Production experience of two shot injection molding

Time:2020-02-22 08:50:21 / Popularity: / Source:

Now let’s talk about experience summary in daily production process of plastic injection molding. I believe that you are interested in learning and it is helpful.
two shot injection molding 
1. In general, shrinkage rate of a two shot injection molding depends on primary material. Because primary material has already supported contours of plastic product, secondary material does not shrink more. As for how to determine primary and secondary materials, there are many factors to consider, such as fluidity of raw materials, shape of plastic products and so on.
2. When designing cavity of second plastic injection molding, in order to prevent cavity from inserting (or rubbing) product that was properly molded for the first time, a partial avoidance can be designed. However it is necessary to carefully consider strength of each sealant position, that is in plastic injection molding, whether there will be deformation of plastic under large injection pressure, which may lead to possibility of rushes in second injection.
3. After front and back molds are rotated 180° from center, they must be matched. This check must be done during design.
4. Spacing of products must be based on spacing of nozzles of plastic injection molding machine. Distance between nozzles of two shot injection molding machines in foreign countries is adjustable, and some are not adjustable, and domestic ones are not adjustable.
5. Two color injection molding must be carefully selected for gate location. It is best to choose a latent glue in one product so that 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 material is a point gate, do a wave, to avoid hitting secondary material due to one entry residue.
6. Ejector plate can only be reset with a spring. It is not possible to force reset by screw because rear die has to be rotated.
7. Side lock must be on four sides of center of mold, front and rear molds are symmetrical. Otherwise, when rear mold is rotated 180, it will not be aligned with front mold.
8. If distance between glue points and nozzles of plastic injection molding machine are different, top stick holes should be made into a waist type because spacing of top pins of plastic injection molding machine is not adjustable. Note that most of injection nozzles of domestic two color injection molding machines are not adjustable.
9. Injection molding factory pay attention to direction of parallel nozzle of plastic injection molding machine provided by customer. It is x-axis or y-axis to determine layout of product.
10. Direction of water in and water out must be on top and bottom side, inflow and out of each circulating water must be on same surface. Water in should not be on the top, and water out should not be on the bottom. Because back mold should be rotated 180 degrees. Size of mold base should not exceed height of water tank of injection molding machine, otherwise water cannot be transported.
Two color injection molding 
11. 99% of cases are hard rubber part of plastic injection molding product first, and then soft rubber part of re-injection product. Because soft rubber is easy to deform.
12. Basic principles of two color injection molding design: (1) 1 time for hard glue, 2 times for soft glue; (2) 1 time for transparent, 2 times for non-transparent; (3) 1 time for plastic with high molding temperature, 2 time for plastic with low molding temperature. As above is basic principle of making a two color injection molding, otherwise mold will be fail; In addition, when sealing, try to use sealant instead of inserting sealant. Even if it is recommended to modify product, try to rely on breaking sealant as much as possible;
13. Note on parting surface: parting surface of rear mold parting surface should be back part after combination of two products; front part parting surface should be taken from a single product, and parting surface of combined product is not available.
14. Depth of front sprue should not exceed 65mm. Interval from top of upper side (large nozzle) sprue to the center of mold is not less than 150 mm.
15. If mold base has been processed in other injection molding factory, nozzle and top stick hole is procesed in our own injection molding factory, and take number based on the center of pitch of four guide pillar guide sleeves. Otherwise deviation is too much and mould is easy to be eclipsed. Two shot injection molding embryo should be specified when ordering mold, four guide post guide sleeve and frame symmetry, rear mold can be matched with front mold after rotating 180 degrees.
16. If it is two-color rotation of rear mold, it is much simpler. Two front cores are same. After hard rubber is injected, rotate 180 degrees (note that product can not be dropped when product is turned, gate can be automatically separated). After the other side, soft rubber is injected. Injection of hard rubber does not need to be placed with thimble but only needs to be placed on soft rubber core. In addition, shrinkage should be noted. If soft rubber is completely entangled with hard rubber, only hard rubber should be mentioned with shrinkage, if contours are connected, hard and soft rubber should be mentioned with shrinkage.
17. If it is a two shot injection molding for one mold, it is a straight barrel, a 90-degree barrel shot, no need to rotate, only one core, soft and hard glue separated by row seal gum.
18. Two shapes of cavity are different, forming one product separately. Two shapes of core are same.
19. Pay attention to whether plastic activity will be impulsive in the second plastic injection molding, and plasticity will be deformed. Assuming this is possible, we must think of ways to improve.
20. Pay attention to position of thimble hole with a minimum interval of 210mm. Large molds must properly increase number of K.O. Moreover, since thimble attached to plastic injection molding machine itself is not long enough, it is necessary to design a long ejector pin in our mold, and thimble grows about 150 mm from mold base.
21. Two positioning rings must be designed on back plate.
22. Total thickness of front mold panel plus 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.
23. Pay attention to positioning of front and rear molds; all insertion and slope of broken surface should be as large as possible, and should be 0.1mm or more.
24. When molding, first injection molded product can be slightly larger in size so that it can be pressed tighter with another cavity during second molding to reach sealant.
two color injection molding design 

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