Systems and methods for controlling injection molding using predicted cavity pressure
In order to improve the consistency of molded products as viscosity shifts throughout a run, a controller of an injection molding machine executes a calibration cycle in accordance with a mold cycle. The controller analyzes a plurality of sensed melt pressure values during the calibration cycle to determine one or more calibration metrics. The controller then uses the calibration metrics when executing each mold cycle of the run. More particularly, during each mold cycle of the run, the controller detects a plurality of sensed melt pressures prior to and during a fill phase of the mold cycle and compares the plurality of sensed melt pressures to the one or more calibration metrics to predict cavity pressure for a pack and hold phase of the mold cycle. The controller then adjusts a set point pressure for the pack and hold phase based on the predicted cavity pressure.
1. A method of controlling an injection molding machine, the method comprising:
executing, by a controller, a calibration cycle in accordance with a mold cycle implemented by the injection molding machine;
analyzing, by the controller, a plurality of sensed melt pressure values during the calibration cycle to determine one or more calibration metrics;
executing, by the controller, a run using the injection molding machine, wherein the run sequentially implements the mold cycle a plurality of times; and
during each mold cycle of the run:
detecting, by the controller, a plurality of sensed melt pressures prior to and during a fill phase of the mold cycle;
comparing, by the controller, the plurality of sensed melt pressures to the one or more calibration metrics to predict a cavity pressure for a pack and hold phase of the mold cycle; and
adjust, by the controller, a set point pressure of the mold cycle for the pack and hold phase of the mold cycle based on the predicted cavity pressure.
2. The computer-implemented method of claim 1 , wherein one of the calibration metrics is a calibration ratio between melt pressure during the pack and hold phase of the mold cycle and melt pressure during the fill phase of the mold cycle.
3. The computer-implemented method of claim 2 , wherein:
the melt pressure during the fill phase of the mold cycle is an average melt pressure during the fill phase; and
the melt pressure during the pack and hold phase of the mold cycle is an average melt pressure during the pack and hold phase of the mold cycle.
4. The computer-implemented method of claim 2 , wherein predicting the cavity pressure for the pack and hold phase of the mold cycle comprises:
comparing, by the controller, the sensed melt pressure during the fill phase of the mold cycle to the calibration ratio.
5. The computer-implemented method of claim 1 , wherein one of the calibration metrics is a calibration error between the measured pressure values and a plurality of set point pressure values for the mold cycle.
6. The computer-implemented method of claim 5 , wherein the calibration error is an average error from a start of the mold cycle through the pack and hold phase of the mold cycle.
7. The computer-implemented method of claim 5 , wherein predicting the cavity pressure for the pack and hold phase of the mold cycle comprises:
determining, by the controller, a percentage a peak melt pressure sensed by the pressure sensor overshot a set point melt pressure for the fill phase of the mold cycle; and
scaling, by the controller, the calibration error based on the determined percentage.
8. The computer-implemented method of claim 1 , wherein adjusting the set point pressure of the pack and hold phase of the mold cycle comprises:
scaling, by the controller, the set point hold pressure of the mold cycle based upon the predicted cavity pressure.
9. The computer-implemented method of claim 1 , wherein the injection molding machine does not include a mold cavity pressure sensor.
10. The computer-implemented method of claim 1 , further comprising:
scaling a set point melt pressure for a subsequent mold cycle of the run based on the predicted cavity pressure for the mold cycle.
11. The computer-implemented method of claim 1 , further comprising:
scaling a set point melt pressure for a subsequent mold cycle of the run based on the ratio between a sensed velocity during the pack and hold phase of the mold cycle to a sensed velocity during a fill phase of the mold cycle.