Insert Molding Service
We mold Metal-to-Plastic (and compatible grades) for functional, structural and aesthetic parts — from low-volume bridge production to high-volume runs.
Metal-to-Plastic (Thermoplastic) Injection Molding Capabilities
Process options selected to match your part geometry, material and annual volume.
In-house Metal-to-Plastic process engineering — material selection reviewed against your mechanical and thermal requirements.
Tight-tolerance metal-to-plastic molding with automated cells for repeatable quality run after run.
Custom tooling & rapid DFM feedback — shorten lead time from design to first article.
One-stop production: molding, secondary operations and inspection under one roof.
Insert Types We Mold
The inserted component can be metal, ceramic, glass or even a hard plastic — the range below is what we run on our Sodick vertical and horizontal machines.
Insert Molding Process, Step by Step
Insert molding integrates the metal component in one operation — competitor benchmarks cite a 50% improvement in bond robustness and roughly 30% fewer process steps versus molding-then-assembling.
Insert preparation
Inserts are knurled, threaded, grooved or through-holed so the plastic locks on mechanically. Brass and steel inserts are pre-cleaned and deburred before loading.
Loading into the cavity
Inserts are placed manually or by pick-and-place robot into the mold. Manual placement typically runs a 45–90 s cycle; robotic loading shrinks it further and removes operator variability.
Injection around the insert
Plastic flows around and through the insert features. The resin shrinks onto the metal as it cools — that clamping force is the core of the mechanical bond.
Cooling and ejection
The part cools in the tool and ejects with the insert captured. Design must account for the different thermal expansion of metal and plastic so the insert neither loosens nor cracks the plastic.
Inspection and secondary work
Insert position, pull-out resistance and dimensions are checked — controlled positions hold ±0.02 mm against the mold pins. Threads arrive ready to use; no post-insertion.
Insert Material Selection Guide
Material choices referenced from First Mold's insert molding page — brass is the default, everything else is application-driven.
| Insert material | Why it is used | Typical parts |
|---|---|---|
| Brass | Corrosion-resistant, affordable, easy to machine — the most common insert material | Threaded inserts, standoffs, electrical terminals |
| Stainless steel | Corrosion and temperature resistance with high strength | Medical device housings, food equipment, fasteners |
| Copper / Cu alloys | Electrical and thermal conductivity | Contacts, terminals, heatsink cores |
| Steel / alloy steel | High strength and wear resistance | Gears, shafts, locator pins, wear pads |
| Aluminum | Lightweight with good strength-to-weight | Electronics housings, EV battery components |
| Ceramic / glass | Dielectric, high-temperature insulation | Heater insulators, HV standoffs, sensors |
Insert Molding Design Rules
- ✓Design the insert with knurls, grooves, undercuts or through-holes — the mechanical lock carries the load, not surface friction.
- ✓Match thermal expansion: brass-in-plastic is the forgiving standard; steel-in-POM or aluminum-in-PC need expansion analysis to avoid cracking or loosening.
- ✓Give the plastic enough wall around the insert to resist hoop stress from shrinkage — thin walls crack around the metal.
- ✓Keep inserts clear of part edges and weld lines — a weld line running through the insert zone is a crack path.
- ✓Locate inserts from the same datum as the rest of the part; position is held by mold pins at ±0.02 mm.
- ✓For high volume, robot-load inserts and review the loading station in DFM — manual loading drives the 45–90 s cycle.
Insert Molding Applications
Connectors & sensors
Metal contacts and terminals molded directly into housings — microelectronic components with tight tolerances, no assembly.
Automotive gears & brackets
High-strength housings with molded-in shafts and bushes, produced under IATF 16949 control with PPAP.
Medical instruments
Stainless steel hubs, blades and sleeves encapsulated in handles — ISO 13485 traceable lots.
Power tools & appliances
Threaded brass inserts molded into housings so screws bite into metal, not plastic.
Electronics enclosures
Aluminum standoffs and heat sinks captured in one shot for EMI shielding and thermal paths.
Aerospace & defense
Ceramic and high-temp inserts for valve bodies and sensor housings in demanding environments.
Insert Molding FAQs
- ✓What insert materials can you mold? Brass (most common), stainless steel, copper alloys, steel, aluminum, ceramic, glass and hard plastics — see the selection table above.
- ✓How strong is the metal-to-plastic bond? Insert molding locks the metal mechanically via knurls and undercuts plus shrinkage clamping — competitor testing benchmarks a 50% improvement in bond robustness over molding-then-assembling.
- ✓Can insert loading be automated? Yes — pick-and-place robots remove operator variability and cut the cycle below the 45–90 s typical of manual placement.
- ✓What tolerance can insert position hold? Insert position is registered by mold pins at ±0.02 mm on controlled dimensions.
- ✓How long does insert molding tooling take? Rapid tools 7–12 days, production tools 25–30 days (45 for automotive-grade), all built in-house alongside our 20 Aida presses for stamped-insert work.
- ✓Do you make the inserts too? We source standard brass/steel inserts and also stamp simple inserts on our 20 in-house Aida presses — one supplier for insert and molded part.
Related Capabilities
Explore the full range of MOLDITQUICK manufacturing services.