The new process centers on altering the surface tension of the puddle by varying the chemistry of the metal directly at the weld
Tungsten Inert Gas (TIG) welding is highly prized for its ability to produce clean, even, and aesthetically pleasing welds that don't actually require any post-welding finishing. The downside is that on average TIG welds are relatively wide, shallow welds, because currently produced ferrous metals now usually contain less sulfur as an impurity. Producing full-penetration welds on thicker base metals therefore requires multiple passes. Consequently full-penetration TIG welds on these sorts of thick metals are time consuming and costly.
A group of Japanese inventors has developed and patented a new technology to overcome this problem by changing the characteristics of the puddle directly at the point of the weld. The patent was actually issued in the United States on March 29, 2011. The process took a full seven years to pass the US patent process, and logic would dictate that the inventors had the good judgment to concurrently file for a Japanese patent as well. However, even before the patent was issued the inventors were already touting their process in esoteric scientific journals as a variant of A-TIG (active flux TIG) that has been dubbed AA-TIG (advanced A-TIG). The patent is actually for the practical application of this type of welding, not the scientific underlying principle itself. According to Welding International, "This enhanced TIG welding effect was discovered at the Paton Research Institute, Ukraine, in the 1960's." Apparently it has taken fifty years for this science to be turned into a practical welding machine.
This new TIG welding process centers on altering the surface tension of the puddle in the weld by varying the chemistry of the metal directly at the weld. Historically a TIG welder uses a single shielding gas surrounding the electrode. The new Japanese TIG welding technology utilizes two concentric streams of shielding gas. The inner layer of shielding gas is the normal inert gas used to protect the weld and the electrode. Around this gas stream is an added layer of an oxidative gas that reacts with the molten puddle. According to the patent, this outer layer of an oxidative gas can be either pure oxygen or carbon dioxide. The choice of gas is obviously going to substantially affect the manner of the reaction, but to the welder the difference will remain largely unnoticeable.
The addition of oxygen to the weld puddle reduces the surface tension at the periphery of the weld puddle, allowing the metal to flow back toward the center. The result from more of the liquid metal flowing back to the center of the puddle is inward and downward heat convection in the molten pool creating a deeply welded metal portion in the base material. (For those who absolutely must know, this is technically called Bénard-Marangoni convection.) Properly applied, the weld is left with an oxide coating of approximately 20μ (microns).
Like nearly every patent, aside from being bombastically cryptic, the patent for this TIG welding technology lists several alternative designs intended to cover the inventors on most other possible ways of performing the operation. In this case the subsequent designs detail two or more separate gas jets arranged around the periphery of the inner shielding gas stream in lieu of a single concentric oxidative gas stream.
According to the tests run by the inventors these various arrangements of the outer gas stream will have varying effects on the weld and the manner of welding, but the net effect of a deeper high-quality weld remains largely the same. In other words, while the subtleties of arranging the outer gas flow make for fascinating consideration to the engineer, chemist or physicist, the affect on the welder and the work they are producing is largely invisible. There is one notable exception perhaps to this, and that is the reduced degradation or consumption of the tungsten electrode. In side by side tests run by the inventors in the process of the development of this welder, the electrode in the twin shielding gas process showed essentially no degradation in the welding electrode. From an operator's point of view this will make the process more efficient since electrode change out will be far less often.
This newly patented TIG welding technology has been assigned to Taiyo Nippon Sanso Corp., one of Japan's largest producers of industrial gasses. This sort of arrangement makes a certain amount of sense. Companies that supply consumable materials, such as gasses in this case, tend to like to be able to offer technologies and equipment that will require the consumption of the products they produce. Whether Taiyo Nippon Sanso will attempt to produce welders of this new technology, or license the production to a company already set up for machinery manufacturing, remains to be seen.
Paul DQ Campbell is an author and technology freelance writer. For more information or to contact Paul, visit www.pdqcampbell.com