INTERNATIONAL Mechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL EN...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
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Effect of punch profile radius and localised compression

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Effect of punch profile radius and localised compression

  1. 1. INTERNATIONAL Mechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – AND TECHNOLOGY (IJMET) © IAEME 6359(Online) Volume 3, Issue 3, Sep- Dec (2012)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online) IJMETVolume 3, Issue 3, September - December (2012), pp. 517-530© IAEME: www.iaeme.com/ijmet.asp ©IAEMEJournal Impact Factor (2012): 3.8071 (Calculated by GISI)www.jifactor.com EFFECT OF PUNCH PROFILE RADIUS AND LOCALISED COMPRESSION ON SPRINGBACK IN V-BENDING OF HIGH STRENGTH STEEL AND ITS FEA SIMULATION Vijay Gautam1, Parveen Kumar2, Aadityeshwar Singh Deo3 1 (Department of Mechanical Engineering, Delhi Technological University, Road, Delhi- 110042, India, vijay.dce@gmail.com) 2 (Department of Mechanical Engineering, Delhi Technological University, Road, Delhi- 110042, India, dahiya.sonu1@gmail.com) 3 (Department of Mechanical Engineering, Delhi Technological University, Road, Delhi- 110042, India, dce.aaditya@gmail.com) ABSTRACT Spring-back is a very common and critical phenomenon in sheet metal forming operations, which is caused by the elastic redistribution of the internal stresses after the removal of deforming forces. Spring-back compensation is absolutely essential for the accurate geometry of sheet metal components. In this study an experimental investigation was carried out to determine the effect of punch corner radii on springback in free V- bending operation. The springback compensation was done by localised compressive stresses on bend curvature by the application of compressive load between punch and the die. This experimental springback phenomenon was analysed and validated by an Explicit finite element program using ABAQUS 6.10. In order to determine spring-back in V-bending operation, six numbers of ‘‘V’’ shaped dies and punches with required clearances were designed and fabricated with included angle of 90° for bending of high strength sheet metal with thicknesses: 0.85, 1.15 and 1.55mm. Keeping other parameters same increase in punch corner radius increases the springback and increase in sheet thickness reduces the springback. Springback compensation by localised compressive stress showed negligible springback and the same results were supported by FEA simulations. This model is very useful to control springback on a press brake equipped with controlled computer integrated data acquisition system. Keywords: Bending dies, Explicit solution, Mn-High Strength steel, Springback, V-bending. 517
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME1. INTRODUCTIONBending is one of the most important sheet metal forming operations by which a straightlength of metal strip is transformed into a curved one with the help of suitably designed dieand punch. It is very common process of forming steel sheets and plates into channels, drums,automotive and aircraft components. Especially V-Bending process has been thoroughly studied and there is plenty of literatureavailable, among which the most important contribution is Hills basic theory on purebending of sheet metals[l]. Hill has derived the complete solution for pure bending of a non-hardening sheet and showed the shift of the neutral surface during bending. Lubahn andSachs [2] studied the bending of rigid perfectly plastic materials in cases of both plane stressand plane strain, and they predicted no change in material thickness by assuming that thesurfaces, including the neutral surface, Crafoord [3]considered the Bauschinger effect byassuming the constant yield surface on reverse straining by fibres overtaken by the neutralsurface. And he predicted obvious thickness thinning of rigid-strain-hardening metal sheets. Pure bending is rarely achieved in actual bending process, except that, it is the desiredprofile of a bend than the temporal stress and strain distribution that is important. Theassumptions made in the study of pure bending are generally different from real conditions inv-die bending. Unlike pure bending, V-die bending is not a steady process. A sheet metal islaid over a die and bent as the punch inserts into the die, the bending moment and curvaturevary continuously along the sheet and during the deformation, the sheet is stressed in tensionon one surface and compression on the other, it is shift of the neutral surface during bendingthat complicates the analysis[4]. The stress state is complex in bending. Around the neutral plane, the stress must be elasticbecause complete tensile and compressive stress-strain curves of the material are traversed onboth bend side. When the forming tool is removed from the metal, the elastic components ofstress cause spring back which changes both the angle and radius of the bent part as shown inFig.1. The part tends to recover elastically after bending, and its bend radius becomes larger.This elastically-driven change in shape of a part upon unloading after forming is referred toas spring back. Figure 1: terminology for springback in bending [5] Spring-back causes following problems in sheet-metal forming: 518
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME1) The assembly of the sheet metal components becomes problematic thereby increasing the assembly time and reducing the productivity.2) In automobile industry different punch corner radius are used for different bending operations which in turn affects the spring-back in components.3) A wide range of thickness is used in sheet-metal components which again affects the spring-back.4) High strength sheets are preferred for automotive body as to reduce the thickness which results in reduction of the overall weight of the vehicle. Lighter vehicles are in demand for higher fuel efficiency. However, spring-back characteristic of IFHS has not been investigated widely and verylittle information is available about its behaviour during V-bending operations. Both material parameters and process parameters affect springback, parameters such aselastic modulus, yield strength, strain hardening ability and thickness of the sheet metal aswell as die opening, punch radius and so on interfere the springback in a very complicatedway. Figure 2: Methods of reducing springback in V-bending operations [5]. We can calculate springback approximately, in terms of the radii Ri and Rf i.e. initial andfinal radius of bend curvature (Fig.1) as[5] : ோ௜ ோ௜ ோ௜ = 4(ா௧)ଷ − 3 ቀா௧ቁ + 1 (1) ோ௙ Note that springback increases as the R/t ratio and yield stress Y of the material increasesand the elastic modulus E decreases [5].2. COMPENSATION FOR SPRINGBACKIn general practice there are different ways for springback compensation as shown in theFig.2 :over-bending (In Fig.2 (a) & (b)), coining or bottoming the punch (shown in Fig.2 (c)and (d)), stretch bending and warm bending[5]. Over-bending is an effective way to compensate for the springback, this can be done in airbending by adjusting the punch/ die angle or punch stroke. Several trials may be necessary toobtain the desired results. Stelson and co-workers have introduced an adaptive control model[6-8] and this model estimates the material characteristics of a sheet being bent from thepunch force-displacement data taken early in the bending process, and the in-process 519
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEmeasured parameters are then used in the calculation of the current final punch position sothat the elastic springback can be compensated by over-bending and desired unloaded angleof a bend can be obtained. By this model, disturbances in operation due to variations inmaterial characteristics of a sheet will not affect the modelling results. To predict the loadedshape and the springback of a sheet being bent, however, strenuous measurement andcalculation must be performed. In analysis of springback in v-die bending, the curvature of asheet metal subjected to bending needs to be known. In most analyses, the inner radius of abend is commonly assumed to be the same as that of the punch. In fact, the radius ofcurvature is a function of both material and process parameters. If the radius of a punch is ofthe same order of the sheet thickness, the radius of curvature underneath the punch will belarger than that of the punch, while a sufficiently large punch will cause a smaller bendingcurvature [9]. Another method is stretch bending, in which the part is subjected to tension while beingbent, the springback is reduced as the neutral surface is shifted out of the sheet metal [10].Since the springback decreases as yield stress decreases, all other parameters being the same,bending may also be carried out at elevated temperatures to reduce springback known aswarm bending [11]. Little data is available for springback compensation by bottoming the punch or coiningand hence localised compression was the main objective of the study.3. MATERIAL SELECTION & METHODOLOGYMaterials and techniques for cutting weight from vehicles and thereby improving fuelefficiency, are a part of routine automotive engineering practice. Large reductions in weightwhile maintaining size and enhancing vehicle utility, safety, performance, ride and handlingare often thought of as the driving force for future vehicles [12].The body of a car, includingthe interior, accounts for nearly 40% of the car’s total weight and offers a high potential forlightweight construction [13]. Materials for car body panels require certain specificcharacteristics to meet the industry’s challenges: rationalisation of specifications for leanerinventory, improved formability for reduced rejection rate and better quality. Higher StrengthLow Alloy (HSLA) steels of thinner gauges are getting preference for weight reduction andthe resulting better fuel economy. Other quality characteristics under demand are higher yieldstress (strength), toughness, fatigue strength, improved dent resistance as well as corrosionresistance in materials used for body panels for improved durability and reliability. Keeping in view of the above factors low carbon high strength steel, was chosen for thespringback study and the sheet metal was procured from leading automobile manufacturerwith thickness 0.85, 1.15 and 1.55mm. Chemical analysis of the material as per the ASTM-E415-08 reveals that the material is high Manganese and low Carbon and the composition ofthe steel is given in TABLE 1. Table 1: Chemical composition of HS-steel (wt %) C Si Mn P S Ti Nb Al 0.077 0.013 1.4 0.05 0.011 0.04 0.001 0.032 520
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME The microstructure of high strength steel was revealed and carefully studied undermagnification of 200X. The microstructure shown in the Fig. 3 depicts the fine grains offerrite and complex Manganese Carbides uniformly distributed in ferrite matrix responsiblefor high strength of the steel.Figure 3: microstructure of high strength steel at 200x showing complex carbides in thematrix of ferrite3.1. Tensile Properties of High Strength SteelThe tension tests were carried out as per ASTM standard E 8M-04 (2004) on INSTRON4482, 100KN machine, in strength of materials laboratory at DTU Delhi. The HS sheets of0.85, 1.15 and 1.55mm thickness were tested for the mechanical properties. The tension testspecimens were cut from the sheet metal at 0° i.e. parallel to, inclined at 45° andperpendicular at 90° with respect to the rolling direction of the sheet metal. The tensile testingof material was carried out with standard size specimen as shown in Fig.4.Figure 4: tensile specimens cut as per ASTM-E8M in direction parallel to, perpendicular toand inclined at 45° to the rolling direction The typical stress strain curve obtained from the tests is shown in Fig.5 to Fig. 7. Since thedeparture from the linear elastic region cannot be easily identified, the yield stress wasobtained using the 0.2 % offset method. UTS was determined for the maximum load andoriginal cross section area of specimen. The tensile properties of the specimens show that thesheet metal is slightly anisotropic. Hence it can be regarded as isotropic material. 521
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 2: Mechanical properties of High Strength steel sheet Young’s Direction Strength Strain Sheet thickness σy yield Modulus wrt. Coefficient hardening metal (mm) (MPa) (MPa) rolling (k) coefficient(n) 0˚ 355 791.39 0.188 High 0.85 210000 45˚ 367 762.0 0.179 strength 90˚ 376 785.4 0.179 0˚ 312 744.7 0.199 High 1.15 210000 45˚ 320 730.18 0.190 strength 90˚ 314 741.7 0.188 0˚ 315 735.9 0.196 High 1.55 210000 45˚ 319 732.0 0.192 strength 90˚ 324 716.51 0.184 Stress- Strain curve for 0.85mm sheet 600 engg stress stress in MPa 400 strain curve X-0-1 200 0 stress strain 0 0.2 0.4 curve:x-90- -200 strain in mm/mm 1Figure 5: engineering stress strain curve of 0.85mm thick sheet as obtained from tensile teston UTM, depicting that the metal is almost isotropic. 522
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME stress -strain curve for 1.15mm sheet 500 400 stress stress in MPa strain 300 curve Y-0-1 200 100 stress 0 strain -100 0 0.2 0.4 curve: y- 45-1 strain in mm/mmFigure 6: engineering stress strain curve of 1.15mm thick sheet as obtained from tensile teston UTM, depicting that the metal is almost isotropic. stress strain curve for 1.55mm sheet 600 engg stress strain Stress in MPa 400 curve z-0-1 200 engg stress 0 strain 0 0.2 0.4 curve z-45- -200 strain in mm/mm 1Figure 7: engineering stress strain curve of 1.55mm thick sheet as obtained from tensile teston UTM, depicting that the metal is almost isotropic. The strain hardening exponent (n) and the strength coefficient (K) values are calculatedfrom the stress strain data in uniform elongation region of the stress strain curve. The plot oflog (True stress) versus log (True strain) which is a straight line is plotted. The power law ofstrain hardening is given as: σ = K. εn (2) Where, σ and ε are the true stress and true strain. Taking log on both sides: log (σ) = log (K) + n. log (ε) (3) This is an equation of straight line the slope of which gives the value of ‘n’ and ‘K’ can becalculated taking inverse natural log of the y-intercept of the line (i.e. ln (K)) as shown inFig.8. 523
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME log stress strain curve n=0.188, K=791.39MPa 6.8 Ln(true stress) y = 0.188x + 6.673 6.6 R² = 0.999 6.4 log stress strain curve 6.2 6 5.8 Linear (log stress strain -4 -2 0 2 curve) Ln (true strain) Figure 8: calculation of n and k value of high strength steel3.2. Fabrication of Bending ToolsAs discussed earlier two sets of dies and punches with the punch corner radius 7.5 mm and 10mm were required for the experimental setup of V-bending in addition to other accessories.The included angle for dies and punches were kept as 90°. The D-2 tool steel for cold working was selected for the bending dies. The drawings oftooling were made in CATIA-V5 as shown in the Fig.9 and Fig.10. The DXF file was used inEDM-wire cut to fabricate the dies and punches. A total of six dies and two punches weredesigned with two different punch corner radii. The clearance between dies and punch wasmade equal to sheet thickness to avoid the localized compressive stresses during bendingoperation. The dies and punches were designed with a holding shank of 25mm length and12.5mm thickness for easy holding and proper alignment in UTM. The setup was designedfor UTM for capturing the data for load and deflection. After fabrication the dies and punches were hardened and tempered in Metallurgylaboratory. D-2 steel dies and punches were heated to 910°C in a muffle furnace for 4hrs.And hardened in air and then tempered at 250°C. After air hardening the hardness was 65Rcand after tempering the hardness was 62HRc. Figure 9: a CAD drawing of the v-die showing various dimensions 524
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Figure 10: a CAD drawing of the v-punch showing various dimensions4. FEA SIMULATIONS: RESULTS AND DISCUSSIONSThe FEA simulations for the above experimental procedure were carried out using ABAQUS6.10 in CAD lab. The material model for 2D deformable blank was prepared as isotropichardening following power law of hardening, with young’s Modulus of Elasticity as210000MPa and Poisson ratio of 0.3 with structure insensitive elastic constants for steel. The plastic data of the steel was directly taken from data acquisition of UTM were truestress and strain. The plastic strain at stress level 350MPa was 0.0, and at 445MPa strain was0.058mm/mm. The dies and punches were modelled as 2D analytical rigid requiring nomeshing properties. The friction condition between the punch and blank was frictionless anda friction value of 0.1 was used between blank and the die. Table 3: Different part attributes used in the FEA Model PARTS 2D DIE ANALYTICAL RIGID PUNCH ANALYTICAL RIGID BLANK DEFORMABLE The simulation results are listed as below:Case-1.Bending of HS steel 0.85mm thick with punch corner radii 7.5mm.Case-2.Bending of HS steel 1.15mm thick with punch corner radii 7.5mm.Case-3.Bending of HS steel 1.55mm thick with punch corner radii 7.5mm.Case-4.Bending of HS steel 0.85mm thick with punch corner radii 10mm.Case-5.Bending of HS steel 1.15mm thick with punch corner radii 10mm.Case-6.Bending of HS steel 1.55mm thick with punch corner radii 10mm. 525
  10. 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME CASE 1: High Strength steel 0.85mm thick with punch corner radii 7.5mm.Figure 11: overlay plot showing springback of HS 0.85mm thick sheet with punch cornerradius of 7.5mm. CASE 2: High Strength steel 1.15mm thick with punch corner radii 7.5mm.Figure 12: overlay plot showing springback of HS 1.15mm thick sheet with punch cornerradius of 7.5mm CASE 3: High Strength steel 1.55mm thick with punch corner radii 7.5mm.Figure 13: overlay plot showing springback of HS 1.55mm thick sheet with punch cornerradius of 7.5mm 526
  11. 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME CASE 4: High Strength steel 0.85mm thick with punch corner radii 10mm.Figure 14: overlay plot showing springback of HS 0.85mm thick sheet with punch cornerradius of 10mm CASE 5: High Strength steel 0.9mm thick with punch corner radii 10mm.Figure 15: overlay plot showing springback of HS 1.15mm thick sheet with punch cornerradius of 10mm CASE 6 High Strength steel 1.55mm thick with punch corner radii 10mm.Figure 16: overlay plot showing springback of HS 1.55mm thick sheet with punch cornerradius of 10mm 527
  12. 12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMETable 4: Comparison of springback values in experimental and simulation results by bending with punch corner radius of 7.5mm when no compensation was done. SHEET CONFORMING ROLLING EXPERIMENTAL BY SIMULATIONTHICKNESS BENDING DIRECTION (IN DEGREE) (IN DEGREE) (mm) LOAD (N) 0.85 0˚ 200 4.61˚ 4.12˚ 0.85 45˚ 200 5.66˚ 4.46˚ 0.85 90˚ 200 4.81˚ 4.33˚ 1.15 0˚ 400 3.21˚ 2.41˚ 1.15 45˚ 400 3.90˚ 2.21˚ 1.15 90˚ 400 3.64˚ 2.10˚ 1.55 0˚ 800 1.92˚ 1.62˚ 1.55 45˚ 800 2.78˚ 2.13˚ 1.55 90˚ 800 2.12˚ 1.92˚Table 5: Comparison of springback values in experimental and simulation results by bending with punch corner radius of 10mm when no compensation was done. SHEET CONFORMING BY ROLLING EXPERIMENTAL THICKNESS BENDIG SIMULATION DIRECTION (IN DEGREE) (mm) LOAD(N) (IN DEGREE) 0.85 0˚ 200 5.76˚ 5.45˚ 0.85 45˚ 200 5.99˚ 5.15° 0.85 90˚ 200 5.76˚ 5.54˚ 1.15 0˚ 400 4.14˚ 3.48˚ 1.15 45˚ 400 4.49˚ 3.18˚ 1.15 90˚ 400 4.91˚ 3.79˚ 1.55 0˚ 800 2.18˚ 2.56˚ 1.55 45˚ 800 2.94˚ 2.44˚ 1.55 90˚ 800 2.98˚ 2.17˚ 528
  13. 13. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Table 6: Table depicts final spring-back values after spring-back compensation due to localisation of compressive stresses. INITIAL FINAL SHEET ANGLE ANGLE SPRING-BACK BY ROLLING LoadTHICKNESS EXPERIMENTAL SIMULATION DIRECTION (N) ( ɵi ) (in (ɵf) (in (mm) (IN DEGREE) (IN DEGREE) degree) degree) 0.85 0˚ 1200 44.95˚ 44.57˚ 0.3805˚ Nil 0.85 45˚ 1200 44.95˚ 44.25˚ 0.7009˚ Nil 0.85 90˚ 1200 44.95˚ 43.43˚ 0.5212˚ Nil 1.15 0˚ 3000 44.92 44.71 0.2101˚ Nil 1.15 45˚ 3000 44.92˚ 44.48˚ 0.4416˚ Nil 1.15 90˚ 3000 44.92˚ 44.33˚ 0.5868˚ Nil 1.55 0˚ 4000 44.96˚ 45.6˚ -0.6351˚ Nil 1.55 45˚ 4000 44.96˚ 45.46˚ -0.4966˚ Nil 1.55 90˚ 4000 44.96˚ 44.72˚ -0.2416˚ NilDiscussions: when a sheet metal is bent as discussed above, it will be in compression onpunch side and tension on die side, and at the mid surface it has elastic stress componentwhich primarily depends on bend angle. When localised compression is applied then theneutral surface vanishes forcing the sheet section in compression only and springback iscompensated by localised compression.5. CONCLUSIONSWith reference to the above studies and results following conclusions are drawn:1. When the bending load was low and enough to conform to the shape of the die then considerable value of springback was seen experimentally and by numerical simulations.2. It was confirmed by numerical simulation that as the sheet thickness increases the spring- back decreases.3. It was determined that as the punch corner radii increases the spring-back effect increases significantly keeping other factors same. The result is in agreement with some of the literatures [14]. 529
  14. 14. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME4. Experiments show that the spring-back can be effectively compensated by localization of compressive stresses by the increase in the load in the final phase of bending when the sheet is conforming to the shape of the die fully. Experiments show negligible springback value but these values should be carefully used while designing the toolings for v-bending operation. Thicker sheets showed negative springback but the same was not reflected in the numerical simulation results.6. ACKNOWLEDGEMENTSThe Authors thank the Management of Delhi Technological University for their continuoussupport and constant encouragement to carry out this research work.REFERENCES[1]. R Hill, the mathematical theory of plasticity Oxford, London, 1950.[2]. J. Lubahn et al, Bending of an ideal plastic metal, Transactions of the ASME, Volume72, 1950, 201-208.[3]. R. Crafoord, Steel sheet surface topography and its influence on friction in a bendingunder tension friction test, International Journal of Machine Tools and Manufacture, Vol. 41,issues 13-14, 2001, 1953-1959.[4]. Z. Tan et al, An empiric model for controlling springback in V-die bending of sheetmetals, Journal of Materials Processing Technology, 34, 1992, 449-455.[5]. S. Kalpakjian and R. Schmid, manufacturing processes for engineering materials 4thedition( Pearson Education Inc., 2003).[6]. K. A. Stelson and D.C. Gossard, An Adaptive Pressbrake control using an Elastic-PlasticMaterial Model, ASME, Journal of Engineering for Industry, 104, 1982, 389-393.[7]. S. Kim and K. A. Stelson, Real time identification of workpiece material characteristicsfrom measurements during brakeforming, ASME Journal of Engineering for Industry, 105,1983, 45-53.[8]. A. K. Stelson, An Adaptive Pressbrake Control for Strain Hardening Materials, ASMEJournal of Engineering for industry, 108, 1986, 127-132.[9]. K. J. Weinmann and R.J. Shippell, Bending of HSLA steel Plate, 6th North AmericaMetal Working Research, Conf. Proc., April-1978, Florida, USA.[10]. ZaferTekiner, An experimental study on the examination of springback of sheet metalswith several thicknesses and properties in bending dies, Journal of Material ProcessingTechnology, 145, 2004, 109-117.[11]. J. Yanagimoto and K. Oyamada, Springback of High-Strength Steel after Hot andWarm Sheet Formings, Annals of CIRP, Vol. 54/1, 2005, 213-216.[12]. De Cicco J.M., Projected fuel savings and emmissons reductions from light vehicle fueleconomy standards, Transportation Research, Part-A: Policy and Practice, Vol. 29, no.3,1995, 205-228.[13]. Auto Steel Partnership, Tailor welded blank design and manufacturing manual,Southfield, MI, Report, 2001.[14]. W.D. Carden, R. H. Wagoner et al, Measurement of springback, International journal ofMechanical sciences, 44, 2002, 79-101. 530

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