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A Finite Element Study of the Deformability of Steel

A Finite Element Study of the Deformability of Steel. Jingyi Wang Qi Rui Jiadi Fan. Background. A real-life problem Use finite element analysis software to simulate the stamping process of bakeware. punch. holder. die. Background. Improper forming condition will lead to defect.

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A Finite Element Study of the Deformability of Steel

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  1. A Finite Element Study of the Deformability of Steel Jingyi Wang Qi Rui Jiadi Fan

  2. Background • A real-life problem • Use finite element analysis software to simulate the stamping process of bakeware punch holder die

  3. Background • Improper forming condition will lead to defect. The wrinkling and fracture defect during deep drawing process • Manufacturing and fixing stamping mold is expensive • Simulation needed to test whether certain mold and forming condition is reasonable before manufacturing

  4. Method • Experimental and Empirical Analysis • 3D model with different parts under dynamic loading– Use ABAQUS • Different forming conditions • Temperatures • Strain rates • Holding force • Compare, design and optimize forming condition to avoid possible defect

  5. ABAQUS

  6. Wrinkling Why wrinkling happens? • During the deep drawing process, metal flows inside. From large perimeter area to small perimeter area. • Under minimum principal stress, the blank will be thickened. Uneven thickening will lead to wrinkling. • We need a reasonable holding force to provide a restriction.

  7. Fracture Why fracture happens? • The friction between holder and blank, die and blank will block metal from flowing. • If the friction is too big, the metal at the corner will fracture because of over-thinning. • If the thickness after deformation reduces to 70% of the original thickness or less, we treat it as fracture.

  8. Temperature effect • As temperature rises, the deformability of metal will improve. • However, good deformability may lead to the over-thinning at the corner. • Higher temperature is also more energy expensive. So, forming temperature is a parameter that need to be balanced. • Suggested temperature (dependent on holding force, material, etc): 550-850 ℃ Maximum stretch depth (mm) Simulation Experiment Temperature ℃

  9. Strain rate effect • Under large strain rate, the deformability of metal is poor. It will be more likely to generate fracture. • Small strain rate decreases the productivity. • In industrial process, strain rate is also a design parameter.

  10. Holding force effect • Oversize holding force can lead to fracture defect • An undersize holding force can lead to wrinkling defect • Dependent on details of the object Maximum stretch depth (mm) Simulation Experiment Holding Force (MPa)

  11. Element type • S4R: 4-node general-purpose shell, reduced integration with hourglass control, finite membrane strains • Membrane theory

  12. Target geometry after deep drawing A realistic geometry 2D and 3D model Animation

  13. Simulation model One quarter of the entire model holder punch die

  14. Material property • 42CrMo high-strength steel • Young’s moldus: 210Gpa • Poison's ratio: 0.31 • Density: 7,830 kg/m^3 • True stress-strain curve

  15. Result—different temperatures Strain rate: 1, holding force: 10,000N Temperature: 600℃ and 650 ℃ The thickness at the corner is smaller under higher temperature. As the thickness ratio are both lower than 70%. It’s unnecessary to simulate a higher temperature. T=600 ℃ T=650 ℃

  16. Result—different strain rates Temperature: 600 ℃, holding force:10,000N Compare strain rate : 0.1 and 1 The thickness at the corner is smaller under higher strain rate =0.1 =1

  17. Result–different holding forces Reasonable holding force range: 7,000~13,000N F=5000N F=10,000N F= 30,000N

  18. Refine the size of blank • After the deep drawing process, the extra blank needs to be cut off. • The former blank is 400*400mm, it will cause a huge waste of material. • Refine it to 300*300mm and 240*240mm.

  19. Result–size of the blank 400*400mm 300*300mm 240*240mm 240*240mm good enough for our bakeware

  20. Conclusion • In our particular case, the best forming conditions are • Temperature: T=600℃ • Strain rate: =0.1 • Holding load: F=7,000-13,000N • Original Blank size: 240*240mm

  21. This is just a simple FE application. ABAQUS is able to do very complicated problems. In our case, the geometry of production is simple. However, in more complicated cases, we need to consider much more.

  22. Thank you for your listening

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