Limitations of the CAD-CAM System in the Process of Weaving

1.1 Deviation of the virtual image pattern dimensions on the screen compared to the pattern dimension in produced woven fabric

Making jacquard fabrics is not only an extremely complex, demanding, and expensive process but also a major challenge in creating patterns of unlimited possibilities in color combinations, weaves, yarn fineness, and the warp and the weft densities – to get a certain pattern on the fabric. The CAD/CAM systems in weaving technology enable the designer to create inexhaustible creations in a short time, making the weaving easier, faster, more economical and ensuring better production. This weaving system represents a firm synergy of preparation for weaving and fabric design, modern electronic weaving machines, and warp and weft compositions. CAD systems facilitate and accelerate the preparation and design of future woven fabrics. Their advantage is that it is possible to see the appearance of the fabric in a very short time and adjust all the parameters required to make the sample. On the basis of the parameters taken from the database (weave, densities, thread thickness, colors, etc.) and their combinations, the desired fabric virtual simulation can be very easily obtained. CAM systems allow quick set up of the machine, data storage, and databases archiving that are essential for weaving preparation and permanent optimization of the production. Some of the software solutions for woven fabric design and computer-supported woven fabric production management are EAT, NedGraphics, Arachne, ScotWeave, Design Dobby, Pointcarre Weave Design, and others.

Woven fabrics with jacquard patterns can have different types of weaves per pattern (effect), different colors of warp and weft, and different raw materials. Each pattern is made up of several effects that differ in at least one of the specified parameters. To make the better-highlighted effects, they often have their weaves, so, in that effect, the warp and weft are interlacing differently, which means they also have different crimp and consequently different shrinkage. This phenomenon does not have to create a problem in the weaving process, but the fabric relaxation, after removal from the machine, is shrinkage in the direction of the warp and the weft, which can lead to additive effects on the woven surface. The consequence of this is the change of dimension by effect, and by pattern. Differences in pattern dimensions are also influenced by other parameters such as tension of the warp and the weft threads during the weaving process, deviations in warp and weft density, and fineness of the warp and the weft threads and even in the colors. After yarn dyeing in different colors, the difference in the thickness of the yarn may occur, although these differences do not have to be noticeable in yarn fineness. In the experimental part of this article, the differences in the thickness of the yarn after dyeing and their impact on the width of the stripes in the fabric will be determined.

1.2 Distinction in the color shades of the virtual image on the screen compared to the woven fabric

When designing a woven fabric sample, the fabric parameters will be selected to get closer as much as possible to the original or preferred fabric appearance. The color catalog and their shades allow the selection of the color that will be approximately equal to the desired sample. As the color catalog is bigger, it is more likely to get the desired design. The evolution of jacquard textiles and accompanying technologies has led to more diverse design solutions and to the ability of production of more complex fabric structures that are most often highlighted in different colors. The traditional structural method remained relatively unchanged, though the jacquard computer applications had significantly increased design efficiency and contributed to innovations in design solutions.

The fabric pattern shown on the screen is very difficult to transfer to the fabric, when, at the same time, designing the fabric is more easily facilitated by using computer technology. Despite the modernization and automation of yarn dyeing machines, color recipe preparation, and drying, there are possible variances in yarn coloration that result from the characteristics of the fibers (their hydrophobicity and hydrophilicity) and the yarn (twist number and direction of twists, yarn tension at dyeing). The appearance of the fabric can deviate from the desired design, despite the well-adjusted color shade for the following reasons:

1. the yarn angle at the weaving point which is under the influence of stiffness and tension of the yarn (higher tension of one thread system enables the greater crimp of the other one allowing the larger bending in weave points and consequently greater visibility on the front side of the fabric)

2. weaves and their various geometries caused by different ways of thread interlacing and floating, for example, diagonal stripes direction at twill fabrics

3. warp and weft densities, or their ratio that affects the difference in coloration of the effect (higher density gives a more intense effect on the front side of the fabric, especially at the flotation places)

Deviations in color shadings per effects on the computer screen compared to the produced fabric can also be the result of a subjective assessment.

3.1 Woven sample pattern deviations

Uneven width of the fabric strips, as well as changes in dimensions on the tested fabric patterns and their individual surfaces that depict individual effects, is not a big problem if fabrics are intended for table or linen woven fabrics. If the fabrics with defects are intended for garments (jackets, dresses, coats, blouses, etc.), then these faults will be noted at the joining points of the cutting parts, where the fit of the specimens is a necessity. However, for the aforementioned clothing items, multicolored and jacquard fabrics are preferred, and these problems are still present in the textile industry.

The shade variability along the fabric length, caused by unevenly dyed cross-wound yarn bobbins or warp beams, where the color shade is gradually changing over the length of the fabric, is not a big problem if the cutting parts are joined from the same layer. Joining of the cutting parts that are not from the same layer of fabric, this defect can occur (Figure 6). In addition, comparing the garments sewn from the upper, middle, and lower layers, it is very likely that the difference in color shades will occur.

Weft distortion is a common defect that can only be observed in multicolored and checkered woven fabrics. Weft distortion may have different shapes, and the most common is bow-shaped distortion extending over the fabric width (Figure 7). The highest distortion intensity of all samples is on the edges of the fabric while in the central part of the fabric weft maintains a relatively straight and at the 90° angle in relation to the warp.

Sample A with the transverse stripes has the slightest degree weft distortion, while the ample with the one color weft (dark blue) has the highest degree of weft distortion. Although fabric samples were made from the same warp, on the same weaving machine and in the same weave, there is a difference not only in the samples width and thread densities but also in the weft distortion amount. Since the samples differ only in terms of design, color, and color scheme, it can be argued that these parameters influence weft distortion degree.

For striped and checkered fabric with the distorted weft, intended for garments, it is not possible to match the lines at the joining places (Figure 6). This problem can be alleviated through the process of weaving and chemical finishing, in a cutting room by making a cutting plan with larger waste, and by carefully combining cutting parts from the same layer. Subsequent adjustment of distorted weft is possible in the chemical finishing processes by passing the fabric over the rollers of specific geometry. In places where the roll perimeter is larger, the fabric is more elongated as compared to the smaller one. Consequently, there may be a gradual increase in the distance between the lines at striped woven fabric leading to a new, sewing problem (Figure 6).