Uniform flex web
A thick land is not a hinge. Keep the web thin and even.
Living hinge
Living Hinges in Injection Molding: Thin Flex Web and Resin
Keep the flex section thin and uniform, and fill along the hinge when you can. DFM review comments on resin and gate before quoting one steel tool.
Design guideline
The hinge is a flex web, not a thick land
A living hinge is a thin, uniform flex web that must survive repeated bend. Polypropylene and some PE grades are common. Brittle grades fail in flex.
Polypropylene and some PE grades are common hinge resins. Brittle grades fail in flex. Gate location should avoid a weld across the hinge when possible. DFM review needs resin and cycle intent. This page does not publish a hinge thickness.
This spoke owns the flex web. Uniform wall thickness owns transitions into the web. Cantilever snap fits are hooks, not hinges. One hardened steel tool still runs the part. The design guide hub lists every topic.
Roles
Which page answers which hinge question
Stay here for the flex web. Open a sibling for snaps, gates, or the CAD check.
| Page | Use it for |
|---|---|
| Living hinge (this page) | Thin flex web, resin, and fill |
| Uniform wall thickness | Transitions into the web |
| Gate location | Avoid a weld across the hinge |
| Cantilever snap fit | A hook, not a hinge |
| Thin wall design | Fill on a thin skin |
| Draft angle | Walls beside the web still need draft |
| Wall thickness | Nominal wall the hinge steps from |
| Fillets and radii | Blends into the web, not a thick land |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on living hinges
Qualitative checks. No figure on this page is a NetProto specification.
Resin family
PP and some PE grades are common. Brittle grades fail. Name the resin.
Fill direction
A weld across the hinge is a fatigue start. Plan the gate.
One steel tool
The hinge is part geometry on the same hardened steel tool.
Decision
A thick hinge land versus a true flex web
Wrong: a thick radius that will not flex. Right: a thin uniform web and a resin that survives bend.
What goes wrong
- A thick land that cracks on first fold
- A weld line across the hinge
- A brittle or highly filled grade on a living hinge
What to try first
- Keep a thin uniform web
- Gate so fill runs along the hinge when you can
- Name a hinge-capable resin family on the RFQ
RFQ
Send these notes with CAD for a living-hinge review
The quote can start from CAD alone. These notes make the DFM pass specific.
Resin family intended for the hinge
Hinge length and location on the part
Expected fold cycles, if known
Intended gate side
Whether a weld across the hinge is acceptable
Draft on walls next to the web
Related
Related design guidelines
Stay on this spoke for its question. Open a sibling for the neighbor topic or the CAD check.
DFM review
How NetProto checks hinge CAD before steel.
DFM reviewFAQ
Living hinge FAQ
What is a living hinge?
A thin uniform flex web molded as part of the piece. It must survive repeated bend. It is not a snap hook.
Which resin works for living hinges?
Polypropylene and some PE grades are common. Brittle and many glass-filled grades fail. Name the family. This page does not publish a grade list.
Can hinges run on one steel tool?
Yes. The hinge is geometry on the same hardened steel tool NetProto quotes. It is not a second tool type.
Do hinges need draft?
The web is thin, but walls next to it still need draft. The draft page owns those faces.
How thick should the hinge be?
Thin and uniform. NetProto does not publish a hinge thickness. Upload CAD for DFM review.
How is this page different from snaps or thin-wall design?
Snaps own hooks. Thin-wall owns fill on a light skin. This spoke owns the flex web. DFM review checks CAD.
Next step
Upload CAD for DFM review of your living hinge
Share resin, hinge location, and gate intent so review can check the web and fill before quoting.