AQL Final Inspection With Critical Metal Findings
A factory offers 5,000 cotton shirts for final inspection under ISO 2859-1, general inspection level II, AQL 2.5 for major defects, AQL 4.0 for minor defects, and zero acceptance for critical defects. The sample size code for the lot is L, giving 200 pieces. Inspectors find 9 major defects (oil stains, broken buttons, open seams), 13 minor defects (loose threads, uneven stitching), and 2 critical defects (a broken needle fragment in a collar and a sharp metal point at a cuff). The production manager argues that the lot should pass because major and minor counts are within their limits, and offers to “average” the critical findings against the good pieces. The buyer’s shipment date is in 6 days. The factory has no metal detector on site, but a nearby unit can rent one for one day. Rework capacity is 300 pieces per day.
1. Apply the sampling plan and decide acceptance, showing the counts against the acceptance and rejection limits.
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For lot size 5,000, general inspection level II, sample size code L gives n = 200.
The limits are:
- Major, AQL 2.5: accept on 10 or fewer, reject on 11 or more. Found 9, so major is within the limit.
- Minor, AQL 4.0: accept on 14 or fewer, reject on 15 or more. Found 13, so minor is within the limit.
- Critical: zero acceptance. Found 2, so the lot is rejected.
The production manager’s suggestion to average the critical findings against the good pieces is not valid. Critical defects are a separate class because they create a safety hazard; they are not offset by acceptable major or minor counts. The lot therefore fails final inspection, even though the major and minor counts are below their limits.
2. Classify the defect types and explain why the two metal findings are critical even though only two pieces are affected.
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- Major: oil stains, broken buttons and open seams affect saleability or function and would cause a customer to reject the shirt.
- Minor: loose threads and uneven stitching are appearance issues that do not usually stop sale, though they lower quality.
- Critical: the broken needle fragment and the sharp metal point are safety hazards. They can injure a wearer, especially a child, and can create legal liability.
Two pieces in a sample of 200 is not a small issue. It suggests the needle-control process has failed somewhere in the line, so the same fault may exist in the 4,800 unsampled pieces. A zero-acceptance rule exists because the risk is injury, not appearance. The lot cannot be accepted on the argument that only 2 of 200 were affected.
3. Recommend disposition of the 5,000 shirts and corrective action, including how to handle the missing metal detector.
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Disposition:
- Quarantine the lot and do not ship.
- Rent the nearby metal detector and pass 100% of the lot through it, not just the sample. Remove and quarantine any pieces with metal findings.
- Rework the major and minor defects; re-inspect the reworked pieces.
- Re-sample the lot or, if the buyer requires, 100% inspect for critical defects before shipment.
- Obtain buyer approval before shipment.
Corrective action:
- Introduce a written needle-control policy: needles issued and returned by number, broken needles logged, machine and floor swept, and missing pieces accounted for.
- Add metal detection as a routine final step.
- Check button attachment and seam quality, since those caused the major defects.
- Train operators and supervisors, and record the corrective action for the buyer’s audit.
With 6 days to ship, 100% metal detection is feasible if the detector is booked immediately; rework of 300 pieces per day can handle the visible defects but must not delay the metal check.