1. Overview and Features
Injection molding is a molding process that uses molds. Materials such as synthetic resin (plastic) are heated and melted and then sent to a mold to cool into the designed shape. The process is called injection molding due to its similarity to the process of injecting fluids using a syringe. The process proceeds as follows: the material is melted and poured into the mold, then allowed to harden naturally, then the product is removed, and finally the edges are finely trimmed.
Through injection molding, parts of various shapes, including parts with complex shapes, can be mass-produced continuously and quickly. Therefore, injection molding is used to manufacture goods and products in various industries.
2. Injection molding machine
There are different types of injection molding machines such as electric motors driven by servo motors, hydraulic machines driven by hydraulic motors, and hybrid machines driven by a combination of servo motors and hydraulic motors. The structure of an injection molding machine can be briefly summarized as consisting of an injection unit that feeds molten material into the mold and a clamping unit that operates the mold.
In recent years, CNC has been increasingly used in injection molding machines, making models that can achieve high-speed injection molding under program control increasingly popular. On the other hand, many specialized machines are also used, such as models that form light guide plates for LCD displays.
Basic structure of injection molding machine
A cylinder (heating material), nozzle (injecting molten material), hopper (feeder),
Mold (material is poured into the mold cavity between two plates)
3. Injection molding process
When injection molding begins, resin pellets (pellets) are poured into a hopper, which is the entry point for the material. The pellets are then heated and melted inside the cylinder in preparation for injection. The material is then forced through the nozzle of the injection unit and then transported through channels in the mold called gates and then into the mold cavity through branching runners. After the material cools and hardens, the mold opens and the formed part is ejected from the mold. To complete the molded part, gates and runners are trimmed from the part.
It is important that the molten material is transported evenly throughout the mold because there are often multiple cavities within the mold, allowing multiple parts to be produced at once. Therefore, the mold shape should be designed to ensure this, such as having runners of the same size. Although injection molding is suitable for mass production, it is necessary to fully understand the various conditions required to produce high-precision products, including the selection of resin materials, the processing accuracy of the mold, and the temperature and speed of melt injection.
A nozzle used to inject molten material. After molding, runners are trimmed from the molded part to complete the process.
