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

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

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

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!

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

Effects of Die Clearance

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

Stress Analysis

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

Effects of Step Height and Distance

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)

Beware bend leg elongation

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

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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