Puckered Side Seams on Cotton–Elastane T-Shirts
A garment unit in Odisha produces 500 cotton–elastane T-shirts (95% cotton, 5% elastane, 180 g/m²) for a domestic brand. The side seams are joined on a 4-thread overlock with size 14 needles, 2.5 mm stitch length, and differential feed at 1.0. The thread is 40/2 polyester core-spun. After three domestic washes at 40°C, 18% of garments show puckered side seams and wavy hems; the problem is more visible on light colours. The cutting room relaxed the fabric for only 4 hours after unrolling and cut a 24-ply lay. The brand rejects at AQL 2.5 major defects and demands a root-cause report before releasing a repeat order for 2,000 pieces. The unit has size 11 and 14 ball-point needles, a 3-thread overlock, and a heat press but no seam-sealing machine.
1. Identify the most likely causes of the puckering and explain why light colours show it more.
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The main causes are stretch and recovery problems, not a single machine fault. The fabric was relaxed for only 4 hours; cotton–elastane needs more time to recover from roll tension. Cutting a 24-ply lay adds compression and can distort the plies. Differential feed at 1.0 gives no compensation, so the overlock stretches the seam as it sews. A size 14 needle is heavy for 180 g/m² and can heat, enlarge needle holes and damage elastane. A 2.5 mm stitch length is short for elastane; it packs more thread into the seam and increases waviness. Thread tension may also be too tight.
Light colours show the fault more because shadows and seam ridges are more visible, and needle burns or heat damage show as discoloration. It is not reliable to blame the dye; confirm by checking the same shade in a different fabric. The 18% failure rate is far above AQL 2.5, so the process is not capable.
2. Recommend machine settings and a test protocol before bulk production.
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Use a size 11 ball-point needle, not size 14. Increase stitch length to about 3.0–3.5 mm. Set differential feed to about 1.2–1.3 so the overlock gathers slightly rather than stretching the seam. Reduce presser-foot pressure and check both looper tensions; the seam should lie flat without being tight. Sew at a steady speed and avoid pulling the fabric.
Relax the fabric for at least 24 hours before cutting, and reduce lay height for the trial. Make three test garments using the corrected settings. Wash them three times at 40°C, dry as the customer would, and assess seam appearance, waviness and shrinkage after 24 hours. Measure side-seam length before and after washing. If the seam still puckers, adjust differential feed and tension in small steps and repeat.
Do not release bulk until the trial passes the brand's seam appearance standard and the AQL sample. Keep a sealed approved sample for the line.
3. The brand asks whether to rework the 90 affected pieces or replace them. Recommend a decision with cost and quality reasoning.
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First inspect all 500 pieces, not only the 90 reported. Rework is viable if the seam can be reopened without leaving needle holes and if the seam allowance is still at least about 1 cm after trimming. Re-sew with the corrected settings, press, and re-wash a sample. Rework cost is usually lower than replacement because the fabric and trim are already consumed.
Replace the piece if there is needle cutting, heat damage, shade marks or a seam allowance too narrow to resew. Do not hide a bad seam under pressing. Because the failure rate is 18%, a 100% inspection is necessary; a spot check would miss too many.
Recommended decision: rework the repairable pieces, replace the irreparable ones, and charge the rework to the process-improvement budget rather than passing it to the buyer. Release the repeat order only after the trial lot meets AQL 2.5.