Pulsed TIG welding

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Dan Knapp
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Pulsed TIG welding

Post by Dan Knapp »

I have an older TIG welder and have constructed some stainless steel vacuum chamber components. I am not a skilled welder, so it is fortunate that vacuum welds are on the inside where they don’t show. It usually takes me several iterations to get a vacuum tight job, and the resulting welds are not pretty; but they remain out of sight inside the chamber and it gets the job done. More recently I acquired a micro pulse TIG welder that I’ve used successfully for very small components of stainless and titanium. I’ve found the micro pulse welding to be much easier than conventional large size TIG, and I wondered whether one could do pulsed TIG welding at conventional scale. A quick google search revealed that pulsed TIG has become an established technique, and commercial TIG machines are now sold with this capability. One of the selling points of this capability is that it produces prettier welds. The questions I am working up to are these. Has anyone on the forum used pulsed TIG welding for vacuum apparatus? Has anyone successfully converted an older TIG welder to pulsed operation?
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Richard Hull
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Re: Pulsed TIG welding

Post by Richard Hull »

I bought my large Lincoln TIG welder back in 1998 for fusor work. I practiced with a lot of junk 304 scraps from our junk yard before ever working on expensive vacuum parts. It is a matter of practice with a straight DC TIG welder. I attach an image of some TIG work on fusor III and IV. I used the welder a lot for vacuum work from 1998 until about 2006 and have used it very intermittently since then. I watched a few videos of how to pulse TIG weld on you tube. I was impressed with the span of options. I fear however it is much like DC TIG in that you still have the learning curve, just with vastly more variability and control.

In general I would not spend a lot of money on a pulsed welder as I no longer weld much (age and unsteady hands). I would suggest it only to younger hands who will make it "pay" for its initial outlay over time.

I found that since almost all welds in vacuum work are rotational in form and if a lot of this work is to be tackled, a very special gimbaled, lockable mount on a rotating base mounting will be of tremendous value in that with a bit of prepositioning of the handpiece spring loaded and held fixed, a "hands-off" weld is the ideal. Position the rotation such that the tip of the torch just touches the area to be welded and once the arc is struck, adjust the spring back position to a fixed arcing distance as the torch circles the weld. It will be flawless. The key to such an assembly jig is that it must be sturdy and adjustable. It is all about setting up the vacuum weld and less about the TIG welder itself, once you have your welder settings correct.

I never used filler metal! I set up all welds via positioning and machining to produce "weld lips" extending into the weld area to supply the excess metal at the joint to supply the metal needed to make the weld.

Richard Hull
Attachments
WeldPix3.jpg
WeldPix.jpg
WeldPix1.jpg
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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
John Futter
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Re: Pulsed TIG welding

Post by John Futter »

pulsed is superior for thin work the high current gets the weld pool established and the lower current stops it getting too hot pulse duty cycle and frequency are adjustable. I have only used it on very thin sheet ie 15 thou" thick.
As to vacuum tight welds--as Richards said practice, practice, practice
Andrew Seltzman
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Re: Pulsed TIG welding

Post by Andrew Seltzman »

I have used it on 1/16" thick wall socket welds for 1/4"-1.5" diameter tubing in conflat vacuum systems. It works beautifully with much lower heat input, especially when pared with a rotary chuck to feed the weld at constant speed.

Here's the rotary chuck I built:
http://www.rtftechnologies.org/general/ ... lding.html

and an excellent site on weld parameter development:
https://www.pro-fusiononline.com/weldin ... rbital.htm

These parameters are a good starting point:
For a ~0.1" wall tube of 3/8 diameter, the welder settings were:
Electrode tip ground to a 90 deg angle
Rotation rate of 4.1RPM => ~5inch/min surface speed
Electrode to tube gap = 0.05"
Pulsed TIG on
3:1 peak to avg current
5 pulse per second pulse rate
35% pulse width
HF continuous
Peak I = 80A
current was decreased to ~80 of starting value manually via TIG pedal during the weld process
Andrew Seltzman
www.rtftechnologies.org
Jerry Biehler
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Re: Pulsed TIG welding

Post by Jerry Biehler »

Pulsed tig has been around for a ling time, you really started seeing it with the first square wave machines because it was easy to do since it had SCRs to do power control. Pulse was often an option that you could get when you bought it or as an add on retrofit or as an external box. (I used to be a miller certified tech)

I have an old Thermal Arc 300GTSW and it does have pulse modes but I almost never use it.

Now that almost all tig machines are inverter based (SMPS) they have incredibly fine current control which makes it a lot easier to weld thin stuff especially if you are doing pure fusion welds like you do for vacuum a lot of the time. Pulse really helps to melt the filler rod. A lot of modern machine also allow you to set a start current which ramps down so you can establish a weld pool and then run lower.

Electrode choice matters too. In the case of miller inverter welders (Dynasty, Maxstar, etc) they are specifically designed to run ceriated electrodes for both ac and dc modes.
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Richard Hull
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Re: Pulsed TIG welding

Post by Richard Hull »

Great jig and setup, Andrew! If you are doing a log of welding for vacuum components, a jig is a must. Thanks for the URL to your efforts.

Jerry is right and mimes my opinion. The wonderful control on pulsed TIG is a godsend for those critical thin material welds. Vacuum tube spot welders rarely exceed 30-50 joule impulses due to the thin materials to be fused together. I have such a vacuum tube welder by Raytheon and used it on my early, true, geodesic grids.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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