The very first thing you would want to know about sheet metal is that its ratio of surface area to volume is very high. Many people confuse sheet metal with plate metal. While both may look similar to the untrained eye, they are very different. The thickness of sheet metal is 1/4 inch or less, while plate metal is more than 1/4 inch in thickness.
While sheet metal is used to manufacture automobile bodies, roofing, airplane wings, beverage cans and the like, plate metal is used to make boilers, bridges, ships, turbines and so on. Plate metal is used for larger parts. While some manufacturing processes used for sheet metal work also can be used with plate metal, generally plate metal requires specialized tools and processes.
Cutting, bending and deep drawing are the main kinds of sheet metal working.
Sheet metal operations are typically performed on a metal press brake using dies and punches. This is perhaps the most economical method when it comes to forming of sheet metal.
Before designing a punch and die set, understanding the mechanics of sheet metal deformation is vital. Without a very good understanding of how this behaves, it will be impossible to produce parts to accurate tolerances and specifications.
Metals such as brass, aluminum, copper, stainless steel, nickel and tin are perhaps the most commonly used ones for making sheet metal. That said, gold, silver, titanium and platinum are also used.
It would be vital to have an excellent understanding of how a given material behaves under stress, how it deforms, and so on. Typically, you would want the material to undergo significant plastic deformation before necking. Localized necking is to be avoided. You would also want to take care to avoid uneven elongation which some materials like low carbon steels are prone to. This can lead to poor surface finish and other unacceptable parameters.
In short, you would need to have an extremely good understanding of how a given material behaves under stress. And different materials can exhibit very different behaviors.
In addition to having a good understanding of how a particular material behaves under stress, you would also want to conduct tests on samples before you start working on a given lot of raw material. You would want to conduct tests to verify raw material composition, tension tests, cupping test and any other tests that may be required. These tests would give you a much better understanding of the raw material.