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  • Weld penetration/testing

    What's a good way to test a weld - for example, I'm doing test welds before trying to put a cage in the Mustang. The material is .130 wall mild steel tube and I have some spare I'm testing with. This is a Hobart 140, running .035 wire at about 320 in/min with C-25 blend at max voltage. The setting is voltage 4 / wirespeed 42ish. I'm getting penetration, but not sure it's enough. What I'm doing is partially welding together a couple chunks of tube, then beating the chunks apart with a 2 lb hammer. I see some bending of the tubing at the weld but also see some of the weld tearing and taking chunks out of the base metal. .030 wire put down a nice bead, but it was just laying on the surface. I stuck some tube to .125 plate by welding 1/3 around the tube, then prying the plate off the tube. Again, I see penetration but the weld seems to tear out of the tube material.

    Hints and comments welcome. The decision I have to get to is "weld or tack". Have a friend with a bigger unit, but the 140 should be able to stick .125 steel with a single pass.

    Using the formula Hobart supplied in the book, for .125 steel the feed rate should be around 200 in/min. Tried that - not even close.
    1967 4 door Falcon 351Cr / 1970 Mustang 351C
    Owner built, owner abused.
    http://raceabilene.com/kelly/hotrod

  • #2
    Is the mild steel tube sufficient strength for a roll cage? Chromoly? Not sure myself.

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    • #3
      Fit up with a gap and bridge tacks. Weld a root pass and stop at the bridge tacks. Grind out the tacks and weld through that area. Go back with a filler/cover pass.
      Two turn tables and a microphone.

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      • #4
        Originally posted by Thomas Harris View Post
        Is the mild steel tube sufficient strength for a roll cage? Chromoly? Not sure myself.
        Yes, for the ET/Speed of this particular car. 1 3/4" OD, .118 mild steel or .083 CM. An 8 point is good down to 6.50 1/8 mile (10 flat 1/4). This car wont see that kind of ET unless we fall in a money pit LOL. If we did, then it goes to a 10 point (halo bar and down bars, maybe with a dash bar.)

        I will play with the gap and bridge tacks. That might be easy on the bench and a good trick with the top bars in the car.

        I'll try to post a pic of the test weld. Thanks for the quick feedback!
        1967 4 door Falcon 351Cr / 1970 Mustang 351C
        Owner built, owner abused.
        http://raceabilene.com/kelly/hotrod

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        • #5
          pics
          Two pieces of tube, beat apart. Stuck well enough that the top tube is bending at the weld.


          Other test pieces flipped and a bead run.

          Last edited by Falcon67; 01-17-2009, 11:26 AM.
          1967 4 door Falcon 351Cr / 1970 Mustang 351C
          Owner built, owner abused.
          http://raceabilene.com/kelly/hotrod

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          • #6
            You could try pre heating with torch to help penetration and cold starts
            Miller 251
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