Controlling delivery of polymer material in a sequential injection molding process

A method of delivering multiple shots of material to a plurality of mold cavities, the method comprising:

• for each of the plurality of mold cavities, providing sensors at two locations of flow in or into the cavity;
• delivering a first shot of a first material simultaneously to the plurality of mold cavities;
• independently sensing for each cavity at the two locations a property that is indicative of a volume or flow of the first material in or into the corresponding cavity;
• independently stopping the step of delivering the first shot to one or more cavities according to a program that uses as a variable a signal indicative of the property sensed at the two locations for the corresponding cavity during delivery of the first shot to estimate when the mold cavity will or has reached a predetermined fill volume, wherein the program uses the signal indicative of the sensed property at the two locations to calculate a flow rate or fill volume of the first material or to compare the signal or a value calculated from the signal to a target value;
• and
• delivering a second shot of a second material simultaneously to the cavities subsequent to the step of stopping the step of delivering the first shot.