1/8in TIG weld concave convex?
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  1. #1

    1/8in TIG weld concave convex?

    So Im going to college to get my degree in welding. Im taking an advanced tig class and the teacher asked for 1/8in tig weld on 1/8in material. So most my steel tig welding ive done before and for other teachers say a semi concave to flat weld is perfect as long as there is no under cut ect. My advanced tig welding teacher now want us to run a bead that is some convex to it. In order to do this you must run cooler and use alot more filler rod. How does everyone else fill a correct 1/8in mild steel weld should look? Many of my other welds were alot more consitant but barley had a concave to the weld. My teacher was finally happy when I welded it like this with some convex to the weld. How do you feel about concave vs convex mild steel tig welds?

    Link to my convex 1/8in tig weld on 1/8in steel.

    http://fabricationzone.com/forum/index.php?topic=4.0

  2. #2
    Join Date
    Dec 2008
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    N.Ridgeville, oHIo
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    Re: 1/8in TIG weld concave convex?

    If you are being graded on your welds, what the instructor wants should be your concern, I would think.


    Rex

  3. #3
    Join Date
    Sep 2009
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    21

    Re: 1/8in TIG weld concave convex?

    A weld should always be flat to slightly convex as that is the reinforcement, if it is concave the effective leg length of the weld is smaller.

  4. #4
    Join Date
    Jan 2009
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    Ohio
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    Re: 1/8in TIG weld concave convex?

    too much concavity or too much concavity are both bad. they have limits on how convex or concave they can be when it comes to acceptance criteria. this is whi i always aim for flush. although slightly conves or convave isnt the end of the world. convexity "too much of it" is a waste of weld metal if you ask me.

  5. #5
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    Jan 2009
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    Re: 1/8in TIG weld concave convex?

    wow i can't spell tonight! why convex concave.....what the bloody hell?

  6. #6

    Re: 1/8in TIG weld concave convex?

    Well I ask this because one teacher tells you to do it one way and the next tells you to do it the other way. I welded it the way he asked for the grade but I want to know for my own best way. Ive always felt flat is about perfect with most steel tig welds.

  7. #7
    Join Date
    Jan 2007
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    UK
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    670

    Re: 1/8in TIG weld concave convex?

    Concave welds place the surface of the weld metal in tension as it cools- more prone to cracks, particually at the toes. A convex weld isn't in tension but the bead has a sharp(er) transition into the base metal- sharp edges, particually at a change of section make for great stress risers and poor fatigue life. Too much of either is also a waste of weld metal/time

    As said, there are acceptance criteria for excessive concavity/convexity depending on the job.

  8. #8
    Join Date
    Sep 2009
    Location
    Sydney Australia
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    21

    Re: 1/8in TIG weld concave convex?

    I like a lot of these answers. Some good points, I favour what rode2rouen said. And maybe its just an exersize.

    In Oz. our welds are mainly measured on leg length, so a concave 10mm (leg length) weld on 10mm steel plate is a bit weak, but may have less stress than a convex weld like hottrodder said. The same weld I like to grow the leg to 11 or 12 mm and concave the weld but still maintain a good strong throat thickness.

    But then you need to work out how the metal is going to cope with the extra heat? As I understand, tig is the process that will put the most heat into a job. If you are working on stainless, its always a consideration. Work out your variables for that welding joint.

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