Abstract:

Objective In order to improve the sewing quality of garments and to solve the current problem of matching fabric properties and sewing processing parameters by skilled workers in sewing relying only on experience, this research selects sewing processing parameters that match fabric properties by establishing a mathematical model of the multi-force field coupling of fabrics in the sewing process, which not only realizes an unmanned and automated production method in the garment industry, but also meets the future trend of multi-batch and multi-variety development in the garment industry.

Method In this research, a structural model of a weft knitted fabric is established followed by an investigation on the influence of the holding force between fabric tissue and yarn on the piercing process of the sewing needle. A novel force-field coupling model is developed based on the mechanical properties of the fabric during the sewing process. A finite element model of the fabric and a geometric model of the sewing needle are developed to verify the correctness of the multi-field coupling model, and a collaborative automatic sewing platform is built to verify the matching between the fabric and the sewing process parameters based on the multi-position coupling model.

Results Larger the needle size resulted in greater frictional resistance of the fabric to the needle. It revealed the puncture force varies with the needle gauge when sewing on the same fabric (Tab.2), and with different fabrics at the same needle gauge. The strain produced by the same needle gauge when piercing fabrics varied with different Poisson's ratios (Fig.11). The strain increased with the increase in the Poisson's ratio, and the largest strain of 0.106 mm was found for a Poisson's ratio of 0.25 and the smallest strain of 0.095 mm for a size 12 needle. On the experimental platform, six knitted weft fabrics were tested using six different pressures and tensile forces, and the relationship between them was described in two sets of graphs (Fig.14(a) and Fig.15(a)), the higher the coefficient of friction, the higher the frictional force to which it is subjected. The higher the coefficient of friction of the fabric, the higher the resulting frictional force and the higher the strain that occurs when the fabric was subjected to the same pressure (Fig.14(b) and Fig.15(b)). It shows the numerical models of the relationship between the tensile force applied to the fabric and the deformation it undergoes in the form of force-deformation curve (Fig.14(c) and Fig.15(c)). As the Poisson's ratio of the fabric increases, the results indicated that the greater the amount of strain was produced for the same tensile force. The fabric sewing shrinkage curves are shown (Fig.16). When comparing the same tensile strengths, No. 12 has the greatest effect on the sewing shrinkage of the fabric and No.11 has the least effect on the sewing shrinkage of the fabric. When comparing adjacent tensile strengths, the sewing shrinkage of the fabric changes significantly when the fabric was subjected to tensile strengths between 100 cN and 150 cN, while the sewing shrinkage of the fabric changes less when the tensile strength was between 150 cN and 200 cN. The sewing crinkle rate tends to increase when the pulling force was greater than 200 cN, indicating that the use of a pulling force greater than 200 cN stretches the fabric and causes the fabric to suffer from excessive pinholes.

Conclusion The greater the radius of the sewing needle when piercing the fabric, the greater the holding force of the yarns during the sewing process, the tighter the fabric structure, and the greater the sewing resistance. Applying a certain amount of tension during the sewing process changes the density of the fabric, thus moderating the effect of the holding force of the yarns and the frictional resistance on the sewing needle. The tension applied to the fabric during the sewing process has a greater impact on the sewing quality of the fabric, and by applying different tensions to different fabrics and choosing the sewing conditions reasonably, the quality of the sewing can be improved and the shrinkage rate of the fabric reduced. In contrast to workers' experience in sewing fabrics with needles and the study of fabric stress and fabric deformation during sewing, modelling and selection of suitable processing parameters for sewing fabrics on a collaborative automatic sewing experiment platform can improve the quality of fabric sewing and provide data for future sewing processes in fully automatic and unmanned production lines.

Key words: fabric structure, force field coupling, sewing technology, automatic stitching, garment fabric