Finite Element Analysis on V-Die Bending Process

Abstract

FEM simulation was applied to investigate the spring-back and spring-go phenomena in a V-die bending process and to investigate the effects of process parameters, including radius and height of the punch. The FEM-simulation results were validated by laboratory experiments. The FEM-simulation results showed that the spring-back and spring-go phenomena could be theoretically elucidated based on material-flow - and stressdistribution analyses. The generation of an S-curve-shaped material-flow feature caused the reversal of stress distribution on the leg of the workpiece. This reverse-stress distribution that the tensile and compressive stresses generated on the punch and die sides, respectively, resulted in a reverse-bending zone on the leg of the workpiece, and the leg of the workpiece tried to move slightly closer to the punch. After compensating the whole stress in the workpiece, the spring-go phenomenon was clearly explained when the stress generated in the reverse-bending zone overcame the stress generated in the bend-allowance zone. In contrast, the spring-back was established when the stress generated in the bend-allowance zone suppressed the stress generated in the reverse-bending zone. In addition to clearly understanding the process, the parameters affecting the spring-back and spring-go features were investigated. The FEM-simulation results illustrated that the radius and height of the punch significantly affected the spring-back and spring-go processes, in addition to the bending angle obtained. The punch radius affected the material flow. Specifically, the Scurve-shaped material flow was stronger as the punch radius decreased. This S-curveshaped material flow resulted in reverse-stress distribution and the reverse-bending zone in the leg of the workpiece, which affected the spring-back and spring-go phenomena. The reverse-stress distribution and reverse-bending zone increased as the punch radius decreased. Therefore, the amount of spring-go decreased as the punch radius increased, whereas the amount of spring-back increased as the punch radius increased. The FEMsimulation results also illustrated that the effects of the punch height could be theoretically explained on the basis of material-flow and stress-distribution analyses. The application of a very small punch height caused a large gap formation between the leg of the workpiece and the die’s side; in addition, a small reverse-bending zone was generated. In contrast, the application of a very large punch height caused a large reverse-bending zone but no gap formation between the leg of the workpiece and the die side. After compensating the whole stress distribution on the workpiece, the effect of the spring-back generated in the bendallowance zone was not sufficient to overcome the large gap and the reverse-bending zone; therefore, the spring-go effect was generated, in which the bending angle obtained was smaller than the required bending angle in both the cases of application of very small and very large punch heights. However, if the spring-back generation on the bend-allowance zone could suppress the gap between the leg of the workpiece and the die’s side, and the reverse-bending zone, spring-back was generated, in which the obtained bending angle was larger than the required bending angle. Therefore, suitable process parameters must be strictly considered to achieve the required bending angle by balancing (i) the compensation of the gap between the leg of the workpiece and the die side, and the stress distribution on the reverse-bending zone and (ii) the stress distribution on the bend-allowance zone. The FEM-simulation results were validated by laboratory experiments. The FEM-simulation results showed a good agreement with those obtained by the experiments in terms of the bending force and bending angle. These results indicated that FEM simulation could be used as a tool for the theoretical elucidation of the mechanisms of the spring-back and