Niche · Niche Process
Overmolding
Hard substrate + soft TPE / TPV / TPU overmolding for integrated grip, anti-slip, and sealing. Covers everything from tool handles to electronic device housings.
What is Overmolding
Overmolding is a process where a rigid substrate is first molded, then placed into a second mold or station where a soft plastic is injected to encapsulate it. The final part is integrally molded from two or more materials, requiring no adhesive or additional assembly.
There are two methods:
- 2K Molding (Two-Shot Molding): Completed in one cycle on a two-shot machine. Suitable for volumes ≥10,000 pieces.
- Insert Overmolding: The substrate is molded first, then manually or robotically placed into a second mold for overmolding. Lower tooling cost, suitable for small batches.
Common Material Combinations
| Substrate | Overmold (TPE Type) | Bonding Method | Typical Applications |
|---|---|---|---|
| ABS / PC / PC+ABS | TPE-S (SEBS-based) | Chemical bond | Electronic device grip, handles |
| PP | TPE-V / TPV | Chemical bond | Automotive seals, outdoor parts |
| PA66 / PA6 | TPE-U / TPU | Chemical bond | Tool handles, sports equipment |
| POM | Modified TPE-S | Requires mechanical interlock | Low-friction transmission + soft touch |
| Metal insert | LSR (Liquid Silicone Rubber) | Surface treatment + locking groove | Medical handles, seals |
Design Guidelines
- Overmold wall thickness ≥ 1.0mm to ensure flow fill; ideal 1.5-3mm
- Substrate surface texture (EDM texture / sandblasting) enhances mechanical interlock; essential for chemically incompatible combinations
- Avoid sharp corners; overmold fillet radius R ≥ 0.5mm to prevent stress concentration
- Color selection: overmold color one shade darker than substrate for better stain resistance (common for electronic device grips)
- Recommended Shore hardness range: Shore A 30-90; A 60-70 offers optimal tactile feel
Typical Applications
- Power tool handles (anti-slip + vibration damping)
- Consumer electronics (toothbrushes, razors, camera bodies)
- Kitchenware (knife handles, spatula handles, sealing lids)
- Automotive (gear shift knobs, steering wheel buttons, seals)
- Medical (surgical instrument handles, endoscope outer sheaths)
- Sports equipment (fitness equipment grips, protective gear liners)