Sheet metal
Flange length measured from the outside of the bend (straight leg + (r+t)·tan(angle/2)): WARNING below max(4t, 0.7 x 6t routine V-die), INFO up to the comfortable 8t-die limit. Offset webs and hem returns are skipped.
Cold bending of flat rolled steel
Sheet metal · CC0-1.0
Model example
The short upright flange is only 7 mm long beyond the bend radius in 3 mm sheet (R1.5), 11.5 mm measured from the outside of the bend. The die-support heuristic asks for at least 12.6 mm from the outside of the bend (larger of 4 × thickness = 12 mm and 0.7 × the 18 mm V-die opening).
Dimensions (approx.): 29.5 × 11.5 × 50 mm
PRU-003 should warn about insufficient flange support: 11.5 mm measured from the outside against 12.6 mm.
Finding expected