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 The Effect of Lockstitch Sewing Machine Processing Parameters on The End-Product Quality
Prof. Dr. Ibrahim Elhawary a, Marwa Issa b
a Professor at Textile Engineering Department, Faculty of Engineering Alexandria university, Egypt. Contact Info: 01119991820, hawary_45@yahoo.com
b PHD Student at Textile Engineering Department, Faculty of Engineering Alexandria university, Egypt. Contact Info: 01200119490, engineermarwasaad@gmail.com

Abstract

In this article we have discussed various processing factors affecting the end product seam quality and what should be considered to obtain the highest quality at minimum cost for satisfying our consumer and manufacturer. In addition, we have investigated lockstitch sewing parameters influence using different fabrics and sewing threads such as stitch density, needle size, type and heat, sewing machine speed, pressure foot, fed dogs, feed timing as well as sewing threads tension. Finally, the most important differences between the normal lockstitch sewing machine and the leather one have been highlighted.
Keywords
Seam quality, Lockstitch sewing machine, stitch density, needle size, type and heat, sewing machine speed, pressure foot, fed dogs, feed timing, Leather sewing machine.

Introduction
Seams can have a great influence on fashion, beauty and its functionality. They should achieve the optimum level of quality to meet consumer needs for different end products such as garments, home textiles, as well as technical textiles and so on. So what is the seam quality? How its’ standards could be gained? And which are the working parameters of the sewing machine affecting the same?  This scientific article will discuss all these answers. 1
The basic structure of sewing machine is the same whether it is hand-operated sewing, treadle sewing machine or electric sewing machine as shown in Figure (1).  The main threading is to pass the upper yarn through the tension regulator, Take up lever and the needle so that each sewing machine will be different than others according to yarn guides layout in which the sewing process action is taken place by the motion of upper and lower threads as shown in Figure (2). Therefore, threads’ tension and needle adjustment are essential to produce uniform and even stitches. 

Seam quality requirements and evaluation 
Pieces of fabric must be joined, and then a seam is used to affect that join in which it meets our requirements in terms of aesthetics factors as well as functional factors as shown in Figure (3). All of these requirements are influenced by sewing processing parameters with right matching with fabric type as well as thread size and type. So the correct adjustment of machine settings results high cloth product quality.
Different techniques were used for evaluating the seam quality consequently seam strength, elongation, efficiency, slippage, puckering, damage, grining and skipped stitches, see Figure (4),  could be considered as the most important factors to measure its esthetics and functional performance.
1)        Seam strength:  refers to the load required to break a seam. Research has revealed that the load required to rupture the seam is usually less than that required to break the unsewn fabric. The ASTM 1683-04 seam strength standard is worth emphasizing due to its accuracy and ease in processing measurements. Hence, this method is widely used by the apparel industry for the evaluation of seam strength worldwide. 
2)        Seam Efficiency: measures the durability along the seam line which is identified as the necessary to satisfactory seam’s functional performance and efficient seam are assumed to be more durable than weak ones. The ASTM 1683-04 method provides an accurate measure of seam efficiency and thus is widely accepted. 
1)        Seam Slippage: Any movement of the warp and weft yarns away from a seam line under transverse stresses exacerbates the potential slippage. The ASTM 1683-04 standard has suggested a measuring of it where the force required for slippage of 0.6 mm of seam has been determined. 
2)        Seam Elongation: It is defined as ratio of the extended length after loading to original length of the seam. The evaluation of seam elongation from ASTM is well accepted by the apparel industry. 
3)        Seam Damage: refers to needle cutting or yarn severance in the fabric during sewing. This is unaccepted in any apparel because it may result in reduced seam strength and poor appearance.

1)        Seam puckering: it can occur due to excess fabric and not enough thread in the seam. There are different methods that are the international standard, laser scanner, seam length and thickness strain methods. It depends in sewing thread properties, stitch length thread tension, sewing speed, and pressure of pressure foot, needle size and the fabric’s properties.
2)        Skipped stitches: This defect occurs due to incorrect machine timing or needle choice related to fabric  type as well as applying bad tension.
3)        Grinning: The reason of such a problem is loose tension or incorrect stitch choice as the tightest lock stitch, the fewer grins we get.

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