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Precision forming and statistical inspection · Lesson 4 of 4

Precision forming and statistical inspection: defects, verification and case study

A defect map for formed angles and legs, a coil-change case worked through the control chart and its action plan, what to do when a stable process is not capable, how to rule out the gauge, and the record a reviewer needs.

You will be able to: Diagnose a forming-precision defect from measurements, separate a real process change from noise and from a measurement problem, and document the correction for review.

12 min · 9 slides · 10 questions

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Slide 1 of 9

Defect map

Module guidance, first suspects:

  • Every piece off by the same angle: springback not yet corrected for this material.
  • The angle shifts after a coil change: new material.
  • A leg off by a constant amount: blank, gauging, or an inside reading.
  • Scatter grows with no shift: check the gauge before the machine.
  • Wrong hem gap: check the order (FlashDraft starts open at 0.125 in, smashed at 0.03125 in).

Sources

Videos for this lesson

What this video shows: One software maker's walkthrough of a gage repeatability and reproducibility study: how much of the variation comes from the measurement system.

Video: How to Perform a Gage R&R Crossed Study | Minitab Tutorial Series by Minitab, on YouTube. AFS checked its description against this lesson.

Glossary

Run rule
A pattern test on a control chart, such as eight points in a row on one side of the center line, that signals a likely process change before any point is beyond the control limits.
Out of control
The conclusion that recent readings no longer come from the same population as the data used to set the control limits, which starts the search for an assignable cause.
Gauge study
A study of a measuring system's repeatability, reproducibility, stability and bias, and often its resolution, before its readings are trusted.