Automation of crochet technology and development of a prototype machine for the production of complex-shaped textiles

In the future, due to the climate crisis and the need to reduce CO2 emissions, an increasing demand for lightweight materials such as textile reinforced composites can be expected. Because of rising raw material and energy costs, the application of more near net-shaped composites is promising for reducing manufacturing costs and waste. However, conventional textile technologies are limited in their ability to produce the necessary complex-shaped textiles. In order to address this problem by using alternative technologies that have not yet been industrially established, this thesis deals extensively with the development of a crochet machine and the investigation of respective textiles. Crochet is a stitch-forming technology in which, unlike knitting, the loops of a stitch originate both vertically and horizontally from previously formed stitches. With versatile crochet, it is especially possible to create complex three-dimensional (3D) shapes because new stitches can be formed at any point on a fabric. Previous crochet machine approaches are inadequate and severely limited in scalability to an industrially applicable machine. Industrially established machinery called crochet machines are misleading in their designation because they are knitting machines that can only roughly mimic crochet structure but cannot form true crocheted fabrics. The Crochet Automaton (CroMat) crochet machine developed and patented here enables for the first time the automated production of chain stitches (CHs), slip stitches (SLs), single crochet stitches (SCs), half double crochet stitches (HDCs), turns (T1 and T2), increase stitches (INCs) as well as decrease stitches (DECs) and other operations according to the principle of flat crocheting based on a chain line. In addition, by manually removing and re-hanging the produced fabric, new stitches can be formed at almost any point to produce complex-shaped 3D textiles according to the capabilities of crochet. For example, it is possible to produce shapes relevant for near net-shaped composites such as double T-beams with the developed CroMat prototype. With manually suspending different stitch rows or fabrics on the machine, it is also possible to join them by simultaneously crocheting a course through them. In addition to the mechatronic prototype with ten axes, the world's first tool for designing machine-crocheted textiles is developed. It includes error checking, generation of the G-code for machine control and a preview of the designed fabrics. Beyond a graphical user interface (GUI) with standardized crochet symbols, a higher-level programmability is added through specifying a shape by 2D polygons and automatically generating corresponding, machine-crochetable patterns. The first topology-based modeling framework for machine-producible crochet structures was developed for the preview. A similar modeling was developed for manually crocheted fabrics, which differ from the machine-produced ones only in the fact that the fabric is turned after each row and thus the stitches are formed from different sides. Both models can be used as a basis for simulative finite element method (FEM) investigations, which were used in this work to simulate crocheted fabrics for the first time. Furthermore, the tensile properties of manually crocheted fabrics were systematically investigated for the first time and the properties of the first crochet composites were researched. Crocheted textiles (and corresponding composites) have basically similar properties as knitted textiles but have a tendency to withstand higher forces. Together with the shaping capabilities, the CroMat crochet machine is generally highly promising for the automation of crochet and especially for the future production of near net-shaped composite reinforcements.