Hi,
Area of the cylinder = Pi * R * RE= Pi * 2.5 * 2.5 = 19.63 sq ins (YUCK, SI rules )
Air pressure = 100 Psi
So force from air pressure = Psi * Area = 100 * 19.63 = 1963 lbs (YUCK, SI rules)
As your application relies on pressure on the work area, you will need to make sure your controller has current limit control to allow for the stalled stepper when your die comes in contact with the foil to apply the stamping force.
Unfortunately this is quite easy to do with air application, but an electronic servo/actuator solution is a bit more involved.
You may need to spring mount the die that you press down with, and get the servo/actuator to stop at a position where the die has contacted the foil and the spring is applying the pressure.
Just a thought, hope it makes sense.
Tom.. 
