The main difference is the number of materials used. 1K uses one material, while 2K uses two, resulting in more complex and functional products.
1. Equipment and Mold Structure
Single-Color Injection Molding:
- Equipment: Only a standard injection molding machine is required.
- Mold: Only one mold is needed (single mold).
- Structure: The structure is the simplest, with low maintenance costs, mainly consisting of a single injection system and a single cooling system.
- Equipment: Requires a two-color injection molding machine, a specialized machine with two injection units (2-shot machine).
- Mold: The mold structure is very complex, usually having two sets of cores (Part A & Part B), and equipped with a rotary table or slider to move the part to the second injection position after the first color is injected.
- Structural Features: Can be "overmolding" or "double-clean color" structure. Overmolding involves placing the semi-finished product into the second mold for injection, while double-clean color involves two injections within the same mold.
2. Molding Principle and Process Flow
Single-Color Injection Molding:
Process: Plastic granules are heated and melted → injected into the mold → cooled and solidified → mold opened and ejected.
Product: The final product consists of one material or one color, and the material properties remain consistent throughout the process.
Two-Color Injection Molding:
Process: Divided into two injections (Two-Shot):
- First Shot: The first color (usually the core or base layer) is injected into the mold (usually the smaller cavity) for molding.
- Mold Rotation: The mold rotates 180° or slides, transferring the first color part to the second injection position.
- Second Shot: The second color (usually the surface layer or covering layer) is injected into the mold (usually the larger cavity) for encapsulation or overmolding.
- Ejection: The final product is ejected in one go after cooling.
- Product: The final product consists of two different materials or colors. Common forms include "hard and soft combinations" (such as the hard outer shell + soft frame of a mobile phone case) or "aesthetic decoration" (such as the hard shell + soft grip of a racket handle).
3. Cost and Production Capacity
Single-Color Injection Molding:
- Cost: Lower mold and equipment costs.
- Production Capacity: Short molding cycle, high production capacity, suitable for mass production.
Two-color injection molding:
- Cost: Due to the need for a rotary table, dual molds, and specialized machinery, the initial investment is very high.
- Production capacity: The molding cycle is long (two injections), and precise positioning control is required, resulting in relatively low production capacity. It is suitable for mid-to-high-end or highly functional products.
4. Main Applications
- Single-color injection molding: Suitable for most plastic parts, such as automotive interior and exterior parts, and ordinary plastic housings.
- Two-color injection molding: Primarily used for products with special requirements for feel, function, or aesthetics:
- Functionality: Such as handles, keyboard keys (soft rubber + hard shell), anti-slip pads (soft rubber + hard shell).
- Decorative: Such as marble-patterned decorative parts, two-color cups, puzzle toys, etc.
- Material characteristics: Such as injecting foaming material inside a hard shell to reduce weight.
