Final inspection, AQL sampling and a broken needle fragment in a collar
A woven-shirt unit finishes 1,200 pieces of a school-shirt order as one lot. The buyer's standard is ISO 2859-1, General Inspection Level II, AQL 2.5 for major defects, 4.0 for minor defects, and zero acceptance for critical defects. The QC team draws a single normal sample and records 4 major defects (two skipped stitches at the placket, one mismatched sleeve length of 8 mm, one open side seam of 15 mm), 6 minor defects (uneven topstitching, loose thread tails, shade variation within one sleeve) and, in the last piece of the sample, a 4 mm broken-needle fragment embedded in the fused collar stand. The production manager argues the lot should pass because the numbers are inside the limit and the order ships tomorrow. The unit has no needle-issue register, and the metal detector at packing has been switched off since its sensor failed three weeks ago.
1. Work out the sample size and the acceptance and rejection numbers for this lot, and state the decision that the attribute counts alone would give. Show the arithmetic.
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Sampling plan
- Lot size 1,200 pieces falls in the 501-1,200 range of the ISO 2859-1 General Inspection Level II table, giving code letter J and a sample size of 80 pieces.
- Major, AQL 2.5 at code J: acceptance number 5, rejection number 6.
- Minor, AQL 4.0 at code J: acceptance number 7, rejection number 8.
Decision on attribute counts alone
- Majors found: 4. Since 4 is less than or equal to 5, the sample is acceptable on majors.
- Minors found: 6. Since 6 is less than or equal to 7, the sample is acceptable on minors.
So on the counts alone, the lot would be accepted: the production manager's arithmetic is correct. Note the margin is thin - one more major defect anywhere in those 80 pieces would have rejected the lot, which is a signal about process capability, not a reason to relax.
A caveat worth recording: the sampling plan protects the buyer at the agreed AQL, it does not certify the lot. With 4 majors in 80 pieces the estimated process average is around 5% defective, which is high for a school uniform programme and should trigger a process review even on an accepted lot.
2. Explain why the lot must nevertheless be rejected, what class the fragment falls in, and what immediate containment you would order before anything ships.
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The attribute counts are irrelevant once a critical defect is present. A broken needle fragment in a collar stand is a critical defect because it can injure a child; critical defects carry zero acceptance, so a single occurrence rejects the lot regardless of how good the major and minor counts are. AQL tables are a sampling risk tool, not a safety limit.
Immediate containment
- Stop packing and quarantine the whole 1,200 pieces plus all work in progress and cut parts in the system, with a red tag and a physical barrier; nothing moves without release signature.
- Place a hold on all other lots sewn in the same period on the same machines - the fragment came from a needle, and needles break on any machine.
- 100% inspection of every piece with a needle-detection method: metal detection if available, otherwise a controlled visual and tap/feel inspection of collars, plackets, cuffs and hems by trained pairs of inspectors, with a count of pieces in and out.
- Switch the packing line to a functioning metal detector or a calibrated hand-held detector before any carton is sealed; a broken detector is a stop-ship condition, not an inconvenience.
- Open a needle control file: count needles in and out per machine per shift, record breaks with the operator name and machine number, and reconcile the broken pieces against the fragment found.
- Inform the buyer in writing the same day - a critical defect found in-house is a communication task, not something to solve quietly.
The 4 majors and 6 minors are then handled on their own merits after containment.
3. The production manager proposes re-inspecting only the collar stands of the remaining 1,120 pieces so the shipment can leave tomorrow. Evaluate that proposal and set out the root-cause and corrective actions you would insist on.
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Why the proposal is not acceptable. It assumes the fragment came from the collar operation, but there is no needle register and the detector has been off for three weeks, so there is no evidence linking the fragment to one machine or one operation. A needle breaks into at least two pieces and fragments travel - carried on fabric, in a pocket, in a bundle. Inspecting only collars leaves plackets, side seams, hems and cuffs, plus every piece already packed in previous days, uninspected. The proposal also treats the symptom, not the cause.
Root causes to confirm
- No needle issue and return control: needles not counted per shift, breaks not logged, fragments not accounted for.
- No functioning metal detection at packing for three weeks - a known, accepted risk.
- Needle breakage causes on the collar line: wrong needle size or point for fused interlining, needle striking the presser foot or plate, operator pulling fabric, machine timing.
- Superseded procedure: whoever switched off the detector had no authority to do so, and no one restored it.
Corrective actions with owners and dates
- Needle control policy: issue one needle at a time per operator, log issue and return, account for every fragment before a new needle is issued.
- Metal detection as a mandatory gate; daily verification with a test piece; detector failure stops packing.
- Fit or restore fragment guards and check needle plate condition on all collar machines; verify needle size against the tech pack.
- Train all operators and supervisors on the broken-needle procedure, with a signed attendance sheet and a short quiz.
- Effectiveness check: for the next four weeks, audit needle reconciliation on 10 machines per week and record fragments found; zero unaccounted fragments for four consecutive weeks closes the action.