Which welder should i use to build a airplane frame?

Discussion in 'Workshop Tips and Secrets / Tools' started by aircraftbuilder, Jul 19, 2014.

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  1. Aug 22, 2014 #21

    nickjaxe

    nickjaxe

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    Hi guys...I'm not thinking of doing any welding on a/c but just wondering why mig is not suitable.

    Nick.
     
  2. Aug 22, 2014 #22

    aerometalworker

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    Hi Nick,
    I would not say that it is not suitable for A/C work, I would just say that it is one of the least suitable for prototype work and is more suited for production work where there is process control. The real downsides to the process are the inability to detect cold laps and other mechanical defects after the weld is completed, and the rapid cooling rate. A production facility will determine the process for each weldment by destructive testing of samples for each critical weldment area to determine machine settings, preheats, weld stop and start locations and the requirement for PWHT. Both Tig and O/A have the ability of the weldor to “feel out” the weldment in real-time and adjust on the fly to ensure consistent penetration etc. Tig and to a much lesser degree O/A may still require pre and post heats. So considering that homebuilts are built as one-of’s , it makes it very difficult to assure a quality weld in every joint.
     
  3. Aug 22, 2014 #23

    nickjaxe

    nickjaxe

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    Thank you for that...makes sense to me now...

    Nick.
     
  4. Dec 23, 2014 #24

    Rosco

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    Gday, I will make a comment, the mig is just as controllable as any thing. I have used the mig for 20 years and on a lot of thin ss and it works well. If you can't weld without doing a cold lap then perhaps the mig is not for you.Most people are frieghtened of the mig because it is like being a drummer, many things happening at once.A good mig welder always wants more heat and more speed so the ability to mig weld thin sections takes skill and bravery. It's fun try it. Cheers Ross
     
  5. Aug 11, 2015 #25

    fly_boy_bc

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    Hi all, Great thread. I have a question.

    Is it acceptable to use MIG (actually gasless MIG) to "tack" 4130 tubing together prior to OA or TIG? I'd like to start a Raceair Zipster once my Fisher 101 is in the air. I don't weld (yet) but I have a brand new Chinese 90A gasless MIG that I was planning to use to build my covered trailer/portable hangar. I thought I might use the gasless MIG to tack the tubing together and have a pro do the actual welding. That way I am only paying for the welding time as the pro will not have to do any set-up.

    I know I would have a slag spot to clean off but since it would only be one tack per joint that should not be a deal breaker.

    Is this a reasonable plan?

    Gary B in BC rebuilding FFP101 to look like a 202 so it's my 101.02!
     
  6. Aug 11, 2015 #26

    TFF

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    Get the right wire and cover the tubes up so splatter does not stick everywhere. Recommended, no, but plenty do it. A pro can tell where it was spot welded even if welded over. If its one of those 10% duty cycle 90A wireless, it will not weld a trailer. It will barely tach the tubes; they are designed to spot in thin sheet metal collision repair.
     
  7. Aug 14, 2015 #27

    fly_boy_bc

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    I will have to look at the duty cycle but I'm pretty sure it's way over 10%!

    Why is it "not recommended"? It would just be a small tack. Good idea to cover the tubes instead of just assuming I can clean it off. It will save time, effort and damage to the tubes!


    What wire would be the "right wire"?

    Gary in BC etc etc.
     
  8. Aug 14, 2015 #28

    TFF

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    There is something that happens to the metal from the MIG tack vs the TIG/OA. I have seen some frowns from pro welders. I dont remember why, but not to. That does not stop most people. Actually flux core is kind of no man's land with 4130.
     
  9. Aug 14, 2015 #29

    Head in the clouds

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    The arc strike causes a hardened and hence brittle zone, whereas the lift start or HF start of the TIG are much 'softer' starts and consequently don't leave that affected zone.

    That said - my HF start doesn't always do its 'thing' so if/when I do get a hard arc start I have to pause and heat the zone to remove the crystallisation. I can't really see why it's a problem to use the MIG to tack though. Since the final welding will weld right through the tack and embrittled zone I would think it should remove any resultant crystallisation.

    With TIG or MIG the harshness of the arc start is pretty much dependent on the distance the arc has to strike across, so keeping the wire/electrode very close to the work as you start the arc is the better way to travel ...
     
  10. Aug 18, 2015 #30

    fly_boy_bc

    fly_boy_bc

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    Understood. What wire would you use?
     
  11. Aug 18, 2015 #31

    Head in the clouds

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    For OA or TIG you should use ER70S-2 filler rods and that would be best for the MIG wire too, if you could get it, but I haven't found it to be available. I wanted to buy a reel of MIG wire to use as TIG filler rod because it was a lot cheaper than the rods here, and also available in more thicknesses.

    If the situation is the same in your area then you would need to use ER70S-6 wire. They're both quite compatible with each other and have similar cleaning qualities although the alloys vary slightly. They have different freeze-up rates which makes one more suited to out of position welding, that's the main difference.

    Just a note - NEVER use stainless steel rods or filler wire on chromoly, it creates a very brittle zone. And although you can buy chromoly filler rods and MIG wire it is not recommended for use on chromoly, I think it doesn't have suitable cleaning alloys, or something along those lines.
     
  12. Aug 19, 2015 #32

    fly_boy_bc

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    So is ER70S-6 available as a cored wire for my gassless rig?
     
  13. Aug 19, 2015 #33

    BoKu

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    I've done a lot of flux core wire welding, but only to make jigs and tooling. And based on that experience, there are very few places where I would use it on flight parts. It could be that someone with a better touch than I could make a go of it, but it's far from a point-and-shoot proposition.

    Thanks, Bob K.
     
  14. Aug 19, 2015 #34

    fly_boy_bc

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    We are talking about tacking only.

    So is ER70S-6 available as a cored wire for my gassless rig?

    Thanks.
     
  15. Aug 19, 2015 #35

    TFF

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    I dont think they make many options for flux wire. Your probably are going to use what you got. practice and see what you get.
     
  16. Aug 20, 2015 #36

    Head in the clouds

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    I'd forgotten you were talking gasless/flux cored. I've never seen anything other than E71T wire for flux cored so you're probably stuck with that. It seems to be quite high tensile judging from the way it snaps, and it rusts quickly so it clearly isn't stainless ...

    Before you go too far though, I see your logic in getting a pro to weld up the airframe once you've fitted up the tubing and tacked it all together, but I would caution about thinking it might not be a costly affair anyway. There are many hours of very demanding welding to weld out the complete frame so I would estimate you'll be looking at several thousands of dollars. It might be worth considering buying a cheap ($1000) TIG or a good OA set and learning to weld it yourself. Just thoughts ...
     
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  17. Aug 20, 2015 #37

    Jay Kempf

    Jay Kempf

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    Nope you're right on. MIG works but it is more suited to sheet metal and jig work. MIG without gas is near useless for anything other than snot welding exhaust parts back together or tack welding something you are going to ablate with some other method. MIG can work for production --read-- robotic work on 4130 tubing but we ain't robots. Been playing with it a bunch. Very capable as a first learning tool and for auto applications. TIG will be my next learning platform. Good to have both. Stick is good for many things as well.
     
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  18. Aug 21, 2015 #38

    fly_boy_bc

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    I have seen a few choices in flux core wire. Not a lot of choice but there are a few.

    Actually I agree that I should probably do my own welding...I have been thinking about it and I like to do all of my own work anyway. A used OA rig can be had for just a couple of hundred bucks and if I practice on scraps first and begin the actual work on the easiest of the joints I should be at a reasonable level by the time I am welding up the big clusters....

    I have seen it mentioned several times to get a lightweight torch or even one designed specifically for aircraft use.

    How does one select a good OA welding torch for aircraft work? What makes one better for the task than another?

    GB..BC etc etc.
     
  19. Aug 21, 2015 #39

    BJC

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    There is an old thread on this. I have a Victor, but would very much prefer a Smith. YMMV


    BJC
     

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