Welding thin stainless

Capt Ahab · Post by **Capt Ahab** » Fri Mar 26, 2004 12:52 am

I posted this question the other day but it was deleted somehow.

I recently built a TIG welder and I've been trying to weld .025" 304 stainless steel with it. I can weld a nice enough bead on it but as long as it's not near the edge. The only way I have been able to get satisfactory results on the edge is if I use a chill bar behind it, otherwise it melts holes very easily. Even with the chill bar it has to have a good fit and be clamped securely or it will warp away from the chill bar and blow holes through. Anyway, I can weld seams ok since they are straight and I can use a chill bar but how do I go about welding the round sections ("combustion chamber", cone, tailpipe) together. I guess I could make a round chill bar that is exactly the right size to fit snugly but there's got to be an easier way.

Thanks

larry cottrill · Post by **larry cottrill** » Fri Mar 26, 2004 3:59 am

Captain -

I only have experience oxyacetylene welding it, but it seems to me that one important characteristic applies to both methods, so please hear me out, take it with a grain of salt, and see if it seems reasonable:

The number one problem with welding stainless is preventing oxidation from the air. The number two problem is that stainless conducts heat unbelievably POORLY. What that means to me is that I need to set up a MUCH SMALLER flame to weld a given thickness of stainless as compared to steel, even thought the metal has to be significantly hotter to weld! This difference is really quite striking, not at all something trivial that can be overlooked.

I think for you it would mean using much lower current than you would set up for steel. I would try 20, 25 or perhaps even 33 percent less than you would expect to need and see how it goes.

With the oxy torch, what you find is that the small flame does take longer to get the metal up to fusion temperature, but once you have a puddle, you can move it right along just as if a bigger flame were used with steel of the same thickness. It's really quite surprising until you get used to it.

An associated difficulty is the heat buckling of two pieces you're trying to weld edge-to-edge: One will usually puff upward more than the other, creating a serious misalignment. Again, it's because the heat just refuses to flow out away from the weld zone very rapidly. You have to learn to quickly adjust the center of your heat more onto the cooler side to bring it up level.

Bruce Simpson pointed out one time that there is a lot smaller heat affected zone with heliarc than with the oxy torch, so these effects shouldn't be as great. They still exist however, as my Dad would testify if he were here [with thousands of hours of heliarc experience]. The poor thermal flow of the metal is just something you have to learn to deal with, and only experience can make you really proficient.

Experiment with your heats and let me know if this seems to make a difference, or if I'm just muddying the waters.

L Cottrill

Capt Ahab · Post by **Capt Ahab** » Fri Mar 26, 2004 4:52 am

Larry,

Thanks for your reply. I certainly understand what you are saying. I wish I could turn down the heat but I'm already as low as I can go and sustain an arc. It works quite well if I'm welding a bead in the middle of the piece but the stainless just won't conduct the heat away well enough when welding on the edge. There's only one direction for it to go instead of two. Perhaps I need to make some modifications to my homemade welder to allow it to work at a smaller amperage. I don't even know what amperage I'm working at since I don't even have an ammeter on it.

I have an oxyacetylene rig. Can I weld it with that? I tried it before using a very carburizing flame and it sortof worked but was really ugly.

TIG does have a much smaller heat affected zone but it still causes warping issues. Sometimes I can start a nice bead butt welding two pieces together that are clamped to a chill bar. It usually starts out ok but then I start blowing holes in it after welding a few inches because the metal heats up and starts warping. The only way I've found to get around this is to clamp it really well, tack weld it in a bunch of places, and weld really fast. It might help if I stopped to let the piece cool off every 20 sec or so too.

Al Belli · Post by **Al Belli** » Fri Mar 26, 2004 1:18 pm

For .024" stainless, You want 20 Amps. with a travel rate of 21"/min.
Straight argon at 6 to 8 CFH flow, and .040" ceriated tungsten elctrode.
If You overlap the sheet at the joint, You can melt back the edge of
the sheet to get a filler rod effect, leaving the inside of the joint clear
of any melt through. For arc stability, I recommend continuous
high frequency as opposed to just using HF start.

Al Belli

larry cottrill · Post by **larry cottrill** » Fri Mar 26, 2004 5:32 pm

I have an oxyacetylene rig. Can I weld it with that? I tried it before using a very carburizing flame and it sortof worked but was really ugly.

TIG does have a much smaller heat affected zone but it still causes warping issues. Sometimes I can start a nice bead butt welding two pieces together that are clamped to a chill bar. It usually starts out ok but then I start blowing holes in it after welding a few inches because the metal heats up and starts warping. The only way I've found to get around this is to clamp it really well, tack weld it in a bunch of places, and weld really fast. It might help if I stopped to let the piece cool off every 20 sec or so too.

Sounds like Al Belli has the scoop on this one. His post sounded just like something my Dad would have said.

To oxy weld it, you've got to have the smallest possible tip ans run fairly low pressures so you can adjust it very finely. Yes, you need a SLIGHTLY carburizing flame to do it -- excess oxygen is death. You also need a good high-temperature flux all over the BACK surface of every area you're welding [unless you can bathe the zone in helium or argon - but then, you might as well use your electric rig!]. The flux I have is called Chromalloy, and had to be special ordered at a good welding shop, at a mere $15US for a 1lb can! [Of course, that quantity should last longer than the remaining lifetime I have available to use it.] My torch is nothing fancy, just a good old Victor rig the same as used in any small aircraft repair shop, but the whole thing is supposed to be a lot easier with those nifty modern ones [can't remember what they're called, but I think it was mentioned earlier in the thread, or in some recent post here somewhere].

It can be done -- my Dad would have sided with Al, though. The heliarc process is undoubtedly much more efficient and satisfactory once you get the hang of it.

In the picture of Cyclodyne parts, the welds holding the flanges [hidden by the big clamp around the nozzle throat] to the narrow ends of the cones are my first acetylene welds of stainless -- you can't see much, though, other than the burned-on flux, like a thin coating of black glass.

L Cottrill

Al Belli · Post by **Al Belli** » Fri Mar 26, 2004 7:59 pm

The torch Larry mentioned is the Henrob.

Expensive, but fantastic.

Go to: http://www.thetorchman.com/ fro more info. and some
nice pictures of typical welds.

Al Belli

Post by **Mike Everman** » Fri Mar 26, 2004 10:12 pm

I just bought a Henrob, it's sweet, but my first experience with welding, so it's slow going. Guages are not so good, and 4psi on both is critical, so I may invest in the precision guages for it.
Have you used one, Al?

Raymond G · Post by **Raymond G** » Fri Mar 26, 2004 11:28 pm

For .024" stainless, You want 20 Amps. with a travel rate of 21"/min.
Straight argon at 6 to 8 CFH flow, and .040" ceriated tungsten elctrode.

Wow! I can't get any kind of welding done on such thin sheet with such a big electrode/amperage. I use .020 thoriated electrode and 5-10 amps on my Lincoln Squarewave 175. Welds .020 316 SS real nice. If I pulse the pedal, hold my breath, and say a prayer to Quanyin, I can weld .012 SS...for about 2 inches. But with .020-.024, you can get pretty close to the edge. Just slowly back off the foot pedal as you approach the edge. You can tell. when you see the heat affected zone (HAZ) start to grow larger as you approach the edge, that's when you start backing off the pedal. Try to keep the HAZ the same size, or even shrink it a little at the edge. You've got to use the pedal and small electrode on the thin stuff, and keep the metal perfectly aligned. Hope this helps.

Raymond

Al Belli · Post by **Al Belli** » Sat Mar 27, 2004 12:44 am

The parameters I listed are for a rectified sinewave, DC power source.
My welder is home brew and takes a 40 Amp. AC input @ 80 volts,
rectifies to DC and superimposes the HF using the typical spark gap
circuit and a coupling coil. Current control is totally adjustable, resistively. I have an analog DC ammeter at the output to the torch, which allows Me to monitor the current constantly.
I have verified the parameters with a welding applications engineer at the
Lincoln Electric Co. 888-921-9353.
.040 ceriated tungsten ( pointed ) is rated for 15 to 40 Amps., and if properly pointed, will do an excellent job on .024" stainless.
Starting is easy, and electrode life is excellent.
I prefer the ceriated tungsten over the thoriated tungsten, since the
cerium gives a higher electron emission and a more stable arc.
Your squarewave power source is apparently producing a higher
total heat output over a time integrated interval, allowing You to
operate at a lower current rating. Al Belli

sparks · Post by **sparks** » Sat Mar 27, 2004 2:06 am

Yes, when oxy/axcetylenwelding stainless its very important to use a flame that almost leaves a soot-trace.

Capt Ahab · Post by **Capt Ahab** » Sat Mar 27, 2004 3:17 am

I just received some .020" 2% thoriated tungstens that I ordered a couple of weeks ago before I knew about this forum. I'd like to give the ceriated stuff a try but I'll have to order it since no one around here carries it. I just gave it a try and I'm greatly encouraged by the results. I was able to weld a seam in some tubing I rolled even better than before. I can finally get the heat down to the level needed to weld this stuff without the use of a chill bar. I used Solar Flux to back up the weld. Does Solar Flux work with oxyacetylene? I don't see why it wouldn't. I still haven't tried welding circular tubes together yet. I need to make up some new ones to practice on.

Raymond, I 'll try the techniques you mentioned about the pedal too. I probably need to make some mods to the pedal too since it is a home brew as well. It's the first thing I made with my TIG welder. It works ok but it's really easy to back off too far and extinguish the arc if your not careful. I usually find myself starting the arc, backing off slightly, and then leaving it alone. Maybe I could put some stops on the pedal to allow me to pulse it back and forth without putting out the arc. Hmmm, I'll give it a try.

Al, I'd really be interested in learning the specifics of your home brew welder. Mine is a 90 amp alternator turned by a 1hp electric motor. The field is controlled by a 12V battery charger with a couple of dimmer switches. One on the welder and one in a homemade foot pedal. I would like to add HF but I haven't figured out how to do it yet. I tried using parts from my pulsejet ignition system which is an automotive coil and it works as long as the alternator isn't hooked up which is, of course, useless. With the alternator hooked up the high voltage from the coil shorts through the alternator. I guess I need some high voltage/high current diodes or something to keep this from happening. Could you point me in the right direction here? Also, could I re-invert the output of the alternator to get AC for aluminum? I came up with a circuit that I think would do this using 4 transistors but they would have to be capable of handling a really high current. What are your thoughts on this?

For anyone else that is interested in building your own TIG welder, I'd be happy to elaborate. It's really simple and mine works far beyond my expectations. It works much better than my oxyacetylene rig or my store bought MIG welder. I've had as much fun messing with it as I've had building jet engines.

tufty · Post by **tufty** » Sat Mar 27, 2004 11:37 am

Capt Ahab wrote:For anyone else that is interested in building your own TIG welder, I'd be happy to elaborate.

Please do. I'm sure I'm not the only one who'd be interested.

Al Belli · Post by **Al Belli** » Sat Mar 27, 2004 4:48 pm

The following diagrams show the essential circuitry that I used to build My homebrew TIG welder.
All electronic parts are available from www.hosfelt.com
The ignition transformer is P/N 2e507 from http://www.grainger.com/Grainger/wwg/start.shtml
Please note that the resistors are made from lower wattage units that are placed in series/parallel arrays to achieve the power handling capacity.

Capt Ahab · Post by **Capt Ahab** » Sun Mar 28, 2004 5:42 am

Al, Thanks for the diagrams. I'm looking to try to adapt your HF system to my welder. I see why yours works where my first idea didn't. It has the HF system inducing a current via a transformer of sorts in series whereas mine just had the HF system in parallel which just shorted through the power source. There is one part I don't quite understand, however. That is the coil arrangement between the spark gap circuit and the welder circuit. I don't quite understand your notation. It looks like 6 turns of wire around a 1/4" copper pipe but what does 2 1/4" phi form mean? What is the physical relationship between the two coils? Are they parallel to one another, concentric, or what? What gauge wire did you use here? Also, what is your initial power source; an AC welder?

Thanks again.

Al Belli · Post by **Al Belli** » Sun Mar 28, 2004 3:33 pm

Hi,
The coils are mounted concetrically ( the small inside the large )
The inner coil is made from 1/8" copper tube wound around a 1 1/4"
form; the outer coil is made from 1/4" copper tube wound around a
2 1/4" form. The inner coil can be made from heavy copper wire
#8 or #10. I used tube since I had it in stock.

See attachments.

Al Belli

www.pulse-jets.com