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  • Welding method

    I noticed on several of the "make" small tools that a lot of the makers do a series of interrupted tack welds to butt weld metal together: a tack at each end followed by several more between these to create a more-or-less continuous weld. Most of these are stick but a few use Mig (gasless, flux core wire). This is subsequently ground smooth and the result - as best I can determine in the video - appears continuous. Now, I am not a welder by any means: generously, I am a joiner of metals (appearance leaves something to be desired but I can get good penetration ) & I would not, for example, consider welding a trailer or a crane (prep the parts but hire a pro for the actual welding). These video results look ok (once ground) but could this produce an acceptable result? What kind of penetration? Versus a continuous bead?

  • #2
    One auto manufacturer I did work for used resistance welding of the seam variety, they are essentially the same as spot welders, very high current, low voltage, but have circular copper rotating wheels instead of a single copper electrode, the weld is pulsating as the material is pulled through the upper and lower wheel.
    In this case it was used to weld the flanges of gas tank halves.
    Max..

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    • #3
      If you are a real welder and not a book type. This is done quite often.

      Bob

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      • #4
        I've enjoyed a bit of wine, so please forgive any muddled phrases. There are some interesting factors to making a joint. One of them is the fact that penetration is not as important as the surface area that is melded into one piece. Beveled edges create more surface area than you get with a 90 degree butt joint. You'll see it in the books that lay out the standards for evaluating welds.

        This means that a good weld of large pieces will often be made up of several overlapping layers that only share a shallow melted (wetted ???) area of a beveled edge. In order for a tack weld to be as secure as a beveled edge you need a lot more heat to melt a wider area, basically making a weld equivalent to an impromptu bevel.

        When making a good butt weld, you most often use a beveled edge and an open root. While it looks like a series of tack welds it's really a melted filler that floods the valley of the beveled joint, melting the surface of both parts to make them one piece of metal. The stitching style of welding is to minimizing distortion.

        Professionals often have very powerful welders available which can melt through a 3/4 inch plate steel, so they can get away with butt welds as mentioned above. A 300 amp welder will melt a long, deep grove in a piece of steel.

        The last point that I'll mention is that the joint only needs to be stronger than the pressure that it's supposed to support, including dynamic stresses. A couple of 1/4 inch plates welded together with a series of 1 inch welds will hold a LOT of weight.

        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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        • #5
          The tack welds are almost certainly done to avoid the joint getting distorted and warping from the heating and cooling in welding. You tack the pieces where you want them, and then weld right through them if you like, to minimize warping.

          It does NOT necessarily minimize locked-in stresses.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            Also, some of the projects I've seen have material too thin for a continuous bead. That would just melt a hole in the metal. A bit of cooling time between each arc makes it possible to do.
            Kansas City area

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            • #7
              Originally posted by MaxHeadRoom View Post
              One auto manufacturer I did work for used resistance welding of the seam variety, they are essentially the same as spot welders, very high current, low voltage, but have circular copper rotating wheels instead of a single copper electrode, the weld is pulsating as the material is pulled through the upper and lower wheel.
              In this case it was used to weld the flanges of gas tank halves.
              Max..
              The Swiss company I used to work for made this type of welder, probably the ones you saw. Semi-automatic and fully automatic seam welders for everything from 7oz juice cans up to 55 gallon drums and water heater tanks. Up to 1000 per minute on beverage cans. The drum welders would be hitting around 30-35,000 amps at the roller electrodes on the secondary side of the transformer. My credit card magnetic stripe would last about a week back in those days. Leave a metal tool within three feet of the weld zone and the magnetic field would heat it to where you would get secondary burn if you picked it up and held it too long. Ah, those were the days......

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              • #8
                Depending on what they are welding a stack of tacks may be to control heat. I've repaired wheel barrows and pickup beds by overlapping tacks with MIG. Seems to work better with gasless fluxcore, but that may just be a function of the environment (usually outdoors) when I am working on a project like that.
                *** 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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                • #9
                  Bob,
                  Flux core runs a lot like 6010 -6011. Fill freeze. Set hotter than you would think and travel fast. Use to weld electrical boxes on tin can studs. 3/32 6011 set at about 90 amps down hand fast. The bead was about 1/8th wide with complete penetration. Pause and you had a hole 3/4 diameter. I used this method to weld race car bodies. 3/4 - 1 inch tack every 6 inches. Then go back to beginning 3/4 - 1 inch skip 6 inches. It has been many years think it was about 75 amps ac. You might try 1/8 th rod same setting as it fills quicker. Close Fast Hot

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