What Are the Classifications of Injection Molds?

Injection molds come in various types, each designed to meet specific manufacturing needs and part complexities. Here's a detailed look at the primary classifications:

1. Single-Parting-Line Injection Mold
When the mold opens, the cavity and the core separate to eject the plastic part. This type is called a single-parting-line mold, also known as a two-plate mold. It is the simplest and most basic form of injection mold. Depending on requirements, it can be designed as a single-cavity or multi-cavity mold. It is the most widely used type of injection mold.

2. Double-Parting-Line Injection Mold
The double-parting-line injection mold has two parting lines. Compared to the single-parting-line mold, it includes an additional movable intermediate plate (also called the runner plate) in the core section. This plate contains the gate, runner, and other necessary components, hence it is also called a three-plate mold (moving plate, intermediate plate, and fixed plate).
It is commonly used for single-cavity or multi-cavity molds with point gates. During mold opening, the intermediate plate separates from the fixed plate at a fixed distance along the guide pillars to allow the removal of the runner system. The double-parting-line mold has a complex structure, higher manufacturing costs, and difficulties in machining parts, making it unsuitable for large or extra-large plastic products.

3. Injection Mold with Side Core-Pulling Mechanism
When the plastic part has side holes or undercuts, a laterally movable core or slider is required for molding. After injection, the moving mold first moves downward a certain distance. Then, the inclined surface of the angled pin fixed on the fixed plate forces the slider to move outward. Simultaneously, the ejector pins of the demolding mechanism push the ejector plate to release the part from the core.

4. Injection Mold with Movable Molding Components
Due to special structural requirements of the plastic part, the mold may need movable components such as movable cores, movable cavities, movable inserts, or threaded cores/rings. These components can move out of the mold with the part during ejection and then be separated from the part.

5. Automatic Thread-Removing Injection Mold
For threaded plastic parts requiring automatic demolding, the mold can be equipped with rotatable threaded cores or rings. The mold opening action, the rotation mechanism of the injection machine, or a dedicated transmission device drives the rotation of the threaded core or ring to release the part.

6. Runnerless Injection Mold
The runnerless injection mold uses methods like insulated or heated runners to keep the plastic in a molten state from the injection machine nozzle to the cavity. This ensures no runner system is ejected with the part. One of these molds is called an insulated runner mold, while the other is called a hot runner mold.

7. Right-Angle Injection Mold
The right-angle injection mold is only suitable for right-angle injection machines. Unlike other molds, the feeding direction is perpendicular to the mold opening/closing direction. The main runner is located on both sides of the parting line of the cavity and core, and its cross-sectional area usually remains constant. To prevent wear and deformation at the nozzle and runner entrance, replaceable runner inserts can be used.

8. Injection Mold with Ejection Mechanism on the core
In most injection molds, the ejection device is installed on the cavity side to align with the ejection system of the injection machine. However, due to the shape limitations of some plastic parts, it is better to keep the part on the core side. In such cases, an ejection mechanism must be installed on the core side to release the part.