The use of thermoplastic components with a complex three-dimensional (3D) shape, manufactured efficiently with thermo-presses, has been increased steadily. Flat knitting technology using reinforcing hybrid yarns in the horizontal and vertical direction is especially suited for producing near-net-shape or fully-fashion multilayer weft knitted fabrics – MLGs (abbreviated from the German word Mehrlagengestrick, meaning multilayer weft knitted fabric). The other advantages of manufacturing such MLGs, using flat knitting technology, are reduced waste and desired reinforcing fibre alignment to obtain improved mechanical properties for high-performance applications. Before knitting 3D shaped MLGs, it is necessary to transfer the 3D component geometry into a suitable two-dimensional (2D) pattern cut by implementing parting lines. The use of computer-aided design (CAD) programs enables an effective development of complex components preforms. The generated 2D pattern cuts are analyzed with the consideration of net-shape preforming processes on V-bed flat knitting machines. The development of a segmented take-down system for effective production of 3D MLG preforms is also discussed.
In the shoe manufacturing sector, products are typically designed for a small number of sample sizes, whereas all other shoe sizes in the range (for example, 2 to 4 shoe sizes below and above) are scaled using grading methods. However, the grading process significantly affects the fit and thus consumer acceptance. In this context, the shoe last forms the basis for all additional components to be used, such as insoles, midsoles, outsoles and heels. The entire shaft construction is based on the last as well. It also determines the fit of shoes. However, a method once established in the 1930s and still used today for the grading of shoe lasts is limited to only two dimensions, i.e. last length and technical ball circumference. The entire last is enlarged or reduced on the basis of these dimensions. The 3D CAD systems available today still employ the principle of mechanical last copying based on machines from the 1930s. Thus, the technical potential of these CAD systems is far from exhausted. An innovative grading process allows shoe companies to better utilize and significantly expand the performance potential and technical capabilities of their 3D CAD systems. As the required amount of manual work in preparation for grading and last generation is considerably decreased, development times are shortened.
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