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Views: 0 Author: Site Editor Publish Time: 2025-11-11 Origin: Site
| Table of Contents |
| 1. Introduction |
| 2. What is an Injection Mold? |
3. How Are Injection Molds Classified? Single-Cavity Injection Mold Multi-Cavity Injection Mold Family Mold Hot Runner Mold Cold Runner Mold 3.3 By Mold Structural Features Two-plate Injection Mold Three-plate Injection Mold
3.4 By Mold Installation Method Fixed Injection Mold Movable Injection Mold
3.5 By Injection Molding Machine Type Horizontal Injection Mold Vertical Injection Mold |
4. How to Choose the Best Injection Mold Type for Your Product? |
| 5. Conclusion |
Plastic products come in countless structural variations, and selecting the most suitable type of injection mold remains a key challenge for many engineers and procurement decision-makers. A poor choice can not only lead to low production efficiency and increased costs but also compromise the final product quality.
As a factory with 23 years of experience in injection mold design and manufacturing, Alpine Mold will systematically sort out all core classifications of injection molds in this blog. Covering key dimensions from cavity number and gating system to parting line structure, we aim to help engineers, product designers, and procurement professionals quickly establish a clear mold selection framework.
An injection mold is a precision tool used for mass production of plastic products. It can manufacture complex-shaped, dimensionally accurate plastic components in one go through the high-pressure injection molding process. This type of mold is an indispensable production equipment in modern manufacturing, widely used in the production of auto parts, electronic product casings, household appliance components, medical devices, and daily plastic products.
From a technical perspective, an injection mold is a tooling system composed of high-precision steel components that imparts specific shapes and structures to molten plastic. After manufacturing, the mold is installed on an injection molding machine. During operation, it forms cavities when closed, and molten plastic is injected into these cavities under high pressure, which then cools and solidifies to form the desired products. Despite the wide variety of plastics and diverse product shapes leading to significant structural differences in injection molds, their basic composition and working principle are consistent.
Injection molds play a pivotal role in the plastic manufacturing industry, with a common industry saying: "Seven parts mold, three parts process." This means the quality and design of the mold have a greater impact on the molding quality of the final product than the injection molding machine itself. An excellent injection mold can not only ensure product dimensional accuracy and surface quality but also significantly improve production efficiency and reduce scrap rates.
Injection molds can be classified according to various standards. Different types of injection molds have distinct characteristics in structural design, gating systems, and application scenarios. Understanding these classification methods helps engineers select the appropriate mold type based on product characteristics and production requirements, optimizing production efficiency and product quality. With over 20 years of experience in the injection mold industry, Alpine Mold has summarized the following core dimensions to systematically analyze the classification of injection molds.
Definition and Features: A mold containing only one product cavity, producing one finished product per injection cycle.
Advantages and Limitations: It has a relatively simple structure, offering cost and time efficiency in mold manufacturing with low initial investment. Debugging is more convenient during mold testing and product design verification. However, it has higher unit production costs and cannot meet the demands of large-scale mass production in terms of efficiency.
Application Scenarios: Mainly suitable for the production of large plastic parts, small-batch trial products, new product development prototypes, and high-value-added products.
Technical Case: Alpine Mold recently customized a large single-cavity injection moldfor refrigerator door frame products, with mold dimensions reaching 2.4 meters × 1.5 meters. The product not only has an extra-large overall size but also requires strict structural rigidity and dimensional accuracy. Restricted by core technical indicators such as the injection molding machine's clamping force threshold, melt filling uniformity, and overall mold stress stability, the single-cavity design becomes the optimal solution balancing molding quality and production feasibility. It effectively avoids problems such as uneven filling and stress concentration that may occur with multi-cavity layouts, ensuring product tolerance control and mass production stability.
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Definition and Features: A mold containing two or more identical product cavities, capable of producing multiple identical products simultaneously per injection cycle.
Advantages and Limitations: It boasts excellent large-scale production efficiency, significantly reducing unit product costs. However, it has a complex mold structure with high requirements for design and manufacturing precision. It also imposes higher demands on the injection volume and clamping force of the injection molding machine to ensure consistent injection quality across all cavities.
Application Scenarios: Specifically designed for large-scale production of high-volume, small standardized products (such as bottle caps, electronic connectors, etc.).
Case Sharing: To meet the high-yield demand for disposable medical products (with the customer's large annual output scale), multi-cavity injection molds become the optimal solution for matching production capacity goals. Alpine Mold initially customized a 4-cavity mold to match the customer's initial needs, and later upgraded to an 8-cavity solution as the customer's annual output continued to grow. By improving single-mold output efficiency, it accurately meets the expanding production capacity requirements.
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Definition and Features: A mold integrating multiple cavities of different shapes in one set, used for one-step molding of a complete set of interassembled or related components.
Advantages and Limitations: It enables simultaneous molding of multiple components, effectively reducing the number of mold sets, simplifying production processes and material management, improving assembly consistency, and saving mold opening costs. However, its design challenge lies in ensuring filling balance and uniform cooling across different cavities.
Application Scenarios: Widely used for products requiring complete set assembly, such as remote controls (upper cover, lower cover, battery cover), walkie-talkies (upper cover, lower cover), etc.
Case Sharing: A customer specializing in air pumps had a product consisting of seven to eight components that needed assembly. To reduce production costs, the customer proposed integrating the entire set of products into one family mold. Alpine Mold conducted an in-depth analysis of the structural characteristics and molding process compatibility of each component, and finally determined that some core components could be integrated into a single mold design. This integrated solution not only accurately met the customer's cost control needs but also simplified the subsequent assembly process and significantly improved supply chain efficiency.
The gating system is a set of channel structures in an injection mold that guides molten plastic from the injection molding machine nozzle into the mold cavity. Its function is to ensure that molten plastic fills the mold interior smoothly under appropriate pressure, speed, and temperature conditions, thereby forming the final plastic part shape. There are two main types of injection molds:
Definition and Features: It keeps the plastic in the runner in a molten state through continuous heating, producing no condensed material.
Advantages and Limitations: It has extremely high material utilization rate with almost no runner waste. It helps shorten the molding cycle, realize fully automated production, and improve product appearance quality. However, its mold manufacturing cost is significantly higher than that of cold runner systems, and it has strict requirements for temperature control precision. The color and material change process is relatively complex.
Application Scenarios: Suitable for long-term, high-volume production projects, especially in fields sensitive to material costs and requiring high product appearance and stability.
Definition and Features: The cold runner mold is a traditional form. After each injection, the plastic in the runner solidifies and is demolded together with the product.
Advantages and Limitations: It has a simple mold structure with low manufacturing and maintenance costs, and convenient and flexible color and material change operations. Its main disadvantage is the generation of runner waste (sprue), which increases material costs and subsequent processing procedures.
Application Scenarios: Cold runner molds demonstrate excellent economy and flexibility in small-batch, multi-variety production scenarios or projects sensitive to initial investment.
Comparison Dimension | Hot Runner Mold | Cold Runner Mold |
Material Utilization Rate | High (no runner waste) | Low (generates sprue waste) |
Mold Cost | High | Low |
Production Efficiency | High (shorter cycle time usually) | Lower |
Production Flexibility | Low (complex color/material change) | High (convenient color/material change) |
Suitable Batch Size | High-volume | Small-batch, multi-variety |
The parting line structure of a mold directly affects the mold opening sequence, product demolding method, and the ease of automation implementation.
Injection molds can be divided into single parting line injection molds and double parting line injection molds, which are often referred to as two-plate molds and three-plate molds.
Definition and Features: It has only one main parting line, and the product and runner can be removed with a single mold opening. This is the most widely used basic structure.
Advantages and Limitations: It has a robust and reliable structure, low manufacturing cost, low failure rate, and simple operation.
Application Scenarios: Suitable for most plastic products with side gating.
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Definition and Features: It has two parting lines. The mold first opens at the fixed mold part to remove the runner, then opens at the main parting line to eject the product.
Advantages and Limitations: It usually adopts a pinpoint gate design, which can automatically cut the gate, leaving only tiny traces on the product surface. However, its structure is more complex, leading to increased manufacturing costs and potential failure risks.
Application Scenarios: Often used for products with high appearance requirements or multi-cavity molds requiring center gating.
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The installation method reflects the integration degree and automation level of the mold with the production system.
Definition and Features: Both the moving mold and fixed mold parts of the mold are firmly fixed on the injection molding machine.
Advantages and Limitations: It has good stability and is easy to realize fully automated production, making it the standard configuration for modern industrial mass production.
Application Scenarios: Suitable for all medium and large-scale, long-term operation mass production projects.
Definition and Features: After molding, the entire mold can be moved out of the injection molding machine for manual demolding or special operations such as insert installation.
Advantages and Limitations: It has high flexibility but low production efficiency and high labor intensity.
Application Scenarios: Mainly used during mold testing or small-batch insert molding processes.
Molds need to match specific types of injection molding machines to ensure production feasibility and stability.
Definition and Features: Designed specifically for horizontal injection molding machines, the mold opens and closes horizontally.
Advantages and Limitations: It realizes automatic demolding by gravity, has extremely high stability, and is easy to integrate with manipulators for automation, making it the mainstream in the market.
Application Scenarios: Suitable for the production of most plastic products.
Definition and Features: Designed specifically for vertical injection molding machines, the mold opens and closes vertically.
Advantages and Limitations: Its biggest advantage is facilitating insert molding, providing convenient operating space for manual placement of inserts (such as metal parts, circuits).
Application Scenarios: Widely used for insert overmolding of electronic and electrical components.
In the product development and mass production process, selecting the appropriate injection mold type is a key step to ensure product quality, control manufacturing costs, and improve production efficiency. As an injection molding solution provider with 23 years of experience, Alpine Mold recommends following a systematic decision-making framework:
Product structural complexity is a core factor affecting the mold design form.
Simple-structured products: Regular injection molds with single parting lines and standard gates can be used.
Products with undercuts, deep cavities, thin walls, or snap structures: May require core-pulling mechanisms, side slides, angled ejectors, or multi-parting line designs.
Products requiring assembly of multiple parts: Family molds can be considered to ensure the consistency and assembly accuracy of matching parts.
Recommendation: Conduct DFM (Design for Manufacturability) analysis in the early stage of the project to effectively avoid rework and additional costs later.
Different production volumes determine the number of mold cavities and gating system type:
Production Scale | Optimal Mold Solution | Features |
Small-batch (< 10,000 pcs) | Single-cavity mold / Cold runner mold | Low cost, short development cycle |
Medium-batch (10,000–200,000 pcs) | Multi-cavity mold / Cold runner mold or hot runner mold | Reduced unit cost, improved efficiency |
High-batch (> 200,000 pcs) | Multi-cavity + Hot runner system | High stability, material saving, low long-term cost |
Products with high appearance requirements and color difference sensitivity: Hot runner molds are recommended to ensure uniform melt flow and high color consistency.
Products with high structural precision requirements: Need to ensure runner balance, and use valve-gated hot runners if necessary to achieve controllable flow.
Cost-sensitive products with general appearance requirements: Cold runner systems are more economical.
Total mold cost = Manufacturing cost + Maintenance cost + Unit molding costWhen selecting a mold, attention should not only be paid to the mold opening price but also to the long-term service cycle:
Hot runners have high initial costs but save materials and labor in the long run, suitable for products with large batches and long life cycles.
Cold runner molds have low initial investment but generate sprue recycling costs, suitable for small and medium-batch projects.
After sorting through the various classification standards for injection molds, we can glean a key insight that goes beyond the technology itself: mold selection is never a simple either-or choice, but a strategic decision that directly shapes a product’s trajectory. Behind variables like cavity count, runner design, and parting line structure lies the core goal—finding the most tailored balance between quality, efficiency, cost, and risk for your specific project.
Yet understanding these classification standards is just the starting point. The real challenge lies in translating these abstract criteria into tangible product applications, while anticipating how they will perform long-term in large-scale production.
This is precisely where Alpine Mold’s core value shines.
With 23 years of in-depth industry experience, we offer more than just a set of precision steel molds. We deliver decision-making logic and risk management solutions honed through thousands of successful projects. We aim to be the most reliable partner in your product manufacturing chain—helping you avoid pitfalls, boost efficiency, and protect your profits right from the start.
Turning your design into a physical product is a journey we want to share with you. If you have a product concept or drawings, feel free to connect with our senior engineering team for a truly valuable and constructive technical exchange.
