1. Gating System
The gating system is the channel through which molten plastic is introduced from the injection molding machine nozzle into the mold cavity, significantly impacting the molding quality and production efficiency of plastic products. It mainly consists of the main runner, branch runners, gate, and cold slug well.
The main runner is the primary channel connecting the injection molding machine nozzle to the branch runners or cavities. Its size and shape must be designed based on factors such as the flowability of the molten plastic and the size of the injection molding machine nozzle. The branch runners distribute the molten plastic from the main runner to each cavity; their layout should aim to ensure uniform filling of each cavity and minimize pressure loss. The gate is the smallest cross-sectional part of the gating system. Its function is to control the flow rate and filling time of the molten plastic, and to facilitate separation of the product from the runner system after injection molding. Various types of gates exist, such as side gates, point gates, and submarine gates. The appropriate gate type must be selected based on the shape, size, and appearance requirements of the plastic product. The cold slug well is located at the end of the main runner or branch runner and is used to collect cold slug at the beginning of injection molding, preventing it from entering the mold cavity and affecting product quality.
2. Ejection System
The function of the ejection system is to smoothly eject the plastic product from the mold cavity after molding. Common ejection methods include ejector pin ejection, ejector sleeve ejection, and ejector plate ejection. Ejector pin ejection is the most commonly used method. Ejector pins are installed on the moving mold, and the ejection device of the injection molding machine pushes the ejector pins to eject the plastic product from the core when the mold opens. Ejector sleeve ejection is suitable for molding plastic products with cylindrical holes. The ejector sleeve (ejector tube) ejects the product, avoiding leaving ejector pin marks on the product surface. Ejector plate ejection uses an ejector plate to push the plastic product out of the entire core, suitable for some large-area, thin-walled plastic products. When designing the ejection system, it is necessary to ensure that the ejection position is reasonable and the ejection force is uniform to avoid defects such as deformation and cracking of the plastic product during the ejection process.
3. Cooling System
The main function of the cooling system is to control the mold temperature, allowing the molten plastic to cool and solidify quickly and evenly within the mold cavity, thereby improving production efficiency and the quality of the plastic products. The cooling system typically uses circulating cooling water channels within the mold to remove heat. The layout of the cooling channels should be optimized based on the shape and wall thickness of the plastic product and the structure of the mold to ensure uniform temperature throughout the mold and prevent defects such as deformation and shrinkage caused by uneven cooling. Water is usually used as the cooling medium, but other media such as oil can be used in some special cases.
4. Venting System
During injection molding, air in the mold cavity and gases generated by the molten plastic must be vented promptly; otherwise, defects such as porosity, scorching, and incomplete filling will occur in the plastic products. The venting system mainly uses venting grooves at the mold parting surface, the core-cavity mating surface, or the gaps between ejector pins and slides for venting. The depth and width of the venting grooves need to be rationally designed based on the fluidity of the plastic and injection molding process parameters to ensure smooth venting while preventing molten plastic from overflowing. In addition, some precision injection molds may employ special venting methods such as vacuum venting.
5. Guiding and Positioning System
The guiding and positioning system ensures accurate alignment of the moving and fixed molds during mold opening and closing, preventing dimensional deviations in the plastic products or mold damage due to misalignment. The guiding system generally consists of guide pillars and guide sleeves. The guide pillars are installed on the moving or fixed mold, and the guide sleeves are installed on their corresponding fixed or moving molds. During mold opening and closing, the guide pillars slide within the guide sleeves, providing guidance. The positioning system uses locating rings, locating pins, and other components to ensure accurate mold placement on the injection molding machine and the relative positional accuracy of each component during mold assembly.