In the production of injection molds, in order to ensure that the mold is assembled and adjusted in a certain direction and position between the male and female molds of the test machine, the guide parts should bear a certain lateral force, so there are certain requirements for the design of the guide structure of the injection mold. The main points are as follows.
1. The guide parts should be reasonably and evenly distributed around the mold or near the edge, and there should be sufficient distance from the center to the edge of the mold to ensure the strength of the mold and prevent deformation after being pressed into the guide post and guide sleeve.
2. According to the shape and size of the mold, a mold generally requires 2-4 guide posts. If there are orientation requirements for the closing of the male and female molds, two guide posts with different diameters or two guide posts with the same diameter but offset positions are used.
3. Since the plastic parts are usually left in the male mold, in order to facilitate the demolding guide column is usually installed in the female mold.
4. The guide post and guide sleeve should have chip grooves at the parting surface.
5. The axis of the guide column, guide sleeve and guide hole should be parallel.
6. When closing the mold, make sure that the guide parts are in contact first to avoid the male mold entering the cavity first and damaging the molded parts.
Mold exhaust slot design method
In the production of injection mold trial molds, underfilling often occurs. Compressed air burns, high internal stress inside the product, surface flow lines and fusion lines, etc. For these phenomena, in addition to adjusting the injection molding process first, it is also necessary to consider whether the mold gate is reasonable. When the two problems of injection molding process and gate are eliminated; then the exhaust of the mold is the main problem, and the main method to solve this problem is to set up an exhaust groove.
1 The role and design of the exhaust slot
1.1 The role of the exhaust slot
The role of the exhaust slot has two main points. One is to exclude the air in the mold cavity when injecting the molten material; the second is to exclude all kinds of gas generated during the heating process of the material. The more thin-walled products, the farther away from the gate, the opening of the exhaust slot is particularly important. In addition, for small parts or precision parts, we must pay attention to the opening of the exhaust groove, because it can avoid the surface burns and insufficient injection volume of the product, it can also eliminate various defects of the product and reduce mold pollution. So, how to exhaust the cavity? Generally speaking, if the molten material is injected at the highest injection rate without leaving a focal spot on the product, it can be considered that the exhaust in the mold cavity is sufficient.
1.2 Exhaust method
There are many ways to evacuate the mold cavity, but each method must ensure that: the exhaust groove is exhausted at the same time, its size should be designed to prevent the material from overflowing into the groove; secondly, it must prevent blockage. Therefore, from the inner surface of the mold cavity to the outer edge of the mold cavity, the length of the exhaust groove above 6 ~ 12mm, the groove height should be placed about 0.25-0.4mm. In addition, too many exhaust slots are harmful. This is because if the clamping pressure acting on the part of the mold cavity parting surface without the exhaust groove is too large, it is easy to cause cold flow or cracking of the cavity material, which is very dangerous. In addition to venting the mold cavity on the parting surface, venting can also be achieved by providing venting grooves at the end of the flow of the pouring system and leaving gaps around the ejector rod. Because of the choice of the depth, width and location of the exhaust groove; if not appropriate, the flash burr generated will affect the appearance and accuracy of the product. Therefore, the size of the gap is limited to prevent flashing around the ejector rod. Special attention should be paid here: when exhausting parts such as gears, even the smallest flash may be undesirable.
This type of parts is best exhausted in the following ways: thoroughly remove the gas in the flow channel; use silicon carbide abrasive with a particle size of 200 # to perform shot peening on the matching surface of the parting surface. In addition, the opening of the exhaust groove at the end of the flow of the pouring system mainly refers to the exhaust groove at the end of the runner. Its width should be equal to the width of the runner, and the height varies depending on the material.
1.3 Design method
Based on years of experience in injection mold design and product trial molds; this article briefly introduces the design of several exhaust slots, as shown in Figure 1. For product molds with complex geometric shapes, the opening of the exhaust groove; it is best to determine after several trial molds. The overall shortcoming of the overall structure in the mold structure design is poor exhaust. There are several exhaust methods for the integral mold cavity core: The groove or insert of the cavity is used for the person's part; The side of the insert joint is used; Partially made into a spiral shape The groove is installed in the longitudinal position The slat core is opened with process holes; When exhausting is very difficult, the mosaic structure is used. If the ※ angle of some molds is not easy to open the exhaust groove, first of all, the mold should be appropriately changed without affecting the appearance and accuracy of the product. Mosaic processing, which is not only conducive to processing exhaust gas cleaning, but also can improve the original processing difficulty and easy maintenance.