Experience summary of two-color mold

At present, the methods of manufacturing two-color products include glue wrapping and two-color injection molding. The molds they use are called "glue wrapping mold" and "two-color mold" respectively. The difference is that the glue wrapping mold is a mold formed twice. First, inject the first product on the first set of mold, and then put this "semi-finished product" into the second set of mold to inject the second product, so that the second product wraps the first product, The finished product is a two-color product. The two-color mold refers to the injection molding of two plastic materials on the same injection molding machine. It is formed in two times. After the injection of the first product, the rear mold rotates 180 °, and the front mold does not move. After the injection of the second product, the product is on a set of molds. But a special two-color injection molding machine is needed. The advantages of two-color mold are high production efficiency, high dimensional accuracy and stable quality of products. Two kinds of plastic materials of plastic coated products are not necessarily injected on the same injection molding machine, nor does it need a special two-color injection molding machine. At present, it is still widely used, but the production efficiency is relatively low and there are many defective products, especially large-scale products.

Basic principles of rubber covering mold design:

1. The shrinkage of the glue wrapping mold. The shrinkage of the glue wrapping mold should be determined according to the requirements of the product material type, product structure and dimensional accuracy, but generally speaking, the mold formed for the first time is calculated according to the normal shrinkage, and the shrinkage of the second product is not needed if it is soft glue.

2. The rubber covering mold is usually soft rubber covering hard rubber. Soft rubber commonly uses TPU, TPE, TPR and other rubber materials, and hard rubber may be ABS, PC, etc. In most cases, the hard rubber part of the product is injected first, and then the soft rubber part of the product is injected, because if the soft rubber is injected first, the second injection will deform the soft rubber.

3. Two color mold injection molding usually uses the same plastic with different colors, or two different plastic raw materials. The softening temperature of the rubber of the first molding product is 20 ° C higher than that of the second molding product, otherwise the rubber of the first molding product will be melted and decomposed to produce color mixing. The fluidity of materials should be considered in the division between different materials, and the appropriate wall thickness should be selected. Because the material of the second molding will climb over the material of the first molding, if the wall thickness of the product of the second molding is not enough, it will cause poor filling, It is easy to cause bad conditions such as lack of glue, shrinkage and weld marks. Generally speaking, the wall thickness of the second formed product should be more than 0.8mm, and the best wall thickness should be 1-2mm;

4. When soft glue adopts point feeding and submerged feeding, the diameter and length of the runner connected with the glue port should be as small as possible, and attention should be paid to the cooling of the gate at the same time, otherwise the runner connected with the glue port is easy to break in the mold and difficult to take out; If it is submerged glue, the nozzle needle needs to make three steps.

Basic principles of two-color mold design:

Hard glue once, soft glue twice;

Transparent once, non transparent twice; Under special circumstances, it must be made non transparent for the first time. The rubber must be resistant to high temperature and will not be decomposed by the second transparent rubber. Plastic with high molding temperature shall be made once, and plastic with low molding temperature shall be made twice; When it's all hard glue, do it for the first time if the proportion of glue is large, and do it for the second time if the proportion of glue is small

The above is the basic principle of making two-color mold, otherwise the mold has the risk of scrap; In addition, when sealing the glue, try to use the touch through sealing glue instead of inserting the sealing glue. Even if it is suggested that the customer modify the product, try to make sure that the touch through sealing glue, side lock, mold embryo, guide post and guide sleeve must be symmetrical up, down, left and right, otherwise when the rear mold rotates 180, it cannot be aligned with the front mold. The two-color mold is also divided into single cavity and double shot (the mold kernel rotates after ejection, or the slider control does not need to rotate), rotating two-color (parallel nozzle two-color and right angle two-color)

5. The shrinkage of the two-color mold should be determined according to the type of product material, product structure, dimensional accuracy requirements and other factors, but generally speaking, the shrinkage of the first product of the two-color mold and the second product are placed together synchronously., At this time, it is necessary to consider the interface effect of the two materials, the difference in shrinkage, and whether the first material is more resistant to high temperature than the second one, and will not be decomposed by the second rubber.

6. The parameters of the injection molding machine that the two-color mold needs to know are: 1. The distance between the nozzles; 2. The injection volume of each nozzle to decide which color to use; 3: Ko position distance and maximum ejection stroke; 4: Size and bearing weight of rotary table; 5: The configuration of water, oil and circuit on the rotary table, and the depth of the nozzle should not exceed 40mm of the panel. Two locating rings must be designed on the bottom plate of the rear mold

7. The front mold of the mold does not move, and the rear mold must be able to be assembled with the front mold after rotating 180 degrees around the center of the turntable, otherwise the mold cannot be closed and formed. This inspection action must be done during the design, especially pay attention to the position and size of the guide pillar guide sleeve, side lock, guide pillar auxiliary device, nylon plug and other parts of the mold embryo;

8. The nozzle spacing on the mold must be subject to the nozzle spacing of the injection molding machine. The nozzle spacing of some two-color injection molding machines is adjustable, and some are not adjustable. It is necessary to understand the injection molding machine parameters of the customer's production and mold testing, but the KO hole spacing of the injection molding machine is not adjustable, so do not adjust the nozzle spacing together with the KO hole spacing when adjusting the nozzle spacing;

Single chamber double injection (after ejection, the mold core rotates, controlled by the slider without rotation, which is also called gate valve double color)

9. When designing the ejection system of single cavity double injection mold, we should pay attention to that the two rubber positions of this mold are formed on a rear mold kernel. When designing a cavity, there is only one set of mold and only one ejection system, because the products formed for the first time do not need to be ejected during production, and they are ejected after the second molding; Use the power of the oil cylinder or the opening and closing mold to drive the relevant mold parts, so that the second color is in two positions and formed in two states respectively. This technology is also called the two-color mold single cavity double injection technology. It is a two-color mold structure with the lowest cost and the highest production efficiency. This structure should be given priority in the design; As shown in the figure: the mold uses the oil cylinder to drive the slider to move a rubber thickness stroke with the insert, so that it can be formed twice in two positions.

10. Design two cavities on a set of molds, and use the gear rack mechanism to drive the mold core to rotate the products formed in the first cavity to the second cavity for forming; Only the rack and pinion mechanism is added to the rear mold to drive the mold core to rotate with the product. It does not need to use the driving mechanism and manipulator of the injection molding machine to replace the cavity for the product. It can be used in the two-color injection molding machine without driving mechanism and manipulator

Take parts to form two-color (the same as the plastic mold)

11. Design two cavities on a set of molds to form two materials respectively. The action principle of this method is to combine two sets of traditional injection molds into a whole set, but the cavities of the rear mold and the front mold are independent. Use the manipulator to quickly take out the products formed in the first cavity and put them into the second cavity for molding.

12. When the second formed product and the first formed product surface need to be sealed, the first product surface should be left with a preload, so that it can be pressed more tightly with the front mold of the first forming during the second forming, so as to achieve the effect of sealing. The preload is generally 0.02-0.05mm.

13. Make some anti inclined holes or inverted hook structures on the first molding products to hold the glue position of the second molding, so that the two kinds of glue can be better combined.

14. How to deal with the situation that the coated product sticks to the front mold: if the front mold of the second molding mold does not need to be sealed, then a spring block can be added to the product surface, and a spring should be added to the bottom of the spring block to prevent the product from being scratched; The draft angle of the second molding product covering the surface of the first molding product should be as large as possible.

15. What to do if there is a batch of rubber coated products: you can burn and weld the front mold or the rear mold of the second molding mold; Or add glue to the front mold or rear mold of the first formed product;

Rotating bicolor (parallel nozzle bicolor and right angle bicolor)

16. The pouring system of the two-color injection molding machine has two nozzles, which can inject glue independently or at the same time. According to the classification of nozzles, there are injection molding machines with parallel nozzles and L-type 90 ° right angle two-color machines. The two-color machines have two sets of independent ejection systems, which can eject independently. Generally, the top bar on the non operating side is closed. The two products of the rear mold are the same, and the thimble is the same. It is a rotation relationship, which must not be made into a translation relationship.

17. The ejector pin plate can only be reset by spring or oil cylinder, and cannot be forcibly reset by pull rod, because the rear mold needs to rotate.

18. Pay attention to the direction of the injection molding machine provided by the customer parallel to the nozzle, which is x-axis or y-axis (generally X-axis), so as to determine the product ranking;

19. If the water collecting block of the injection molding machine is not installed on the turntable, the direction of water transportation and water inlet and outlet must be on the same side, and the water cannot enter the sky, and the water outlet is on the ground side, because the rear mold needs to rotate 180 degrees, and pay attention to the appropriate spacing between the mold embryo and the water collecting block of the injection molding machine, otherwise the water cannot be transported.

20 the products injected for the first time should be placed on the non operating side, because after the first injection, the products should be rotated 180 degrees for the second injection, just turn to the operating side, so that it is convenient to take products.

21. For some two-color injection molding machines that require full-automatic clamping of molds, the coding position should be set on the operating side and non operating side, not on the side of the heaven and earth. It should be understood clearly before design, because automatic coding is required for product molding. 22. When designing the parting surface in 3D parting, one product drawing after the combination of the two products should be designed, so that the rear mold and the front mold of the second molding can be separated. The rubber level surface of the front mold of the first molding should be designed based on the product drawing of the first molding; The cooling circuits of the two front and rear molds should be designed as fully as possible, balanced and the same; Locating pins or locating blocks, or HASCO shouldered guide sleeves, shall be designed between the templates to prevent the template from being offset due to the gap of the screws; Liquidity analysis should be carried out with the help of model flow to reduce the risk of failure;

23. The tolerance of the front and rear flanges is minus 0.05mm, the tolerance of the distance between the two flanges is plus or minus 0.02mm, the gap between the top rod and the top rod hole is unilateral 0.1mm, the center distance tolerance of the front and rear mold guide sleeve guide post is plus or minus 0.01, and the four sides and depth of the mold frame should be subject to tolerance, otherwise when the rear mold is rotated 180 degrees, there will be sharp edges due to the inconsistency of height and low. The tolerance of frame depth is negative 0.02mm.

24. If the mold has been processed in the mold factory, when the factory wants to process the nozzle and top rod hole, it should take the distance center of the four guide pillar guide sleeve holes as the benchmark, otherwise the deviation is too much, and it is easy to jam the mold. When setting the mold embryo, it should be noted that it is a two-color mold embryo, the four guide pillars, guide sleeves and frames are symmetrical, and the rear mold can match the front mold after rotating 180 degrees.

25. Pay attention to the position of the top rod hole, with a minimum spacing of 200mm. For large molds, the number of ejector pin holes must be appropriately increased. (when the ejector demoulding mechanism on the two-color injection molding machine cannot be used, the ejector plate needs to be installed with an oil cylinder for resetting). Because the ejector rod attached to the injection molding machine itself is not long enough, we must design an extended ejector rod in our mold, and the ejector rod grows out of the mold base plate by about 150mm.

26. When designing the front mold for the second injection molding, in order to prevent the front mold from scratching the rubber position of the first molded product, local avoidance can be designed. (under special circumstances, the front mold core cannot be avoided, such as the two-color tail lamp, because the product is transparent. If it is avoided, the product will have an impression when it is formed for the second time. Experience has proved that there are traces when it is avoided for 0.05mm. Once a set of mold has been lowered three times, which is impressive) if the product is PMMA package, PMMA needs to consider mold vacuum pumping, because PMMA rubber is fragile, and the product will have the risk of cracking at the moment of mold opening, Therefore, the exhaust is also very critical. The ejection must be balanced. There must be enough ejector pins or ejector blocks. If it is a PC package, the effect is much better. It is not the appearance part, but also the strength of each sealing position must be carefully considered, that is, in injection molding, whether the plastic will deform under large injection pressure, resulting in the possibility of batch sharp edges in the second injection molding

27. Before closing the mold of a and B plates, pay attention to the mold closing sequence when the front mold has a slider or inclined top

28. The gate position of the two-color mold must be carefully selected. It is best to choose the latent glue feeding for primary products, so that the products and flow channels can be cut off automatically. When latent glue feeding cannot be adopted, three plate mold or hot runner mold can be considered. If the primary material is a point gate, it is necessary to make a wave to avoid damaging the secondary material due to the residue of the primary feeding point. If an open hot runner is used, avoid the air at the corresponding rubber port of the second front die.

29. Two color injection molded products are generally made of ABS, PC and other hard plastics combined with TPE or TPU soft plastics. Due to the cost or application, it is necessary to fully consider that there may be no good adhesion and fusion between the two materials. Between the two materials (generally there will be embossed lines, or columns or bumps and perforations on the first color products to increase the adhesion between the products) in order to make the two plastics "stick" tighter, Consider the "Stickiness" between materials and the roughness of the mold surface. Two color injection molding has special TPU materials; The smoother the mold surface, the tighter they "stick.".

30. Pay attention to the positioning of the front and rear formwork; The slope drop of all insertion should be as large as possible, more than 0.15mm, and the insertion surface should be at least 3-5 °, otherwise it will burn.

31. When abs/pc, abs/pc, ABS, abs/pmma, PMMA two-color injection molding, it is necessary to inject the one with higher temperature first. If the product is transparent, the hot runner of sequential valve is mostly used in the mold.

If the two-color mold is divided into two sets of molds, the mold sequence during mold trial is:

a. First set up a set of mold on the non operating side of the injection molding machine and lock the screws. Note: at this time, the mold cannot be adjusted to produce high pressure, otherwise the injection molding machine will be damaged;

b. After the injection molding machine is opened, the moving die on side a rotates 180 degrees to side B;

c. Set up the front mold on side B and cooperate with the moving mold on side A. after the mold is set up, open the mold, and the moving mold on side a rotates 180 degrees to return to side a;

f. Then set up the movable die on side B, and adjust the die after two sets of dies are set up; Molding production

a. The first shot and the second shot of raw materials should correspond to the correct nozzles for the first molding and the second molding respectively;

b. Set the ejection, generally 1 ejection ejection is closed, 2 ejection is open, and the mold can be closed only after confirming that the ejector pins of both sets of molds are normal;

c. Whether the molding conditions are set to match the raw materials, material tubes and molds

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