Control Charts Are Not Inspection Charts
Distinguish inspection conformance from statistical process-control evidence in supplier monitoring.
Do not confuse conformance with control. A supplier can ship conforming parts while the process is moving toward the edge of specification. Incoming inspection may not see that movement until it becomes a failure. SPC exists to make process behavior visible before the customer sees the defect. Lot result Lot inspection answers a narrow question: did the sampled units meet the requirement at this moment? It is useful for release, quarantine, and immediate protection. Process behavior A control chart answers a broader question: is the process behaving predictably over time? It helps detect special causes such as tool wear, material…
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