Zero radius internal corner
- Flow hesitation at the corner
- Stress concentration in service
- Difficult polish and vent at the root
DFM
Corner Design: Injection Molding Design Rules
Internal and external corners drive flow, stress, and where the parting line can land.
DFM
Corners are where flow, stress, and polish collide
External and internal corners need different DFM thinking.
External corners can use small breaks to reduce stress and improve mold polish access.
Internal sharp corners stall flow and concentrate stress in the plastic and steel.
Parting lines often land on external corners, which changes witness and flash control.
DFM
Quote this rule with your CAD upload
NetProto DFM review flags these geometry patterns before steel is ordered.
- Call out draw direction and cosmetic faces on the model.
- Note resin family even when the grade is not final.
- Tighten tolerances only on mating features that need them.
Geometry
Sharp internal corner versus radiused pocket
Mold steel fails first on sharp internal ribs in production.
Controlled internal radius
- Smoother fill around the pocket
- Better mold life on deep features
- Easier alignment with fillet callouts elsewhere
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
Design guide hub
All DFM topics on one route.
Design guide hubDFM article
Long form engineer guide.
DFM articleFillets and radii
Minimum radius callouts.
Fillets and radiiSharp corner stress
When zero radius is still requested.
Sharp corner stressDraft angle
Release before fighting corners.
Draft angleVisual reference
Molding context for this rule
Images from the Forge media library illustrate typical programs.
Injection molded part design review on CAD
Injection molded part design review on CAD
Plastic housing with ribs and bosses
Plastic housing with ribs and bosses
Engineer measuring molded component
Engineer measuring molded component
FAQ
Corner questions
Do external chamfers replace draft?
No. Draft still controls release; chamfers reduce burrs.
What radius is enough?
Program dependent. Call out minimum internal radius on critical pockets.
Can corners hide gate vestige?
Sometimes on hidden external corners with approved witness.
Next step
Radius corners before quoting
Upload CAD with internal corner and parting line notes.