Hello folks, as a welding instructor I sometimes find myself acting as a welding detective. The other day a student brought in some welds to have them critiqued. This particular student had started the program quite some time ago and then had taken a job part way through, worked for a year or so and then realized that returning and finishing might be a good choice for him. When he set-up in the booth that morning he noticed that the feeder power cable had been unplugged from the power source, he didn't notice the polarity. The day before another individual had done some welding with an LN-25 using NR 232 wire, straight polarity. The student on this day was running .035 ER70 S-6 with 75/25 shielding gas attempting to run some downhill beads with an S22A feeder, he didn't recognize the incorrect polarity, but noticed that he had an extreme amount of LOF at the toes of his beads. When he came to show me the beads he pointed out the LOF and asked what he was doing wrong. I first inquired about his machine parameters, they didn't sound extremely out of range. At that point we made a trip to his booth and I stepped in and ran a bead for myself, WOW, that was some different stuff that I really hadn't encountered before. The detective work kicked in at that point, the machine was an XMT 304 CC/CV, 75/25 argon/CO2 shielding gas, .035 solid wire. Everything pretty much checked out. Looked at parameters, that's when I noticed the ground connection and the feeder connection, he hadn't altered the ground from it's use the previous day, thus he was operating on straight polarity. I have included some pictures that show how there was almost NO penetration whatsoever, in fact, you can see the chalk line underneath the weld metal where he was using it for a guide to help with bead straightness. I was able to get a hold of the end of the weld metal with my thumbnail and peel the bead back as it appears in the pictures. I don't believe he will make a polarity error anytime soon. Thought some of you might get a chuckle out of these photos. Best regards, Allan
That is amazing..
What a teachable moment Allen!
I'm going to sabotage a couple of CP302's on Monday next week and see if I can get some welds to peel up.
aevald
Thanks for sharing.
Marshall
Nice pics Allan, thanks for sharing.
For those reading who might not be familiar with NR232, it is a self shielding FCAW wire that runs on straight polarity(DC-), and the GMAW ER70S-6(solid wire) runs on reverse polarity(DC+).
That is not one I have encountered before. Totally a learning experience for more than just your student Allan.
Thanks for sharing the info and pics.
Have a Great Day, Brent
Hello Brent, It's kind of funny, but when I was strictly out in industry I guess I worked around folks, who for the most part, had a really good grasp on proper polarities, parameters, and any number of other details for making a weld correctly. I really don't recall running into many of the interesting issues that I often see as an instructor. There are certainly learning moments as they relate to welding instruction and when you are in this position you become familiar with just about every variation that you can imagine for ways "other" than those that are prescribed for properly setting up and operating welding equipment.
Tommy, if you read this, I can also relate to your statement of welding magnesium with aluminum filler metal, that pretty little bead will literally fall out of wherever you put it so that you can do a fine inspection of it's face and also every portion of it's underside where you thought it should have adhered to the base material. I knew that there would be a number of folks who would enjoy those pictures. Best regards, to all of you, Allan
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