Meaning
Statistical metrics measuring the relationship between manufacturing tolerance limits and process variation evaluate whether a production line consistently meets design specifications. Industrial supply contracts use cpk process capability to determine whether a manufacturing partner maintains acceptable precision levels during mass production. The metric applies to continuous dimensional or material attributes with upper and lower specification limits, but fails to evaluate non-measurable visual attributes or transient machine setup errors.
Index Calculation
Mathematical evaluation compares the distance between the process mean and the nearest specification boundary against three standard deviations of the process distribution. Calculating cpk process capability accounts for both process spread and mean shift away from nominal targets. Centred distributions with low standard deviation generate higher capability scores than skewed processes operating near specification limits.
Acceptance Threshold
Supply agreements specify minimum index values required for part approval and production authorization. Automotive and aerospace contracts demand minimum scores before approving volume production runs.
Nonconformance Remedy
Values falling below agreed contract thresholds trigger mandatory corrective action reports and process audits. Manufacturers operating with low index scores must perform hundred percent inspection on outgoing lots at their own expense until capability is restored. Failure to maintain required index values gives buyers the legal right to reject delivered batches and terminate procurement agreements for breach of contract.
Warranties link part failure rates directly to statistical control metrics established during qualification trials.
