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MIG Welding Reverse Polarity

Advanced TIP TIG Welding
TIP TIG Welding is always better quality than TIG and 100 to 500% faster with superior quality than TIG - MIG - FCAW.




Only in America!

Question: Ed can you describe the difference between straight and reverse polarity in MIG welding?.

Answer: As we can all likely do with some humor in our lives, I thought, rather than answer this common weld question in the traditional manner, that I would tell you about a welding application I was involved in a few years ago.

A Midwest company that supplies exhaust systems to the after market had major MIG welding problems. The owner of the company asked if I would visit his plant and report on the welding issues. He told me that some of his customers were complaining that the carbon steel welded flanges were falling of the exhausts while in delivery.

I arrived at the exhaust manufacturing plant just before lunch. Like many automotive companies, the plant could not afford an $8 an hour receptionist, and no one answered the lobby phone. To get access to the plant, I walked around to the back door. I entered the plant in the weld shop area and my welding senses went immediately on high alert. The "weld sounds" I heard from the approx. 40 MIG weld booths were unique, but I had heard them before.

As I stood in the plant digesting the arc sounds, a six foot four individual with hair growing in places I had never seen before, walked over to me. This man who had never seen a Gillette blade was the plant-welding supervisor. Weighing in at about 300 pounds with his stomach bulging out of his stained black leather vest and Harley T shirt, he was without question a character to be reckoned with.

The welding supervisor leaned into my face, and with the smell of stale Budweiser, and deep fried pork and onions floating from his beard, he snapped, " what dea want". I told the "gentleman" that the owner of the plant had asked that I examine the plant's welding issues.

He burped, or it could have been a small fart and glared down at me, he was obviously not impressed by a weld expert from out of town. The supervisor spat vile black liquid chewing tobacco close to my foot and then in his best English politely informed me "there were no f______ing weld issues in his weld shop".

Having spent my life around interesting characters, it only took a short conversation with this individual to figure out that the reason he was made the plant welding supervisor, there was no one in the plant that could wrestle him.

While trying to be polite with one of the reasons the welding industry has a poor image, I wandered off and walked among the weld cells to verify the root cause of the strange MIG weld sounds. I watched the welders and examined the nearest MIG equipment. As I suspected it was a polarity issue. I noted the ground cable was attached to the positive terminal on the MIG equipment. On further examination I noted that the "straight polarity" was being used by every MIG welder in the plant.

Straight polarity when used in the traditional short circuit wire feed range produces a softer crackle, plopping sound from the formation of larger weld droplets. In contrast short circuit with reverse polarity (RP) produces a crisp crackle sound from smaller droplets that transfer in a more rapid manner.

Reverse polarity is used for all MIG welds. With RP the electrons travel from cathode spots on the negative work to the positive anode on the MIG wire tip. The RP electrons impart the majority of the arc energy at the MIG wire tip, melting the wire in a consistent manner.

In contrast with straight polarity the electrons travel from the wire tip to the work, with the majority of the arc energy now in the metal being welded and thanks to the conductivity of the base metal that heat is quickly dispersed. Straight polarity does not provide a stable arc and for most applications the lack of heat at the wire tip can cause insufficient energy in the weld leading to lack of weld fusion especially on parts > 1.5 mm.

I asked the supervisor why the whole plant was using straight polarity instead of reverse. He told me that after "playing around" with the MIG equipment, the change to straight polarity reduced the weld burn through on the exhaust weld joints which had gaps.

The exhausts manufactured at this plant were so poorly built that weld gaps ranging from 3 to 6 mm were common. I politely informed the supervisor, yes I am always polite when the person I am having a welding discussion is taller and weighs 150 pounds more than I do, that the SP weld that lacks weld energy does reduce weld burn through with gaps. However when SP is used on the parts that don't have gaps, especially the thicker flange to tube welds, the resulting welds will have insufficient weld fusion.

I also pointed out to the supervisor that if the primary issue for this plant was the excessive weld gaps, perhaps it would it logical for the plant engineers and managers who were too busy to see me, to address the gap issues. Of course I also informed him that he should also switch back to RP and use the MIG equipment the way the power source equipment designers intended it. I then offered to show him what a real weld would look like.

The weld supervisor with a glazed look in his eyes, muttered something about for the last 15 years, this is the way we have done always done it , he turned his back on me and stomped away.

I was relieved in a way because I thought he was going to ask me to wrestle him. I went back to the Airport had a plate of grits and took the next flight out. The following day I went back to the owner in his ivory tower and reported on his plant's weld issues. He was shocked, however as far as I know nothing was done because the owner was not into wresting and did not have the will to address either the supervisor or apathetic managers and engineers about the weld gap issues.

To this day, every time I see an exhaust especially one in which the flange has broke off in the weld area, I have to smile at my recollection of the only plant in America or perhaps the only plant in the world that uses MIG with straight straight polarity for all it's production parts. Only in America!


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