1. Basic principles of two-color mold design:

(1) Hard rubber is made once, and soft rubber is made twice;

(2) Transparent once, non-transparent twice;

(3) The plastic with high molding temperature is made once, and the plastic with low molding temperature is made twice;

The above are the basic principles for making two-color molds, otherwise the mold will be wasted; in addition, when sealing the glue, try to use a break seal instead of a break seal, even if it is recommended that the customer modify the product, try to use a break seal;


2. The guide post and guide sleeve of the mold base must be symmetrical in the upper, lower, left and right directions, as well as symmetrical between the front and rear molds.


3. The rear mold should be rotated 180 degrees, while the front mold remains unchanged.


4. The spacing between products must be based on the spacing of the nozzle of the injection molding machine. Some dual-color injection molding machines have adjustable nozzle spacing abroad, while some do not have adjustable nozzle spacing, and domestic ones do not have adjustable nozzle spacing.


5. There are two independent ejection systems, and there are also two ejector pins. The two products in the back mold are identical, and the ejector pins are also identical, with a rotational relationship. It is important not to make them have a translational relationship.

6. The thimble plate can only be reset with a spring, not with a screw, because the back mold needs to rotate.


7. The side locks must be on the four sides of the mold center, symmetrical between the front and rear molds, otherwise the rear mold will not align with the front mold when rotated 180 degrees.


8. If the distance between the injection points and the distance between the injection molding machine nozzles are different, the top rod holes should be made into a waist shape, as the distance between the injection molding machine top rods cannot be adjusted. Note that most injection molding nozzles on 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, to determine the layout of the product arrangement.



The direction of water transport in and out must be on the side of the sky and earth, and the in and out of each circulating water must be on the same side. It is not allowed to have water entering from the sky and leaving from the earth side, because the rear mold needs to be rotated by 180 degrees. It is important to note that the size of the mold base cannot exceed the height of the injection molding machine’s water tank, otherwise it will not be able to receive water transport.


11. The first injection molded product should be placed on the non-operating side, as the product needs to be rotated 180 degrees for the second injection after the first injection, which will bring it to the operating side for easy access.


12. The code mold position of the export mold should be on the operation side and the non-operation side, not on the sky and earth sides, because their products need to be fully automated.


13. Precautions for the parting surface: For the rear mold parting surface, the parting surface obtained after merging the two products should be used as the rear mold parting surface; for the front mold parting surface, it is sufficient to take the parting surface of a single product, and it is not allowed to take the parting surface of the merged product.


The tolerance of the front and rear flanges is negative 0.05mm, the tolerance of the spacing between the two flanges is positive or negative 0.02mm, the clearance between the top rod and the top rod hole is 0.1mm on one side, and the tolerance of the center distance between the front and rear mold guide sleeves is positive or negative 0.01. The tolerances of the four sides and depth of the mold frame should be added, otherwise when the rear mold rotates 180 degrees, there will be a lot of burrs due to inconsistent height. The frame depth tolerance is negative 0.02mm.


If the mold base has been processed in the mold base factory and the factory needs to process the nozzle and top rod holes, the center of the four guide post guide sleeve holes should be used as the benchmark for taking measurements. Otherwise, there will be too much deviation and the mold may get stuck. When ordering the mold base, it is necessary to specify that it is a two-color mold base, with four guide posts, guide sleeves, and frames symmetrical, and that the rear mold can be rotated 180 degrees to match the front mold.


16. If it is a two-color mold with a rotating back mold, it is much simpler. The two front mold cores are the same, and after injection of the hard plastic on one side, rotate it 180 degrees (note that the product cannot fall during rotation, and the gate can be automatically separated). After rotating to the other side, inject the soft plastic again. When injecting the hard plastic, there is no need to arrange the ejector pin, just arrange it on the soft plastic side of the mold core.


In addition, it is important to pay attention to shrinkage. If the soft rubber completely wraps around the hard rubber, only the hard rubber needs to be shrunk. If the contours are connected, both the hard and soft rubbers need to be shrunk.


If it is a two-color mold for a set of molds, it is a straight barrel, a 90-degree barrel for shooting plastic, without rotation, requiring only a mold core. The separation method for soft and hard plastic is by line-position sealing.


18. The two shapes of the cavity are different, forming one product each. However, the two shapes of the core are identical.


19. The front and rear molds of the mold must be aligned after rotating 180° from the center. This check must be performed during design.


20. Pay attention to the position of the thimble holes, with a minimum spacing of 210mm. For large molds, the number of thimble holes must be appropriately increased. Moreover, due to the insufficient length of the thimble attached to the injection molding machine, it is necessary to design a lengthened thimble in our mold, with the thimble protruding about 150mm from the mold base plate.


21. It is necessary to design two locating rings on the rear mold base plate.



The total thickness of the front mold panel plus the a-plate cannot be less than 170mm. Please carefully review other reference data for this model of injection molding machine, such as maximum mold thickness, minimum mold thickness, and top rod hole spacing.


23. The depth of the front sprue should not exceed 65mm. The distance from the top of the upper (large water) sprue to the center of the mold base should not be less than 150mm.


When designing the cavity for the second injection, in order to prevent the cavity from scratching (or rubbing) the previously molded product, a partial clearance can be designed. However, it is necessary to carefully consider the strength of each sealing position, that is, whether there is a possibility of plastic deformation under high injection pressure during injection molding, which may cause burrs to form during the second injection;


During injection molding, the size of the first injection molded product can be slightly larger to allow it to be pressed more tightly with another cavity during the second molding process to achieve the effect of encapsulation.


Before clamping the a and b plates, it is important to note whether the front mold slider or lifter can be reset first and crush the product. In this case, it is necessary to find a way to clamp the a and b plates first, and then reset the front mold slider or lifter.


27. The water transport arrangement of the two cavities and the core should be as full, balanced, and uniform as possible.


In 99% of cases, the hard plastic part of the product is first injected, followed by the soft plastic part of the product. Due to the ease of deformation of soft plastic.


29. During the second injection, pay attention to whether the movement of the plastic can affect the previously molded product, causing the plastic level to deform. If this is possible, we must find ways to improve it.


30. The gate position of the two-color mold must be carefully selected. It is best to choose a latent injection for the first product, so that the product and the runner can be automatically cut off. When latent injection is not possible, consider using a three-plate mold or a hot runner mold. If the first material is a point gate, it is necessary to make a wave to avoid breaking the second material due to residuals from the first injection.



31. Two-color injection molds often use rotary injection molds. The male/female molds on the two positions of the rotary injection mold require consistent dimensions and accuracy, and must be well-coordinated with the female/male molds. When it is not possible to use the ejection mechanism on the two-color injection molding machine, a hydraulic ejection mechanism must be installed on the rotary table.


32. For two-color mold injection molding, usually the same plastic of different colors is selected, or two different plastic materials can be used. In this case, it is necessary to consider the interfacial effects, shrinkage differences, and processing parameters of the two materials


Two-color injection molded products are generally made of ABS, PC, and other hard plastics combined with TPE soft plastics. Due to cost or application considerations, it is important to fully consider the possible lack of good adhesion and compatibility between the two materials used, as well as mold processing at the joint between the two materials (typically there will be a phenomenon of embossed patterns or the need for mold sealing slots), as well as the thickness of the material and many other issues!


In order to make the two plastics “stick” more tightly, it is necessary to consider the “viscosity” between the materials and the roughness of the mold surface. Two-color injection molding has a dedicated TPU material; the smoother the mold surface, the more tightly they “stick.”.


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 the primary and secondary materials, there are many factors to consider, such as the fluidity of the raw material, the shape of the plastic product, and so on.


34. Pay attention to the positioning of the front and rear molds; try to make the slope difference of all the insertion and breakage surfaces as large as possible, with a minimum of 0.1mm.


When injecting ABS/PC, ABS/PC+ABS, ABS/PMMA in two-color injection molding, it is necessary to first inject the higher temperature PC, PC+ABS or PMMA. If it is a transparent surface shell mold, most of them use a flip-chip mold structure.


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

a. The reserved position of the gate must be agreed upon in advance with the mold factory;

b. The recommended material thickness is above 0.8mm for transparent materials and above 0.7mm for non-transparent materials. Non-transparent materials should be as light-colored as possible, and care should be taken to block light when using LED lights;

The width of the transparent part’s parting surface and holes should be consistent, with a recommended width of 0.5mm. The surface should be smooth, avoiding unsightly visibility from the side and minimizing holes;

The thickness of non-transparent parts is limited, and the structure of the ribs on them should be as thin as possible, between 0.5-0.6mm, to avoid shrinkage;

e. For now, it is not recommended to do dual-color injection molding with main lenses. The cost of molds and products is too high, and there are considerable requirements for the equipment and technical level of mold manufacturers. If it is done, the other party needs to provide a detailed solution for the entire process for evaluation, and all intermediate steps need to be reviewed;

For large-area two-color injection molded parts, two key tests are drop and thermal shock. In these two tests, transparent and non-transparent parts are prone to separation. Thermal shock -40 -65, time 48 hours.

g. The structure on 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 on non-transparent parts should be as small as possible, ranging from 0.5 to 0.6, to avoid shrinkage.