Date of Award

12-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Angstadt, David C

Committee Member

Huang , Yong

Committee Member

Mears , Laine

Abstract

Increased demand for micro-scale parts and devices is being met in many cases by micro-injection molding of polymer parts. However, part inspection is difficult due to the micro-scale dimension in the micro-injection molding process. In addition, process control also becomes challenging since the process is susceptible to slight changes in process parameters such as mold temperature, injection velocity, and packing pressure. To address these issues, a suitable process monitoring method such as cavity pressure monitoring can be employed to detect any process deviation that may cause defects in part quality. Cavity pressure has been found to be a reliable process indicator in injection molding for both part quality and process monitoring. Specifically, it has been found to provide real-time detection of part and process deviation. As such, cavity pressure measurement holds potential for monitoring part quality in micro-injection molding where direct part inspection is difficult and often costly due to part handling issues and microscopic feature sizes. The goal of this study is to determine the feasibility and robustness of using cavity pressure for process and quality monitoring of a molded hollow cylindrical cap.
Molding of the small cap was conducted using polypropylene under varying processing parameters to observe how cavity pressure responded to the different molding conditions. Initial investigation was carried out by varying different processing parameters that include injection velocity, pack pressure, and mold temperature. The investigation was followed by altering the switchover settings while keeping other parameters unchanged. The final part of the investigation involved using the Design of Experiment approach to include a broader range of processing parameters.
Although the processing window for micro-injection molding was smaller than macro-molding, the cavity pressure curves were able to capture the differences in molding conditions. Furthermore, attributes obtained from the pressure curve such as peak cavity pressure and area under curve were found to have good correlation with part weight which was used as the quality metric. In terms of defects among the parts, both peak cavity pressure and area under curve were able to detect defective parts based on the measured peak cavity pressure value and the calculated area under curve. The finding from the current investigation demonstrates significant potential for cavity pressure to be utilized as an indicator of part quality as well as a process monitoring tool for the micro-injection molding process.

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