Air bending involves pressing sheet metal using a punch into a bottom mold called a die. Sheet metal bending by air bending is possible because of the low tonnage of metal required. The bottom die does not need to have the same radius of the punch. The tools used can be adjusted and air bending offers greater flexibility than other forms of bending. Air bending requires less bend force than other forms of bending. Air bending has its limitations and does not guarantee accurate results. Sheet metal of different thickness can be bent into a range of shapes by using air bending.
Bottom bending popularly known as bottoming forms V bends on sheet metal. The punch forces sheet metal against the V opening of the bottom die. Bottom bending requires five times the force used by air bending and offers greater accuracy in sheet metal bending than air bending. Bottom bending requires different sets of tools for different angles of bends and for different thicknesses of sheet metal. This makes the bottom bending process more cumbersome than air bending. Bottom bending lacks the flexibility of air bending.
The coining bend process involves pressing metal into the bottom die with a bend force of 5 to 30 times that of an air bend. This force causes permanent shaping of the metal sheet. Coining offers the highest precision among bend processes. The high cost of coining makes it a less popular method compared to air bending.
Rotary bending does not require a punch to press metal into shape and uses a rocker to press metal into the bottom die. The rocker is a freely rotating cylinder and rotates as the press forms shapes on the metal sheet. Rotary bending makes angles greater than 90 degrees in a single press.