Leak Problem A3 at an Electronics Assembler
At an electronics assembler, the final seal leak rate has been 3.2% for three months against a 0.5% target. Each leak costs $18 in rework and 8,000 units are built per week. A kaizen team runs a 5 Whys and concludes that operators are not seating the seal correctly; the top action is to retrain all operators and add a reminder sign. Two weeks later the leak rate is still 3.1%. Meanwhile, a new seal supplier was introduced six weeks before the problem began, and the leak rate is 5.0% on second shift versus 1.4% on first. The team wants to close the A3 because training completion is 100%. The quality manager asks you to review the investigation before the next management review. The seal is pressed by a manual fixture; first shift uses one fixture, second shift another. No measurement system study has been done on the leak tester.
1. Critique the 5 Whys and the countermeasure. What additional analysis would you require before accepting the root cause?
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The 5 Whys is too shallow and single-path. It jumped from a symptom to operator error without testing alternative causes. The evidence contradicts a pure training cause: the problem began after a supplier change, and second shift is 5.0% versus 1.4% on first, which points to supplier lot, fixture, or shift method. A sign and retraining would not fix a material or fixture interaction.
Require stratification of leak rate by shift, fixture, seal lot and supplier, operator tenure, and time; a measurement system study on the leak tester; seal incoming inspection for hardness and dimensions; and a review of press force, alignment, and seating depth. Use a fishbone and Pareto, then verify the likely cause with a small trial. Training may remain as a control, but it is not the root cause until the data support it.
2. Outline a corrected A3 problem-solving approach, including containment, verification, and standardization. What should happen to the training action?
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Corrected A3: (1) problem statement with gap: 3.2% versus 0.5%, costing about 256 leaks per week × $18 = $4,608 per week; (2) containment: quarantine suspect seal lots, 100% leak test or supplier certification, and sort suspect WIP; (3) data stratification and root-cause verification; (4) countermeasure matched to cause, such as supplier corrective action and incoming lot control, fixture maintenance, or a poke-yoke for seating; (5) results check with a run chart; (6) standardize: update standard work, control plan, supplier specification, and audit; (7) yokoten to other lines.
Do not close the A3 on training completion. Keep training as a supporting action and verify its effect separately. Report containment and the verified cause at management review.