No pics and it doesn't happen all of the time, but sometimes as I finish a tack weld on a body panel the center of the tack grows a strange bubble as it cools. It's hollow when you hit it with the grinder and sometimes deep enough to leave a pinhole after you finish. At first I thought it might be lack of shielding gas, but if it's really cold in the shop sometimes the valve on my gun will momentarily stick and keep flowing gas for a couple of seconds after I release the trigger - but it happen the too sometimes.
Typically you should have a small amount of post flow to keep the air away from the fresh weld momentarily. I would vote for contamination in the weld. Oil or paint will sometimes case this. Frank
Keep the gun is position for a few seconds after the weld run is completed. See above posting re: "Post flow". Same for TIG welding.
I think he's right. I had the same problem and solved it by changing the settings for a 2 second post flow. Can you do that with your welder?
Yeah..."porosity" or "slag inclusion"... In any event, it indicates a contaminated weld site. Trace rust, grease, paint...even residue from a grinding disc...you have to make sure the weld site is clean. Someone already mentioned this, but other causes/contributors can be a lack of shielding gas at the weld site, common if you are welding anywhere there is a strong breeze, as well as the tip of the wire. When you are tacking, you are going slowly, and each time you tack, you create a "slag tip" (there is probably a REAL term for it) on the end of the wire. This burnt end of the wire is no longer clean wire...it's oxidized, and equivalent to mill scale on hot rolled steel. So, when you go to your next tack, the first thing the weld sees is contamination. The remedy to that is to keep your MIG pliers handy and trim the end of the wire between tacks.
Usually when I get the little volcanoes, it's time to change or clean the nozzle & tip. Matter of fact it happened yesterday during a patch panel job. swapped out the tip, cleaned the nozzle, and it was back to working normal.
This is great, I have the same problem with my pissy second hand 110 mig. Its OLD, run down but I thought it would be good to learn on. The regulator leaks so I think Im not getting enough shielding gas. Thanks for helping me too Kevin! Doc.
This happens to me all too often. I've been told that it is related to gas afterflow. the holes that allow the gas to flow into shielded weld area can become blocked over time as the threaded collar begins to back out with use. See my pictures below. First one is the proper position with the holes clear and the second one is partially blocking the holes restricting the flow of gas after you release the trigger. So when you go clean the tip and tighten everything up it works good for a while and in time you get back to the same old slag bubble because the collar has loosened itself and is blocking the gas flow. I'm also told that you can install this collar backwards which covers the hols and restricts the gas flow.
Make sure you don't have a bad spool of wire..I had a spool of wire at work that was rusty about half way through the spool and it was causing porosity. Now i have something like a woman's hair clip with a piece of Scotchbrite wrapped around the wire just before the feeder,so it will clean the wire before it goes into the feeder...it makes a big difference...it will keep the liner in the whip in better shape ...But like the others have said clean weld prep,make sure the defuser and the nozzle are in good shape,clip the wire before you start a new weld and check the gas flow
Oh man. It's contamination - definitely not a post flow problem. I promise to clean everything before welding from here on out. Tman is going to be so happy.
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