Research of Precision Injection Control System Based on the on-Line Measurement of Polymer Melt Density

Abstract:

Based on the quality factors of the precision injection product, the control system structure of precision injection molding product and proposes the on-line measurement of melt density which controls the injection weight is analyzed in this thesis. The important of the on-line measurement of melt density is shown in this paper. Then, the approach of off-line and on-line measurement of melt density is introduced. At last, the control approach and the precision injection control principle of using the on-line measurement of melt density is discussed also.

• Periodical: Advanced Materials Research (Volumes 383-390)
• Pages: 5136-5141
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.383-390.5136
• Online since: November 2011
• Authors: Hong Xu, Da Ming Wu, Qun Xong Zhu, Ya Jun Zhang
• Keywords: Injection Weight Control, Polymer Melt Density, Precision Injection Control, Repeated Accuracy, Ultrasonic Measurement Technology

References

[14] Figure3 shows the measurement and control principle structure diagram of the precision injection molding control system. Fig. 3 Measuring and control principle of precision injection machine Figure3 demonstrates that the precision control of the temperature and the pressure can be realized with the direct measurement of the temperature and pressure sensor, also with the advanced control technology (such as the fuzzy control etc). In the existing research of the precision injection molding[15, 16], when the temperature and pressure control accuracy reached the requirements, the injection quantity of the precision control injection product is an important factor to ensure the geometry precision of precision injection product theoretically. The Injection Weight Control Method Based on the Melt Density Online Measurement. The precision injection molding process is a multi-level injection molding process, therefore, the melt density in the injection molding process is a variable parameter with the pressure and the temperature. The precision control over the quantity of injection during the precision injection molding process can be realized by the online measurement of melt density and the control over the span of each level of injection. The multi-level control quality of the injection molding process can be obtained by equation 6. (6) In order to ensure the whole precision injection molding injection weight W in the control of the deviation area, the multilevel injection molding speed is set in advance under the speed control pattern, the injection process is driven by servo-motor ball screw. Therefore, the ball screw span can be controlled by the controlling of rotational speed of servo-motor, then all levels of injection molding span in the injection process can be controlled to realize the injection weight precision control. Its control principle diagram is given in Figure4. Fig. 4 The principle diagram of precision injection molding machine injection weight control The relationship of injection speed (vi), the span (si) and the ball screw pitch (T), the rotational speed of servo motor (n) is shown below. (7) In (7), vi(cm/s) is the injection speed, T (mm) is the ball screw pitch, N (rpm) is the rotational speed of the servo-motor, si (cm) is the span of injection process. The pressure and the melt density change with the injection speed, but the temperature does not change. Therefore, when all levels injection speed (V1) is fixed, under all kinds of injection speeds, the injection span determines the injection time that can be obtained by (7). According to the real-time online measure of the melt density, the injection weight can be obtained by equation 8 separately. · · · (8) When the set weight is fixed, all levels of injection weight W1, W2… can be obtained by (8). However, the injection weight value which the injection time is not determined by (7), it is determined by the difference between the set weight in the (8) and the all preceding levels of injection weight. The injection is controlled by the difference between the melt weight measured on line and the fixed value and it stops when the two are equivalent. Conclusions Molding products of high-accuracy can be assured by improve the accuracy of injection weight of high precision injection with the data of injection weight measured on line through the application of ultra-sonic wave measurement technology to the online measurement of the melt density of the polymer density and the accurate control realized by the precise control of servo drive moves. Through the application of ultra-sonic wave measurement technology to the online measurement of the melt density of the polymer density, the injection weight of high precision injection with the data of injection weight is measured on line. Then by control the precise control of servo drive, the repeated precision of the injection are controlled very good. Refernces.

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