The hottest induction heating injection molding

2022-08-22
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Induction heating injection molding

induction mold heating is a deformation of mold dynamic temperature control. This makes it possible to generate a large temperature gradient in a small area of the mold in an extremely short time. This can significantly reduce the cooling time

The basic idea of induction heating in injection molding combines several advantages, especially with the traditional temperature control system. For example, heat is not transferred by conduction, but is accurately transferred to the designated area of the mold surface in a non-contact manner, and its adjacent area is only slightly heated. Therefore, a high temperature gradient can be generated on the cavity wall in a short time

if the installation position of the inductor is appropriate, the temperature near the surface of the mold cavity can also reach the required value. The advantage of surface effect is that only much less heat energy is transferred to the mold. In the fluid system, the heat channel transfers heat along the cavity wall. As a result, most parts of the mold that do not need to be heated are also heated. If the heat transferred to the mold can be quickly dissipated, induction heating can only slightly extend the processing cycle

arrangement of two inductors

in principle, there are different ways of induction heating for injection molding. In this project, researchers used two kinds of sensor arrangement:

an external sensor

the inductor is integrated into the injection mold

the former deformation provides the greatest degree of freedom, because there are fewer factors to consider when unloading in mold design. Different from the second deformation, this deformation does not need to improve the mold, because it is equipped with a handle unit to move the inductor into the open mold and position it in front of the heated mold cavity surface

integrating the inductor into the injection mold is a great challenge. The designer must make design measurements to ensure that the inductor and its necessary connecting units (circuits and waterways) can be integrated into the mold. At the same time, ensure that the corresponding areas in the mold can be selectively heated, and avoid other areas that do not need to be heated

in addition to investigating the feasibility of induction heating of injection molding and formulating the corresponding specific scheme, the project team also investigated some other problems, such as, what is the best temperature measurement system? How do different temperature control systems affect the thermal balance of mold industrialization

trial mold test

at the beginning of the project, the goal of the project participants was to integrate the inductor into the mold. This requires that the sensor can work reliably for a long time, and can be inserted into the mold in the simplest way possible. In the next work, an experimental mold is designed and processed, in order to obtain the preliminary experimental results in the real injection molding process on the injection molding machine with the necessary auxiliary equipment

in the experiment, researchers found that it was more important to pay attention to the measurement of temperature than initially thought. Researchers tested and evaluated different measurement systems based on whether integrated or external sensors were used to heat the mold. In this case, the control of mold temperature is more important than that of standard injection molding, so different temperature control systems are introduced into the trial mold, and their effects on mold thermal balance, cycle time and component quality are studied

in the temperature curve obtained from the test mold running for a long time (as shown in Figure 1), the induced heat on the surface of the red curve begins to produce. The peak represents the rise of temperature during induction heating. From the starting temperature of 80 ℃, the temperature increased by about 12 ℃. Temperature fluctuations can be explained by other ways of heat transfer during induction heating, which is generated by a low-power temperature control system connected to the mold. This means that the heat transferred in cannot be removed from the mold within the available time range. This brief thermal fluctuation disappeared after about 15 minutes (as shown by the light brown curve in Figure 1). It is worth noting that the curve in the figure does not represent the temperature change of the cavity wall. According to the results measured in the thermal stable state, the temperature of the mold surface reaches the maximum value of 150 ℃ when heated for 2 seconds

the purpose of further optimization process is to avoid the above temperature fluctuation process, so that the temperature of the mold can reach 80 ℃ at the end of a cycle in an ideal state. Figure 2 shows an optimized temperature control system (light brown and black curves) compared with the traditional temperature control method (red curve). The red curve here represents the temperature stability of the mold. That means that the initial mold temperature is 80 ℃ (see Figure 1)

the light brown curve shows that when the same peak temperature is used, the optimized system can reach the starting temperature about 2 seconds earlier. It should be noted here that when the mold temperature starts from a low level, a large amount of heat is transferred to the mold to ensure that the mold temperature can reach the same temperature value to the greatest extent. On the other hand, the black curve means that it has roughly the same heat transferred into the mold as the red curve. The result is that the peak temperature is low at 80 ℃ and about 92 ℃. It can be seen from the curve that the heat in the mold decreases much faster

by optimizing the temperature control system, we can achieve two basic goals - avoiding temperature fluctuations and reducing cycle time. In specific cases, the scope of application of these results must be verified

more heat demand

as mentioned above, the main advantage of using external sensors is that there is no need to modify the mold. However, compared with the method of integrating sensors into the mold, this arrangement requires more complex temperature measurement and different temperature control. Because the temperature of the mold surface may drop at the beginning of the clamping and injection stages, the mold temperature should be heated above the actual required temperature during the heating stage. The mold cavity temperature protective cover indicates through the guide wheel curve (as shown in Figure 3) that the mold temperature begins to drop immediately after the heating phase. Depending on the process used to heat the mold surface, the cooling process between 60 and 100 ℃ can be observed within two seconds after the heating phase is over, and how much plastic is burned and buried

during the experiment, when the mold temperature exceeds the set upper limit temperature, we can observe the change of the mold surface, which is also the need of temperature control. It should be necessary to improve the level of mold engineering

avoiding weld lines and repeated microstructures

several studies have focused on avoiding visible weld lines on the surface of produced parts, and these repeatable phenomena have been studied by X-ray phase photos of different surfaces. For example, compared with the traditional temperature control system, the mold temperature of the mold processed by EDM increases mainly with the increase of the induced heat, and the surface of the production parts is smoother. The structure of the produced parts with higher reproduction accuracy is also the embodiment of the previous results. In some cases, the mold surface can be accurately processed repeatedly (even 100% accuracy). Because the mold does not need to be heated and cooled as a whole like the traditional dynamic temperature processing, it can even get products with good repeatability in microstructure and shorten the production cycle

the picture at the title shows a flat plate with many openings and double gates, which will lead to a large number of fusion joints. The picture shows that there are flow marks in the form of dents on the surface of the parts with high smoothness (as shown in Figure 4). If the induction mold heating technology is adopted, there is no visible welding dent on the surface of the part (as shown in Figure 5). Although the traditional temperature control system is adopted here, and the produced parts have higher surface quality, the production cycle is also equivalent to the standard process

summary and outlook

the induction heating of injection molding takes into account the consideration of product quality and economy. It is used in occasions where high mold cavity temperature is required to improve the quality of parts or applied to the following manufacturing processes:

avoid surface defects (fusion joints)

improve the accuracy of repeatability (microstructure, optical components)

it is convenient for the production of thin-walled parts and micro injection molding

reduce the stress in the area close to the surface of the part

dilute electroplated coating

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