Plastic injection mold cooling introduction and design key factor

2 weeks ago I went to the Injection Molding Exhibition in Shenzhen.  kinds of new injection molding machines, very short cycle-time moulds(64 cavity with 8 seconds cycle time), various auxiliary automatic Robot to replace expensive labor, auto-material supply system to keep feeding to injection machine, transducers monitor every microsecond of the molding process, with these new technologies support, The injection molding factory will make more and more money, is it true?

what is an injection mold

when you seat down and think carefully, can these new technologies and new processes really bring huge profits? The answer is negative. Nowadays, the injection molding industry is very common Technology, no matter how the technology is innovated, its three core parts remain the same: plastic Material, Plastic injection mold, and plastic injection molding machine.

Today lets discuss about cooling, one of factor of injection mold, before we dig deep this topic, what is injection mold cooling? What is the function of the cooling? This is common question for the newer of this industry. No worry, today we can explain step by step.

What is injection mold cooling? What is the function of the cooling?

Everyone knows that the basic process of injection molding is to use pressure to inject molten plastic into the mold cavity, and quickly cool down the product in the cavity through the mold cooling system, As the core part of the mold, the cooling system of the injection mold is very important for the entire injection molding. The cooling system takes away all the heat transferred from the high-temperature plastic to the mold as quickly as possible, so as to keep the temperature of the mold within a certain range, and cool the product quickly to obtain the best product quality.

Plastic injection mold cooling system Design

In order to improve production efficiency and ensure product quality, the design of the injection mold cooling system should follow the following principles

1.Determine the size and distance of waterline

mold temperature is closely related to the size and density of cooling channel. The larger the diameter of the cooling channel, the denser the cooling channel quantity, and the more uniform the mold temperature distribution. Generally speaking, it is common that the center distance between channel is 3 to 5 times the cooling channel diameter.

Picturer a) and b) The cooling Channel ensure uniform temperature distribution on the surface of the cavity.

Picturer c) and d) Because the distance between the Cooling Channel is too big, the temperature distribution on the surface of the cavity has a large span, ranging from 45°C to 61.66°C,  resulting in uneven shrinkage of the product.

plastic injection mold cooling time

2. The distance between the cooling Channel and the cavity surface should be reasonable

If the distance is too large, the thermal resistance will decrease, which will reduce the cooling efficiency; while the distance is too small will cause uneven surface temperature of the cavity. According to experience, the distance from the cooling water channel to the surface of the cavity should be between 1 and 2 times the diameter of the channel. For parts with constant thickness, in order to make the cooling uniform, the distance from the water channel to the surface of the cavity should be equal. , As shown in Figure 2-4, a) is better than b). For parts with varying thickness, the cooling should be strengthened at the wall thickness. Figure c) is better than d)

plastic injection mold cooling system design

3.Strengthen the cooling at the gate area

Since the melt material is injected into the cavity from the gate, the temperature near the gate is the highest. It is necessary to strengthen the cooling near the gate, use this as the cooling liquid population, and make the overall flow of cooling water and The direction of plastic melt flow tends to be the same (water and material are parallel). Figure 2-5a) shows the arrangement of the cooling water circuit with the gate at the center; Figure 2-5b) shows the arrangement of the cooling water circuit with the film gate.

plastic injection mold water cooling channel

4.Minimize the temperature difference between the outlet water and the inlet water of the mold cooling channel

Coolant has a heat absorption process in the mold, the temperature of the outlet water is higher than the temperature of the inlet water, but if the temperature difference between the two is too large, the surface temperature of the mold cavity will be uneven, which will cause uneven cooling of the plastic parts, especially for larger parts. For plastic parts, this effect is even more obvious. Therefore, in order to make the cooling rate of the whole product approximately the same, in addition to shortening the cooling circuit, the arrangement of the cooling water channels can also be reasonably arranged to effectively reduce the temperature difference between the outlet and the inlet water of the cooling pipeline. Figure 2-6a) The design of the cooling channel is not very reasonable.

plastic injection moldbase cooling design

5.The structure of the plastic part and the parameter of the material should be considered in the layout of the cooling channel

For different parts structure, the particularity of its size and shape should be considered when arranging the cooling circuit.

6. The connector of waterline should be designed on the same side of the mold

The cooling water channels are connected by hoses. In order to facilitate connection and reduce space, it is best to design them on the same side of the mold. The water pipe joint should be lower than the outer surface of the mold. This is to prevent damage to the mold handling joint and affect the sealing of the cooling water channel. At the same time, in order not to affect the workers. Operator operation, the joints are generally set on the back of the injection molding machine. The structural design of the cooling water channel must pay attention to its processing technology, be easy to manufacture, and try to use simple processing techniques such as drilling. For the built-in combined cooling water channel, attention should be paid to the sealing of the water channel to prevent the cooling water from leaking into the cavity and causing corrosion of the cavity.

Conclusion

Injection molding should be both fun and boring. The fun side comes with psyching out the process to balance everything. All this effort should come when you first run/qualify the mold. If you did your homework properly, the boring part is sitting back and watching the profits roll in.