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Post Mold Inserts: Injection Molding Design Rules
Post mold inserts trade mold complexity for secondary handling and press install.
DFM
Post mold inserts skip in cavity shutoff at the cost of handling
Press or heat stake inserts after molding when mold loading is impractical.
Boss inner diameter and depth must match the insert vendor press spec.
Cosmetic faces stay cleaner when inserts never see cavity steel shutoff.
Secondary operations belong in the program quote, not as hidden assumptions.
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.
Secondary plan
Document post mold insert intent
Clarify this before comparing mold only quotes.
Insert vendor and installation method
Boss pilot and depth after shrink
Tolerance on insert flush to surface
Volume high enough to automate or low enough for bench press
Related rules
Design guide
Jump to sibling rules before you freeze CAD.
DFM article
Long form engineer guide.
DFM articleMolded in inserts
In cavity alternative.
Molded in insertsSelf tapping screw bosses
Thread without metal insert.
Self tapping screw bossesSecondary operations
NetProto secondary scope.
Secondary operationsVisual 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
Post mold insert questions
Does NetProto run insert press in house?
Confirm secondary scope on the qualified program quote.
Can post mold inserts migrate in service?
Retention geometry and boss design still matter.
Is post mold cheaper on tooling?
Often on mold capital, not always on total landed cost.
Next step
Separate mold and insert install scope
Upload CAD and state post mold insert intent in project notes.