Forming method

Molding methods: core rotation, cutting plate rotation, core retraction, cavity retraction, and cavity sliding. Two tone injection molding typically uses the same plastic of different colors, which provides a strong bond between the substrate and the insert. If different types of plastics are used for injection molding, a bonding performance test must be conducted first, and if necessary, grooves should be set on the substrate to increase bonding strength.

1、 Segmentation of secondary products

When conducting primary and secondary product segmentation, there are several factors that must be considered, which are related to the success or failure of the entire mold design. The first thing to consider is the flowability of the material (which plays a significant role in selecting the appropriate sprue), followed by choosing the appropriate product thickness. As secondary products need to form on the surface of primary products, if the thickness is not enough, it will cause poor flowability, which can easily lead to defects such as material shortage and shrinkage. Generally speaking, the meat thickness of secondary products should account for half or more of the total meat thickness of the product.

Selection of Gate Position

The selection of gate position for two-color molds is very particular. It is best to use mold flow analysis software for gate position analysis and flow detection to reduce the risk of mold production failure. In addition, it is necessary to change the shape of the primary product or add auxiliary adhesive positions in appropriate places to improve the direction and speed of secondary material flow. When using side injection molding for secondary materials, the gate should be tilted upwards and the gate width should be increased as much as possible to increase the liquid velocity and make the fluid rush upwards towards the fixed mold during feeding. This can avoid flushing the primary material and causing leakage of the primary product.

Inner membrane design

The two fixed mold cores of the two-color mold have different shapes, forming one appearance each. In general, the shapes of the two moving molds are exactly the same. When designing the fixed mold core for the second injection molding, it is necessary to design the second fixed mold to avoid scratching the fixed mold core by the first material head, so that the first material head can be automatically cut off from the product. Sometimes, a hot runner or three plate mold is used, and if the mold does not push out after the first injection molding, some material heads will remain on the moving mold core. Therefore, when designing the fixed mold core for the second injection molding, in order to avoid scratching the fixed mold core by the first material head, it is necessary to design the second fixed mold to avoid the first material head from entering the avoidance position smoothly during the second mold forming injection molding. Sometimes, in order to avoid the second fixed mold core from inserting (rubbing) and damaging the first formed product adhesive position, a partial avoidance can be designed, but each adhesive position must be carefully considered. The strength of the distance between the outer wall of the product and the avoidance position should be at least 5mm. Pay attention to the maximum slope difference between the inserted and broken surfaces of the fixed and moving mold kernels, and make pipe positions at the four corners to facilitate good fit when closing the mold. The design of the first fixed mold and the second insertion should be appropriately compressed while ensuring strength.

Mold design

The two fixed molds and two moving molds of the mold need to be completely coordinated with each other, so when designing the mold core and mold frame, it should be noted that the processing of the mold core and mold frame should use the method of taking numbers from four sides; The total thickness of the two fixed mold parts should be equal; The four guide columns should be symmetrical about the center (reference angle guide column eccentricity cannot be used like single color molds), and ensure that the unilateral clearance tolerance between the guide column and the guide sleeve is within 0.025mm; The perpendicularity, parallelism, and flatness tolerances of the mold blank are guaranteed to be within 0~+0.03mm.

Mold positioning

The dynamic mold of the mold needs to rotate 180 degrees after one injection molding before the second injection molding can be carried out. Therefore, it is necessary to check whether the corners of the two columns on the injection molding machine will interfere with the four columns on the injection molding machine when rotating. The gap between the two should be at least 10mm. If it is less than 10mm, it should be considered to cut the two corners of the mold near the guide column. Pay attention to the position and size of the positioning column of the rotating plate of the moving mold. This requires selecting different injection molding machines according to the size, stroke, and height of the mold, and then determining the position and size of the positioning column, as well as the radius of the gate and positioning ring, based on the parameters of the two-color injection molding machine. It is best to design a set of molds that can be used on different models of injection molding machines, so that flexible scheduling can be achieved in situations where production tasks are tight.

Cooling system

The water distribution of two fixed molds and two moving molds should be as sufficient, balanced, and symmetrical as possible. And the inlet and outlet water pipe joints of the mold should be located as close to the ground as possible, because if the water pipe joints are placed on both sides of the mold during operation and reverse operation, it will be inconvenient to install the water pipe joints on the inner side. Reasonable water transportation design is of great help to injection molding operations.