Research for process control of switching over from injection to holding and holding based on cavity pressure

The plastic injection molding process is composed of many phases, such as injection phase, filling phase, compressing phase, and holding phase, etc. In the paper, the simulation models of cavity pressure are established at the phase of switching-over from injection to holding and multistage holding. Simulation researches are made by applying the following algorithms: PID; advanced PID; Dahlin; and AMF. The experimental results show that the response of cavity pressure in instantaneous processes, and each cavity pressure distribution over the cavity surface is the same, in spite of the difference of response time and peak value. The peak value can be controlled by controlling injection pressure, injection time, holding pressure and holding time to avoid molded part defects caused by over filling or under filling