I got myself some piezo speakers, just a round piezo element glued to substrate and two wires.
I want to stick them onto a plastic foil and see weather I can bend the foil. Sort of like a wing. How can I do that?
what is typical voltage & current applied to these things?
Not sure about number 1.
But with regard to 2, these units are normally used as input transducers or microphones rather than speakers. Being high impedance they take very little current but could take a high voltage. It all depends on the actual type you have bought. You really need a data sheet.
1) I want to stick them onto a plastic foil and see weather I can bend the foil. Sort of like a wing. How can I do that?
You probably can't - but it wouldn't hurt to try. From what I have read, piezo disks only "flex" in the sub-millimeter (very "sub") range. You could potentially try to stack them (epoxy the disks together?) to potentially gain more working "length"...
There do exist piezo actuators that "flex" more - and are used for short distance mechanical positioning - such as what this company supplies:
They aren't cheap!