Pressure Control and Motion System Analysis of Plastic Injection

In the process of Medical Double-Color Plastic Injection Molding Companies, whether it is a hydraulic or electric injection molding machine, all the movements during the injection process will generate pressure. Proper control of the required pressure is the key to producing high-quality finished products. Pressure Control and Metering System In a hydraulic injection molding machine, all movements are performed by the oil circuit, including:

1. Screw rotation during the plasticization stage.

2. Movement of the slide channel (nozzle, inlet bushing).

3. Axial movement of the injection screw during injection and holding pressure.

4. Close the substrate on the injection rod until the elbow is fully extended or the piston mold stroke is completed.

5. Start the assembly ejector to eject the finished product.

On a fully electric injection molding machine, all movements are performed by a brushless synchronous motor with permanent magnets, using a ball bearing screw to convert rotational motion into linear motion. The efficiency of the entire process depends in part on the plasticization process, in which the screw plays a vital role.

Mitsubishi introduced a new solution in the production process of all-electric models, including a filling screw (second flight holding roller) and a screw tip with mixing elements. This design maximizes plasticizing capacity and mixing effect, shortens the screw length and achieves high speed. The screw must ensure melting and homogenization of the material and avoid overheating through back pressure adjustment. The flow rate of the mixing element cannot be too high to avoid polymer degradation. Each polymer has its maximum flow rate, exceeding this limit will cause molecular stretching and main chain rupture.

During injection and holding pressure, it is crucial to control the forward axial movement of the screw. Factors such as inherent stress, tolerance and warpage during cooling also directly affect product quality, which are determined by the quality of the mold. Optimizing the cooling channel and ensuring effective closed-loop temperature regulation are key to ensuring high-quality finished products.

Hydraulic injection molding machines achieve this regulation by detecting oil pressure. Specifically, the oil pressure activates a set of valves through the control board, and the fluid is acted, regulated and released through the manipulator. Injection speed control includes open-loop control, semi-closed-loop control and closed-loop control schemes. The open-loop system relies on a common proportional valve to apply proportional tension to create pressure in the injection barrel, which moves the injection screw at a certain speed.

The semi-closed-loop system uses a closed-loop proportional valve to control the oil flow ratio. The closed-loop system uses a speed sensor (usually a potentiometer type) to monitor the tension change in real time and compensate for speed deviations. Closed-loop pressure control ensures uniform pressure during injection and holding phases, and maintains uniform back pressure in each cycle.

The proportional valve is adjusted by the detected pressure value to compensate for deviations according to the set pressure value. It is also effective to detect the melt pressure in the nozzle or mold cavity while monitoring the hydraulic system. Combined with pressure and temperature detection, it helps process management and predicts the actual weight and size of the molded part.

In hydraulic equipment, the average hydraulic pressure can reach 140 bar, which is suitable for injection molding. To reduce energy consumption, variable displacement pumps and pressure storage cylinders can be used during peak discharge periods. Fixed displacement pumps move the same amount of oil per rotation, so the selection of oil pumps needs to be based on the amount of oil required in a specific time.

All injection molding machines are equipped with proportional servo valves of different quality levels to precisely control various aspects such as mold opening speed, mold closing speed, injection, feeding, suction and ejector. The auxiliary motor sends the amplified output signal to the valve through the weak input signal to realize the regulation function. The precise control of the high-tech servo transmission valve can basically eliminate the lag phenomenon and enhance the repeatability of the function.

Medical Double-Color Plastic Injection Molding Companies need to pay attention to the control and optimization of each link in this process to ensure product quality and production efficiency.