Injection molding is a process in which molten plastic is injected into a mold and then cooled and solidified to form a plastic product of the desired shape. Its core principles include the steps of plastic melting, injection, pressure holding, cooling and demolding.
1. Plastic melting
The first step of injection molding is to feed granular or powdered thermoplastic raw materials into the hopper of the injection molding machine. The raw materials are melted into a viscous melt under the action of the heating device, and this process is called plasticization.
2. Injection filling
The molten plastic is pushed by the screw or plunger of the injection molding machine under high pressure and injected into the closed mold cavity through the nozzle. The filling stage starts from the mold closing until the cavity is filled to about 95%. The shorter the filling time, the higher the molding efficiency.
3. Pressure holding and compaction
After the filling is completed, the injection molding machine continues to apply pressure to compact the melt, increase the plastic density, and compensate for the shrinkage behavior of the plastic. The pressure holding stage lasts until the gate is solidified and sealed, at which time the mold cavity pressure reaches its peak.
4. Cooling and curing
The cooling stage is the longest link in injection molding, usually accounting for 70% to 80% of the entire molding cycle. Reasonable cooling system design can ensure that the plastic product is demolded after reaching a certain rigidity to avoid deformation.
5. Mold opening and demolding
After cooling, the mold is opened and the molded product is removed from the mold through the ejection device. The demolding process needs to avoid uneven force on the product to prevent deformation or damage.
6. Process advantages
Injection molding has the characteristics of high efficiency, high precision and strong adaptability. It can produce plastic products with complex shapes and precise dimensions, and is widely used in automobiles, home appliances, medical devices and other fields.
Through the above steps, injection molding realizes the rapid and efficient transformation from raw materials to finished products, and is an indispensable and important process in modern plastic processing.
