What is plastic injection molding? Ultimate Guide 2022

April 15, 2022

What is plastic injection molding?

What is plastic injection molding? Plastic products are increasingly popular and diverse in daily life as well as in the industrial field. The strong development of the plastic industry led to the development of the design and processing of plastic injection molds.

Designing and processing plastic injection molds play an important role in creating beautiful, convenient, and useful plastic products.

So what is a plastic injection mold, what types of plastic injection molds are there, what is the process of designing and processing plastic injection molds and where is the processing?

Let’s learn together with Tip-Top Molds in this article.

What is plastic injection mold?

  • A plastic injection mold is a metal tool (equipment) used to shape products according to the shaping method. Each mold is typically made and used for a certain number of molding/pressing cycles, which can be one or more times.
  • A plastic injection mold is a group of assembled parts, where the plastic is injected, cooled, and then ejected.
  • The texture and size of the mold depend on the size, shape, quality, and quantity of the product to be created.

Each plastic injection mold has a common structure including the following main parts:

 What is plastic injection molding? Mold body: where the mold cavity locates, the mold body is divided into two halves, a stationary half and a movable half. As well, the stationary half is mounted on the fixed plate of the injection molding machine and the movable half is mounted on the movable plate of the injection molding machine. 

  • The space between the stationary half and the mobile half is the void that will be filled by molten plastic, then the plastic is cooled to shape and then removed from the mold cavity.
  • Mold base: clamp the mold firmly into the machine table when processing.
  • Guide and positioning system: responsible for keeping the correct working position of the mold body when assembled.
  • The system of leading plastic into the mold cavity: responsible for supplying plastic from the injection machine to the mold.
  • Product ejection system: responsible for pushing the product out of the mold when pressing is complete.
  • Exhaust system: responsible for bringing out the remaining air in the mold cavity, helping the plastic fill the mold cavity. The product does not leak air or burn.
  • The cold mold-making system has the effect of cooling after we finish machining.

What is plastic injection molding? In a mold part, the recess determines the outer shape of the product (also called the cavity), and the protrusion determines the inner shape of the product called the core. Moreover, a mold set may have one or more cavities and cores. The part of contact between the cavity and the core is called the parting surface.

The mold cavity (negative mold) and core (positive mold) are in a closed state.

Classification of plastic injection molds

Classification based on the number of layers of the mold cavity:

  • 1 tier mold
  • Multi-layer mold

Sort by runner:

  • Mold using hot channel
  • Mold using cold channel

Sort by channel layout:

  • Two-plate mold
  • Three-plate mold

Sort by the number of plastic colors that make up the product:

  • Mold for single color products
  • Mold for multi-colored products (Integrating many different molds on one set of molds).
  • Among the types of molds mentioned above, the two-plate mold is the most common and common form.

Mold material

  • Steel is a metal commonly used to make molds and plays an extremely important role in determining the quality of molds and products.
  • Steel material for plastic molding.
  • The quality of the steel is the decisive factor in precision mold machining.

In addition, ordinary steels have low hardness, easier machining, less tool wear, and easy cooling, but the surface will not achieve a high gloss. Meanwhile, high-quality steels, with higher hardness will give a perfect product surface and good mechanical properties such as impact resistance; good wear resistance, high-temperature resistance for a long time, anti-rust, and increase durability for molds.

The choice of steel to make molds depends on factors such as:

  • The type of plastic that will spray the mold because there are resins that are harmful to the mold steel.
  • Surface gloss, complexity, the function of plastic products.
  • The number of products requires.
  • The resistance to abrasion and chemical corrosion.
  • The weld ability and detail resilience


In order to make molds that meet the technical requirements such as mold making to ensure the accuracy of the shape and size of the product, and the product to be removed from the mold easily, the mold must have reasonable structure, and not too complicated to suit the purpose of use, etc., the mold design and processing are very important factors determining the quality of the mold.

Furthermore, the mold design and manufacturing process are very important. Precise mold design and manufacturing process helps to produce high-quality plastic products.

Mold design process:

In general, the mold design process at Tip-Top Molds for plastic products includes the following steps:

  • Step 1: Receive mold design requests from the customers.
  • Step 2: Discuss with customers to agree on requirements such as mold material, mold characteristics, product material, and product shape and size… in order to control mold quality and the cost of designing & processing suitable molds.
  • Step 3: Review the parameters and requirements of the customer provided.
  • Step 4: Eventually, preliminarily determine the mold structure to send to the customer, waiting for the customer’s feedback to come to a final agreement on the design plan.
  • Step 5: Conduct mold design on the software…
  • Step 6: Hand over the design to the customer, wait for the customer’s feedback, and make adjustments to come to the final solution.
  • Step 7: Acceptance with customers.

Mold processing:

What is plastic injection molding?  Lastly, the manufacturing process of plastic molds at Tip-Top Molds carries out according to the following steps:

  • Step 1: Get standard parts, cast steel, plan, and make a production diagram.
  • Step 2: Design and create machining data on CAD/CAM.
  • Step 3: Process surfaces and details with simple shapes by 2D shaping machining methods.
  • Step 4: Assemble the mold plate together into blocks.
  • Step 5: Machining complex surfaces.
  • Step 6: Polish the mold details.
  • Step 7: Inspect and test the mold.

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