Quality Assurance and Inspection
This domain tests fabric quality parameters, inspection routines, sampling and the link between process control and customer acceptance.
Core rules
- Key parameters: greige and finished width, EPI, PPI, GSM, crimp, shrinkage, skew, bow, colourfastness, tensile and tear strength.
- Inspection checks width, density, mass, defects and shade. Cuttable width is narrower than greige width and is what the garment maker can use.
- AQL sampling uses lot size, inspection level and acceptance number. A sample must be random; a convenient sample invalidates the decision.
- SPC uses control charts for count, width, GSM and defects. Common-cause variation needs process change; special-cause variation needs investigation.
- Quality costs include prevention, appraisal, internal failure and external failure. Internal failure includes mending and seconds; external failure includes claims.
- First-quality, second-quality and reject grading must use written standards, not operator preference.
Worked example
Warp 40 Ne at 100 EPI, weft 40 Ne at 80 PPI, crimp 5% both ways. Use GSM = (EPI/Ne warp + PPI/Ne weft) × 23.25 × (1 + crimp). Basic sum = 100/40 + 80/40 = 4.5. GSM = 4.5 × 23.25 × 1.05 = 109.9 g/m², approximately 110 g/m².
Traps
- Using finished sett for a greige GSM calculation.
- Treating AQL as a defect-free guarantee.
- Selecting samples from the top of the roll only.
- Confusing cuttable width with full fabric width.
- Comparing GSM without a regain or conditioning basis.