TIG welding, or tungsten inert gas welding, also known as GTAW (gas tungsten arc welding), is one of my personal favorites. It consists of a piece of tungsten (the electrode), used to conduct electricity to the work, held in a “torch”, with an inert gas such as argon flowing from the nozzle of the torch to protect the weld area from atmospheric contamination. Tungsten is used because it’s considered non-consumable, the electrode isn’t consumed as the weld progresses, unlike SMAW. Since the electrode isn’t consumed, a filler rod is used although it isn’t always needed on thin materials. This process is looks similar to oxyfuel welding in that it uses a ‘torch’ that has a bright cone (the hot tungsten), and a filler rod. Unlike oxyfuel though, TIG requires more sophisticated equipment.
The electrode for TIG welding is made of tungsten. A green band at one end indicates that the tungsten is pure, a yellow band means it has 1% thorium, a red band is 2% thorium, and a brown band is tungsten with zirconium. For welding with DC, the tungsten needs to be ground to a point linear to the rod, not so that the grind marks make circles around the point. For welding with AC, the tungsten needs to be balled at the end. To do this, set the machine to reverse polarity, the high frequency switch to continuous, hold the torch above some scrap metal and start the arc with the foot pedal, the tungsten will melt and form a ball in a second or two, then let off the pedal and let the tungsten cool before switching to AC.
TIG welding uses a constant current power supply to stabilize the arc. The polarity can be DC straight, DC reverse or AC. DC straight polarity means that the electrode is negatively charged. This produces higher temperatures in the base material and is used with steels. DC reverse polarity is just the opposite, causing greater temperature in the electrode. Usually this is used with a bigger electrode to weld more heat sensitive materials. AC current is a little stranger and with some power supplies, the amount of time it takes to switch between positive and negative can be controlled. AC is good for welding aluminum, providing deep weld penetration as well as a little cleaning action.
Then there’s the shielding gas. Argon is the standard, but helium is used as well. Mixes of the two gasses can be used too depending on what’s needed and desired. Argon is good for cleaning action, and helium is good with weld penetration.
The TIG torch is an interesting device. It has a copper holder for the electrode called a collet and a collar or gas diffuser that conducts the inert gas to the work. The collar is usually made of ceramic because of its heat resistant qualities. Of course these are connected to the main unit by cables and hoses, the length depending on what you want or need for your specific project. TIG machines can also be fitted with a foot switch that can control the current within a variable range.
TIG welding is an excellent process if you need high-quality welds on abnormal materials. Because of its great weld properties, it is used a lot in the aerospace industry to make spacecraft. Also because TIG is is great for thin metals and thin-walled tubing, it is used to make bicycle frames. TIG is also used to obtain a superior root-pass for some piping jobs. The greatest drawback to TIG welding is the operator, since it requires significantly more skill than other processes.
The Miller welding company has a great line of TIG machines for basic, around-the-shop TIG welding called the Dynasty Series. It starts with the 200 which is very versatile being able to hook into any input voltage, although the duty cycle is limited on 120V. It has presets allowing for tungsten sizes from .02 – 1/8 inches as well as a high frequency arc starter so that you don’t need contact to start the arc. The basic model is air cooled but water cooled is available for a little more money. Their website at http://www.millerwelds.com/products/tig/dynastyseries.php has a lot of great information concerning this series of machines. Hopefully this has helped a bit in better understanding the TIG welding process. Good luck and happy welding.
Written by Dustin Saunders
