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Design and injection molding of two-color molds-2

  1. Two positioning rings must be designed on the rear mold base plate.
  2. The total thickness of the front mold panel plus A-board cannot be less than 170mm. Please carefully check other reference data of this type of injection molding machine, such as maximum mold thickness, minimum mold thickness, ejector hole distance, etc.
  3. The depth of the front SPRUE should not exceed 65mm. The distance from the top of the upper side (big nozzle) SPRUE to the center of the mold base is not less than 150mm.
  4. When designing the CAVITY for the second injection molding, in order to prevent the CAVITY from being inserted (or scratched) from damaging the glue position of the product that has been molded for the first time, a partial void can be designed. However, the strength of each sealing position must be carefully considered, that is, during injection molding, whether there is a possibility that the plastic will deform under high injection pressure, resulting in the possibility of sharp edges in the second injection molding.
  5. During injection molding, the size of the first injection molded product can be slightly larger so that it can be pressed more tightly with another CAVITY during the second molding to achieve the sealing effect.
  6. Before clamping plates A and B, pay attention to whether the front mold Slider or Lifter will reset first and crush the product? In this way, we must find a way to close the mold on plates A and B first, and then the SLIDER or LIFET of the front mold can be reset.
  7. The water transport arrangements of the two CAVITY and CORE should be as adequate, balanced and consistent as possible.
  8. In 99% of cases, the hard rubber part of the product is injected first, and then the soft rubber part of the product is injected. Because soft glue is easy to deform.
  9. Pay attention during the second injection molding. Will the movement of the plastic affect the product that has been formed for the first time, causing the plastic position to deform? If this is possible, we must find ways to improve it.
  10. For two-color molds, the gate location must be carefully selected. It is best to choose latent glue feeding for a single product, so that the product and the flow channel can be automatically cut off. When latent glue feeding cannot be used, a three-plate mold or a hot runner mold can be considered. If the primary material is a point gate, it should be waved to avoid the secondary material being penetrated by the residue from the primary entry point.
  11. Two-color injection molds often use rotary injection molds. The male/female molds at the two positions of the rotary injection mold must be consistent in size and accuracy, and must cooperate well with the female/convex mold. When the ejection and demoulding mechanism on the two-color injection molding machine cannot be used, a hydraulic ejection and demoulding mechanism must be installed on the rotary table.
  12. Two-color mold injection molding usually uses the same plastic in different colors, or two different plastic raw materials. At this time, it is necessary to consider the interface effect, shrinkage difference, processing parameters, etc. of the two materials. Two-color injection molding products are generally made of hard plastics such as ABS and PC combined with soft TPE plastics. Due to cost or application, it is necessary to fully consider that the two materials used may not have good adhesion and fusion. There are many issues such as mold processing at the joints (generally there will be embossing patterns or mold sealing grooves need to be made), as well as the thickness of the material! 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 material; and the smoother the mold surface, the tighter they “stick.”
  13. Generally speaking, the shrinkage rate of two-color molds depends on the primary material. Because the primary material has already supported the outline of the plastic product, the secondary material will not shrink more. As for how to determine primary materials and secondary materials, there are many factors to consider, such as the fluidity of raw materials, the shape of plastic products, etc.
  14. Pay attention to the positioning of the front and rear molds; the slope difference of all insertion and break surfaces should be as large as possible, and should be more than 0.1mm.
  15. When using ABS/PC, ABS/PC+ABS, and ABS/PMMA two-color injection molding, the PC, PC+ABS or PMMA with higher temperature needs to be injected first. If it is a transparent shell mold, most of it uses a flip-chip mold structure.
  16. Transparent and large two-color injection molding requires attention in terms of structural design:
    A. The reservation of the gate position must be agreed in advance with the mold factory;
    B. The material thickness is recommended to be more than 0.8mm for transparent materials and more than 0.7mm for non-transparent materials. Try to use light colors for non-transparent materials. Pay attention to shading when there are LED lights;
    C. The width of the parting surface of the transparent part is the same as that of the hole. The width is recommended to be 0.5mm. The curved surface should be connected smoothly to avoid side view. It can penetrate far and is unsightly. Minimize the hole as much as possible;
    D. The thickness of non-transparent parts is limited, and the upper ribs and other structures should be between 0.5-0.6mm as much as possible to avoid shrinkage;
    E. At present, it is not recommended to do two-color injection molding with a main lens. The cost of molds and products is too high, which requires considerable equipment and technical level of the mold manufacturer. If it is done, the other party needs to provide a detailed solution for the entire process. For evaluation, all intermediate links need to be reviewed;
    F. For large-area two-color injection molded parts, the two key tests are drop and hot and cold shock. In these two tests, transparent parts and non-transparent parts are easy to separate. Hot and cold shock -40 -65, time 48 hours.
    G. The structure of the two-color parts should be simplified as much as possible, and the complex parts should be placed on the matching parts. The width of the ribs of non-transparent parts should be as low as 0.5-0.6mm to avoid shrinkage.

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