Principle Of Two-Color Injection Molding

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Principle of two-color injection molding

The most common form of two-color product molds is that two identical movable molds should correspond to two different fixed mold cavities, in which the cavity volume of the second color shell product is often larger than that of the first color base product cavity. After injection, the mold is opened first, and then the movable mold is rotated 180° by the rotatable structure of the injection machine, and then the mold is closed and the second injection is performed with raw materials of different colors or different raw materials from the first injection.

After the second mold opening, the punch that has completed two injections is demolded. The first raw material injection and the second raw material injection are carried out at the same time, requiring two injection nozzles on the injection machine to inject different colors or different raw materials respectively, and the fixed plate of the movable mold should be equipped with a rotary device that can rotate 180° , For most of the matching materials, two-color injection molding can be formed by rotating the fixed plate of the movable mold. At this time, the movable mold is not ejected, and then the mold is closed, and the injection of the second material is carried out. After the heat preservation and cooling, the fixed and movable molds are opened, and the products on the movable mold side are ejected.

With the increasing complexity of products. Three-color or even four-color molding needs began to appear. Usually, there are two types of three-color machines, namely two-station three-color machine (commonly known as "false three-color") and three-station three-color machine (commonly known as "true three-color"). ). In fact, the difference between the two is not true or false, but according to the different product structure design, different turntable control methods are used. Similarly, the four-color machine can also be divided into "two-station" and "multi-station" models.

In terms of technology, the control accuracy requirements of the multi-station turntable are significantly higher than those of the two-station, and the manufacturing cost of the machine is relatively high. Therefore, it is not necessary to blindly pursue the multi-station multi-color machine, but should be selected according to the product structure. the most appropriate solution.

Structure type of two-color mold

1. Core rotary two-color injection molding structure

First, the first part of the two-color part is produced by injection molding, and then the mold is opened and closed, and the first molded product is transferred into the large cavity to become an insert, and the injection device injects another color of plastic into the large cavity. By encapsulating the inserts, two-color parts can be formed. At the same time, the injection device injects the first plastic into the small cavity, and the next plastic insert is formed. After the product is solidified and formed, the mold is opened, the two-color plastic part is pushed out, the movable mold is rotated, and the mold is closed, which completes an injection molding cycle. .

Using this technology can greatly improve the degree of freedom of product design, so it is often used in the processing of adjustable wheel toothbrushes and disposable razors for automobiles.

2. Shrinking mold core type two-color injection structure

The shrink mold core type two-color injection molding technology mainly uses hydraulic devices to compress the mold. First, under the control of the hydraulic device, the core that can move up and down is pushed to the position where the top rises like a piston, and the plastic raw material is injected. After the first raw material is solidified, the movable core is controlled to fall down, and then Inject another plastic raw material, and then control the hydraulic device to make the core rise and press, and wait for it to solidify and form.

3. Removal plate rotary two-color injection structure

The mold is closed first, and a plastic is injected into the first cavity, and the movable mold part of the opening mode retreats. Since the shear gate is set in the fixed mold, the shear runner is cut off from the core part during parting, but the core part is separated. The laminate is still on the movable mold part release plate. The moving die continues to retreat, and the main sprue condensate is pushed out from the cold material cavity in the rotating shaft through the ejector rod and the pulling rod, and then the stripping plate is pushed out through the connecting rod and the rotating shaft.

4. Core sliding two-color injection structure

First move the primary core to the cavity of the mold, close the mold, inject the first plastic, and then cool and open the mold. The core is moved to the cavity part, the mold is closed, the second plastic is injected, cooled, the mold is opened, the product is ejected, and one molding is completed. Core slides are used to form larger plastic parts.

5. Seesaw structure

After one injection, the mold is opened, and the broken needle goes down under the action of the push rod, so that the seesaw rotates around the rotating shaft, and will be pushed up by the broken ejector plate under the push of the seesaw, so that the broken needle moves up, and the once At the boundary of the closed area of the product, there is a break hole. Then, when the secondary injection mold is closed, the broken needle moves downward under the action of the return pin on the broken plate, leaving a circular hole, so that the secondary material can be drilled into the closed area from the broken hole.