Aluminium MIG welding steping or straight?

Discussion in 'Metal Boat Building' started by Jackphilps, Feb 2, 2009.

  1. Jackphilps
    Joined: Dec 2008
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    Jackphilps Junior Member

    As an Aluminium welder ive allways welded in a wipping or steping style and have passed several lloyds and DNV tests using this technique throughtout my welding life. Since starting a new job i have been told this technique is bad because it effects the strength of the weld. Can any welding engineers or experienced ally welders out there tell me if this is true? and if it is why?

    Thankyou,

    Jack.
     
  2. welder/fitter
    Joined: Jun 2008
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    welder/fitter Senior Member

    Jack,
    Before I jump in too deep here, what series are you welding, 5xxx? Which filler wire? fillets?

    I'm probably going to mention what you've already considered, but it's a start. If the reason given was strength, perhaps, it is because there is often a lack of fusion for the first few inches of beads - that's why "hot start" came along - but any other thoughts of mine are problems involving; thermal expansion & crater cracking , which are usually less of a problem with your method(assuming you build your craters); or prepwork, which is a production/contamination concern. Therefore, should you be welding on 5xxx series alloy, your boss may be of the opinion that a continuous bead will only be subject to a risk of lack of fusion for the first 3inches, or so, whereas each stitch could have a lack of fusion for 50% or more of it's length. I'd suggest that you check with either your foreman/chargehand/supervisor or the "go to" welder that every jobsite has. Miller & Lincoln have "experts" that may be able to give you answers, as well. Well, now I won't get any sleep until I figure this out - time to hit the books. Most of my work is on steel, though I do work aluminum, when made to do so(lol). Usually, I just do it the way my chargehand wants & that way no one gets hurt! Where's kmorin at a time like this? Maybe, send him a pm.
     
    Last edited: Feb 3, 2009
  3. Jackphilps
    Joined: Dec 2008
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    Jackphilps Junior Member

    5083 plate, using 1.2 lincoln filler wire, welding 6, 8mm fillets, 8mm butts etc. im not sure if these factors would have to much effect, maybe more on the lines of the application. Im a fronius man myself and i often use the hot start to begin a weld and the cooler end (on the 4 step mode) to fill craters. I know you get less distortion in a straight run because the heat is spread more evenly than supposed to steping or whiping. I perform straight runs when im welding lighter gauge ally, i like to step on heavier plate 8m> because i feel i have more control generally and of the weld size. I get the impression it might be somthing to do with the stresses passing through the weld, knowing that aluminium cools quickly and when laying beads it may have somthing to do with the lack of fusion or cracking points in between beads?
     
  4. Guest62110524

    Guest62110524 Previous Member

    hello
    I have built many , some under lloyds
    I never had a failure,ever, i give 10 years hull warranty, see my gallery
    weld like this on a seam , reach along to your right til you are comfortable, run fast as you can at right heat to fill the prep for up to a metre back chip with skilsaw(never grinder, leaves impurities) then take another reach and run towrds the backchip
    the weld speed is very fast compared with steel, there is much less distortion I used to backstep in small increments but gradually found the length made no difference
    wont get into a (discussion) here , you can pm if you have queries
     
  5. kmorin
    Joined: Apr 2005
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    Location: Alaska

    kmorin Senior Member

    MIG style bead in Aluminum

    Jackphilps,

    When you whip or pattern a weld in aluminum MIG you could make a pattern so long the original puddle was chilled or frozen before you got back to it. If this happened, and I'm not saying it does with experienced welders, but if it did, a welding engineer might be concerned with the lack of continuous fusion.

    Not addressing the newer synergistic digitally powered welding power supplies now in use- most of us whip to get the 'best of both worlds'. By carrying a higher than normal amperage the aluminum arc will (would in the past) normally stay in spray mode but the finish of that mode is much less attractive and the edge fusion is much less clean than short arc mode.

    But in short arc mode the travel speed is usually slower and often the parent metal base heat is not as hot therefore leading to a 'cold weld' more often that with spray mode.

    Most welders who did MIG beads, with older power supplies, learned that they could create a ))))) shape or backwards C that would allow the center of the new puddle to be spray mode and the back whipped )))), or C, motion to be in short arc. That meant a hot spray center of the puddle and a short arc finish. The reason is the contact tip is moved closer to the parent metal and the CVoltage power supply drops the amperage when you whip the tip back around the )))) each time, just before you travel by pulling the torch with the off hand.

    This type of weld is characterized by a change in sound and the 'row of dimes' look that is common using older power supplies without the pulsed or pulse-on-pulse arc modes now available.

    The bend break test is the final word on any aluminum weld- xray, die penetrant and other tests not withstanding. If it won't bend over and back, or if one weld will bend without breaking more than another - that's the better weld.

    Its possible the people at your new location are not thinking in terms of your skill set, but more the overall industry where there might be people who cold lapped a whipped puddle? Its possible the newer power supplies give better bend break test results without patterning the puddle?

    Either way, if the weld is whipped the results are; better finish and uniformity, better distribution of the weld filler over a wider root face to given a higher tensile adhesion for a given volume or wire or rate of travel, and a means of helping the welder to provide more uniformity by putting a patterned movement onto the basic drag travel along the bead.

    Not sure if these remarks are helpful but that's my take,

    cheers,
    Kevin Morin
     
    1 person likes this.
  6. orcaboatsaust
    Joined: Feb 2009
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    orcaboatsaust Junior Member

    I have heard of wormholes of porisity can be made through the weld if not careful , thus creating failure in the weld.....any thoughts
     
  7. Guest62110524

    Guest62110524 Previous Member

    if you a re a boatbuilder you should be doing nick break tests, and fillet break test,
    prep two plates, weld as if you were on the job, cut into strips , say 50,, across weld, hold the weld to the bandsaw and nick a groove into it, then break open, this will show how much porosity there is and IF the root is fully fused, class societys and weld test xrays dont allow lack root fusion, some porosity is allowed
    with the fillet test, just weld one side and break it, there you will see lack root fusion other tests are bending the weld around a mandril
     
  8. orcaboatsaust
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    orcaboatsaust Junior Member

    yes thats right ,got a cupboard full of test sample pieces....keep for records. I not having any problems, was just a reason why puddle weld might be not accepted .

    cheers
     
  9. kmorin
    Joined: Apr 2005
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    kmorin Senior Member

    Porosity in Alum MIG

    orcaboatsaust,

    Most porosity, that is tiny root face porosity common to even decent quality aluminum MIG, is just hydrogen left from the arc's separation of water into components where the gases didn't all get out before the puddle freezes, this is one reason some welders 'whip'/pattern/step/jog their MIG bead in aluminum; the increased molten time allows more gases out of the root face before the puddle hardens.

    Worm holes or surface porosity are usually the result of poor gas coverage or contamination that hasn't been cleaned adequately, sometimes gas coverage is related to cup to work distance other times flow at the gas bottle. Oils, dampness or wire contamination will all lead to unacceptable porosity, as will dew or dampness retained in mill scale not removed prior to welding.

    Stepping/whipping/patterning the weld will not lead to porosity if done correctly.

    And as whoosh says- bend breaks are the final word.

    cheers,
    Kevin Morin
     

  10. Guest62110524

    Guest62110524 Previous Member

    i have hard time getting to grips with this Ken, take robotic welding, the arc is JUST on the spray, the angle of the wire to work, and the stick out are set, travel is set, voila, perfect!! Myself I set up like this , I neither stirr or try anything but make the leg, throat consistant,
    For those who are starting or have some exp. I usually rest my left small fingure on the work, and slide it for seams and butts
     
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