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What is Two Color Injection Molding?

Views: 0     Author: Site Editor     Publish Time: 2023-01-09      Origin: Site


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What is two-color injection molding?

Bi-color molds are gaining traction in the market for their capacity to elevate product aesthetics and simplify color variation without the need for additional painting processes. However, their adoption is tempered by significant costs and the prerequisite for specialized technical knowledge. 

In bi-color molding, also termed two-shot molding, two distinct plastics are utilized, resulting in products with clearly defined dual-color attributes. Employing a bi-color injection molding machine equipped with dual injection units, these molds enable the sequential injection of different plastics, yielding bi-color products with precision and efficiency.


Types of bi-color molds

Bi-color molds are categorized by their structural design, including core rotation, core pullback, and plate rotation types. Within the core rotation category, two subtypes exist: split type and integrated type. While the split type employs two sets of molds on a single injection molding machine, the integrated type achieves bi-color injection molding within a singular mold. Split-type core rotation molds are more commonly utilized in practice.


Female molds feature two distinct shapes, each forming a specific product type, whereas the male mold exhibits identical shapes. Achieving precise alignment after rotating the mold halves demands meticulous design and machining to ensure accurate positioning. The combined thickness of the front mold plate and A plate should not fall below 170mm, considering factors like maximum and minimum mold thickness and KO hole spacing. Preferably, design the sprue of a three-plate mold for automatic ejection, with attention to feasibility, particularly for soft rubber sprues. Incorporating venting areas in the female mold for the second injection is advisable to prevent damage to existing product cavities, balancing sealing area strength to avoid plastic deformation and flash. To ensure a proper seal, the product dimensions from the first injection can be slightly larger, facilitating a snug fit during the second injection. Evaluate the potential impact of plastic flow during the second injection on previously formed products to mitigate deformation risks. Prevent premature resetting of the front mold slide or angled top before the A and B plates close to prevent product damage. Ensure a balanced distribution of water channels in both female and male molds for efficient cooling. In most scenarios, injecting the rigid part of the product first, followed by the soft part, is recommended due to the soft rubber's susceptibility to deformation.

Bi-color injection molding

Bi-color injection molding involves injecting two distinct materials into identical molds, resulting in components with differing colors or hardness. This process enhances product aesthetics and assembly performance by combining materials with varied properties.



Bi-material co-injection molding presents several advantages over traditional injection molding:

It allows for the use of low-viscosity core materials, reducing injection pressure.

Recycled secondary materials can be environmentally friendly core materials.

Different materials can be tailored for specific usage characteristics, such as using soft material for surface layers and hard material for the core.

Lower-quality core materials can be employed to cut costs.

Special surface properties, like anti-electromagnetic interference or high conductivity, can be imparted by expensive surface layer materials.

Combinations of surface layer and core materials can reduce residual stresses, enhance mechanical strength, or improve product surface properties.

The process enables the creation of unique patterns, such as marble veining, in the products.

Development and Applications


The features and uses of multi-color injection molding and bi-material co-injection molding point to a growing trend of supplanting conventional injection molding methods. Advanced injection molding technologies not only enhance precision and manufacturing capabilities but also broaden the range of applications in the field. To address the increasingly varied demand for top-tier, value-added products, innovative injection equipment and processes are indispensable.

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