Sheet metal form prototyping involves a wide range of processes that manufacture parts for a vast amount

of purposes.Sheet metal prototyping processes are characteristic in that the metal being processed 

is plastically deformed to shape it into a desired geometry.In order to plastically deform a metal,a powerful 

force must be applied that will exceed the yield strength of the material.When low amounts of stress are 

applied to a metal,it will change its geometry slightly,in correspondence to the force that is exerted. 

Think of stretching a rubber band,then releasing it,it will go back to its original shape.This is called elastic 

deformation.Once the stress on a metal increases past a certain point,it no longer deforms elastically,

but starts to undergo plastic deformation.In plastic deformation,the geometric change in the material is no 

longer directly proportional to stress and geometric changes remain after the stress is released;meaning

that the material does not recover its shape.The actual level of stress applied to a metal where elastic 

deformation turns to plastic deformation is called the proportional limit,and is often difficult to determine 

exactly.