Injection molds are the key to injection molding and play a crucial role in determining the quality of products. Injection molds have been used for a long time. If maintenance work is not done well, they will be easily damaged, resulting in inability to use or excessive repair costs. This is undoubtedly a huge burden for injection molding factories.

Injection mold is the core equipment of injection molding. Its design and manufacturing quality directly determines the quality and production efficiency of the product. The manufacturing of injection molds not only involves the comprehensive application of knowledge in materials, graphics, processes, etc., but is also one of the prerequisites and core of the production of plastic products.

The precision of the injection mold has a big effect on the look, size, and internal structure of the product. So, the integrity of the injection mold is one of the keys to making sure the stable molding quality of plastic products. By controlling the design and manufacturing precision of injection molds, and also maintaining and maintaining injection molds, you can effectively improve product quality and production efficiency.

This article will deeply explore the various reasons why injection molds might have problems, so that you can better understand how to solve problems that might happen with molds during the injection molding production process, and reduce your business operating costs.

Ⅰ.Basic Knowledge of Injection Molding Machine Molds

1.1Injection Mold Description

An injection mold is a tool used in factories to make plastic stuff. The way it works is that you melt plastic and squirt it into the mold. Then you let it cool and take it out of the mold. The mold is made up of a bunch of parts, like the part that squirts the plastic, the part that holds the mold together, the part that moves the mold, the part that cools the mold, and the part that takes the stuff out of the mold. People use injection molds to make all kinds of plastic stuff, like cups, plates, toys, and car parts.

1.2 The Role of Mold in the Injection Molding Process

1. Selection of Injection Molding Machine

Because of the limitations of the injection molding machine and the mold, there is a certain range of mold specifications that can be installed on a type of injection molding machine. That is to say, when the mold is made, the corresponding minimum machine has been determined. This ensures that the injection molding company has matching injection molding machines. Otherwise, it is possible to increase the model of the injection molding machine, which will inevitably cause a waste of machines.

2. Product Quality

Molds are responsible for at least 70% of the factors that affect product quality. For high-precision injection molding machines, molds have an even greater impact. When it comes to the appearance of a product, the texture of the surface depends on the texture effect of the mold. The smooth and mirror-like surfaces depend on the quality of the mold cavity surface polishing. For the non-appearance surface of the product, the quality of the mold surface is directly reflected in the roughness of the product surface. In terms of product size, in addition to the impact of product shrinkage and injection molding process, the most direct impact is the dimensional accuracy of the mold. The higher the dimensional accuracy of the mold, the higher the dimensional accuracy of the product.

3. Molding Cycle

When it comes to mold design, where you put the gate, how you lay out the waterways, and so on, will all affect the molding cycle of your injection molding production. A shorter molding cycle means you can make more parts in the same amount of time, which means you can make more parts with the same injection molding machine, which means you can make more parts without buying more injection molding machines, which means you can make more parts without spending more money.

4. Raw Materials – Production Costs (Waste)

The design of the mold runner system will affect the amount of waste generated by injection molding. This waste actually increases production costs.

5. Production Automation Level

When designing the mold, you need to think about how to make it easy to eject, without any post-processing, and can be produced stably without any quality risks. If the mold cannot meet these requirements, you have to have someone to watch it during production, which will increase labor costs and make the quality of the product unstable.

6. Post-Processing Work

If the mold design is reasonable and the product meets the requirements, there is no need for post-processing, such as flash trimming, gate trimming, orthopedics, full inspection, etc.

7. Increase Productivity

Using injection molds can really help you speed up production. With automated injection mold equipment, you can automate the whole process, which means you can cut down on labor costs and time, and increase your production efficiency.

8. Ensure Product Quality

When making injection molds, you can control the temperature, pressure, speed, and other production parameters of the plastic. This makes the product the right size, smooth, and good quality.

9. Reduce Manufacturing Cost

Using injection molds can help you save money. Compared to other ways of making things, injection molds can make a lot of things at once. This means you don’t have to pay as much for people to work on it, or for the time they spend working on it, or for the stuff you use to make it.

10. Wide Range of Applications

Injection molds are widely used in various industries, not just for plastic products, but also for metal products. You can make all kinds of products, like car parts, medical equipment, electronics, and everyday things.

11. Energy Saving

Using injection molds to make products is more energy-saving and environmentally friendly than traditional production methods. There is no environmental pollution such as waste gas and waste water during the production process of injection molds. At the same time, the production method of injection molds also reduces the waste of waste and energy.

1.3 Common Injection Mold Types

Injection molds can be divided into single-plate molds, composite molds, and multi-cavity molds based on their scope of use and production efficiency. Among them, multi-cavity molds can produce multiple plastic products at the same time under the same mold size and machine unit pressure, achieving multiple times of production efficiency, high efficiency, and energy saving, so they are widely used.

1.4 Injection Mold Manufacturing Process

The manufacturing process of injection molds mainly includes mold design, processing, assembly, mold trial, mold repair and other links. Mold design is the first step in injection mold manufacturing. It analyzes and determines the molding process, mold materials, and model structure. Next is the processing step, which mainly involves milling, drilling, milling, wire cutting, laser cutting and other processes of mold parts. Next comes mold assembly and mold trial to test the molding effect of the plastic products, and further improve and modify the mold based on the results. The entire injection mold manufacturing process requires continuous optimization of processes and technologies to ensure the quality and performance of the mold.

Ⅱ. Common Causes of Mold Damage

2.1 Reasons Why Injection Molds are Damaged During Work

1. If you choose the wrong parts for your injection mold, they might get all messed up after a while.

2. When you put parts in and take them out of your injection mold, don’t hit them with a hammer. You’ll mess them up.

3. If the angle of the cone in your mold is too big, the plastic will have a hard time getting through. That might make the support ribs on the cone break.

4. The outside of your mold and the inside of your mold are too soft. That’s why they’re all scratched up and your plastic parts look like crap.

5. If you make a mistake while adjusting the mold, you might break the mold adjustment screws, warp the die or the sizing sleeve, and then you can’t use them.

2.2 Frequent Damage to the Injection Mold Tilt-Top Car

1. Material Issues

The choice of materials for the injection mold tilt-top car directly affects its performance and service life. Some cheap and inferior materials can easily cause problems such as deformation and cracking of the tilt-top car, and accelerate the aging and damage of the mold.

2. Structural Issues

Another reason for damage is the poor design of the injection mold tilt-top car. If the design of the tilt-top car is poor, it will be subjected to excessive stress during injection molding production, which will cause damage.

3. Create Problems

If the manufacturing process and technology are not up to standard, it will cause damage to the injection mold tilt-top truck during use. For example, problems such as insufficient processing accuracy, improper tightness, and non-compliant dimensions will affect the overall quality and stability of the mold.

4. Usage Issues

Tilt-top trucks for injection molding are also prone to damage during use. If not properly installed, maintained, and used, they can easily damage the tilt-top truck.

2.3 Reasons Why Molds are Prone to Failure and Scrapping

1. Plastic Deformation Failure

Mostly because the mold material is not strong enough, or the heat treatment process is not done properly, so that the steel does not achieve the best strength and toughness; or the mold is not used properly, causing local overload; or the hot working mold is softened at high temperature, causing the mold to fail due to thermoplastic deformation. Plastic deformation failure can cause the mold to deform, which ultimately affects the quality of the forging.

2. Mold Wear and Failure

The main reason for the wear and failure of the mold is the friction between the mold and the blank. However, the specific form and wear process of wear are related to many factors; the pressure, temperature, billet deformation speed and lubrication conditions of the mold during the working process, etc. For hot work molds, because the cavity surface is softened by high temperature and the wear resistance decreases, and the oxide scale itself also acts as an abrasive, the wear process is more complicated. The wear and failure of the mold mainly leads to the wear of the forging die and affects the accuracy of the forging.

3. Mold Fatigue Failure

The main reasons for the fatigue failure of the mold are stress concentration and cyclic loading. Although the load on the mold is sometimes much lower than its yield strength, due to the local stress concentration, microcracks will still be generated at the stress concentration point under the low load. The mold usually works in a state of high strength and low plasticity. Once microcracks are generated, they can easily expand and eventually lead to fatigue fracture under the cyclic load of the mold.

4. Thermal and Cold Fatigue Failure of Mold

For hot-working molds, the surface temperature of the mold often rises to the range of 600~900°C due to the interaction with the hot blank during operation. In order not to reduce the strength of the mold, it is necessary to spray coolant on the demoulded mold to cool it down. Repeatedly like this, the mold surface repeatedly undergoes a process of rapid cooling and rapid heating, which accumulates considerable cyclic thermal stress on the surface of the mold. This stress is eventually released in the form of thermal fatigue, forming thermal fatigue cracks. As for high-temperature oxidation, coolant corrosion, and friction between the mold and the high-temperature billet, they accelerate the process of thermal fatigue.

5. Failure Under the Influence of Comprehensive Factors

Because molds are so complicated, they can get damaged in a lot of different ways all at once. When that happens, the different kinds of damage can make each other worse and make the mold break faster.

2.4 What Factors Affect the Service Life of Injection Molds?

1. The Content of Inclusions Increases

Steel inclusions are the cause of cracks in the tool and die. Specifically, inclusions like brittle oxides and silicates don’t deform plastically during hot processing, so they break brittlely and form microcracks. These cracks then cause the mold to crack during subsequent heat treatment.

2. Failure Caused by Uneven Distribution of Carbides

Cr12, Cr12MoV, Cr12Mo1V1, and other Lebbur-type mold steels have a lot of eutectic carbides. When the forging ratio is small or the pouring temperature is not controlled well, it is easy for the steel to segregate into belt-like or network-like carbides, which will cause the mold parts to crack during quenching. The cracks are usually along the belt or network carbide, or the internal cracks will get bigger during use and cause failure.

3. Failure Caused by Poor Forging Quality

If you don’t heat the steel properly before you start forging, or if you don’t forge it right, you can end up with all kinds of problems. You can overheat it and burn it. You can get surface cracks. You can get internal cracks. You can get corner cracks. If you’re working with high-carbon or high-chromium ledeburite steels, they don’t conduct heat very well. If you heat them up too fast and don’t let them soak long enough, you can get a temperature differential between the outside and the inside of the billet. That can cause internal cracks.

4. Poor Surface Quality

If the surface of the alloy mold steel is severely decarburized, there will still be a residual decarburization layer after machining. In the final heat treatment of the mold, obvious stress will be caused due to the different structures of the inner and outer layers, which will lead to quenching cracks in the mold; on the other hand, the hardness of the surface layer of the mold after quenching is low, and the cross-section hardness distribution is uneven, which reduces the service life of the mold.

5. Failure Caused by Improper Heat Treatment Process

Heat treatment is a big deal for molds. If you quench them too hot, you’ll get big grains, which makes the mold less tough, less able to take a hit, and more likely to crack. If you quench them too cold, they won’t get hard enough, and they won’t wear as well, so they won’t last as long. If you temper them too hot or too long, they’ll get soft, and they’ll change size, so they won’t be as accurate, and they won’t last as long.

6. Failure Caused by Improper Use and Maintenance

When you use a mold, if you hit it too hard, overload it, overheat it, or use it improperly, it will crack, wear, deform, and damage the mold, which will affect the life of the mold. In addition, maintaining the mold is also very important. If you don’t clean, lubricate, and rust-proof the mold in time during use, it will cause problems such as corrosion and increased wear on the surface of the mold, which will shorten the life of the mold.

In summary, there are many factors that affect the life of the injection mold, including the content of inclusions, the distribution of carbides, the quality of forging, the quality of the surface, and the heat treatment process. Therefore, in order to extend the life of the mold, it is necessary to improve the manufacturing quality, use, and maintenance level of the mold from multiple aspects, so as to ensure the stability and reliability of the mold.

Ⅲ. Conclusion

Injection molds are super important in the mold system. Their quality decides the quality of molded plastic products. As the use time increases, injection molds are prone to failure. About half of the failure problems are mainly because of changes in the surface roughness of the injection mold. As the use time increases, the surface roughness of the injection mold gradually increases. If the mold surface roughness is too high, it will not only reduce the accuracy of molded plastic products, but also affect the durability of the mold, directly leading to a shortened service life of the mold.

Maintaining and caring for injection molds is an important way to keep them running smoothly and make them last longer. By cleaning and caring for them regularly, and by greasing and maintaining them, we can make sure they’re clean, smooth, and accurate, and we can make our production faster and our products better. Also, we need to know and remember some important things about maintaining injection molds, like controlling temperature, avoiding uneven cooling, not using them too much, and caring for them regularly.