Meaning
Statistical threshold adjustments are performed to update the operating control limits of a manufacturing process when the baseline variability of the system changes. Executing a standard deviation limit recalculation ensures that control charts continue to reflect the actual, current capability of the assembly line rather than obsolete historical performance. This task is not applicable to unstable processes that have not reached a state of statistical control.
Threshold Adjustment
Statistical limits must be updated after a major process improvement or a change in raw material suppliers. When performing a standard deviation limit recalculation, engineers compile a new dataset of measurements from a series of stable production runs. This calculation updates the upper and lower control limits on the charts, preventing false alarms that would occur if the old limits were kept.
It ensures that the control charts remain a reliable tool for identifying true process shifts.
Variance Estimation
Sample sets are gathered over several consecutive days to ensure that the data represent the full range of normal process variation. This methodology provides a reliable foundation for the new limits.
Control Integrity
Quality audits are performed periodically to verify that the recalculated limits are being applied correctly by the line operators. This review maintains the integrity of the statistical process control system.
