THE EXHAUST MANUFACTURING COMPANY THAT
USES MIG WITH STRAIGHT POLARITY

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

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 company that supplies exhaust systems 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. My welding senses went immediately on high alert. The short circuit "weld sounds" I heard from the 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 heard of Gillette blades was the plant-welding supervisor. Weighing in at about 300 pounds with his stomach bulging out of his black leather vest and black Harley T shirt, he was a site for my sore eyes.

The welding supervisor leaned into my face, and with the smell of old Budweiser, pork hot dogs and onions floating from his beard, he snapped, " what dea want". I told the "gentleman" that the owner had asked that I examine the plant's welding issues.
He burped, glared and was obviously not impressed. The supervisor a man of few words informed me there were no f________ g weld issues. It only took a short conversation with this individual to figure out that the reason he was made the plant welding supervisor,
was no one in the plant could out wrestle him.

While trying to be polite with one of the reasons the welding industry has a poor image,
I watched the welders and the MIG equipment used. I noted the ground cable on the MIG equipment was attached to the positive terminal on the MIG equipment. On walking around the weld department I noted that the "straight polarity" was being used by every welder in the plant.

Straight polarity when used in the traditional short circuit wire feed range produces a softer crackle (plopping) sound than short circuit with reverse polarity (RP). With RP the electrons travel from the 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 as it's fed to the work. 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. Straight polarity does not provide a stable arc and for most applications the lack of heat at the wire tip can cause a lack of weld fusion.

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 with weigh 150 pounds more than I do, that SP does reduce weld burn through with gaps. However when SP is used on the parts that don't have gaps, especially the thicker flanges which are welded to the thin exhaust pipes, the resulting welds will have insufficient weld fusion.

I also pointed out to the supervisor that the primary issue for this plant was the excessive weld gaps. I explained that it would be 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 designers intended. The weld supervisor with a glazed look in his eyes, muttered something about this is the way we have done always done it for the last 15 years, he turned his back on me and stomped away.

I went back to the owner and reported on the weld issues. As far as I know nothing was done because the owner was not into arm wresting and did not have the will or the people resources to address the weld gap issues. However to this day every time I see an exhaust especially one in which the flange has broke off, I have to smile at my recollection of the only plant in America that uses straight polarity.