This project was aimed for study of springback effect in perforated sheet metal with variation in various controlling parameters like percentage of open area, ligament ratio,shape of hole, size of hole, pattern of hole arrangement.
FINITE ELEMENT ANALYSIS OF SPRINGBACK 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 Manufacturing processes by S. Kalpakjian and S. Schmid αi: bend angle before springback αf: bend angle after springback Ri: bend radius before springback Rf: bend radius after springback
Literature Review Cho et.al studied the effect of punch corner radius, the punch-die clearance and friction coefficient on Springback effect. Chan studied spring-back angles of the work piece by varying the punch angle, punch radius and die-lip radius. Panthi et.al studied the effect of material properties (yield stress, Young’s modulus, 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 the accuracy of springback calculation. Chakrabartty et.al studied the elastic/plastic analysis of the sheet bending process under conditions of plane strain.
Contd.. Romen et. al studied that the spring backs increasing classical trends are related to radius decrease, yielding stress increase, bending radius increase and Young’s modulus decrease. Tan et.al studied that due to the non-homogeneous plastic deformation across thickness, springback will result in redistribution of internal stress and 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 .
Design of Perforated Sheet MetalThe various controlling parameters on which the design ofperforated 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
Material Chosen• The material chosen for Punch and Die is Cast Iron having Young’s modulus 210 Gpa and Poisson’s Ratio 0.25.• The material chosen for perforated sheet metal is commercial pure aluminium having Young’s modulus 70 Gpa and Poisson’s Ratio 0.33.• Plastic properties of commercial pure aluminium are :
Meshing• Element type : Solid45• Meshing type : Mapped meshing• Element size : For sheet metal 0.75 mm and for punch and die 10 mm.
Conclusion The springback effect was studied on perforated sheet metal and the following conclusions were drawn:• The value of springback effect increases with increase in the percentage of 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. Sheet metal with square hole showed greater springback than those with circular hole because strength of square hole is less than strength of circular hole.• The value of springback effect decreases with the increase of load on the perforated sheet metal. This holds good for both the square and circular hole.• The value of springback effect decreases with increase in hole size for both circular as well as square holes when open area, ligament ratio and thickness of sheet metal is kept constant. The values are higher for square holes.
Contd..• During bending process when the ligament ratio between the holes is increased the value of springback also gets increased while keeping the other controlling parameter constant.• When the thickness of perforated sheet metal increases for circular hole arranged in square pattern then the value of springback value gradually decreases.• The value of springback in square hole arranged in square pattern was found 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 circular hole.• The value of springback for circular hole arranged in triangular pattern was found to be less than that of circular hole arranged in square pattern because the strength of triangular pattern is more than that of square pattern.
ReferencesJournal Articles:  J. Chakrabarty, W.B. Lee and K.C. Chan (1999), An Analysis of the Plane-Strain Bending of an Orthotropic Sheet in the Elastic/Plastic Range, Journal of Material Processing Technology,104, pp 48-52 You-Min Huang, Tsung-Chia Chen. An elasto-plastic finite element analysis of sheet metal camber process, Journal of Materials Processing Technology, 2003, pp 432-440. Xuechun Lia, Yuying Yanga, Yongzhi Wanga, Jun Baoa and Shunping Lib (2001), Effect of the Material-Hardening Mode on the Springback Simulation Accuracy of V-Free Bending, Journal of Material Processing Technology, pp 209-211. Zhong Hu, Elasto-Plastic solutions for springback angle of pipe bending using local induction heating, Journal of Material Processing Technology (200) pp – 103 Z. Tan, W. B. Li and B. Persson ( 1993), On Analysis and Measurement of Residual Stresses in the Bending of Sheet Metals, Pergamon, vol 36, pp 483-491.  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 Processing Technology, pp 109-116.
Contd.. W.M. Chan, H.I. Chew, H.P. Lee and B.T. Cheok (2003), Finite Element Analysis of Springback of V–Bending Sheet Metal Forming Processes, Journal of Material Processing Technology, pp 15 – 24. 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, Materials and Design, pp 657-662. Z.Tan, B.Persson and C.Magnusson (1994), Plastic Bending of Anisotropic Sheet Metal, Pergamon, vol. 37, pp 405-421. F.Pourboghrat and E. Chu (1995), Prediction of Spring-Back and Side-Wall Curl in 2-D Draw Bending, Journal of Material Processing Technology, pp 361-374. M.L. Garcia-Romeu , J. Ciurana and I. Ferrer (2007), Springback Determination Of Sheet Metals In An Air Bending Process Based On An Experimental Work, Journal of Material Processing Technology, pp 174-177. Z.T.Zhang and S.J.Hu, Stress and Residual-108, Stress distribution in plane strain bending, Journal of Mechanical sciences pp- 543-553 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 Manufacturing Engineering, pp-179-186
Contd.. D. Schmoeckel (I) and M. Beth at Institute for Production Technology and Forming Machines, Springback Reduction In Draw-Bending Process of Sheet Metals, Technical University Darmstadt Germany, Annals of CIRP, vol. 42, pp 339 – 342. Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, Third Edition, by Mikell P. Groover, 4/25/2008.Books ANSYS Structural Analysis, ANSYS Release 9.0, November 2004 Manufacturing processes by S. Kalpakjian and S. Schmid, 4th Edition published by Dorling Kindersley, 2008. Mechanics of sheet metal forming by Z.Marciniak, J.L.Duncan and S.J.Hu, 2nd Edition published by Butterworth-Heinemann 2002. Z.Marciniak, J.L. Duncun, S.J. Hu Text book of Mechanics of Sheet Metal Forming 82-107. P.S.G. Design Data BookLectures  Lecture on Plastic Deformation By R.Ganesh Narayanan, IITG