Insert Molded Parts

Metal inserts molded in.
Strong threads.
Single-piece function.

Insert molded parts: pre-placed metal components (threaded brass inserts, electrical contacts, magnets) with plastic molded around them. Stronger thread engagement than tapped plastic. Integrated electrical terminals. Simpler assembly than separate components.

Insert Molded Quote Overmolded parts

Brass threaded inserts Electrical contacts Magnets molded in Single-piece assembly

01 · Insert types

Common insert types.

Different insert types solve different assembly problems. Brass inserts for threads, electrical contacts for connections, magnets for closures — all molded into plastic in single operation.

Brass threaded inserts

Standard · M3-M10

Heat-set or molded-in brass threaded inserts. Much stronger than threads tapped directly into plastic. Common sizes M2.5-M10.

Electrical contacts

Copper / brass

Electrical contacts molded into plastic housing. Eliminates wire-termination steps in assembly.

Magnets

Rare earth · standard

Rare earth magnets molded into plastic parts for closures, holding, positioning features.

Metal structural parts

Steel / brass

Metal reinforcement molded into plastic for strength — load-bearing mounting points, hinges.

Bearing races

Steel · precision

Rolling element bearing races molded into plastic housings for smooth rotation.

Electrical contact pins

Bronze · plated

Spring-loaded or fixed contact pins for electrical connectors and switches.

Strain relief wires

Wire · integral

Pre-placed wires with integral strain relief and cable exit features.

PCB mounting inserts

Brass · standoff

PCB standoff inserts molded into housings for circuit board mounting.

02 · Insert molding applications

Where insert molding wins.

Consumer electronics

Electronic device housings with integrated screw bosses and connector contacts

Automotive connectors

Automotive electrical connectors with integrated contact pins

Medical devices

Medical device housings with stronger threaded mounting points

Tool handles

Tools with metal-reinforced handles for structural strength

Electrical switches

Light switches, relays with contacts molded into plastic body

Appliance housings

Appliances with threaded inserts for repeatable assembly/disassembly

Industrial sensors

Sensor housings with integral electrical connections

Gear housings

Plastic gear boxes with bearing races molded into housings

Specialty assemblies

Complex assemblies where combining metal and plastic in single operation reduces assembly cost

FAQ

Insert Molded questions.

Plastic threads tapped directly into plastic: pull-out strength 50-100 N typical for M4 thread. Strip out on 5-10 assembly cycles of high-cycle use. Brass heat-set insert in plastic: pull-out strength 500-1000 N. Survives 100+ assembly cycles. For parts requiring repeated fastener installation (service covers, maintenance access), brass inserts are essential. Use brass inserts for: any thread experiencing > 1 removal cycle, any thread under significant load.

Heat-set inserts: installed after molding via heat stake or ultrasonic. Flexible — same plastic part can accept different inserts depending on application. Insert molded: installed during molding — inserts placed in mold before injection. Stronger bond between insert and plastic (chemical bond). More expensive due to mold complexity and cycle time. For production: insert molding if volume justifies; heat-set for flexibility.

Challenges: (1) Hot plastic can degrade electrical plating — specify plated-after-molding or plastic-compatible plating. (2) Electrical contacts must be exactly positioned in mold — automated placement preferred at volume. (3) Interface between metal contact and plastic needs seal to prevent moisture intrusion. (4) Thermal expansion mismatch can cause delamination at high temperature. All manageable with appropriate design and materials.

Insert molding tooling cost: 1.2-1.5× standard injection tooling. Extra complexity: insert placement fixtures, possibly pneumatic inserts that retract during plastic injection. Automation of insert placement: important for high volume. For 10,000+ annual production, fully automated insert placement and handling integrated with injection molding cell.

Key rules: (1) Minimum wall thickness around insert 2× insert diameter to prevent shrinkage voids. (2) Insert diameter should be 80-100% of hole diameter in plastic. (3) Knurled or undercut insert surface improves plastic-to-metal bond. (4) Insert should not sit flush with surface — slight recess prevents flash issues. (5) Consider differential thermal expansion in service — brass expands more than plastic.

Insert molding adds $0.05-0.30 per insert depending on volume and automation. Manual insert placement: $0.20-0.50 per insert. Automated placement: $0.05-0.15 per insert. For threaded inserts, cost comparable to secondary operation (heat-set) at mid volumes. Savings: eliminated secondary assembly operation + improved joint strength + cleaner appearance (no heat-set marks).