OEM Overmolding Services & Specialized Factories

Two-shot (also known as 2K, multi-shot, or dual-injection) molding utilizes a specialized injection press equipped with two separate injection barrels and a rotating platen or index plate. The substrate is molded first, immediately indexed, and the secondary elastomer or contrasting resin is injected within the same closed tool cycle. In contrast, insert overmolding involves placing pre-fabricated inserts (such as CNC-machined metal bushings, stamped copper busbars, or pre-molded plastic skeletons) into an injection mold cavity prior to shot injection. Two-shot molding is preferred for ultra-high-volume plastic-to-plastic assemblies, whereas insert overmolding is essential for metal-to-plastic integration, extreme mechanical structural reinforcement, and encapsulated electrical electronics.

Interfacial bond reliability is established via a dual engineering protocol: 1. Chemical / Thermal Fusion: We select compatible polymer pairings whose melt temperature and polarity match (e.g., Polyurethane/TPU bonding to Polycarbonate or ABS). In insert molding over metals, we apply automated atmospheric plasma surface activations or specialized heat-activated silane chemical primers. 2. Mechanical Interlocking: We integrate undercuts, knurled diamond grooves, cross-hatched geometries, and through-hole anchor channels into the substrate drawing. Even in extreme thermal shock or chemical solvent exposure, the elastomer mechanically locks into the core skeleton, preventing peel initiation.

During cavity injection, polymer melt pressures can reach 500 to 1,500 bar, which risks deflecting or floating unsupported metal inserts. Our toolmakers design precision core locating pins, spring-loaded shut-offs, and custom vacuum or magnetic retaining seats inside the tool steel. Furthermore, Moldflow analysis ensures balanced gate locations so that polymer flow fronts converge symmetrically around the insert, equalizing hydraulic lateral forces and preventing core shift or dimensional runout.

Every shipment from Sunmy Hardware is backed by an auditable First Article Inspection (FAI) report, batch-specific raw resin and metal mill certificates (chemical composition and mechanical strength), in-house Zeiss CMM coordinate inspection reports, durometer hardness verification (Shore A / Shore D scales), and 100% visual inspection on critical shut-off lines to guarantee zero burrs or cosmetic flash. For electrical applications, hipot dielectric isolation test records are provided upon request.

Yes. Prior to commissioning multi-cavity hardened H13 or S136 steel production tooling, we offer rapid bridging options: precision CNC machining of metal inserts coupled with silicone urethane vacuum casting (simulating production TPE and ABS durometers), or rapid prototype aluminum tooling (yielding 500 to 5,000 real production parts) to validate ergonomic tactile grip, sealing compression deflection, and assembly fits in actual field operating conditions.