Modeling and analysis of yarn catenary in 3D spherical braiding

3D braiding technology is a crucial approach for the low-cost and rapid production of composite materials. However, the length of the fiber catenary changes during the braiding process. To keep the yarn tension stable, it is necessary to retract and release the yarn. Defects in the preform caused by unstable tension during this process occur frequently in 3D braiding. A 3D spherical braiding machine is proposed in this paper to solve this problem. A general model of guide slider trajectory in the track is proposed to describe the spatial motion of the carrier. The nonlinear mapping relationship between carrier motion and fiber catenary length is established. The track models of spherical and cylindrical braiding machines are established, respectively. The spatial position of the carrier outlet serves as the boundary condition to analyze the dynamic change principle of fiber catenary. Finally, experiments are conducted using a 3D spherical braiding machine and a cylindrical braiding machine of YunLu Composite and KUKA robot. The model is reliable and the error is mainly caused by the offset of the fell point due to the interaction force between the yarns and the clearance in machines. The fluctuating speed of the catenary can be reduced by 43.2% and the storage capacity of the carrier is reduced by 51.8%. The proposed spherical braiding machine has great application potential for higher precision and lower wear braiding of important structural components.