Map the Causes of Coating Defects
Create a balanced cause map and convert priority branches into evidence tests.
18 minutes
Scenario
A metal-parts plant saw coating defects rise from 2.1% to 5.4% on Line 3 over six weeks. The plant manager believes the new operators are responsible.
- Your role
- Quality improvement facilitator
- Method
- Ishikawa Diagram
Evidence pack
People
Three operators joined, but defect rates rose on shifts with and without new staff.
Machine
Nozzle pressure varies beyond the maintenance target twice per shift.
Material
A new coating batch entered use four days before the increase.
Method
The cleaning interval changed from 4 hours to 6 hours.
Measurement
Thickness gauge calibration is current; sampling fell from 10 to 5 parts per hour.
Environment
Humidity exceeded the process range on 9 of 30 days.
Constraints
- The diagram cannot be used as proof.
- Priority must be based on impact, plausibility and test value.
- At least one popular hypothesis must be challenged with evidence.
Case steps
Work through each prompt using the evidence pack. Answers and rubric weights stay protected in the interactive flow.
Write the effect statement with line, rate and period.
Place e1–e6 into cause families and add one plausible sub-cause for any three branches.
Choose three hypotheses to test first and justify priority.
Define a test that could support or reject each priority hypothesis.