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Injection molding machine operation

Injection molding machine operation

Jul 23,2020
1.1 Action program of injection molding machine
Clamping → Pre-molding → Reverse → Nozzle forward → Injection → Holding pressure → Nozzle backward → Cooling → Mold opening → Ejection → Door opening → Take workpiece → Door closing → Mold closing.

1.2 Injection molding machine operation project: The injection molding machine operation project includes three aspects: control keyboard operation, electrical control cabinet operation and hydraulic system operation. Select the injection process action, feeding action, injection pressure, injection speed, ejection form, temperature, current and voltage monitoring of each section of the barrel, and adjust the injection pressure and back pressure.

  1.2.1 Action selection during injection
General injection molding machines can be operated either manually or semi-automatically or fully automatically.
Manual operation is in a production cycle, each action is realized by the operator toggle the operation switch. Generally, it is only used when the test machine adjusts the mold.
In semi-automatic operation, the machine can automatically complete a work cycle of action, but after each production cycle, 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.
In full-automatic operation, the injection molding machine can automatically enter the next working cycle after completing the action of one working cycle. In the normal continuous working process, there is no need to stop to control and adjust. However, it should be noted that if full-automatic work is required, (1) do not open the safety door halfway, otherwise the full-automatic operation will be interrupted; (2) timely feeding; (3) if the electric eye sensor is used, care should be taken not to cover the electric eye.
In fact, in the fully automatic operation, it is usually necessary to temporarily stop halfway, such as spraying the mold release agent to the machine mold.
In normal production, semi-automatic or fully automatic operation is generally selected. When the operation starts, 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 toggled accordingly.
The semi-automatic and fully-automatic working procedures have been determined by the circuit itself. The operator only needs to change the speed and pressure, the length of time, the number of thimble, etc. on the surface of the electrical cabinet, and it will not be caused by the operator adjusting the wrong button. Chaos in working procedures.
Before each action in a cycle is not adjusted properly, you should first select manual operation, confirm that each action is normal, and then select semi-automatic or fully automatic operation.

  1.2.2 Pre-plastic action selection
According to whether the injection seats of the front and back of the pre-plastic feeding are retracted, that is, whether the nozzle leaves the mold, the injection molding machine generally has three options.

(1) Fixed feeding: the nozzle is always attached to the mold before and after pre-plasticizing, and the injection seat does not move.

(2) Front feeding: the nozzle is pressed against the mold for pre-plastic feeding. After the pre-plastic 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 resist the nozzle during pre-molding, to prevent the melt from flowing out of the nozzle when the back pressure is high, and to prevent the nozzle and mold from contacting for a long time and generating heat transfer after pre-molding, affecting them The respective temperatures are relatively stable.

(3) Post-feeding: After the injection is completed, the injection seat retreats, the nozzle leaves the mold and is pre-molded, and the injection seat advances after pre-plasticization. This action is suitable for processing plastics with particularly narrow molding temperatures. Due to the short contact time between the nozzle and the mold, heat loss is avoided, and solidification of the melt in the nozzle hole is also avoided.

After the injection is completed and the cooling timer has timed out, the pre-plastic action begins. The rotation of the screw squeezes the plastic melt into the front of the screw head. Due to the check valve at the front end of the screw, molten plastic accumulates at the front end of the barrel, pushing the screw backward. When the screw retreats to a predetermined position (this position is determined by the travel switch to control the distance the screw retreats to achieve quantitative feeding), the pre-plastic stops and the screw stops rotating. It is followed by a retraction action, which means that the screw makes a slight axial retreat. This action can release the pressure of the molten material accumulated at the nozzle and overcome the "salivation" phenomenon caused by the imbalance of the pressure inside and outside the barrel . If retraction is not required, the retraction should be stopped, and the switch should be adjusted to the appropriate position to stop the pre-plastic. At the same time the switch is pressed, the reverse stop switch is also pressed. When the screw retracts to the upper stop switch after retracting, the retracting stops. Then the seat began to retreat. When the injection seat is retracted to press the stop switch, the injection seat is stopped and retracted. If the fixed feeding method is adopted, the position of the travel switch should be adjusted.
In general, the production adopts a fixed feeding method to save the operation time of the injection seat advance and retreat and speed up the production cycle.