Stretch Forming Capability
1.5
Stretch forming is a forming process in which the material is subjected to equal or unequal tensile forces in the two main directions of its surface.
Fig. 1
Stretch forming
① Sheet metal ② Clamping element ③ Punch
No clear statements can be made about the stretch forming capability of a sheet metal material from individual tensile test characteristics. Therefore, the stretching value S was determined statistically from over 60 combinations of the individual characteristics of the tensile test.14
Eqn. 1
| Stretching value | S | = |
| Tensile strength | Rm | = | MPa | |||
| Yield strength | Rp 0,2 | = | MPa | |||
| Smallest perpendicular anisotropy | rMin | = | ||||
| Mean strain hardening exponent | nm | = |
Calc 1
Stretching value S
With the help of the stretch forming value S, it is possible to assess the stretch forming capability of a sheet metal material:
S < 3 Low stretch forming capability
S > 3 S < 4 Medium stretch forming capability
S > 4 High stretch forming capability
Werkstoff | Zugfestigkeit Rm [MPa] | Streckgrenze Rp0,2 [MPa] | Kleinste Senkrechte Anisotropie rMin | Mittlerer Verfestigungs- exponent nm | Streckziehwert S |
|---|---|---|---|---|---|
St 14 | 292 | 176 | 1.438 | 0.216 | 4.8 |
1.4301 | 631 | 292 | 0.764 | 0.349 | 4 |
AlMg3 W19 | 218 | 108 | 0.434 | 0.153 | 3 |
Al 99,5 W7 | 72 | 26 | 0.362 | 0.253 | 3.7 |
Al 99,5 G9 | 74 | 44 | 0.675 | 0.173 | 3.2 |
Al 99,5 G13 | 126 | 124 | 0.757 | 0.045 | 2.6 |
AlMg3 G27 | 260 | 204 | 0.434 | 0.153 | 2.3 |
BHZ 300 | 447 | 374 | 0.976 | 0.176 | 3.3 |
CHLY 40 | 466 | 231 | 0.827 | 0.217 | 3.9 |
PHZ 26 | 471 | 225 | 0.722 | 0.224 | 3.8 |
ZStE 260 | 382 | 289 | 1.087 | 0.162 | 3.7 |
Tbl. 1 Characteristic values from tensile test14 | |||||
14
Doege, E.; Breidohr, B. / EFB-Forschungsbericht Nr. 35: Untersuchungen zum Tiefziehen von Teilen mit unebenen Bodenformen / Europäische Forschungsgesellschaft für Blechverarbeitung e. V. / Hannover / 1988 / …