Shift during fill
The insert must stay put under melt pressure. Call out location and count.
Molded-in inserts
Molded-In Inserts: Retention and Shutoff Before Steel Is Cut
The insert must survive fill without shifting. Plan knurl or undercut retention and mold shutoff. DFM review comments on CAD before quoting.
Design guideline
The insert is in the tool during fill
A molded-in insert is loaded in the cavity and the plastic locks around it during fill. Retention and shutoff must be planned before steel is cut.
Location must survive fill without shifting. Retention knurls or undercuts hold the insert after demold. Insert molding is the capability when metal is in the shot. DFM review needs insert type, count, and tolerances on CAD.
This spoke owns in-cavity inserts. Post-mold inserts go in after the shot. Insert retention owns pull-out. Bosses own the post. The design guide hub lists every topic.
Roles
Which page answers which in-cavity insert question
Stay here for inserts loaded during fill. Open a sibling for after-the-shot or the post.
| Page | Use it for |
|---|---|
| Molded-in inserts (this page) | Metal in the cavity during fill |
| Post-mold inserts | Heat-set or press-in after the shot |
| Insert molding | The capability page |
| Insert retention | How the insert stays put |
| Boss design | The plastic around the insert |
| Self-tapping screw bosses | Skip metal when a screw can cut plastic |
| Molded-in threads | Plastic threads instead of an insert |
| Wall thickness | Nominal wall around the insert boss |
| DFM review | CAD check before steel |
Checks
What DFM review looks for on molded-in inserts
Qualitative checks. No figure on this page is a NetProto specification.
Retention geometry
Knurl or undercut holds after demold. The retention page owns pull-out.
Shutoff on metal
Cavity steel must seal around the insert. Plan witness on cosmetics.
Warp and pack
Metal and plastic cool differently. Mark critical fits near inserts.
Decision
Molded-in versus post-mold press
Wrong: add inserts after T1 with no steel plan. Right: pick in-cavity or after-the-shot before the tool is cut.
What goes wrong
- Add inserts after T1 with no shutoff or load plan
- Leave insert type and count off the CAD
- Ignore how metal and plastic shrink together
What to try first
- Lock insert type, count, and location on CAD
- Plan retention and shutoff before steel
- Use post-mold inserts if metal should stay out of the cavity
RFQ
Send these notes with CAD for a molded-in insert review
The quote can start from CAD alone. These notes make the DFM pass specific.
Insert type, material, and count
Who supplies the inserts
Retention feature: knurl, undercut, or hex
Location and position tolerance
Cosmetic faces near insert shutoff
Fits that cannot warp around the insert
Related
Related design guidelines
Stay on this spoke for its question. Open a sibling for the neighbor topic or the CAD check.
Insert molding
Capability page for metal in the shot.
Insert moldingDFM review
How NetProto checks insert programs before steel.
DFM reviewFAQ
Molded-in inserts FAQ
What is a molded-in insert?
It is metal loaded in the cavity so plastic locks around it during fill. Retention and shutoff must be in the tool plan.
Who supplies the inserts?
Say on the RFQ. Programs quote when insert type, count, and tolerances are defined on CAD. Do not leave supply as an assumption.
Can inserts be added after T1?
A late add usually needs steel work. Decide in-cavity versus post-mold before the tool is cut.
Do inserts affect warp?
Yes. Metal and plastic cool at different rates. Mark critical fits near inserts and keep walls even around the boss.
How is insert molding different from post-mold install?
Insert molding puts metal in the shot. Post-mold install happens after. This page owns the in-cavity path.
How is this page different from bosses or retention?
Bosses own the plastic post. Retention owns pull-out. This spoke owns loading metal during fill. DFM review checks CAD.
Next step
Upload CAD for DFM review of molded-in inserts
Share insert type, count, location, and who supplies the metal so review can check retention, shutoff, and warp before quoting.