Views: 0 Author: Site Editor Publish Time: 2025-07-22 Origin: Site
Two-shot molds are designed with rotating cores or indexing plates to allow sequential injection of two materials:
Rotary Mold: The mold core rotates 180° after the first shot to align with the second cavity.
Shuttle/Indexing Mold: The mold or platen moves linearly to position the part for the second injection.
First Shot (Base Material)
The primary material (e.g., rigid ABS or PC) is injected into the first cavity.
The partially molded part cools but remains in the mold.
Mold Reconfiguration
The mold rotates or shifts to position the part for the second shot.
Second Shot (Overmold Material)
The secondary material (e.g., soft TPE or a different-colored plastic) is injected, bonding to the first shot.
The final part is ejected after cooling.
Bonding Strength: Materials must adhere well (e.g., PP+TPE, ABS+PC). Conduct peel tests during prototyping.
Melting Temperatures: The second material’s melt temperature should be lower to avoid remelting the first shot.
Shrinkage Rates: Mismatched shrinkage can cause warping or delamination.
✔ Precision Alignment – Critical to prevent flash or misalignment (tolerance ≤ 0.02mm).
✔ Runner & Cooling Optimization – Separate runners and cooling channels for each material.
✔ Gate Placement – Ensure proper flow to avoid weak bonding or air traps.
Injection Parameters: Adjust pressure, speed, and temperature for each shot.
Cooling Time: Longer cooling may be needed for the first shot to prevent deformation.
Clamping Force: Must withstand higher pressures due to multiple injections.
| Problem | Cause | Solution |
|---|---|---|
| Poor Material Bonding | Incompatible materials/low temperature | Use adhesives or plasma treatment |
| Short Shots | Uneven flow or insufficient pressure | Optimize runner design & injection speed |
| Warping | Uneven cooling/shrinkage | Adjust cooling time & material selection |
| Factor | Two-Shot Molding | Overmolding |
|---|---|---|
| Cycle Time | ✅ Single cycle, faster | ❌ Two separate cycles |
| Equipment Cost | ❌ Requires specialized machine | ✅ Works with standard machines |
| Precision | ✅ Higher accuracy | ❌ Manual handling risks misalignment |
| Applications | High-volume production (e.g., automotive) | Low-to-medium volume (e.g., prototypes) |
Consumer Electronics: Soft-touch grips on razors or phone cases.
Automotive: Seals, buttons, and multi-color interior components.
Medical: Dual-material syringe grips or ergonomic handles.
Two-shot molding improves functionality, aesthetics, and assembly efficiency but requires careful material selection, mold design, and process control.
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