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4
Tool Design
4.2
Die radius
206 Articles  2274 Elements

Die radius

4.2
Tool geometry
Fig. 1
Tool geometry for ① recoil draw ② flangeless draw
rb bottom radius rST punch radius rM die radius pN blankholder pressure uZ clearance

When passing through die radius rM , the sheet experiences tangential pressure due to the reduction in diameter. These compressive stresses are superimposed by indirect tensile stresses, which are transferred by the drawing die over the edge into the forming area. An oversized die radius can cause wrinkles in the material.

In addition, the sheet metal bends and bends back as it passes through. die radius creates areas with varying contact normal stresses.

A drawing die radius that is too narrow can disrupt the flow of the sheet material, which can lead to cracks in the bottom area.

Eqn. 1
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M}=\left(5 … 15\right)\cdot s_{\color{myred}0}=C\cdot s_{\color{myred}0}
Die radiusrM=8mm 
ConstantC = 8
Sheet thicknesss0 = 1mm
8
Calc 1
Eqn. 2
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M~n}=\left(0,6 … 0,8\right)\cdot r_{\color{myred}Mn-1}=C\cdot r_{\color{myred}M~n-1}
Die radius redrawingsrM n=5.6mm 
ConstantC = 0.7
Die radius preferredrM n-1 = 8mm
0.70
Calc 2
*

According to Oehler* if the radius of the drawing edge is too small, this leads to cup base fractures. Excessively large die radii facilitate undesired wrinkling, which leads to jamming in the clearance, flattened wrinkles and frame fractures in the frame.

Eqn. 3
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M}=\frac{0,04\cdot D_{\color{myred}0}}{d_{\color{myred}1}\cdot\beta_{\color{myred}100}}\cdot\left[50+\left(D_{\color{myred}0}-d_{\color{myred}1}\right)\right]\cdot\sqrt{s_{\color{myred}0}}
Die radiusrM=6mm 
Blank diameterd0 = 200mm
Diameter punchd1 = 100mm
Limiting drawing ratioβ100 = 2
Sheet thicknesss0 = 1mm
200
Calc 3

The empirically determined factors of 0.04 and 50 are based on the experience that the rework required for tools with short tool lives due to abrasion, scratches and adhesion leads to a continuous increase in rM.

The following rule applies here: 5 < rM / s0 < 10 because according to the bending component from rM / s0 > 5 there is no reduction in sheet thickness and at rM / s0 < 10 there is no longer any lifting of the sheet from the drawing edge under the effect of tangential compression stresses.

This is often related to insufficient blank holder pressure or blank holder deflection. Deflection of the press table and clamping elements leads to compression wrinkles and rapid tool wear.

Drawing edge radii that are too large cannot be reduced. Drawing edge radii that are too small, whether intentional or unintentional, are increasing. An intended tool life increase through surface treatment and coating processes must specifically cover this area without errors.*

Eqn. 4
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M}=0,035\cdot\left[50+\left(D_{\color{myred}0}-d_{\color{myred}0}\right)\right]\cdot\sqrt{s_{\color{myred}0}}
Die radiusrM=5.25mm 
Blank diameterd0 = 200mm
Diameter punchd1 = 100mm
Sheet thicknesss0 = 1mm
200
Calc 4

Between the optimal There is a quadratic relationship die radius and the sheet thickness.* The sheet thickness has a significant influence on the bending force. There is also a quadratic relationship between the bending force at die radius and the sheet thickness.

Eqn. 5
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M~opt}=(0,125-0,78\cdot \mu)\cdot R_{\color{myred}P~0,2}\cdot s_{\color{myred}0} {^{\color{myred}2}}
Optimum die radiusrM opt=1.4mm 
Coefficient of frictionμ = 0.15
Yield strengthRp 0,2 = 175MPa
Sheet thicknesss0 = 1mm
0.15
Calc 5
Optimum die radius

This relationship applies to:

  • Sheet steel DC04, DC04ZE, ZstE340ZE, ZstE250i, Zst300BH
  • Aluminum sheet AA5182-0, AA6009-T4, AA6016-T4

With the properties:

  • μ = 0.02 … 0.15
  • s0 = 0.7...1.5
  • RP 0.2 = 150 … 350 MPa

Material parameters eg from the table for sample materials.

Friction values see table of friction values or friction & tribology.

Eqn. 6
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M~max}\leq16\cdot s_{\color{myred}0}
Max. die radius aluminiumrM max Alu≤16mm 
Sheet thicknesss0 = 1mm
1
Calc 6
Eqn. 7
\require{color}\definecolor{myred}{RGB}{255,0,0} r_{\color{myred}M}=\left(0,5 … 0,8\right)\cdot\sqrt{\left(D_{\color{myred}0}-d_{\color{myred}1}\right)\cdot s_{\color{myred}0}}=C\cdot\sqrt{\left(D_{\color{myred}0}-d_{\color{myred}1}\right)\cdot s_{\color{myred}0}}
Die radiusrM=6mm 
ConstantC = 0.6
Blank diameterd0 = 100mm
Diameter punchd1 = 50mm
Sheet thicknesss0 = 2mm
0.60
Calc 7
Matrix radius according to Hellwig**

The values ​​determined in this way can be reduced by 20% after* if

  • the drawn part retains a flange or
  • the draw ratio β1 <1.4
*
Oehler; Kaiser / Schnitt-, Stanz- und Ziehwerkzeuge / Springer Verlag / Berlin / 1993 / 7. Auflage
*
Radtke, H. / Genaue Hohlkörper durch Blechumformen / expert Verlag / Esslingen / 1995 / 1. Auflage
*
Tschätsch, H. / Praxis der Umformtechnik / Vieweg / Wiesbaden / 2003 / 7. Auflage
*
Mönig, Elmar / Tiefziehen rotationssymmetrischer Blechformteile / unveröffentlicht / Bestwig / 2002 / …
*
Farr, Mathias Tilmann / Zieh- und Stempelkantenradien, IFU Beiträge zur Umformtechnik Nr 31 / DGM Informationsgesellschaft Verlag / … / … / …
*
Haller, Günther / Werkzeuge für die Fertigung von Aluminiumteilen / Vortrag DIF / … / 2002 / …
*
Herold, G.; Kluge, M. / EFB-Forschungsbericht Nr. 61: Simulation des Formstempeltiefziehens im Weiterschlag / Europäische Forschungsgesellschaft für Blechverarbeitung e. V. / Hannover / 1994 / …
*
Kolbe, M.; Hellwig, W. / Spanlose Fertigung Stanzen / Springer Vieweg / Wiesbaden / 2015 / 11. Auflage
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