Steps of mold injection molding
1. Heating and pre-plasticization
Driven by the transmission system, the screw conveys the material from the hopper forward and compacts it. Under the mixed action of shear and friction of the heater outside the barrel, the screw and the barrel, the material gradually melts. A certain amount of molten plastic has accumulated at the head of the barrel. Under the pressure of the melt, the screw slowly retreats. The retreat distance depends on the amount required for one injection of the metering device. When the predetermined injection volume is reached, the screw stops rotating and retreats.
2. Mold closing and locking
The clamping mechanism pushes the mold plate and the mold moving mold part installed on the moving mold plate to close and lock the mold moving mold part on the moving mold plate to ensure that sufficient clamping force can be provided to lock the mold during molding.
3. Forward movement of the injection device
When the mold closing is completed, the entire injection seat is pushed and moved forward to make the injection machine nozzle fit the main runner of the mold completely.
4. Injection and pressure holding
After the clamping and nozzle are completely fitted to the mold, the injection hydraulic cylinder enters the high-pressure oil, pushing the screw forward relative to the barrel, and injecting the melt accumulated at the head of the barrel into the mold cavity with sufficient pressure. The plastic volume shrinks due to the temperature drop. In order to ensure the density, dimensional accuracy and mechanical properties of the plastic parts, it is necessary to maintain a certain pressure on the melt in the mold cavity to replenish the material.
5. Pressure relief
When the melt at the mold gate freezes, the pressure can be relieved.
6. Injection device retreats
Generally speaking, after the pressure relief is completed, the screw can rotate and retreat to complete the next feeding and pre-plasticization process. (Under normal circumstances of existing injection molding, the action of the injection seat withdrawing from the main gate of the mold has been cancelled. This action is performed for materials with severe drooling, such as PA).
7. Mold opening and ejection of plastic parts
After the plastic parts in the mold cavity are cooled and shaped, the clamping mechanism opens the mold and pushes out the plastic parts in the mold.