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bending
16.5
U-Bending & Die Stamping
203 Articles  2254 Elements

U-Bending & Die Stamping

16.5
U-bending 1
Fig. 1
U-bending21
lB Bending length εa Elongation of outer fiber FSt Punch force F St max UT Maximum punch force Bottom dead center rM Die radius rSt Punch radius ub Bending gap s0 Wall thickness

The conditions for U-die bending correspond to free bending with twice the bending length b. At bottom dead center (BDC), the punch hits hard and the process switches to stamping. A higher embossing force FSt max UT is then required to ensure the flatness of the workpiece base.

Eqn. 1
\require{color}\definecolor{myred}{RGB}{255,0,0} F_{\color{myred}St\;max}=\frac{k_{\color{myred}fm}\cdot s_{\color{myred}0}^{\color{myred}2}\cdot l_{\color{myred}B}}{4\cdot q}\cdot\xi
Eqn. 2
\require{color}\definecolor{myred}{RGB}{255,0,0} F_{\color{myred}St\;max\;UT}\geq2\cdot F_{\color{myred}St\;max}
Eqn. 3
\require{color}\definecolor{myred}{RGB}{255,0,0} \xi=\frac{\cos\left(\frac{\mathrm\pi}2-arc\cos\left(\frac{r_{\color{myred}M}+r_{\color{myred}St}+s_{\color{myred}0}}{r_{\color{myred}M}+r_{\color{myred}St}+u_{\color{myred}b}}\right)\right)+\mu\cdot\sin\left(\frac{\mathrm\pi}2-arc\cos\left(\frac{r_{\color{myred}M}+r_{\color{myred}St}+s_{\color{myred}0}}{r_{\color{myred}M}+r_{\color{myred}St}+u_{\color{myred}b}}\right)\right)}{\sqrt{\left(\frac{r_{\color{myred}M}+r_{\color{myred}St}+u_{\color{myred}b}}{r_{\color{myred}M}+r_{\color{myred}St}+s_{\color{myred}0}}\right)^{\color{myred}2}-1}+\mu\cdot\frac{s_{\color{myred}0}}{2\cdot\left(r_{\color{myred}M}+r_{\color{myred}St}+s_{\color{myred}0}\right)}}
Eqn. 4
\require{color}\definecolor{myred}{RGB}{255,0,0} u_{\color{myred}b}>s_{\color{myred}0}\;,\;u_{\color{myred}b}\leq s_{\color{myred}0}+\sqrt{0,2\cdot s_{\color{myred}0}}
Eqn. 5
\require{color}\definecolor{myred}{RGB}{255,0,0} \varphi_{\color{myred}m}=\ln(1+\frac{\varepsilon_{\color{myred}a}}2)=\ln\left(1+\frac1{4\cdot c+2}\right)
Eqn. 6
\require{color}\definecolor{myred}{RGB}{255,0,0} c=\frac r{s_{\color{myred}0}}
Eqn. 7
\require{color}\definecolor{myred}{RGB}{255,0,0} W_{\color{myred}B}=F_{\color{myred}St\;max}\cdot h_{\color{myred}B}\cdot m_{\color{myred}B}
Max. punch forceFSt max=1.77kN 
Maximum punch force UTFSt max UT>3.54kN 
Coefficientξ=1.3 
Medium natural strainφm=0.04 
Bending factorc=5 
Bending workWB=26.55J 
Die radiusrM = 5mm
Punch radiusrSt = 5mm
Sheet thicknesss0 = 1mm
Bending gapub = 1.4mm
Bending lengthlB = 100mm
Average work hardeningkfm = 600MPa
Coefficient of frictionμ = 0.1
Mean factor bendingmB = 0.75
Bend heighthB = 20mm
5
Calc 1
U-Bending & Die Stamping
The tensile strength Rm can be used as an approximation for kfm.
By using a flow curve and the mean degree of deformation φm
more precise values for kfm can be determined.
21
Kluge, Siegfried / Prozesse der Blechumformung / Carl Hanser Verlag / München / 2020 / …
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