Abstract:

Objective The carrier track for the traditional track-and-column three-dimensional (3-D) braiding is fixed, resulting in low flexibility. In quadrangular and hexagonal 3-D braiding machines, the area ratio of the yarn carrier to the braiding plate is relatively small, resulting in low utilization of the braiding plate area. The triangle braiding process has the highest chassis utilization rate and excellent mechanical properties, and makes it significant research topic. To further study the braiding technology and algorithm of the triangular 3-D braiding, it is necessary to digitally model the braiding components and movements and to establish geometrical models of meso-structure of fabrics, which can provide a guidance for the development of new braiding techniques.

Method In the triangular braiding process, the horn-gears and the switch-gears drove the carriers while they were alternately rotating, resulting in the yarns interlacement. Horn-gears, switches, and carriers were simulated to study the movement rules of carriers. The path of carriers and the height of the braiding node jointly determined the spatial topological structure of the fabric. The cubic B-spline curve was used to optimize the spatial paths of the yarns, and the Python script was written to drive CATIA to establish the meso-structure of preforms. Furthermore, the visual interface of the fabric structure was developed with PyQt5.

Results The machine bed of the triangular braiding device mainly consists of three-wing gears and yarn carriers. These gears were independently driven by stepper motors, thus providing high flexibility. The gears were divided into two groups: horn-gears and switch-gears, with rotation angles being multiples of 120° and not exceeding 360°. The movements of the horn-gears, switch-gears, and yarn carriers were progrmmed, relating the movement of ths yarn carriers to that of horn-gears. The movement of the yarn carrier was classified into two scenarios: tracking the motion of the horn-gear and tracking the motion of the switch-gear, and corresponding formulas for position exchange were derived for each case. The projected curve of the spatial trajectory of the yarn conforms to the proportion relationship with the yarn carrier's motion path. By adjusting the scaling factor, the yarn arrangement kept compact and without penetration. Combined with the lifting height, the 3-D coordinates of the yarn trajectory points were obtained. The obtained yarn trajectory was interpolated and fitted using cubic B-spline curves, driving CATIA to establish a detailed meso-structure. A fabric structure simulation software was developed with the PyQt5 library to interactively set braiding process parameters and the initial layout of horn-gears, output spatial trajectories of all yarns, and generate fabric geometric structures. When the rotation directions of horn-gears and switch-gears were the same and their angles were both 120°, the yarns would not able to intertwine, thus unable to form a prefabricated structure. When the rotation directions of horn-gears and switch-gears were opposite, and their angles were both 120°, the yarn projection trajectories would form triangles, with the three sets of trajectories interweaving, resulting in a uniform and compact prefabricated structure. The braiding experiments were conducted on the rectangular cross-section fabrics, demonstrating good consistency between the theoretical model and experimental specimens. This validates the accuracy of the process modeling method proposed in this paper.

Conclusion The triangular 3-D braiding process could make yarns interlace with each other to form a braiding compact fabrics. The proposed modeling algorithm could simulate the meso-structure of fabrics with different braiding angles, and the fabric model was consistent with the experimental fabric. The developed fabric simulation software could visually display fabric models under different parameter combinations. In the future, the multiple structures of braiding fabrics could be obtained based on the triangular 3-D braiding process, thereby providing guidance for studying their mechanical properties.

Key words: 3-D braiding, braiding preform, braiding algorithm, meso-structure model, process software