Injection Mold Tooling: Plastic Molding Tool Fabrication

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Injection molds are the backbone of the injection molding process, shaping raw plastic materials into precise functional parts. Injection molds have a significant impact on the quality, efficiency and overall success of a manufacturing operation during the injection molding process. As technology advances, the injection molding industry continues to evolve, and injection mold tooling methods keep improving.

Careful design, professional construction and maintenance of injection molds directly affect the quality, cost, efficiency and capacity of plastic part production. Sungplastic is a reputable and long-established injection molding manufacturer, we have various types of injection molds and experienced injection mold experts to produce high-quality plastic parts for you.
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What is Injection Molds ?

Injection molds are specialized tools used in the injection molding process to shape molten plastic material into specific shapes and sizes. Injection molding is a key component of the injection molding process and is a widely used manufacturing method for high-volume, high-precision, and consistent production of plastic parts. It consists of two main components: cavity and core. The cavity is the space within the mold where the molten plastic flows and forms the desired final product shape, while the core provides the negative space that defines the internal features of the part. As the cornerstone of the injection molding process, injection molds have a profound impact on the efficiency, precision and cost-effectiveness of plastic manufacturing.
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Systems of Injection Molds

Injection molds play a key role in shaping and forming molten plastic material into precise, complex and consistent parts. These molds are carefully designed and crafted to ensure perfectly shaped plastic products. There are several systems within the injection mold that perform key functions during processing, mainly divided into distribution, cooling and injection systems.

Distribution System for Injection Molds

Initially, the injection unit is filled with molten plastic. Prior to injection, the clamping unit securely closes and holds the two halves of the mold together without any air in the injection mold.

The mold contains a distribution system that facilitates the transfer of molten plastic from the injection unit to the injection mold. The duration required for this transfer is influenced by factors such as injection volume, injection pressure, and injection power.

Using pressure, the injection device introduces molten plastic through the gate bushing, along the gate, through the runner, through the gate, and into the cavity mold. As molten plastic fills the cavity mold, any air is expelled through narrow vents integrated into the mold.

If trapped air remains trapped, it may be compressed into the corners of the cavity mold, causing defects in the plastic product. In some cases, it may even ignite and cause the plastic to burn. The viscosity of the molten plastic prevents it from escaping through the vent.

Due to its compact size, the gate is the first part to solidify, preventing molten plastic from flowing into the cavity of the mold.

Cooling System for Injection Molds

The injection mold is equipped with a cooling system that accelerates the solidification of the plastic material. The duration required for this cooling process can be estimated based on the thermodynamic characteristics of the plastic and its maximum wall thickness.

Below the interior of the cavity mold, there are drilled channels. Within these channels, hoses are positioned and filled with coolant, often water, supplied by an external pump. As the molten plastic flows through these hoses, the coolant absorbs heat from it. This meticulous temperature control ensures that the mold maintains the optimal conditions for efficient solidification.

During the cooling phase, the molten plastic undergoes a transformation, gradually solidifying into its final form. Concurrently, the plastic experiences a reduction in volume, causing it to adhere tightly to the ejector mold (B Plate). This cooling process is usually completed in less than a minute.

Excessive shrinkage of the molten plastic during cooling can lead to issues such as warping, cracking, or improper ejection. Accounting for shrinkage is a critical consideration in the design of an injection mold and is influenced by the quantity of plastic utilized in the process.

Ejection System for Injection Molds

Lastly, the injection mold is equipped with an ejection system to extract the final plastic product. The duration required for this process can be estimated based on the time it takes for the mold to open, remove the plastic product, and subsequently close.

Once the molten plastic completes the solidification process, the mold is gradually opened to allow air in and break the vacuum seal. Subsequently, the ejector mold (B Plate) rapidly moves away from the injection mold (A Plate) and employs ejector pins to propel the completed plastic product away from the mold. It is noted that marks left by injection molds are often visible on plastic products.

Subsequently, the injection mold is resealed, marking the beginning of the next production cycle.

Components of Plastic Injection Mold

A plastic injection mold is a sophisticated tool used in the injection molding process to shape molten plastic into specific parts or products. It consists of several components that work together to create the desired part. Here are the main components of a plastic injection mold:

  • Cavity Plate: The cavity plate forms the exterior surface of the final part. It contains the cavity, which defines the outer shape, appearance, and surface finish of the part.
  • Core Plate: The core plate forms the interior surface of the final part. It contains the core, which defines the internal features, such as holes, threads, and other intricate details of the part.
  • Runner System:
    A: Sprue: The entry point for molten plastic from the injection machine’s nozzle.
    B: Runners: Channels that direct the molten plastic from the sprue to the various cavities.
    C: Gates: Small openings through which the molten plastic enters the cavity. The gate design and placement influence material flow and part quality.
  • Cooling System:
    A: Cooling Channels: A network of channels within the mold that circulate cooling fluid (usually water) to regulate the temperature of the mold during the cooling and solidification stages.
    B: Baffles and Inserts: Additional components added to enhance cooling efficiency in specific areas of the mold.
  • Ejection System:
    A: Ejector Pins: Pins or rods that push the solidified part out of the mold cavity after the cooling phase.
    B: Ejector Plate: A plate that contains the ejector pins and moves them simultaneously to eject the part.
  • Alignment and Locking Mechanism:
    A: Guide Pins and Bushings: Ensure proper alignment of the mold halves during mold closing.
    B: Mold Clamps: Securely hold the mold halves together during injection and cooling.
    C: Mold Base: The foundation of the mold assembly that holds all the components together. It provides stability and rigidity to the mold structure.
  • Venting: Small gaps or vents strategically placed to allow air and gases to escape as the molten plastic fills the mold cavity. Proper venting prevents defects like air traps and incomplete filling.
  • Slides and Lifters: Used to create undercuts or complex features in the part design that would otherwise hinder mold opening and part ejection. Slides and lifters enable these features to be produced.
  • Mold Inserts and Spare Inserts: These can be used to replace specific mold components without creating an entirely new mold. They are particularly useful for making changes to a part’s design or accommodating different materials.
  • Ejector Return Mechanism: Springs or other mechanisms that reset the ejector pins and prepare the mold for the next cycle.
  • Inserts and Overmolding Components: Additional components, such as metal inserts or other pre-molded parts, can be placed in the mold to be encapsulated by the molten plastic during injection.

Each of these components has a specific function in the injection mold, helping to improve the overall quality, efficiency and performance of the injection molding process. The design and precision of these components play a critical role in achieving accurate, consistent, and defect-free plastic parts.

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Complete Steps to Injection Mold Tooling

Injection mold tooling involves several essential steps to design, fabricate, and prepare the mold for the injection molding process. Here’s an overview of the typical steps involved in injection mold tooling:

Part Design and Analysis

  • Begin with a detailed design of the plastic part to be manufactured.
  • Utilize Computer-Aided Design (CAD) software to create a 3D model of the part.
  • Conduct mold flow analysis to simulate the filling and cooling of the mold, identifying potential issues and optimizing the design.

Mold Design

  • Based on the part design and analysis, create a mold design that includes the cavity, core, cooling channels, gating system, ejector system, and other mold components.
  • Ensure proper draft angles, wall thicknesses, and features that facilitate part ejection and cooling.

Mold Fabrication

  • Convert the mold design into physical components using precision machining techniques.
  • Craft the cavity and core plates, runners, gating components, cooling channels, and other mold elements.
  • Ensure tight tolerances and smooth finishes to maintain part quality.

Inserts and Special Features

  • Integrate any required inserts, such as metal components or pre-molded parts, into the mold design.
  • Design and incorporate special features like slides, lifters, or collapsible cores for complex part geometries.

Manufacturing and Assembly

  • Assemble all mold components, ensuring proper alignment and fit.
  • Integrate the cooling system, runner system, gating system, and ejection system according to the mold design.

Finishing and Surface Treatment

  • Polish the cavity and core surfaces to achieve the desired surface finish for the molded parts.
  • Apply coatings or treatments to enhance mold durability and part release.

Testing and Validation

  • Conduct testing to ensure proper mold function, including mold open/close cycles, ejection, and cooling system performance.

Mold Setup

  • Install the mold into the injection molding machine and align it accurately.
  • Adjust settings such as injection pressure, temperature, and cycle time according to the mold’s requirements.

Trial Runs and Optimization

  • Run initial injection molding cycles to produce sample parts.
  • Evaluate the parts for quality, dimensional accuracy, surface finish, and defects.
  • Make any necessary adjustments to optimize the process and part quality.


  • Once the mold and process are optimized, move into full-scale production of plastic parts.
  • Continuously monitor and maintain the mold to ensure consistent production and part quality.

Maintenance and Repair

  • Regularly inspect and clean the mold to prevent buildup and wear.
  • Address any wear and tear promptly through mold maintenance or repair to avoid production issues.

The process of injection mold tooling requires collaboration between design engineers, mold makers, and production teams to ensure that the final mold is capable of producing high-quality plastic parts efficiently and consistently.

Details of Mold Fabrication

Mold fabrication is a critical stage in the injection mold tooling process, where the design concepts and specifications are translated into physical mold components. This process involves precise machining techniques and craftsmanship to create the mold components that will shape and form the plastic parts during the injection molding process. Here’s a detailed breakdown of mold fabrication:

Metal Materials Preparation

  • Begin with the mold design, which serves as the blueprint for the fabrication process.
  • Prepare the raw materials for the mold components, typically high-quality tool steel or aluminum.

Cavity and Core Machining

  • Use Computer Numerical Control (CNC) milling and machining to shape the cavity and core plates.
  • CNC machines follow the design specifications to remove excess material, leaving behind the desired shapes and features.
  • Create precise cavities and cores that mirror the shape and dimensions of the intended plastic part.

Runner and Gating System

  • Machine runners and gating components that guide the molten plastic from the injection machine to the cavity.
  • Ensure smooth material flow and minimize pressure loss through the runner system.

Cooling Channels

  • Drill or mill cooling channels into the mold components.
  • Cooling channels help regulate the temperature of the mold during the injection and cooling phases.
  • Optimize channel placement and design for efficient heat dissipation.

Ejection Mechanism

  • Craft ejector pins, sleeves, or plates that will be used to push the solidified part out of the mold.
  • Design the ejection system to ensure uniform and controlled part ejection without causing damage.

Additional Components

  • If the mold design includes features like slides, lifters, or collapsible cores, create and integrate these components into the mold.

Precision and Tolerance

  • Ensure high precision and tight tolerances throughout the fabrication process.
  • Machining techniques must account for the required part dimensions, surface finishes, and clearances.

Heat Treatment

  • Apply heat treatment to enhance the hardness and durability of the mold components.
  • Heat treatment processes like quenching and tempering help achieve the desired mechanical properties.

Surface Finishing

  • Polish and finish the cavity and core surfaces to the specified smoothness and texture.
  • Proper surface finish aids in part ejection and reduces the risk of defects or imperfections.

Assembly and Fitting

  • Assemble the various mold components according to the design specifications.
  • Ensure precise alignment of the cavity, core, runners, gating components, and cooling channels.

Quality Control

  • Perform thorough quality checks to verify the accuracy of dimensions, alignments, and overall functionality.
  • Use measuring instruments like calipers, micrometers, and coordinate measuring machines (CMMs) to ensure compliance with design specifications.

Mold fabrication demands skilled craftsmanship and attention to detail, as even minor inaccuracies can lead to defects in the final molded parts. Properly fabricated molds are essential for achieving consistent and high-quality plastic parts during the injection molding process.

Reliable Injection Mold Tooling Supplier—Sungplastic

Injection molds are the foundation of injection molding, affecting the quality of plastic products, production efficiency, cost-effectiveness and innovation capabilities. When making parts, injection molding manufacturers should prioritize well-designed, high-quality injection molds to ensure accurate, complex and consistent parts are produced.

At Sungplastic, we understand the importance of injection molds to plastic injection molding, so our well-designed molds can help reduce cycle time, optimize material utilization and minimize waste. Remember, the quality of a custom plastic part depends first on the quality of the mold, and using a mold that fits a specific part design helps in innovation and product differentiation in a competitive market.

Let Sungplastic provide professional advice and technical support for your custom plastic parts, and we will work closely with you to make your project a success.

FAQ: About Injection Molds

  • Can injection molds be reused for different parts?
    Injection molds can often be reused for different parts, especially if the molds are designed with flexibility in mind. However, the feasibility depends on factors like part geometry, size, and material compatibility.
  • Why is mold design important for part quality?
    Mold design directly impacts part quality by influencing dimensional accuracy, surface finish, strength, and other properties. A well-designed mold ensures consistent and defect-free parts.
  • What services does Sungplastic provide besides injection molds?
    Sungplastic provides a range of services beyond injection molding, including part design assistance, prototyping, material selection, mold testing, quality control, assembly, packaging, and logistics support. If you want to know more about injection molding, please contact us, we will answer you one by one.
About Sungplastic

About Sungplastic

Sungplastic is a plastic product manufacturer with rich experience in injection molding. According to the different product development requirements, we flexibly adjust the manufacturing process to achieve high quality, high efficiency and more economical.

We offer a variety of manufacturing services: Rapid Prototyping, Tool Making, Injection Molding, Product Design and Development, CNC Machining and Metal Stamping. You can choose from a variety of plastics, silicone rubber, or metal for your product. Regardless of mass production or small batch customization, Sungplastic has always been committed to providing assured, efficient and more economical one-stop processing services for your projects.

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