since it's not something that is readily seen or noticed. I make it a point to look at it every year at annual (I always try to assist) and every time I change my oil...just because.

    I'm not concerned about it being tagged during annual in the least.
     
  35. Tom-D

    Tom-D Taxi to Parking

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    Until you can tell me the carb air box's aluminum alloy, and it's heat treatment process, you can't tell me your weld repair is legal.
    I may ride a high horse, and I may be too cautious, But I do know a legal repair when I see one. So why don't you change your attitude and make comments useful to this thread.
     
  36. airdale

    airdale Pattern Altitude

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    ROFL.

    The OP just wanted to pass along some interesting information/a simple, successful repair and the result is he is getting excoriated by the lunatic fringe.

    Get a life, people. No GA airplane is perfectly legal.
     
  37. Tom-D

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    who takes the hit when these aircraft are discovered by the FSDO? Owner? last IA that signed off the annual?

    Weld repairs on aluminum are very seldom legal, and very easy to spot. When they are legal, they are a major repair and documented as such.
    Simply because the manufacturer does not give them as authorized in the structural repair manual.

    Any other IAs here seen a weld repair on aluminum in service, and have a legal return to service entry?

    Yes, I know about the 43,13 weld repairs given for 4130- steel tube. we are talking aluminum.
     
  38. Checkout_my_Six

    Checkout_my_Six Touchdown! Greaser!

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    Yes Tom.....induction manifolds/tubes crack and are weldable....minor repair. But, that's not a sheet metal part.

    [​IMG]
     
    Last edited: Apr 22, 2015
  39. Clark1961

    Clark1961 Touchdown! Greaser!

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    Welcome to POA where the lunatics parade as experts to shout down the non-conformists! All hail the party line!
     
  40. Tom-D

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    true. I should have stipulated heat treated sheet stock. But remember the welding of engine structural parts is a major repair. 43.A