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A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
A. Mentella Esaform 2008
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A. Mentella Esaform 2008

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  • 1. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France A new method for feasibility study and determination of the loading curves in the rotary draw-bending process A. Mentella1, M. Strano2, R. Gemignani3 1 alessia.mentella@unicas.it 2m.strano@unicas.it 3roberto.gemignani@blm.it UNIVERSITÀ DEGLI STUDI DI CASSINO Dipartimento di Ingegneria IndustrialeBLM S.p.A. CASSINO (FR), ITALY
  • 2. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Table of contents Conventional • Stretch bending – Rotary-draw bending – Compression bendingbending methods Rotary-draw • Bending process – System configurations – Applications - Defects bending • Development of a computational methodology for the determination of theAim of the work optimal displacement curves of booster and pressure die Algorithm • Presentation of the computational methodology presentation Finite element • Description of the FEM model modeling FE Model • Results of experimental test, using a stainless steel (AISI 304) tube validationApplication of the • Results obtained in 3 different bending operations method Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 3. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Conventional bending methodsStretch bending Rotary-draw bending Compression bending Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 4. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Rotary-draw bending Università degli Studi di CassinoBLM S.p.A. Dipartimento di Ingegneria Industriale
  • 5. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Rotary-draw bendingBasic tooling for simplest cases More complex tooling for hardest cases Booster Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 6. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Rotary-draw bending Main applications of cold formed metal tubes Cold air intake component Bull bar Aluminum 2024, 5052, 6061 Inconel 600, 625, 718 Stainless Steel 304, 316, 321 Cres 21-6-9 Exhaust Hastelloy-X System Titanium Università degli Studi di CassinoBLM S.p.A. Dipartimento di Ingegneria Industriale
  • 7. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Rotary-draw bending Main applications of cold formed metal tubes Fluid lines and conditioning Furnishing Design Università degli Studi di CassinoBLM S.p.A. Dipartimento di Ingegneria Industriale
  • 8. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Rotary-draw bending Main defects and failures in tubular partsHump at endof the bend Wrinkling throughout bend, Tool marks on extended into wiper die area Overbend at 90° centerline of bend Heavy wrinkles through bend area and linear scratches in grip area indicating, clamp slippage Excessive collapse Excessive collapsewith or without wrinkling Mandrel balls hump after tubing is pulled throughout the bend off mandrel balls Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 9. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Rotary-draw bendingProcess parametres and Pressure die/booster configurations A B C A: pressure die only (A1 stationary, A2 follower, A3 boosted) B: pressure die(boosted) with connected booster block C: pressure die (C1 follower, C2 boosted) and indipendent axial booster Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 10. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France The C configurations, with Very limited studies or procedures areindependent booster, provide available in the scientific literaturethe greatest process flexibility providing criteria for selecting the axial and performance. assist of the rotary draw bending process A constant axial load is Aim of the generally applied to control the independent booster work A displacement control is generally used when the pressure die is boosted Development a simple computational methodology, that enables to rapidly obtain feasible, close to The proposed method is based optimal velocity curves for the most critical cases, on displacement control of when configuration c2 must be adopted. both booster and pressure die. Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 11. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Algorithm presentation INPUT VALUES AND ASSUMPTIONS vM = ω ⋅ RM (tangential velocity of the bend die = axial velocity of the tube at the section immediately before the bending region, if no axial assist is provided ) vS = vM ⋅ γ S (tangential velocity of the pressure die) strictly correlated to vM v B = vM ⋅ γ B (tangential velocity of the booster) γ S γB Factors used for tuning a proportional law between vM and the tools velocityε1 + ε 2 + ε 3 = 0 ε1 ⇒ − = %th ⇒ ε1 = 2th% (axial strain, assuming volume constancy) ε 2 = %th = ε 3 2 Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 12. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Algorithm presentation INPUT VALUES AND ASSUMPTIONSThe maximum principal true strain at the tube extrados (axial strain ε1), ifassuming isotropic material behaviour and no shift of the neutral axis, can beroughly calculated as:   OD− t    α ⋅  RM +  − d0  ε1 = ln 1 = ln  l 2   = ln1+ OD− t − ∆   l0  α ⋅ RM   2⋅ RM     where : • α is the bend angle; • Δ is the normalized amount of the reduction in lenght of external ∆ = d 0 fiber, due to the axial assist of the pressure die and the booster. α ⋅ RM Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 13. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Algorithm presentation OD − t ε1 OD − t 2th % ∆ = 1+ − e = 1+ −e 2 ⋅ RM 2 ⋅ RMThe total axial stroke d of the tube at the extrados, immediately before the bendingregion, can be written as: The term a⋅RM is mainly due to the bend die and the term d = γ ⋅ α ⋅ RM = α ⋅ RM + d 0 d0 is mainly due to the assist tools. A correction factor can now be calculated as: α ⋅ RM + d 0 d0 OD − t γ= = 1+ = 1+ ∆ = 2 + − exp(2th%) α ⋅ RM α ⋅ RM 2 ⋅ RM Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 14. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Algorithm presentationThe factor γ can be interpreted as the amount of extra axial feed which must beprovided by the assist tools, if the target maximum thinning thmax must be reachedand, therefore, can be used to find the values of γS and γB.The axial assist effect should be distributed between the booster and the pressuredie. γS >γB Because the pressure die acts mostly on the extrados, while the booster acts on the whole tube section. CONSTRAINS (γ S + γ B ) ≈ 1.1⋅ γ Otherwise, not all the displacement of the booster and of the pressure die could be transformed into displacement of the tube at the section immediately 2 before the bending region. Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 15. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Finite Element Modeling σ (ε p ) = K (ε e + ε p ) n Material AISI 304 Ultimate tensile strength σf 788 MPa Extensibility A% 53 Poisson’s ratio ν 0.28 Pressure die Initial yield stress σs 205 MPa Hardening exponent n 0.224 Mandrel balls Strenght coefficient K 954 MPa Clamp Young’s modulus E 196.5 GPa Mandrel body Contact interface Static f. c. Dynamic f. c.Booster Tube/Pressure and bend dies 0.57 0.35 Tube/Wiper die 0.30 0.15 Bend die Tube/Clamp die 1.99 1.99 Tube/Mandrel 0.075 0.055 Tube Ball/Mandrel (spherical joint) 0.055 0.055 Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 16. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Model validation by experimentOutside diameter, OD 35mmInitial Thickness, t 0.8mmMean radius of the bend, RM 40mmBend angle, α 90° Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 17. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Model validation by experiment Università degli Studi di CassinoBLM S.p.A. Dipartimento di Ingegneria Industriale
  • 18. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France Application of the methodBy running several FEM analyses with different combinations of γS and γB, the γ S = max (1.25 ⋅ γ , 1)following rules have been identified as optimal: γ B = max (0.92 ⋅ γ , 1) PROCESS DATA CASE 1 CASE 2 CASE 3 Outside diameter, OD 35mm 85mm 76mm Initial Thickness, t 0.8mm 2mm 1.5mm Mean radius of the bend, RM 35mm 85mm 114mm Bending angle, α 90° 90° 90° Difficulty Ratio FD=(OD2)/(t⋅RM) 43.75 42.5 33.8 Booster coefficient, γB 1.05 1.05 1.0 Pressure die coefficient, γS 1.42 1.42 1.25 Target maximum thinning, thMAX 0.15 0.15 0.14 Output maximum thinning, thMAX 0.15 0.14 0.14 Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 19. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France ConclusionsThe amount of axial displacement of the assist tools (booster and pressuredie), expressed through the parameters γS and γB, is particularly importantin critical bending conditions. In fact, experiments and simulations show thatthe maximum thinning decreases as γS and γB increase.However, these values cannot be indefinitely increased, sincewrinkling may occur, especially as γB increases.The study proposed a method for determining γS and γB.The method has been evaluated by successfully applying it to threedifferent critical bending operations. Università degli Studi di Cassino BLM S.p.A. Dipartimento di Ingegneria Industriale
  • 20. 11° ESAFORM Conference on MATERIAL FORMING April 23-25, 2008 Lyon, France A new method for feasibility study and determination of the loading curves in the rotary draw-bending process A. Mentella1, M. Strano2, R. Gemignani3 1 alessia.mentella@unicas.it 2m.strano@unicas.it 3roberto.gemignani@blm.it UNIVERSITÀ DEGLI STUDI DI CASSINO Dipartimento di Ingegneria IndustrialeBLM S.p.A. CASSINO (FR), ITALY

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