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Injection molds: The Cornerstone of Precision Manufacturing and New Trends in Industry Development

• 2025-07-08

Injection molds: The Cornerstone of Precision Manufacturing and New Trends in Industry Development

In the modern industrial production system, injection molds play a crucial role and are the core support for the large-scale and high-quality production of plastic products. From plastic tableware and mobile phone casings in daily life to complex interior parts and precision optical devices in the automotive field, behind almost everywhere plastic products, the precise shaping of injection molds is indispensable. This article will delve deeply into the principles, structures, manufacturing processes of injection molds, as well as their applications in various industries and future development trends, comprehensively showcasing the unique charm and value of this "industrial mother mold ".

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

I. Basic Principles and Structures of Injection Molds

The principle of injection molding

Injection molding is a complex physicochemical process that transforms plastic particles into molded products. Firstly, in the barrel of the injection molding machine, plastic particles gradually melt into a fluid with good fluidity under the heating effect of the heater and the shearing effect of the screw. Subsequently, the injection molding machine rapidly injects the melt into the closed mold cavity under high pressure. Inside the cavity, the melt comes into contact with the low-temperature mold, rapidly cools and solidifies, replicating the precise shape of the cavity. After the product is fully set, the mold is opened and the product is ejected through the demolding mechanism, completing one injection molding cycle. This process is like a precise "material reshaping magic trick". The precise control of parameters such as temperature, pressure and time determines the quality of the final product.

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

Ii. Manufacturing Process of Injection Molds

(1) Mold Design: The starting point of precise planning

Mold design is the "soul link" in injection mold manufacturing, directly determining the performance of the mold and the quality of the product. Designers need to have a thorough understanding of the usage requirements, appearance standards, dimensional accuracy, etc. of the products, and use professional mold design software (such as UG, Pro/E, AutoCAD, etc.) for 3D modeling and scheme planning. During the design process, the fluidity and shrinkage rate of plastic materials should be comprehensively considered. The gating system and demolding mechanism should be rationally laid out, and the cooling water circuit of the mold should be optimized (to ensure uniform mold temperature, improve the quality of product molding and production efficiency). For instance, for crystalline plastics (such as polyethylene and polypropylene), it is necessary to precisely calculate the shrinkage rate and reserve shrinkage space during mold design. For thin-walled and complex products, it is necessary to simulate the flow state of the melt in the cavity, adjust the gate position and runner size, and avoid defects such as short shot and trapped gas.

(2) Mold material selection: Balance between Performance and Cost

The selection of mold materials is related to the service life, forming accuracy and manufacturing cost of the mold. Commonly used die steels include pre-hardened steels (such as P20, 718), hot work die steels (such as H13), cold work die steels (such as Cr12MoV), etc. Pre-hardened steel already has a certain hardness when leaving the factory and can be directly used for mold processing, saving subsequent heat treatment time. It is suitable for molds with small batch sizes and moderate precision requirements. Hot work die steel features excellent high-temperature strength and thermal fatigue resistance, capable of withstanding the repeated heating and cooling of the mold during the injection molding process. It is often used in die-casting molds and high-performance injection molds. Cold working die steel features high hardness and excellent wear resistance, making it suitable for manufacturing die parts with extremely high wear resistance requirements (such as cores and cavity inserts). In addition, for some molds with special requirements, non-ferrous metal materials such as copper alloys (used in the cooling water channels of the molds to enhance cooling efficiency) and aluminum alloys (to reduce the weight of the molds, suitable for large molds or situations where lightweight is required) are also adopted. When choosing materials, it is necessary to take into account factors such as the application scenarios of the mold, the production batch of the products, and the precision requirements, and find the best balance point between performance and cost.

(3) Mold Processing: The Game between Precision and Efficiency

1. Numerical control machining

CNC milling, CNC turning, CNC electrical discharge machining (EDM), CNC wire cutting (WEDM), etc. are the core methods of mold processing. CNC milling can achieve high-precision processing of complex curved surfaces and three-dimensional contours of molds. Combined with high-speed milling technology, it can significantly improve processing efficiency and surface quality. CNC turning is mainly used for processing rotary parts of molds (such as guide pins, gate sleeves, etc.). CNC electrical discharge machining utilizes pulse discharge between the electrode and the workpiece to erode metal materials. It can process deep cavities, narrow slits, complex-shaped cavities and cores in molds, and is particularly suitable for processing hard materials. CNC wire cutting processing cuts out the high-precision contour of mold parts through the reciprocating motion of electrode wires, and is often used for processing inserts of blanking dies and injection molds, etc. In mold processing, the precise application of numerical control machining technology can transform the three-dimensional models on the design drawings into actual mold parts, achieving processing accuracy at the micrometer or even nanometer level.

2. Surface treatment of molds

To enhance the wear resistance, demolding performance and corrosion resistance of molds, surface treatment is usually carried out after mold processing is completed. Common surface treatment processes include nitriding treatment (enhancing the hardness and wear resistance of the mold surface, forming a dense nitrided layer, and improving the mold's anti-sticking ability), hard chromium plating (plating a layer of hard chromium on the mold surface to make it smoother and more wear-resistant, facilitating demolding of products, and simultaneously improving the mold's corrosion resistance), and PVD coating (physical vapor deposition coating) Such as TiN, TiAlN, etc., which feature high hardness and low friction coefficient, can effectively extend the service life of molds and improve the surface quality of products. Different surface treatment processes are tailored to different mold requirements. For instance, when injection molding PVC plastic products, as corrosive gases are released during the PVC processing, chromium plating of the mold can effectively resist corrosion. For molds with high wear resistance requirements, PVD coating is a better choice.

(4) Mold assembly and debugging: Integration from parts to the whole

Mold assembly is the process of assembling processed mold parts into a complete mold in accordance with design requirements, which demands that assembly workers possess exquisite skills and rich experience. During the assembly process, the installation accuracy of each part must be strictly controlled to ensure that the fit clearance between the guide post and the guide sleeve, as well as the fit accuracy between the cavity and the core, comply with the design standards. After the mold assembly is completed, it enters the debugging stage. Through the trial mold (conducting actual injection molding tests on the injection molding machine), the molding quality of the product is observed, such as dimensional accuracy, surface quality, and demolding conditions, etc. Based on the results of the mold trial, adjustments are made to the mold, which may involve modifying the gate size, optimizing the cooling waterway, and adjusting the demolding mechanism, etc. Only when qualified products are produced can the mold be considered to have been officially manufactured. This process often requires repeated iterations and continuous optimization, and it is a key link to ensure the performance of the mold and the quality of the products.

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Iii. Applications of Injection Molds in Various Industries

(1) Automotive industry: The demand for lightweighting and precision

In the field of automotive manufacturing, injection molds play a crucial role in facilitating the lightweighting of automobiles and the precise production of components. Automobile interior parts (such as instrument panels, door interior panels, seat guards, etc.) extensively employ injection molding technology. Through molds, complex-shaped and diverse surface textured interior parts can be manufactured, enhancing the comfort and aesthetic appeal of the vehicle. Meanwhile, plastic parts around the car engine (such as intake manifolds, oil pan guards, etc.) can be integrally formed with the help of high-precision injection molds to achieve complex structures, reducing the weight of the car and improving fuel economy. In the field of new energy vehicles, the plastic casings of battery packs and the insulating components of motors also rely on injection molds for precise manufacturing to meet the requirements of electric vehicles for safety, lightweight and high performance. For instance, in the mold of automotive intake manifolds, it is necessary to precisely control the flow and cooling of the melt to ensure that the airways of the manifold are smooth and the dimensions are accurate, thereby enhancing the intake efficiency and power performance of the engine.

(2) Electronic Information Industry: The pursuit of miniaturization and high quality

Electronic information products are updated and replaced rapidly, and there are strict requirements for the miniaturization, high precision and high quality of injection molds. The dimensional accuracy requirements for the shells of mobile phones and tablet computers reach 0.01mm or even higher. The molds need to have extremely high processing accuracy and demolding reliability to ensure the consistency of the appearance and assembly accuracy of the shells. Electronic connector molds are the "precision representatives" among injection molds. The minute structures such as pins and sockets of connectors need to be precisely formed through molds. Even the slightest deviation can lead to poor contact of the connectors and affect the signal transmission of electronic devices. In addition, the plastic components of smart wearable devices (such as smartwatches and wireless headphones) are small in size and complex in shape, posing a huge challenge to the miniaturization design and manufacturing technology of molds, and driving the development of injection molds towards greater precision and smaller size.

(3) Medical Device Industry: Ensuring Safety and Compliance

Medical devices have extremely high requirements for product quality and safety, and injection molds shoulder a special mission in the manufacturing of medical devices. Disposable medical devices such as syringes, infusion sets and medical catheters must have molds that strictly follow medical-grade materials and production standards to ensure that the formed products are non-toxic, odorless and have good biocompatibility. When manufacturing high-precision medical testing equipment parts (such as sample cups for blood analyzers and reaction cups for biochemical analyzers), molds must ensure the dimensional accuracy and chemical stability of the products to avoid deviations in testing results due to mold issues. Meanwhile, with the innovative development of medical devices, such as the micro-catheter molds for minimally invasive interventional medical devices and the supporting molds for 3D printed customized medical devices, the application boundaries of injection molds in the medical field are constantly expanding, and higher requirements are being put forward for the personalized design and customized manufacturing capabilities of molds.

(4) Daily Necessities Industry: Support for diversified and efficient production

The consumption of daily necessities is large and the varieties are diverse. Injection molds are the key to achieving large-scale and efficient production of them. From plastic tableware and toothbrush handles to plastic storage boxes and children's toys, injection molds can quickly replicate daily necessities of various shapes and sizes. In the production of daily necessities, the cost control and production efficiency of molds are particularly important. The wide application of multi-cavity molds (such as disposable plastic cup molds, which can be set with dozens or even hundreds of cavities) has significantly increased the output per unit time and reduced product costs. Meanwhile, to meet consumers' diverse demands for the appearance and functionality of daily necessities, mold design is constantly innovating. For instance, plastic stationery molds with special textures and color combinations can produce personalized stationery products, enhancing the market competitiveness of the products.

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4. Conclusion

Injection molds, as the "cornerstone" of industrial production, support the development and innovation of numerous industries, ranging from microscopic electronic components to macroscopic automotive parts. Its manufacturing process covers multiple precise links such as design, materials, processing and assembly, and demonstrates unique value in applications across various industries. Facing the future, with the evolution of the trends of intelligence, greenness and innovation, the injection mold industry will constantly break through technological boundaries, inject new impetus into the high-quality production of plastic products and the upgrading and transformation of industrial manufacturing, continuously shape the infinite possibilities of the "molding world", and promote human production and life to move towards a more precise, efficient and environmentally friendly direction.