Thin Wall Tube Forming Limitation 1

[adock]

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Hi all,

I'm impressed by what's possible in thin wall tube forming but I'm concerned my current design isn't possible. I'm disconnected from the fabricator and I'm interested to know if this is possible before I go much further with it.

It's .039" wall, 1.5" OD, 304 SS

On the OD, I'd like to bend the tube back over itself to protect the threads (threads are formed, not shown correctly in image)

 

[EdStainless]

I don't know if you can cold back that tight and that far.
You will need to send it to them and see what the response is.
They may need to do this 305 (higher Ni, more formability, more $).

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P.E. Metallurgy, consulting work welcomed

 

[adock]

Interesting, thank you Ed

 

[GregLocock]

I'd be looking at the old aluminium (?) cigar tubes, they had rolled threads. I suppose you could form the threads, screw in a mandrel to protect them, and then do some bashing to get the fold back, but I don't think it'll be neat, you've stretched the 'disc' too much. You could just slip a second tube over the thread and loctite it.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[TugboatEng]

Also, you have chosen stainless steel. Is this to resist corrosion internally or externally? This geometry is a recipe for disaster for an externally corrosive environment.

 

[Sparweb]

Does it absolutely have to *fold* or can you freeze a sleeve over the tube instead?
If you're not familiar with what I mean, think in terms of differential thermal expansion. It's done frequently and rather easy to set up.

 

[Stress_Eng]

To get something to look like what you want, based on fabrication from one piece only, I think will look a bit messy. I can only think of cutting very thin slots every say 15 deg around the circumference, equal to the length of the outer sleeved section, and fold each piece 180 deg back on themselves. To make the folding easier, you could drill holes at the ends of each slot. Thing is, you’ll be left with numerous lengthwise slots butting up against each folded length. I guess you could stitch weld along the slots a few times, and clean up after. I think the easiest thing would be to put a sleeve over the outside and stitch weld where the fold would be, something like that.

 

[MintJulep]

I don't see anything that aggressive on the sites I posted on this thread.

thread404-512062

 

[adock]

Thanks all! This helps a lot, I will abandon this idea for a sleeve. It's an option, I was just noodling with the idea of doing it with a form as a cleaner and more economical option, sounds like that's not the case. Laser welding is used elsewhere on the assembly so that's an option. I'll have to look into 'freezing' the sleeves. Is this something that's done on large batch sizes?

The assembly is used in a medical environment and cleaned regularly with 70% IPA, that's the driver for the material choice

 

[EdStainless]

If these need to be hygienic then you do not want that sleeve.
That is a heck of a crevice that you cannot assure will get cleaned out.

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P.E. Metallurgy, consulting work welcomed