Pultrusion of hybrid bicomponent fibers for 3D printing of continuous fiber reinforced thermoplastics

Continuous lattice fabrication is a newly introduced method for additive manufacturing of fiber-reinforced thermoplastic composites that allows to deposit material where it is needed. The success of this technology lies in a printing head in which unconsolidated continuous fiber-reinforced composite is pulled through a pultrusion die before the material is extruded and deposited out of plane without the use of supporting structures. However, state-of-the-art composite feedstock like commingled yarns shows limits in achievable material quality and part dimensions due to the underlying fiber architecture where thermoplastic fibers are mingled with reinforcement filaments. Hybrid bicomponent fibers overcome these constraints because each individual reinforcement filament is clad in a thermoplastic sheath. This results in absence of time-consuming fiber impregnation steps that would negatively effect void content and material quality.

This study compares the material quality of pultrudates made from hybrid bicomponent fibers to that of commercially available commingled yarns at various processing conditions. Experiments are reported in which polycarbonate composite profiles with a diameter of 5 mm containing 50 vol% to 60 vol% E-glass fibers are pultruded at different die filling degrees, mold temperatures and pultrusion speeds. The results show that the pultrudates obtained from hybrid bicomponent fibers have lower void content than those manufactured under the same conditions from commingled yarns. We assess this to be caused by the difference in consolidation mechanism which in the case of the hybrid bicomponent fibers is dominated by coalescing of the thermoplastic sheaths compared to the Darcian flow-dominated consolidation of commingled yarns.