HTP Revolution 2500 Manual page 13

Pulse in DC TIG
You typically use the DC pulse function to reduce the heat input when welding to prevent distortion
or excessive discoloring of the base metal. The Amperage display shows the maximum amperage,
and you set the background amperage and the peak time (pulse-on time or duty) based on that
maximum amperage. You set both the background amperage and the peak time as a percentage of
the maximum amperage. Peak time refers to the peak pulse current number. The actual duration of
the peak time, in seconds or in fractions of a second, depends on the third variable—the pulse
frequency. The pulse frequency determines the speed, for lack of a better word, of the time it takes
to switch between the higher and the lower amperage. There are two schools of thought:
• Use low-speed pulse frequencies between 0.5 and 2.0 PPS (pulses per second or Hz) to create a
ripple effect in the weld bead. The pulsing can easily be seen by the human eye. When using low-
speed pulse frequencies, you typically will not experience any interference or other technical
difficulties with either fixed shade or auto-darkening welding helmets.
• Use high-speed pulse frequencies between 25 and 100 PPS to create a smooth weld bead, much
like DC TIG without pulse. The pulsing usually cannot be seen by the human eye. You typically use
high-speed pulse frequencies when welding stainless or mild steel out of position, when heat
affected zones need to be kept to a minimum, or when warpage or distortion of parts are a concern.
When using auto-darkening welding helmets, depending on the frequency of the cartridge in the
welding helmet and the frequency you set the machine to, there may be a very narrow band of
specific frequencies where interferences are possible. Whether interferences happen at all, or at
what frequency the interferences occur at, depends on the welding helmet you use (make, model,
etc.); we cannot predict who will experience interferences. If, when welding, you notice flickering,
change your frequency by +/- 20 PPS and try again.
For most applications, we recommend setting the background amperage to 25% and the peak time
(pulse-on time or duty) to 25%. Example: You set your max amperage to 100 amps, your
background amperage to 25%, and your peak time to 25%. For 25% of the time, you weld at 100
amps, and for 75% of the time, you weld at 25 amps.
Using these settings during a low-speed pulse application (with the right torch movement and either
no filler or while using a lay wire technique) allows you to produce nice ripples. Using these
settings during a high-speed pulse application allows you to achieve penetration close to what 100
amps of straight DC gives, but with significantly lower heat input and a much more controllable
puddle. Even though you only reach 100 amps 25% of the time, and 25 amps 75% of the time, in a
high-speed pulse scenario it is NOT safe to assume that the first quarter at 100 amps and the second
through fourth quarters at 25 amps equal 43.75 amps of overall heat input (100 + 25 + 25+ 25 =
175/4 = 43.75). While the math does not hold true in high-speed pulse applications, the math comes
a lot closer in low-speed pulse applications. In a high-speed pulse application, at a 25 PPS pulse
frequency setting, you introduce 100 amps into the base material 25 times per second, and at a 50
PPS pulse frequency setting, you introduce 100 amps into the base material 50 times per second.
Even though this occurs for a short or a very short period of time, the time between the 100 amp
bursts is not long enough to let the material really cool down to an average of 44 amps of heat input.
Nevertheless, a high-speed pulse application is significantly cooler than just DC TIG.
The strongest effects and the best results occur when you set the difference between the peak
amperage and the background amperage rather high. With the Revolution 2500, you can adjust the
pulse frequency from 0.4 to 1000 PPS, the background amps from 10 to 90%, and the peak time
(pulse-on time or duty) from 10 to 90%.