Controlling delivery of polymer material in a sequential injection molding process

1. 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.

2. The method of claim 1 wherein each cavity has a corresponding nozzle fluidly communicating with the cavity and having a first bore for delivery of the first shot, the nozzle having a valve pin adapted to open and close the first bore, and the step of independently stopping the first shot comprising closing the first bore.

3. The method of claim 1 wherein the step of delivering the second shot comprises delivering the second shot subsequent to stopping delivery of the first shot to all of the plurality of cavities.

4. The method of claim 1 wherein the step of delivering the first shot comprises delivering the first material to all of the plurality of cavities from a single source of injection.

5. The method of claim 1 wherein the step of delivering the second shot comprises delivering the second material to each cavity from a separate source of injection.

6. The method of claim 1 wherein the step of independently sensing comprises sensing a volume of the first material.

7. The method of claim 1 wherein the step of independently sensing comprises sensing a flow of the first material.

8. The method of claim 2 wherein each nozzle has first and second bores for delivering the first and second materials respectively to the corresponding cavity, the valve pin reciprocating between positions to open and close the first and second bores, and the program including instructions to direct the valve pin to move between the positions to fill the cavity to a predetermined volume of the first material.

9. The method of claim 2 wherein the two locations are within the bore of the nozzle or within the corresponding cavity.

10. The method of claim 1 wherein the program calculates the flow rate of the first material.

11. The method of claim 1 wherein the program calculates the fill volume of the first material.

12. The method of claim 2 wherein

the nozzle communicates with sources of pressurized feed of the first and second materials;

a drive mechanism drives one or the other or both of the sources of feed and the valve pin for the nozzle, the drive mechanism starting and stopping flow of each of the first and second materials in a predetermined sequence through the nozzle;

a controller, interconnected to the drive mechanism, receiving one or more signals from the two sensors and directing the drive mechanism to deliver at least the first shot of the first material and the second shot of the second material after the first shot.