During large-scale production, mold cavity pressure is used for continuous quality monitoring of the molded parts. If this quality fails to meet (or no longer meets) the required standards, a scrap gate or a robot can be used to automatically separate defective parts from the batch based on cavity pressure measurements. This integrated quality assurance system ensures the detection of flawed parts at the earliest possible stage of the production process. The cavity pressure curve reveals the most important quality attributes of each molding immediately after the molding cycle. Reject diverters or robots can be actuated directly and the defective parts removed. All this makes it feasible to get the batch rejection rate right down to zero. The data measured in the production cycle can subsequently be used in quality documentation.
During production, the maximum and/or the integral as well as other values are calculated from the mold cavity pressure curves for each cycle, and the values are checked in relation to limit values. In the event that a limit value is violated, a signal is sent and either the entire shot is withdrawn or one part is rejected from the batch. The limit values to be monitored can be determined, for instance, by means of design experiments.
Due to the high quality standards required there is usually no other option than to equip every single cavity with a mold cavity pressure sensor. Only in rare cases is it possible to assess the quality in one cavity based on the pressure in another cavity. The systems used are either fully integrated into the injection molding machine or they operate as stand-alone peripheral systems. In the former case the measured mold cavity pressures are displayed and evaluated on the injection molding machine; in the latter case external systems are used, operating independently and sending good/bad signals to the injection molding machine or robot or scrap gate.