Plastic mold injection process

1) Injection process action selection:

General injection molding machine can be manually operated, can also be semi-automatic and fully automatic operation.

Manual operation is in a production cycle, each action is realized by the operator to switch the operation button switch. Generally, it is only selected when the test machine is adjusted.

When semi-automatic operation, the machine can automatically complete the action of a work cycle, but after each production cycle is completed, the operator must open the safety door, remove the workpiece, and then close the safety door, the machine can continue the next cycle of production.

When fully automatic operation, the injection molding machine can automatically enter the next work cycle after completing the action of one work cycle. In the normal continuous work process without stopping the control and adjustment.

In normal production, semi-automatic or fully automatic operation is generally selected. At the beginning of the operation, the operation mode (manual, semi-automatic or fully automatic) should be selected according to the production needs, and the manual, semi-automatic or fully automatic switch should be converted accordingly.

2) Pre-plastic action selection

According to whether the injection seat is backward before and after the pre-plastic feeding, that is, whether the nozzle leaves the mold, the injection molding machine is generally provided with three options. (1) Fixed feeding: pre-molded and pre-molded nozzles are always stuck into the mold, and the injection seat does not move. (2) Pre-feeding: The nozzle carries out pre-plastic feeding against the mold. After pre-molding is completed, the injection seat retreats and the nozzle leaves the mold. The purpose of choosing this method is to use the injection hole of the mold to assist the nozzle during pre-molding to avoid the melt flowing out of the nozzle when the back pressure is high. After pre-molding, the nozzle and the mold can be avoided from long-term contact and heat transfer, which affects the relative stability of their respective temperatures. (3) Post-feeding: After the injection is completed, the injection seat retreats, the nozzle leaves the mold and then pre-molded, and the injection seat advances after pre-molding. This action is suitable for processing plastics with particularly narrow molding temperature. Due to the short contact time between the nozzle and the mold, the loss of heat is avoided, and the solidification of the melt in the nozzle hole is also avoided.

At the end of the injection and the completion of the cooling timer, the pre-plastic action begins. The screw rotates to melt and extrude the plastic in front of the screw head. Due to the role of the check valve played by the stop ring at the front end of the screw, molten plastic accumulates at the front end of the barrel, forcing the screw back. When the screw retreats to a predetermined position (this position is determined by the travel switch or electronic ruler to control the distance of the screw retreat and realize quantitative feeding), the pre-plastic stops and the screw stops rotating. This is followed by the ejection (also called glue extraction) action, which means that the screw makes a small amount of axial retraction. This action can relieve the pressure of the melt gathered at the nozzle and overcome the imbalance of the pressure inside and outside the barrel. The phenomenon of "drooling" caused. If there is no need to shoot back, the shoot back stop switch should be adjusted to the appropriate position (the last section of the storage position and the shoot back position are set to be the same when the electronic ruler is used), so that the shoot back stop switch is also pressed at the same time when the pre-plastic stop switch is pressed. When the screw moves back to press the stop switch, the ejection stops. Then the seat starts to retreat. When the seat moves back to the stop switch, the seat stops moving back. If the fixed feeding method is adopted, the position of the travel switch should be adjusted.

In general production, fixed feeding is used to save the operation time of the injection seat and speed up the production cycle.