There are many injection mold types, from simple single-cavity molds to complex multi-shot molds, and each types of injection mold has distinct advantages depending on production requirements and part specifications.
Generally, there are 8 different types of injection mold, which can be classifed as following.
1. Numbers of Cavities
- Single Cavity Mold
- Multi Cavity Mold
- Family Cavity Mold
2. Feed System
- Hot Runner Mold
- Cold Runner Mold
3. Mold Opening and Ejection System
- Two-Plate Mold
- Three-Plate Mold
What Is an Injection Mold?
Injection molding is a manufacturing process that involves injecting molten material into a pre-designed mold to create specific shapes and components. The mold, often made of high-grade steel or aluminum, contains the exact shape of the part to be created. Once injected, the molten material fills the cavity of the mold, cools down, and solidifies into the desired shape. After cooling, the mold is opened, and the part is ejected. The injection mold determines both the quality and functionality of the final piece.
Molds serve as the framework that shapes the material into the final product. The role of the mold is integral to ensuring the consistency, accuracy, and efficiency of the molding process.
Molds are made in various types depending on the material used, the complexity of the part, and the desired outcome. Different Injection mold types are capable of handling different materials, including thermoplastics, thermosets, elastomers, and metals. The mold type chosen will determine the part’s structural integrity, surface finish, and cycle time.
Key Components of an Injection Mold
An injection mold consists of several key components that are carefully engineered to ensure effective molding and high-quality output. These components include:
- Cavity and Core: The cavity is the hollow space within the mold that defines the exterior shape of the part. The core defines the interior features of the part. The interaction between the cavity and core is crucial in determining the overall design and functionality of the product.
- Sprue: The passage through which the molten material enters the mold. The sprue connects the injection nozzle to the mold cavity.
- Runner System: A network of channels that directs the molten material from the sprue to the cavity and core. The runner system ensures even material flow and is a critical factor in molding efficiency.
- Gate: The point where the molten material enters the mold cavity from the runner system. Gates are designed to control the flow of material into the cavity.
- Ejector System: This system ejects the molded part from the mold once it has cooled and solidified. It consists of ejector pins or plates that push the part out.
- Cooling System: Cooling channels are integrated into the mold to cool and solidify the molten material quickly. Proper cooling is essential to reduce cycle time and ensure part consistency.
What are all the components of an injection mold? Read our post Understanding Injection Molding Mold Parts and Their Roles.
Types of Injection Molds
In this section, we will explore the different injection mold types that are commonly used in the industry and discuss their advantages and applications.
Single Cavity Mold
A single-cavity mold is the simplest form of injection mold. It consists of just one cavity and one core, meaning it produces only one part per injection cycle. This type of mold is ideal for low-volume production or when producing a single, highly detailed part. Although it has a slower production rate compared to multi-cavity molds, its simplicity and lower upfront cost make it a popular choice for prototyping or niche products.
Advantages:
- Low initial tooling cost.
- Ideal for small production runs or prototyping.
- Simpler to design and manufacture.
Disadvantages:
- Slower production rates compared to multi-cavity molds.
- Not cost-efficient for high-volume production.
Multi Cavity Mold
A multi-cavity mold contains multiple identical cavities within the same mold tool. This allows for the production of several parts in one cycle, making it highly efficient for mass production. By using a multi-cavity mold, manufacturers can significantly reduce the time and cost per part in high-volume applications.
Advantages:
- Increased production efficiency.
- Reduced cycle time per part.
- More cost-effective for large production runs.
Disadvantages:
- Higher initial tooling cost.
- More complex design and manufacturing process.
Family Molds
A family mold is designed to hold multiple cavities for different parts, which may or may not be the same. These molds are useful when producing several parts that are related or used together, but require different shapes or sizes. The family mold minimizes the number of mold changes needed, making it efficient for creating multiple components in a single cycle.
Advantages:
- Reduces the need for multiple molds and tooling.
- Reduces cycle time for producing different components.
- Cost-effective for producing a variety of related parts simultaneously.
Disadvantages:
- Design complexity is higher.
- Can lead to uneven material flow if parts are of different sizes or weights.
Hot Runner Mold
A hot runner mold utilizes a heated system to maintain the temperature of the molten plastic as it flows through the runner channels. Unlike cold runner systems, which allow the material to cool as it flows through the mold, hot runner systems keep the material at an optimal temperature, which reduces waste and ensures consistent material flow.
Advantages:
- Less material waste due to the elimination of sprues and runners.
- Shorter cycle times due to efficient material flow.
- Ideal for thermoplastic materials.
Disadvantages:
- Higher initial investment costs.
- More complex design and maintenance requirements.
Cold Runner Mold
A cold runner mold relies on a simpler system, where the runner channels are not heated. As a result, the material cools in the runners before it reaches the cavities, which means the sprue and runners must be removed from the final product. Cold runner molds are more common for smaller, less complex parts or when the material is not sensitive to temperature changes.
Advantages:
- Lower initial cost compared to hot runner systems.
- Easier to maintain and repair.
- Suitable for applications where material waste is less of a concern.
Disadvantages:
- Increased material waste as runners must be discarded.
- Longer cycle times due to cooling of the material in the runners.
Read this complete guide to find out What are the Differences Between Hot Runner and Cold Runner Systems
Two-Plate Mold
A two-plate mold consists of two halves—one for the cavity and one for the core. When the mold opens, the parts are ejected. The two-plate mold is one of the most common injection mold types and is used for simpler designs where no complex ejection or parting line is necessary.
Advantages:
- Simple design and easier to manufacture.
- Lower cost compared to more complex molds.
Disadvantages:
- Limited to simpler part designs.
- It may not be suitable for high-volume production or complex parts.
Three-Plate Mold
The three-plate mold features an additional plate that separates the runners and cavities. This design allows for the production of parts that require more advanced gating systems and can be used to reduce the need for flash on the final part. The three-plate mold is suitable for complex parts that require multiple gates.
Advantages:
- Ideal for complex parts and multiple gating points.
- Reduces flash on parts, leading to a cleaner final product.
Disadvantages:
- More complex mold design and higher cost.
- Increased cycle times.
Stack Molds
Stack molds are designed to have multiple mold layers stacked on top of each other. Each layer produces a part simultaneously, which significantly increases production capacity without the need for multiple separate molds. Stack molds are used in high-volume production environments where efficiency and speed are critical.
Advantages:
- Very high production output.
- Reduces the need for multiple molds and tooling.
Disadvantages:
- Extremely high initial cost and complex design.
- Not suitable for all types of parts or materials.
Selecting the Right Injection Mold Types
Choosing the appropriate plastic injection mold types is crucial for ensuring optimal production efficiency and part quality. Whether it’s a single-cavity mold or a complex multi-shot design, each type offers distinct advantages based on various factors. A thoughtful approach to mold selection can save time and money and reduce the risk of production challenges.
Factors to Consider When Choosing Between Mold Types
When selecting the mold type, several factors must be carefully evaluated to ensure the final product meets both design and production requirements. These factors include:
- Part Design and Complexity: More intricate designs may require more advanced molds, such as multi-cavity or stack molds. Simple parts can be produced with basic two-plate molds.
- Production Volume: High-volume production demands more efficient molds like multi-cavity or stack molds, which maximize output per cycle.
- Material Compatibility: Certain materials require specific mold types for optimal flow and cooling, such as hot runner molds for thermoplastics.
- Part Tolerances and Surface Quality: For parts requiring high precision or a specific finish, multi-plate or two-shot molds may be necessary.
Matching Mold Types to Part Requirements
Each injection mold type aligns with specific part characteristics. Here’s a general breakdown of how different molds fit different part requirements:
- Single Cavity Mold: Ideal for prototyping and small production runs with simple parts.
- Multi Cavity Mold: Best for high-volume production of identical parts.
- Family Molds: Useful when producing several different but related parts in a single cycle.
- Hot Runner Molds: Efficient for thermoplastic materials requiring consistent flow.
- Cold Runner Molds: Suitable for applications where material waste is less of a concern.
Cost Considerations
Cost is one of the most significant factors in deciding between injection mold types. Although more complex molds like stack molds or multi-cavity molding come with higher upfront tooling costs, they may prove to be more cost-effective in the long run due to their increased production efficiency. On the other hand, simpler molds, such as single-cavity molds or two-plate molds, have a lower initial cost but might be less efficient for high-volume production.
When evaluating costs, consider the following:
- Tooling Costs: More intricate molds require more precise manufacturing, driving up the tooling cost.
- Cycle Time: Molds that can produce more parts per cycle will reduce per-part costs.
- Material Waste: Hot runner molds may reduce waste, saving on raw material costs.
Conclusion
The injection mold types range from simple to highly complex systems, each designed to meet specific production requirements. Whether it’s a single-cavity mold for low-volume production, a multi-cavity mold for high-efficiency manufacturing, or a family mold for creating related parts in one cycle, each mold has distinct features. Advanced molds such as hot runner systems and insert molds cater to more specialized needs, while cost-effective solutions like cold runner molds are suitable for less complex projects.
Choosing the right mold type boils down to a thorough analysis of part requirements, production volume, material selection, and cost considerations. It’s essential to align your injection mold types with the specific needs of your project to maximize efficiency and minimize costs. Consulting with experts in mold design and manufacturing, ensuring that your choice is both technically sound and financially viable.
