FINITE ELEMENT ANALYSIS OFSPRINGBACK EFFECT ON

PERFORATED SHEET METAL

GUIDE:Prof. G.Venkatachalam

TEAM MEMBERS:Ashish Devarth (08BME037)

Bhupendra Singh (08BME055)

Ravi Shekhar (08BME181)

Introduction

• The elastic strain recovery in the formed part after deformation is called

springback effect.

• Springback is the increase in included angle of the formed part relative

to the included angle of the forming tool after the tool is removed.

• With the knowledge of springback, tool dimensions, die design, force

and punch motion can be modified to produce the products with

required dimensions.

• Perforated sheet metal is made through sheet metal stamping and sheet

metal manufacturing process.

Contd..

Springback Effect in Bending

αi: bend angle before springbackαf: bend angle after springbackRi: bend radius before springbackRf: bend radius after springback

Manufacturing processes by S. Kalpakjian and S. Schmid

Literature Review

Cho et.al studied the effect of punch corner radius, the punch-dieclearance and friction coefficient on Springback effect.

Chan studied spring-back angles of the work piece by varying the punchangle, punch radius and die-lip radius.

Panthi et.al studied the effect of material properties (yield stress, Young’smodulus, strain hardening) and geometric parameters (thickness of sheet,die radius, sector angle) on springback effect at minimal load condition.

Lia et.al studied the material’s hardening model and its affect on theaccuracy of springback calculation.

Chakrabartty et.al studied the elastic/plastic analysis of the sheet bendingprocess under conditions of plane strain.

Contd..

Romen et. al studied that the spring back's increasing classical trends arerelated to radius decrease, yielding stress increase, bending radius increaseand Young’s modulus decrease.

Tan et.al studied that due to the non-homogeneous plastic deformationacross thickness, springback will result in redistribution of internal stressand residual stress can be observed in a bent specimen.

On the basis of Literature Survey following observations were drawn:

Parameter Value Springback

Yield Strength of Material Increase Increase

Thickness of Sheet Metal Decrease Increase

Modulus of Elasticity Decrease Increase

Punch Die Clearance Increase Increase

Contd..

Parameters Value Springback

Friction Coefficient Increase Increase

Punch Velocity Decrease Increase

Force Applied Decrease Increase

Bend Radius Increase Increase

Punch Radius Decrease Increase

Punch angle Decrease Increase

Valley Springback angle Decrease Increase

Area of Plastic Deformation Decrease Increase

Problem Statement

• Springback effect is a major cause of concern for sheet metal forming

industries which leads to inaccuracies in the final product produced and

eventually leads to problems in assembly.

• From literature review it is clear that springback effect in case of

perforated sheet metal has not been studied . The problem being taken

for the project is to study the effect of springback phenomenon on

perforated sheet metal.

• The study accounts for various controlling parameters for perforation of

sheet metal .

Methodology

Design of Perforated Sheet Metal

The various controlling parameters on which the design of

perforated sheet metal depends are:

• Percentage of open area

• Ligament ratio

• Size of the hole

• Shape of the hole

• Pattern of hole arrangement

• Area of sheet

• Thickness of sheet

• Material of sheet

Circular holes arranged in Square Pattern

Design of Bending Process

Punch

Die

Assembly

• The material chosen for Punch and Die is Cast Iron having Young’smodulus 210 Gpa and Poisson’s Ratio 0.25.

• The material chosen for perforated sheet metal is commercial purealuminium having Young’s modulus 70 Gpa and Poisson’s Ratio0.33.

• Plastic properties of commercial pure aluminium are :

Material Chosen

Meshing

• Element type : Solid45

• Meshing type : Mapped meshing

• Element size : For sheet metal 0.75 mm and for punch and die 10mm.

Contact Pair

• Surface-to-Surface contact: CONTA174

• Node-to-Surface contact: CONTA175

• Target Element: TARGET 170

Surface-to-surface contact Node-to-surface contact

Boundary Condition

• Die : Constrained in all DOF

• Punch: Constrained in X and Z direction

• Perforated Sheet: Constrained in X and Z direction

Simulation

Von mise Stress Von mises Strain

X - Component Y - Component

After Bending

After Unloading

Results and Discussion

Springback Vs Open Area (Circular Hole)

Springback Vs Open Area ( Square Hole)

Springback Vs Load ( Circular Hole)

Springback Vs Load ( Square Hole )

Springback Vs Ligament Ratio ( Circular Hole)

Springback Vs Ligament Ratio ( Square Hole)

Springback Vs Load ( Circular Hole )

Springback Vs Load ( Square Hole)

Springback Vs Hole Size ( Circular Hole )

Springback Vs Hole Size ( Square Hole )

Springback Vs Load ( Circular Hole )

Springback Vs Load ( Square Hole )

Springback Vs Thickness

Springback Vs Load

Springback Vs Shape

Springback Vs Pattern

Conclusion

The springback effect was studied on perforated sheet metal and thefollowing conclusions were drawn:

• The value of springback effect increases with increase in the percentageof open area for circular hole as well as square hole when the hole size,ligament ratio and thickness of sheet metal were taken as constant. Sheetmetal with square hole showed greater springback than those with circularhole because strength of square hole is less than strength of circular hole.

• The value of springback effect decreases with the increase of load on theperforated sheet metal. This holds good for both the square and circularhole.

• The value of springback effect decreases with increase in hole size forboth circular as well as square holes when open area, ligament ratio andthickness of sheet metal is kept constant. The values are higher for squareholes.

Contd..

• During bending process when the ligament ratio between the holes isincreased the value of springback also gets increased while keeping theother controlling parameter constant.

• When the thickness of perforated sheet metal increases for circular holearranged in square pattern then the value of springback value graduallydecreases.

• The value of springback in square hole arranged in square pattern wasfound to be more than the value of circular hole arranged in square pattern.This is because the strength of square hole is less than that of a circularhole.

• The value of springback for circular hole arranged in triangular patternwas found to be less than that of circular hole arranged in square patternbecause the strength of triangular pattern is more than that of squarepattern.

References

Journal Articles:

[1] J. Chakrabarty, W.B. Lee and K.C. Chan (1999), An Analysis of the Plane-Strain Bending ofan Orthotropic Sheet in the Elastic/Plastic Range, Journal of Material ProcessingTechnology,104, pp 48-52

[2] You-Min Huang, Tsung-Chia Chen. An elasto-plastic finite element analysis of sheet metalcamber process, Journal of Materials Processing Technology, 2003, pp 432-440.

[3] Xuechun Lia, Yuying Yanga, Yongzhi Wanga, Jun Baoa and Shunping Lib (2001), Effect of theMaterial-Hardening Mode on the Springback Simulation Accuracy of V-Free Bending,Journal of Material Processing Technology, pp 209-211.

[4] Zhong Hu, Elasto-Plastic solutions for springback angle of pipe bending using local inductionheating, Journal of Material Processing Technology (200) pp – 103

[5] Z. Tan, W. B. Li and B. Persson ( 1993), On Analysis and Measurement of ResidualStresses in the Bending of Sheet Metals, Pergamon, vol 36, pp 483-491.

[6] J.R.Cho, S.J.Moon, Y.H.Moon and S.S.Kang (2003), Finite Element Investigation on Spring-back Characteristics in Sheet Metal U-Bending Process, Journal of Material ProcessingTechnology, pp 109-116.

Contd..

[7] W.M. Chan, H.I. Chew, H.P. Lee and B.T. Cheok (2003), Finite Element Analysis ofSpringback of V–Bending Sheet Metal Forming Processes, Journal of Material ProcessingTechnology, pp 15 – 24.

[8] S.K. Panthi, N. Ramakrishnan, Meraj Ahmed, Shambhavi S. Singh and M.D. Goel (2009),Finite Element Analysis of Sheet Metal Bending Process to Predict the Springback, Materialsand Design, pp 657-662.

[9] Z.Tan, B.Persson and C.Magnusson (1994), Plastic Bending of Anisotropic Sheet Metal,Pergamon, vol. 37, pp 405-421.

[10] F.Pourboghrat and E. Chu (1995), Prediction of Spring-Back and Side-Wall Curl in 2-DDraw Bending, Journal of Material Processing Technology, pp 361-374.

[11] M.L. Garcia-Romeu , J. Ciurana and I. Ferrer (2007), Springback Determination Of SheetMetals In An Air Bending Process Based On An Experimental Work, Journal of MaterialProcessing Technology, pp 174-177.

[12] Z.T.Zhang and S.J.Hu, Stress and Residual-108, Stress distribution in plane strain bending,Journal of Mechanical sciences pp- 543-553

[13] M.A.Osman, M. Shazly, A.El-Mokaddem, A.S.Wifi, Springback prediction in V-bending:modelling and experimentation, Journal of achievement in Material and ManufacturingEngineering, pp-179-186

Contd..

[14] D. Schmoeckel (I) and M. Beth at Institute for Production Technology and FormingMachines, Springback Reduction In Draw-Bending Process of Sheet Metals, TechnicalUniversity Darmstadt Germany, Annals of CIRP, vol. 42, pp 339 – 342.

[15] Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, Third Edition,by Mikell P. Groover, 4/25/2008.

Books

[16] ANSYS Structural Analysis, ANSYS Release 9.0, November 2004

[17] Manufacturing processes by S. Kalpakjian and S. Schmid, 4th Edition published by DorlingKindersley, 2008.

[18] Mechanics of sheet metal forming by Z.Marciniak, J.L.Duncan and S.J.Hu, 2nd Editionpublished by Butterworth-Heinemann 2002.

[19] Z.Marciniak, J.L. Duncun, S.J. Hu Text book of Mechanics of Sheet Metal Forming 82-107.

[20] P.S.G. Design Data Book

Lectures

[21] Lecture on Plastic Deformation By R.Ganesh Narayanan, IITG

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