The structure of an injection mold is determined by the type of injection molding machine and the structural characteristics of the plastic part; every mold consists of a moving half and a fixed half. The moving half is mounted on the moving platen of the injection molding machine, while the fixed half is mounted on the stationary platen. During injection, the two halves close to form the gating system and the mold cavity. When the mold opens, the plastic part remains on the moving half side and is subsequently ejected by an ejection mechanism housed within that half. Based on the functions of their various components, an injection mold can be divided into the following sections:
1. Molding Parts
Components that impart shape, structure, and dimensions to the molding material; these typically include cores (male molds), cavities (female molds), threaded cores, and inserts.
2. Gating System
The channel system that directs molten plastic from the injection machine nozzle into the closed mold cavity; it usually consists of the sprue, runners, gates, and cold slug wells.
3. Guiding Components
Components designed to ensure precise alignment when the moving and fixed mold halves close, serving a guiding and positioning function. They consist of guide pillars and guide bushings; some molds also feature guiding components on the ejector plate to ensure the smooth and reliable operation of the ejection mechanism.
4. Ejection Mechanism
A device that facilitates the release of the plastic part and the gating system from the mold. There are many structural variations, with the most common being ejector pins, ejector sleeves, ejector plates, and pneumatic ejection systems. They generally consist of ejector rods, return pins, springs, ejector retainer plates, ejector plates (or rings), and guide pillars/bushings for the ejector assembly.
5. Mold Temperature Control System
A system required to regulate the mold temperature-often using heating elements-to meet the specific requirements of the injection molding process.
6. Venting System
A system designed to allow gases to escape smoothly from the mold cavity; venting channels are typically cut into the parting line and at the interfaces of inserts or sleeves.
8. Other Structural Parts
Components included to satisfy the structural requirements of the mold (e.g., mounting plates, moving/fixed mold plates, support pillars, support plates, and connecting screws).