The minimum threshold
A practical rule:
Minimum flange height ≈ V / 2 + tV12 die, 2 mm sheet: minimum flange around 8 mm. V50 die, 6 mm sheet: minimum flange around 31 mm.
Below that, the blank no longer rests on enough of the die shoulders.
What to do when the flange is too short
- Move to a narrower V-die — the threshold drops with it. But bending force rises, so re-check machine tonnage and the die's own limit.
- Change the bend sequence — bend the short flange first, while the blank is still long and has somewhere to rest.
- Leave extra material and trim — bend with a longer flange, then cut off the excess.
Why to check this at the design stage
Discovering a too-short flange after the whole batch is cut means losing the whole batch. Checking the threshold on the drawing takes seconds.