Industry News

Injection molds: The Cornerstone and Future Trend of Precision Manufacturing

• 2025-07-12

Injection molds: The Cornerstone and Future Trend of Precision Manufacturing

Basic understanding of injection molds

    Injection molds are the most crucial process equipment in plastic molding processing and are widely used in numerous fields such as automobiles, electronics, home appliances, and packaging. It forms the required plastic products by injecting molten plastic material into a cavity of a specific shape, and after cooling and solidification, it is like a precise "money printing machine", endowing plastic with precise shapes and functions.

    Structurally speaking, injection molds are typically composed of two major parts: the moving mold and the fixed mold. The fixed mold is installed on the fixed plate of the injection molding machine and remains stationary during the injection process. It mainly undertakes the injection of the plastic melt and the initial cavity construction during molding. The moving mold is installed on the mobile template of the injection molding machine and can perform opening and closing actions driven by the injection molding machine to complete subsequent operations such as demolding of plastic products. The two work in coordination to complete the molding cycle of plastic products.

    Inside the mold, there are multiple key systems. The gating system is responsible for introducing the plastic melt ejected from the injection molding machine nozzle into the mold cavity, ensuring uniform and rapid filling of the melt. Its design directly affects the flowability and molding quality of the plastic. The cooling system, by setting up cooling water channels inside the mold, uses the circulating cooling liquid to carry away the heat generated during the plastic molding process, accelerating the cooling and curing of plastic products. This plays a significant role in shortening the molding cycle and ensuring the dimensional accuracy of the products. The ejection system, after the plastic products are formed, pushes the products out of the moving mold through parts such as ejector pins and ejector blocks to achieve smooth demolding, which is a key link to ensure the continuity of production.

Auto Mould_Taizhou Jiefeng Mould Co.,Ltd. (jfmoulds.com)

Key points of injection mold design

Product Analysis

    Before designing injection molds, in-depth product analysis is the first step. A comprehensive analysis of the three-dimensional model or drawing of plastic products is required to understand the shape and dimensional accuracy requirements of the products. For instance, for the shells of electronic devices, the dimensional accuracy requirement is often ±0.1mm or even higher to ensure the precise assembly of each component. For some daily plastic products, the requirements for dimensional accuracy are relatively loose. At the same time, it is also crucial to clearly define the appearance requirements of the product, such as whether a high-gloss surface is needed and whether there are any special textures. The functional application of a product determines the focus of its structural design. For instance, for automotive parts, factors such as mechanical strength and weather resistance need to be taken into account, so as to enhance the structural strength of the corresponding parts in the mold design.

Material selection

    The selection of mold materials is directly related to the service life, manufacturing cost and forming quality of the mold. Commonly used mold steels include P20, 718, NAK80, etc., which have different properties. P20 has a relatively low price, good processing performance and certain wear resistance, and is suitable for injection molds with general requirements. Based on P20, 718 has better hardness and polishing performance, and is often used to manufacture molds with high requirements for surface quality. NAK80, with its outstanding mirror polishing performance and excellent machinability, is suitable for manufacturing injection molds with extremely high appearance requirements, such as optical products and high-end cosmetic packaging. In addition to steel, for some molds with special requirements, hot work die steel, beryllium copper alloy and other materials are also used.

Structural design

    1. Parting surface design: The parting surface serves as the interface between the moving and fixed molds of a mold. Its selection determines the demolding method of plastic products and the complexity of the mold structure. The parting surface should be selected as much as possible at the largest contour of the plastic product to facilitate smooth demolding. At the same time, the appearance requirements of plastic products should be taken into consideration to avoid leaving parting line marks on the appearance surface. For instance, for a plastic casing with a curved surface, the parting surface may be designed to be tangent to the curved surface to ensure the integrity of the casing surface.

    2. Gating system design: The gating system consists of the main runner, the runner, the gate and the cold material cavity. The main runner is the channel connecting the nozzle of the injection molding machine to the runner. Its size and shape affect the flow rate and pressure loss of the plastic melt. The runner evenly distributes the plastic melt from the main runner to each cavity. Its cross-sectional shape can be circular, trapezoidal, etc. The selection should be reasonable based on factors such as the type of plastic, the size of the product, and the number of cavities. The gate is the most crucial part of the gating system, controlling the speed and flow rate of the plastic melt entering the cavity. Common gate forms include side gates, point gates, and latent gates, etc. Different gate forms are suitable for different types of plastic products. For example, point gates are suitable for plastic products with high appearance requirements and small dimensions, and can automatically cut off the gate solidified material.

    3. Cooling System Design: The design objective of the cooling system is to ensure uniform cooling of plastic products while minimizing the cooling time as much as possible. The layout of the cooling water channels should be optimized according to the shape and wall thickness of the plastic products to ensure that the coolant can fully remove the heat. For plastic products with uneven wall thickness, the density of the cooling water channels can be appropriately increased or the diameter of the water channels can be enlarged at the parts with thicker walls. At the same time, attention should be paid to the distance between the cooling water channels and the mold cavity, core and other components to avoid reducing the mold strength due to being too close or affecting the cooling effect due to being too far.

Motorcycle Mould_Taizhou Jiefeng Mould Co.,Ltd. (jfmoulds.com)

The manufacturing process of injection molds

Mechanical processing

    1. CNC milling: CNC milling is one of the most commonly used processing methods in injection mold manufacturing. By using a CNC machine tool to control the movement trajectory of the cutting tool according to the pre-written program, the mold blank can be machined, and the shape and internal structure of the mold cavity, core, mold base and other components can be precisely processed. For instance, when processing complex mold cavities, the multi-axis linkage function of CNC milling can be utilized to produce various curved surfaces and irregular structures at one time, significantly enhancing processing efficiency and accuracy.

    2. Electrical Discharge Machining (EDM) : When certain parts of a mold have complex shapes and are difficult to complete directly through mechanical processing, EDM plays a significant role. It uses the high temperature generated by discharge to corrode the metal, thereby achieving the purpose of processing. When processing mold parts with fine structures, deep holes, narrow slots and other features, electrical discharge machining can achieve high-precision processing, such as processing small inserts and complex core structures in precision injection molds.

    3. Wire cutting processing: Wire cutting processing uses a moving fine metal wire (electrode wire) as the tool electrode and cuts the workpiece through pulse discharge. It is mainly used for processing various irregular holes, narrow slits and complex contour shapes of molds. It can produce parts with high precision and high surface quality, and can also process materials with very high hardness. It is often used for processing irregular holes of fixed plates, unloading plates and other parts of molds, as well as punch and die of blanking dies.

Surface treatment

    1. Nitriding treatment: Nitriding treatment involves penetrating nitrogen atoms into the surface of the mold to form a nitrided layer with high hardness, good wear resistance and strong corrosion resistance. After nitriding treatment, the surface hardness of the mold can be significantly enhanced, which can effectively extend the service life of the mold, improve its wear resistance and anti-adhesion performance, and reduce the damage to the mold surface caused by plastic products during demolding. It is suitable for all kinds of injection molds, especially those with high wear resistance requirements.

    2. Hard chromium plating treatment: Hard chromium plating involves coating a layer of hard chromium on the surface of the mold. The chromium layer features high hardness, good wear resistance, and a bright and beautiful appearance. Hard chromium plating treatment can enhance the smoothness of the mold surface, reduce the friction between plastic products and the mold surface, making plastic products easier to demold. At the same time, it can also improve the corrosion resistance of the mold and is often used in injection molds with high requirements for appearance quality and demold performance.

The application fields of injection molds

The automotive industry

    In automotive manufacturing, injection molds are widely used in the production of various interior and exterior trim parts and components. The dashboard, center console, door interior panels and other components of the car interior not only need to have a good appearance texture, but also need to meet certain mechanical strength and performance requirements such as fire resistance and environmental protection. Injection molds can produce plastic products that meet these requirements through precise design and manufacturing, while achieving large-scale production and reducing production costs. The exterior parts of automobiles, such as bumpers, lamp housings, and air intake grilles, as well as components like engine hoods and radiator frames, also extensively employ injection molding processes. Injection molds, while ensuring the dimensional accuracy and appearance quality of the products, can meet the automotive industry's demands for lightweight and high-strength components.

The electronics industry

    The trend of miniaturization and thinning of electronic devices has put forward higher requirements for the precision and complexity of injection molds. The casings of electronic products such as mobile phones, tablets and laptops not only need to have an attractive appearance, but also meet functional requirements such as heat dissipation and signal transmission. Injection molds, by adopting precise processing techniques and advanced design concepts, can produce thin-walled and high-precision shell products, while integrating multiple functions, such as directly forming heat dissipation holes, signal Windows and other structures on the shell. For the internal components of electronic devices, such as connectors, sockets, and buttons, injection molds also play a significant role. They can produce components with high dimensional accuracy and stable performance, meeting the strict requirements of the electronics industry for product reliability and consistency.

Home appliance industry

    There are a wide variety of household appliances, ranging from large ones like refrigerators, washing machines and air conditioners to small ones such as microwave ovens, rice cookers and hair dryers, all of which rely on the application of injection molds. Injection molds can produce various shapes and sizes of household appliance shells and internal components, meeting the design requirements of different household appliances. When manufacturing the shells of household appliances, injection molds can achieve a variety of appearance designs, such as high-gloss, matte, brushed and other surface effects, enhancing the appearance grade of household appliances. When manufacturing internal components, it can ensure the dimensional accuracy and assembly accuracy of the components, guaranteeing the normal operation and service life of household appliances.

The development trend of the injection mold industry

Intelligent manufacturing

    With the in-depth development of Industry 4.0 and the concept of intelligent manufacturing, the injection mold industry is also moving towards intelligent manufacturing. Intelligent manufacturing is reflected in every link of mold production. For instance, in the mold design stage, artificial intelligence (AI) technology is utilized to optimize the mold structure. By simulating and analyzing the plastic flow, temperature distribution and other conditions during the injection molding process, the mold structure parameters are automatically adjusted to enhance the rationality and success rate of mold design. In the mold manufacturing process, intelligent processing equipment and automated production lines are adopted to achieve real-time monitoring and adaptive adjustment of the processing process, thereby enhancing processing accuracy and production efficiency. By leveraging Internet of Things (iot) technology, injection molds are connected with injection molding machines, production management systems, etc., enabling remote monitoring of mold status, fault early warning, and intelligent maintenance. This enhances the utilization efficiency and reliability of molds and reduces maintenance costs.

Green and environmentally friendly

    Against the backdrop of the growing global environmental awareness, the injection mold industry is also actively responding to the requirements of green environmental protection. On the one hand, environmentally friendly mold materials and surface treatment processes are adopted to reduce environmental pollution during the production and use of molds. For instance, develop and use degradable mold materials that can naturally degrade after the molds are scrapped, reducing the generation of waste. Adopting environmentally friendly surface treatment processes such as chromium-free passivation to replace traditional chromium-containing surface treatment processes can reduce the discharge of heavy metal pollutants. On the other hand, optimize the design and manufacturing process of injection molds, increase the utilization rate of plastic materials, and reduce the generation of waste. By improving the design of the gating system, the generation of concrete at the gate can be reduced. By adopting hot runner technology, waste-free injection molding of plastic melts is achieved, reducing production costs and resource consumption.

High precision and high performance

    With the continuous improvement of the market's requirements for the quality and performance of plastic products, injection molds are also developing towards high precision and high performance. High-precision injection molds can produce plastic products with higher dimensional accuracy and better surface quality, meeting the demands of high-end fields such as optical lenses, medical equipment, and aerospace components. To achieve high precision, mold manufacturing enterprises are constantly introducing advanced processing equipment and inspection technologies, such as five-axis linkage machining centers and high-precision coordinate measuring instruments, to enhance the processing and inspection accuracy of molds. In terms of high performance, injection molds need to have higher strength, wear resistance and corrosion resistance to meet the special process requirements such as high-speed injection molding and high-temperature injection molding, while extending the service life of the molds and reducing production costs.

    Injection molds, as an important foundation of modern manufacturing, play an irreplaceable role in various fields. From basic structural understanding, rigorous design points, precise     manufacturing processes to a wide range of application fields, every link of injection molds embodies technology and wisdom. Facing the future development trends of intelligence, green environmental protection, and high precision and high performance, the injection mold industry is constantly innovating and transforming to adapt to market demands and continuously contribute to the high-quality development of the manufacturing industry. Its development prospects are broad and full of infinite possibilities.