To bend sheet metal, you must apply enough force to exceed the metal’s yield strength. There are multiple methods of bending sheet metal. V-bending is the most common method using a punch and die. Its subgroups ‘bottoming’ and ‘air bending account for the majority of metal bending work. Bottoming is when the punch presses a metal sheet onto the surface of the die. The finished metal piece angle will mirror the angle of the die. Air bending is similar to the bottom, except the punch does not press the metal into the die. This means that the sheet metal’s final angle does not depend on the angle of the die but on how far down the punch presses. If you have a 90º die, you can get any result between 180 º and 90º.