Abstract
The limits of the processing window for deep drawing, collected in a deep drawing diagram, are affected by material behavior, process parameters and size effects. A size effect, more specific a density effect, explains the changes in forming behavior of foils with respect to the forming limit, denoted by the limiting drawing ratio. It is shown that it occurs in so called Tiffany structures. The changes in the tribology in deep drawing have an influence on the clamping limit of the processing window. The changes are induced by changes of the drawing speed. They can be explained by the lubricant pocket model only if one takes the temperature dependence of the viscosity of the lubricant into account.
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Abbreviations
- μ:
-
Coefficient of friction from Coulombs law
- μeff :
-
Effective coefficient of friction from numerical identification using the formula by Storoshew
- μff(p):
-
Coefficient of friction as function of contact pressure, given by the so called friction function
- μH :
-
Coefficient of friction for hydrodynamic contact
- μS :
-
Coefficient of friction for solid contact
- μT :
-
Total coefficient of friction
- A0 :
-
Macroscopic contact cross section area (mm2)
- AL :
-
Liquid contact area (mm2)
- AS :
-
Solid contact area (also: real contact area) (mm2)
- d:
-
Diameter (mm)
- dB,0 :
-
Initial blank diameter (mm)
- dp :
-
Punch diameter (mm)
- F:
-
Force (N)
- FB :
-
Blank holder force (N)
- FH :
-
Normal force transferred by hydraulic medium (N)
- FN :
-
(Total) normal force (N)
- FP :
-
Punch force (N)
- FS :
-
Normal force on solid contact (N)
- lp :
-
Punch travel distance during forming process (mm)
- p:
-
(Contact) pressure (N/mm²)
- pB :
-
Blank holder pressure (N/mm²)
- pB,0 :
-
Initial blank holder pressure (N/mm²)
- pL :
-
Lubricant pressure (N/mm²)
- pS :
-
Pressure of solid contact (N/mm²)
- r:
-
Radius (mm)
- rD :
-
Drawing radius (edge radius of drawing ring) (mm)
- rP :
-
Punch radius (radius between bottom and mantle) (mm)
- s0 :
-
Sheet thickness (mm)
- T:
-
Temperature (K)
- T0 :
-
Temperature at viscosity η0 (K)
- v:
-
Velocity (m/s)
- vP :
-
Punch speed (m/s)
- α:
-
Viscosity temperature index
- β:
-
Drawing ratio (ratio of blank diameter to punch diameter)
- βmax :
-
Limiting drawing ratio
- ΔdD :
-
Drawing clearance (mm)
- η:
-
Viscosity (m²/s)
- η0 :
-
Viscosity at temperature T0 (m²/s)
- ρ:
-
Density (g/cm³)
- φmax :
-
Maximum strain
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Acknowledgments
The author is grateful for the financial support of the Deutsche Forschungsgemeinschaft (DFG) of the projects B1 and B3 of the Collaborative Research Center SFB 747, where the results were obtained. The author also thanks for support by Dipl.-Ing. S. Grünenwaldand Dr.-Ing. Z. Hu whilepreparingthismanuscript.
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Vollertsen, F. Effects on the deep drawing diagram in micro forming. Prod. Eng. Res. Devel. 6, 11–18 (2012). https://doi.org/10.1007/s11740-011-0355-5
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DOI: https://doi.org/10.1007/s11740-011-0355-5