A study of problems associated with fabric sewing in commercial garment manufacture
This thesis reports the results of a study of problems associated with fabric sewing, such as seam pucker and sewing damage, in commercial garment manufacture. Part 1 continues previous work by the author on seam pucker in structurally jammed fabrics; in particular it has been shown that initial Young's modulus of a fabric is a measure of the ability of the fabric to accommodate compressive forces during sewing. This result provides an additional means of predicting the tendency of a fabric to exhibit seam pucker. The static mechanism of seam pucker proposed previously, based upon the relative magnitudes of bending stiffness of thread and fabric, has been revised by establishing that sewing machine dynamics and pucker are closely related. It has been shown that presser foot bouncing in particular induces pucker and that the sewing thread needs to be positively controlled during stitch formation. These results were verified by simple experimental methods, suggesting that modifications to the sewing machine are needed. Such modifications are beyond the scope of this work. Following the earlier static mechanism of seam pucker, it has been shown that seam pucker in fabrics is reduced significantly when the bending stiffness and extensibility of the sewing thread is reduced. In addition seam pucker can be eliminated by improving fabric stiffness locally along the seam area, by incorporating a stiffening material in the seam; this is based upon the technique of pucker elimination found in the author's previous work. In this study this technique is implemented with considerable success in other types of seams and commercially available stiffening materials have been selected. Part 2 investigates sewing damage to fabrics due to sewing needle penetration. Preliminary studies suggested the need for a reliable testing facility. This was made by instrumenting an industrial overlock sewing machine. The instrumentation was based on measuring the force which is exerted by the sewing needle when penetrating the fabric. The testing facility consists of the sewing machine with a strain gauged sewing needle and plate, and a shaft encoder for stitch marking, which with proper signal amplification and conditioning could be fed to a transient recorder and osciloscope for signal capturing and plotting. Investigations with fabrics revealed that the magnitude of the peak force of each stitch cycle can be related to the degree of sewing damage in the fabric. Based on these results the most important variables in sewing damage were fabric softening and its effective application during finishing, and sewing needle size. Studies of sewing damage under dynamic conditions have shown that sewing damage is a frictional problem between yarns in the fabric and between yarns and the metal of the sewing needle, foot, plate and feed dog. The size of the needle plate of the sewing machine seems to affect the degree of damage and fabric "flagging" during sewing damage has been experienced. Finally in the latter section of this study a prototype routine sewing damage tester has been developed and each stage of its development is described. This tester is based on an instrumented overlock sewing machine, which is interfaced with an IBM PC for computerised data capture and analysis in real time.