Injection‐molding process control—A review

Abstract

This paper reviews control strategies employed in the injection-molding process. For clarity, the controlled variables have been categorized into all-phase control, phasedependent control, and cycle-to-cycle control. All-phase control includes variables that must be monitored and controlled at all times; i.e., in all the phases. Control of variables that are triggered during a specific phase are discussed under phase-dependent control. In cycle-to-cycle control, previous data are used to predict future trends and take appropriate corrective actions. The cyclic, dynamic, and unsteady state nature of the injection-molding process is discussed with respect to the conventional proportional-integral (PI) and proportional-integral-derivative (PID) controllers as well as the more advanced control schemes such as self-tuning control, optimal control, and statistical process control. Suggestions involving specific advanced control schemes and recommendations for future research in injection-molding process control also are made.

A review of current developments in process and quality control for injection molding

“…19 Therefore, it is rational to control the process variables rather than the machine variables in order to achieve desirable and consistent part quality. As early as the late 1980s, Agrawal et al 47 suggested using "plastic variables," which are referred to as process variables here, as controlled parameters since plastic variables are the true indicators of the condition of the plastic inside the mold. The validity of the suggestion has been proven in numerous research efforts which show that the polymer melt temperature and pressure have a very strong influence on the quality of the molded part.…”

“…As reported in Agrawal et al, 47 intelligent computation-based methods were used to model the temperature process dynamics, and advanced control strategies based on a relatively large amount of online calculation were implemented to achieve performance superior to conventional PID controllers.…”

“…It was found in the early research that mold separation, which is on the order of microns at the moment when the mold cavity is volumetrically filled, was a reliable indictor of part weight or thickness. 47,[71][72][73] Buja 71 and Wenskus et al 72,73 studied the application of mold separation control to improve the consistence of part weight. In their work, a mold separation signal was directly used to determine the switchover point from filling to packing, replacing the traditional switchover criterion based on ram position or hydraulic pressure.…”

An Ultrasonic Sensor to Monitor the Mold Cavity Conditions During Injection Molding

“…They suggest that process parameters such as melt temperature and cavity pressure have a simpler, more direct relationship with product quality than the machine variables. [1] Others have treated the process as a linear multivariate system. [2] Attempts at intelligent or learning strategies include such studies as an expert system based on cavity pressure feedback [3], and a technique that useS an evolutionary strategy to search for the machine settings that optimize part quality.…”

“…To provide this control, feedback is needed; a method (preferably automatic) is required to provide a quantified measurement. The need for new sensor technologies has been discussed in [1] and [5], and several techniques have been investigated in [6].…”