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Multiple Pass Welding Question...

Discussion in 'The Tool Shed' started by FinoCJ, Dec 2, 2019.

  1. Dec 2, 2019
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

    Denver, CO
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    Didn't want to bump Doug's question about welders off topic too much, so thought I would start a new post. Given the cost of a bigger 220V welder is sometimes out of the price range for some of us...and the reality that 90% of the already limited welding some of us do is 1/8" or less....multiple passes is the reality for welding thick stuff. As I struggle with multiple passes, any good tips people could pas along?

    From my limited and somewhat (un?)successful experiences: Obviously the voltage goes to max setting, but I have trouble not overfilling the work gap. I am thinking I get better results when I slow the wire feed down quite a bit...and as I feel like I need to move along the work slowly to ensure I get enough heat and penetration, it seems like I end up filling the weld, and I have to grind some of the weld fill out to make a second pass....Am I on the right track?

    I have definitely found that it helps to pre-heat the work a bit with a torch - for the 3/16" sliders I made, I got solid, single pass welds (on the bottom flat/butt joint) even with my small machine rated to 1/8". I wasn't so successful on the top 90 degree joint, and had trouble with trying multiple passes.
     
  2. Dec 2, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    :pics:

    ^ I say that because it’s hard to visualize. What type of weld are you referring to? A V’d butt weld? A lap weld? A T weld?

    All of them have different characteristics, and it’s hard to give one answer without looking at the weld. One look could tell if it’s ok or too cold. If the edges of the weld are flowing nicely into the base metal, the fillit itself isn’t too bulbous, the underside of the plate sees some discoloration... these are signs that there is good heat with proper wire speed.

    Your machine might be doing fine with the thicker stuff, but it’s duty cycle might peter out quickly, so follow its duty cycle recommendations if you can.

    You may feel like the heat is way higher than (not proportionately equal to) the wire speed, but the wire speed will always have more adjustment than the heat. The reason why: the thicker the wire, the slower the wire speed is needed to make the same weld. .045 wire will be depositing a lot more metal than .022 wire at the same feed speed, so the .022 wire might need double the speed to make the same weld. Don’t crank up the wire speed just because you cranked up the heat. Play it by ear. Watch videos on welding, but look away and listen. A proper wire speed has a very distinctive sound. Too fast will start with a tap-tap-tap sound followed by erratic choppy zaps. Too slow you’ll hear an arcing sound, like “waaaa”. Anywhere in between is good. I’m guessing you were pushing it at a faster wire speed, and you were getting a weld that looked a little worm-like? That happens when the filler is entering at too high of a rate, and the heat can’t keep up, creating a cold buildup of filler.
     
  3. Dec 2, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

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    Also, take notes. When you find a heat/wire speed you’re happy with, write it down on a piece of tape and stick it to your welder. I have a bunch of notes stuck under the hood of my machine. At a glance, I know to weld roll cage tubing at “.030 - 3/1/4+” with my model. That’s .030 wire, rough voltage at 3, fine voltage at 1, and wire speed at just a hair past 4.
     
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  4. Dec 2, 2019
    45es

    45es Member Sponsor 2019 Sponsor

    Naches, WA
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    As you have noted, if your machine does not have the ability to provide the necessary amperage to obtain adequate penetration pre-heating will help. Wire size will have an effect or you can look at the type of shield gas you are using. C25 gas (25% argon 75% co2) will give a good clean weld with little spatter. Straight co2 gas can improve penetration because of a hotter weld but does increase spatter requiring more cleanup.
     
  5. Dec 2, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

    Hills of NH
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    This talk makes me glad that I have an old fashioned stick welder. :)

    Not so good on real thin stuff though.
     
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  6. Dec 2, 2019
    Greevesman

    Greevesman Sponsor Sponsor

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    Suggest weldingtipsandtricks.com. He has a lot of good info and videos on his site.
     
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  7. Dec 2, 2019
    47v6

    47v6 junk wrecker! Sponsor

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    Even an old fashioned arc welder will need multiple passes for certain operations or specs. Think lincoln pipe liner on the alaskan pipeline. I am not a very good welder, but a decent grinder for sure!
     
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  8. Dec 2, 2019
    BobH

    BobH Sponsor Sponsor

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    For those of who have never welded (but want to) can someone explain duty cycle and how to know when you have reached it and the importance of it.
     
  9. Dec 2, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

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    A welder might be advertised to be capable of welding at a full 210 amps at 20% duty cycle. This means you can weld at its full potential for 20% of a minute (12 seconds), then you need to let it cool for the remaining 80% of that minute (48 seconds). If you exceed those limits, the world won’t end, but the weld stability and heat will suffer, and you risk damaging the machine.

    It works on a sliding scale, where the lower the voltage you use from the machine, the higher the duty cycle. So if you’re welding thin sheet metal with thin wire on that same machine, you could effectively weld with little to no breaks.
     
  10. Dec 2, 2019
    BobH

    BobH Sponsor Sponsor

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    Thank you sir. That sets the importance of duty cycle.
    Is there any way of knowing when you have reached it other than of watching the time?
     
  11. Dec 2, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

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    Nah, I’ve never used a machine that had its performance drop off a cliff at a certain moment. “Seat of the pants” performance is hard to notice, but I’m sure you could see it on diagnostic equipment. As electric components heat, resistance increases, performance suffers. It’s hard to notice a few volt/amp drop at those numbers, but it is putting added stress on the machine. The newer computer controlled units are more sensitive, so they might suffer in the longevity department more than the older analog beasts.
     
  12. Dec 2, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

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    And now we know why some critical welds fail unexpectedly. :(
     
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  13. Dec 2, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

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    It’s still 99% on the operator...
    I’ve worked with weldors who were 1% duty cycle.
     
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  14. Dec 2, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

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    I totally agree it's based on the operator. :)
     
  15. Dec 2, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member Sponsor

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    I'm not knocking what anyone is doing, I do however totally disagree with using a machine that in reality doesn't have enough amps to correctly do the job.
     
  16. Dec 2, 2019
    tarry99

    tarry99 Member Sponsor

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    Normally Duty cycle is referred to in Minutes.......on a 10 minute scale.
     
  17. Dec 2, 2019
    ITLKSEZ

    ITLKSEZ Volvophilic

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    Agree 99%. :D
     
  18. Dec 2, 2019
    Twin2

    Twin2 wasn't me Sponsor 2019 Sponsor

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    for light shop work . sheetmetal . 1/8 iron . flat or angle . a good 120V will get the job done . still it's a duty cycle thing
    heaver metals 1/4 3/8 1/2 . or any work that requires continuous welds . 220V is the game
    .
     
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  19. Dec 2, 2019
    tarry99

    tarry99 Member Sponsor

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    Generally if you have to go multiple passes on 1/4" ....what makes you think the added weld will add any strength since in most cases it's just sitting on top of the existing weld with little or no penetration? ( more mass= more heat).........yes some pre-heating may help..........perhaps a better design with 3/16" material that is more in line with your equipments capabilities would be a better solution.
     
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  20. Dec 2, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

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    Fer Sure. But cheaper and simpler for a shade tree dubber like me.

    Parts of my 80' bridge I built up almost an inch of lost section with 7018 rods, on 100 year old wrought-iron. It is still standing. So far...

    DSC03803.jpg
     
    Last edited: Dec 2, 2019
    jeepstar, dozerjim, 47v6 and 3 others like this.

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