Quality management

Poka-yoke is a Japanese error-proofing method that prevents defects by making a human error impossible to commit or immediately visible the moment it happens. Shigeo Shingo developed it at Toyota in the 1960s. There are three types: contact methods for wrong physical attributes such as orientation, fixed-value methods for wrong quantities, and motion-step methods for wrong sequences.

The cost of poor quality (COPQ) is the total cost a plant carries because its processes do not produce good output the first time, from scrap and rework inside the facility to warranty claims, recalls and lost customers outside it. The prevention-appraisal-failure model sorts quality costs into four categories: prevention, appraisal, internal failure and external failure.

Corrective action deals with a quality failure that has already happened: it investigates the root cause and puts in a countermeasure to stop it recurring, and is triggered by events such as an NCR or a customer complaint. Preventive action deals with a risk that has not yet produced a failure, and is triggered by risk work such as an FMEA or trend data showing a process drifting toward its control limits.

First pass yield (FPY) is the percentage of units that complete a process correctly the first time, without rework, repair or scrap at any stage: good units divided by units started, multiplied by 100. It shows the capacity lost to rework that a final yield figure hides.