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Old 06-01-2018, 12:59 PM
Rick Mullin Rick Mullin is offline
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Join Date: Mar 2012
Location: Malvern,PA
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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.

Rick
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