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  • weld strength question

    guys,
    in general, is a weld weaker or does a weld make the material weaker if the weld bead is wider than the material thickness, and in particular a MIG welded weave bead ?
    say, if the material being welded is 3/8" thick, and the weaved MIG weld is wider than 3/8" wide, is that weld weaker because of that, or does the wide weld make the material weaker ?
    just curious.
    thanks
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  • #2
    The usual D1.1 3G/4G test weld setup is 3/8" 22.5 bevel, 1/4" gap with a 1/4" backer. I just did the math and came up with .57" edge to edge. Figure in a little overlap and it's a ~3/4" wide weld on 3/8" material. The cap is usually 3 stringer beads wide with stick and 2 stringers wide with mig (more allowable weave with mig). Even with an open root without a backer the weld's still going to be about 1/2" wide by the time you wash over the edges of your bevel. Not positive, but I think the only way to get a 100% pen weld on 3/8" and keep bead width equal or <3/8" wide would be a double groove (beveled on both sides of joint).

    Short answer: I think it's OK to have a bead wider than material thickness as long as you don't have excess reinforcement (bead height)
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    • #3
      thanks for the info MR57.
      the mig weld im referring to is on armor steel with butt joints and T-joints.
      in one breath our engineers are saying a weld bead that is wider than the material thickness makes the weld and material weak, while on a print that came from a defense source for something different shows a 1/4 wide bead when welding 3/16" thick aluminum to 5/8" thick aluminum, tig welded....
      my argument is why is it good for tigged aluminum and not for migged steel ?
      would like to hear more input for others too...
      thanks again.
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      • #4
        Sounds like kind of a catch22.

        I was taught that a good design should fail outside of the weld. And that a weld should be no smaller than the thinnest member. And that weld symbol size is minimum. So a 1/4" weld could be bigger than 1/4". Depending on which spec is called out the maximum can vary.

        But on the other hand you have to follow the engineer's directives. In the end it is their butt on the line. If you do it to print, you did it right.

        Could be armor plate weakens from excessive heat?
        Nothing welded, Nothing gained

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        • #5
          Fillet Welds

          Originally posted by FABMAN View Post
          thanks for the info MR57.
          the mig weld im referring to is on armor steel with butt joints and T-joints.
          in one breath our engineers are saying a weld bead that is wider than the material thickness makes the weld and material weak, while on a print that came from a defense source for something different shows a 1/4 wide bead when welding 3/16" thick aluminum to 5/8" thick aluminum, tig welded....
          my argument is why is it good for tigged aluminum and not for migged steel ?
          would like to hear more input for others too...
          thanks again.
          Full strength fillet welds are based on the formula (w= 3/4 t) Material < 1/4" will have a minimum 1/8" weld. They are measured by the leg size of the largest right triangle that may be inscribed within the cross-sectional area. A fillet weld gauge is used to measure the throat, which is a better index of strength.

          When joining material of different thickness, the weld size is figured by the thinner metal.

          Are your engineers referring to the HAZ of the weld area?
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          • #6
            thanks for your input shovelon....
            its kind of a run around at my shop, with one team of welders putting the other team down. the other guys are putting us down, generally saying that a mig weave weld that is wider than the thickness of the material is gonna fail, significantly.
            but there was no real call out on those set of prints...
            kind of a pissing match between us all.
            i was just curious if "generally" a weave mig bead wider than material thickness is weak or suspect of failure ?
            thanks a bunch
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            • #7
              Originally posted by davedarragh View Post
              Full strength fillet welds are based on the formula (w= 3/4 t) Material < 1/4" will have a minimum 1/8" weld. They are measured by the leg size of the largest right triangle that may be inscribed within the cross-sectional area. A fillet weld gauge is used to measure the throat, which is a better index of strength.

              When joining material of different thickness, the weld size is figured by the thinner metal.

              Are your engineers referring to the HAZ of the weld area?
              im kind of lost on that formula davedarragh...(w=3/4 t).
              and, when you say, "When joining material of different thickness, the weld size is figured by the thinner metal", are you saying to keep the bead size no bigger than the thinner material ? if so, will a wider bead make it or the material weaker ?
              thanks for the helpful input...
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              • #8
                Originally posted by FABMAN View Post
                thanks for your input shovelon....
                its kind of a run around at my shop, with one team of welders putting the other team down. the other guys are putting us down, generally saying that a mig weave weld that is wider than the thickness of the material is gonna fail, significantly.
                but there was no real call out on those set of prints...
                kind of a pissing match between us all.
                i was just curious if "generally" a weave mig bead wider than material thickness is weak or suspect of failure ?
                thanks a bunch
                I cannot understand why they would single out a weave weld. Weaves are great for spreading stresses away from the weld joint. Personally I would rather see the part fail rather than my weld. You aint gonna stay in biz long if you welds keep a breakin'. Just don't over do it.
                Nothing welded, Nothing gained

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                • #9
                  Originally posted by davedarragh View Post
                  Full strength fillet welds are based on the formula (w= 3/4 t) Material < 1/4" will have a minimum 1/8" weld. They are measured by the leg size of the largest right triangle that may be inscribed within the cross-sectional area. A fillet weld gauge is used to measure the throat, which is a better index of strength.

                  When joining material of different thickness, the weld size is figured by the thinner metal.

                  Are your engineers referring to the HAZ of the weld area?
                  formula (w= 3/4 t)

                  Do you mean that weld can be 3/4 that of the thickness? For example the weld for 1" plate can be 3/4"?
                  Nothing welded, Nothing gained

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                  • #10
                    Yes, If your thinest plate is 1" , the your weld should be 3/4" .

                    .......... Norm
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                    • #11
                      Originally posted by nfinch86 View Post
                      Yes, If your thinest plate is 1" , the your weld should be 3/4" .

                      .......... Norm
                      thanks... if the thinnest plate is 1", will a 1" or wider bead weaken the material ?
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                      • #12
                        Weld size

                        I was taught that a fillet weld should be large enough such that even if there is zero penetration, the diagonal size of the weld is the same size as the material thickness.

                        If I try to apply that to 1/4 inch thick material, the weld fillet would be 3/8" up the side of the material, dimension "a". The attached drawing shows what I mean. The "E" dimension should be at least the thickness of the thinner material.

                        Richard
                        Click image for larger version

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                        • #13
                          Originally posted by nfinch86 View Post
                          Yes, If your thinest plate is 1" , the your weld should be 3/4" .

                          .......... Norm
                          I repsectively disagree with this Norm. If the thinnest plate is 1" the weld should be 1". It's not all about the width of the bead. The throat is a much more important aspect. Break out the fillet gauges when in doubt.
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                          • #14
                            lots of great info guys, thanks a bunch.

                            but for arguments sake, say material thickness is 3/8", would a 3/4" wide bead weaken either the bead or the material and cause failure due to the wide bead ?
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                            • #15
                              but for arguments sake, say material thickness is 3/8", would a 3/4" wide bead weaken either the bead or the material and cause failure due to the wide bead ?
                              For arguments sake and as a generalization no it wont weaken it but is generally a waste to use more weld than is needed. You could certainly find argument with this argument in specialized cases, highly engineered scenarios, etc.
                              Generally if filling a grove you are putting in as good or better material than the base but wide filler ground flush would certainly for all practical purpose be as good or better than the base.

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