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  • No mulitpass in MIG?

    I have a Lincoln Pro-Core 100 that I have using for several years for flux core welding. The recommended settings tell me I can weld up to 1/4" thick with flux core if I take multiple passes, which I've done many times, but it tells me I shouldn't do this in MIG. Why?
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    Definition: Racecar - a device that turns money into noise.

  • #2
    Probably because of the size of the wire. They might be saying to "use the proper tool for the job at hand". Using 0.030" wire to butt weld two 1/4" panels would probably take all day. In that case, it's time to break out the stick welder.

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    • #3
      You certainly can do multi pass in mig
      but
      a smaller welder might not be able to produce enough thermal energy to heat up a big chunk of base metal so a bigger machine of different process might then be preferred

      heating/cooling/repeat could increase stress in the HAZ, warp the weldment, etc. a machine/process that lets you do it in fewer passes would then be good.

      and what slk001 says about deposition rate…

      btw, a 100 amp machine is really straining to weld 1/4” anyway.

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      • #4
        Originally posted by fjk View Post

        btw, a 100 amp machine is really straining to weld 1/4” anyway.
        Correct. You better also have some good joint prep and some preheat wouldn’t hurt if you were going to do it.

        Sure, you can stick some 1/4” (or thicker) things together and it might be fine for some non critical projects but it does give some false sense. Even more so when “marketing” puts it on the machine that it “can” do it.

        Once you use a big machine and really see just what 1/4” can take in the MIG process you will realize what the small machines really can’t do.

        FWIW OP, I believe that flux core gives a little better penetration over the MIG process. Most likely that is why the chart on that machine is the way it is.

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        • #5
          The plate does not say that you can't use multi pass with MIG. It says that you MUST use multi pass for flux core and steel thickness 10 ga and over.

          Dan
          At the end of the project, there is a profound difference between spare parts and left over parts.

          Location: SF East Bay.

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          • #6
            Only if the fluxcore is rated for muti passes.
            John b. SW Chicago burbs.

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            • #7
              Originally posted by john b View Post
              Only if the fluxcore is rated for muti passes.
              John raises a very good point.

              A lot of the wire with the GS suffix is rated for single pass use only.
              One pass and everything is fine but on subsequent passes the dilution ratio between base and filler metal is wrong as one side of the pass is on the parent metal while the other side is fused with filler metal creating an unsatisfactory blend that can lead to cracks or outright failure in heavily loaded applications.

              I haven't tried the E71T-GS wire myself on multipass welds as I usually use a much larger machine with solid wire for multipass welds, which is an industry accepted procedure given proper joint prep.

              The E71T-GS is a very popular wire, the other one that comes to mind as being popular is the E71T-11, which is suitable for multipass applications.
              Lots of other flux cored products available but bare in mind most are aimed at commercial users and do not come in the smaller package sizes like the 2-10 spools.
              Link below from ESAB outlining AWS standards for the various types of flux cored wire.

              https://www.esabna.com/euweb/fm_handbook/577fm5_2.htm
              Home, down in the valley behind the Red Angus
              Bad Decisions Make Good Stories​

              Location: British Columbia

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              • #8
                Thanks all. That's what I needed to know.
                Definition: Racecar - a device that turns money into noise.

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                • #9
                  Originally posted by fjk View Post
                  You certainly can do multi pass in mig
                  but
                  a smaller welder might not be able to produce enough thermal energy to heat up a big chunk of base metal so a bigger machine of different process might then be preferred

                  heating/cooling/repeat could increase stress in the HAZ, warp the weldment, etc. a machine/process that lets you do it in fewer passes would then be good.

                  and what slk001 says about deposition rate…

                  btw, a 100 amp machine is really straining to weld 1/4” anyway.
                  "Might not"?

                  "CAN'T" is a better description. I once tried to do that with no preheat (had no facility), because the boss said to try it (I was the only guy in the shop who had been trained in welding). Parts were 10 x 10 and 14 x 18"

                  It was a little Lincoln flux core, and just as I started to get a puddle going, it tripped out on duty cycle. Of course, after that, it was already hot, and it would not do anything, even after waiting the 10 minutes. By then the metal had cooled and it was a start from zero again..

                  Preheat "might" have helped, but, I had no torch that could do anything reasonable, so I do not know how much it would have taken.

                  A 100A welder with a 100% duty cycle rating might have done the weld. I don;t know, because I never even got it decently started.

                  I mentioned the issue here, and got told that "you should have done multiple passes". That was an abysmally ignorant suggestion, since the thing could not get ONE pass even started.

                  Basically, it might have worked on SMALL pieces of 1/4", where the welder could have heated the small parts up fast enough that no preheat would have been needed. Other than that, it was a total marketing LIE.

                  You have to put heat into the metal faster than it is conducted away. If you do, you can weld. If you don't, you cannot.
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                  Keep eye on ball.
                  Hashim Khan

                  Everything not impossible is compulsory

                  "There's no pleasing these serpents"......Lewis Carroll

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                  • #10
                    I've found that the cheapest flux core welders simply CAN'T weld heavier stock. 3/16 - 1/4 was the max I could get with my old Harbor Freight blue box Century. Even after I added a massive cooling fan the duty cycle was negligible. That being said a buddy and I used it 3/4 inch at a time to convert a C channel frame boat trailer to a flatbed trailer for hauling a scissor lift. I used that trailer for that purpose for close to ten years and it didn't break. Now I am thinking I would like to convert it back to a boat trailer. LOL. I have better welders now.

                    My Lincoln ProCore was better, but only marginally. By better I mean it had a marginally longer duty cycle.
                    Last edited by Bob La Londe; 05-04-2022, 01:23 PM.
                    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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                    • #11
                      I used to weld HR steel with mig that would later be galvanized. The materials were all 1/8" thick and often to 1/16" wall cold drawn tubing. We made hangers for watering machines that rode on overhead rails. Then a customer called and said they were experiencing broken welds. I went out and got some hangers from the big box of maybe 1000 galvanized parts. I quickly broke half a dozen that had beautiful looking welds but little penetration! All welded with a big machine and 0.035" wire. I tossed the whole box about $3000 worth of parts. I then welded up a bunch with 0.045" wire and couldn't break any after galvanizing. We started welding everything with 0.045 wire and all the breaking stopped. We sometimes sent parts out for welding and I put a big not on every drawing that no parts would be accepted if welded with 0.045" which got lots of complaints but no broken welds. You can't just lay a nice looking bead on top. There has to be enough heat to melt the base metal and mix the wire material with the base.

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                      • #12
                        Originally posted by garyhlucas View Post
                        I .........................................You can't just lay a nice looking bead on top. There has to be enough heat to melt the base metal and mix the wire material with the base.
                        There are a lot of people doing welds that really need to get that basic concept rammed into their understanding of what they are doing!
                        4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        "There's no pleasing these serpents"......Lewis Carroll

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                        • #13
                          X2 what JTiers said -- you need a lot of machine to run flux core generally and the homeowner sized ones ain't it. Commercial sized machines have no problem with it, it is an approved process for very heavy stuff -- my experience is that it goes best with a spray-transfer (very hot and smooth) mode. They build skyscrapers and bridges with flux core nowadays BUT they are using 600-amp machines with .072 diameter wire. And engineers -- actual engineers with degrees design those weld joints and get it approved.

                          And a 110v machine isn't capable of that. They sell these machines because they are at a good price point and don't necessarily need gas. But it is best to be aware of their limitations. I find them useful to do exhaust work on cars, but thats about it.
                          Last edited by nickel-city-fab; 05-13-2022, 05:43 AM.
                          25 miles north of Buffalo NY, USA

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                          • #14
                            Originally posted by garyhlucas View Post
                            I used to weld HR steel with mig that would later be galvanized. The materials were all 1/8" thick and often to 1/16" wall cold drawn tubing. We made hangers for watering machines that rode on overhead rails. Then a customer called and said they were experiencing broken welds. I went out and got some hangers from the big box of maybe 1000 galvanized parts. I quickly broke half a dozen that had beautiful looking welds but little penetration! All welded with a big machine and 0.035" wire. I tossed the whole box about $3000 worth of parts. I then welded up a bunch with 0.045" wire and couldn't break any after galvanizing. We started welding everything with 0.045 wire and all the breaking stopped. We sometimes sent parts out for welding and I put a big not on every drawing that no parts would be accepted if welded with 0.045" which got lots of complaints but no broken welds. You can't just lay a nice looking bead on top. There has to be enough heat to melt the base metal and mix the wire material with the base.
                            One has to wonder what went wrong in the procedure setup when using .035 wire on 1/8" and 1/16" material.
                            True a nice appearance means nothing without acceptable and adequate penetration but .035 wire is likely not the culprit here. I regularly run .035" wire at up to about 180 amps on much heavier material than 1/8" or 1/16" in heavily loaded applications with good penetration and no failures. Those settings with .125 or .062 material would vaporize the work.

                            While .045 wire is certainly capable of welding the material in the gauges mentioned it certainly is not a requirement. There has to be more here than meets the eye. Any idea of what the wire feed speed and voltage settings were when using .035 wire?

                            I do know that the hot dip galvanizing process can also be a contributor to cracks in weldments if all of your ducks aren't in a row. However your parts done with .045 wire did not have issues. More going on here than than wire size alone.
                            Heat input, time, heat affected zone, or a combination of these factors in conjunction with all that goes on during the hot dip galvanizing process.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

                            Location: British Columbia

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                            • #15
                              It's always worth cutting, filing, polishing and etching a sample or test coupons every now and then, just to see what's going on.
                              Location- Rugby, Warwickshire. UK

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