An injection molding machine (IMM) consists of two main components: the injection unit, which melts and injects the plastic into the mold, and the clamping unit. The functions of the clamping unit are as follows:
1. Keep the mold securely closed under injection pressure;
2. Eject the finished product.
The injection unit melts the plastic before injecting it into the mold and controls the pressure and speed of injection. Two common types of injection mechanisms are currently in use: screw-type preplasticizers (or two-stage units) and reciprocating screws. The screw-type preplasticizer uses a preplasticizing screw (first stage) to inject molten plastic into the injection plunger (second stage).
Advantages of screw preplasticizers include consistent melt quality, high pressure and speed, and precise shot control (achieved through mechanical stops at both ends of the piston stroke). These features are essential for producing transparent, thin-walled products and achieving high production rates. Disadvantages include uneven residence time (which may lead to material degradation), higher equipment costs, and increased maintenance expenses.
The most commonly used reciprocating screw injection unit does not require a plunger to melt and inject the plastic.
Types of injection molding machines include vertical, horizontal, and all-electric models. However, regardless of the type, all injection molding machines perform two basic functions:
1. Heat plastic to its melting point;
2. Apply high pressure to the molten plastic to inject it into the mold cavity.
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