Poka-Yoke in 8D

I have reviewed too many D6 sections where the corrective action was 'added an extra inspector' or 'retrained the operator.' If your permanent fix depends on a human staying alert for eight hours in a hot factory you have not fixed anything — you have formalized the gamble. The gold standard of D6 is Poka-Yoke: error-proofing that makes the defect physically impossible. Shigeo Shingo classified Poka-Yoke into three levels. Level 1 is prevention at the source — the mistake is impossible. Level 2 is detection before the defect is created — the process stops when an error occurs. Level 3 is detection after the defect — bad parts caught before shipping. Most factories claim they have Poka-Yoke when they really just added Level 3 inspection. A specific case: a transmission line where operators installed a snap ring into a bore. About once per shift someone forgot the ring. The first D6 solution was a proximity sensor with a buzzer. Within a week operators disconnected the buzzer because coolant false-triggered it and the noise slowed them down. The detection device was sabotaged by the production system it was supposed to protect. We replaced it with a mechanical fixture using a spring-loaded...