Technology of two color injection molding that every technician must to know!

Two color injection molding technology is also called double-material plastic injection molding technology, which is a technology that uses two plastic materials to mix and mold plastic products. Technical connotation is actually using a mold assembly to shape and weld molding work in the mold. Therefore fundamental principle is to plasticize two different plastic raw materials, and then use mold for welding installation, in order to achieve purpose of two shot injection molding.

•  Two shot injection molding technology type

1.1 Core Rotary two color injection molding technology
This technology is also known as transfer molding core two shot injection molding technology. Technical principle is to inject the first raw material plastic by injection equipment, inject it into small hole of mold, and become the first plastic after molding. Then mold is rotated by 180°, second raw material plastic is injected by same injection equipment, and after second plastic is molded, final encapsulation work is performed, and a basic two shot injection molding work is completed.
Use and operation of this technology is relatively simple, and generally trained workers can operate freely, and can greatly enhance design freedom of plastic injection molding products, and can be processed with simple tools.

1.2 Shrinking mold core typetwo color injection molding technology
Shrinking mold core type two shot injection molding technology mainly utilizes a hydraulic device to compress mold. First, under control of hydraulic device, core that can move up and down is pushed to top as piston is generally pushed and plastic raw material is injected. After the first raw material is solidified, movable core is controlled to fall, and another plastic raw material is injected, and then hydraulic device is controlled to press core up and solidify.
Plastic injection molding products pressed by this technology are initially produced, and then formed plastic mold parts are taken out for subsequent processing. This technical operation is also relatively simple, and it is necessary to control timing of movement of hydraulic device.

1.3 Principle of rotating two color injection molding technology
This technique first involves injection of the first material before proceeding. At the time of injection, the other parts of mold are subjected to mold clamping treatment, cutting and separating are gradually performed during injection, rear part of insert is gradually retracted, but still exists on the part of release sheet and mold is dynamically retracted. After ejector rod and granule portion of entire plastic injection molding machine are cooled and detached, the first part is completed; the second part of plastic injection molding operation is generally same as the first part, but the second plastic injection molding uses two nozzles simultaneously to inject. After curing is completed, two parts are ejected together and an plastic injection molding cycle is completed.

1.4 Core sliding two color injection molding technology
Principle of core sliding two shot injection molding technology is to classify core into two. The first core is used to slide core to specified position for implementation of mold clamping operation. The first raw material plastic is injected into mold, after cooling, mold is opened once.
Transmission slides first core out, slides second core to cavity, and performs a second plastic injection. After it is cooled and formed, it completes an injection cycle and two finished products are slid out. This technical model is more suitable for needs of large two shot injection molding plastic mold parts.

• Characteristics of two color injection molding process

2.1 Two-component structure of two color injection molding machine
Due to influence of purpose of product, two shot injection molding machine needs to be equipped with two identical plasticizing injection devices. This is not only demand of process, but also ability to perform rotational transformations. These two sets of injection devices of same specification need to have same function except for structure. When plastic injection molding is carried out, temperature of raw materials, injection pressure and injection rate in two sets of equipment can be uniformly adjusted, so that indexes of plastic products injected are kept at a consistent level for related integration and welding. If parameters of two sets of equipment are inconsistent, try to adjust to a consistent level.

2.2 Machine structure difference between two color injection molding components and ordinary plastic injection molding components
Due to unique characteristics of plastic injection molding products produced by two shot injection molding assembly, there are some significant differences between mechanical setup of machine and ordinary plastic injection molding machine.
Firstly, two shot injection molding assembly uses a higher melt temperature, which has a certain gap compared with ordinary plastic injection molding components. It requires a high temperature to maintain ability to operate in mold. Pressure of injection is also large, not only because two different plastic raw materials are used, but it is necessary to use a strong pressure for fusion, and it is designed to overcome huge resistance of molten material flowing in mold to ensure smooth plastic injection molding.

2.3 Material parameter setting of two color injection molding technology
Two shot injection molding technology uses two different materials for production of plastic injection molding products. Therefore it is necessary to consider materials before plastic injection molding. It is necessary to consider not only quality standards of selected materials, but also control of parameters such as temperature and pressure during plastic injection molding.
Since mold used in two shot injection molding technology is different from ordinary plastic injection molding mold, it is required that material usage parameters of two shot injection molding technology have a higher melt temperature to ensure that melt does not solidify before injection molding is completed. At the same time, injection device is used to control pressure of raw materials so that they can smoothly reach various parts of mold, thereby achieving purpose of plastic injection molding.

• Two color injection molding products and mold design points

3.1 Structural characteristics of two color injection molding molded products
Structure of two shot injection molding molded product is very different from that of ordinary plastic injection molding products. Since plastic injection molding is performed using two different materials, product has two different properties, which is fundamentally different from ordinary plastic injection molding products; Before plastic injection molding, detailed two shot injection molding structure design is required, and compatibility characteristics of two materials should be fully considered.
Combine function and environment of plastic injection molding products to design mixing ratio and connection mode of two materials, analyze complexity of process in detail, and design strength of use, so that two shot injection molding products can meet relevant material standards and requirements.

3.1.1 Choice of two materials
Two color injection molding technology uses two different materials for plastic injection molding, so selection of two different materials is also an important process. Generally, two different colors of plastic are selected, which can greatly improve strength and durability of plastic injection molding products. At the same time it makes it easier to fuse. However, special-purpose products may need to take advantage of extremely different nature of two materials, which requires solving problem of difficulty of fusion of two large differences. Mainly there will be stratification and shedding problems, which is a fatal blow to plastic injection molding products. Therefore, for shrinkage rate and different interface conditions, careful consideration is required, and proportion of materials used must be adjusted.

3.1.2 Design of internal structure and shape of product
Design of structure and shape of product first needs to be considered from purpose and use of product, and detailed research on size and internal structure. Generally, it is necessary to increase contact area of two raw materials to enhance firmness. Here a large number of small grooves and convex grooves can be designed inside the product for inlaying and stitching, which achieves purpose of increasing contact area of two materials. When plastic injection molding is performed, use strength and service life of product can be better improved, and practicality is enhanced.

3.2 Rotary mold two-speed plastic injection molding
This kind of mold needs different considerations in molding part. Firstly, concave and convex grooves of two plastic injection molding need to be strictly designed, and it is ensured that seams can be tightly combined during docking, and mold release mechanism is required to perform mold release work after second injection. Different plastic injection molding methods are also required to be carefully distinguished. After mold is released from vertical rotary injection machine, product is ejected to complete relevant work. Demoulding that cannot be taken out by injection machine requires use of a hydraulic device for demolding.

• Conclusion

In summary, two shot injection molding technology has been developed for many years, but it has been gradually valued and applied in recent years, because finished product has a good adaptability to use environment, and production efficiency is extremely high. Different practical requirements can be satisfactorily met, so they are gradually being widely used. They have good economic benefits in automotive industry and other fields, and are a technology with great development potential.

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