Structure and applications of plastic injection molds in life

Plastic injection molds or plastic molds are commonly used to create plastic products for life, transportation, electricity – electronics, construction, national defense, aviation, automobiles… Based on Plastic injection mold structures are divided into 2-plate molds, 3-plate molds, multi-layer molds, etc. Not only do they require high precision, but plastic injection molds must also have aesthetics, high durability, and ensure productivity. So what is the applications of plastic injection molds? Let’s find out from Hanoi Mold!

1. What is plastic molding?

Plastic molding is a tool used to shape plastic products. It is designed based on the desired shape of the product and consists of multiple components assembled to form a cavity where molten plastic is injected and then cooled to create the final product.

The product’s shape and size determine the plastic mold’s dimensions and structure. Productivity and output play a significant role in mold design. For small-scale production, a simple mold design may be sufficient, while large-scale production requires more complex mold designs.

Creating a plastic mold involves two main processes: mold design and mold machining. To calculate the mold design, a complete product design drawing is required.

2. Structure of plastic injection mold

Structure and applications of plastic injection molds in life
Structure and applications of plastic injection molds in life

A plastic mold consists of two main parts: the movable part (male mold) and the stationary part (female mold).

  • The stationary mold half (female mold):

This part is attached to the injection molding machine and remains fixed in position throughout the injection process. The hot molten plastic material is injected into the mold cavity, which is connected to this stationary part of the mold.

  • The movable mold half (male mold):

This part performs the mold closing movement to mold the product and opens the mold to release the product. A system of ejector pins is designed within the movable mold to push the product out.

a. Basic components of a plastic mold

The two main parts of a plastic mold are composed of 17 basic components in the structure of the mold (as shown in the diagram above), with the following functions:

  1. Upper clamp plate: used to clamp onto the stationary part of the machine. The drawing clearly describes the front clamp plate with a protruding width compared to other mold plates, and this protruding part is used for clamping the mold.
  2. Stationary plate (female mold): this plate is the stationary part of the mold.
  3. Sprue bushing: functions to guide the molten plastic from the machine’s nozzle into the mold (initially guiding the plastic into the runner channels).
  4. Locating ring: used to position the mold with the machine, ensuring that the machine’s nozzle is accurately positioned with the corresponding position of the sprue bushing. This component has a circular shape and protrudes higher than the upper surface of the front clamp plate to fit into the corresponding hole on the machine’s stationary part.
  5. Hex screw: helps secure the clamp plate and the mold plate together.
  6. Cooling channels: these are the mold’s cooling system, which also serves to maintain the mold temperature during the heating process for plastics with low melting temperatures.
  7. Movable plate (male mold): the mold plate on the movable part.
  8. Backing plate: helps increase the rigidity of the movable mold plate, and this plate is only used when the movable plate is too thin.
  9. Support pillar: consists of two plates on both sides forming a pair, providing support for the movable plate and creating a space to accommodate the ejector system.
  10. Ejector retainer plate: holds the ejector pin system in place during mold operation.
  11. Ejector plate: this plate connects to the ejector rod of the molding machine and functions to push the ejector pin system.
  12. Lower clamp plate: used to clamp the movable part of the injection molding machine.
  13. Ejector pins: these pins are responsible for pushing the product out of the mold.
  14. Springs: push the ejector system back to prepare for the next injection cycle.
  15. Return pins: help guide the clamp plate and the ejector plate to move linearly in the correct direction to prevent them from sliding out, while also protecting the ejector pins from bending during the product ejection and retraction process.
  16. Guide bushing: facilitates easy movement and positioning of the guide pins.
  17. Guide pins: ensure accurate positioning of the movable and stationary parts of the mold throughout the mold closing process.

b. Basic systems of a plastic mold

The components mentioned above are assembled to form the basic systems of a mold, including:

  1. Guiding and positioning system: includes guide pins, guide bushings, core positioning, cavity positioning, etc., which ensure the correct working position of the movable and fixed mold parts when they are closed to create an accurate mold cavity.
  2. Plastic injection system: includes sprue bushing, runner channels, and gate nozzle, which supply the molten plastic from the injection molding machine’s nozzle into the mold cavity.
  3. Slide system: includes side cores, slide cores, guide bars, cam locks, hydraulic cylinders, etc., used to remove the parts that cannot be directly ejected in the mold’s opening direction.
  4. Ejection system: includes ejector pins, return pins, support pins, support bushings, ejector plates, retainer plates, etc., which push the product out of the mold after the molding process is completed.
  5. Venting system: includes venting grooves, and venting valves, which remove trapped air from the mold cavity, ensuring that the cavity is properly filled with plastic and that the products are free from air bubbles, burn marks, or material shortage.
  6. Cooling system: includes water channels, cooling grooves, heat transfer pipes, connectors, etc., which regulate the mold temperature and rapidly cool down the products.
  7. Hot runner system: also known as a hot manifold system.

The mold components may require bolts and screws to fasten the mold plates and other components together.

For a 3-plate plastic mold, an additional plate is added to connect the movable and fixed parts. The 3-plate mold is used in the hot runner system. The runner system is arranged on two planes, and when the mold is opened, there are two open spaces: one for removing the product and the other for removing the runner. The product is ejected using a pin ejector system located on the side of the movable mold part. The runner is removed using a stripper plate arranged on the fixed part to separate the runner from the product.

A 3-plate plastic mold is used when it is necessary to arrange the gate(s) at the center or have multiple gates for separate flow into the mold cavity. Point gates are used for thin-walled parts with wide and long flow paths.

Due to complexity and cost, 3-plate molds are less commonly used. Designers always strive to optimize the mold manufacturing process by designing 2-plate plastic molds.

3. Applications of plastic injection molds

Plastic injection mould for automotive parts










Applications of plastic injection molds in producing a large quantity of components:

Plastic molds are an important tool in the manufacturing and production industry, used to create plastic products with specific shapes and sizes that are familiar in everyday life. Here are some common applications of these types of molds:

  1. Consumer products manufacturing: Household items such as water pipes, food containers, water bottles, electric kettles, pots, toy cars, plastic vases, decorative lights, etc.
  2. Automotive industry: Production of plastic components for cars, such as differential housings, interior control panels, and exterior body parts.
  3. Medical field: Manufacturing of medical products like syringes, tubing, medicine bottle caps, and medical cushions.
  4. Electronics industry: Production of plastic casings and components for electronic products such as mobile phones, tablets, computers, and household electronic devices.
  5. Food and beverage industry: Manufacturing plastic products for food and beverage packaging, such as food containers, water bottles, and food storage bags.
  6. Construction industry: Production of plastic products used in construction, such as drainage pipes, water pipes, and insulation materials.
  7. Packaging industry: Manufacturing plastic products used in packaging, such as non-woven bags, product containers, and plastic packaging materials.

These are just a few examples of the diverse applications of plastic molds in creating a wide range of components for various industries.

4. Common types of plastic molds in the market:

2-plate molds:

The 2-plate mold is typical and widely used in the market. It has a simple structure and is easy to use in the production process. The product is formed between two halves of the mold, and the space between the two plates is filled with molten plastic. Once the plastic product has cooled down, it is ejected from the mold.

Despite its simple structure, the 2-plate mold ensures high accuracy of the product. This type of mold is often used in the manufacturing of simple household products.

3-plate molds:

The structure of a 3-plate mold is more complex than a 2-plate mold. This type of mold is an injection mold that uses a cooling channel system arranged on two planes. When the mold is opened, there is an opening space for easy removal of the product and another opening space for removing the runner.

Multi-cavity molds:

The structure of multi-cavity plastic molds typically consists of three mold sets, with the middle set having both sides as the mold cavity. When the mold is opened, it creates two empty spaces, and both spaces are used for the products to fall out. Multi-cavity molds are suitable for manufacturing a large quantity of products and help reduce machine clamping force, but the ejection system is more complex.

Side-plate molds:

Side-plate molds are a special type of mold that does not allow the product to be ejected through the opening and closing method. To remove products with holes or lateral recesses from the mold, a side-plate mold is used, which features movable elements that extract the product by pulling out the details creating the recess or hole.

These are some of the common types of plastic molds available in the market, each with its advantages and suitable applications.

Learn more about Hanoi Mold Company’s plastic mold production process here

Chat Zalo

Bấm để gọi (Tư vấn 24/7)0912 308 979