DesignandCADInnovationinWovenTextileResearch

Design and CAD Innovation in Woven Textile ResearchJulie A SodenSchool of Art and DesignUniversity of Ulster at BelfastYork StreetBelfast BT15 1EDBiographical NotesThe author graduated in 1991 and moved directly into research where she spent seven years with The Engineering Composites Research Centre at the University of Ulster researching and developing the design and fabrication of 3D reinforced woven fabrics in high performance fibres. Findings from this research have been published on a national and international scale. She is currently completing her DPhil thesis for submission this year and has recently been appointed as Lecturer in Constructed Textiles at the University of Ulster within the School of Art and Design where she is building the research profile of the woven textiles area.AbstractThis paper reports the ongoing developments in woven textile research at the University of Ulster. The research described forms the textile part of a multidisciplinary team developing carbon fibre reinforced composites. It describes an area of research that focuses on using woven textiles in a science and engineering environment, rather than in an art and design environment. The practice of combining art and science-based processes is a current trend running through textiles. Engineers and scientists have realised that woven textiles with reinforcement built into the longitudinal, transverse and thickness axes, offer a strong, lightweight and mouldable material that can be manufactured with specific strength requirements using high performance fibres. These qualities have enabled it to compete as an alternative material to metals used presently, particularly in aerospace and automotive industries. This paper describes recent CAD technology developed and utilised for the design and manufacture of specific engineering preforms, and details the 3D woven fabric architectures used. It focuses on how the conventional textile process of weaving has the potential to facilitate the production of 3D reinforced flat and shaped woven structures with load-bearing properties suitable for use in cross-discipline areas such as engineering, aerospace and biomedical applications. The paper also indicates that research within technical textile design is an exciting and innovative pathway open to textile graduates. It offers an opportunity to work at the leading edge of research in a cross-discipline environment and encourages a more informed designer equipped with good technical understanding and a variety of transferable skills. IntroductionComplex woven textiles have many versatile characteristics that have enabled them to infiltrate industries such as engineering, aerospace, automotive, biomedical, leisure and even Art and Design applications. Primarily they were introduced in high performance fibres such as carbon and glass as an alternative to traditional metal structures. They offer a light yet strong, drapable and mouldable textile where reinforcement could be tailored to meet mechanical requirements in specific regions. Their potential for cost-effective processing and waste reduction made them attractive especially in the aerospace industry 1. Many research programmes have developed a substantial array of 3D reinforced weave architectures that can only be produced on specialist machines 2,3. However, only selective structures such as the angle interlock architectures have been widely used 4. At the University of Ulster, the aim of this particular research programme was to investigate and develop the versatility of the conventional weaving machine and commercially available CAD software to produce 3D reinforced woven preforms in carbon fibre. Rigid parameters based on maintaining conventional elements within the machinery were enforced, so any new technological developments were required in a compatible format which could be readily transferred for exploitation and development by the textile industry with a view to mass production. This paper overviews the rationale behind the design methodology, the shortcomings of conventional machinery and innovative CAD developments undertaken in order to produce complex 3D shaped structures. The invention of a specialist CAD program specifically for 3D preforms forms an inherent part of a more recent research programme which is developing a computer based system for the design, manufacture modelling and analysis of 3D woven composites 5. Loom TechnologyDobby and Jacquard weaving are the two methods of cloth forming that have been utilised for the design and production of 3D reinforced preforms. The suitability of Dobby woven textile preforms for reinforced composites was investigated by McLaughlin 6 and Harper 7 where a range of multilayer shaped fabrics were produced in cotton and glass fibre yarns using a 24 shaft Dobby handloom. The production of a diverse range of constructions including T-Sections, I-beams, and locally reinforced fabrics, demonstrated that these structures could be replicated on a larger scale, in different fibres with the potential for mass production. Limitations of the Dobby handloom, the drawbacks associated with an unautomated design system and other related production difficulties indicated the need for more advanced technology and design tools. This necessitated the introduction of the electronically controlled Jacquard power loom and textile design system Scotweave 8. The transfer from Dobby to Jacquard design and loom technology facilitated the fabrication of a diverse range of flat and shaped preforms in more complex configurations with new technical and design attributes 9. CAD design packages such as Scotweave are essential tools for the design and production of apparel, interior and a limited range of technical fabrics. The variety and complexity of CAD programs available is immense, however programs suited for the design and production of multilayer weaves are more specialised and less common. Usually most design and weave packages are limited to accommodating a maximum of three layer (triple cloth) designs. Multilayer designs would normally contain a minimum of 4 warp and 4 weft layers and could potentially consist of up to 12 warp and 12 weft layers. The only feasible way to create such a fabric on a standard system such as Scotweave was to approach the design as if it were a single layer fabric. This enables the generation of a correct liftplan but prevents a realistic view of the fabric appearance.When a fabric is designed, a visualisation, representing the lay out of the coloured threads, gives an impression of the fabric surface once an interlacement sequence or weave structure is added. This process becomes complicated with the introduction of multiple layers, and the designer not only needs to view the surface of the fabric or a plan view, but also a cross-sectional view of each thread to understand how the layers are connected in the thickness direction. The limitations and restrictions of a standard design package could not accommodate these complex multilayer designs and as a result, a unique program was developed which would encompass all the many aspects of multilayer fabric design and manufacture.The development, in-house of a specialist CAD program for the design, manufacture and analysis of 3D reinforced woven preforms provided a unique insight into the design process. The system is based on designing the reinforcement architecture in multiple groups which when combined, form the complete 3D structure. The design and specification of the program ensured the format required to form 3D fabrics on a standard loom was compatible with conventional practice. All the processes combined continue to enhance the cost-efficiency of 3D multilayer reinforcement manufacture.The CAD Design SystemThe cross-sectional design program is a fundamental design tool and facility that amalgamates the collective interests of a multi-disciplinary group researching the many facets of textile composites. Primarily designed as a textile program, it facilitated the design rationale and methodology employed to produce a diverse range of flat and complex shaped reinforcements in a variety of weave architectures 5. The system automated the complex design methodology of 3D woven composite reinforcements. It provided an interface to Scotweave to combine all design data with loom control data, thus enabling preform manufacture on a conventional loom; thereby formulating links between computer-aided-design (CAD) and computer-aided-manufacturing (CAM). The program also generated the output of data, in an agreed file format, compatible with a modelling and structural analysis software package. The textile preform visualisation part of the program needed to be comprehensible to all disciplines working in the fibre reinforced composite field, to enable each to understand the structure of the basic composite component - the 3D fibre preform. The program and data generated has evolved into the foundation for a knowledge based system for fibre reinforced composites. Other researchers have developed computer based systems for the design, manufacture and analysis of textile composites. Three-dimensional geometric modelling systems for woven, braided and hybrid textile composites have been developed at NASA Langley Research Centre by Naik 10, who developed TEXCAD (Textile Composite Analysis for Design), and by The Computational Textile Composites Group 11, at Philadelphia School of Textiles and Materials Technology. System RequirementsA system was developed by using a cross-sectional schematic of a multilayer weave architecture as the anchor feature to unite the design, manufacture and analysis disciplines.The program would permit flexible design creation without restrictions to enable it to: Facilitate different numbers of warp and weft layers within and between cross-sectional groups (a group is defined as a section containing a proportion of yarns in the overall design repeat) Facilitate structures with varying ends per layer within and between cross-sectional groups. Ability to combine groups to provide a schematic of the repeating unit cell ie, repeat across the fabric width and along the fabric length. Automatic generation of a weave liftplan and denting sequence. Printing output of groups and other design information. Program outputs to modelling and analysis with the generation of relevant data Design Approach The system produces cross-sectional designs across the weft as warp interlinking is the interlacing method most utilised on conventional looms and can therefore be more easily adapted to commercial applications. The program uses the monitor screen as a template so that warp and weft yarns can be displayed, manipulated into basic layer assemblages and allocated interlacement sequences to build up a group. The weave pattern used has some influence on the group size. This is often determined by the number of threads comprising the weave repeat within each layer, and the denting arrangement of the design. If a combination of weave structures is used, then the number of groups required depends on the lowest common multiple of all the repeats.Individual yarns can be activated, repeats assigned and colours allocated for visualisation purposes. Figure 1 displays the main design screen showing warp and weft yarns assembled into a group (centre) with the automatically generated liftplan (right). Also displayed is the group denting sequence, user icons, warp “stations“ (left) and colour palette.Figure1: XS Program Main Design Screen Once a group has been completed, it can be saved and the next group created. The program provides a cyclic facility that enables the user to view all the groups within the repeat sequentially across the width of the fabric. The user can therefore visualise the distribution and position of interlinking and binding points between groups. Figure 2: Example of a XS Group of a 6 Layer FabricAccommodating changes to the number of warp and weft layers between groups and options to delete individual or whole rows of weft picks enabled the program to facilitate complex preforming developments in the form of locally reinforced fabrics, tapered fabrics and a range of near-net shaped fabrics. Warp yarns can also be deleted, or if only weaving intermittently, can float on either top or bottom surface and will be trimmed after manufacture.The program format permits the retention of equal numbers of warp and weft threads between groups, or has the option to build an alternative configuration if different numbers of warp threads are required between groups. With these additional features, the program format is therefore capable of accommodating the variety of weave architectures necessary for complex 3D preforming.DentingThe yarns within a cross-section can normally be classified into specific yarn roles depending on their interlinking characteristics. These are inplane interlacers, inplane stuffers and through-the-thickness interlinking yarns. Inplane interlacers remain in their layer of origin at all times, following a designated interlacing weave pattern. Stuffers are straight uncrimped yarns that lie in their layer of origin and do not partake in any interlacing. Through-the-thickness yarns contribute to the (Z)-axis proportion by forming connections to other layers that penetrate a proportion of, or the total fabric thickness. The number of through-the-thickness interlinks possible is therefore dependent on, and restricted by the type of weave pattern used. For specific architectures (orthogonal type weaves), a denting rule was applied where through-the-thickness yarns required their own dent thus preventing unnecessary fibre damage during shedding, and inplane interlacers and stuffers could share a dent. In the program, the denting of groups finalises the position and sequence of warp yarns across the width of the fabric, and the final arrangement is translated into the liftplan for use within the Scotweave Design program to link with loom configuration data.The Unit Cell Repeat in Warp and Weft Directions The unit cell repeat is the fundamental unit for creating a complete cross-sectional file. The program builds up a unit cell repeat that represents all yarn paths required to form a particular fabric architecture. It contains the specified repeat sizes along the fabric length and across the fabric width of individual warp threads in each group. The unit cell or total repeat can then be multiplied to form the dimensions of the complete preform or the unit cell itself can form the entire preform.Figure 3 displays separate warp groups (or cross-sectional slices) that form part of a typical unit cell repeat. The first and third groups have an identical weave structure combining a 3/1 twill with warp stuffers, and the centre group is arranged in a plain weave pattern with the outer layers penetrating a larger proportion of the thickness than the inner layers. Since a 3/1 twill pattern is used, the unit cell repeat will require a total of four groups to represent the twill pattern, and two groups to represent the plain weave pattern. Twill groups interlink in the through-the-thickness direction once every 4 picks in comparison with alternate picks in the plain weave group.Figure 3: Example of 3 Groups That Form Part of a Unit Cell RepeatProgram Outputs to CAM and Output of XS Schematic and Design InformationAn interface to SCOTWEAVE has been produced which combines design data created in the program with the Jacquard loom configuration data. This information is transferred onto a floppy disk for automatic preform manufacture on the electronic Jacquard power loom. The direct link between computer-aided-design and computer-aided-manufacture provides a commercial approach and lends itself to further development in order to exploit the industrial potential for the production of 3D reinforced composite structures on conventional looms.Program Outputs to Modelling and Analysis The program also permits the creation of a data file, in text format, which can be read by the textile modelling and analysis software, thus providing structural data covering different weave architectures. The analysis file is created by reading each end from each dent in turn. The file provides a schematic layout of data for each warp and weft thread in the repeat of the structure and contains the intersection plan, yarn spacing and sett information. It provides the modelling software with the data required to generate mechanical performance analysis.3D Fabric ArchitecturesThe versatility of the system has permitted the creation of a diverse range of weave architectures for use in a variety of applications. Over time, sub-groups have been formed to catalogue structures according to the characteristics of their specific architectures. These divide preform designs into flat or shaped configurations and secondly by the interlinking architecture of the through-the-thickness yarns. The groups utilised most frequently are described below.Integrated structures are a diverse family of fabric architectures (often based on the plain, twill and satin weaves) where each layer interlaces in a specific weave pattern and through-the-thickness interlinks can be co-ordinated at interlacement points in the weave penetrating a proportion of the fabric thickness. In Figure 4, a 2/1 twill architecture is used and a through the thickness interlink is formed on every third pick, when the warp yarn interlaces under a weft yarn. In certain structures, all of the warp yarns form interlinks in the through-the-thickness direction and it is common for each layer to have an identical interlacement sequence. Other structures combine different weave patterns that inherently contain different crimp levels to facilitate the folding capability required for shaped component structures, such as T-sections and I-sections 11. The integrity, s