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From principle to application, understand this "shaping master" in industry

• 2025-07-16

From principle to application, understand this "shaping master" in industry

    Plastic products can be seen everywhere in life - drinking cups, mobile phone casings, car parts... Most of these plastic parts of various shapes are "transformed" by injection molds. Injection molds are like precise "shaping experts", capable of transforming ordinary plastic particles into various shapes we need. Perhaps many people haven't thought carefully about how it works. In fact, there is a lot of knowledge hidden in it. This article will explain injection molds in plain language, starting from their most basic working principles, to what to pay attention to during design, then to the new manufacturing methods available now, and the roles they play in various industries, allowing everyone to truly understand this important role in industrial production.

Car bumper mold Manufacturer in China (jfmoulds.com)

1.How does an injection mold work? What are the main components?

    The working principle of injection molds is not complicated at all. It relies entirely on the property of plastic that it "melts when heated and hardens when cooled". First, put the plastic pellets into the heating cylinder of the injection molding machine. After heating, the plastic turns into a liquid that can flow like syrup. Then, the injection molding machine uses high pressure to rapidly press these liquid plastics into the "cavity" of the mold - the cavity is the recessed part in the mold, and its shape is exactly the same as the plastic part we are going to make. After the plastic liquid fills the cavity, the cooling water pipes in the mold start to work, causing the plastic to cool down and harden rapidly. Finally, the mold is opened, and the formed plastic part is pushed out with a ejector pin. A complete process is thus completed.

What should be noted when designing injection molds? What new ideas are there now?

    Designing injection molds is not just about drawing randomly. Many practical issues need to be considered. It is necessary to ensure that the plastic parts are both practical and good-looking, while also making the molds durable and highly efficient in production.

    First of all, it is the precision and surface of the plastic parts. For instance, if the size of a mobile phone case differs by even the slightest bit, it might not fit a screen. If there are scratches or depressions on the surface, it won't be sold. Therefore, when designing, it is necessary to accurately calculate the shrinkage amount of the plastic after cooling - different plastics have different shrinkage rates. For instance, polyethylene will shrink by about 2%, and this amount should be added when designing the mold. For those with high surface requirements, the mold cavity should be made of high-quality steel and polished to an extremely smooth surface, or even chrome-plated, so that the surface of the plastic parts can be bright.

2.there are production efficiency and mold lifespan. Everyone wants to produce quickly so that the molds wear out more slowly. 

So nowadays, many molds are designed to be "multi-cavity", capable of producing several plastic parts at once. For instance, the mold for disposable spoons can produce dozens of them at a time. There is also the "hot runner" technology, which keeps the plastic in the gating system in a molten state all the time, eliminating the need to remove the solidified material head each time. This not only saves materials but also shortens the time. The material of the mold is also crucial. For molds with large production volumes, steel with high hardness and wear resistance should be used, such as Cr12 steel, which can be used for hundreds of thousands of times after heat treatment. For small-batch production, ordinary steel or even aluminum alloy might be sufficient, which can save costs.

Nowadays, the methods of designing molds are becoming increasingly advanced. It is no longer the case that experienced masters draw pictures based on their experience.

    Computer-aided design and simulation: Designers use CAD software to draw 3D diagrams, allowing them to directly see the appearance of the mold and making it convenient to modify. Even more impressive is the CAE simulation software, which can "virtually" demonstrate how the plastic liquid flows and cools before the mold is made, and identify problems in advance. For instance, if it is found after simulation that the plastic in a certain corner cannot be filled up, the position of the gate can be changed promptly. If it is found that the plastic parts will warp after cooling, the layout of the cooling water pipes can be adjusted.

    Intelligent design: Nowadays, it can even be assisted by artificial intelligence. By inputting the successful mold design data from the past into the computer, the AI can learn the patterns. When encountering new shapes of plastic parts, it can automatically recommend suitable cavity structures and gate positions. Designers only need to make slight adjustments, which greatly speeds up the design process.

    Environmental protection considerations: Nowadays, the design of molds also emphasizes "green". For instance, try to use recyclable steel as much as possible and reduce material waste during the design process. Optimize the cooling system to consume less water and electricity. Even considering that the molds can be disassembled and recycled after use, so as not to generate too much garbage.

Bumper Mould Manufacturer in China (jfmoulds.com)

3. How are injection molds made? What are some new methods?

Making a set of injection molds is like a precise "engraving" process. In the past, it relied on workers milling and grinding bit by bit. Now, with many high-tech devices, it is both fast and accurate.

The traditional manufacturing methods mainly include the following types:

Mechanical processing: Using machines such as milling machines, lathes and grinders, steel is cut into the shape of molds. For instance, milling a cavity is like digging a hole in wood with a chisel, except that the precision requirement is much higher, with an error not exceeding 0.01 millimeters. The grinding machine is responsible for smoothing the surface, making the inner wall of the cavity as smooth as a mirror.

Electrical discharge machining: When encountering particularly complex shapes, such as small holes or deep grooves on plastic parts that ordinary tools cannot reach, electrical discharge machining is used. It gradually "burns" into shape by the electric spark discharge between the electrode and the steel, just like "embroidering" on metal with high temperature.

Surface treatment: After the mold is completed, the surface of the cavity also needs to be treated, such as chrome plating. This can make the surface harder and smoother, making it less likely for plastic parts to stick to it and making the mold more durable.

Nowadays, new technologies have made mold manufacturing even more powerful:

High-speed milling: Utilizing milling cutters with extremely high rotational speeds (tens of thousands of revolutions per minute) for processing, it is both fast and precise. The smoothness that used to take half a day to achieve through grinding can now be accomplished in one high-speed milling session, greatly saving time. For instance, when making molds for mobile phone casings, high-speed milling is used to process the cavity, and the surface can be so smooth that no further polishing is needed.

Five-axis linkage machining: Ordinary machine tools can only move up, down, left, right, forward and backward (three axes). When encountering molds with many curved surfaces, such as those for car lampshades, multiple clamping is required, which is prone to errors. Five-axis machine tools can have two more rotation directions, being as flexible as a human wrist. They can process complex curved surfaces in one go with higher precision.

3D printing, also known as additive manufacturing, is a major breakthrough. In the past, making molds was about "subtraction", cutting off the excess parts of the steel. 3D printing is an "addition". By piling up metal powders layer by layer, you can create any shape you want. For instance, conformal cooling water pipes can be printed out - the shape of the water pipe fits perfectly with the inner wall of the cavity, and the cooling effect is particularly good. Moreover, 3D printing is very fast for making mold prototypes. It used to take several weeks, but now it can be done in just a few days, which is convenient for quick trial and error.

Automated production: Nowadays, many mold factories use robots and automated production lines to automatically complete the entire process of steel clamping, processing and measurement. Workers do not need to keep a close watch all the time, which not only reduces human errors but also enables 24-hour non-stop operation, greatly improving efficiency.

4. In which industries can injection molds be applied? What special functions does it have?

The application of injection molds is so extensive that almost all industries that require plastic products cannot do without them. Moreover, in different industries, their roles also have their own focuses.

In the automotive industry, there are a large number of plastic parts in cars, from the dashboard and door handles in the interior to the bumpers and lamp housings in the exterior, and even some plastic parts in the engine, all of which rely on injection molds. The requirements for plastic parts in automobiles are light, strong and heat-resistant. For instance, in the case of bumper molds, it is necessary to create complex shapes to protect pedestrians, while also ensuring that the plastic has sufficient toughness to prevent it from breaking easily upon impact. The molds and cavities of the plastic parts near the engine should be made of high-temperature resistant steel because the plastic parts have to withstand the high temperature of the engine.

Home appliance industry: refrigerators, washing machines, air conditioners, microwave ovens... The shells, inner tanks and buttons of these household appliances are mostly made by injection molding. Home appliances value appearance and cost, so molds should be capable of creating surfaces of various colors and textures. For instance, the patterns on refrigerator doors are engraved on the mold cavity. At the same time, it should be suitable for mass production. One set of molds can produce thousands of parts in a day, reducing costs.

In the electronics industry, electronic products such as mobile phones, computers and cameras have small components and high precision, which impose more stringent requirements on molds. For instance, for the mold of a mobile phone SIM card tray, the dimensional error must not exceed 0.005 millimeters; otherwise, the card tray cannot be inserted. The mold and cavity of the mobile phone case need to be polished to be as smooth as a mirror to make the phone case bright and flawless. Nowadays, electronic products are updated rapidly. Mold factories also need to be able to quickly produce new molds to keep up with the pace of product replacement.

In the medical device industry, injection molds are also used for syringes, infusion sets, medicine bottles, and the shells of some medical equipment. This industry places the greatest emphasis on "safety", so molds must be made of non-toxic and corrosion-resistant steel. During processing, they must be extremely clean to prevent any impurities from falling into the plastic. For instance, for the mold of a syringe, the inner wall of the syringe barrel must be extremely smooth; otherwise, it will scratch the blood vessels. The sealing performance should also be good and no liquid leakage is allowed.

The packaging industry: Packaging items such as beverage bottles, food boxes, and cosmetic bottles are in large quantities and come in various shapes. The molds used for packaging emphasize efficiency. For instance, the molds for the bottle caps of mineral water bottles can produce dozens or even hundreds at a time, and a batch can be made in just a few seconds. Sealing performance should also be taken into account. For instance, the threads on the beverage bottle cap and the mold must be precise to ensure they fit tightly against the bottle mouth without leakage.

5. What are the current difficulties in the injection mold industry? How will it develop in the future?

Although injection molds are widely used, this industry also has many headache-inducing problems. Nowadays, market competition is becoming increasingly fierce and customer demands are getting higher and higher: molds must have high precision and good quality, as well as be produced quickly and at a low price. The prices of raw materials such as steel and electrode materials have risen, and workers' wages are also increasing. As a result, the costs of mold factories are getting higher and higher. Moreover, environmental protection requirements have become stricter. During the production process, wastewater and waste gas cannot be discharged at will, and the treatment of these also costs money.

However, there are opportunities amid challenges. With the advancement of technology, the injection mold industry will witness these new trends in the future:

Smarter: Molds in the future might be able to "speak for themselves". Sensors are installed on the mold to monitor temperature and pressure in real time. Once any abnormality is detected, such as when the temperature in a certain area is too high and a problem may occur, it will automatically alarm and even stop the machine. When designing molds, AI is more powerful and can almost automatically complete most of the designs. Humans only need to make the final confirmation. Factories that produce molds will also become "digital factories", with the entire process from design to manufacturing managed by computers, which will be more efficient and have fewer errors.

More environmentally friendly: In addition to considering environmental protection during the design process, the production process will also be greener. For instance, by using more energy-efficient processing equipment, wastewater and waste gas can be treated more thoroughly, and more parts of the molds that are worn out can be recycled and reused. Even research will be conducted on using biodegradable plastics as mold materials to reduce the impact on the environment.

More flexible: Nowadays, consumers prefer personalized items, such as phone cases with various patterns and cups with different shapes. This requires that the molds can quickly "transform", and it is also cost-effective for small-batch production. 3D printing technology can come in handy here. A set of small-batch production molds can be made in just a few days to meet personalized demands.

More integrated: In the future, molds may not only "make parts", but also be able to complete assembly incidentally. For instance, when making molds for toys, once formed in one go, several parts of the toy are already joined together, eliminating the need for manual assembly and significantly saving time.

Going global to compete: Domestic mold technology is getting stronger and stronger. In the future, more of it will be exported abroad to compete with mold factories around the world. This requires our mold factory not only to have excellent technology but also to be good at management, capable of producing in accordance with international standards, and ensuring quality and delivery time.

6. Conclusion

Injection molds may seem insignificant, but they are the "unsung heroes" in industrial production. From the small items we use every day to the large parts in cars and planes, none of them can do without its "shaping" ability. Although its working principle is based on the simple characteristics of plastic, the design and manufacturing process conceals countless meticulous considerations and technical wisdom.

Nowadays, injection molds are evolving towards being smarter, more environmentally friendly and more flexible, constantly adapting to new market demands. Perhaps in the future, the plastic products around us will become lighter, more durable and more creative due to the advancement of mold technology. Understanding injection molds is actually about understanding the world around us that is built of plastic and the industrial wisdom that supports the operation of this world.