How do injection molds work?

1, Structural design of injection molds
Injection molds are usually composed of two parts: the moving mold (lower mold) and the fixed mold (upper mold), which are tightly closed by the clamping mechanism of the injection molding machine to form the mold cavity. The mold cavity is the embodiment of the final shape and size of plastic products, and its design accuracy directly determines the quality of the product.
The mold cavity is usually composed of components such as the core, cavity plate, sprue sleeve, cooling water channel, etc. The core and cavity plate respectively form the inner and outer walls of the product, while the sprue sleeve is responsible for guiding the molten plastic into the mold cavity. The cooling water channel reduces the mold temperature and accelerates the cooling and solidification of the product by circulating cooling media such as water or oil.
2, The workflow of injection molds
The workflow of an injection mold includes steps such as mold closing, injection, pressure holding, cooling, and mold opening. Each step is closely connected and together constitutes the entire process of injection molding.
Mold closing: The mold closing mechanism of the injection molding machine drives the closing of the moving and fixed molds, forming a closed mold cavity. During the mold closing process, the guiding mechanism of the mold ensures precise alignment between the moving and fixed molds to avoid defects such as burrs or misalignment in the product.
Injection: The injection device of the injection molding machine injects molten plastic into the mold cavity through the sprue sleeve. During the injection process, molten plastic rapidly fills the mold cavity under high pressure and speed, forming the initial shape of the product. Parameters such as injection pressure and injection speed have a significant impact on the quality of the product.
Pressure holding: After the injection is completed, the screw or plunger of the injection molding machine continues to apply pressure to the molten plastic to compensate for the shrinkage of the plastic during the cooling process. The pressure holding stage helps to increase the density and strength of the product, and reduce the porosity inside the product.
Cooling: After the pressure holding stage, the molten plastic inside the mold cavity begins to cool and solidify. During the cooling process, the cooling water channel of the mold reduces the mold temperature and accelerates the cooling rate of the product by circulating cooling medium. The length of cooling time depends on the thickness of the product, the material, and the cooling efficiency of the mold.
Mold opening and demolding: After the product is completely cooled and solidified, the mold closing mechanism of the injection molding machine drives the separation of the moving mold and the fixed mold, exposing the product. Subsequently, the product is ejected from the mold through the ejector mechanism of the mold or manually, completing the entire injection molding process.
3, Maintenance and upkeep of injection molds
The maintenance of injection molds is of great significance for extending their service life, improving product quality, and increasing production efficiency. Here are some key maintenance measures:
Regular cleaning: Regularly clean the dirt and residue on the surface of the mold to keep it clean and dry. This helps prevent mold rust, corrosion, and blockage.
Lubrication and rust prevention: Apply an appropriate amount of lubricant on the sliding parts and guide mechanism of the mold to reduce friction and wear. At the same time, regular rust prevention treatment should be carried out on the molds to extend their service life.
Inspection and repair: Regularly inspect the wear, cracks, and deformation of the mold, and promptly repair or replace it. This helps ensure the accuracy and stability of the mold, and improve the quality of the product.
Reasonable storage: When not in use, the mold should be stored in a dry, ventilated, and non corrosive gas environment to avoid moisture, heat, or direct sunlight.