MIG vs TIG re: Kitfox use MIG?

Discussion in 'Tube and Fabric' started by Zoomzoooie, Mar 30, 2011.

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  1. Mar 30, 2011 #1

    Zoomzoooie

    Zoomzoooie

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    I dont' know, this has probably been answered somewhere, but I haven't found it.

    I am going to build a modified Raven (Kitfox clone) from plans.

    So the census seems to be TIG or gas and not to use MIG. So why would Kitfox, who have so many successful flying aircraft out there use MIG and minimal normalizing?

    I have noticed that Kitfox seem to be using MIG welding. In a few video clips you can see what appears to be MIG welding. I also came across something which I can't find now, stating they use MIG and normalized only the critical areas. Pictures I've seen showing close ups of the joints under the paint appear to have inconsitant beads like MIG might have.
    Has anyone been to the factory and seen the welding process who can confirm this and tell me the process they use?

    I am considering purchasing a TIG welder, but if the MIG will do the job, the expense saved of buying a TIG could go into the project. I have a MIG and considering Kitfox seem to use MIG couldn't I use MIG and take the airframe to a fabrication shop to have the joints normalized later? How much would a shop charge to normalize the frame. Would the cost off set be worth it or should I just go ahead with getting the TIG?
     
  2. Mar 30, 2011 #2

    JIC

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    I live in Idaho and only a few miles from where avid and kitfox had there factories when they where going strong.
    I have visited both places and the both of them were using mig to weld there fuselages together. The may reason they
    did this was because it could be done at a faster pace then tig or oxyacetly. I don't know whether they normalized any of the welds or not. I do know that Avid would weld half of a cluster then go to the next; then after the first cluster cooled the would
    go back and finish the weld. They claim this was to prevent blow out cause by heat.
    I perfer oxyaccy myself, easier to get into the places you want to weld and better control of the weld puddle and penetration.
    If you are really really good with a mig, then go for it.
    JIC
     
  3. Mar 31, 2011 #3

    TFF

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    You ask the loaded question. Can MIG be used? Yes. Will it be as good? Maybe. The problem with MIG is you cant control the puddle. Point and shoot; you have a weld. With aviation welds you are supposed to have 100% penetration. Very hard to be that consistent with MIG, because you cant stop adding metal and just add heat like you can Oxi or TIG. You will have to do tests to see if you can do it just as good. Sticking the pieces together is not good enough.
     
  4. Mar 31, 2011 #4

    57Marty

    57Marty

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    It's all about production and speed. Someone who is doing it every day, same welds, fit up in a jig, everything just right can get away with MIG and they have the high end welding rigs also. For the rest of us, Gas is more forgiving but slow (my preference) and low investment. TIG gives you versatility but is still high investment and like anything; practice. Everything I have read says for the home builder to stay away from MIG.
    57Marty
     
  5. Mar 31, 2011 #5

    Lucrum

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  6. Apr 1, 2011 #6

    Zoomzoooie

    Zoomzoooie

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    Seems there are many who say you have to normalize the joints when you use MIG on an airframe. That doesn't seem to be much of a concern for Kitfox. I did find that info regarding the welds they do. It's in the Kitfox II manual.
    I can see the point of speed for production so it makes sense they use MIG, and like you say if a guy knows what he's doing the welds will be perfecty fine. I think the main concern is the brittle metal around the weld. Even though there have not been too many reports of tubing failure on Kitfox aircraft and those I know of are at the tube the landing gear bungee wraps around and they change the tubing size to a thicker wall to fix that, but brittle metal around the welds will always be looming as well as the weld penetration issues. All in all MIG seems to be working great for Kitfox, but I think I want a little more piece of mind since I don't weld for a living. I plan to be doing bush flying and rough field landings might take it's toll on the tubing and structural failure is not on my list of things to do.

    I'm really leaning towards getting a TIG and one brand I've been looking at, which is affordable and was recommended on a TIG welding tutorial is Everlast. They have a 250 amp that is very versatile that is just under $1700CAD and has a 3 year warranty.
     
  7. Apr 1, 2011 #7

    Dan Thomas

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    The old Champs were oxyacetylene welded. The newer American Champion airplanes are MIGged. ANd those newer airplanes are a lot heavier. I think, to make MIG work OK in the factory, they use heavier tubing so they can get penetration without blowout. If I was to build a tube airplane, I'd buy the TIG and learn to use it and build a lighter design.

    Dan
     
  8. Apr 1, 2011 #8

    TFF

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    The advantage with the OxAc is that you can weld and normalize with the same tool; where the others you need both welders. Normalizing MIG is more of insurance. THe weld heat is more concentrated which is good and bad. Good because it does not effect the next structure but bad because in complicated welds like a cluster you have different stresses created, as the whole thing did not get heated together; one tube pulling this way while the other is trying to twist, that sort of thing. Normalizing just gives everything a chance to start out together stress wise. I know it helps because I had something break that was not normalized, and after I re fixed it and normalized it, just fine.
     
  9. Apr 1, 2011 #9

    BBerson

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    I have gas, MIG and TIG. The MIG is what I use.
    MIG is controllable with trigger pulsing. I can mig weld .028" wall tube.
    Must be a quality welding machine. I use a Miller 135. It doesn't need to be big for thin wall.
     
  10. Apr 1, 2011 #10

    Zoomzoooie

    Zoomzoooie

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    I dont' know the wall thickness and all tubing sizes the later Kitfoxes use, but I think most is still .035 and .049 along with upsizing in critical areas comparing the sizes from the Raven plans and studing any Kitfox IV airframe photos I can get, so I don't believe they would use thicker wall just for MIG to work better. I think MIG would make a heavier frame only because of the added material you get from a MIG weld compared to gas and TIG.


    From what I have read in posts and other information, normalizing is not neccessary with TIG although having a gas rig in the shop would be handy. I have to replace mine, it's too old and the hoses are all cracking, so I haven't used it in a very long time. I would have learn TIG and relearn gas either way.


    It's just a bit suprizing that some manufactures use MIG considering the cons. It seems MIG is a dirty word when it comes to opinions when used on airframes, but appears to be accepted by some manufacturers and is proven since you don't hear of a lot tubing failure.

    I'm tempted to try my MIG on thin wall just to see how I do, but I will still get the TIG.
     
  11. Apr 2, 2011 #11

    Marc Bourget

    Marc Bourget

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    I also have OA gas, TIG (GTAW) and MIG welders. After reading "Welding Tubular Steel Fuselages", Elzia's "Aircraft Welding", and, most significant, spending some time with the "Tinman" on an Advanced Class Welding Day, I'm going to stick with gas welding. Learned a long time ago in John Thorp's Burbank shop that there's a false economy in "speed" (of building)

    The thing that makes me "gulp" with this decision was the opportunity to see the stripped fuselage of a Beechcraft Staggerwing at Hawthorne Airport. True manufacturing "art." The spirit is willing but the "flesh" may be weak !

    There's a reason Kent White has sampled all sorts of welding torches.

    Onward and upward.

    Marc Bourget
     
  12. Jan 29, 2012 #12

    millerdvr

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    I still do not understand all the negativity towards MIG welding on aircraft frames ! Most tubing is .035 or .049 of an inch, which is just over 1/32 of an inch! Mig will get you 110% penetration all day long on thin wall tubing, it is quicker, cleaner, easier, and is just as strong as any other process. As long as you are using an E-70 wire then you are good to go. You could even go up to an E-80 wire if you choose to.
    I am a metal fabricator by trade and I use MIG for as much as I can, It has gotten such a bad name over the years but in the right hands it will produce better results, better penetration, cleaner deposits and superior user appeal than any other process in all positions.
    Just remember that we are welding extremely thin wall tubing, I see so often that when builders are welding they have such a tendency to lay down waaaaaay to much metal, they are putting 3/8" fillet welds on 1/32" tubing. That is way to much metal. It doesn't take much to put a perfectly good weld on this thin wall tubing, more is not better and remember that the weld metal is stronger than the base metal so you shouldn't be worrying about your weld strength.
    Most airframes have a great deal of redundancy engineered into the frame, in all actuality they are overbuilt by design, so we don't need to overbuild out weld joints.
     
  13. Jan 29, 2012 #13

    GrizzlyV6

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    Hey ZZ,
    Just some fyi, I use mig to tack my tubing together as it's much easier to do when working by myself as I usually do. Then go back and tig the cluster or joint.


    Jim
     
  14. Jan 29, 2012 #14

    Geoffrey Thorpe

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    If you know what you are doing, MIG is fine. I assume that the negativity comes from the assumption that if you are a first time learn-yourself-to-weld guy, it's easy to make welds that look pretty from the outside without realizing that, well, appearance is not everything. Eh?
     
  15. Jan 29, 2012 #15

    TFF

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    When MIG was first used on airplane frames, the frames broke. Most of the problems was not adapting what was needed to MIG. Joints snapped just off the welds in accidents; I have seen a 60 year old Cub balled up with no weld breaks, just tubing breaks. Not a lot of info on using MIG with airplanes at the homebuilt level and with 100 years of airplane O/A and 50 years of TIG make it easy to stick with the known. I think new Citabrias are MIG but dont know what they do after the welding is done.
     
  16. Jan 29, 2012 #16

    Zoomzoooie

    Zoomzoooie

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    My understanding is MIG has no penitration at bead start up and that it brittles the metal around the weld,making normalizing neccesary . I could see this on thick metal, but we are dealing with thin metal so maybe penatration from bead start up is enough. and the beads are not pretty like TIG or Gas. Normalizing is something we can't do at home, so this is still a concern. I think this is what gives MIG a bad name for aircraft use. I dont' recall anyone in the form saying they use MIG exclusive on building an airframe either. I would consider practicing on the MIG to get my skills up to par if normalizing was not an issue.

    I still have not got a TIG yet and have actually been concidering the DHC 2000 gas welder for a few reasons. I don't have 220v in the garage for a TIG and this little gas welder seems to be versatile and can make 1/16" cuts, is easily portable and uses less gas then conventional gas welders. The only draw back is the price.

    I have several months for summer temperatures to make up my mind before I can start welding since there is no heat in the garage either.

    ZZ
     
  17. Jan 29, 2012 #17

    BBerson

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    Agreed, with an experienced thin sheet MIG welder, it works fine.
    I use my MIG and love it.
    The secret is setting the controls a bit hot, then pulse the trigger for heat control as needed. Takes practice, as all type of welding require practice.

    edit:
    Must use a quality machine (I have a small Miller 135)
     
  18. Jan 30, 2012 #18

    millerdvr

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    You couldn't be farther from the truth. Just about all welders(brand name, not harbor freight quality) have a built in "hot start" that boost the voltage/amperage upon the strike of the arc which deals with just that.
    As far as "normalizing", that all depends on who you want to listen to and believe, you won't find race car builders "normalizing" their roll cages and they hold up just fine. I personally have never felt the need to reheat any weld joint unless the engineering called for it in the process details.
    If you think about it, even with OA and TIG welding of a tube fuselage there is a point on the welded joint where the heat effected zone is heat effected the same as it would if you MIG welded it, so why does everyone feel the need to Normalize only when MIG welding?
    Just something to ponder.
     
  19. Jan 30, 2012 #19

    millerdvr

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    Very true about the machine. I have a Miller 350 XMT which does fantastic with any and all welding process', I have used many machines in my time and the new inverter types are phenomenal, compact size with an astounding range of capability. Run it on 3 phase and for the money they are very hard to beat.
     
  20. Jan 30, 2012 #20

    millerdvr

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    That very well may be but the advances in welding technology, filler metals, gasses, and know how make it all the more possible these days. We don't know what they were using for current, filler metal, set up etc. to bastardize the whole process is just absurd.
    Has anyone looked through the Lincoln filler metals selection these days? It is amazing what they have to offer not only for MIG but FCAW, SMAW and TIG filler. I have a 4' x 5' x 3' rod oven at work with at least 13 different spools and boxes of different rod and wire for the select metals I work with. It is getting harder to keep up with it all!
     

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