Pulsed TIG

Now that I redid my CyberTIG to use a modern microcontroller, I have a question. Just when is pulsed TIG necessary? It is helpful for all
kinds of welds, or just for thin wall stuff?
Also, what would be good parameters to just try it out. Say, 135 amps max, 35% of that in low, 5 times per second, 35% duty cycle, does that sound sensible?
i
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You can try different settings and see how the arc responds. I prefer using a pulsar, I like the control it gives me. 5 pulses per second is very slow, I am usually above 100 pps, but again it depends on what your welding, play with the settings and you'll develop your own preferences.
Richard

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From past posts of mine:
Pulser Description
wrote:

A pulser is a device used to interrupt a welding arc. Mostly used on TIG, but can also be used for MIG. The idea is to cycle the arc from high amperage to low amperage. The metal melts at the high amperage and solidifies at the low amperage.
There are 3 settings for a pulser. 1. Background amperage This sets the low amperage and is usually set as a percentage of the main amperage. So if you main amperage is 100 amps, and the Background Amperage is set for 50%, then you Background Amperage is 50 amps.
The lower the background amperage, the colder the weld will get between the pulses. The thinner the material, the lower the background amperage % should be.
2. Percentage of On time. This sets how much of each pulse cycle is spent at the high amperage and how much a the low level, once again by percentage. A setting of 50% evenly splits the cycle between low and high amperages. Less than 50% on On time gives a Spikier Pulse. Greater than 50% gives a Softer Pulse.
The spikier the pulse the colder the weld will get between pulses.
3. Cycles per second. This is the really confusing one, because it has the most profound effects. Older TIG pulsers only allow up to a maximum of 10, or less, Cycles Per Second (Hertz - Hz), but the newer Inverter TIGs allow much higher frequencies. My Maxstar 200DX goes up to 200hz.
The lower pulse frequencies are for traditional pulser use, where you run between 1 and 2 hz on the pulse. adding filler metal on every pulse or every other pulse as you progress across the weld.
The higher frequencies have a much different effect, in that they tend to make the metal super-liquid, allowing it to flow and wet out much smoother. These higher settings work very well with autogenous welds where no filler metal is added at all. These are also called Fusion or Flow welds. I also found these higher frequencies worked well for vertical welds in heavy Silicon Bronze, and when repairing stainless steel piping in breweries.
Now the reason for all this pulsing is rather simple. Lets start with a piece of 16 ga steel. At 0.062" thick the proper amperage would be 1 amp per 0.001" of thickness or 62 amps, for a flat-butt weld, full penetration, single pass. You could easily TIG weld a seam in 16 ga Steel using a continuous 62 amps. However a spike of high amperage will melt the metal much faster than a low amperage, so you could weld faster at 80 amps than 62 amps, but at that heat you risk overheating the metal and causing undue warpage or burning of the steel, so you mix an interval of 80 amps with an interval at 40 amps. The low amperage interval allows the puddle to solidify back into steel, without allowing the arc to break. By pulsing the weld across the bead you get a very orderly row of rings, that give that distinct stack-of-dimes look to the weld bead. You adjust the exact pulse frequency to suit your style and speed of welding as well as the thickness of the metal. The other benefit is that over all, you have put less heat into the metal, so you have less distortion.
A smaller, consistent weld bead is often stronger than a larger inconsistent weld bead.
The more consistent a weld is the more the stresses apply along it's entire length. Any peak or valley in a weld becomes a stress point for failure to occur.
Whether you choose to add filler metal on every pulse, every other pulse, every third pulse or not at all is dependent upon your own welding style and the circumstances of the weld.
Where pulsers become bewildering is when you start messing with the percentage settings for the Background Amperage and percentage of On Time. The number of possible combinations is huge, and there is little or no guidance given in the welding world as to application.
Pro-Fusion has an excellent series of webpages with online calculators that allow you to punch in the overall required amperage you want and how fast you want to weld and it will generate pulser settings for you.
http://www.pro-fusiononline.com/welding/pulserate.asp http://www.pro-fusiononline.com/welding/pulseparams.asp
It still gives no guidance as to when you want a Spike pulse, or a Soft pulse, but it gives you something to play with.
50%, 50% and 1.4hz, is a setting that works as a starting point.
All I can say is that until somebody puts out some really authoritative research showing what pulser settings are best for what combination of weld and materiel, we will all be out there experimenting on our own.
I have searched for such a book for 5 years, and given up. Hopefully some day soon the welding engineers will decide to enlighten us lowly welders.
The guideline I can give you is that the thinner the materiel the more it benefits from a spikier pulse. I have yet to find a benefit to a really soft pulse.
An example of an extreme spike pulse is that you can weld a popcan at 120 amps, as long as you set your pulser to 2% On Time and 2% background amps.
Sequencer Description
Subject: Re: New Maxstar 200 DX ... Setup?
Newsgroups: sci.engr.joining.welding Date: Sat, Nov 30, 2002 10:46 PM

What does a sequencer do? Well pretty much everything except make your coffee.
A sequencer is gods gift to repetitive welding jobs.
Any machine with a built in sequencer will have what is called a 2MT-Hold setting. This allows the sequence to be controlled by 2 button taps.
The first part of the sequence is initiated by the first button tap.
1. Preflow gas - This will purge air from the line and torch before the arc initiates.
2. Arc initiation via high frequency.
3. Initial Amperage - This is the amperage the machine starts at once the arc is initiated.
4. Up Slope - this is the amount of time the machine takes to ramp up from the initial amperage to the working amperage.
5. Working amperage - the amperage needed to weld the material.
or
5. Pulsed weld amperage.
Then a second button tap when the weld bead is complete.
6. Down Slope - the time it takes to get from the working amperage to the final amperage. A longer down slope prevents a pit from forming in the end of the weld bead.
7. Final amperage - what the machine slopes down to before terminating the arc.
8. Post flow gas - This shields the tungsten and weld area as both cool.
So all that with just 2 button taps.
To give you an idea of settings, my machine is currently set up for tack welding together stainless steel picket railings.
1/2 second preflow gas, 2 amps initial amperage, 1 second up slope, 80 amps working amperage, pulser is set to 40% on time, 50% background amperage and 1.2 pulses per second, 3 seconds of downslope to a final amperage of 3 amps and 15 seconds or postflow. I adjust the working amperage a little up or down depending on how the welds are going.
Older machines that don't have a 2MT-Hold setting require you to push and hold the button. Releasing the button starts the second half of the sequence.
The Syncrowave 351 at school doesn't have 2MT-Hold so we just use the foot pedal to trigger the sequence.
The main challenge of using a sequencer is figuring out what amperage you really NEED to weld a bead.
Trial and error can get you there.
Here are some guidelines for minimum amperages.
Start with 1 amp for each thousandth of an Inch of thickness (0.001"). So 1/8" steel or aluminum = 0.125" thick = 125 amps. Simple and easy. Now 2 complications. For inside fillet welds, increase amperage by 30% For outside fillet welds, decrease amperage by 30%
Those numbers are for Steel or Aluminum.
For stainless steel, decrease amperage by 30%. For copper, increase amperage by 100%. For bronze, decrease amperage by 50%.
Use of a pulser will skew this amperage estimate. Usually you have to increase the amperage a bit to compensate.
To hook up a control button for the sequencer you can either just buy a remote contactor control button from CK Worldwide, or make your own. I make my own because CK's is just too big to be comfortable. I use OEM replacement buttons for plasma cutter torches ($20 each). They are armored in black silicon rubber so you don't get a shock from any high freq bleed through. The wires for the switch are run along the TIG torch cables. You can just wrap electrical tape every foot or so. I use a heavy fiber sheath to encase the whole lot. The button is just electrical taped to the torch handle. I have tried making fancy brackets and electrical tape works better.
The wires hook up to the first 2 pins for your remote connector. Usually pins A and B.
--
Welding Instructor - South Seattle Comm. Coll.
- Divers Institute of Technology
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Art and Ernie, thank you. I saved Ernie's post for my future reference, it is great.
i
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