Are you sure the stainless is magnetic? Some kinds are not.
Yes, it can be affected by the magnet. The TIG response will depend upon how close the arc is to the magnet.

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Are you sure the stainless is magnetic? Some kinds are not.

The most common type of stainless sheet is 304, which is non-magnetic. 400 series stainless are slightly magnetic.

 

Keep in mind, magnets are great for tacking multiple pieces together just enough to hold and remove the magnets with parts staying tacked up. Magnets don’t hold up too well to being overheated from welding. keep the tack welds and magnets far enough away from each other and arc blow should not be an issue.

 

Thanks for the info! My plan as it stands involves Using the magnets as a locating feature while welding. Maybe that's just a bad plan...

Before I give up on it completely though, how far would you say the arc has to be from the magnets to not be affected?

Thanks.

 

How large a finished part (weight?), and can all the joints be reached to weld them if everything is first tacked together? If so, could the old-style oil-based modelling clay be used to hold parts in position while tacking, if careful to not overheat any sections? Or maybe even some kind of tape?

 

Hi Oldiron2, thanks for the reply. We're looking at upwards of 560lbm (253kg). Of course not all that weight is supported by magnets in the current plan, but we think there'll still be a decent clamping load required (we're estimating 50lbf from some napkin calcs but not sure). It's also not possible to get C-clamps in there cause there's nowhere for the arm to go around.

I've never worked with this clay stuff. I tried looking it up and couldn't find much. Is it strong? Where can I get some if it is?

Thanks.

 

Magnets and TIG, especially TIG on sheet metal are an exercise is frustration. At high enough amperages the force of the arc can overcome nearby magnetism but at amperages suitable for sheet metal the magnet will affect the arc.

It'll be nothing but horrible Arc starts, ruined torch parts and an impossible to control weld puddle unless you get the magnets far enough away from the arc that the magnetic field doesn't mess with it. At that point the magnets aren't doing anything for you because they're so far away.

Better to use hard fixtures to setup and hold things. Blocks of aluminum/steel with square corners or even aluminum angle iron work pretty well for clamping sheet metal to. If you don't sandwich the part with a shim between the hard fixture and the clamps you can get weird bubbles in between clamping surfaces. I usually use ~1/8" thick 1" wide aluminum plate as the shim but you can use whatever to spread the clamping force out more.

 

Thanks for the answer dude. Not what I wanted to hear, but probably what I had to hear. Unfortunately, I can't get a C-Clamp in there because there's nowhere for the arm to go. Do you have any other ideas for getting two sheets (with curvature) to line up nicely?

Thanks.

 

@psacustomcreations Thanks for the answer! No, it's 304 or 316. The currrent plan is use electromganet on one side of sheet, with a permanent magnet on the other so they clamp together.

 

any chance of providing some photos of your set up so that we can get a feel for size and shapes and configuration?


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Hi Lis, thanks for engaging. I really wish I could, but it's proprietary. I understand that that limits the kinds of advice you can give.

 

Could you use this type of clamp?
https://www.amazon.com/Toolly-Pack-...et+Metal+Clamp&qid=1687277507&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

 

I'm familiar with the clamp idea, but don't have any such clamps. What is the joint width required to fit them in? 1/16", maybe .050"? If made with a thicker thru-piece, any reason it couldn't be thinned? Sounds promising.

Hi Oldiron2, thanks for the reply. We're looking at upwards of 560lbm (253kg). Of course not all that weight is supported by magnets in the current plan, but we think there'll still be a decent clamping load required (we're estimating 50lbf from some napkin calcs but not sure). It's also not possible to get C-clamps in there cause there's nowhere for the arm to go around.

I've never worked with this clay stuff. I tried looking it up and couldn't find much. Is it strong? Where can I get some if it is?

Thanks.

It is, I believe, just fine ceramic clay mixed with some kind of oil to make a plastic mass that can be molded into shapes. Used to be sold in boxes with four 'sticks', each a different color, but may have been replaced by modern "safer" crappy products. For something that size and weight, it probably wouldn't be suitable.

If the above sheetmetal clamp idea doesn't suit you, you could use blocks of wood to make multi-angle jigs, fitted to the edges of the metal near the joints, and use contact cement or something similar to adhere the metal to them. It would be strong but would require lots of time and work. Heat would likely be needed to remove them, once done tacking.

If your sections are big enough to have the magnets far from the edges, if the magnet pairs are strong enough to hold the parts, and if the magnets can be joined together securely enough to maintain multiple section positions accurately enough, I think it would work. Easy to test the idea with some similar pieces of material and same joint type.

How many of these devices are being made? Enough to justify building a multi-arm jig to hold all or most pieces at one time, so fitting the later/last sections in isn't a problem due to distortion or slippage?

Are these devices for use on earth or in space? What quality welds does it need; absolute perfection in all ways, or 'normal strength' only?


.

 

Keep magnets away from 20 ga stainless. I have had some really terrible outcomes from welding near magnets without knowing they were there. It was a food grade stainless chute , and I didn't know there was a set of rare earth magnets inside. Nothing welded, arc swirled around and would not focus, or puddle. By the time I reallized what was happening, I had several holes I had to repair.

Have you tried a longer clamp :

View attachment exlongvicegrip.JPG


I have found using aluminum backers to be the best method they also act as chill bars on thinner stainless. Holding together manually and "Flash Tacking" on the aluminum is my go to method. Jodie explains it well in this video, Hope this helps.

[video=youtube;mpAle-YFn_A]https://www.youtube.com/watch?v=mpAle-YFn_A[/video]

 

If you don't have a slip roller to make curve forms, you can just hand bend 11 ga. over something with a similar radius to the one you need. I often use a welding cylinder. If you have any larger aluminum pipe tube or duct, that can be fitted also. A few minutes fitting it up can save you time and material. Stainless is expensive, and unforgiving.

Will you be gas purging/shielding at all ?

Best of luck

 

At least give us rough dimensions and shape.
Curves, sharp angles, etc.
Are we looking at a 3 foot tall sculpture like this dog, or something dozens of feet wide?

Can you use a wooden or other material form on the inside and outside to keep the pieces in place. Leave gaps where the tack welds will be placed.

More info without giving away proprietary designs is still possible.

Less info means less desire to help or completely irrelevant suggestions.

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First off, that dog is really cool.

And yeah, the community here has been very helpful and this thread has grown a lot in scope from what I originally intended, which has been helpful. I've thought it over and there is some fairly easy info to give over.

The complexity of this part of the assembly is more in its size, material and weld method than in geometry. It's easy to draw, but not easy to weld. We have a circle of ~4-5ft diameter made from 4ft-wide sheet (~20 gauge, 304/316SS) that gets looped on itself and welded end-to-end, making a 4-5ft diameter, 4ft deep cylinder. We do that twice so we get two cylinders and then we have to weld them together to make an 8 foot cylinder.

The circumference weld has been my big headache, since we have to jig both circles to align perfectly (fusion weld w/ no filler) while the material isn't gonna want to keep its shape.

 

@Oldiron2,
I posted this before but it seems to have disappeared into the internet Never-Never Land. He might use Babbitt putty for the process you suggested it can withstand a bit of heat.

 

It's stickier than what I initially mentioned, but if his parts are large, heavy and unwieldy, I'm not sure it would hold well enough. Might be worth trying though. We're still guessing about most details

IMHO, the OP needs to comment better about previous suggestions such as the sheet metal clamps.

 

Yah without some decent details it is pretty hard to say but I am getting the idea that this is fairly large. You may have to make some specialized fixturing. If you made a few stands with a heavy base and then articulated arms with and end being the screw from a clamp or just threaded rod, then you could position them wherever needed, adjust them in 3D and place them opposite each other so they press against the sheet metal to clamp it. You might need a ton of weight on the bases, or else tie them together with a strap or something welded temporarily to the bases to hold them in place (together). Hard to describe but you didn't post any images either

Alright, here. I'm thinking something like a giant sized dial indicator stand with a long screw/threaded rod on the free end
View attachment 2023-06-20_21h10_53.jpg

If you can't reach around it with a clamp, you need a room sized clamp... And yeah this will not be trivial to create or use!

 

maybe a couple of contortionists with ppe and these suction cup lifters

i


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Haven't read any of the other comments yet... I use aluminum foil tape to hold parts in position for welding if I can't easily clamp something. The acrylic adhesive cleans up easily with acetone.

https://www.amazon.com/FSK-Foil-Scr...vqmt=e&hvbmt=be&hvdev=m&hvlocint=&hvlocphy=&hvtargid=pla-4584001436407508&psc=1

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The latching end clamp is a good idea too.

Hopefully the OP has a decent rotary positioner they can put it on otherwise the poor welder is going to be there for awhile on that circumferential.

I've done some development work on ~3ft diameter large length 0.040" thick Inconel and unless you have a roll planishing machine with a deep enough throat then plan on having to deal with the weld distortion. Especially at the start/stops. I lucked out with the parts I did, they got hydroformed after welding so the mismatch from weld distortion wasn't a big deal.

If you guys have to make them on the regular it's probably worth buying a longitudinal seam welder and/or a boom & column. I know companies have them for rent but I don't know what tooling or prices are like.