The difference between two-color mold and overmolding

The difference between two-color mold and rubber-coated mold

1. Advantages of two-color injection molding

Two-color molds can combine two resins and colors with different characteristics into a single two-color product, which can reduce the assembly and post-processing of molded products. Save the cost of melting and printing, increase the beautiful visual effect of the product, and enhance the grade and added value of the product. Not only does it have the functions of anti-slip and increasing friction, the flexible resin material makes it more ergonomic and feels better. Two-color injection molding products have high quality stability, easy control of product deformation, short molding cycle and high output. The loss can be 7% lower than that of overcoated injection molding, and the product manufacturing cost can be 20%-30% lower than that of overcoated injection molding.

2. Two-color molding principle

Two-color injection molding usually refers to the molding of two colors or different types of plastics. Since the two sets of injection units and nozzles of a two-color machine are independently separated, the colors of the finished products are mostly clear and not mixed together. The biggest difference between a two-color injection molding machine and a general injection molding machine is the design of the movable template of the injection unit. Generally speaking, a two-color machine has two sets of independent injection units, while a general injection machine has only one set of injection units. The configuration of two groups of injection units has various forms depending on the design of each manufacturer. As for the design of the movable template, it must provide a rotation mechanism. Common designs such as adding a turntable or a rotating shaft mechanism, etc., to provide 180° reciprocation The rotation function enables the mold to produce cyclic and alternating movements. There are also some special two-color molds that do not require a turntable or rotating shaft mechanism, but the mold slides alternately or rotates horizontally.

3. Characteristics of the production process of injection molded two-color products

1). The two-color injection molding machine consists of two sets of plasticizing injection devices with identical structures and specifications. The nozzle should have a special structure according to the production method, or be equipped with two sets of molds with identical structures that can be rotated and transposed. During plasticizing injection, the melt temperature, injection pressure, injection melt volume and other process parameters in the two sets of plasticizing injection devices are required to be the same, and the difference in process parameter fluctuations in the two sets of devices must be minimized.

2). Compared with ordinary injection molded plastic products, two-color injection molded plastic products require higher parameter values for the melt temperature and injection pressure during injection. The main reason is that the mold flow channel in two-color injection molding is relatively long, the structure is relatively complex, and the flow resistance of the injection melt is large.

3)． Two-color injection molding plastic products must use raw materials with good thermal stability and low melt viscosity to avoid decomposition due to high melt temperature and long residence time in the flow channel. The most commonly used plastics are polyolefin resins, polystyrene and ABS materials.

4)． When two-color plastic products are injection molded, in order to ensure that the two different colors of melt can be well welded in the mold during molding and ensure the molding quality of the injection molded product, a higher melt temperature and a higher mold temperature should be used. , higher injection pressure and injection rate.

4. Two-color mold structure

Traditional two-color injection molds have two forms: "punch translation" and "punch rotation".

① The "punch translation" mold has two concave molds and one punch. When the first barrel injects glue, the punch and the first die are closed. Complete the injection of the first plastic. After the first plastic solidifies, the concave and convex molds are separated, and the semi-finished product formed of the first plastic stays on the male mold and moves with the male mold to a position aligned with the second concave mold. After the injection molding machine is closed, the second barrel is injected with the second plastic. After the second plastic solidifies, the injection molding machine opens the mold and removes the complete product.

② The "punch rotation" two-color mold has two concave molds and a punch composed of two back-to-back combinations. This punch can be rotated. The injection molding machines equipped with both sides have two barrels. The second barrel is preferably designed in the vertical direction of the movement direction of the injection molding machine. Two different plastics can be injected at the same time. When the two injected plastics solidify, the injection molding machine opens and automatically ejects the complete product. After taking out the product, the "rotatable punch" rotates 180 degrees. The injection molding machine closes and proceeds to the next cycle.

Since the first and second barrels of the "punch translation" mode are injected in turn, the first and second barrels of the "punch rotation" mode are injected at the same time. Therefore, for the same product, the production efficiency of the "punch rotation" mode is twice that of the "punch translation" mode.

5. New technology of two-color mold

The two-color injection molding machine is equipped with two barrels. The mold is single-cavity, with common cavities required for both the first plastic ("hard glue") and the second plastic ("soft glue"). This technology requires a single die and punch, which is fundamentally different from the first two production modes. After the first plastic is injected into the first barrel, wait until the first plastic is partially solidified or solidified. The power cylinder that controls the opening drives the blade that plays the role of isolation and retreats to be flush with the surface of the punch. At this time, the second barrel is injected with the second plastic. After the second plastic is completely solidified, the injection molding machine is opened and the complete product is taken out. The injection molding machine then shuts down and proceeds to the next cycle. The obvious advantage of this technology is that it simplifies the mold and reduces the demand for the working space of the injection molding machine (a smaller two-color injection molding machine can be used to reduce investment and energy consumption). Moreover, the output can be increased exponentially compared to the previously used "gluing method", and defective products caused by putting the shrunk and deformed "hard glue" back into the mold cavity are fundamentally avoided.

6. The difference between rubber-coated mold and two-color mold

1). Two-color mold: Two plastic materials are injected on the same injection molding machine and molded in two times, but the product is only ejected once. Generally, this molding process is also called double-material injection molding, which is usually completed by a set of molds and requires a specialized two-color injection molding machine. Two-color molds can combine two resins and colors with different characteristics into a single two-color product, which can reduce the assembly and post-processing of molded products. Save the cost of melting and printing, increase the beautiful visual effect of the product, and enhance the grade and added value of the product. Not only does it have the functions of anti-slip and increasing friction, the flexible resin material makes it more ergonomic and feels better. Two-color injection molding products have high quality stability, easy control of product deformation, short molding cycle and high output. The loss can be 7% lower than that of rubber-coated injection molding, and the product manufacturing cost can be 20%-30% lower than that of rubber-coated injection molding.

2). Overmolding mold (secondary molding): The two plastic materials are not necessarily injection molded on the same injection molding machine and are molded in two times; after the product is taken out of one set of molds, it is then placed in another set of molds. Perform the second injection molding. Therefore, this molding process is usually completed by two sets of molds, without the need for a special two-color injection molding machine. The mold structure is the same as that of a single-color injection mold, and the seed material is mainly controlled by adjusting the flow rate of the injection parameters. juncture point. The rubber-coated mold is mainly soft rubber wrapped in hard rubber. The soft rubber is commonly used artificial rubber, TPU, TPR and other rubber materials, and the hard rubber can be ABS, PC, PP, etc.

If you have other suggestions ,please leave your comments .