Insert Molding with Metal Components
Plastic parts with metal molded in place – threaded inserts, pins, bushings and bus bars encapsulated in PA66, POM, ABS, PC or PEEK from our China workshop. One integrated part, no post-assembly.
Free Consultation24h
Rapid Quote
±0.02mm
Tolerance
China
Factory
100 pcs
MOQ
Materials
| Grade | Properties | Typical Applications |
|---|---|---|
| PA66 (Nylon 66) | Tensile Strength: 80-90 MPa, Density: 1.14 g/cm³, high mechanical strength, excellent wear resistance, low friction; 30% glass-filled reaches 190 MPa | Gears, bearings, structural components, automotive underhood, connector bodies |
| POM (Acetal) | Tensile Strength: 60-70 MPa, Density: 1.41 g/cm³, high stiffness, excellent dimensional stability, low friction and creep | Gears, bearings, precision mechanical parts, pump components, clips |
| ABS | Tensile Strength: 40-48 MPa, Density: 1.04-1.07 g/cm³, excellent impact resistance, good dimensional stability, easy to plate and paint | Housings, enclosures, automotive interior, consumer products |
| PC (Polycarbonate) | Tensile Strength: 55-70 MPa, Density: 1.20 g/cm³, high impact and clarity, good heat resistance | Transparent housings, electrical enclosures, medical and safety parts |
| PEEK | Tensile Strength: 90-100 MPa, Density: 1.32 g/cm³, high temperature (260°C), chemical and wear resistant | Aerospace, medical, semiconductor and high-performance parts |
Process Parameters
| Parameter | Standard Range |
|---|---|
| Injection Pressure | Up to 220 MPa depending on material |
| Dimensional Tolerance (Precision) | ±0.02mm on critical dimensions (with DFM review) |
| Dimensional Tolerance (Standard) | ±0.10mm general (per general tolerance standards) |
| Wall Thickness | 0.8mm - 4.0mm typical; 0.5mm with high-flow resins |
| Draft Angle | 0.5° - 2° per surface texture |
| Surface Roughness (Cavity) | SPI A2 (Ra 0.05μm) to SPI C3 (Ra 3.2μm) |
| Max Part Size | 800mm x 600mm x 400mm (up to 2,000g shot weight) |
| Mold Steel | P20, 718H, S136, NAK80, H13; hardened to HRC 48-52 |
| Cavity Count | 1, 2, 4, 8, 16, 32 cavities |
| Mold Life | 100k - 1M+ shots depending on steel and resin |
Surface Finishes
SPI A1/A2 (Mirror Polish)
High-gloss polished cavity, Ra 0.012-0.05μm. For optical lenses and premium cosmetic parts.
SPI B1/B2 (Fine Grit)
Fine sanded cavity, Ra 0.05-0.1μm. Standard for most cosmetic exterior parts.
SPI C1/C3 (Lapped)
Semi-gloss lapped finish, Ra 0.35-3.2μm. General-purpose functional surfaces.
SPI D1/D3 (Dry Blast)
Matte textured finish, Ra 3.2-18μm. Hides flow lines and provides non-slip grip.
Texture / Etching
Custom leather, wood or geometric textures via mold etching (MT-11000 series and custom patterns).
Pad / Screen Printing
Multi-color logos, symbols and markings on 2D and gently curved surfaces.
Painting (2K / UV)
Automotive-grade paint systems with custom colors, soft-touch and matte/gloss options.
Design for Manufacturing (DFM)
- Free DFM analysis within 24 hours for uploaded STEP/IGES files
- Select insert type deliberately: threaded inserts (brass/nylon), turned pins, stamped bus bars or nuts – each needs different retention features
- Design retention features into the insert: knurls, grooves, flutes or flattened sections so the plastic grips and torque does not spin the insert
- Account for thermal mismatch: metal and plastic expand differently; allow clearance and avoid stress cracks around rigid inserts
- Position inserts for automated placement and reliable mold sealing to avoid flash at the insert parting line
- Balance wall thickness around the insert to control shrinkage, sink and warpage
- Choose gate location and type so flow does not displace or over-stress the insert
- Keep draft and texture consistent so parts eject cleanly around encapsulated metal
Tooling & Capacity
| Type | Lead Time | Suitable For |
|---|---|---|
| Prototype Mold (Soft Tooling) | 2-3 weeks | 25-500 pieces, design validation and pre-production |
| Production Mold (P20 / 718H) | 4-6 weeks | 100k-500k shots, standard volume |
| Production Mold (S136 / NAK80) | 5-7 weeks | 500k-1M+ shots, corrosive or high-wear resins |
| Multi-Cavity / Hot Runner | 6-8 weeks | High-volume production, 2-32 cavities for lower per-piece cost |
Quality Assurance
- Incoming material inspection – resin and metal inserts verified on incoming lots
- First Article Inspection (FAI) with CMM measurement; full dimensional report on the first article
- Insert placement verified each cycle (presence, position, orientation) before and after molding
- In-process checks at molding and trimming stations
- Dimensional inspection with calipers, gauges and CMM on critical features including insert position
- Visual inspection for flash at inserts, short shots, sink and surface defects
- Pull-out / torque checks on retained inserts where specified
- Lot traceability with inspection records and traveler documents retained per batch
Applications
- Threaded inserts and nuts molded into plastic housings for reusable metal threads
- Electrical connectors with molded-in metal contacts and terminals
- Bus bars and conductive paths encapsulated for insulated power distribution
- Sensor housings with embedded metal cores and shielding
- Automotive fasteners and brackets combining plastic body with metal function
- Medical device components with metal cores for strength or conductivity
- Structural brackets joining plastic to metal sub-assemblies in one part
- RF shielding components molded around metal mesh or frames
Why Choose FHY Precision
One integrated part: metal function and plastic body in a single molding – eliminates post-assembly and loose components
Strong retention: engineered knurls and grooves hold inserts against pull-out and torque
Reduced assembly cost: no press-fit, welding or adhesive steps after molding
Material flexibility: PA66, POM, ABS, PC, PEEK and more, with brass, steel or copper inserts
Tight tolerance: ±0.02mm on critical dimensions, insert position verified per cycle
Free DFM analysis: upload STEP/IGES for a report within 24 hours on inserts, walls, gates and cost
Rapid tooling: prototype mold in 2-3 weeks; T1 samples in 3-5 days
One-stop: molding, finishing (texture, print, paint) and inspection from China
FAQ
1. What is insert molding and when should I use it?
Insert molding places a metal component (threaded insert, pin, nut or bus bar) into the mold and injects plastic around it, fusing them into one part. Use it when you need a metal feature – a reusable thread, a conductor, or a rigid core – inside a plastic body, and you want to remove a separate assembly step. If the metal is only partially encased or added after molding, that is overmolding, which we also support.
2. What insert types can you mold in?
Common inserts are brass threaded inserts (heat- or mold-in), turned steel pins and shafts, stamped bus bars and contacts, nuts and standoffs, and copper or steel cores. Each needs retention features such as knurls, grooves or flutes so the plastic grips it. Send us your insert or print and we will recommend retention geometry.
3. Do you support overmolding as well as insert molding?
Yes. Insert molding encapsulates a pre-placed metal part; overmolding (e.g. soft-touch TPE/TPU over a substrate) adds a second material layer. Both are used to combine materials in one part. The free DFM review helps decide which is right for your design.
4. What tolerances can you hold?
Standard molded tolerance is ±0.10mm; we hold ±0.02mm on critical dimensions, including the position of the molded-in insert, which we verify every cycle. We review the tolerance plan in the DFM report.
5. How do you prevent flash and defects around the insert?
Flash at the insert parting line comes from poor seal or insert position. We design insert seats for reliable mold sealing, verify placement each cycle, and balance gate location so flow does not disturb the insert. In-process and final inspection catch short shots, sink and flash.
6. What is your minimum order quantity?
MOQ is 100 pieces for insert molding (25 pieces with soft tooling for early validation), because tooling is required. We advise the most economical entry volume in the quote.
7. How long does tooling and production take?
Prototype mold: 2-3 weeks with T1 samples 3-5 days after. Production mold: 4-6 weeks. Recurring production ships in 1-3 weeks per batch depending on volume. Dates are confirmed in writing.
8. Can you mold PEEK or other high-performance resins?
Yes. We mold PEEK and other engineering/ high-temperature resins for aerospace, medical and semiconductor applications, with the higher melt-temperature tooling and process control they require.
9. Can you sign an NDA and protect my design?
Yes. NDA signage is standard before reviewing files; drawing access is limited to the project team and parts are never shown without written permission.
10. Do you ship insert-molded parts internationally?
Yes, worldwide. Samples by express (3-7 business days); volume by air or sea freight (2-6 weeks). Export paperwork includes commercial invoice, packing list and origin documentation, with suitable packing for transit.
11. How do I start?
Send your STEP/IGES (or drawings) plus the insert specification. We return a free DFM report within 24 hours and a quote covering tooling, piece price and lead time. After approval, tooling starts and T1 samples follow in 2-3 weeks.
12. How much stronger is a molded-in insert than a self-tapping screw?
Consistently several times stronger. Pull-out testing shows molded-in brass inserts typically achieve 100-400N depending on size and resin, against 50-250N for self-tapping screws – and the screw figure degrades with every disassembly. Real-world cases are starker: a pump housing where self-tapping screws stripped at 7 N·m during assembly (40% below the 12 N·m spec) held 18 N·m with molded-in M6 brass inserts, a 50% margin. If your product will be assembled and disassembled repeatedly, molded-in inserts are the engineering answer.
13. What boss design rules apply around molded-in inserts?
The boss outside diameter should be 2.5-3.0 times the insert outer diameter for molded-in inserts – an M6 insert with 8-9mm OD needs a boss around 20-27mm OD. Thinner walls stress-crack during tightening or service. Keep the boss wall close to the part wall thickness with a small radius at the base so it cools at a similar rate; a thick boss base looks fine in CAD but sinks visibly on the opposite face after molding. Draft of 0-0.5° is typical for molded-in boss geometries.
14. How do you control thermal expansion mismatch between insert and plastic?
Metal and plastic shrink at different rates, so every insert joint carries residual stress at the interface – the goal is managing it, not eliminating it. Our controls: keep boss walls uniform so cooling is balanced, avoid sharp corners that concentrate stress, specify insert retention features (knurling, grooves, undercuts) that carry load mechanically rather than relying on shrink fit alone, and validate with thermal cycling where the application demands it. Properly designed molded-in joints retain about 96% of initial pull-out strength after 10,000 cycles from -40 to +85°C.
15. What insert materials can you mold in?
Brass (C36000) is the default for threaded inserts – it machines easily, resists corrosion and accepts knurling that locks into the plastic. Hardened steel (12L14) for high-strength structural joints, stainless 303/304 for medical, food and marine environments, and aluminum 6061-T6 where weight matters. For electrical contacts we mold brass or phosphor bronze terminals. The resin side matters too: PA6-GF30 and PPS are our usual recommendations when dimensional stability and retention are both critical.
16. How do you prevent insert displacement and flash blocking the thread?
Two failure modes, two controls. Displacement during injection comes from inadequate insert location – we use positive location features in the mold so the insert cannot shift under melt pressure, and we verify position on first-off parts before the run continues. Flash over the thread face comes from poor shut-off; we design positive shut-off at each insert face so the threaded hole stays clean. Both are verified on first articles, because a blocked thread discovered at assembly is a batch rework, not a single-part defect.