Sheet metal bending or press brake forming, is a metal forming process that produce plastic deformation over an axis. Bending usually don’t generate change in the thickness of the sheet metal. In industry this process is used to impart strength and stiffness to sheet metal, to change part's moment of inertia or to improve products appearance.
To carry out this process is often used a punch and a die. Punch and die more common materials are gray iron and carbon steel. To apply necessary force a press is needed. The punch, die and press assembly is called press-brake.
This deformation cause tensile and compressive stress within the material. But deformation are not completely plastic, all metals have an elastic region and when the force goes down an effect called springback occurs. Springback is the partial recovery of the work from the bend to its geometry before the bending force was applied. To eliminate springback and get the desired angle commonly two methods are used:
Overbending: The amount of springback is calculated and the sheet metal is over bent this quantity.
Bottoming the punch: elimination of springback is by plastically deforming the material in the bend region by applying additional force through the tip of the punch after completion of bending.
Stretch forming: Subjecting the workpieceto tensile stress while bending will force the elastic region to be plastically deformed. Thismethod is not allowed to sharp angles.