Two color mold design and injection precautions

I. Precautions for Two - Color Mold Design

(1) In terms of mold structure

1. Parting surface design
   Determine the position of the parting surface reasonably. For two - color molds, since two injection - molding operations are required, the parting surface should take into account the molding requirements of both plastic materials. For example, during the design, the demolding method of the first injection - molded part should be considered to ensure that it does not affect the mold closing and plastic flow during the second injection - molding.
   The parting surface should be as simple and flat as possible, avoiding complex shapes, so as to reduce the difficulty of mold processing and improve the sealing performance during injection - molding.

2. Cavity layout
   Optimize the cavity layout according to the shape and size of the product. The position arrangement of different - color or different - material parts of the two - color product in the cavity should consider factors such as the injection sequence and plastic flow balance.
   It is necessary to ensure that during the two injection - molding processes, the stress on each part of the mold is uniform, avoiding the situation where excessive local pressure causes mold deformation or damage.

   
   

   
   

   

(2) In terms of material selection

1. Compatibility of plastic materials
   When selecting two plastic materials for two - color injection - molding, consider their chemical compatibility and differences in shrinkage rate. For example, the shrinkage rates of the two materials should not differ too much, otherwise it will cause problems such as product deformation and cracking.
   At the same time, the two materials should not undergo chemical reactions under injection - molding temperature, pressure and other process conditions, so as not to affect the performance and appearance of the product.

2. Mold material
   The mold material should have sufficient hardness, wear resistance and thermal stability. Since the mold needs to withstand two different injection - molding conditions during the two - color injection - molding process, the performance requirements for the mold material are higher.
   For example, common mold steel materials such as H13, etc., whose hardness and toughness after heat treatment can meet the usage requirements of two - color molds.

(3) Design of hot runner system

1. Hot runner balance
   For the hot runner system of two - color molds, it is necessary to ensure the balance of plastic flow in the hot runner. During the two injection - molding processes, each hot runner branch corresponding to each cavity should be able to evenly deliver plastic.
   This can be achieved by reasonably designing the diameter and length of the hot runner and using appropriate hot runner control technology to avoid the phenomenon of insufficient filling or over - filling in some cavities.

2. Temperature control of hot runner
   During two - color injection - molding, different plastic materials may require different injection - molding temperatures. The hot runner system should be able to accurately control the temperature of different parts to meet the injection - molding requirements of the two plastics.
   For example, use independent temperature controllers to control different hot runner areas to ensure that the plastic is in a suitable molten state during the first and second injection - molding.

II. Precautions for Two - Color Mold Injection - Molding

(1) Injection - molding process parameters

1. Injection - molding temperature
   Set an appropriate injection - molding temperature according to the characteristics of the two selected plastic materials. For example, if the melting point of the plastic material for the first injection - molding is low, the injection - molding temperature can be appropriately reduced; during the second injection - molding, the temperature should be determined considering the bonding situation with the first injection - molded part and its own molding requirements.
   Too high a temperature may cause plastic decomposition, discoloration or flash and other defects, while too low a temperature will make the plastic have poor fluidity and result in incomplete filling.

2. Injection - molding pressure and speed
   During two - color injection - molding, adjust the injection - molding pressure and speed reasonably. During the first injection - molding process, ensure that the plastic can fully fill the cavity, but without generating excessive internal pressure.
   During the second injection - molding, the injection - molding pressure and speed should take into account the fusion with the first injection - molded part. If the pressure and speed are inappropriate, it may lead to poor bonding between the two materials or delamination.

   
   

   

(2) Injection - molding sequence

1. Determine the injection - molding sequence
   Determine which color or material of plastic is injected first according to the design requirements of the product. Generally, inject the internal structure or basic part first, and then inject the external decoration or function - enhancing part.
   For example, for some two - color products with a combination of soft and hard plastics, inject the hard plastic part first as a support structure, and then inject the soft plastic part to achieve a comfortable hand feeling or sealing function.

2. Positioning during the injection - molding process
   Between the two injection - molding operations, ensure that the injected part in the mold can be accurately positioned. This can be achieved through positioning structures in the mold, such as positioning pins, positioning rings, etc.
   If the positioning is inaccurate, it will cause the bonding position of the second injection - molded part and the first injection - molded part to shift, affecting the appearance and function of the product.