36 experiences in two shot injection molding

Two-color mold: Two plastic materials are injected on the same injection molding machine and are molded twice, but the product is only molded once. Generally, this molding process is also called double-material injection molding, which is usually completed by a set of molds and requires a special two-color injection molding machine. TWO SHOT INJECTION MOLDS are currently becoming more and more popular in the market. This process can make the appearance of the product more beautiful, easy to change colors without spraying, but the cost is expensive and the technical requirements are high.

3.  The rear mold should be rotated 180 degrees, and the front mold will not move.

1. Basic principles of two-color mold design：

(1) Do 1 time for hard glue and 2 times for soft glue；

(2) Do it once for transparency, 2 times for non-transparency；

(3) Do it once for plastics with high molding temperature and twice for plastics with low molding temperature；

The above is the basic principle of making a two-color mold, otherwise the mold will be made in vain; in addition, when sealing the glue, try to rely on the broken sealing glue instead of inserting the broken sealing glue. Even if it is recommended that customers modify the product, they should try to rely on the broken sealing glue as much as possible.；

2.  The guide sleeve of the mold embryo guide post must be symmetrical up and down, left and right, and the front and rear molds must be symmetrical.

4.  The product spacing must be subject to the spacing of the nozzle of the injection molding machine. The spacing of the nozzle of some foreign two-color injection molding machines is adjustable, some are not adjustable, and the domestic ones are not adjustable.

5.  There are two independent ejection systems, and there are also two ejection sticks. The two products of the rear mold are the same, and the thimble is the same. It is a rotation relationship, and it must not be made into a translation relationship.

6.  The thimble plate can only be reset with a spring, not with screws, because the rear mold has to be rotated.

7.  The side locks must be on all four sides of the center of the mold, and the front and rear molds are symmetrical, otherwise, when the rear mold rotates 180, it will not match the front mold.

8.  If the pitch of the glue inlet point is different from the pitch of the nozzle of the injection molding machine, the top stick hole should be made waist-shaped, because the pitch of the top stick of the injection molding machine cannot be adjusted. Note that most of the injection nozzles of domestic two-color injection molding machines cannot be adjusted.

9.  Pay attention to the direction of the parallel nozzle of the injection molding machine provided by the customer, whether it is the x-axis or the y-axis, in order to determine the layout of the product ranking.

10.  The direction of transporting water in and out of the water must be on the side of heaven and earth, and the inlet and outlet of each circulating water must be on the same side. The inlet must not be in the sky and the outlet on the ground, because the rear mold must be rotated 180 degrees. Pay attention to the size of the mold embryo should not exceed the height of the outlet tank of the injection molding machine, otherwise it cannot be transported.water.

11.  The product injected for the first time should be placed on the non-operating side, because after the first injection, the product should be rotated 180 degrees for the second injection, just to the operating side, which is convenient to take the product.

12.  The code mode position of the export mold 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.

13.  Precautions for the parting surface: The parting surface of the rear mold should be the parting surface obtained after the merger of the two products is the rear mold; the front mold parting surface should be the single product, and the combined product parting surface is not advisable.

14.  The tolerance of the front and rear flanges is minus 0.05mm, the tolerance between the two flanges is plus or minus 0.02mm, the gap between the top rod and the top rod hole is 0.1mm on one side, and the center distance tolerance of the front and rear mold guide sleeve guide post is plus or minus 0.01. Tolerance must be added to the four sides and depth of the mold frame.Otherwise, when the rear mold is rotated 180 degrees, the batch front will be generated due to inconsistent height. The frame depth tolerance is negative 0.02mm.

15.  If the mold embryo has been processed in the mold embryo factory, when the factory wants to process the nozzle and the top rod hole, the center of the spacing of the 4 guide post guide sleeve holes should be used as the reference to take the number, otherwise the deviation is too much, it is easy to get stuck in the mold. Mold injection molding master WeChat: mojuren should indicate that it is a two-color mold embryo when ordering the mold embryo. The four guide post guide sleeves and frame are symmetrical, and the rear mold can be rotated 180 degrees to match the front mold.

16.  If it is a two-color rotating rear mold, it is much simpler. The two front mold cores are the same, and the hard glue is injected on one side. Rotate 180 degrees (note that the product cannot be dropped when it is rotated, and the gate can be automatically separated), turn to the other side and then inject the soft rubber. There is no need to arrange the thimble for injection molding the hard rubber. Just arrange the mold core on the soft rubber side. In addition, please pay attention to shrinkage. If the soft rubber is completely wrapped around the hard rubber, the mold core should be arranged.If you live, you only need to shrink the hard glue, and if the contours are in contact, the hard glue and the soft glue must shrink.

17.  If it is a two-color mold with a set of molds, it is a straight barrel and a 90-degree barrel that shoots glue. There is no need to rotate. Only one mold core is required. The separation method of soft glue and hard glue depends on the position of the glue sealing.

18.  The two shapes of cavity are different, and one product is formed separately. The two core ones have the same appearance.

19.  After the front and rear molds of the mold are rotated 180° at the center, they must match. This inspection action must be done when designing.

20.  Pay attention to the position of the thimble holes, the minimum interval is 210mm. For large molds, the number of top stick holes must be appropriately increased. Moreover, since the thimble attached to the injection molding machine itself is not long enough, it is necessary to lengthen the thimble in our mold, and the thimble will grow out of the mold embryo base plate by about 150mm.

21.  Two positioning rings must be designed on the base plate of the rear mold.

22.  The total thickness of the front mold panel plus the a board must not be less than 170mm. Please carefully check the other reference data of this type of injection molding machine, for example, the maximum mold thickness, the minimum mold thickness, the hole spacing of the top stick, etc.

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

24.  When designing the cavity for the second injection molding, in order to prevent the cavity from inserting (or wiping) the glue position of the product that has been molded for the first time, a partial air avoidance can be designed. However, it is necessary to carefully consider the strength of each sealing position, namely: in injection molding, whether there will be deformation of the plastic under high injection pressure, resulting in the possibility that the second injection molding may have a batch front.；

25.  When injection molding, the size of the product for the first injection molding can be slightly larger so that it can be pressed tighter with another cavity during the second molding to achieve the effect of sealing glue.

26.  Before the a and b plates are closed, it is necessary to pay attention to whether the front mold slider or lifter will be reset first and crush the product? In this way, it is necessary to find a way to close the mold on the a and b boards first, and then the slider or lifet of the front mold can be reset.

27.  The water transportation arrangements of the two cavities and core are as adequate as possible, balanced and the same.

28.  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 the soft glue is easy to deform.

29.  Pay attention to whether the activity of the plastic will affect the product that was molded for the first time during the second injection molding, causing its glue position to deform? Assuming that this is possible, we must think of ways to improve it.

30.  The two-color mold must carefully choose the gate position. It is best to choose a latent glue inlet for one product, so that the product and the flow channel can be automatically cut off. When latent glue injection 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 Bozai to avoid touching the secondary material due to the residue of the primary entry point.

31.  Two-color injection molds often use rotating injection molds. The punch/die in the two positions of the rotating injection mold requires the same size and accuracy, and it fits well with the die/punch. When the ejection and release mechanism on the two-color injection molding machine cannot be used, a hydraulic ejection and release mechanism must be provided on the rotary table.

32.  Two-color mold injection molding usually uses the same plastic of different colors, or it can be two different plastic raw materials. At this time, it is necessary to consider the interface between the two materials, the difference in shrinkage, and the processing technology parameters. Aspects.

    Two-color injection molded products are generally based on hard plastics such as abs and pc with soft plastics such as tpe. Due to the relationship between cost or application, it is necessary to fully consider that there may be no good adhesion and fusion between the two materials used, and the mold treatment at the junction between the two materials (generally there will be embossed lines). PhenomenonOr you need to make a mold sealing groove) There are many problems such as the thickness of the material thickness! In order to make the two plastics “stick” tighter, it is necessary to think about the “viscosity” between the materials and the roughness of the mold's appearance. There are special tpu materials for two-color injection molding; and the smoother the appearance of the molds, the tighter they “stick."

33.  Generally speaking, the shrinkage rate of a two-color mold 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 the primary material and the secondary material, there are many factors to be taken into account, such as the fluidity of raw materials, the shape of plastic products, and so on.

34.  Pay attention to the positioning of the front and rear molds; the slope gap between all inserts and the breaking surface should be as large as possible, and it should be more than 0.1mm.

35.  When two-color injection molding of abs/pc, abs/pc+abs, and abs/pmma, pc, pc+abs or pmma with a higher temperature need to be injected first. If it is a transparent surface shell mold, most of the flip-chip mold structure is used.

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

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

b.  The thickness of the material is recommended to use transparent 0.8mm or more, non-transparent 0.7mm or more, and non-transparent try to use light colors. When there are led lights, pay attention to shading.；

c.  The parting surface of the transparent piece is the same width as the place of the hole. The width is recommended to be 0.5mm. The curved surface is smooth to avoid side view. It can pass far away and is not beautiful. Minimize the hole.；

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

e.  For now, it is not recommended to do two-color injection molding with main lenses. The cost of molds and products is too high. There are considerable requirements for the equipment and technical level of mold manufacturers. If you do, you need to give a detailed solution for the entire process for evaluation, and the intermediate links need to be reviewed.；

f.  For large-area two shot injection molded parts, the two key tests are drop and hot and cold shock. In these two tests, transparent and non-transparent parts are easy to detach. Heat and cold shock-40-65, the time is 48 hours.

g.  The structure of the two-color parts should be simplified as much as possible, and the complex parts should be matched. The width of the ribs of the non-transparent parts should be as low as 0.5-0.6 to avoid shrinkage.