Ductile Metal That Holds Its Shape?

[ajensen]

I'm selecting a metal material for a project in which the metal needs to be ductile (high plasticity) in order to hand-form minor bends, yet rigid enough once formed to hold its shape when small loads (~ 1 lb)are placed on the formed faces. The forming will happen often (perhaps a hundred times over the course of a few years), so it needs to be resistant to fatigue. The metal will be cut into strips roughly 1" x 4-6" x ___ thick (TBD based on ductility of metal, but probably between 1/16" and 3/16"). The bends will be 30-60 degrees with bend radii of 3/4" or greater.

Metals such as Gold, Lead, ,Copper and Aluminum should be ductile enough, but I haven't found much info regarding their resistance to fatigue when subjected to repeated forming of the magnitude described above. Beyond that, Gold is too expensive and lead is too heavy, which leaves only Copper and Aluminum. Does anyone know which would be more resistant to failure in fatigue? Or are there better candidates that I've overlooked?

 

[MikeHalloran]

Most any aluminum in the -0 temper should work.
As will lead.

Reconsider your fatigue life criteria. If you make it user-replaceable, you can tell the users to be careful and bend gently. ... and you can sell replacements.



Mike Halloran
Pembroke Pines, FL, USA

 

[ajensen]

Mike, thanks so much for the tip! And great idea about making it replaceable. For this particular application they'll be sealed off, though.

Do you think the -0 temper Al will hold up to the fatigue?

 

[MikeHalloran]

Whether the part will hold up will depend greatly on the bend radius and the number of cycles. Since you're relying on users to do the bending, you have no control over it.

Early models of Coulter Counter (r) used a small strip of lead to position a 222 lamp and holder so as to illuminate a small aperture that was observed with a microscope. Most of them lasted for the life of the instrument. ... but they were adjusted infrequently, the load was nowhere near 1lb, and they started out nominally flat.

That last characteristic, a flat blank with a few holes in it, may have contributed to longevity. You are asking a lot to expect a user to form a piece of metal to a specified radius, and get it right on the first, or tenth, try. Perhaps you can put the bend in some other part, and do it in a factory so you control it.



Mike Halloran
Pembroke Pines, FL, USA

 

[ajensen]

Thanks, Mike. I think you're right that I may be asking too much of this material. I'll get a hold of some Al and see how it behaves. Thanks again for your input.

 

[racookpe1978]

Doesn't copper stress harden quickly?

I'd like to see the boss's face when solid gold is recommended .. 8<)