What is spring back?

In general, all materials have properties of elastic deformation (shape after deform is same as before deform) and plastic deformation (shape after deform isn’t same as before deform). Final deformation is elastic deformation or plastic deformation will depend on applied force and elastic recovery. In case of applied force is greater than elastic recovery, plastic deformation will occur. If applied force is smaller than elastic recovery, material will recover back to pre-deform shape, this is elastic deformation.

In bending process, this recovery phenomenon is known as spring back. Spring back will make final bend angle smaller and final bend radius larger than before spring back had affected. This is normal phenomenon that could take place not only in flat sheets or plates, but also in bending bars, rod and wire of any cross section. Factors that effected to spring back are bend radius and material thickness. The greater the bend radius, the greater the spring back effect. While the more material thickness is, the less spring back effect.

Resource : Kalpakjian, S., and S.R. Schmid, Manufacturing Process for Engineering Materials, Prentice Hall, 2003