Technology of 3D Woven Domed Fabrics

1.Introduction

Textile material and products are increasingly used for technical applications. In some areas, textiles with 3D shapes are essential. Recent research has enabled an easily mountable add on devices for looms that makes it possible for the production of 3D domed fabrics and possibly fabrics with other 3D shapes. To evaluate the domed effect of the fabrics, a dome index is defined and approves as a valid measure. It is possible to measure the dome effect and also fabric mouldability.

Fabrics with double curvatures (dome shape) are necessary in certain technical and apparel applications. In manufacturing textile composites moulds are often used to achieve double curvatures where extra strain will inevitably be introduced into the reinforcement. Helmets for the military and riot police could be made with seamless fabrics with double curvature to improve protection and increase production efficiency. Other examples include bra cups in fashion and clothing, just to mention a few.

2.Review of earlier method

Cut and sew has been the commonly used method for producing dome shapes in the textile and clothing industry, but seams are big disadvantage in technical applications, where the continuity of fibres is destroyed. Seams definitely reduce the level of reinforcement and protection. Physically, seams in thicker materials cause major problems in items such as female body armor. In addition, cut and sew creates extra waste of material and labour. Another method of manufacturing fabrics with double curvature is moulding. Woven laminates moulded into double curvature shape leads to changes in the orientations of the fibre layers and the yarns, which leads to shear deformation, extension in the yarns, crimp loss, sliding of fibres, and local wrinkles. Obviously, these could be serious problems for technical applications. In order to make fabric more mouldable, elastic yarns are used for some applications such as car door linings, but using elastic yarns in such fabrics makes it difficult to form sharp concave corners.

Earlier efforts to make 3D domed fabrics required a high cost weaving machine, and hence the fabrics proved to be unnecessarily expensive. Recent developments have attempted to create an easy, economical way to make 3D domed woven fabrics. Also attempts have been made to develop methods to evaluate the domed effect and mouldability.

Technical aspects of 3D Domed fabrics

Patchy design

Recently dome forming has been done using a mixture of weaves with long and short float lengths, inspired by honeycomb weaves, which resulted in uneven fabrics. It was very interesting to observe what effect a patched design would have on the fabric surface. Figure 1 shows one of these patchy designs with different weaves for different parts in the design; the plain weave, the tightest, is arranged in the middle, and a five end satin, with the longest average float length and thus the loosest weave of the three types is used for the outer ring, The weave for the middle ring is a 2/2 twill. In fabrics with the same warp and weft densities, the plain patch tends to occupy a larger area and therefore will grow out of the fabric plane, the part of the fabric with the five end stain tends to be squeezed, thus enhancing the domed effect. Consequently, the height difference between the lower and higher planes forms a dome. These patches are then arranged across the width of the fabric in different formations to even out the warp tension. The ideal situation is to supply warp ends from a creel, in which case the tension for these ends is controlled individually.

The patchy design method has been moderately successful in forming the desired dome shapes in fabrics. This method is a quick, easy, and economical way to produce fabrics that require relatively small domed effects. However, it appears that for fabrics requiring larger domed effects, the patchy design method is difficult because it depends only on the combination of weaves. To create fabrics with more obvious domed effects, add on devices are required on the loom, which alters the take up rate across the width of the fabric.

Add on device

Increasing the take up rate obviously causes the cloth to move forward more quickly, which then decreases the weft density. Weaving under normal circumstances is a balanced process, i.e. the ratio of input to output of the weaving machine is constant. Different values for the ratios correspond to different weft densities. The weaving process is said to be balanced when equation 1 is satisfied:

Where S is the take up length of the fabric for e.g. one cycle of the loom operation. l is the let off length of the warp ends for the same period of the time, Δl is the extension of l due to warp tension, and α is the weaving angle of the fabric.

In normal weaving, every effort is made to ensure that the balance between the input and output of the loom is maintained, because any disturbance will strike the weaving process off balance, which will certainly cause variations in the fabrics weft density. In weaving abnormal fabrics such as domed fabrics, the balance will need to be disturbed to achieve the required effect by introducing interruptions from, for example, the take up and the let off. In making domed fabrics, it is necessary to divide the fabrics into a number of sections and to maintain each section in its own balance in a controlled way. This requires a method by which the fabric can be taken forward at different rates across these sections. In order to keep the ratios of input and output constant for these sections, it is necessary to deliver their warp ends separately, which requires a multi beam or, ideally, a creel for the warp supply.

A dome shaped profile facilitates variations in cloth take up, and there are three warp beams for the warp supply. The add on concept has been used to create the special take up device, since a loom that can weave domed fabrics should also be able to be used as an ordinary loom for ordinary fabrics. This obviously provides a convenient and economical solution for making domed fabrics.

The add on device is a combination of a roller, a profile chain that is engaged on the roller, and a frame holding the roller and chain. This frame can be easily mounted on and taken off the loom. The profile shape is spherical for this application, but it is flexible for changing the profile to other shapes for different application. Flexibility is one of the reasons for using a combination of roller and profile chain rather than a profiled roller.

Figure 2 shows the take'up systems after the add on device is mounted. Obviously, the device lengthens the fabric path before reaching the cloth roll. The main part of this add on device is the profile chain. The profile chain roller is designed in such a way that it rotates to provide the same liner speed, guaranteeing that there will be a stretching or slackening of the fabrics before they reach the cloth roll. The profile chain contains any profile of choice for making fabrics with different requirements. The profile used here produces hemispherical shapes.

To compensate for warp tension variations in weaving, three weaver's beams are used for the warp supply. The use of warp ends from the weaver's beams is roughly determined according to the dome location in fabric design. Figure 3 shows the relation between the warp supply and the dome location.

Designing of 3D domed fabrics

In technical textiles, a woven fabric may need to have many different structural features, such as the number of layers, weave types, and thread densities. A series of fabrics have been produced to investigate the ability to form 3D domed shapes. Single layer fabrics are designed using the plain, 2/2 twill, four end, and six end sateen. Double cloth, treble cloth, and angle interlock fabrics with two and three layers of weft yarns could also be designed and manufactured. Table 1 lists the warp and weft densities for the different fabrics. A cotton yarns of 66 tex has been used for both warp and weft in all fabrics.

Evaluation of dome effect

Two methods were used for the dome effect evaluation. The first, the dome index I, is defined by the change in weft density of the fabric:

Where Di is the weft density measured from the flat section of the fabric, and Dm is the weft density taken from the top of the dome. Because no extra weft yarns were added in the formation of the dome, the dome index l reflects the relative change in the weft density, and hence is a valid parameter to indicate the dome effect. Obviously, the higher the index, the more remarkable the dome effect. Note that the definition of the dome index uses only the weft density variation, not that for the warp density. This is because the warp ends are firmly held by the reed in weaving and do not vary much in the formation of domes.

The second method for measuring the dome effect uses a piece of test equipment known as the mouldability tester. It measures the dome depth or height under different loading conditions as an indicator of the dome effect, and can also measure fabric mouldability.

Dome index

Single layer dome fabrics

Studies have shown that the dome index and the designed weft density has a remarkable influence on dome formation. Since a lower weft density leads to better dome formability and vice versa. As already mentioned, dome formation is mainly caused by the uneven take up rate across the fabric and by the warp supply from a multiple beam let off system. With such an arrangement, it is the weft yarns, not the warp ends, that tend to be displaced and curved to form the dome. Apparently, a higher weft density would hinder and a lower weft density would help the displacement of weft yarns and hence the formation of the domes.

It has been found that the plain weave, which has the shortest average float length, marks dome formation most difficult. The six end sateen, with the longest average float length in the group, produces the highest dome index values. Dome formation causes relative movement between the warp and weft yarns, and it is common knowledge that a loose fabric allows more such movement than a tighter counterpart. Hence, fabrics with looser structures have a higher ability to form domes and vice versa.

Non - Single Layer Fabrics

The non- single layer fabrics in this context include double and treble cloths, each layer using the plain weave, and angle interlock structure with two and three weft layers. The number of fabric layers have a bearing on the dome index. For comparison purposes, results for the single layer fabrics made from the plain weave are also included. For fabrics with the same warp density and different weft densities, a higher number of fabrics layers will lead to lower dome index values. That is fabrics with more layers have lower dome formability.

For angle interlock fabrics, increasing the weft densities per weft layer reduces the dome index value; this is true for fabrics with both two and three weft layers. It also indicates that generally the more weft layers involved in the angle interlock fabrics, the smaller the dome index values. This is in general agreement with the results for multilayer fabrics.

Testing of dome depth

There are different ways of using the deformation tester to measure the dome depth. One method uses a metal probe weighing 188g to measure dome depth, the fabrics being firmly held by the ridge on the top ring and the groove at the bottom ring. This method tests the dome effect and also fabric mouldability. The second method, on the other hand, uses a very light plastic tube probe weighing 11.2g. In this case, a board with a hole of the same diameter as the rings is used between the two rings to support the fabric and to prevent the two rings from engaging. Due to the small weight of the probe, the reading for the measurement is purely the depth, and the fabric is not deformed by moulding.

Single layer fabrics

In the case of both above mentioned testing methods, the dome depth decreases as the weft density increases. This is true for all single layer fabrics with different weaves. Test results from the two methods for fabrics made from the 2/2 twill have shown that the dome depth measured by first method is always higher than measured by second method for obvious reasons.

For both test methods, the dome depth parameter generally increases as the average float length of the weave increases. This trend agrees with the dome index test results, in that looser fabrics are more dome formable in weaving.

Multi Layer Fabrics

For multilayer fabrics, the tests show that the higher numbers of the fabric layers result in low dome depth. For angle interlock fabrics, the weft density increase causes the dome depth to decrease. This is true for both methods 1 and 2.

Comparison of the dome index and dome depth

The correlation between the two evolution parameters for the plain woven single layer fabrics and for the multilayer fabrics has been compared. These correlations are highly significant, with confidence levels not less than 95%, and both evaluation methods are valid for measuring the dome effect. The dome index method can be used where the mouldability tester is not available, but the dome depth method is a much quicker way of getting results when there is a mouldability tester available.

Conclusion

This paper reviews the recent work on engineering, creating, and evaluating 3D dome shape woven fabrics. The new add on device created is an effective and economical way of making domed woven fabrics from single layer, multilayer, and angle interlock fabrics. Changes in the profiles can easily enable the loom to produce 3D fabrics with differently shaped double curvatures, and domed fabrics with many different fabric structural parameters have been successfully created. The recent method compares favorably to the shape weaving method, in that the add on device is quicker and more economical. Also, this new method does not rely on any specifically made looms.

Two evaluation methods for domed fabrics by use of the mouldability tester for measuring the dome effect have been briefly discussed. The dome index method depends on counting fabric densities, whereas the dome depth method uses the mouldability tester development here. The two methods agree well, and thus both are regarded as valid for the purpose.

References

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About the author:

N. Gokarneshan & P. Ramesh are in TIFAC CORE in Textile Technology, Kumaraguru College of Technology, Coimbatore 641 006. Email: advaitcbe@rediffmail.com