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Tie-Bar Elongation Based Filling-To-Packing Switchover Control and Prediction of Injection Molding Quality

1
Bachelor’s Program of Precision System Design, Feng Chia University, 100, Wenhwa Rd., Seatwen, Taichung City 40724, Taiwan
2
Department of Mechatronics Engineering, National Kaohsiung University of Science and Technology, 1 University Rd., Yanchao Dist., Kaohsiung City 824, Taiwan
*
Author to whom correspondence should be addressed.
Polymers 2019, 11(7), 1168; https://doi.org/10.3390/polym11071168
Received: 15 June 2019 / Revised: 5 July 2019 / Accepted: 7 July 2019 / Published: 9 July 2019
(This article belongs to the Special Issue Processing and Molding of Polymers)
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Abstract

Filling-to-packing switchover (also called V/P switchover) is critical for assuring injection molding quality. An improper V/P switchover setting may result in various defects of injection-molded parts, such as excessive residual stress, flash, short shot, and warpage, etc. To enhance a consistent molding quality, recent V/P switchover approaches adopt cavity pressure profiles requiring sensors embedded in mold cavities, which is invasive to mold cavities and more expensive. Instead of using cavity pressure sensors, by working with the most popular screw position switchover control, this study hereby proposes a novel approach of tuning V/P switchover timing using a tie-bar elongation profile. In this investigation, a dumbbell testing specimen mold is applied to verify the feasibility of the method proposed. The results show that the mold filling and packing stages can be observed along the tie-bar elongation profile, detected by mounting strain gauges on the tie bars. Also, the characteristics of the cavity pressure are similar to those of the tie-bar elongation profile under a proper clamping force condition. Moreover, the varying process parameter settings which include injection speed, V/P switchover point, and holding pressure, can be reflected in these profiles. By extracting their characteristics, the application of the V/P switchover is proved to be realistic. This research conducted an experiment to verify the proposed V/P switchover decision method based on the tie-bar elongation profile. The result showed that the fluctuation of the part’s weight corresponding to a slight change of the barrel’s temperature from 210 °C to 215 °C can be successfully controlled with this method. Besides, the maximum clamping force increment extracted from the tie-bar elongation profile was found to be a good indicator for online monitoring of the reground material variation. View Full-Text
Keywords: clamping force; filling-to-packing switchover; injection molding; process control; tie-bar elongation clamping force; filling-to-packing switchover; injection molding; process control; tie-bar elongation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Chen, J.-Y.; Liu, C.-Y.; Huang, M.-S. Tie-Bar Elongation Based Filling-To-Packing Switchover Control and Prediction of Injection Molding Quality. Polymers 2019, 11, 1168.

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