Pulse welding, keep gas flowing when pausing?

  1. Nial Member

    Messages:
    45
    Edinburgh
    I've got a mini lined up that needs a lot of bodywork done, I've only
    used a MIG for 1" box section before so am now practicing with thin
    sheet. (I've also used Gas before).

    I've an old BOC Migmate 130 and am using BOC Argoshield.

    I've been practicing Malcom's pulse welding technique, but have noticed
    that the weld pool takes a second or two to go solid. During the cooling
    off period should I depress the trigger enough to keep the gas flowing?

    Trying this last night my welds seemed to look a bit better.

    One other thing I noticed when trying this was that on the bottom side
    some of the big 'penetration pools' (hard to describe) had small central
    pits that were devoid of metal. Does anyone know what would cause this?


    On another note, when trying to do a 'normal' weld run and not stopping
    I can see the weldpool is up to about an inch long behind the point
    I'm welding. This seems to produce a weld that isn't porous, but the
    surface is dull grey with a thin slag type covering. Is this because I'm
    moving so fast the gas isn't shielding the weld long enough?

    I've stack more questions, but my wife's working this weekend and one
    of our girls has just woken up, better go.


    Thanks for any pointers,

    Nial.
     
  2. malcolm

    malcolm & Clementine the Cat

    Messages:
    9,134
    Location:
    Bedford UK
    Oops, disappeared for the weekend and the forum becomes busy. Welcome Nial.

    For "pulse welding" it's best to keep the gas running continuously - this helps prevent oxidisation and also cools the metal.

    The central pits are caused by oxidisation (I think). You can get the same thing at the end of a weld if you lift off the shielding gas while the metal is still molten. The shielding gas doesn't cover the other side of the metal, so I guess the issue is excessive penetration.

    An inch seems a little long for a weld pool. normally you'd expect maybe 3/8 inch of molten metal followed by maybe an inch of red hot metal. Presumably you are using a circular or side to side motion rather than running the weld in a straight line?


    Malcolm
     
  3. Nial Member

    Messages:
    45
    Edinburgh
    I wondered where you'd got to!

    Is this technique used often? I haven't had any formal training, I've just
    read a leaflet and picked things up as I've gone along. Can you release the
    trigger just enough to keep the gas going when you finish a weld, or just
    release then depress the trigger enough to get it flowing again?

    Aye, I was experimenting with a higher current and 'bonkers' wire
    feed speeds to see what sort of weld I would get. I think the thin
    sheet just can't get the heat away quickly enough.

    I was, but this is thin (1mm ?) sheet and as above, it just doesn't seem to
    be able to dissipate the heat quickly enough, hence my experimentaton with
    the pulse technique.

    I'll keep on playing and will post results.

    Nial.
     
  4. geetee Member

    Messages:
    32
    Edinburgh
    the wee hole in the back of the weld is simply a lack of gas at the back of the weld. probably too much penetration.
    timing is important when welding thin sheet steel, after each weld leave the metal to cool down and it will shrink again, to a certain extent. then start the next weld.

    what i do with car panels is turn the voltage and wire up slightly and spot weld the panel at say 1 - 2 inch intervals, turn the welder down again, then join them up with continuous welds.
    because the welder is set higher you can just give the panel a quick blast for the spots, and there`s less spread of heat.
    dunno if its the way to do it but it works for me.

    :D
     
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