Injection Molding Tools: The Key of Plastics Production

In primitive times, humans learned to use stone tools, woods and other tools to hunt. Since ancient times, human production cannot do without tools, just like fish cannot without water. Tools play an important role in manufacturing, Tools can help to boost production, improve product quality, consistency and standardization.

Injection molding tools is used for assisting to manufacture the custom plastic parts or products in the molding process. These molds for plastic injection always made from steel and aluminum materials, because these kinds of materials is very suitable for dealing with plastic.

At Sungplastic, you can know more about how to manufacture custom molds for plastic injection. We often deal with all kinds of plastics and are able to make high-quality injection molding tools to produce custom plastic parts or products.
If you have similar projects, please read this and consult with us.

injection molding tools fabrication

What are Injection Molding Tools?

Injection molding tools, also known as molds, dies or tooling, are specialized equipment used in the injection molding process to produce plastic parts or products. Injection molding tools are designed to shape molten plastic material into the desired form and are typically made from high-quality steel or aluminum. Injection molding tools play a pivotal role in determining the quality, consistency, and efficiency of the final product.

YouTube video

Key Components of Injection Molding Tools

Injection molding tools are typically designed and manufactured based on the specific requirements of the plastic part being produced. They play a critical role in the injection molding process, enabling the mass production of high-quality plastic components used in various industries.
Let’s Know about the key components pf injection molding tools.

    • Mold Cavity
      This is the core component of the mold that forms the shape and features of the final plastic part. It is created with precision to match the desired product design.
    • Mold Core
      The mold core complements the mold cavity and helps create the desired shape by forming the internal features of the part.
    • Sprue
      The sprue is the channel through which the molten plastic material is injected into the mold. It connects the injection molding machine’s nozzle to the mold cavity.
    • Runners
      Runners are channels that distribute the molten plastic material from the sprue to multiple cavities in a multi-cavity mold. They ensure even flow of material and help in efficient filling of the mold.
    • Gates
      Gates are the openings through which the molten plastic enters the mold cavity from the runners. They control the flow of material and are designed to minimize defects such as excessive flash or air traps.
    • Ejector Pins
      These pins are used to push the finished part out of the mold once it has solidified. They are typically located on the side opposite to the gate and can leave small marks on the part, known as ejector pin marks.
    • Cooling System
      Injection molding tools incorporate a cooling system, usually in the form of channels or passages, to rapidly cool the molten plastic and solidify it within the mold. This helps in achieving faster cycle times and better part quality.
    • Venting System
      Venting is crucial to allow the escape of air or gases from the mold cavity during injection. Venting channels or slots are incorporated into the mold design to prevent defects like burns, voids, or short shots caused by trapped air.

Types of Injection Molding Tools

Injection molding tools are a critical component of the injection molding process. They come in various types, each designed to fulfill specific production requirements. The choice of injection molding tools types and materials depends on factors such as production volume, part complexity, material compatibility, cost constraints, and lead time.

Types According to Using Purposes

Different using purposes need different injection molding tools, due to specific production requirements, such as efficiency, lead times, precision, costs and so on.

Single Cavity vs. Multi-Cavity Molds

Single Cavity Molds
These molds for plastic injection produce a single part per cycle. They are commonly used for small-scale production runs, prototyping, or when the part is large or complex, making multi-cavity molding impractical. Single cavity molds are less expensive to manufacture and maintain but have lower production rates.

Multi-Cavity Molds
These molds for plastic injection have multiple cavities, allowing for the simultaneous production of multiple parts in a single cycle. They are ideal for high-volume production as they significantly increase production rates and efficiency. However, they are more complex to design and manufacture, and maintenance can be more challenging.

Hot Runner vs. Cold Runner Molds

Hot Runner Molds
In hot runner molds, a heated manifold is used to maintain the molten plastic at a consistent temperature as it flows from the injection unit to each cavity. This ensures that the material remains in a molten state, reducing waste and improving cycle times. Hot runner molds are often used for high-precision parts and reduce the need for post-processing.

Cold Runner Molds
In contrast, cold runner molds have a system of runners and gates that are at a lower temperature than the molten plastic. This can result in some material waste as the runners and gates need to be removed from the finished parts. Cold runner molds are more straightforward to design and maintain, making them a cost-effective choice for many applications.

Prototype vs. Production Molds

Prototype Molds
These molds are designed for low-volume production runs or for creating prototypes and testing new designs. They are typically less expensive and have a shorter lead time compared to production molds. However, they may have limitations in terms of durability and the number of parts they can produce.

Production Molds
Production molds are built for high-volume manufacturing and are engineered for durability and longevity. They can withstand the stresses of continuous operation, making them suitable for long production runs. Production molds are typically more expensive to design and manufacture but offer significant cost savings over time due to their efficiency.

Types According to Mold Materials

Different materials can create different injection molding tools. Each material can provide different kinds of properties and performance.

Steel Molds

Steel molds are the most common choice for injection molding tools due to their durability and longevity. They are made from various grades of steel, such as P20, H13, and S136, depending on the specific requirements of the project.

Steel molds can withstand high temperatures and pressures, making them suitable for a wide range of materials and production volumes. These molds for plastic injection offer excellent surface finish and dimensional accuracy.

Steel molds are more expensive to manufacture and maintain compared to other materials. These molds for plastic injection also have longer lead times for production.
WordPress website

Aluminum Molds

Aluminum molds are a cost-effective alternative to steel molds, especially for prototyping and low to medium production runs. They are typically made from alloys like 7075 or 6061.

Aluminum molds are quicker to manufacture, making them a suitable choice for rapid prototyping and short-run production. These molds for plastic injection have good thermal conductivity, which can aid in faster cooling times.

Aluminum molds may not be as durable as steel molds, making them less suitable for high-volume production. They may also have limitations in terms of the materials they can handle due to lower heat resistance.
WordPress website

Molds of Other Specialized Materials

Depending on the specific requirements of the project, these molds for plastic injection can be made from other specialized materials.
These specialized materials are chosen based on the unique properties they offer, but they are often more expensive than steel or aluminum molds and may have longer lead times for manufacturing.

For example:
Beryllium copper molds are used for applications requiring high thermal conductivity and electrical conductivity.
Invar molds are employed for parts that require minimal dimensional changes with temperature fluctuations.

Design of Injection Molding Tools

When we manufacture our injection molding tools, we need to know about design considerations of them. Good design of injection molding tools will lead to the creation of quality plastic parts.

Part Design

Part design is the initial step in creating an injection molding tool. It involves designing the shape, size, and features of the plastic part to be produced.

Key considerations include:

    • Draft angles
      Ensuring that the part can be easily ejected from the mold.
    • Wall thickness
      Maintaining uniform wall thickness to prevent defects like warping and sink marks.
    • Ribs and gussets
      Adding structural support without compromising part aesthetics.
    • Fillets and radii
      Incorporating curves and rounded edges to reduce stress concentrations.
    • Surface finish
      Specifying the required surface finish for the part.

Material Selection

The choice of material for the injection molding tools depends on factors such as the expected production volume, mold complexity, and the type of plastic material being molded.
Common materials for injection molding tools include high-quality steel, such as tool steel or stainless steel, and aluminum.

Steel molds are generally preferred for high-volume production and complex parts due to their durability and heat resistance.
Aluminum molds are suitable for low to medium production volumes and simpler part designs, as they offer faster cooling and easier machining.

Gate Design

The gate is the point at which molten plastic enters the mold cavity. The gate design influences the flow pattern, pressure distribution, and the appearance of the part.
Proper gate design is crucial for achieving high-quality parts. Considerations include:


    • Gate location
      Determining the ideal placement for the gate to minimize visible marks or defects on the part.
    • Gate type
      Choosing between various gate types such as sprue gates, edge gates, and hot runner systems.
    • Gate size
      Calculating the appropriate gate size to balance flow and minimize gate vestiges.
    • Gate vestige management
      Strategies to remove or hide gate marks, like secondary operations or part design.

Runner Design

Runner design in injection molding tools refers to the layout and configuration of the channels that distribute molten plastic from the sprue to multiple cavities in a mold. An optimized runner design ensures efficient material distribution, minimal pressure drop, and uniform filling of all cavities, resulting in consistent high-quality parts.

Key aspects of runner design include:

Types of Runners
Single Runner: Connects the sprue directly to the mold cavity in a single-cavity mold.
Multi-Cavity Runner: Branches out from the sprue to distribute material to each cavity in multi-cavity molds.
Types include cold runners (material solidifies and is discarded) and hot runners (material remains molten).

Runner Layout
A balanced layout ensures equal flow to each cavity, minimizing variations in fill time and pressure.
Designs may include straight runners, U-shaped runners, H-shaped runners, or optimized layouts based on the part and mold requirements.

Runner Size and Shape
Runner size affects flow rate, pressure drop, and material stress, determined by part volume, fill time, and material viscosity.
Shape can be rectangular, circular, or trapezoidal.

Runner Balance
Achieving balanced flow is crucial for consistent part quality. Imbalances can cause variations in dimensions and appearance. Techniques like runner sizing, balancing inserts, or flow restrictors are used to achieve balance.

Ejection System

The ejection system is responsible for removing the molded part from the mold once it has cooled.

Design considerations involve:


    • Ejector pin placement
      Ensuring even ejection force distribution and preventing part deformation.
    • Ejection method
      Deciding between various ejection methods, such as ejector pins, sleeves, or stripper plates.
    • Ejector system size
      Determining the number and size of ejector pins or components based on part complexity.
    • Ejector sequence
      Planning the order in which ejectors activate to prevent part damage.

Cooling System

Efficient cooling is essential for maintaining proper cycle times and part quality. Cooling system design involves:

    • Coolant channel placement
      Strategically positioning cooling channels to maintain uniform temperatures throughout the mold.
    • Cooling channel design
      Optimizing the cross-section and layout of cooling channels for efficient heat transfer.
    • Baffles and bubblers
      Using these components to enhance cooling efficiency and reduce warping.
    • Temperature control
      Incorporating temperature control systems like heaters and cooling jackets for precise temperature regulation.

Mold Flow Analysis

Mold flow analysis, often performed using specialized software, simulates the flow of molten plastic within the tool cavity.
It helps identify potential issues such as flow imbalances, weld lines, air traps, or excessive pressure that may affect part quality.
By analyzing the flow behavior, adjustments can be made to the mold design, gate locations, or runner system to optimize the filling process.

Venting Considerations

Venting refers to the release of trapped air or gases from the mold cavity during injection.
Insufficient venting can lead to defects such as burns, voids, or short shots.
Proper venting is achieved by incorporating venting channels or slots in the mold design to allow the air to escape without compromising the part’s integrity.

Tooling Cost and Complexity

The cost and complexity of injection molding tools depend on various factors, including part complexity, material selection, mold size, and manufacturing processes.
More intricate part designs or higher production volumes often require more complex and expensive injection molding tools.
Balancing the cost of injection molding tools with the desired part quality, production volume, and expected tool lifespan is crucial.

Manufacturing Process of Injection Molding Tools

The injection molding tool manufacturing process requires a combination of design expertise, material selection, precision fabrication techniques, surface finishing, and meticulous assembly and testing. By following these steps with attention to detail and quality control, manufacturers can produce reliable and efficient injection molding tools capable of producing high-quality plastic parts.

Mold Design and Engineering

Mold design is a crucial step in the injection molding tool manufacturing process.
It involves translating the product design requirements into a detailed mold design that encompasses the mold cavity, core, runner system, gates, cooling channels, and other necessary components.
Mold designers use specialized computer-aided design (CAD) software to create 3D models and optimize the mold design for efficient production and part quality.
Engineering considerations include part shrinkage, draft angles, ejection mechanisms, and ensuring proper venting and cooling.

Materials Used in Injection Molds

The choice of material for mold construction depends on factors such as the expected production volume, costs, part complexity, and required tool lifespan. Common materials for injection molding tools include high-quality steel, such as tool steel or stainless steel, and aluminum. Each materials has different properties.

Mold Fabrication Techniques

Mold fabrication involves the manufacturing of the mold components based on the approved mold design.
The fabrication process may include various techniques such as milling, turning, grinding, and electrical discharge machining (EDM) to shape the mold components. CNC (Computer Numerical Control) machines are often used for precision and accuracy in mold fabrication.
Fabrication techniques may differ based on the choice of mold material and complexity of the mold design.

CNC Machining

CNC (Computer Numerical Control) machining is a common method for creating injection molding tools.
The CNC machining process involves:

    • Material selection
      Choosing the appropriate tool steel or aluminum alloy based on the expected production volume and part complexity.
    • Rough machining
      Using CNC mills and lathes to remove excess material and create a rough mold shape.
    • Finish machining
      Precisely shaping the mold cavities, cores, and other features to meet design specifications.
    • Electrode production
      Designing and machining electrodes for EDM processes.

EDM (Electrical Discharge Machining)

EDM is used for creating complex, intricate, or small features in injection molding tools.

The EDM process includes:


    • Wire EDM and Sinker EDM
      Selecting the appropriate EDM method based on the desired feature and material.
    • Electrode machining
      Creating custom electrodes for EDM operations.
    • Precision machining
      Using electrical discharges to erode material and achieve tight tolerances and fine surface finishes.

Surface Finishing and Polishing

Surface imperfections can transfer to the molded parts, affecting their appearance and functionality. After the mold components are fabricated, surface finishing and polishing are performed to ensure smooth and defect-free mold surfaces.

Techniques such as sanding, polishing, and bead blasting are employed to achieve the desired surface finish. High-precision injection molding tools may require additional processes like diamond polishing or chemical treatments to achieve exceptional surface quality.

Surface finishing processes involve:

    • Polishing and buffing
      Smoothing and polishing mold surfaces to achieve specific gloss levels.
    • Texturing
      Adding textures or patterns to replicate desired surface finishes on molded parts.
    • Coatings
      Applying coatings like chrome or nickel to enhance durability and prevent corrosion.

Mold Assembly and Testing

Once the individual mold components are finished, they are assembled to create the complete injection molding tool. The mold assembly process involves precise alignment and fitting of the mold components, including the mold cavity, core, runner system, and ejector system.

After assembly, the mold undergoes rigorous testing to ensure its functionality and performance.
Testing may involve trial runs to check for proper part filling, ejection, and cooling, as well as the detection and resolution of any issues or defects. Mold testing helps verify that the tool meets the required specifications and can produce high-quality parts consistently.

Quality control measures include:


    • Measurement and inspection
      Using precision measurement tools like CMMs (Coordinate Measuring Machines) to verify dimensions and tolerances.
    • First-article inspection
      Testing the mold with initial production runs to identify and correct any issues.
    • Process validation
      Validating the tooling process to ensure consistent part quality over time.
    • Documentation
      Maintaining comprehensive records of design, manufacturing, and quality control processes for traceability.

Advances in Injection Molding Tools Technology

Advances in injection molding tool technology offer manufacturers enhanced capabilities, improved efficiency, and greater flexibility in meeting diverse production needs. These advancements address challenges related to precision, speed, cost-effectiveness, and automation, providing opportunities for innovation and improved outcomes in the injection molding industry.

High-Precision Tooling

Advancements in machining techniques, automation, and metrology enable the production of high-precision injection molding tools with tight tolerances and complex geometries.
High-precision tooling is essential for industries such as medical, aerospace, and electronics that require intricate and accurate parts.

Rapid Tooling Techniques

Rapid tooling methods, such as additive manufacturing (3D printing) and aluminum tooling, provide faster and more cost-effective solutions for low to medium production volumes or prototyping.
Rapid tooling allows for quick iterations and reduces the time and cost associated with traditional tooling processes.

Hot Runner Systems

Hot runner systems eliminate the need for cold runners, reducing material wastage and improving cycle times.
These systems maintain the plastic material in a molten state throughout the injection molding process, enabling more efficient and consistent filling of multiple cavities.

In-Mold Labeling (Iml) Technology

IML technology integrates the labeling process directly into the injection molding cycle, creating labeled parts without the need for secondary operations.
This technology improves efficiency, reduces costs, and enhances the aesthetic appeal of the final product.

Multi-Cavity and Family Molds

Multi-cavity molds enable the simultaneous production of multiple identical parts in each molding cycle, increasing productivity and reducing unit costs.
Family molds allow for the production of different but related parts in a single mold, optimizing efficiency and minimizing tooling requirements.

Tooling Automation

Automation technologies, such as robotic systems for mold handling and part extraction, improve productivity, reduce labor costs, and enhance overall process efficiency.
Automated systems also contribute to safer working environments by minimizing human intervention in potentially hazardous operations.

Injection Molding Tools Maintenance

To keep injection molding tools in optimal condition, routine maintenance procedures should be established and followed diligently.


Regularly clean the mold surfaces, including cavities, cores, and cooling channels, to remove any residual plastic, dirt, or contaminants that can affect part quality or cause damage, and prevent contamination and corrosion. Cleaning can involve using specialized solvents, brushes, or ultrasonic cleaning techniques. Use appropriate cleaning agents and methods for different materials.


Apply lubricants to moving parts and guide pins to reduce friction and wear. Ensure the lubricants used are compatible with the tool materials and won’t contaminate the molded parts. Preventive maintenance practices should be followed, including scheduled lubrication, inspection of hydraulic systems, and calibration of sensors and controls.

Inspection, Repair and Refurbishment

Verify that the cooling channels are clear and functioning effectively. Avoid reducing cooling efficiency due to mineral deposits and rust can accumulate.
Periodically inspect the tool for signs of wear, damage, or deformation. This includes checking for cracks, dents, or excessive wear on the mold surfaces.
Check alignment and ensure that the mold components are correctly aligned and that the ejection system functions smoothly. Avoid defects in the molded parts due to misalignment.
Check and tighten fasteners, such as bolts and screws, as needed to maintain structural integrity.

Repairs can involve fixing minor issues, such as replacing worn-out components or repairing damaged surfaces.
Refurbishment may be necessary to modify the mold for design changes or improve performance.

Tool Storage and Handling

Tools should be stored in a clean and controlled environment to avoid exposure to moisture, dust, or extreme temperatures.
Implementing a tool storage system with proper racks or shelves helps prevent accidental damage.
When handling the tools, care should be taken to avoid dropping, mishandling, or causing impact that could result in damage.
During tool changes or maintenance, following proper procedures and using appropriate lifting equipment ensures safe handling and minimizes the risk of accidents.

Cost Considerations for Injection Molding Tools

When we produce injection molding tools, we will certainly consider the costs and hope to save in some ways, although the costs of injection molding tools is one of the higher costs in the production process.

Factors Affecting Tooling Costs

The costs of injection molding tools can vary significantly based on several factors:

    • Tool Complexity
      Complex molds with intricate part designs or multiple cavities tend to be more expensive.
    • Material Choice
      The choice of tooling material, such as steel or aluminum, affects costs. High-grade steel molds are more expensive but offer greater durability.
    • Tool Size
      Larger molds require more material and machining time, leading to higher costs.
    • Surface Finish
      High-precision molds with polished surfaces may cost more due to the additional machining and finishing steps.
    • Tolerances
      Tight tolerances and precision requirements can increase tooling costs as they demand more precise manufacturing processes.

Reducing Costs of Injection Molding Tools

Manufacturers can implement various strategies to manage and reduce tooling costs:


    • Design Optimization
      Collaborate closely with designers to simplify part geometry, reduce undercuts, and minimize the number of cavities while maintaining functionality.
    • Material Costs Saving
      Evaluate the feasibility of using less expensive tooling materials, such as aluminum, for prototypes or short production runs.
    • Standardization
      Standardize tooling components and designs where possible to reduce customization and machining costs.
    • Supplier Selection
      Choose reliable tooling suppliers with a track record of quality and cost-efficiency.
    • Maintenance
      As discussed earlier, invest in routine maintenance to extend the life of expensive tooling and avoid premature replacement costs.

Get a free quote and design analysis today.

We’ll reply to you within 6 working hours.
We respect your privacy.

+86 139 2927 4777 (WhatsApp, Wechat)