sheet metal MIG
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Thread: sheet metal MIG

  1. #1
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    sheet metal MIG

    If I'm not worrying about warping, is it reasonable to run a bead on 20ga, maybe a butt weld, without burning through after a couple inches? Running C25 and .025 wire, trying to figure out if it's my technique/settings or just not really possible.
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    Re: sheet metal MIG

    Do any of the machines in your signatures have continuous voltage control or are they all tapped machines? If they are tapped that may be part of your problem. the heat will also make the seams want to pull apart. Are you tack welding first?
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  3. #3
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    Re: sheet metal MIG

    Yes, one of them has continuous voltage control (the Craftsman). Even with it, I end up burning through if I try to do a decent length weld without stitching it. I can TIG a long stretch without burning through, but that's a different story than MIG.

    Yes, I'm tacking first. However, even if I'm just trying to lay a bead across a continuous sheet, I'll end up burning a hole at some point.

    If it isn't reasonable to do a continuous weld on 20ga, I'll stop trying. If it is reasonable, I'll keep practicing.
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    Re: sheet metal MIG

    Fit-up is important. Should be no gap between pieces for metal that thin. Can you clamp the pieces to your table or to a thick strip of metal to act as a heat sink?

    Also, try a "whipping" (forward and back) motion with the gun, or make a series of short beads, almost large tacks, with a short cooling period in between. Should be doable with practice.

    Edit: what you call stitching is pretty much what I described. May be necessary on thin metal, just make sure your starts are not too cold to fuse with the previous weld.

    John
    Last edited by Silicon-based; 11-05-2012 at 08:59 PM. Reason: New info
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  5. #5
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    Re: sheet metal MIG

    Most of how I learned to weld was in a community college course, on fairly thick material. Most of it was stick, at that. We were never MIG welding on anything that we had to worry about burning through on. For the purposes we were taking it, it was a great class - and the instructor was kind enough to let me show up to other sections for practice - but we did very little on thin stuff. He was kind enough to let me practice on whatever I wanted to, but the MIGs were all set up with .035 or bigger - fairly different from .023-.025 wire.
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    Re: sheet metal MIG

    Can you do a lap weld or do you have to do an edge weld. A back up copper heat sink might help but pretty expensive. Stich welding might be better where you move along the weld starting and stopping,basically as series of tacks.

  7. #7
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    Re: sheet metal MIG

    I'd like to learn how to do everything I can. Most of the time I'm sure I could get away with a lap weld but it's nice to be able to do a butt weld when I need to.

    Running straight CO2 it's damn cheap to weld, on C25 it's a bit more but not too bad.

    Mostly I just don't want to practice something if it isn't really possible.
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  8. #8
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    Its possible but u probably need to speed up as the metal heats up. I would check with your past instructor and see if u can pring your machine in and get a bit of coaching... the machine itself will make more of a difference on the thin stuff too. 2 different brand migs can feel like 2 different processes running the same settings.
    Just thought of 1 thing, you are pushing and not dragging the torch right?
    Last edited by soutthpaw; 11-05-2012 at 10:11 PM.
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  9. #9
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    Re: sheet metal MIG

    I was mostly taught pulling but I tried pushing and was still having issues with burn through.
    Lincoln 175HD

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    How long of a bead are you trying to run on the 20 ga. without burning through?

    -Pat

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    Re: sheet metal MIG

    Currently, I can get something like 1-1.5" before I burn through. Would be nice to be able to run double that, but if it isn't possible anyway I won't keep trying.
    Lincoln 175HD

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    Re: sheet metal MIG

    Quote Originally Posted by slotard View Post
    Currently, I can get something like 1-1.5" before I burn through. Would be nice to be able to run double that, but if it isn't possible anyway I won't keep trying.
    3" is really pushing it for butt joint on 20 ga.

    (I don't understand how you can state that you're not concerned about distortion.)

    --As others have mentioned, you really need to consider changing joint design
    via lapping, backing strips, etc.

    Pushing the MIG bead imparts less heat than pulling.

    Reversing the MIG polarity-from 'normal' will impart less heat.
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    Re: sheet metal MIG

    Quote Originally Posted by dave powelson View Post
    Reversing the MIG polarity-from 'normal' will impart less heat.
    You mean setting the wiring as if he was going to use Flux Core Wire instead of solid wire?

    I have heard that changing polarity when stick welding does have this effect, but never heard about doing it when wire welding!

    Are you sure this is going to work? Legit question, no kidding.

    Mikel

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    Re: sheet metal MIG

    Normally gas shielded is run DCEP, self shielded DCEN. I was under the impression that EN puts more heat into the base metal than EP.

    In fact, when I picked up the MIG I'm playing around with on Sunday, it was set up all wrong: the roller was wrong, the tip was wrong, and the polarity was wrong. I tried welding with it before checking those, and (on the 20ga sheet metal I was using) I was getting cold looking welds and burn-through at the same time - so I don't think changing the polarity would help.
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    Re: sheet metal MIG

    Quote Originally Posted by soutthpaw View Post
    Do any of the machines in your signatures have continuous voltage control or are they all tapped machines? If they are tapped that may be part of your problem. the heat will also make the seams want to pull apart. Are you tack welding first?
    I don't understand why you think the unit having a variable voltage dial or tapped selection would make a difference. Set up with an.023 wire and C25, my Migmaster 250 and Ironman 230 both dial down to a gentle arc that allows you to run a couple plus inch long weld beads on a tight fitting butt joint constructed out of 20 ga.

    Most tapped and variable units are able to be dial down to around 25 - 30 amp on the low end. Keeping this in mind, the more important factor in how successful a unit is going to be at performing the task being discussed is the type of low end arc characteristics the unit produces. Due to the design of the choke and also slope, some unit produce a softer gentler low end than others.
    Last edited by Dan; 11-06-2012 at 03:00 PM.
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    Re: sheet metal MIG

    I gotta ask are you using any type of weave? Trying to run a stringer? Nobody else has really asked much about technique.

  17. #17
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    Re: sheet metal MIG

    practice is generally a good thing but throwing out a major, real-world variable like warpage means that what you are doing now is wasting time, wire and gas.

    Practice means that ALL the real world variables are IN PLAY and you weld and keep welding for months and years until the result catches up with your expectations.

    I think what you are doing now is wasting time.
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  18. #18
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    Re: sheet metal MIG

    Quote Originally Posted by slotard View Post
    If I'm not worrying about warping, is it reasonable to run a bead on 20ga, maybe a butt weld, without burning through after a couple inches? Running C25 and .025 wire, trying to figure out if it's my technique/settings or just not really possible.
    Not possible.



    This is the problem with Mig welding sheet metal- you can't control the heat like you can with a Tig machine.

    As you weld you are heating up the metal and as you go along it takes less heat to make the weld since you are basically pre-heating the metal before you get to the next spot.


    If you want to drop 5 grand you can look for a machine with Pulse capabilities

    and as mentioned you do want to be concerned with distortion because 20g will want to move so much it will drive you nuts. All metal moves anyway and controlling the amount it moves is part of the process.

    take a strip of 1/8" thick 2" wide by 4" long- weld a bead across it, watch it banana.
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  19. #19
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    Re: sheet metal MIG

    Quote Originally Posted by Jimmy_pop View Post
    practice is generally a good thing but throwing out a major, real-world variable like warpage means that what you are doing now is wasting time, wire and gas.

    Practice means that ALL the real world variables are IN PLAY and you weld and keep welding for months and years until the result catches up with your expectations.

    I think what you are doing now is wasting time.
    I don't think he was wasting time- I think he was looking for an answer as to whether or not it is possible to run a long bead on 20g. If it is possible what is he doing wrong?

    But it is not possible with the machine he has, so now he knows that it is not technique.
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  20. #20
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    Quote Originally Posted by Dan View Post
    I don't understand why you think the unit having a variable voltage dial or tapped selection would make a difference. Set up with an.023 wire and C25, my Migmaster 250 and Ironman 230 both dial down to a gentle arc that allows you to run a couple plus inch long weld beads on a tight fitting butt joint constructed out of 20 ga.

    Most tapped and variable units are able to be dial down to around 25 - 30 amp on the low end. Keeping this in mind, the more important factor in how successful a unit is going to be at performing the task being discussed is the type of low end arc characteristics the unit produces. Due to the design of the choke and also slope, some unit produce a softer gentler low end than others.
    I was asking about the machines in his signature. Not a MigMaster 250 of which I have owned one. which does an awesome job on sheet metal. But you have 24 overlapping voltage settings and the butter soft arc of an ESAB. Hence why I hade said 2 different machines with the same settings can weld totally different. Also we r talking voltage not amperage. Amperage is dependant on wire diameter and speed.
    Also the minimum voltage of each machine is different too. Good point about the slopes. Look at a transformer and inverter machine u will often find drastic differences in slop/amp/voltage curves
    Last edited by soutthpaw; 11-06-2012 at 04:06 PM.
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  21. #21
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    Re: sheet metal MIG

    Quote Originally Posted by Mikel_24 View Post
    You mean setting the wiring as if he was going to use Flux Core Wire instead of solid wire?

    I have heard that changing polarity when stick welding does have this effect, but never heard about doing it when wire welding!

    Are you sure this is going to work? Legit question, no kidding.

    Mikel
    Reverse the polarity and try it yourself. There is nothing
    anybody can say, show or do--that replaces 'the doing'.
    While you're futzing with the polarity, setup to run vertical
    down or a down at some pretty good angle.

    This is only for thin gauge and will help some. I guess the new age folks
    are scrambling around for a Magic Bullet--and it ain't to be had.
    There's lots of little things that can help or hurt MIG setup
    and a whole bunch of operator technique comes into play.

    The claim that 'distortion is not an issue'--really begs the question
    of why bother to worry about the OP's welds in any case.

    This is not a cure-all for dealing with poor, poor joint design--as apparently
    is the case--combined with the OP's lack of experience.

    Big item in throttling DOwn MIG welder (which some of our resident 'experts'
    fail to comprehend--as seen in this thread)......The bigger the unit,
    the higher the bottom end--min. Amps it puts out, even when cranked
    to ZERO. 3 phase machines about 40, 220 machines about 20, 120 machines
    maybe 10 amps----that has everything to do with welding thin.
    ....and the rheostats help one crank it down further, than the stepped can do, southpaw.
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  22. #22
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    Re: sheet metal MIG

    If the comment disregarding distortion was to specify focus on the burn through, ok. But as other posters stated, all parameters affect the end result quality.

    I asked the same during the short welding portion of the basic auto body VOTEC class I took: one of the widely accepted practices is usually making short welds or stitches on thin sheet.

    We did a rust-out patch on a fender; the patch was a lap fit up and we just skipped around the clock face tacking. I did the same for the 1" .0625 stainless tube for the handle on my mig cart, because I'm not so good at it yet.

    Its just the way it is, so if you get good 1" or so welds, don't try to re-invent the wheel.
    Last edited by jtcnj; 11-10-2012 at 11:56 AM.
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  23. #23
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    Re: sheet metal MIG

    I think the way I would approach this is mark the seam at every 1 inch. Weld an inch then move to another area. Since you can't get longer than 3 inches, just weld an inch and backstep until done.

    If it is a low stress joint, then ESAB Easygrind wire is a godsend. Burns soft and clean on C25 gas.
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