Abstract
Quality control is a crucial issue in the injection molding process with target of obtaining a high yield rate and reducing production cost. Consequently, effective methods for monitoring the injection conditions (e.g., pressure, velocity, and temperature) in real-time and adjusting these conditions adaptively as required to ensure a consistent part quality are essential. This study proposes a quality index based on the clamping force increment during the injection cycle, as determined by four strain gauges attached to the tie bars of the injection molding machine. Also, various quality indexes for online quality monitoring and prediction purposes based on the pressure, viscosity, and energy features extracted from the pressure profiles obtained at the load cell, nozzle, and molding cavity, respectively, are compared. The feasibility of the proposed quality indexes is investigated experimentally for various settings of the barrel temperature, back pressure, and rotational speed of the plasticizing screw. It is shown that all of the quality indexes are correlated with the injection-molded quality and hence provide a feasible basis for the realization of an on-line quality monitoring and control system. Particularly, the tie-bar elongation quality index requires no modification or invasion of the injection molding system or cavity and hence provides a particularly attractive solution for monitoring and controlling the part quality.
Highlights
Injection molding is a well-established technique for the mass production of plastic components
Even though current all-electric driven injection molding machines provide an extremely precise motion control, even very small variations in the raw material properties and/or plasticizing and injection molding conditions may result in significant variations in the molding quality
As to the present study, we further proposed an online part quality inspection method based on quality indexes, in particular, a new quality index based on the clamping force increment during the injection cycle, as determined by four strain gauges attached to the tie bars of the injection molding machine
Summary
Injection molding is a well-established technique for the mass production of plastic components. Even though current all-electric driven injection molding machines provide an extremely precise motion control, even very small variations in the raw material properties and/or plasticizing and injection molding conditions may result in significant variations in the molding quality. While they can confirm that the molded components satisfy the design criteria, in the event that they do not, they provide no clues as to why this is the case. Such methods are time-consuming and expensive, but are of only limited use in adjusting the injection molding conditions adaptively in such a way as to improve the consistency of the molding quality. More effective methods for performing the on-line monitoring and control of the part quality are urgently required
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