Additive Manufacturing of Composites

Robot-assisted 3D printing

FFF process optimization and uncertainty analysis

Highlights |

  • Experimental study of the uncertainties in bead level dimensional accuracy.
  • Characterization of multi-level mechanical properties and void contents.
  • Optimal process parameters for improved strength and stiffness with higher dimensional accuracy and reduced void contents.
  • Stochastic modeling to predict the process-induced void contents and structural performance.

Fracture toughness analysis of polymer composites

Experimental setup for compact tension fracture test
Crack propagation for 45/-45 degree layup sequences
Load-COD curves

Highlights |

  • Significant improvement in critical stress intensity factor and critical energy release rate were recorded for 5 wt. % CF loading on FFF processed composites.
  • Bead layup sequence, fiber pullout, interfacial de-bonding, and void formation are deemed to be the major factors to the fracture toughness.
  • FFF-based 3D printing is still inferior to conventional manufacturing processes.
  • ​The effect of higher intra-bead voids, microcracks, poor interfacial bonding between fiber and PLA matrix and enlarged intra-bead voids around the fiber surface were critical at higher fiber loading.

Effect of process parameters on AM parts quality

Effect of fiber surface treatment on interfacial bonding between fiber and polymer
Effect of annealing on crystallinity
Effect of nozzle geometry on void contents and void shapes

Highlights |

  • A square-shaped nozzle deposited the beads with a square-like cross-section that increased the bead contact surface area and improved the inter-bead bonding with successive beads.
  • Functionalization improved the composite synthesis process that enhanced the fiber-matrix bonding and reduced the tendency of micropore formation at the interface.
  • The FFF-printed part possesses some sort of crystallinity, which is an advantage of the printing process. However, post-processing annealing increased the degree of crystallinity, which enhanced the mechanical properties significantly.

Numerical model of bead spreading architecture

Highlights |

  • VOF-based computational fluid dynamics model was developed with different nozzle geometries to study the free-form melt flow and bead spreading architecture.
  • The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian, and non-isothermal flow is assumed.
  • The governing equations are solved on a regular stationary grid following a transient algorithm.
  • The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment.

Thermal and fluid flow model of the polymer FFF process

Temperature distribution of the 3D printing liquefier
Temperature profile at different cross-sectional planes along the spreading direction
Comparison of nozzle, swelling, and bead shape of circular, square and star-shaped nozzle

Highlights |

  • Bead usually maintains the temperature halfway through its cross-section before starting to cool down.
  • The top surface of the bead is always at a higher temperature, which is invariable to the bead location along the spreading direction.
  • The cooling rate is higher at the bottom surface.
  • The longer distance the bead travels means prolonged exposure at a lower temperature, driving the cooling process.