Effects of Material Properties and Punch Tip Radius on Spring-Forward in 90° V Bending Processes

Bending process is one of the most significant fields of application of sheet metal die. Sheet metals are exposed to some spring-back or spring-forward depending on elastic deformation following bending process. S235JR (1.0038) materials having a thickness of 4 mm were bent with 90° punches having 5 different tip radiuses. The bending process was carried out by making the punch waited on the material for 30 s (30 s wait bending) and by removing the punch without waiting (direct bending). Specimens were prepared in three forms as non-heat-treated, normalized and tempered. At the same time, all experiments were performed at a deformation speed of 25 mm/min. As a result, it was determined that as punch tip radius increased, the amount of spring-forward decreased. Although normalizing process applied to specimens increased the amount of spring-forward, tempering process decreased it. The amount of spring-forward was decreased in 30 s wait bending process.