Operating Principle and Maintenance of Injection Molding Machine

Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding - melt plasticization - pressure injection - mold filling and cooling - mold opening and part extraction. After removing the plastic part, close the mold again and proceed to the next cyle. The operation of injection molding machines includes three aspects: keyboard control, electrical control system operation, and hydraulic system operation. Select the injection process action, feeding action, injection pressure, injection speed, and ejection type separately, monitor the temperature of each section of the barrel, and adjust the injection pressure and back pressure.

The working principle of an injection molding machine is similar to that of a syringe used for injection molding. It uses the thrust of a screw (or plunger) to inject melted plastic (i.e. viscous flow state) into a closed mold cavity, and after solidification and shaping, the product is obtained.

The molding process of a general screw injection molding machine is as follows: firstly, granular or powdered plastic is added into the barrel, and the plastic is melted by the rotation of the screw and the heating of the outer wall of the barrel. Then, the machine performs mold closing and the injection unit is moved forward. Then, pressure oil is injected into the injection cylinder to advance the screw forward, so that the molten material is injected into the closed mold with low temperature at high pressure and fast speed. After a certain period of time and pressure maintenance (also known as holding pressure), cooling, and solidification, the product can be taken out of the mold.

The basic requirements for injection molding are plasticization, injection, and molding. Plasticization is a prerequisite for achieving and ensuring the quality of molded products, and in order to meet the requirements of molding, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a corresponding high pressure is generated in the mold cavity, so there must be sufficient clamping force. It can be seen that the injection device and the mold clamping device are key components of the injection molding machine.

Injection molding machine is a specialized plastic molding machine that utilizes the thermoplasticity of plastic. After being heated and melted, it is subjected to high pressure to quickly flow into the mold cavity. After a period of pressure holding and cooling, it becomes various shapes of plastic products.

　　(1) The Working Cycle of Injection Molding Machine

        Cooling and pressure maintenance: Maintain the pressure of the barrel according to various set pressures and time periods, while cooling the mold cavity for molding. Locking the mold: The mold plate quickly approaches the fixed mold plate (including slow-fast-slow), and after confirming that there are no foreign objects present, the system switches to high pressure to lock the template (maintaining the pressure inside the oil cylinder). Move the nozzle forward to the designated position (with the nozzle tightly attached to the mold).

        Injection molding: The screw can be set to multiple speeds, pressures, and strokes to inject the molten material at the front end of the barrel into the mold cavity. Cooling and pre molding: The product inside the mold cavity continues to cool, while the hydraulic motor drives the screw to rotate and push the plastic particles forward. The screw retracts under the set back pressure control. When the screw retracts to the predetermined position, it stops rotating, and the injection cylinder is loosened according to the setting, which is expected to end.

　　(2) Electric Energy Consumption of Injection Molding Machines　　

        The electrical energy consumption of injection molding machines mainly manifests in the following parts: the electrical energy consumption of the circulating cooling water pump, of which the power consumption of the hydraulic oil pump motor accounts for more than 80% of the total electricity consumption of the injection molding machine, the electrical energy consumption of the hydraulic system oil pump, and the electrical energy consumption of the heater. Therefore, reducing their power consumption is the key to energy saving of injection molding machines.

Excessive temperature rise in injection molding machines will lead to a decrease in oil viscosity, increased leakage, and a significant decrease in pump volumetric efficiency and overall system efficiency. Due to the decrease in oil viscosity, the oil film of moving parts such as slide valves becomes thinner and cut, resulting in increased frictional resistance and intensified wear. This will shorten the service life of the machine.

Excessive temperature rise in injection molding machines can lead to poor working quality of components: it can lead to poor working quality of components, causing dissolved air in the oil to escape and create air pockets, resulting in reduced hydraulic system performance. At the same time, it also reduces work efficiency.

Excessive temperature rise in injection molding machines can accelerate the oxidation and deterioration of oil, precipitate asphalt substances, and reduce the service life of hydraulic oil. The precipitation blocks the damping small holes and gap type valve ports, causing the pressure valve to get stuck and unable to operate, the metal pipeline to elongate and bend, and even rupture.

(1) Injection molding machines are composed of mechanical, hydraulic, electrical, and specialized components, which are organically combined according to the needs of injection molding processing technology. They have a high degree of automation and are closely related to each other; The injection molding machine can operate continuously for 24 hours in 3 shifts. If a component of the injection molding machine malfunctions, it will cause the machine to shut down.

(2) The injection molding machine has large fixed assets investment, large production scale, large consumption of raw materials, high labor productivity and large output value. It is a form of production organization with high labor efficiency.

(3) Although the operation of injection molding machines is simple and there are few workers, the technical content of management and maintenance of injection molding machines is high, and the workload is also large.

　　Ensure that the injection molding machine is always in good condition, and it is necessary to strengthen the management of the injection molding machine and strictly control the occurrence of injection molding machine failures. To achieve the goal of reducing failure rates, minimizing maintenance costs, and extending service life.