A comparison of seven filling to packing switchover methods for injection molding

The effectiveness of seven methods for controllingswitchover from the filling to packing stage wereinvestigated, including: (1) screw position, (2) injectiontime, (3) machine pressure, (4) nozzle pressure, (5) run-ner pressure near the sprue, (6) cavity pressure nearthe gate, and (7) cavity temperature at the end of flow.The activation threshold for each of the seven switch-over methods was iteratively determined so as to pro-duce similar part weights relative to a standard pro-cess. A design of experiments was implemented foreach of the seven switchover methods that perturbsthe process settings by an amount equal to six stand-ard deviations of the standard process so as to repli-cate the expected long-term process variation. Theresults suggest that conventional switchover methods(e.g., screw position) had lower short-term variation,but other methods were more robust with respect torejecting long-term process variation. The merits ofdifferent dimensional measurements for quality controlare also discussed relative to the society of the plas-tics industry (SPI) standard tolerances.