Closed loop control of injection moulding hold time

Closed loop control of the hold time set point for injection molding is demonstrated. Using feedback from a cavity pressure transducer which indicates gate seal from a feature of the pressure profile during molding, the closed loop system has demonstrated the ability to respond to changes in the machine operating point and continually produced well packed parts. This control strategy does not directly control the weight of the part or any other quality parameter. However, it ensures that every part is fully packed according to the existing molding conditions; ensures that every machine cycle operates in the minimum time corresponding to a fully packed part; and relieves the machine operator of a tedious adjustment process. These accomplishments should reduce the number of rejected parts, reduce the machine cost per part, and reduce the required operator labor.