Seam Appearance Research Articles

Single-sided laser beam welding of a dissimilar AA2024–AA7050 T-joint

Abstract In the aircraft industry double-sided laser beam welding of skin–stringer joints is an approved method for producing defect-free welds. But due to limited accessibility – as for the welding of skin–clip joints – the applicability of this method is limited. Therefore single-sided laser beam welding of T-joints becomes necessary. This also implies a reduction of the manufacturing effort. However, the main obstacle for the use of single-sided welding of T-joints is the occurrence of weld defects. An additional complexity represents the combination of dissimilar and hard-to-weld aluminium alloys – like Al–Cu and Al–Zn alloys. These alloys offer a high strength-to-density ratio, but are also associated with distinct weldability problems especially for fusion welding techniques like laser beam welding. The present study demonstrates how to overcome the weldability problems during single-sided laser beam welding of a dissimilar T-joint made of AA2024 and AA7050. For this purpose a high-power fibre laser with a large beam diameter is used. Important welding parameters are identified and adjusted for achieving defect-free welds. The obtained joints are compared to double-sided welded joints made of typical aircraft aluminium alloys. In this regard single-sided welded joints showed the expected differing weld seam appearance, but comparable mechanical properties.

Effects of welding parameters on weld geometry during high-power laser welding of thick plate

During high-power deep-penetration laser welding of thick plate, the geometrical characteristics of weld cross section were investigated under different welding conditions. The molten metal behaviors were observed by using the high-speed camera and X-ray imaging system to study the formation mechanism of weld cross section. With the increase of welding speed, the width and depth of weld seam decreased, and the geometry of weld cross section changed from big-head shape to needle-like shape. The change of focal position of laser beam led to the variation of molten metal behavior which thus resulted in different geometries of weld cross sections during laser welding. The accumulation of high-temperature molten metal at both the top surface of molten pool and the middle depth of molten pool could lead to a higher heat-transferring efficiency of the molten metal which could lead to a wider weld width. The stable molten metal behavior on the molten pool surface resulted in a low heat-transferring efficiency, and the sound appearance of weld seam could be obtained when the focal position was inside the metal.

The sewability of lightweight fabrics using X-feed mechanism

The drop-feed mechanism in sewing machines is universally used for apparel manufacturing, and is also one of the common reasons for ply slippage. Typical Corporation, China, had invented a new feed mechanism called X-feed. To explore the efficacy of X-feed mechanism in controlling ply slippage and seam appearance in lightweight fabrics, an experiment was conducted covering all possible seam types achievable in garment manufacturing. Four different lightweight fabrics in six different pattern shapes are sewn in 10 different combinations of superimposed seam using both drop-feed and X-feed sewing machines. Except feed mechanism, all other parameters that may affect ply slippage and seam appearance were kept constant. The X-feed mechanism resulted in a flatter seam appearance with an average of 4.3 pucker rating in comparison to 3.8 of drop feed, lesser amount of ply slippage at 1.24% to drop feed's 3.08% and lesser occurrence of ply slippage at 24.34% to drop feed's 60.18%.

Effect of Some Fabric and Sewing Conditions on Apparel Seam Characteristics

Many previous studies showed that seam appearance as well as performance depends on the interrelationship of fabrics, threads, and the stitch/seam selection and lastly on the sewing conditions, which include the needle size, needle thread tension, stitch density, and the appropriate operation and maintenance of the sewing machine. Present investigation elucidates the effect of blend composition, sewing thread size, and sewing needle parameters on garment seam characteristics (i.e., seam strength, seam strength efficiency, seam puckering, seam stiffness, and drape coefficient). The seam quality characterization is studied through the L9 orthogonal design methodology. In good quality apparels, compatibility of the seams with the functional requirement is very important for serviceability and life of the apparel. Reversibility as well as repairing of seams in the apparel is very limited in the condition of seam failure. Seam strength efficiency is higher for the uniform fiber matrix in the structure of fabrics. The polyester dominated suiting fabrics give minimum seam stiffness because polyester component has low flexural rigidity. The cotton dominated suiting fabrics have less seam puckering due to increase in fabric stiffness.

Cuantificación de la contaminación del gas de protección en procesos de soldadura con arco eléctrico por medio de mediciones de oxígeno en la superficie del material base

The method presented in this paper is based on the measurement of oxygen on the surface of the base metal to enable a quantitative assessment of the contamination in the shielding gas. The gas used in arc processes affected arc properties and simultaneously protected the welding pool. The contamination of the shielding gases, e.g. with atmospheric air, damages the properties of the weld joint. The contamination in the shielding gas is not only dependent on the purity of the utilized gas, but also on the components of the welding torch. The level of contamination in the gas produced by the torch had been analyzed so far only by empirical evaluation of the quality and appearance of the welding seam. The measurement of oxygen on the surface of the base metal is a simple and accurate method to analyze the level of contamination in the shielding gas. This method allows a quantitative assessment even in the presence of the arc. This work shows the possibilities of using this method for the development and analysis of arc welding processes using the example of TIG and MIG / MAG torches.

Seam Quality: Experimental and Modelling Works using the Structural Equation Methodology

Seam quality in terms ofappearance and strength were investigatedfor very light weight fabrics (weight less than 80 g m"). Seams were constructed with different sewing parameters, which included types ofthread, stitch densities and needle size. Before constructing the seam for appearance and strength evaluation the mechanical properties of all fabrics were determined. The mechanical properties of 48 fabrics were determined using the Kawabata Evaluation System (KES-F), the Fabric Assurance Simple Test (FAST) and an Instron Tensile Tester. Evaluation ofseam quality was performed with respect to all the sewingparameters and the seams were ranked accordingly. The same evaluation ranking for seam appearance and strength was used for further analysis using Structural Equation Modelling (SEM) under AMOS. SEM was used to establish the relationship between seam quality with respect to appearance andstrength, andfabric mechanical properties. SEM was adopted to perform confirmative analysis to identify the fabrics mechanical properties that influence seam quality. From the experimental work, it was established that seams constructed with 100 % spun polyester thread with a ticket number of75gave the best ranking in terms ofseam strength. This threadperformedat optimum values when used with 6.5 stitches per centimetre (spcm) with a Metric needle size (Nm) of 90. For seam appearance, 100 % spun polyester with a ticket number of120 and Metric needle size of80 gave the best ranking. SEM established that extensibility and shear were the main fabric mechanical properties that determine seam quality ofvery light weight fabrics.

Seam Quality: Experimental and Modelling Works using the Structural Equation Methodology

Seam quality in terms of appearance and strength were investigated for very light weight fabrics (weight less than 80 g m-1;. Seams were constructed with different sewing parameters, which included types of thread, stitch densities and needle size. Before constructing the seam for appearance and strength evaluation the mechanical properties of all fabrics were determined. The mechanical properties of 48 fabrics were determined using the Kawabata Evaluation System (KES-F), the Fabric Assurance Simple Test (FAST) and an lnstron Tensile Tester. Evaluation of seam quality was performed with respect to all the sewing parameters and the seams were ranked accordingly. The same evaluation ranking for seam appearance and strength was used for further analysis using Structural Equation Modelling (SEM) under AMOS. SEM was used to establish the relationship between seam quality with respect to appearance and strength, and fabric mechanical properties. SEM was adopted to perform confirmative analysis to identify the fabrics mechanical properties that influence seam quality. From the experimental work, it was established that seams constructed with I 00 % spun polyester thread with a ticket number of 75 gave the best ranking in terms of seam strength. This thread performed at optimum values when used with 6.5 stitches per centimetre (spcm) with a Metric needle size (Nm) of 90. For seam appearance, I 00 % spun polyester with a ticket number of 120 and Metric needle size of 80 gave the best ranking. SEM established that extensibility and shear were the main fabric mechanical properties that determine seam quality of very light weight fabrics.

Relationship between the Stitch Size and the Seam Opening Evaluation of Function and Appearance of Seams of Sewn Fabrics for Japanese Style Clothes (Part 2)

Relationship between the Stitch Size and the Seam Opening Evaluation of Function and Appearance of Seams of Sewn Fabrics for Japanese Style Clothes (Part 2)

Evaluation of Function and Appearance of Seams of Sewn Fabrics for Japanese Style Clothes (Part 1)

Evaluation of Function and Appearance of Seams of Sewn Fabrics for Japanese Style Clothes (Part 1)

Fusion-brazing Joining for Dissimilar Metals Between 5A02 Aluminium Alloy and Zinc-coated Steel Based on Laser-MIG Hybrid Welding

High efficiency and quality fusion-brazing joining between 5A02 aluminium alloy and zinc-coated steel sheet, based on laser-MIG hybrid welding, is successfully done. The seam appearance and the mechanical properties as well as the microstructures of the joints are analyzed. The results indicate that a high speed fusion-brazing joining can be achieved with this welding method, and the highest welding speed is up to 5 m/min. A brazed joint between the aluminium alloy and the steel is formed, and the steel sheet under the seam is not melted. The top tensile strength of the joint is 153.1 MPa, about 75.7% of that of the aluminium alloy base metal. It is almost as high as that of the aluminium alloy’s fusion joint. In tensile test, the specimen fracture is in the heat-affected zone of aluminium aside. It can be sure that the main fracture form of the joint is ductile fracture, but has the trace of brittle fracture. The analysis on the microstructure of joint shows that a thin intermetallic compound layer is generated on the brazing interface, but its average thickness is only about 1.51 μm. It’s confirmed that the compound layer is composed of Fe3Al, FeAl2, Fe2Al5 and FeAl3, and the zone of these intermetallic compounds abounds in silicon.

Predicting Seam Appearance Quality

The appearance of a garment is affected by the quality of the fabrics used in its manufacture, as well as a number of factors determined by the technology of the garment manufacturing process. Since fabric quality, as the most important element of garment appearance, is determined by its mechanical properties, it is obvious that these properties directly impact fabric processing properties. It can be seen through various forms of fabric behavior under the loads that occur in sewing. Investigations of the correlations of the stress and fabric behavior are aimed at constructing a system to predict fabric behavior in garment manufacturing processes, as well as to predict the appearance of the garment to be manufactured. The investigation presented here deals with the impact of fabric mechanical properties on the quality of seam appearance, as defined by seam puckering and work-piece flotation. Machine learning methods included in the Orange software package were used to establish the importance of mechanical properties with respect to fabric behavior.

Determination of the sewing thread friction coefficient

The quality of sewing threads, as defined by their mechanical and physical properties, is connected with seam quality and seam strength. Seam quality and seam appearance depend mainly on the following sewing thread properties: bending properties, dimensional stability, thread twist and twist direction, fineness, regularity and surface properties on used fibres. The friction on the guide elements of the sewing machine depends on the surface treatment of the thread and affects the tensile force during the stitch formation process. It is important therefore, to know the friction coefficient when choosing the appropriate sewing thread. This contribution presents the influence of the sewing thread movement velocity over the guide element, the influence of the contact angle between the thread and guide element and the influence of the guide element material on the friction coefficient. The results of the research show that on increasing the thread velocity over the guide element, the friction coefficient slightly increases, whilst with the increase of the contact angle between the thread and guide element, the friction force exceedingly decreases. Furthermore, the results show that the friction coefficients using the steel guide are lower when compared with the ceramic guide. The behaviour of the sewing thread during the sewing process, can be concluded, based on these statements.

Chemically induced grain boundary dynamics, forced motion by curvature, and the appearance of double seams

The free boundary model of diffusion-induced grain boundary motion derived in Cahn et al. [3], Fife et al. [6] and Cahn & Penrose [4] is extended, in the case of thin metallic films, to account for bidirectional motion, together with the appearance of S-shapes and double seam configurations. These are often observed in the laboratory. Computer simulations based on the extended model are given to illustrate these and other features of bidirectional motion. More generally, the extension accounts for the motion of grain boundaries whose traces on the film's surface are curved. The new free boundary model is one of forced motion by curvature, the forcing term possibly changing sign due to the bidirectionality. The thin film model is derived systematically under explicit assumptions, and an adjustment for grooving is included.

Influence of Sewing Conditions on the Appearance of Blind Stitch Seams.

The relation between the appearance of blind stitch seams and sewing conditions was examined. The seam appearance was evaluated by sensory tests. Under the conditions that the height of ridge forming disc was low with loose thread tension, the seams had good appearance. It was shown that the conditions that the stitches begin to appear on the right side of seam correspond to the boundary between positive and negative levels of the average preference of seam appearance. From the result of the discriminant analysis, all of the factors affecting on seam appearance, important ones were the height of ridge forming disc and fabric thickness. As for SMD obtained from KES system, the stitches in seams tended to appear with the increase in SMD value but it was not always conspicuous actually. By the result of the principal component analysis for sewing fabric, it was deduced that the first principal component stands for fabric volume and the second one, the roughness of the fabric structure. From the viewpoint of blind stitch sewing, the first principal component was considered to be connected with the fabric characteristics to blind the stitches on the right side of seam and the second one, visual inconspicuousness of existing stitches. Using the plots of the first and the second principal scores, information on sewing condition for fabric can be obtained easily.

Study of the tensile force of thread in relation to its pre‐tension

The perfect interlacing of needle and bobbin thread in the stitch formation process and seam appearance depends first of all on correct pre‐tension of the tension regulator. Changes in the pre‐tension settings also have a direct influence on the tensile force during the sewing process. This contribution presents the influence of pre‐tension in a defined area on the tensile force in important phases of the stitch formation process. In addition the influence of the stitch velocity on tensile force was investigated. On the basis of statistic analysis it was ascertained in which pre‐tension area and stitch velocity the significant differences between tensile forces occurred.

The impact of tectonic deformation upon coal seams in the South Wales coalfield, UK

Observations on the nature and appearance of coal seams, which were deformed during the late Carboniferous Variscan orogeny, have been made over several years within a number of opencast coal sites located across the South Wales coalfield. The deformation of coal seams was dominated by brittle failure and subsequent movement along fracture planes. Examination of hand specimens and smaller-scale samples using a scanning electron microscope reveals the presence of two distinct types of small-scale, tectonic fracture markings within deformed coals. Striated fracture surfaces with prominent ridges and grooves can bear a superficial resemblance to shatter cones in appearance but are unique to coal in their tectonic setting and appear to have formed by static shear failure, whereas strongly polished fracture surfaces result from movement across fracture planes. Deformed coal seams are also affected by distinctive, large-scale, tectonic fracture sets. The extent of fracturing within coal seams can be assessed using different techniques including measuring fracture frequency directly, performing various strength and hardness tests, making relatively simple subjective assessments on the appearance of the coal or monitoring the size distribution of the coal product. By applying some of these methods within working opencast sites, it can be shown that large amounts of abnormally fractured coal were formed along coal-based thrust flats or detachments but that the distribution of fractured coal along detached seams is rarely homogeneous. Enhanced fracturing often occurred in association with the localised thickening of seams along small-scale thrusts or within coal duplexes. Variable seam thicknesses and pockets of structurally thickened coal are seen as the most efficient means by which the presence and location of significant amounts of fractured coal can be predicted from borehole evidence during prospecting.

The Performance of Sewing Threads with Respect to Seam Appearance

This paper reports an experimental investigation into the effect of the physical and mechanical properties of sewing threads on the seam appearance of lightweight fabrics, which are prone to seam pucker. In this work, a range of forty-two commercial sewing threads of various ticket numbers, yarn structures, and from various suppliers were used, and their performance ranked according to the appearance of the seams after sewing. Based on a statistical analysis, the important physical and mechanical properties of sewing threads related to seam appearance were identified and a quantitative relationship between these properties and the performance rankings of sewing threads in terms of seam appearance was established. A parameter, called ‘Sewing Thread Pucker Index’, which incorporates those properties of sewing threads which are important with respect to seam appearance, is proposed to provide an objective measure of performance.

Progress in NC Stitching Machines: Improving Shoe Seam Appearance

In recent years NC controlled lock‐stitch sewing machines operating on shoe upper sub‐assemblies held in flat pallets have become well‐established in shoemaking businesses. However, a major problem for manufacturers of high‐quality footwear is that such machines are subject to malformation of the lockstitch when the pallet moves in certain directions with respect to the sewing head. The stitch malformation, known as half‐hitching, results in seams which have an inconsistent and unsightly appearance. Examines the reasons for half‐hitching and strategies for its prevention. One approach involves rotating the stitching head about a vertical axis so that the direction of sewing is always maintained at a tangent to the seam. Systems such as this have been proposed in the past but have been prohibitively complicated and cumbersome. Introduces a stitching machine concept which enables a much simpler demonstration rotating head stitching machine to be built. It is expected that industrially‐developed units using the principle illustrated will find widespread use in the shoemaking industry. They will be relevant not only in conventional pallet loaded NC stitching machines, but also in a new generation of palletless machines.

Seams of Different Ply Properties. Part II: Seam Strength

In the first part of this series, the effects of differences in ply properties and of the mean properties of the plies on seam appearance were examined and discussed. The present part is concerned with the effects of the same factors on seam strength; it also discusses factors affecting fabric strength along different bias angles.

Seams of Different Ply Properties. Part I: Seam Appearance

This paper presents the results of experiments on seams sewn under constant sewing conditions when the mechanical properties of the plies are different. By using plies of the same fabric along different directions, the effects of the mean properties of the plies as well as their incompatibility are studied, while the other two important factors, the fabric thickness and the compressive modulus, are kept unchanged. The extensibility and strength of such seams will be studied in the second part of this series.