Learning Goal: Use root cause analysis tools to solve recurring quality issues permanently.

Complete Lesson Content:

When a defect repeats, a quick fix won’t solve it. Use the 5 Whys technique, fishbone (Ishikawa) diagram, and Pareto analysis. The 5 Whys: ask “why” repeatedly until reaching the fundamental cause. 

Fishbone diagram categorises potential causes: Man, Machine, Material, Method, Measurement, Environment. Pareto principle: 80% of defects come from 20% of causes; fix the vital few.

Definitions:

  • 5 Whys – iterative questioning to drill down to the root cause.
  • Pareto Chart – bar chart showing defect frequencies in descending order, with a cumulative line.

Step‑by‑step Explanation:

  1. A defect is identified: e.g., skipped stitches on side seam.
  2. Assemble a small team (operator, supervisor, mechanic).
  3. Ask: Why? Machine skipped stitches. Why? Needle was bent. Why? Needle hit a pin. Why? Pinning method caused needle to hit. Why? Operator not trained on new fabric thickness.
  4. Root cause: lack of training for new fabric; action: retrain all operators on pinning and needle selection.
  5. Track defect rate to verify solution.

Best Practices: Involve the operators who do the work; they often know the real cause. Use simple paper charts on the line.

Common Mistakes: Stopping at the first superficial answer; real root cause often hidden.

Real Industry Example: A factory reduced its top defect by 70% after a Pareto analysis showed that three of the ten defect types accounted for 80% of rejects, and focused improvement on those.

Mini Case Study: A recurring stain on white shirts was blamed on operators. 5 Whys revealed the maintenance team used dirty oil; cleaning the oil system eliminated the defect.

Practical Activity: Use the 5 Whys on a hypothetical scenario: “Buttonholes are consistently too small, causing buttons to not pass through.”

Assignment: Choose a common garment defect (e.g., puckered seam) and create a fishbone diagram with at least three potential causes in each category (Man, Machine, Method, Material).

Lesson Summary: Fix the cause, not just the symptom; structured analysis prevents recurrence.

Key Takeaways:

  • 5 Whys goes deep.
  • Fishbone organises causes.
  • Pareto focuses on the biggest impact.
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