Insert molding
- Insert locked in by surrounding resin
- Loading step in every cycle, manual or automated
- Tool must locate and shut off around the insert
Decision guide
Insert Molding vs Post Mold Assembly: When to Mold the Insert In
Insert molding locks the insert in resin during the shot. Post mold assembly adds it after ejection. Retention load and volume usually decide.
Insert joints
Mold it in or add it later
Both routes end with a metal or plastic insert in the part. The tool and the labor differ.
Insert molding places the insert in the tool so resin forms around it. Post mold assembly adds the insert after ejection by press fit, heat staking, ultrasonic insertion, or fasteners.
NetProto quotes insert molding and post mold insert installation. The right answer depends on retention load, volume, and how often the insert design changes.
Side by side
What changes between the two routes
The joint load and the loading step are the main differences.
Post mold assembly
- Standard tool with a molded boss or pocket
- Separate installation step after molding
- Insert type or supplier can change without a tool change
Routing table
Signals for each route
Qualitative only.
| Factor | Insert molding tends to fit | Post mold assembly tends to fit |
|---|---|---|
| Retention | Highest pull-out and torque loads | Moderate loads with a well designed boss |
| Volume | Steady volume that justifies loading | Lower volume or frequent insert changes |
| Tool | Insert pockets and shutoffs in steel | Simpler core with a boss |
| Risk | A misplaced insert scraps the shot | Boss cracking if the press fit is too tight |
Quote inputs
Send this with your CAD
Describe the joint, not only the part.
Insert drawing or part number, including material and plating
Pull-out and torque loads the joint must hold
Annual volume and how inserts will be supplied
Whether the insert could change supplier during the program
Continue exploring
Related comparisons
Decision guides and the pages that go deeper.
Compare hub
All comparison guides.
Compare hubMolded threads vs threaded inserts
Plastic threads or a metal insert at the joint.
Molded threads vs threaded insertsUltrasonic welding vs adhesive bonding
Joining molded halves for strength and seal.
Ultrasonic welding vs adhesive bondingInsert molding
Inserts retained in the mold during the shot.
Insert moldingMolded in inserts
DFM rules for inserts placed in the tool.
Molded in insertsPost mold inserts
DFM rules for inserts installed after molding.
Post mold insertsFAQ
Common questions
Does insert molding always raise piece price?
Not always. Loading adds cycle time, but it can remove an assembly step. Describe the joint and the quote can compare both routes.
Can I switch routes later?
Moving from post mold assembly to insert molding changes the tool. Decide before steel is cut when possible.
Next step
Quote the insert joint the way it will run in production
Upload CAD with the insert drawing. NetProto manufacturing is ISO 9001 certified.