Two-Color Injection Mold Design Points
Classification
The previous article has already talked about the classification of injection molding machines for two-color molds. The structure of the two-color mold is closely related to the two-color injection molding machine. There are seven categories of two-color machines, but two categories are commonly used. Correspondingly, there are two types of two-color injection molds, namely Asian two-color molds and European two-color molds. The two-component injection molding machines in Taiwan and Japan have two parallel injection systems. In the European two-color injection molding machine, one barrel is horizontal and one barrel is vertical, and there is only one two-color mold. But the principle is basically similar, the shape of the upper and lower rows of the front mold is different, the rear mold rotates 180 degrees and the front mold is formed once and twice.
Asian two-color molds usually have two molds, the front mold is mounted on the fixed plate of the machine, and the rear mold is mounted on the rotary plate. The back molds of the two molds are exactly the same. The first front mold is different from the second front mold. When the first color plastic injection is completed, the front and rear molds are opened, and the first back mold takes the first product and rotates 180 degrees to reach the second color injection position for the second injection. , You can get two-color parts. In this cycle, there will be a mold primary product and a secondary product in each molding cycle.
The two Asian two-color mold bases can also be simplified into one mold base depending on the mold structure. For the Asian two-color mold base, when ordering the mold base, you need to pay attention to the position of the reference angle guide post and guide sleeve not to shift, otherwise it will be difficult to close the mold after rotating. Two Asian two-color mold bases, when ordering mold bases, you need to pay attention to the offset of the reference angle guide post and guide sleeve, which will not affect the mold clamping.
2. Design considerations
1. Before designing, be sure to understand the parameters of the injection molding machine, such as the type of injection molding machine, the size of the screw hole of the code mold, the specifications of the turntable, the size and ejection position of the ejector, the size and specifications of the shaft; when the product is ranked, determine the maximum mold The external dimensions are smaller than the rotating diameter of the turntable.
2. The first injection product should be placed on the non-operating side, and it is difficult for the operator to grasp the first-time material. When the one-time injection is designed to feed the glue at the point gate of the three-plate mold, the first-time injection runner needs to be designed with a ballistic runner device to facilitate fully automatic production. After the first injection, the product should be rotated 180 degrees for the second injection, and it is just turned to the operating side for easy access to the product. Special attention should be paid to whether the demoulding action of the soft glue nozzle is reliable.
3. The gate must be automatically cut when the glue is fed once, so as to avoid the residual protruding secondary glue position and the formation of defective products. The secondary gate should cover the primary gate as much as possible; the secondary gate should be designed in a concealed part as much as possible, using latent gate, horn gate, point gate or bottom lap to inject the glue. Be careful not to impulse the primary plastic with the material flow of the secondary injection molding, leaving marks on the surface of the product.
4. Pay attention to the repetitive positioning accuracy of the moving and fixed molds; the slope drop of all the penetrating surfaces should be as large as possible, which should be more than 0.1mm. When sealing, try to use the surface sealant instead of rubbing the surface sealant.
5. The basic principles of two-color mold design:
(1) 1 time for hard rubber and 2 times for soft rubber;
(2) 1 time for transparent materials and 2 times for non-transparent materials;
(3) One time for plastics with high molding temperature and 2 times for plastics with low molding temperature;
6. The shapes of the two fixed molds are different, and the two materials are formed separately. The shapes of the two movable molds are exactly the same. The movable and fixed molds must be matched after rotating 180º at the center. Rotation inspection must be done during mold design. When the mold is processed, it is necessary to improve the processing accuracy to ensure that the difference between the dimensional accuracy of the two movable molds is not more than 0.01mm.
7. When designing the cavity for the second injection, in order to avoid the cavity inserting (or scratching) the glue position of the product that has been formed for the first time, the first hard glue can be partially avoided. However, the strength of each sealing position must be carefully considered, that is, during injection molding, will the plastic be deformed under high injection pressure, which may lead to the possibility of cracking in the second injection?
8. When injection molding, the size of the first injection molding product can be slightly larger, so that it can be pressed tighter with another cavity during the second molding, in order to achieve the role of sealing glue. Note that during the second injection, will the flow of the plastic impulse the product that has been molded the first time, causing it to deform the glue position? If this is possible, we must find ways to improve it.
3. Design examples
Figure 1 shows the product picture of the phone's two-color buttons. The numbers and letters on the top of the keys are molded by two-color injection molding. The material used for the two injections is ABS, and the buttons with two-color injection molding can avoid the defects that the handwriting on the printed buttons is easy to wear off.
The mold design is shown in Figure 2. It adopts a two-color mold structure with a middle plate ejection rotating. The middle plate ejector rotating two-color mold is an integral two-color mold, one mold base, one ejection system, and it is only installed on the side of the secondary injection. As the name implies, the movable mold does not need to rotate the whole set of molds, and the movable mold only rotates after the middle plate is ejected and then closes the mold. The top numbers and letters of the phone's two-color buttons are formed during the first injection, and the glue position fills up the entire numbers and letters during the second injection, forming a button with a smooth top. In the first injection, a point gate was used to inject the glue at the top of the button avoiding the numbers and letters. The second glue is injected into the top surface of the connecting bridge between each button, and point gates are also used. There are some capital letters "O", "P", "Q", "A", "B", "R", "D", etc., as well as numbers "0", "4", "6", "8 ", "9" and so on have a closed structure. If the secondary material cannot be filled into the closed structure of the primary material, the "seesaw" mold structure or the middle plate ejection rotating mechanism must be adopted.
1. Fixed mold seat plate 2. Runner push plate 3. Locating pin 4. A plate 5. Nylon buckle 6. Middle plate 7. Movable mold backing plate 8. Spring 9. Push rod fixed plate 10. Push plate 11. Move Mold backing plate 12. Soft plastic sprue sleeve 13. Soft plastic fixed mold cavity 14. Core 15. Hard plastic fixed mold cavity 16. Core 17. Hard plastic sprue sleeve 18. Hard plastic movable mold insert 19. Inlay Fixing plate 20. Guide bushing 21. Support sleeve 22. Spline shaft 23. Soft rubber movable mold insert 24. Push rod 25. Push rod
This set of molds uses the middle plate to eject and rotate, which can replace the "seesaw" mold structure. Note that the primary movable mold insert 18 and the secondary movable mold insert 23 adopt different top structures. The top structures of the two movable mold inserts are different, and they are fixed and non-rotating. The hard rubber movable mold insert 18 is made of several raised steel materials at the non-number and letter strokes to collide with the fixed mold. After the mold is opened, the spline shaft 22 pushes the middle plate 6 and the core 14 out of the movable mold, and the semi-finished product of the primary glue position is separated from the movable mold insert 18, and after rotating to the secondary injection station, the middle plate is retracted to close the mold. The semi-finished product of the primary glue position is combined with the secondary movable mold insert 23, and the vacant position of the piercing groove is convenient for filling of the secondary glue. After the injection is completed, the mold is opened, the nozzle material is taken out, and the plastic part is ejected on the secondary injection side. The whole set of molds are arranged 2X2, with two holes each for one-shot injection and two-shot injection.
