Near-perfect Turning of Robot-Based 3D Printing Continuous Carbon Fiber Reinforced Nylon Composites Based on Fiber-Scale Internal Stress Characterization

Mechanical metamaterials based on continuous fiber reinforced composites exhibit excellent mechanical properties. Continuous fiber 3D printing is counted as an ideal manufacturing approach for mechanical metamaterials. Currently, most metamaterial lattice structures are printed at centimeter-scale. The significant change in the width of the printed filament caused by fiber twist and shift during steering is an obvious defect when turning with minor radius. Near-perfect turning is proposed herein as a turning under the smallest possible printing radius, and the printed filaments present superior width retention rate. The key to printing highprecision composite lattice structures below centimeter-scale is to assess the near-perfect turning radius. Therefore, a fiber near-perfect turning placement model was established and the near-perfect turning radius ra was assessed by measuring the fiber-scale internal stress required in the model. The precision evaluations show that the near-perfect turning radius calculated by the model is in good agreement with the experimental value, proving the model's validity. In the case of the Robot-based printing platform and Nylon-carbon fiber composites, the near-perfect turning radius is 2.0 mm. This study establishes a solid process foundation for metamaterial manufacturing below the centimeter scale.