Pick your brain

[Iron man]

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

[aametalmaster]

Is it the hole where the weld stopped? Sometimes when the weld is done it leaves a hole....Bob

[Frank865]

Is the part sealed?

[Iron man]

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"

[SkidSteerSteve]

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

[Fat-Fab.com]

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

[Hot Rod]

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.

[Alan Bechard]

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.

[Iron man]

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

[tsalagi]

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.