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Experimental Conditions. The velocity of the piston is set up constant and the melt temperature is set at 150℃.For the vibration device, eight frequency rates are also heuristically set as 0 (no vibration included), 2, 3, 4, 5, 7,9, and 19 Hz, respectively, with a nominal signal amplitude of 0.15mm.
Case of Study. First, polymer materials are melted in heaters. Then, the polymer melt is transported into the injection mold crossing the sprue of the mold in which the vibration device is located. Thus, the rheological parameters of the polymer melt can be obtained according to the in situ measurement and subsequent estimation. This estimation is made by measuring displacement and weight. The decrease in viscosity due to the induced vibration improves the filling step for the injection molding process. This improvement is directly proportional to the length R of the solidified spiral pattern as seen in Fig. 5. R is easily determined with a direct angular measurement according to Eq. (1).
Results
Table 1 displays results from one of the experiments in which eight previously set frequencies are used during the injection of the samples. Figure 6 is the graphical representation of Table 1, for the displacement, and from this curve it can be seen that close to 3Hz is the optimal excited vibration frequency because at this frequency the polymer displaces more in the injection mold, getting a maximum. On the other hand, the improvement can also be observed by weighing the injected mass as graphically shown in Fig. 7. This result exhibits a nonlineal behavior with respect to the displacement curve, but reaches its best result around 3 Hz, similar to displacement curve. The improvement effect on displacement and weight is due to the apparent reduction of viscosity after introducing vibration.
Discussion
According to the obtained results using this new method, it can be said that, conceptually, vibrating the melt with the proper amplitude and frequency, the melt assumes a momentary change of viscosity during the mold filling. This phenomenon shows the strong relation between the viscosity and the oscillating frequency. Low frequencies, ranging from 2Hz to 4 Hz, produce higher decrease in the polymer viscosity. It makes the length of the injected spiral increase 30% around 3 Hz. Table 2 summarizes the improvement of the proposed method compared with those values reported by [9, 11, 12],showing an evident advantage over other techniques in spite of the apparatus simplicity.
Conclusions
In this work, the filling step of the injection molding process is improved with the development of a new simple vibrating device, designed as a mold accessory. It is notorious that due to the induction of vibration on the injection process, the apparatus reaches better results in comparison with previously reported techniques in spite of the simplicity of the apparatus with the consequent cost reduction. Another advantage of this new method over the aforementioned is that it is not strictly necessary to modify the injection machine because it was conceived as a mold accessory. This fact makes possible to greatly reduce the apparatus complexity, and to allow its adaptation in both new and existent injection molding machines. Furthermore, the application of the proposed device is not limited to the injection molding process; it is also possible to use it in similar applications such as the extruding process.
References
1. Cardozo, D. A brief history of the filling simulation of injection molding. Journal of Mechanical Engineering Science 2009, 223,711–721.
2. Benitez-Rangel, J.P.; Dominguez-Gonzalez, A.; Herrera-Ruiz, G.; Delgado-Rosas, M. Filling process in injection mold: A review. Polymer-Plastics Technology and Engineering 2007, 46, 721–727.
3. Kumar, A.; Ghosh dastidar, P.S.; Muju, M.K. Computersimulation of transport process during injection mold-filling andoptimization of the molding conditions. Journal of MaterialsProcessing Technology 2002, 120, 438–449.