The quality department, on their speed control data recorder, verified the change. This control required on-time testing and feed back to the setup/process technician who would make adjustments in screw speed when required. The speed was monitored to know what revolutions were required to keep the process in control even if molecular weight varied ever so slight. As a result, any minor variations in material would be adjusted at the machine with screw RPM’s (revolutions per minute) speed adjustment. The incoming test laboratory was then required to draw material samples for molecular weight testing every two hours, from the primary feed system (at the machine feed hopper) to verify molecular weight distribution. The PCI index calculated during the process out of control went from 0.5 up to 1.33, a process in control, but not yet within Six Sigma values.
The PCI (process-capability index) (PCI = upper specification minus lower specification limit divided by Six Sigma product standard deviation) was calculated and new data collected. Joseph Gordon Jr., in Six Sigma Quality for Business and Manufacture, 2002 PROCESS-CAPABILITY INDEX Six Sigma Improvements in Business and Manufacturing
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