Finite element analysis of springback in L-bending of sheet metal

1. Finite element analysis of springback in L-bending of sheet metal Y.E. Ling H.P. Lee B.T. Cheok 7 February 2007 A Presentation by: Rose Wieland

2. Overview • Introduction • Set up • Effects of Die Clearance • Effects of Step Size • Conclusion/Recommendations

3. Introduction • Increasing demand for tight tolerances • Springback is biggest problem to tolerances • FEM models allow for effect of die clearance, die radii, and step size to be analyzed • Idea of how to minimize springback

5. History • 1958 – first mathematical model for springback corrections • 1991/1992 – FEM models used to analyze springback • Never in the paper is the accuracy of FEM models versus real experimental data discussed!

6. FEM Model • Die, punch, and pressure pad rigid • Workpiece is a deformable mesh • Die step height, step distance, die clearance, and die radii varied • Material used : AL2024-T3

7. Effects of Die Clearance

8. Bend Leg analysis Bend leg curves between clearances of 1t and 0.8 t with maximum between 0.9 t and 0.95 t Otherwise, bend leg remains strait

9. Stress Analysis

10. Effects of Die Radius • K = springback factor • A = bend angle after springback • A1= bend angle during bending Springback factor of 1 most desirable

11. Effects of Step Height and Distance

12. Design Recommendations • Die radius, clearance, and step height and distance all effect springback • Die radius and clearance have greatest effect • Effects are exclusive and additive i.e. die radius = 2.0t die clearance = 0.75t; step height = 0.2t step distance = 0t. springback reduction for die radius 2.0t and die clearance 0.75t is 1.37◦ springback reduction for using a step height of 0.2t and step distance 0t at that die radius and clearance is 1.08◦ The total springback reduction is 1.37◦ + 1.08◦ = 2.45◦ (values from Table 2 and Table 3)

13. Beware bend leg elongation

14. Accounting for Elongation • Radius most important factor to elongation • Bend leg elongation only happens at clearance less than the thickness • Step height and step distance do not alter bend allowances significantly

15. Conclusion • Established trends for effect of die clearance, die radius, step height and distance • Need for research with other materials • This research took 1000+ hours • Perhaps small samples of other materials could be tested to show trends

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