Note that new high-strength steels have a greater amount of springback as compared to basic mild steels, general grades of stainless, and many aluminums. However, springback increases dramatically as the inside radius of the bend increases in relationship to the material thickness. In common materials, if the material thickness and the inside radius are equal, the springback is usually 2 degrees or less in common material types. The amount of springback that occurs is a property of the material and radius. During air forming the workpiece springs back slightly when released from pressure, as it attempts to return to its original shape. The air forming zone shows that when the press brake exerts pressure on the sheet, the metal begins to bend. When enough force/penetration is applied, the material reaches its yield point, and permanent deformation of the metal begins to occur. The elastic zone is where the material is moved but not bent when the stress is released, the material returns to its original shape without any permanent deformation. (see Figure 2).įigure 3 shows how stress-strain properties are affected by the three different bending methods: air forming, bottom bending, and coining. The compressive forces are less than the tensile forces on the outside of the bend, and this causes the material to try to return to its flat position. As the material is bent, the inner region of the bend is compressed while the outer region is stretched, so the molecular density is greater on the inside of the bend than on the outer surface. The first has to do with displacement of molecules within the material, and the second has to do with stress and strain. Why exactly does springback occur? There are two reasons. Efficiently predicting and accounting for springback are critical, especially when working with profound-radius bends, as well as thick and high-strength material. The tensile strength and thickness of the material, type of tooling, and the type of bending all greatly influence springback.
Overbending to the bending angle allows the desired bent angle to be attained when the part is released from pressure (see Figure 1). When fabricating on the press brake, an operator will overbend to the bending angle, which is angularly past the required bent angle, compensating for the springback. Springback occurs when the material angularly tries to return to its original shape after being bent. To a press brake operator, a bending angle is different from a bent angle, and it all has to do with that ever-present forming variable: springback. So that the metal springs back to the desired bent angle. The bendingĪngle is the beginning angle to which the operator overbends Springback is ever-present in sheet metal forming.
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