I. What is an injection mold?
Molds are tools used in the manufacturing industry for shaping or mass production of products. Injection molds, specifically, are used to produce plastic products, providing them with various structures and dimensions. Injection molds can significantly improve production efficiency when mass-producing complex products. Their working principle involves injecting molten material under high pressure into the mold cavity, where it cools and solidifies to form the final shape.
II. Structural Components of Injection Molds?
1. Molded parts
Parts that give shape, structure and size to molded materials are usually composed of cores (punches), concave cavities, threaded cores, inserts, etc.
2. Gating system
It is a channel that guides molten plastic from the injection molding machine nozzle to the closed mold cavity, and it usually consists of a main runner, branch runners, gate, and cold slug well.
3. Guide components
The guide component is designed to ensure precise alignment when the moving mold and the fixed mold are closed. It plays a guiding and positioning role and consists of guide pillars and guide sleeves. Some molds also have guide components on the ejector plate to ensure smooth and reliable movement of the demolding mechanism.
4. Demolding mechanism
Devices that enable demolding of plastic parts and gating systems come in many structural forms. The most common demolding mechanisms include ejector pins, ejector tubes, ejector plates, and pneumatic ejection mechanisms. They are generally composed of ejector pins, return pins, springs, ejector pin fixing plates, ejector plates (ejector rings), and ejector plate guide pillars/sleeves.
5. Core-pulling mechanism
For plastic parts with side holes or side recesses, side core pulling or separating the sliders (side parting) must be performed before they can be ejected from the mold to ensure smooth demolding.
6. Mold temperature control system
Mold temperature control systems (such as cooling water, hot water, hot oil, and electric heating systems) regulate the mold temperature to meet the required temperature.
7. Exhaust System
Venting grooves are typically created at the parting line of the mold to facilitate gas escape. Additionally, the gaps between ejector pins or other moving parts (such as sliders) in many molds can also serve a venting function.
8. Other structural parts
Parts designed to meet the structural requirements of the mold (such as: fixed plate, moving/fixed template, support head, support plate and connecting screws, etc.).
III. What are the classifications of injection molds?
1. Single parting surface injection mold
When the mold opens, the moving mold and the fixed mold separate to remove the plastic part. This is called a single parting surface mold, also known as a two-plate mold. It is the simplest and most basic form of injection mold. It can be designed as a single-cavity injection mold or a multi-cavity injection mold as needed, and it is the most widely used type of injection mold.
2. Double parting surface injection mold
Double parting surface injection molds have two parting surfaces. Compared to single parting surface injection molds, double parting surface injection molds add a partially movable intermediate plate (also called a movable sprue plate, which houses the sprue, runner, and other parts and components required by the fixed mold) to the fixed mold section. Therefore, they are also called three-plate (moving plate, intermediate plate, fixed plate) injection molds. They are commonly used in single-cavity or multi-cavity injection molds with point gate injection. During mold opening, the intermediate plate separates from the fixed platen at a fixed distance on the guide pillars of the fixed mold to allow the solidified material of the gating system to be removed between the two platens. Double parting surface injection molds have a complex structure, higher manufacturing costs, and more difficult parts processing, and are generally not used for molding large or extra-large plastic products.
3. Injection mold with side parting and core pulling mechanism
When the plastic part has side holes or side recesses, a side-moving core or slider is required for molding. After injection molding, the moving mold first moves downward a certain distance, and then the inclined section of the bent pin fixed on the fixed platen forces the slider to move outward. At the same time, the ejector rod of the demolding mechanism pushes the ejector plate to remove the plastic part from the core.
4. Injection molds with movable molding parts
Injection molds are equipped with movable molding components, such as movable punches, movable dies, movable inserts, movable threaded cores or rings, to create special structures. These components can be removed from the mold along with the plastic part during demolding and then separated from the plastic part.
5. Automatic unscrewing of threaded injection molds
For threaded plastic parts, the threaded core or threaded ring can be rotated and ejected by the mold opening action or the rotation mechanism of the injection molding machine.
6. Runnerless injection mold
By using a method of heat insulation heating of the runner, the plastic between the injection molding machine nozzle and the cavity is kept in a molten state, so that no solidified material from the gating system is injected when the plastic part is removed from the mold.
7. Right-angle injection mold
Right-angle injection molds are only suitable for angle injection molding machines. In this type of mold, the feeding direction is perpendicular to the mold opening and closing direction during molding. Its main runner is located on both sides of the parting surface between the moving and stationary molds, and its cross-sectional area is usually constant. To prevent wear and deformation of the injection molding machine nozzle and the main runner inlet, replaceable runner inserts can be installed at the ends of the main runner.
8. The demolding mechanism on the fixed mold of the injection mold
In most injection molds, the demolding device is installed on the moving mold side, which facilitates the operation of the ejection device in the injection molding machine's mold opening and closing system. In actual production, due to the shape limitations of some plastic parts, it is better to leave the plastic part on the fixed mold side for molding. Therefore, in order to remove the plastic part from the mold, a demolding mechanism must be set on the fixed mold side.
