Injection moldings with multi-cavity mold are widely used in industry. They could increase the efficiency and decrease the cost of product. These are advantages. However, the filling processes in cavities are always not equilibrium, generating the short injection, bending, shrinking phenomena. These problems affect product quality and development process.
Main factors causing the disequilibrium of filling process are mold manufacture, assembly, or plastic problems, injection pressure control of machine. In order to overcome these problems, FCS developed an “intelligent flow balance system” with automatic calculation and adjustment of parameters for melt filling balancing in cavities, which can be applied for full series of FCS injection molding machines.
Temperature sensor is installed in each cavity to measure temperature of plastic melt at the corresponding location. When filling processes in cavities are not balance, the times to reach to desired temperature in each cavity are different as shown in Figure 2. These are called time difference.
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Figure 1 Cavity temperature and filling time difference |
Figure 2 Intelligent flow balance system |
The intelligent flow balance system will use these time differences to compute the temperature which need to compensate from mold heater machine to each cavity temperature.
Firstly, the hot-runner temperature is set 230°C as temperature of the nozzle, and the intelligent flow balance system is not activated for 10 cycles then activated with 4-cavity mold. It is obvious that, when the intelligent flow balance system is not in operation, the time difference is about 0.042s.
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Figure 3 Cover mold with four cavities |
Figure 4 100 mold cycles results of weight stability |
When the intelligent flow balance system is activated, and after 10 cycles training process, the time difference is about 0.02s, the time difference is thus reduced 50%.
After the system was verified in product weight stability, 100 molds of weight stability were then tested, in which first 50 molds were tested without activation of the intelligent flow balance system, and last 50 molds were tested using this system as shown in Figure 4.
It is obvious that, when using the intelligent flow balance system, the weight standard deviation is reduced 81.7 % and the weight average in each cavity is reduced 30.8 %. In the other words, the weight stability is improved with the intelligent flow balance system.
From industrial 4.0 overview, this case with target of energy saving and automation, the intelligent flow balance system is developed via plasticization and injection values of all electric injection molding machine to overcome the disequilibrium of filling process by compensating the temperature of hot runner.
With product quality improvement target, it can execute the unmanned product monitoring, improve the manufacture efficiency and reduce the cost.
