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Thread: Pick your brain

  1. #1
    Join Date
    Nov 2006
    Location
    Greeneville TN,
    Posts
    91

    Default Pick your brain

    Hi I have a question. We have a millermatic 300 at work it is attached to a rotating welding fixture it welds a 8" diamater girth weld all you do is load the part and turn it on. the problem is on about every other part it will leave a whole in the weld not poreosity or (gas) just one single whole that is about the diamater of the wire .035 it dosent always leave the whole in the same spot it varies. We also wipe all parts down so there is no oil on them.The gas by the way is 75/25 and welding mild steel.I have tried everything I can think of so any help would be appreciated. Thanks

  2. #2
    Join Date
    Sep 2005
    Location
    Salem ,Ohio
    Posts
    3,919

    Cool

    Is it the hole where the weld stopped? Sometimes when the weld is done it leaves a hole....Bob
    Bob Wright, Grandson of Tee Nee Boat Trailer Founder
    Metal Master Fab Salem, Oh 44460
    Birthplace of the Silver & Deming Drill
    1999 MM185 w/185 Spoolgun,1986 Thunderbolt AC/DC
    Spool Gun conversion. How To Do It. Below.
    http://www.millerwelds.com/resources...php?albumid=48

  3. #3
    Join Date
    Sep 2005
    Location
    East Tennessee
    Posts
    141

    Default

    Is the part sealed?

  4. #4
    Join Date
    Nov 2006
    Location
    Greeneville TN,
    Posts
    91

    Default

    The hole is never where the weld stops it will do it randomly during the weld but never at beginning or end.It is not sealed we make a cone shaped piece out of 16 gauge sheet metal then it is welded to a ring that is 8"od. x 2" wide x3/4" thick. So the welder has to run at high heat to get good burn in on the
    thick ring.The cone is pressed over the ring about 3/4"

  5. #5
    Join Date
    Aug 2006
    Location
    Oklahoma City, Oklahoma
    Posts
    304

    Default

    Have you checked to make sure nothing has contaminated the wire spool or liner. I had a spool one time that had gotten drop or something. Several layers of the wire had a slight crease in them and it would hang up at random points and leave a brief pause in wire delivery. SSS

  6. #6
    Join Date
    Dec 2006
    Location
    Alaska
    Posts
    732

    Default Volts

    You may be over volt cap. for the size wire. You might try some pre heat
    TJ______________________________________

  7. #7
    Join Date
    Dec 2006
    Posts
    4

    Default Pick your brain

    Hi Iron Man. You didn't mention if the hole goes through the 3/4" thick ring.
    I think you gave us a clue when you said it has a hole the size of the welding wire (.035 inch).

    Seems like the work piece is loosing electrical continuity for a split second, the welding wire continues to feed into the puddle, the puddle cools around the wire, the work piece continues to rotate, the arc reinitiates and continues welding until it's done.

    Assuming you're using the right size contact tip. Check that the contact tip is not loose, dirty, or worn out.

    Assuming the work piece isn't out of round. If it were, the wire could possibly be pushed through the puddle without melting completly at the high point.

    Loose or dirty connection. Check where the weld power is connected to the ground cable and the mig gun. Check where the ground cable is connected to (table or rotating fixture), how the work piece is attached to the rotating fixture (clean and tight). Also, check how the ground is transfered through the rotating fixture.


    Best guess.
    I'm guessing that the rotating fixture is never in the EXACT SAME SPOT when the work piece is mounted; hence the hole is not in the same spot. Also, the rotating fixture may not be making good electrical/mechanical contact (work piece expands as it's heated) and as the work piece rotates, it could shift slightly and just briefly losing contact.

    TAKING A VIDEO OF THE PROCESS WOULD HELP A LOT.

    I hope this may help your situation.

    Hot Rod.

  8. #8
    Join Date
    Nov 2006
    Location
    Clarksville, TN
    Posts
    5

    Default

    Sounds like welding on tourqe converter. If they are not fresh washed and then welded while still hot coming out of the washer, the shop I work with sometimes has issues with them having holes. (porosity) when doing the pressure check.

  9. #9
    Join Date
    Nov 2006
    Location
    Greeneville TN,
    Posts
    91

    Default

    Thanks for the info guys, the part is always located in the same position as all the rings are cnc milled and when placed on the welding fixture they are located by a dowle pin, the parts aren't out of round as we have to hold A
    .010 tolerence. the parts are freshely machined and cleaned so oil or dirt is not A problem. the hole does not go all the way through the ring just a hole in the weld.It is not from lack of sheilding gas there are no fans or grafts in the area.Also it is the correct contact tip. does the same with new or old tip.
    as for shooting a video I am not allowed to do so. we do gouvernment contracts for military defense. not that it is top secret or anything like that LOL, just not allowed to freely give out info.The idea on the ground is the best so far it grounds through a brass spring loaded pin that presses against the back of the fixture it could be getting worn or spring may be weak.
    again thanks alot

  10. #10
    Join Date
    Dec 2006
    Location
    collinsville, ok
    Posts
    86

    Default

    are you using mig or flux core? i've been welding duplex stainless with pulse arc for the last year and theese bug holes do just come out of nowhere. my first thought is trash burning out but you shot that one down. we run this pulse arc pretty hot (wire speed of 275 to 350, .045 ni,cr,mo) to burn out the silicone. it may have to do with the heat and speed combo, puting so much down so fast air could get traped.

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