[Agoo]

I am a new bee in welding and trying to learn and make a stainless steel bellows. It contains 4 circular 0.2 mm thick and 15 cm diameter with a circular 5 cm diameter cut (hole) at the centre. These sheet have to be edge welded from outside and inside to make a circular bellows and has to be 10^-8 mbar vacuum tight. Anyone can suggest what type of machine (Tig? AC/DC? Pulse? frequency? ...) is the best for this purpose?

[weldin mike 27]

Hey,

Me thinks you are trying to fly to space when leaning how to make kindergarten paper planes.

No offence, but this welding is Way beyond the skill of most of the welders in industry let alone a newb. Besides its probably welded with a laser or an electron beam welder.

Sorry to be the harbinger of bad news.

Mick

[Otto Nobedder]

Welcome on, Agoo,

I do high-vacuum welds all the time, and TIG is the only option available that "MAY" do what you want. This will require a machine that is very stable in the 2-10 Amp range, and you will not be using a filler rod. You'll simply be using very low power to fuse the edges.

Our machines at work are barely stable at 10A, so I can't do those welds. I've attempted repairs on 0.2mm with limited success.

You will be wanting a high-quality inverter machine for this work.

Look at the next to last post (at the moment... near the end of page three), where member "dsmabe" has fused two razor-blades without filler. This is what you're looking for.

http://forum.weldingtipsandtricks.com/v ... 9&start=20

Steve S

[Rick_H]

Steve is right on point...tough weld for a beginner. I've also done this type of work right now I use a Miller Maxstar 150 sth with. 040 tungsten, gas lens, I've been successful with a good start at 5 amps

[Agoo]

Close inspection indicates welder used the attached trick not to let 0.2 mm sheet to melt. Actually torch aims at the steel plate and the melt flow towards 0.2 mm sheet and welding take place. This way I think I need a much higher amperage to melt the steel plate. right?

[TRACKRANGER]

Close inspection indicates welder used the attached trick not to let 0.2 mm sheet to melt. Actually torch aims at the steel plate and the melt flow towards 0.2 mm sheet and welding take place. This way I think I need a much higher amperage to melt the steel plate. right?

On the drawing you show where the torch aims but not where the intended weld join is. Could you highlight that too?

Frankly I'm not confident with that approach. I don't know how you'll get the necessary precision focus of the arc.

Your updated drawing will help me understand.

Thanks

Ranger

[Agoo]

This is how it is in the original welding. I meant torch should not aim at the 0.2 mm sheet otherwise it may melt. Right?
I haven't done even a single weld yet but this much I understand from what I have learned so far from close inspection of the original part. Most people I talked to they said this weld in impossible or very difficult and it needs fixture which will cost lot more than the cost of the welding itself. I want to have expert opinion here where or not this weld could be done manually without fixture?
It needs to be vacuum (10^-8 mbar) tight not look nice or whatever.
From what I saw from videos it shouldn't be that difficult and it is possible as far as I use low amperage, AC machine and proper tungsten wire and proper lens. Right? I need as much advice as possible and need to see videos close to my case.

[TRACKRANGER]

This is how it is in the original welding.

Does that mean you are going to TIG weld the 0.2mm (0.008") stainless to the stainless steel plate, with relevant sizes similar to what is shown in the drawing?

Are you sure it's a TIG Weld, and not perhaps something like Silver Soldering / sweating the two parts together?

[dsmabe]

I actually missed part of the razor blades in the picture I took, 5 amps blew away some material until I could get moving.
If your wanting to weld that thin material to thicker material, and it being stainless, I'd say mock up the joint and practice alot!
I may have overlooked it but how thick is the material that the .2mm sheet is going to be welded/fused to?
You definitely will have to point the tig torch toward the thicker material. Depending on the thickness, that may be a easier weld than it sounds like at first.
Again like another member said though, if you are first starting out, this is a weld that is most likely beyond what you are going to be capable of without some practice.

[MinnesotaDave]

I haven't done even a single weld yet...

From what I saw from videos it shouldn't be that difficult....

Truthfully not trying to be offensive - but your statements remind me of the Dunning-Kruger effect.
Your really don't know, what you don't know.

http://en.wikipedia.org/wiki/Dunning%E2 ... ger_effect

[Agoo]

I understand. Sure I will need a lot of practicing before I can get any reasonable welding. In the future I will need this sort of welding a lot so I thought probably that is a good idea to learn and practice this myself.

Plate I intend to solder the 0.2 mm sheet is about 1 cm thick. I have two method in my mind (attached photo). Method at the left and method at the right. Both is possible. It remains which is better and easier? Please let me know which one you prefer to do and why.

Also I have following questions:

1- Do I need AC or Dc machine?
2- Do I need Pulsed or continues?
3- Is 0.8 mm tungsten ok?
4- TIG or PLASMA or ?
5- what else do I need to consider?

Agoo

[noddybrian]

This post is getting really good ! I never tried welding that thin but I know what a pain it's going to be from say .5mm that I have done - machine will influence the results as mine & many others are not stable this low - but even if the machine is capable - to keep a tight arc length at that power is beyond most guys just starting Tig - you have to admire the confidence though - I can't help thinking the original is not hand welded - maybe some sort of automated process or even a continuous resistance weld like fuel tank seams often are - perhaps someone should consult a " world renowned Tig expert " on this job !- if not I guess it's just needs a redneck - " how hard can it be - hold my beer & watch this ! )

All joking aside - good luck to the OP - I hope you do have success & we will all be interested to see the results if you manage it.

[Leejohnson1313]

30+ years ago, I was the engineer on a project requiring a similar configuration bellows for a high hermeticity (low leak rate) weld. We ended up successfully producing parts with an autogenous electron beam weld similar to the config shown by Agoo on the left of his post of Thu Sep 25, 2014 11:17 am. Our config was an approx.2.5 inch diameter bellows edge that was level with the top surface of the plate & as near to zero radial clearance as we could manage. I recall the bellows was about 0.3 mm thick, EDM'd to final dimension from solid Kovar plate (low thermal coefficient of expansion iron-nickel-cobalt alloy). The piece it was welded to was also Kovar.

Our successful leak rates (not every try succeeded, but pass rate was 75% or better) were in the range of 10-8 atmospheric-cc/sec Helium.

I, too, will be very interested to see how Agoo proceeds & what results he achieves.

Lee

[dsmabe]

20140922_122122.jpg (43.34 KiB) Viewed 2120 times

The first example with just a notch in it would probably be the best bet. It should allow efficient heat soak allowing the greatest chance of success. You are looking at the tig process, plasma is for cutting. The smallest tungsten possible will help with the low amperage start. I used 3/32 welding these razor blades and my machine only goes down to 5 amp. But where you are welding something so thin to technically plate material, 5-7 amps could probably be used with a correct torch angle to make a good weld.

Machine settings I would try this at;
Foot pedal control with a maximum of 10 amps
DC
Gas lens torch
1/16 or smaller tungsten (smaller the better in this weld) I use a e3, but find out what is going to work the best with the machine you decide to use
As for machines (tig welders), what do you plan to use it for now and in the future?
If you plan to only do steel, stainless, etc. then a dc only machine would be fine. If you think there is ever a chance of needing to weld aluminum, then you need a ac/dc machine with high frequency start. Your best bet is also a inverter based machine which means stay away from pure tungsten, most inverters are not recommended to use pure tungsten.

[kiwi2wheels]

My 0.02c to consider would be to machine a thin wall adapter sleeve with a raised ( 0.3-0.4 high ) rib, maybe 0.4 -.0.5 wide and fuse the rib to the bellows. If the sleeve is a tight fit in the bellows ID, it will act as a heat sink and you could then weld the sleeve to the body /whatever. Weld a short distance and alternate sides. And experiment a lot !!

I did a similar thing with convoluted 321 bellows, but the material thickness was probably .032" which made it a bit easier.

You will have fun........

[Otto Nobedder]

Actually, I find Agoo's drawing very workable.

I've not tried this as an "original build", but only as a repair, where that excess metal is already used up. The idea of fusing a built-up ring to the .02mm makes perfect sense.

However, I'd have my torch angle at 90*, or even pointed back to the heavy material, focused .08mm to 1.0mm away from the edge of the 0.2 material, and allow the puddle to trail my arc and make the fusion. I've done this on somewhat thicker material with good success.

Steve S

[dsmabe]

I just was figuring the thickness in inches, is that thickness correct? .2mm = approximately .00078"

[Otto Nobedder]

0.039" Still unnaturally thin...

[dsmabe]

Screenshot_2014-09-26-21-09-02.png (89.88 KiB) Viewed 2105 times

[Otto Nobedder]

Yep, I did the math backward.

0.008 is correct.

Steve S

[dsmabe]

I was gonna say that was a easy weld if it was .039, i butt weld .032 @ work from time to time.
We have some .005 shims @ work, I might try welding it to some thicker steel tomorrow, I'll try to take pictures of how it turns out. Granted it will be mild steel and on a transformer machine, and 1/8 tungsten, so not quite apples to apples comparison.

[Agoo]

MEWASA is one of the company makes these kind of bellows. Here (http://www.youtube.com/watch?v=ArTXGU-oED4) shows a video of a TIG automatic machine welds this kind of bellows nicely but I think it could be done by hand too. It might not come up as nice but as long as it is vacuum tight I wouldn't mind.

[Oscar]

I understand. Sure I will need a lot of practicing before I can get any reasonable welding. In the future I will need this sort of welding a lot so I thought probably that is a good idea to learn and practice this myself.

more like YEARS of UNRELENTING PRACTICE, lol. I mean, honestly, it's all in how bad you want it.

Also I have following questions:

1- Do I need AC or Dc machine?
2- Do I need Pulsed or continues?
3- Is 0.8 mm tungsten ok?
4- TIG or PLASMA or ?
5- what else do I need to consider?

Agoo

It looks as if you're trying to get ALL your knowledge from an internet forum. Rest assured there are plenty of qualified individuals here who could surely answer all your questions, but I think it would be a gesture of good faith if you would also do some very basic research, as some of those questions you should already know the answer to if you are really planning on doing this kind of welding.

One thing I will say though, IMO, you will need to be able to hold an extremely tight arc length, around 1/2 to 1/4 the thickness of the thinnest piece in order to not have to dump so much heat into the joint that the thin piece gets obliterated. Might be quite difficult to do, but then again, this is just what I have personally used when joining thin to thick, but no where near as thin as what you are trying to attempt.

[dsmabe]

From the original pictures and the video that was posted, I have a question. Are you only having to weld the .2mm material to the thicker material or do you also have to make .2mm to .2mm welds?

[awill4wd]

Another thing is that the machine welding shown in your video is actually plasma welding and I suspect the hand held welding is plasma welding as well. I just couldn't get a close enough look at the head of the hand held torch.
Regards Andrew from Oz.