Today we talked for the 2 shot mold

 Part One. Advantages of 2shot injection molding:

The 2 shot mold can combine two resins with different characteristics and colors 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 improve the grade and added value of the product. Not only has the function of anti-slip and increasing friction, but 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, and the loss can be 7% lower than that of plastic overmolding, and the manufacturing cost of products can be 20%-30% lower than that of plastic overmolding.

Part Two. 2 shot 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 the two-color machine are independently separated, the colors of the finished products are mostly two-color distinct and not mixed together. The biggest difference between the two-color injection molding machine and the general injection molding machine lies in the design of the movable template of the injection unit machine. Generally speaking, a two-component injection molding machine has two separate injection units, while a general injection molding machine has only one injection unit. The configuration of two groups of injection units varies with the design of each manufacturer. As for the design of the movable template, a rotation mechanism must be provided. Common designs such as adding a turntable or a rotating shaft mechanism to provide 180° reciprocation The rotation function makes the mold produce cyclic and alternating actions. There are also some special two-color molds that do not need a turntable or a rotating shaft mechanism, but are slid alternately or horizontally rotated by the mold.

3. Production process characteristics of injection molding 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 molding dies with the same structure that can be rotated and transposed. During plasticizing injection, it is required that the process parameters such as melt temperature, injection pressure, and injected melt volume in the two sets of plasticizing injection devices are the same, and the fluctuation difference of process parameters in the two sets of devices should be minimized.

2. Compared with ordinary injection molded plastic products, two-color injection molded plastic products have higher parameter values for the melt temperature and injection pressure during injection. The main reason is that the mold runner in the two-color injection molding is relatively long, the structure is relatively complicated, and the flow resistance of the injected molten material is relatively large.

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

4. When two-color plastic products are injection molded, in order to make the melts of two different colors weld well in the mold during molding and ensure the molding quality of injection molded products, higher melt temperature and higher mold temperature should be adopted. , higher injection pressure and injection rate.

4. Structural form of two-color mold

The traditional two-color injection mold has two forms: "punch translation" and "punch rotation".

The mold of "convex translation" has two dies and one punch. When the first barrel is injected, the punch is closed with the first die. Complete the injection of the first plastic. After the first plastic is solidified, the concave and convex molds are separated, and the semi-finished product formed by the first plastic stays in the convex mold and moves together with the convex mold to the position aligned with the second concave mold. After the injection molding machine is closed, the second barrel injects the second plastic. After the second plastic has solidified, the injection molding machine opens the mold and removes the complete part.

The two-color mold in the form of "punch rotation" has two dies and a punch composed of two back-to-back combinations. This punch can be rotated. The equipped double-sided injection molding machine has two barrels, and 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 are solidified, the injection molding machine is turned on and the complete product is ejected automatically. After taking out the product, the "rotatable punch" turns 180 degrees. The injection molding machine is closed for the next cycle.

Since the first and second cylinders of the "punch translation" mode are injected alternately, while the first and second cylinders of the "punch rotation" mode are injected simultaneously. 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 a common cavity required for both the first plastic ("hard") and the second plastic ("soft"). The die and punch required for this technology are single, which is fundamentally different from the first two production modes. After the first barrel is injected with the first plastic, wait for the first plastic to partially solidify or solidify. The power oil cylinder at the control head drives the blade which acts as isolation, and retreats to be flat with the surface of the punch. At this time, the second barrel injects the second plastic. After the second plastic is completely solidified, the injection molding machine is opened and the complete product is removed. The injection molding machine is then shut down for 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 (smaller two-color injection molding machines can be used to reduce investment and energy consumption). And it can double the output compared with the "encapsulation method" used before, and fundamentally avoid the defective products caused by putting the shrunk and deformed "hard glue" back into the mold cavity.

The characteristics of the two-color mold:

1. The two shapes of the front mold are different, and one product is molded respectively. And the two shapes of the back mold are exactly the same. (Note: If there is any difference, make a front mold slider to ensure that the rear mold is consistent)

2. After the front mold of the mold is rotated 180º from the center, it must match the rear mold. This must be taken into account when designing.

3. When designing, please carefully check the parameter data of the two-color injection molding machine, such as the maximum mold thickness, the minimum mold thickness, the distance from the ejector pin hole, etc.

4. The nozzle of the three-plate mold should preferably be designed so that it can be automatically demoulded. Pay special attention to whether the demoulding action of the soft glue nozzle is reliable.

5. When designing the cavity for the second injection, in order to prevent the cavity from inserting (or scratching) the glue position of the product that has been formed for the first time, you can design a part of the void. However, the strength of each sealing position must be carefully considered, that is, during injection molding, is there a possibility that the plastic will deform under high injection pressure, resulting in the possibility of a batch front in the second injection molding?

6. During injection molding, the product size of the first injection molding can be slightly larger, so that it can be pressed more tightly with another cavity during the second molding, so as to achieve the effect of sealing.

7. Pay attention to whether the flow of plastic will impel the product that has been formed for the first time during the second injection molding, causing its glue position to deform? If this is possible, we must find a way to improve it.

8. The water transportation arrangement of the two cavities and the core should be as sufficient as possible, balanced and uniform.

9. In 99% of the cases, the hard rubber part of the product is injected first, and then the soft rubber part of the product is injected. Because the soft rubber is easy to deform.

10. In order to make the two plastics "stick" tighter, the "stickiness" between the materials and the roughness of the mold surface must be considered. Two-color injection molding has a special TPU; and the smoother the surface of the mold, the tighter they "stick".