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John Buchtenkirch 05-29-2018 03:36 PM

Volcano plug welds ???....... (Mig type)
My longtime friend and swap meet buddy “Big Mike” is still banging out heavy collision work. He asked me why plugs welds (rosette welds) sometimes get a volcano effect. I told him contamination but have been second guessing myself on this all day on this. I’ve had the same effect and noticed just one pinhole in the center and no porosity on the sides so I’m kinda doubting my own initial comment.

So my first question is what are the theories on why mig welding plug welds occasionally gets this volcano effect ? And the more important second question is what is the cure ? Thank you in advance ~ John Buchtenkirch

mastuart 05-29-2018 03:59 PM

I think contamination. Like paint or epoxie. Clean bare metal doesn't usually have this happen. What is strange is if it is still wet most of the time it doesn't happen . It just catches on fire.

Chris_Hamilton 05-29-2018 04:37 PM

John, I'm a heavy collision guy, and usually it's from contamination on the backside. Usually happens to me if I'm plugging a used panel. Especially if I don't take the time to get it completely clean of the various things they put on them now...foam, epoxy panel bond etc. Bigger problem for me is welding the various high strength steels on cars now with a conventional MIG welder. Nearly all cars '12 and up use it everywhere now and unless you are using a pulsed MIG it is very difficult to join the thin stuff to thicker stuff or multiple layered stuff. It just wants to burn as soon as the arc touches it. Forget making pretty nearly level plug welds like in days past. Heavier gauge stuff welds ok but I find it nearly impossible to put a conventional nice plug on the thin HSS.

MP&C 05-29-2018 04:40 PM

Contamination from paint liquefying and outgassing as the weld fills the plug weld hole or rusty metal, could be on the back side where it isn't noticed.

monster88 05-29-2018 08:50 PM

I think that you might be trapping shieding gas in.

Mike Rouse 05-30-2018 11:09 AM

I had that problem too. It was due to dirty metal. To solve this I took a drill bit the size of the weld hole and cut the cone off the end and then sharpened that end like an end mill. Using a hand drill use the drill bit to clean the base metal down to clean metal. It also helps to blow the hole clean with compressed air.


Oldnek 05-31-2018 10:27 AM

I notice this happens a lot when you apply a rust convertor to the base, and on clean CRS it does it if you hold the torch head to close, so possible out gassing effect.

Rick Mullin 06-01-2018 12:59 PM

I rarely MIG weld so I can only relate to this problem as a similar issue I occasionally get with the TIG. I believe you are all correct to say that it is contamination but of a different nature. When doing a small rosette plug weld or a high speed high amp tack weld, I occasionally get an occlusion (often an eruption of the surface). This is almost guaranteed to happen if I back off too quickly with the amperage and gas coverage. This is because I have trapped a small speck of oxidation in the weld. The contamination that is floating on the puddle can get trapped in the puddle. Increasing the gas coverage by shortening the tungsten and ramping down ever bit more slowly will eliminate the problem every time. Once the occlusion exists, the only solution is to clean it out with a carbide Dremil bit. I then re-weld that spot with a tiny drop of .035 70s-6 high amp quickly and come down slower allowing the post purge to complete.

To relate this to MIG, I would suggest slowing down on the completion of the weld and tail out slowly allowing the post purge to complete. Increasing gas pressure is not the answer. Oxidation can also be created by contamination build -up in the gas cone. I use a spray nozzle cleaner when I MIG.


hot rivet 06-01-2018 01:59 PM

When you say "volcano" are you talking porosity or excessive shrinkage in the centre?

John Buchtenkirch 06-01-2018 04:09 PM


Originally Posted by hot rivet (Post 146691)
When you say "volcano" are you talking porosity or excessive shrinkage in the centre?

Actually ending up with a small pinhole in the center of the weld that pretty much resembles a volcano in most cases. I donít think itís always structurally that bad but you hate having the customer seeing it :mad:. ~ John Buchtenkirch

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