Inverter technology has changed the market on Tungsten for GTAW. This has opened industry to the use of multiple tungstens and sizes for different applications.
When the original transformer power supplies were used the balance of positive to negative (cleaning & penetration) was at 50/50. This put a substantial amount of heat on the tungsten causing it to ball up, generally requiring a larger sized tungsten. To stop this from happening a pure tungsten was used and pre-balled to achieve a more stable weld pool, although it would often fall into the weld pool causing a void.
Current inverters allow you to change the balance. The higher the balance, the more penetration and less cleaning. This can be seen at the toe of the weld, if it is white the oxides layer has been broken up, if it is gray or black the oxide layer has not been completely removed. However this does not make a weld good or bad, different applications require different surface appearances. In the case of anodizing you may not want to have a wide zone clear of oxides, it can cause an uneven layer of anodizing. With a change in balance you can also get away from using a pure tungsten and often use one size smaller tungsten. You can now use a thoriated (red), ceriated (grey), zirconium (brown), rare earth (purple), lanthanated (gold or blue), or pure (green).
Balance at 50%
Balance at 69%
When preparing the tungsten for welding, the balance setting allows you to use a steeper preparation angle. With a steeper preparation angle from 22.5-45 degrees you can more precise arc placement, this does not mean the arc will be narrower. Be sure to include a flat on the tip of the tungsten, it must be wide enough to handle the current or it will still start to ball.
The frequency is also a new setting programmable to new inverters. The higher the frequency the narrower the arc, the lower the frequency the wider the arc. If the arc is narrower it can cause a problem when starting the weld pool, forming porosity under the weld. This was not an issue with the fixed frequency of older transformer power supplies; since the arc was wider it allowed gases to escape the weld pool.
One of the most well known inverters is the Miller Dynasty, which comes in multiple sizes and options. The most common sizes are the 200, 280, 350, and 700. As you can see from the instrument panel below you will find the frequency, balance, and polarity. Miller Dynasty’s also have a pulser setting where you are able to pulse current. This allows you put minimal heat input into parts and also make visually appealing welds.
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