What is a hinge bend?
A hinge bend is a long, gentle radius along the edge of a sheet, formed so the edge can flex repeatedly without cracking. The radius is large relative to the thickness, which is the opposite of a hem, and the tooling has to support the sheet across that wide span.
What tooling does a hinge bend need?
A large-radius bottom die and a punch with a matching radius at the tip. The opening is much wider than the eight times rule would give for a sharp bend, because the radius is the point of the bend, and the sheet has to reach down into the die without bottoming.
| Aspect | What it needs |
|---|---|
| Bottom die | Wide, fully radiused to the finished inside radius |
| Punch | Radiused tip that does not dictate a smaller radius |
| Force | Low per unit area, but check the long-span deflection |
| Springback | Grows with the radius-to-thickness ratio |
| Support | The sheet must not bottom in the middle of the bend |
Why does springback matter more on a hinge bend?
Springback grows as the radius-to-thickness ratio grows, and a hinge bend has the highest ratio of any common bend. The angle recovery can be several degrees, so the ram depth has to be over-corrected and confirmed on a test piece before the batch runs.
Where do hinge bends fail?
At the two ends of the bend, where the radius runs out, and in the middle, where the punch deflects. Run-out relief in the tooling and crowning compensation on long bends are the two standard answers.
Related technical pages
Radius dies
Bottom dies for deliberate large radii.
Minimum bend radius
The smallest radius each material accepts, and why large radii are kinder.
Hemming dies
The opposite extreme: folding the edge back flat.
U bending
Forming U sections, and the radius choices that go with them.
Next step
Send the hinge radius, material and bend length and we will confirm the die and punch set.
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