Compared with a traditional TIG power source, a TIG inverter with advanced controls offers increased control over the welding arc that allows the operator to tailor the bead profile, improve arc starting, increase travel speeds, perform better on thinner materials and thinner sections as well as experience other production benefits.
A traditional power source uses a transformer to turn high voltage, low amperage primary power into low voltage, high amperage power required for welding. Therefore, we will explain tig welder settings and waveform controls.
An inverter power source, such as the Miller Dynasty 350, takes input power, filters it to DC, and, using fast solid-state switches, increases its frequency to 20,000 to 100,000 Hz.
Then, it transforms the current it into useable welding power through an advanced level of control over the arc.
Inverter technology provides the capability for high speed pulsing in DC mode. In AC mode, an inverter allows waveform shaping and more control for optimal results in the weld. We’ll take a look at some of the benefits behind these additional capabilities and how they can be used.
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TIG Pulsed Welding
TIG pulsing refers to switching from peak amperage to a lower background amperage. This is useful on ferrous metals for which welding heat input must be minimized, or for which penetration has to be accurately and repetitively controlled.
For out-of-position welding, pulsing may prevent weld metal sagging or drop through. In addition, pulsing allows thin metals to be welded with less distortion.
On thin stainless, a lot of times you use a pulse just as a way to strengthen the arc. Instead of having the tendency to want to spread out, pulsing focuses the arc.
High speed pulsing also can lead to faster travel speeds. You can cut your welding time in half by switching from a conventional power source to inverter TIG that supports pulsed GTAW.
Traditional technology usually allows for 1 pulse-per-second to 10 pulses-per-second. Common ranges for inverters are 100 pulses-per-second to 500 pulses-per-second. That provides increased penetration, arc stability and travel speeds.
More advanced inverter power sources, such as the Miller Dynasty 350 and 700, can pulse at 5,000 pulses-per-second, to further enhance stability and to increase travel speed. The increased number of pulses per second also is beneficial in automated applications.
Some inverter power sources allow the user to set the percentage of time at peak and background amperage to control heat input more closely, and to improve the appearance of the weld bead. Increasing the peak-on time increases the puddle fluidity and helps to fine-tune penetration.
A good starting point is to set peak time at 50 percent to 60 percent of each cycle, and adjust the peak time to suit your application.
Some inverters allow you to set the background amperage. This affects heat input into the part, and helps to determine the size of the weld puddle and arc, especially during the background portion of the pulse cycle at low pulses-per-second settings.
At low pulse frequencies, the background amperage should be high enough to keep the puddle from solidifying; it should shrink in diameter but not solidify. For stainless and carbon steel, a good starting point is 20 percent to 30 percent of peak amperage.
AC Output — Welding Aluminum and Magnesium
AC Output Frequency
Conventional technology limits AC frequency to either 50 Hz or 60 Hz, the same as single-phase input power.
Inverter technology allows output frequency to be adjusted from 20 Hz to 400 Hz. Increasing AC frequency provides a more focused arc with improved directional control and a narrower bead and cleaning area. A lower frequency softens the arc and results in a wider weld puddle and bead.
An arc cone at 400 Hz is much tighter and more focused at the exact spot at which the electrode is pointing than an arc cone operating at 60 Hz. The result is significantly improved arc stability and increased penetration, ideal for fillet welds and other fit ups that require deep, precise penetration.
AC Balance Control
AC Balance Control adjusts the balance between penetration (EN) and cleaning action (EP). Inverter-based TIG welders allow the operator to set the amount of EN from 30 percent to 99 percent for greater control and to fine-tune the cleaning action for TIG welding aluminum.
More cleaning action is not necessarily better. To produce a good weld, you need only a 0.1-in. etched zone surrounding the weld, although different joint configurations may have different requirements. Using the least amount of cleaning action necessary — setting the balance at the highest practical EN — helps to maintain the tungsten point, reduces balling and provides deeper and narrower penetration.
Insufficient cleaning action 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. Too much cleaning action can lead the tungsten tip to ball and will reduce penetration. A good starting point is 75 percent EN, and it can be fine-tuned from there.
Amplitude Control
Independent amplitude control is available only on some inverters. It allows the EN and EP amperage values to be set independently.
Independent control of the EN and EP portions of the AC cycle allows the operator to direct more or less energy into the work piece, and takes heat off the tungsten.
For example, when welding a thick piece of aluminum, the operator can put 250 amps of EN into the work and only 60 amps of EP into the tungsten. This provides faster travel speeds, faster feed of filler rods, deeper penetration, and the potential to eliminate pre-heating. Some companies cut production time by as much as two-thirds using this technology.
Independently increasing EN amperage while maintaining or reducing EP amperage also narrows the arc cone, and lets the operator use a smaller diameter electrode to make narrower welds. This also may allow the use of straight argon shielding gas in place of the standard argon/helium mixture.
TIG Welder Settings And Waveform Controls
Some inverters also bring control over the waveform itself to meet a specific requirement or operator preference. Some of the waveforms include:
- Advanced Squarewave, which gives fast transitions for a responsive, dynamic and focused arc and better directional control.
- Soft Squarewave, which provides a smoother, softer arc with a more fluid puddle than the squarewave.
- Sine wave, which gives the soft-arc feel of a conventional power source, while using square transitions to eliminate the need for continuous high frequency.
- Triangular wave, which combines the effect of peak amperage while reducing overall heat input. The triangular wave also leads to quick puddle formation and, because of lowered heat input, reduced weld distortion, especially on thin material.
Achieving maximum productivity often depends on the inverter’s ability to produce a weld bead profile and characteristics that meet the application needs without over-welding or under-welding, and without requiring excessive post-welding grinding or weld repair. In critical or high-volume applications, only advanced AC controls provide this benefit.
For example, with the Dynasty (an inverter-based AC/DC TIG power source by Miller Electric), you can weld much quicker. And when you strike an arc, it draws a puddle at least twice as fast as conventional TIG.
Many shop owners find that the inverter-based TIG source increases production, provides a quick turn around time per machine, and improves weld bead consistency.
