Mig welder set-up

  1. paulo1974 Member

    Messages:
    210
    Location:
    porto
    I thought that was the other way around, first measure the metal thickness, tem set up the voltage (amps) and then fiddle around with the wire speed.


    Can anyone give me some technical details about mig welding? The more i dove into it the more i´m confused. With mma or tig amperage is one of the key factores on welding but on mig its voltage and wire feed.
    I know that mig transfer modes differ with different gas and voltage . So for example i can´t get globular or spray transfer with co2 .
    I want to have more theoretical details on mig welding than just push some buttons on the welder.
     
  2. Munkul

    Munkul Jack of some trades, Master of none

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    Location:
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    wrong... you said it yourself - "set up the voltage (amps)" - erm, which is it??? Volts, OR amps? :)

    It's a common trap to fall into.
    You up the voltage on a MIG, and you get more energy and a hotter looking weld, right? And if you turn the wirespeed up too far, you get a ropey, cold looking weld, right?
    So more voltage must be better, and wirespeed is a necessary evil to adjust??
    No.

    Well the mechanics are, that MIG/MAG welding uses a constant voltage machine.
    Voltage = arc length. Arc length is what controls spatter (to a point) and the weld bead width. Too little voltage or too much wire speed, and you get a horrible looking weld. BUT, voltage increases arc energy a little and doesn't increase penetration at all. It just wastes the extra heat around the weld, instead of putting it into the puddle.

    In reality, MIG welding is similar to MMA or TIG, in that amps = penetration. It's just controlled in a totally different way.
    As more wire has to melt off, it drops the voltage, and the machine supplies more current to maintain the set voltage - remember, constant voltage machine?
    Wire carries current, and, more wirespeed = more amps.

    Remember that P=IR : Power = voltage x current. Your current can vary from 50 amps to 500 amps... that's a huge change in power input. Whereas voltage will vary from around 13 to 40 volts... not so huge.

    Ignore the transfer modes for now. The wirespeed, current and voltage relationship remains the same for each one.

    Read the starter guides, they are very helpful :)

    Also, this can explain it better than I can:
    https://www.twi-global.com/technica...amperage-control-on-a-mig-welding-powersource
     
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  3. MK1 RS Bruce Member

    Messages:
    42
    Location:
    NE Scotland

    Agree with everything you said but the way you described it previously is confusing. For example if you measure the wire speed and set it to what you want then change the voltage on that particular machine the wire speed will adjust to the new voltage. So in my opinion you need to do it the other way round. Set the voltage based on the thickness then measure and adjust wire speed to suit.
     
  4. Munkul

    Munkul Jack of some trades, Master of none

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    Location:
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    The wirespeed doesn't adjust with voltage... the arc length adjusts.

    Unless it's a synergic machine, wirespeed is totally seperate from voltage.

    You think you're setting the voltage to suit the material, but in reality you're setting it to what you remember worked last time. The wirespeed is critical to achieving good welds... the number of failed MIG welds around is because people use too low a wirespeed, and therefore don't get penetration.

    you can lay some nice looking beads with a low wirespeed and a nice weave, but it will have no penetration at all.

    Or, you can lay the same amount of weld metal at a high wirespeed and faster travel speed to suit, but the high amperage will give you penetration as well.

    In either case (low wirespeed or high wirespeed) you THEN should adjust the voltage to give you a good bead width, good toe wetting, but not too much spatter.

    Again, when you adjust the voltage first, it's only because you know it's what worked last time :)
     
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  5. Munkul

    Munkul Jack of some trades, Master of none

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    Here's another one, just to throw it into the mix: the wirespeed will always be the same recommendation, no matter WHAT the brand and model of welder.

    But some machines have a bigger voltage droop than others, and it will droop more with more current as you get up to the capacity of the machine. So even if, say, a cheap 200 amp machine can deliver say 26 volts at 100 amps, it may not be able to deliver even 20 volts at 200 amps, even on the same voltage tap.
    So maybe 15 volts at 200 amps (for sake of argument, with a further droop on that) produces a terrible looking weld.
    So people turn the wirespeed down to suit the volts available.
    Then carry out some pretty looking MIG welds with no penetration.

    And then sometimes it will fail after a while.

    Contrast that with a high end inverter: If you set a welding voltage of 14 or 30 volts, then that's the voltage it will weld at, whether it's 50 amps or 300 amps.

    Not that I reccomend 14 volts at 300 amps :D My Miller XMT will do it at 250 amps, but it's not pretty.
     
    Last edited: Sep 14, 2020
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  6. MK1 RS Bruce Member

    Messages:
    42
    Location:
    NE Scotland
    My point is that THIS machine, as far as I am aware varies the wire speed at a given set point on the dial depending on the voltage.

    E.G the wire speed at point 5 on the dial is not the same for all the voltage levels it increases as voltage does.
     
  7. Munkul

    Munkul Jack of some trades, Master of none

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    I had a machine like that once.

    It made life simple, but again, only once you understood what setting number did what.

    Ultimately I hated it.
     
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  8. Robert Mullins Member

    Messages:
    109
    Location:
    Salisbury, uk
    I've posted this before, so here goes, I've been welding since 1978; I've probably developed (welding) habits that the welding engineers and technical bodies would rather not see,
    Many, many moons ago, maybe 1979, one of the old time welders who had me dumped upon him said; and this is word for word; "if it 'aint burning through then it ain't too hot"
    What I was taught then, and is how I still set my plant up; is to set the voltage, and adjust the wire speed to the voltage setting, if it's not fusing both edges, or the weld profile is wrong, I turn the volts up/down, and adjust the wire speed to suit; keep on doing so until it's doing what I want, as I've been doing this for 40+years, it's second nature and only takes a few moments, you will soon learn it: Don't be afraid to run it as hot as you need, remember that many more welds have failed testing due lack of penetration as opposed to too much
    The mig welding method can be prone to cold lap, lack of fusion due to the small arc and volume of weld metal it can put down, so run it as hot as you can, keeping the weld beads narrow, do not weave as it is possible to bridge the root,
    Also, it's the arc that does the welding, not the weld pool, so watch where the wire end is, where the arc is, the weld pool will follow
     
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  9. Munkul

    Munkul Jack of some trades, Master of none

    Messages:
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    Location:
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    It sounds like it ;)

    I completely agree.

    I know a lot of people do this, and get great results... but it still doesn't alter the fact that you're getting penetration from having your wirespeed in the right range for the thickness. You've obviously learned the right voltage and right wirespeed through years of experience :)

    This could be a bit misleading...
    The arc does the welding by melting parent and filler material, but in doing this the arc creates the weld pool and moves it along, which is in turn creating the end result you're looking for. So both are important.
    Too long an arc means heat goes everywhere except into the pool, and wastes energy. Too short an arc creates it's own problems, because the wire doesn't burn into the pool properly. That's voltage.

    The arc should be at the front edge of the pool while you travel, to keep it moving and focus the arc energy in melting and and moving the pool. If you're hanging back in the pool (usually because you haven't got enough wirespeed to deposit the required weld size) then this arc energy is wasted in the pool, rather than fusing and penetrating.
    If you have marginal amps for the job, then this is the no.1 cause of failed MIG welds - hanging back in the pool. And people say it's technique at fault.

    All these people saying "manipulate the weld, do little "e"s, or circles, etc" - this often works because it helps to keep the arc at the leading edge of the puddle for the inexperienced. It's by no means perfect though, I agree - you want to be welding stringers rather than weave, for a perfect weld. I like to move-pause-move-pause.

    If you have plenty amps, you'll penetrate regardless of technique, but because amps also = weld deposit, you'll naturally travel faster and stay at that leading edge anyways.

    Taking it a step further, I was reading about using NR233 fluxcore wire... apparently it cuts through metal like butter with an extremely focused arc, and the way you control the burn-though is actually by hanging back in the puddle, and letting that energy disperse a bit more freely... quite cool, I thought :)
     
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  10. Nick DV

    Nick DV "You must unlearn what you have learned."

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    "A long time ago in a galaxy far, far away...."
    I know I'm a mere novice compared to you guys, but I've been ignoring the desire to circle or 'e' my welds and have only been using stringers :thumbup: I've been using the same method as you after seeing Bob Moffat of weld.com do it on YouTube.I may actually be doing something right :dontknow:
     
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  11. Munkul

    Munkul Jack of some trades, Master of none

    Messages:
    3,144
    Location:
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    I don't MIG weld every day, but I do look after the guys that do... and if I asked them what their technique is, they'll shrug their shoulders and say "i dunno, I set it right and then I just weld" :laughing:
     
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  12. Nick DV

    Nick DV "You must unlearn what you have learned."

    Messages:
    891
    Location:
    "A long time ago in a galaxy far, far away...."
    :laughing: Maybe it's just me but the 'move- pause' stringer method seems natural where the 'e' or circles feels awkward :vsad:
     
  13. metalmelt Member

    Messages:
    590
    Location:
    UK
    Hobbyweld 5 is a tri mix gas and has 2% oxygen in it which is excellent for sheet steel.
     
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