Can you do this with a mig welder

Discussion in 'Boat Design' started by shakey78, Sep 23, 2009.

  1. shakey78
    Joined: Sep 2009
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    shakey78 Junior Member

    Just wanted to no how much tig welding is done on boats from 18ft to 30ft these days or do most build with mig, Cause ive seen some picture perfect welds and they said it was all Mig welded, I ve tried to get my Transmig 200 setup for aluminium and can not get perfect puddle welds like my tig welds,

    also I when I weld with mig I get soot on one side of the weld but none on the weld (yes all is clean) can you weld with out the soot with mig???
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    Just look at these welds done with a mig spool gun they say!!!
     
  2. lewisboats
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    lewisboats Obsessed Member

    Sure...in the hands of a robot. I think a human's would be just a bit less symmetrical and precise...at least with a wire feed gun. A TIG up close would be a challenge but doable. That upper right hand pic sure looks like TIG to me (and I weld SS all the time with an air-cooled TIG) Yes you can get soot free welds but you need to back-gas and have the correct volume of gas to match the arc heat. I usually get soot or burnt Argon but occasionally I get it right and the welds come out rainbow colored with no soot or blackening. The "burnt sugar" is prevented by back-gassing the area to be welded...usually a small box on the back side of the area filled with the shielding gas.
     
  3. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Agree with Lewisboats; though upper left probably manual, the lower pic might be as well. You can see that the soot has been brushed away in the last pic.

    That look will be achieved with the machine set up for "drip feed" (electronically, or with high inductance in output line), and small, regular "dipping" movements by the welder. To my eyes, the last example is slightly cold. With the material thickness shown, I would have preferred higher voltage and feed, giving a smoother weld with better penetration.

    And, btw, the soot is said to be burned particles of alloying substances (Mg, Si,..), which is the reason to have a slightly higher concentration of these in the MIG wire. Aside from strength considerations, the weld seam and the rest of the surface will have different galvanic potentials, causing galvanic corrosion in sea water.

    The shape of the gas nozzle is also critical; lately we got a delivery of nozzles, that internally had an edge which caused turbulence and mixing with air. It became nearly impossible to get a clean, non-porous weld.
     
    Last edited: Sep 24, 2009

  4. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    In addition to that noted above, the simple rule is:
    TIG = Thin.

    If you ahve lots of thin plate, then most prefer to use TIG, but it can be very labour intensive. Also where difficulties arise in obtaining a good seal TIG can be useful too. Generally any boat that size would be MIG welded.

    You can MIG weld thin plate too, but one needs to be very skilled at ally welding to do this and pass class certs too. One of my mates just got his LR cert on 1.8mm ally, overhead using MIG....but he is a genius anyway, piece of cake for him.

    A picture perfect weld does not always = quality.

    Set up, preparation and following correct procedures is the key. One can never cut corners and expect to get away with it...regardless what the weld "looks like".
     
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