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Thread: Thin Material

  1. #1
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    Default Thin Material

    I have to arc weld some 25x25x1.6 mild steel in an upcoming project and could use some advise on technique, the last time I tried arc welding 1.6 steel it was a real pig of a job, I couldn't find a sweet spot between sticking and blowing holes.

    The smallest rods I can find are 2mm.

    I saw a guy on YouTube doing multiple stop starts to allow the material to cool a little so he wouldn't blow holes, how long a pause when arc welding before you need to clean up the weld to start again?

  2. #2
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    That's getting down to about the thickness where I start reaching for the TIG as it is so much easier in terms of control.
    However, a couple tips that may make the job more achievable.


    • At that sort of thickness your fit up has to be spot on - mitred joints for example should have no gaps as it just invites blow through. Full penetration is possible with no joint prep on materials under 3mm thick, so there is no need for a gap.
    • Try to keep things horizontal where possible as then you don't get into arguments with gravity to add to your grief.
    • If you can get away with a stitch weld, then do so. It helps keep total heat down. I can't remember the name of the technique but there is one where you weld back to your previous weld in 30 or 40mm increments - again, helps keep heat down, although in this case it allows the heat at the end of the previous weld time to dissipate before the next lot arrives.
    • Lastly, think about where the heat is flowing. Blow through happens when the heat into a joint is greater than the heat that can transfer away from the joint, so start on outside corners while they are cool and weld into thicker sections if you can. The other one is if you are doing a T joint with RHS. There are two thicknesses of material taking the heat away on the cross piece and only one thickness on the upright, so weave a bit and spend 2/3 of your weld time on the cross piece. I tend to weld mainly on the cross piece while flicking the arc across just enough to get fusion.


    Michael

  3. #3
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    Thanks Michael,

    I wish I could reach for a TIG in this situation but unfortunately I don't have one, yet.

    Now that you mention it I also recall a welding instructor talk of a technique where you weld back to your previous run, will have to investigate further.
    I better do a lot of practicing before the main event.

  4. #4
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    I was quite surprised that the lunchbox DC inverter welder I bought for less than $200 can be fitted with a TIG torch. I suspect that it is not as easy as it might seem but for a simple steel job (and when Bunnings will refund the cost of a gas cylinder when you are finished) it's not as out of reach as it once was.

    From some posts made in the welding section a while back, the technique is called 'back stepping'?

    Michael

  5. #5
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    Yeah, my 170A Jasic inverter has lift start, it's a great little welder with decent duty cycle and I fully intend on setting it up for TIG once I get settled in Vic.

    I'll do some digging and see what I come up with

  6. #6
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    Hi Nedshead,

    Ok! you have an arc welder. Ok an inverter.

    If you have an inverter its a piece of cake. Connect to electrode negative.
    What is the intended joint construction -butt welded-end to end or a tee joint or both?

    DC is better because the arc is way softer. On 25 x 25 x 1.6mm, I would tack the outside corners, depositing, say no more than the volume of 2 match heads.

    If you are shaky like I now am, you might have trouble with the 2mm electrode in getting it to straddle the joint line. It is possible using a semi-vertical down bead to get a almost mig like finish where the flux rooster tails and is easily cleaned off.

    With AC the arc is fiercer for the same DC current values and tends to blow holes when you strike your arc. Its here the dab technique is better.

    The last point is that much of the 25 x 25 SHS come dura- galled and while people say otherwise I have found the finished bead is usually with inclusion and porosity because of the zinc gasses generated, agitate the weld pool. Dip the weld area in vinegar and rinse with water to remove itto minimise this problem.

    With a bit of finesse and a steady hand, often the grinder disc is not needed and the weld as finished is presentable.


    Cheers
    Grahame

  7. #7
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    I found a pic I took in 2012 of a 25 x 25 x 1.6mmm SHS butt weld using a rutile electrode.

    It was set up about 60 degrees off vertical and the electrode run semi vertically down.

    A short arc and a rapid speed are the order of the day. The arrowhead formation gives an indicator of the speed needed.

    The crater at the bottom needed a touchup but the pic shows what can be achieved with the right technique.

    Grahame

    RHS butt weld cleaned.jpg

  8. #8
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    Ned is the job SHS or sheet steel? Can you elaborate on what you wish to make?

  9. #9
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    Hi Graham,

    I'm making a trailer cage.

    My welder is a DC inverter and all welds will be tee joints, I'll set up electrode negative as suggested.

    I haven't ventured far outside of F1 and F2, G1 and G2 and I am a bit shaky so I'm hoping I can get by with just these two positions, until I get a bit more practice anyway.

    Is there zinc under the blue coated SHS?

    Thanks,

    Ben.
    Last edited by NedsHead; 3rd Jan 2018 at 10:59 PM. Reason: added info

  10. #10
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    The blue coated SHS and RHS is epoxy painted from memory and that should be thoroughly removed as well.

    Why I asked what you were making tells me that the whole weldment is still able to be inclined. Using the short arc technique combined with the high speed vertical down motion, the results you should expect will be good.

    The angle and the ( down) speed are things you need to experiment with.There's a sweet spot of angle versus speed.Too much angle and the molten flux will overoll your arc. Not enough speed and you can blow a hole in the thin box section.

    The whole outcome is dependent on NOT allowing the molten flux to come forward of the arc on your downhill passes.

    The arc is kept so short that the electrode covering is virtually touching the parent metal. With the arc so short the amperage can be increased slightly to stabilise the arc but means the travel speed has to be quick as you will certainly blow a hole if you linger.

    Finally ,I implore you don't use Satincraft electrodes as you will increase your chance of slag holes by 50%. The flux coating thickness means there's far too much molten flux to deal with and it will over roll your arc for sure. For best results I would go with Austarc 12Ps or thier equivalent .
    I have cut and pased some of the advertising blurb for the electrode.
    <Easy starting, smooth running, popular all positional mild steel general purpose electrode. Austarc 12P has the extra arc force and fast freezing slag required for vertical down welds.>
    I know people will google vertical down electrode welding and not find much reference to 6012 welding downhill. It seems to be an electrode that does not appear much in the yank catalogues as they know almost nothing but 6011 s and 7018s.Consequently 6012 appearance in google searches is minimal. In the smaller shops we grew up using 6012 and 6013s.

    I know the above, all sounds like the ravings of a madman but I assure you it can work. It just requires some positional tweaking and a bit of practice.

    When you do not have the ideal equipment it often can be overcome with a bit of knowledge and practice. Lets us know how you fare.
    Grahame

  11. #11
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    I have another question about fitting a toolbox to the brawbar of the trailer, is it safe to weld some brackets to the brawbar or should I find another way using square U bolts etc.?

  12. #12
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    Its ok to weld brackets but only parallel to the length of the drawbar but NEVER,NEVER across the drawbar.

    This link will tell you why.

    Trailer Sauce :: Drawbar Welding

    A few 25mm length competently welded fillet beads are plenty good enough.

    Grahame

  13. #13
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    I had some spare time today to lay a few practice beads on the 25x25x1.6

    Below are the results using 2.5mm rods @ 60A DC- welding in the flat horizontal position, this time was so much nicer than last time I tried to arc weld this stuff, even with the 2.5 rods. You can see where I backstepped at the end of the weld but it's probably unnecessary.

    I'm feeling pretty confident that my trailer cage won't fly apart down the highway.

    DSC_0457.jpg
    DSC_0456.jpg

  14. #14
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    Hi Nedshead,

    Top stuff mate .

    Its good to see you have a win with stick welding.

    It will encourage those blokes who think this type of welding can't be done without a tig or a mig.

    Good on ya!

    Grahame

  15. #15
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    Hi Guys,

    Cancel the "thanks for pictures" My mouse finger twitched. Sorry
    Best Regards:
    BaronJ.

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