How Are Plastic Injection Molds Made?

Chart illustrating the plastic injection molding process.

Plastic injection molding is a manufacturing process used to produce high-precision plastic parts. Understanding how injection molds are made is essential for appreciating the intricacies involved in producing quality plastic components.

What Is Plastic Injection Molding?

Plastic injection molding involves melting plastic pellets and injecting the molten plastic into a mold cavity where it cools and solidifies into the final product. The process is widely used due to its efficiency and ability to produce complex shapes with high precision.

Step-by-Step Process of Making Plastic Injection Molds

1. Design Phase

  • Conceptual Design: The process begins with a Conceptual Design of the plastic part. Engineers use CAD software to create detailed 3D models.
  • The 3D models given by the client and Bigmate Philippines Inc will be coordinated for the fabrication with the Mold Maker sub-contractor.
  • Material Selection: Choosing the right plastic material is crucial. Factors such as strength, flexibility, and temperature resistance are considered.
  • Usually, the specification of the required material will be fixed by a client however, it depends on the products or requirements of the client Bigmate Philippines Inc. will be the one who selects the proper material for the plastic injection.

2. Prototype Mold Development

  • Testing and Refinement: The prototype Mold undergoes testing, and necessary adjustments are made to the design.

3. Mold Design

  • Cavity and Core: The mold consists of two main parts: the cavity (the Fixed side)  and the core (the movable side).
  • Cooling Channels: Design a cooling Line to ensure even cooling of the molded part, preventing warping and defects.
  • Ejection System: Design the ejection system to remove the part from the mold without damaging it.

4. Final DFM (Design for Manufacturing) confirmation

  • First DFM Approval: By confirmation of above No.1 to No.3, Bigmate Philippines Inc. will verify whether the DFM provided by Mold Maker fits our production and client requirements or not.
  • Final DFM Approval: Once Bigmate Philippines Inc. approves the DFM proposal, it will proceed for final approval by a client. The final verification by the client will be conducted in the meeting and if there are some requirements to adjust it will be revised and 2 to 3 days will be re-submitted to the client.
  • The above two processes are most important before proceeding with mold fabrication so the initial start-up process will be smooth.

5. Start the Machining process

  • Mold Base: The mold base is typically made from hardness of steel and is machined to precise specifications using CNC machines.
  • Core and Cavity Machining: The core and cavity are machined separately, and intricate details are added using EDM (Electrical Discharge Machining).
  • Insert and slider machining: Especially the precision parts will be designed with an insert to be easy to maintain and replace and the sliding part is needed to move during mold opening due to the undercut design.
  • The other detailed parts will be machining which are Ejector holes, Cooling line, Air vent, etc… 

6. Surface Treatment

  • Texture: If the design requires a textured surface before conducting heat treatment it must be preceded by the necessary texture design.
  • Hardening: The mold components undergo heat treatment to increase their hardness and durability.
  • Tempering: Tempering relieves stresses in the metal and improves toughness.

7. Assembly and Testing

  • Mold Assembly: The core and cavity, along with other components, are assembled into the mold base.
  • Testing and Adjustments: The injection molding process tests the assembled mold with several parameter adjustments. The necessary adjustment will be decided after inspection of the appearance condition and dimension/function evaluation result.

8. Pre-Production Evaluation

  • Pre-Production: Once completed until above process No.6, before proceeding with Mass production it’s necessary to evaluate the stability of Quality and Productivity. 
  • Bigmate Philippines Inc. has a standard process to guarantee the required quality and productivity for a client.

8. Production

  • Mass Production: Once the mold is perfected, it is used for mass production. The injection molding machine continues injection into the mold repeatedly, producing consistent, high-quality parts.

Benefits of Plastic Injection Molding

  • Efficiency: Capable of producing large quantities of parts quickly.
  • Precision: High precision and consistency in part production.
  • Versatility: Suitable for a wide range of materials and complex shapes.


Plastic injection molds are crafted through a meticulous process involving design, fabricating prototyping mold(In case required by a Client), machining, Surface treatment, Assembly, and Trial. This ensures the production of high-quality plastic parts that meet stringent standards. Understanding this process highlights the skill and technology required to produce everyday plastic items.

Explore more about plastic injection molding solutions on Bigmate Philippines Inc.’s website:

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