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In-depth Analysis of Injection Molds: A Full-Process Exploration from Design to Application

• 2025-07-10

   In-depth Analysis of Injection Molds: A Full-Process Exploration from Design to Application

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

I. Overview and Industry Value of Injection Molds

    Injection molds, as the core equipment for plastic processing, play a crucial role in modern industrial production. It transforms thermoplastic or thermosetting plastics into various precision products through injection molding processes and is widely used in numerous fields such as automobiles, electronics, medical care, and daily necessities. From mobile phone casings to car bumpers, from medical device components to household items, the quality of injection molds directly determines the precision, performance and production cost of plastic products.

    In the global manufacturing landscape, the injection mold industry continues to grow. With the upgrading of consumption and the impetus of emerging technologies, the demand for high-precision and complex-structured molds is constantly rising. Meanwhile, under the concept of environmental protection, the green design and manufacturing of molds, such as the use of recyclable materials and the optimization of energy efficiency, have also become the development direction of the industry, contributing to the achievement of sustainable production goals.

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

Ii. Key Points of Injection Mold Design

(1) Product analysis and mold planning

    Before designing injection molds, it is necessary to de

eply analyze the requirements of plastic products. This includes the geometric shape of the product (such as complex curved surfaces, thin-walled structures), dimensional accuracy (tolerance requirements), and material properties (fluidity, shrinkage rate, etc.). Take the mobile phone casing as an example. It is not only necessary to consider the aesthetic appeal of the surface and the feasibility of demolding, but also to adapt to the installation accuracy of the internal electronic components and control the dimensional deviation caused by the shrinkage of the plastic.

    Based on product analysis, plan the basic structure of the mold, determine the number of cavities (single cavity or multiple cavities) and the position of the parting surface (which affects demolding and appearance). Multi-cavity molds can enha

nce production efficiency, but it is necessary to balance the filling consistency of each cavity. The selection of the parting surface should take into account both the appearance of the plastic part and the difficulty of mold processing to avoid defects such as flash.

(II) Design of the gating System

    The gating system is the channel through which the plastic melt enters the cavity, including the main runner, the runner and the gate. The main runner design needs to match the injection molding machine nozzle to ensure the smooth introduction of the melt. The cross-sectional shape (such as circular or trapezoidal) and size of the runner should be optimized to reduce the resistance to melt flow and heat loss. The common circular runner is conducive to uniform melt flow, but the processing cost is slightly higher.

    There are various types of gates, such as side gates, point gates, and hidden gates, etc. The side gate is suitable for various plastic parts and is convenient for processing and adjustment. The point gate can be automatically cut off and is suitable for products with high appearance requirements. The concealed gate is hidden inside the plastic part and does not affect the appearance, but it has high requirements for the precision of the mold. When choosing a gate, the material of the plastic part, its shape and the requirements of automated production should be comprehensively considered.

(3) Design of cooling and heating systems

    The cooling system is crucial for controlling the molding cycle and quality of plastic parts. By rationally arranging the cooling water channels (conformal cooling water channels are gradually becoming a trend, adapting to the complex shapes of plastic parts and improving the uniformity of cooling), the heat of the mold is removed, enabling the plastic parts to cool and set quickly. The spacing, diameter of the water channels and the flow rate of the coolant need to be precisely calculated to avoid warping and shrinking of the plastic parts due to uneven cooling.

    For some special plastics (such as high-temperature engineering plastics), a heating system needs to be designed to ensure good flow and molding of the plastic in the mold. The heating methods include resistance heating, hot oil circulation heating, etc. The selection should be based on the size of the mold and the characteristics of the plastic to ensure uniform temperature distribution and improve the molding quality.

(4) Design of demolding mechanism

    The demolding mechanism is responsible for pushing the formed plastic part out of the mold and must ensure that the plastic part does not deform or get damaged. Common ones include push rod demolding, push tube demolding, and release plate demolding, etc. The ejection structure of the push rod is simple and widely used, but it is prone to leaving marks on the surface of the plastic part. Push tube demolding is suitable for ring-shaped and tubular plastic parts, and the demolding force is uniform. The demolding of the release plate is friendly to thin-walled plastic parts and can avoid deformation caused by the push rod. When designing, the demolding force should be calculated, and the demolding components should be reasonably arranged to ensure synchronous movement.

Processing equipment_Taizhou Jiefeng Mould Co.,Ltd. (jfmoulds.com)

Iii. Material Selection for Injection Molds

(1) Classification and Application of Die steel

    Die steel is the main material for injection molds and is classified into cold work die steel, hot work die steel and plastic die steel according to its performance. Plastic mold steels such as P20 and 718 have excellent polishing properties, wear resistance and toughness, and are suitable for making plastic molds of general precision. For high-demand molds, such as transparent plastic part molds, steel grades with good corrosion resistance and mirror polishing performance (such as S136) should be selected to ensure the appearance quality of the plastic parts.

    Hot work die steel (such as H13) can be used in molds that require high-temperature injection molding. It features resistance to thermal fatigue and high high-temperature strength, and is widely applied in engineering plastic molds to cope with the high-temperature and high-pressure impact of plastic melts.

(2) Auxiliary applications of non-metallic materials

    In addition to die steel, some non-metallic materials are also used for die components. For instance, the mold insulation board, made of composite materials such as epoxy resin and glass fiber, can reduce heat transfer from the mold and enhance energy efficiency. Although mold release agents are not mold materials, they can assist in demolding plastic parts. New environmentally friendly mold release agents (water-based and silicone-free types) are gradually replacing traditional oil-based mold release agents, which is in line with the concept of green production.

In mold maintenance and rapid prototyping, 3D printed photosensitive resins, nylon and other materials are also applied, which can quickly manufacture mold inserts, verify models and shorten the mold development cycle.

Iv. Processing and Manufacturing Flow of Injection Molds

(1) Precision machining of mold parts

    Mold processing begins with part manufacturing, including key components such as cavities, cores, and sliders. CNC machining centers are used for milling, drilling and other operations to achieve high-precision processing of complex curved surfaces, with an accuracy of ±0.005mm. Electrical discharge machining (EDM) is used to process difficult-to-machine parts such as deep cavities and narrow slits in molds. It erodes metals through electrode discharge to form precise shapes. The electrode materials commonly used are copper or graphite, and the electrode size and discharge parameters need to be precisely designed.

    Grinding processing is used to enhance the surface roughness and dimensional accuracy of mold parts. Processes such as surface grinding and cylindrical grinding can reduce the surface roughness Ra of parts to below 0.05μm, meeting the requirements for mold assembly and plastic part forming.

(2) Mold assembly and debugging

    Mold assembly requires the combination of processed parts in accordance with design requirements to ensure the clearance and positioning accuracy of each component. The fit accuracy of guide pins and guide sleeves affects the stability of mold opening and closing. Generally, H7/h6 clearance fit is adopted. The installation of mold inserts should be firm to prevent displacement during injection molding. During the assembly process, dimensional inspection, parallelism inspection, etc. are required to ensure the accuracy of the mold.

    Debugging is a crucial step in mold manufacturing. Through mold testing, the forming condition of the plastic part is observed, and the injection molding process parameters (such as injection pressure, temperature, and time) and mold structure (such as gate size and cooling water channels) are adjusted. If flash occurs, the gap of the parting surface or the injection pressure needs to be adjusted. If the plastic part is short of material, the gate can be optimized or the melt temperature can be increased until the quality of the plastic part meets the standard.

V. Application Cases of Injection Molds in Various Industries

(1) Automotive industry: Molds for complex structural components

    Molds for automotive interior parts (such as instrument panels and door trim panels) need to achieve precise forming of multiple curved surfaces and multiple clips. A certain automotive dashboard mold adopts hot runner technology and conformal cooling water channels to enhance the efficiency of melt filling and the uniformity of cooling, ensuring that the surface of the plastic part is free of shrinkage marks and deformation, meeting the high-quality requirements of automotive interiors.

    The plastic component molds around the car engine need to withstand high-temperature and oily environments. The cavities are made of hot work die steel and combined with special coatings (such as nitriding treatment) to enhance the wear resistance and corrosion resistance of the molds, ensuring long-term stable production.

(2) Electronics Industry: High-precision small molds

    The shell molds of electronic devices such as mobile phones and computers have extremely high requirements for dimensional accuracy and appearance. The mold for the decorative ring of the mobile phone camera has a dimensional tolerance controlled within ±0.01mm. It adopts mirror-polished mold steel and point gate design to ensure that the surface of the plastic part is smooth and free of gate marks, which is suitable for the exquisite appearance of electronic devices.

    The electronic connector mold needs to form fine pin and socket structures. The cavity is processed by slow wire electrical discharge machining to ensure dimensional accuracy and surface roughness. Combined with high-speed injection molding technology, efficient production is achieved to meet the large-scale demands of the electronics industry.

(3) Medical industry: Sanitary grade molds

    The molds for syringes and infusion sets in medical devices must meet hygiene standards, and the mold materials should be non-toxic and easy to clean. The syringe piston mold is made of medical-grade plastic mold steel and has undergone strict polishing and disinfection treatment. The formed piston surface is smooth and free of burrs, ensuring the safety of medical use.

Disposable medical test kit molds focus on the consistency and precision of the cavities. The multi-cavity molds, through precise gating system design, ensure uniform filling of each kit cavity, enhance the reliability of the test results, and facilitate the efficient conduct of medical diagnosis.

Vi. Development Trends of Injection Molds

(1) Intelligence and Digitalization

    The mold design and manufacturing integrate CAD/CAM/CAE integrated technology, and optimize the mold structure and injection molding process through simulation analysis to reduce the number of mold trials. The application of Internet of Things (iot) technology in mold production monitoring enables real-time collection of data such as mold temperature, pressure, and wear, facilitating predictive maintenance and enhancing mold reliability and production efficiency.

    Artificial intelligence-assisted mold design optimizes design schemes through machine learning, automatically matches materials and process parameters, shortens the mold development cycle, and responds to personalized and customized market demands.

(II) Greening and Sustainability

    Promote the concept of green mold design, adopt recyclable and easy-to-disassemble mold structures, and facilitate the recycling and reuse of materials after mold scrapping. Optimize the mold manufacturing process, reduce the consumption of cutting fluid and energy, apply dry cutting and high-speed processing technologies, and minimize environmental impact.

    The popularization of biodegradable plastics has driven the adaptation of molds to the molding demands of such new materials. The development of targeted mold structures and processing techniques has facilitated the production of environmentally friendly plastic products, aligning with the global trend towards low-carbon development.

(3) High-end and precision

    With the development of industries such as 5G and new energy, the demand for micro, precise and complex molds is increasing. For instance, the plastic accessory molds for new energy vehicle battery modules need to form thin-walled and high-strength structures, with mold manufacturing precision reaching the micrometer level. For the molds of microelectronic components, it is necessary to achieve ultra-small size and multi-cavity precision forming, and promote the breakthrough of mold technology towards more advanced and precise directions.

Conclusion

    Injection molds, as fundamental equipment in the manufacturing industry, embody technology and wisdom in every aspect, from the ingenious design concept to the precise selection of materials, the meticulous control of processing, and the extensive expansion of applications. Driven by industry trends, intelligence, greenness and high-end will continue to lead its development, providing support for the innovative upgrading of plastic products, promoting modern industrial production to constantly reach new heights, becoming a key bridge connecting design creativity and physical products, and empowering various industries to achieve more efficient, higher-quality and more sustainable development.