The basic principles of two-color injection mold design

- Mar 27, 2019-


The basic principles of two-color injection mold design


(1) Hard plastic is done at first, and soft rubber is done sencond;


(2) 1 time for transparency and 2 times for non-transparency;


(3) The plastic with high molding temperature is made  first, and the molding temperature is low second


  The above is the basic principle of making a two-color mold, otherwise the mold will be failed; in addition, when do the over mold, try to use the flat surface to seal, instead of any shut-off surface, even if it is recommended that the customer modify the product, it must be use the flatness surface for over molding sealing .  if not , the part will have big flash and will fail for the over molding;


1. The guide bush guide bushing must be symmetrical up and down, left and right symmetrical.


2. The back mold should be rotated 180 degrees, and the front mold does not move.


3 The product spacing must be based on the spacing of the injection molding machine's gun nozzle. The nozzle spacing of some foreign two-color injection molding machines is adjustable, some are not adjustable, and the domestic is not adjustable.


4. Two separate ejector systems, two top sticks. The two products of the rear die are the same, the thimbles are the same, and the rotation relationship is not made into a translational relationship.


5. The ejector plate can only be reset with a spring. It is not possible to force the reset by the screw because the rear die is to be rotated.


6. The side lock must be on the four sides of the center of the mold, and the front and rear molds are symmetrical. Otherwise, when the rear mold is rotated 180, it will not be aligned with the front mold.


7. If the distance between the glue points and the distance between the nozzles of the injection molding machine are different, the top stick holes should be made into a waist type because the spacing of the top pins of the injection molding machine is not adjustable. Note that most of the injection nozzles of domestic two-color injection molding machines are not adjustable.


8. Pay attention to the direction of the parallel nozzle of the injection molding machine provided by the customer. It is the x-axis or the y-axis to determine the layout of the product.


9. The direction of water in and out of the water must be on the side of the heaven and earth, and the inflow and out of each circulating water must be on the same surface. The water should not be in the sky, and the water should be on the ground side. Because the back mold should be rotated 180 degrees, pay attention to the mold. The size should not exceed the height of the water tank of the injection molding machine, otherwise the water cannot be transported.


10. The first injection of the product should be placed on the non-operating side, because the first injection of the product should be rotated 180 degrees for the second injection, just to the operating side, easy to take the product.


11. The pattern position of the exit die should be on the operating side and the non-operating side, not on the heaven and earth side, because their products should be fully automatic.


12. Note on the parting surface: the parting surface of the rear mold parting surface should be the back part after the combination of the two products; the front part parting surface should be taken from a single product, and the combined product is not available. Parting surface.


13. The tolerance of the front and rear flanges is minus 0.05mm, the tolerance of the two flanges is plus or minus 0.02mm, the gap between the top and the top of the top stick is 0.1mm, and the center tolerance of the guide bushes of the front and rear die guide sleeves is positive or negative. 0.01, the tolerance of the four sides and the depth of the mold frame. Otherwise, when the rear mold rotates 180 degrees, the front end is generated due to the inconsistency of the height. The frame depth tolerance is minus 0.02 mm.


14. If the mold base has been processed in the mold factory, the factory should process the nozzle and the top hole, and take the number of the center of the guide hole of the four guide pillars as the reference. Otherwise, the deviation is too much and the card is easy to be used. Die die. When ordering the mold embryo, it is necessary to indicate that it is a two-color mold base. The four guide pillar guide sleeves and the frame are symmetrical, and the rear mold can be matched with the front mold after being rotated by 180 degrees.


15. If it is the two-color rotation of the rear mold, it is much simpler. The two front cores are the same. After the hard rubber is injected, rotate 180 degrees (note that the product can not be dropped when the product is turned, the gate can be automatically separated). After the other side, the soft rubber is injected. The injection of the hard rubber does not need to be placed on the thimble. It only needs to be placed on the soft rubber core. In addition, the shrinkage should be noted. If the soft rubber is completely entangled with hard rubber, only the hard rubber should be placed. Shrinkage, if the contours are connected, the hard rubber softener should be shrunk.


16. If it is a two-color mold of a mold, it is a straight barrel, a 90-degree barrel shot, no need to rotate, only one core, soft and hard glue separation method by row seal gum.


17. The two shapes of the cavity are different, forming one product separately. The core's two shapes are the same.


18. After the front and back molds of the mold are rotated 180° from the center, they must be matched. This check must be done during design.


19. Pay attention to the position of the ejector pin with a minimum spacing of 210mm. Large molds must properly increase the number of jack holes. Moreover, since the thimble attached to the injection molding machine itself is not long enough, it is necessary to design a long ejector pin in our mold, and the thimble grows about 150 mm from the base of the mold base.


20. Two positioning rings must be designed on the back plate.


21. The total thickness of the front mold panel plus the a board shall not be less than 170 mm. Please carefully review other reference data for this type of injection molding machine, for example, maximum die thickness, minimum die thickness, and top hole spacing.


22. The depth of the front sprue should not exceed 65mm. The interval from the top of the upper side (large nozzle) sprue to the center of the mold is not less than 150 mm.


23. When designing the cavity of the second injection molding, in order to prevent the cavity from inserting (or rubbing) the glue position of the product that was formed for the first time, a partial avoidance can be designed. However, it is necessary to carefully consider the strength of each sealant position, that is, in the injection molding, whether there will be deformation of the plastic under the large injection pressure, which may lead to the possibility of the second injection.


24. When molding, the first injection molded product can be slightly larger in size so that it can be pressed tighter with another cavity during the second molding to reach the sealant.


25. Before the a and b plates are closed, pay attention to whether the front mold slider or lifter will first reset and crush the product. Therefore, it is necessary to make the method to clamp the a and b plates first, then the slider or lifet of the front die. Talent reset.


26. The transport of the two cavity and core is as full as possible and balanced.


27. 99% of the cases are the hard rubber part of the first injection molding product, and the soft rubber part of the re-injection product. Because the soft rubber is easy to deform.


28. Pay attention to whether the plastic activity will be impulsive in the second injection molding, and the plasticity will be deformed. If you have this possibility, you must improve the method.


29. Two-color molds must be carefully selected for the gate location. It is best to choose a latent glue in one product so that the product and runner can be cut off automatically. Three-plate molds or hot runner molds can be considered when latent feed cannot be used. If the material is a point gate, do a wave, to avoid hitting the secondary material due to one entry residue.


30. Two-color injection molds often use rotary injection molds. The punch/die at two positions of the rotary injection mold requires uniform size and precision, and works well with the die/emboss. When the ejection mechanism on the two-color injection molding machine cannot be utilized, a hydraulic ejection and release mechanism must be provided on the rotary table.


31. Two-color mold injection molding usually uses the same plastic of different colors, or two different plastic raw materials. At this time, it is necessary to consider the interface effect, shrinkage difference, processing parameters and other aspects of the two materials.


Two-color injection molding products are generally made of hard plastics such as abs and pc, and tpe soft plastics. Due to the cost or application, it is necessary to fully consider the two materials that may be used without good adhesion and fusion. Mold treatment at the joint (generally there will be a phenomenon of embossing the road or need to be used to seal the groove) and the thickness of the material and so on! In order to make the two plastics "sticky" tighter, we must think about the "between the materials" Viscosity and the roughness of the mold surface. Two-color injection molding has a special tpu material; the smoother the mold appearance, the more tightly they stick.


32. In general, the shrinkage rate of a two-color mold depends on the primary material. Because the primary material has already supported the contours of the plastic product, the secondary material does not shrink more. As for how to determine the primary and secondary materials, there are many factors to consider, such as the fluidity of the raw materials, the shape of the plastic products, and so on.


33. Pay attention to the positioning of the front and rear molds; all the insertion and the slope of the broken surface should be as large as possible, and should be 0.1mm or more.


34. ABS/PC, ABS/PC ABS, ABS/PMMA two-color injection molding, you need to first injection high temperature pc, pc abs or pmma. In the case of a transparent face shell mold, most of the flip mold structures are used.


35. Transparent large two-color injection molding is a place to pay attention to structural design:


a. The reservation of the gate location must be agreed in advance with the mold factory;


b. The thickness of the material is recommended to be transparent 0.8mm or more, non-transparent 0.7mm or more, non-transparent as far as possible to use light color, when there is a led light, pay attention to shading;


c. The width of the parting surface of the transparent part and the hole are the same, the width is recommended to be 0.5mm, the surface is smooth, avoiding the side view, can pass through far, unsightly, and minimize the hole;


d. The thickness of the non-transparent parts is limited, and the structure of the upper ribs and the like is as far as possible between 0.5 and 0.6 mm to avoid shrinkage;


e. For the current time, it is not recommended to do two-color injection molding with main lens. The cost of mold and product is too high. There are quite a lot of requirements for the equipment and technical level of the mold manufacturer. If you do, you need to give the whole solution a detailed solution for the whole process. For evaluation, the intermediate links need to be reviewed;


f. For large-area two-color injection molded parts, two key tests are drop and thermal shock. In both tests, the transparent and non-transparent parts are easily disengaged. Hot and cold shock -40 -65, time 48 hours.


g. The structure on the two-color parts should be as simple as possible, and the complex parts should be made above the matching parts. The width of the ribs of the non-transparent parts should be 0.5-0.6 as much as possible to avoid shrinkage.



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