Understanding AC TIG Balance Control
A comprehensive look at the benefits of adjustable AC TIG balance control found on today's welders from Miller Electric Mfg. Co.
We Set The Standard For AC TIG Welding
In the mid-1970s, Miller Electric Mfg. Co. developed its first Syncrowave® AC/DC welder and introduced its squarewave AC output with Balance Control.
This set the standard for AC TIG welders, with today's welders continuing to utilize this feature to keep their work even more consistent.
To understand how Balance Control works, you first need to understand why aluminum and magnesium require an AC welding output.
Fig. 1. AC current is used to weld aluminum because its positive half cycle provides a "cleaning" action and its negative half cycle provides penetration.
How AC TIG Balance Control Works Improves Your Weld
When aluminum is exposed to air, it forms an oxide layer that melts at a much higher temperature than the base metal. For example, aluminum oxide melts at about 3600 degrees F, while aluminum melts at just 1200 degrees F.
The oxide layer can inhibit proper weld fusion and puddle fluidity if not removed. Fortunately, the squarewave alternating current (see Fig. 1) inherently provides a "cleaning" action (see Fig. 2).
The electrode positive (EP) portion of the AC cycle—where current flows from the work to the electrode—actually "blasts" off surface oxides.
This then allows the electrode negative (EN) portion of the cycle (where the current flows from the tungsten into the work) to melt the base metal and fuse the joint.
Fig. 2. Notice the lighter colored "etched zone" or "cleaning action" created by the AC arc.
Why AC TIG Balance Control Is Important
Until Miller invented balance control, the amount of EP (commonly referred to as the "cleaning action", and the EN, or "weld action") remained balanced at 50/50. AC “cleaning action” and “weld penetration action” remained balanced at 50%.
A comparison between greater (top) and lesser (bottom) amounts of EN.
Unfortunately, this generalized one size fits all approach didn’t provide the ideal arc for all applications.
Today, welders use Balance Control to tailor the TIG arc for the job.
Transformer Syncrowave product allows you to set Balance Control on range from 0 to 10, or Minimum Cleaning to maximum cleaning. This correlated to an EN portion of the AC cycle from 45 to 68%.
In other words, you spend 68% of the AC cycle (which is 1/60th of a second), ultimately putting energy into the workpiece.
More modern, inverter-based Syncrowaves have a balance setting of 60-80% EN while the Dynasty™, extends Balance Control even further, allowing EN duration times from 30 to 99%.
Balance Control Benefits
Making the EN portion of the cycle last longer:
- Oxide removal with a secondary characteristic of tungsten geometry.
- May permit increasing travel speeds.
- Narrows the weld bead.
- Increases tungsten electrode life and reduces balling action.
- May permit using a smaller diameter tungsten to more precisely direct the heat or make a narrower weld bead.
- Reduces the size of the etched zone for improved cosmetics (see Fig. 4).
Reducing the EN portion of the cycle:
- Produces greater cleaning action to remove heavier oxidation.
- Minimizes penetration, which may help prevent burn-through on thin materials.
- Widens the bead profile, such as for catching both sides of a joint.
- Decreases tungsten electrode life and increases balling action.
How to Use Balance Control
There are no hard rules about setting Balance Control, but the typical error involves too much cleaning or not enough.
Too much cleaning action (electrode positive duration) causes excess heat build-up on the tungsten. This creates a large ball on the end of the tungsten.
Subsequently, the arc loses stability and you lose the ability to control the direction of the arc and the weld puddle. Arc starts will begin to degrade as well.
Insufficient cleaning or too much penetration results in a “scummy” weld puddle. If the puddle looks like it has black pepper flakes floating on it, add more cleaning action to “blast” away oxides and other impurities.
For a modern inverter based Syncrowave or Dynasty welder working on clean aluminum, a good starting point would be setting the EN between 60 and 75 %. In all cases, make practice welds on scrap pieces before welding to determine the best Balance Control settings.
Miller Electric Mfg. Co.'s Syncrowave® AC/DC welder set the standard for AC TIG welders, with its squarewave AC output and Balance Control feature.
Today's welders continue to utilize this feature to keep their work even more consistent.
If you're new to using Balance Control, keep a journal of the material type and thickness along with the weld parameter settings.
Be sure to note the material type, thickness, joint configuration, welding position, tungsten type and diameter and application.
Reach out to your Miller Sales Representative for more information about how you can take advantage of our Syncrowave welders' Balance Control features in your welding projects!