Manufacturing process engineering · Lesson 4 of 4

Manufacturing process engineering: defects, verification and case study

Preventing versus detecting defects, how to read control charts and capability indices, why the instrument comes first, a five-step root-cause method, and a case study and checklist built only from sourced or AFS-register material.

You will be able to: Choose a verification method (first-article check, control chart, capability index), read it correctly, and run a five-step root-cause analysis on a plausible defect, documenting the evidence.

13 min · 12 slides · 9 questions

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Prevent and detect

A limits check and a verified approval prevent a mistake from going forward; an inspection or a control chart detects one that has already happened.

Poka-yoke belongs to the first kind. Inspection, charts and capability studies belong to the second, and a good process uses both.

Sources

AFS order flow: limits check while drawing, verified approval, shop queue and next-business-day delivery - Architectural Flashing Supply (internal register)
Poka-Yoke (Lean Lexicon) - Lean Enterprise Institute

Glossary

Control chart: A chart of a quality characteristic over time with a center line at the mean of the in-control process and upper and lower control limits.
Cp: A capability index equal to the specification width divided by six standard deviations; it does not account for a process that is off-center.
Cpk: A capability index equal to the smaller of the distances from the mean to each specification limit divided by three standard deviations, so it accounts for centering and is never above Cp.
Subgroup: A small set of measurements taken together, for example five legs measured in one hour, whose mean and range are plotted on X-bar and R charts.
Root cause analysis: A systematic process to find the underlying causes of a problem so the issue does not recur, rather than treating the symptom.
Traceability: Relating a measurement result to a reference through a documented unbroken chain of calibrations, each adding to the measurement uncertainty.