Two-shot molding (Two-Shot Molding), also known as two-material injection molding, is a technology that injects two different plastics in a single molding cycle to create an integrated product with different colors, materials or functions. It seamlessly combines two materials like a "sandwich biscuit" without need for post-bonding or assembly, and is widely used in consumer electronics, daily necessities, automobiles and other fields.
Classic product cases:
�� Electric toothbrush: hard body (ABS) + non-slip soft rubber handle (TPE);
�� Car lights: transparent lampshade (PC) + black sealed base (PP);
�� Mobile phone buttons: translucent characters (PMMA) + matte base (ABS).

Core of two-color injection molding lies in precise coordination of mold movement and injection molding timing. Common process is as follows:
1. First injection molding
Mold A cavity is closed, and the first material (such as hard glue) is injected to form base part of product;
After mold is opened, mold core with semi-finished product is rotated 180° (or translated to another station).
2. Second injection molding
Mold B cavity is closed, and second material (such as soft glue) is injected on the base to cover or embed a specific area;
After cooling, it is ejected to obtain a two-color one-piece molded product.
Key equipment:
Rotary mold (with servo motor drive); Dual-nozzle injection molding machine (can independently control two materials); High-precision temperature control system. (Suggested illustrations: Schematic diagram of two-color mold rotation process, working diagram of double-nozzle injection molding machine)

1. Ultimate integration
Hard glue and soft glue, transparent and opaque materials are seamlessly combined, without glue and screws;
Typical applications: smart watch straps (TPU+PC), medical device handles (PP+silicone).
2. Functional upgrade
Two-color keyboard: translucent characters + light-shielding base layer, uniform backlight without light leakage;
Sealed structure: automotive sensor housing (PA66+TPV), waterproof and dustproof level is improved.
3. Cost savings
Omit assembly, printing, lamination and other processes, and reduce labor costs by more than 50%;
Case: A Bluetooth headset uses a two-color mold, the shell logo is directly molded, and silk screen process is eliminated.
4. Design freedom
Can achieve gradient colors, three-dimensional textures, and hidden structures;
Case: High-end cosmetics bottle caps (outer transparent PETG + inner pearlescent ABS), with a strong sense of light and shadow layering.

1. Material compatibility
Thermal matching: Melting point temperature difference of two materials must be less than 20℃, otherwise bonding surface is prone to cracking;
Chemical compatibility: For example, ABS and TPU have strong adhesion, while PP and PC need to add compatibilizer.
2. Mold complexity
Precision of rotating mechanism must reach ±0.02mm to prevent misalignment and glue overflow; Difficulty of runner system design is doubled, and cross-contamination of two materials must be avoided.
3. Cost threshold
Mold cost is 2~3 times that of ordinary molds; Suitable for mass production (usually more than 100,000 pieces are required to dilute the cost).

Three-color/four-color mold:
Automotive interior parts (leather texture + metallic paint + translucent atmosphere light strip);
Technical difficulties: More mold stations and more complex timing control.
Bio-based material combination:
PLA (corn starch-based plastic) + natural fiber, used for environmentally friendly packaging.
Intelligent parameter adjustment:
AI monitors temperature and pressure of bonding surface in real time and automatically optimizes injection molding parameters.

 

Two-color mold technology allows plastic products to move from "single function" to "intelligent composite", which is not only a breakthrough in industrial aesthetics, but also a leap in manufacturing efficiency. With advancement of material science and precision control, we may see more "impossible combinations" born from molds in the future.