Bend design rules: minimum flange, relief and hole-to-bend distance
The press brake needs room to work, and the metal needs room to move. Three geometry rules that keep a folded part from cracking, distorting or slipping off the die.
The tool needs room, the metal needs room
A press brake folds metal by pressing a punch into a V-die. That means two things every bent part has to respect: the flange has to be long enough to sit on the die, and the metal near the bend has to be free to stretch. Break either and the part cracks, distorts, or won’t form at all — usually discovered at the brake, after it’s already cut.
Give every flange something to stand on
The flange is the leg you’re folding up. If it’s too short it doesn’t bridge the die opening — it slips in, folds unevenly, or can’t be held at all. As a safe minimum, keep the flange at least four times the material thickness, measured from the bend to the edge.
| SHEET t | MIN FLANGE | INSIDE RADIUS |
|---|---|---|
| 1.0 mm | ~4 mm | 1.0 mm |
| 1.5 mm | ~6 mm | 1.5 mm |
| 3.0 mm | ~12 mm | 3.0 mm |
| 6.0 mm | ~24 mm | 6.0 mm |
Exact minimums depend on the die we tool up — treat these as the safe design floor.
Relieve a bend that stops short of the edge
When a bend runs to the edge of the part, the metal is free to move. When it stops partway — a tab folded up out of a larger face — the material at the end of the bend is torn between folding and staying put, and it rips. The fix is a relief: a small notch cut at each end of the bend line so the fold has a clean place to start and stop.
Keep holes back from the bend
A hole too close to a bend line gets dragged into the stretch zone and pulls into an oval or a "D". Keep the edge of any hole at least two and a half thicknesses back from the bend, plus the radius. Closer than that and you either move the hole or drill it after folding — which costs a second operation.
Before you fold
A folded part that respects the brake goes from flat to finished in one setup. Quick pre-flight:
- 01 Every flange ≥ 4 × t The shortest leg still has to sit on the die.
- 02 Relief on every partial bend Notch the ends so the fold doesn’t tear.
- 03 Holes ≥ 2.5 × t from bends Or accept a drill-after-fold operation.
- 04 Consistent inside radius Reuse one radius (≥ t) across the part so we tool it once.
Bends giving you trouble?