Influence of coined-bead die on spring-back characteristics in V-die bending process using the finite element method

The coined-bead technique is an effective approach for controlling the spring-back characteristics involved in sheet-metal bending. Most previous studies have focused on the application of the coined-bead punch. In this application, bead marks are commonly formed on the inner radii of the bent components. To ensure the precision of the inner bent radius, a coined-bead die can be employed. However, information and data pertaining to coined-bead die applications are currently lacking. In the present research, the influences of the coined-bead die on the spring-back characteristics during V-die bending are investigated for aluminium alloy sheets (AA1100-O), by using the finite element method (FEM) and related physical experiments. Based on material flow and stress distribution analyses, it is found that the bending mechanism of coined-bead die application (particularly in the coining stage) is different from that of coined-bead punch application. Moreover, an increase in the punch radius-to-workpiece thickness ratio and decreases in the bend angle and coined-bead width result in increased spring-back characteristics. It is revealed that the coined-bead die can be applied to prevent spring-back characteristics and the bead mark at the inner radius. However, it was also noted that the V-shape parameters should be carefully considered for coined-bead applications. In addition, it is recommended that the width of the coined-bead die should be larger than that of the coined-bead punch.