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
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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

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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!

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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

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Effects of Die Clearance
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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
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Stress Analysis
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Effects of Die Radius

• K springback factor
• A bend angle after springback
• A1 bend angle during bending

Springback factor of 1 most desirable
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Effects of Step Height and Distance
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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)
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Beware bend leg elongation
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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

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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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References

• 1 A.G. Gardiner, The spring back of metals,
  Trans. ASME, J. Appl.Mech. 79 (1957) 19.
• 2 W. Johnson, T.X. Yu, Springback after the
  biaxial elastic-plastic pure bending of a
  rectangular plate I, Int. J. Mech. Sci. 23 (10)
  (1981)619630.
• 3 W. Johnson, T.X. Yu, On the range of
  applicability of results forthe springback of an
  elastic/perfectly plastic rectangular plate
  aftersubjecting it to biaxial pure bending II,
  Int. J. Mech. Sci. 23 (10)(1981) 631637.
• 4 R.A. Ayres, SHAPESET a process to reduce
  sidewall curl springbackin high-strength steel
  rails, J. Appl. Metalworking 3 (2) (1984)127172.
• 5 C. Wang, G. Kinzel, T. Altan, Mathematical
  modeling of planestrainbending of sheet and
  plate, J. Mater. Proc. Tech. 39 (3/4)(1993)
  279304.
• 6 Y.K.D.V. Prasad, S. Somasundaram,
  Mathematical model for bendallowance calculation
  in automated sheet-metal bending, J. Mater.
• Proc. Tech. 39 (3/4) (1993) 337356.7 D.K. Leu,
  A simplified approach for evaluating bendability
  andspringback in plastic bending of anisotropic
  sheet metals, J. Mater.Proc. Tech. 66 (1997)
  917.
• 8 J.C. Nagtegaal, L.M. Taylor, Comparison of
  implicit and explicitfinite element methods for
  analysis of sheet forming problems FESimulationof
  3-D Sheet Metal Forming Processes in
  AutomotiveIndustry, 894, VDI, Berichte, 1991, pp.
  705725.
• 9 A.P. Karafillis, M.C. Boyce, Tooling design
  in sheet metal formingusing springback
  calculations, J. Mech. Sci. 34 (1992) 113131.
• 10 H.B. Sim, M.C. Boyce, Finite element
  analyses of real time stabilitycontrol in sheet
  metal forming processes, ASME J. Eng.
  Mater.Technol. 114 (1992) 80188.
• 11 M.J. Finn, P.C. Galbraith, L. Wu, J.O.
  Hallquist, L. Lum, T.L. Lin,Use of a Coupled
  ExplicitImplicit Solver for Calculating
  SpringBack in Automotive Body Panels, Livermore
  Software TechnologyCorporation, Livermore, CA,
  1992.
• 12 L. Wu, C. Du amd, L. Zhang, Iterative FEM
  Die surface designto compensate for springback in
  sheetmetal stampings, inProceedings of NUMIFORM
  95, Ithaca, NY, 1995, pp. 637641.13 A.P.
  Karafillis, M.C. Boyce, Tooling and binder design
  for sheetmetal forming processes compensating
  springback error, Int. J. Mach.Tools Manuf. 36
  (4) (1996) 503526.
• 14 M. Sunseri, J. Cao, A.P. Karafillis, M.C.
  Boyce, Accommodation ofspringback error in
  channel forming using active binder force
  controlnumerical simulations and experiments,
  ASME J. Eng. Mater.Technol. 118 (1996) 426434.
• 15 Y. Ming, K. Manabe, H. Nishimura,
  Development of an intelligenttool system for
  flexible L-bending process of metal sheets,
  SmartMater. Struct. 7 (4) (1998) 530536.
• 16 I.N. Chou, C. Hung, Finite element analysis
  and optimization onspringback reduction, Int. J.
  Mach. Tools Manuf. 39 (3) (1999)517536.
• 17 M. Samuel, Experimental and numerical
  prediction of springbackand side wall curl in
  U-bending of anisotropic sheet metals, J.
  Mater.Proc. Tech 105 (3) (2000) 382393.
• 18 N. Narkeeran, M. Lovell, Predicting
  springback in sheet metal formingan explicit to
  implicit sequential solution procedure, Finite
  Elements,Anal. Des. 33 (1) (1999) 2942.
• 19 Baumeister, Avallone, Marks Standard
  Handbook For MechanicalEngineers, 8th ed.,
  McGraw-Hill, 1979.
• 20 G. Sachs, Principles and Methods of Sheet
  Metal Fabricating, 2nded., Reinhold Publishing
  Corporation, New York, 1966.