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How to tell if a MIG Weld is Good?

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  • How to tell if a MIG Weld is Good?

    How can I accurately tell by looking at a MIG weld if its good? I mean I look at the welds and they look real nice, like a roll of coins, however, I have heard that MIG can look real good but can also not be good even though it looks it. Any and all feedback is appreciated. Thanks.

  • #2
    You about have to see as you are doing it, make sure its melting into the base metal. The arc needs to be ahead of the puddle or it just kind of floats up on top and just tends to lay on the pieces you are trying to weld. Another thing is to match the input parameters of wire speed, voltage and amps to make sure you are making enough heat. I dont know of a good way to tell with welds already made in a small shop besides some destructive testing on samples. Operator skill is crucial with small machines on thick pieces. Its difficult to explain here just what to look for.


    • #3
      Select some test material of the desired thickness. Set your machine for the correct wire speed and amperage. Slow your hand movement until you see burn through, then speed up slightly, you will be close to max penetration. Then practice...practice...practice.

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      • #4
        72BOSS cool name

        Practice is the magic, the more familiar you become with the machine and the settings the better you will be. Not knowing what type of weld joint your working on and thickness, it will be hard to give any definite accurate help.

        Give us a little more,


        • #5

          As Sberry said it is hard to "tell" what to look for in a "good" MIG weld. I don't like the stacked coins in a MIG weld as the potential for surface weld increases and the possible lack of penetration increases. I prefer a clean straight bead where the filler wire is constantly kept at the leading edge of a very fluid puddle as the weld progresses. Keep the puddle hot, wire in the leading edge, and watch for the base material melting and being filled back with the wire electrode. Hopefully the arc will have nice snappy crackle ; and the spatter will be minimal. All this in combination SHOULD lead to the PROBABILITY of a sound weld. The higher the argon content in your shield the less penetration and the hotter the weld. When using a shielding gas with more than 75% argon pay extra attention to the weld toes as a fast travel in the short arc mode can result in undercut.


          • #6
            These are great guys. I really appreciate the feedback.


            • #7
              The point of destructive testing is to, as Sberry said, train you to know while you're welding. It's part of the feedback loop. I couldn't agree more with the statement that if you don't see the puddle melting in with the base metal, you're probably not getting good penetration. It took me learning O/A (started on MIG) to really get that point.

              The backside of the weld will also tell you something about the penetration, but it's only part of the puzzle. If you're getting full penetration, you'll see just a little bit where the base metal was molten under the weld. Discoloration just means that it got hot, which may or may not mean a good weld.


              • #8
                Ok some dumb questions, but I appreciate any insight
                I'm going to go download some materials and read up on some basics.

                Just talking about a practice piece here, so burn through is not a worry, for example some 1/8" scrap steel strips from Home depot, with 135 amp Mig.

                What's a good way to get more penetration?
                Turn the current control all the way up... obviously?
                Slow the wire speed all the way down, or up?
                turn the gas flow up? hopefully 20% C02 is hot enough.
                Need to look up recommended gas flow had it up to 20-25.

                First sign of burn through I guess will have to discern to adjust wire speed or current or both.... need practice here.

                Now what if you had two pieces too close together, or sandwiched, and you want to tac or weld the sides to fuse it as one piece.

                Example two rectangles on top of each other.

                I take it you really have to space them a part, or maybe grind a gap on the inside edge of both pieces?

                Ok starting to make more sense just asking retarded questions.



                • #9
                  The wire speed IS the current adjustment. Its what gives it the heat, or power. The voltage has to be brought up with it to increase the arc intensity to stabilize the arc. Its like a garden hose sort of. When you increase the hose size (more wire speed) the volume goes up but the pressure drops, so you have to turn up the pressure (voltage) This is kind of a lame explanation, maybe someone can help with it?


                  • #10
                    Penetration and fusion often get kind of confused here. Depending on material thickness penetration is from proper joint design allowing the weld to go al the way thru. Fusion is the melting of the base metal. In a T style joint often penetration is irrelevent but fusion is critical. In this steels the penetration comes more naturally, it melts thru the steel anyway but thicker joints need to be designed to allow the weld to get thru. Pipe joints are a good example, they are beveled to allow for penetration to the root. After the first pass it is all about fusion. If you cut pipe square and butt them tightly the weld may fuse but will not penetrate very much. If you leave a gap between the butts it will penetrate, if you bevel it will penetrate further. Still somewhat rudimentary explanation.


                    • #11
                      Say you want to splice a 1/4 flat bar. Often it will jus get butted up with a 1/8 gap, this will allow some of the filler to penetrate, maybe half way thru, just say, then you flip the bar over and grind it back into the weld from the back and weld it again, now you have a fully penetrated weld. A lot of tanks are built this way, welded from one side then backgouged and weld the gouge full.


                      • #12
                        DOH, that explains alot, thanks...!!!
                        I had voltage tapped to the top, and wire speed at 3.5 (on a scale of 10), LOL.
                        Lots of pressure through a tiny garden hose.


                        • #13
                          Here is an example and vaires with material thickness. I have a 175 tapped machine and I run 030 in it. WFS 2 1/2 on V tap B for light sheet, as the thickness increases I want more power so I go to 3 1/2 and tap C and 5 on Tap D for even thicker materials. As you increase the wire (= more current) you need to bring the pressure up to burn it off at the same intensity. These are not exact numbers, but look at the chart on your door to get a feel for the relationship between WFS and V,,, and remember, many of these small machine come setup for fluxcore, make sure you are on DC+ for solid wire withgas.


                          • #14
                            WOW WHAT A DIFFERENCE with the wire speed turned up a bit. That current and wire flow made such a better bead. I need to work on my steady hand.

                            That and my gas nozzle was not quite as tight as it should have been.
                            Just for giggles, I needed some practice, so I welded my name on a flat piece of 1/8 Inch mild steel, haha
                            I needed the practice, now I can watch and manipulate the puddle Soooo much better, I can hold it longer and watch the base metal heat up and get more penetration, it's a fine line though, when you need more penetration, but you don't want to deposit too much metal.
                            Too much fun, I'm far from perfect, but this helped alot.
                            I'm making an egr block-off plate out of two rectangular pieces of steel, I'll post pics after I weld it right, well...... maybe not right, but alteast better.

                            Thanks alot for the insight!!!!


                            • #15
                              Thanks for the help with the wire speed and such. I am still learning to weld so the feedback is awsome to me. One question I have is how do i control the puddle when welding overhead. For example, last evening I was welding a cyclindrical piece of steel like 1" Round bar horizontally to a 1/2 steel plate. When I welded underneath which was overhead, the nozzle kept getting clogged and I kept screwing up because the puddle was just falling on me. Besides some good hot metal in the head I made it out ok... But seriously what is the proper technique for welding circles overhead?