Multi-axis material extrusion of continuous carbon fiber composites: tool design and mechanical characterization

Abstract

Multi-axis material extrusion (MEX) additive manufacturing enables alignment of continuous fiber–reinforced (CFR) materials to 3D load paths, dramatically improving part strength. However, CFR deposition tools available for multi-axis MEX are limited. This work presents a new CFR deposition tool capable of (1) cutting and restarting fiber deposition and (2) in situ fiber volume fraction control, while (3) maintaining a slender collision volume. Using this tool, tensile properties of continuous carbon fiber–reinforced (CCF) polylactic acid (PLA) are evaluated relative to short carbon fiber–reinforced (SCF) and neat PLA. The CCF-PLA samples had a much higher tensile strength (190.76 MPa) and modulus (9.98 GPa) than PLA (60.31 MPa, 3.01 GPa) and SCF-PLA (56.92 MPa, 4.30 GPa) in the fiber direction. However, the introduction of CCF reduced the intra- and inter-layer properties; compared to neat PLA, CCF reduced the (1) intra-layer tensile strength by 66% and tensile modulus by 63% and (2) inter-layer properties by 86% and 60%, respectively. To understand the impact of multi-axis MEX, a curved tensile bar geometry was printed from CCF-PLA and SCF-PLA using multi-axis and XY-planar toolpaths. Multi-axis, CCF-reinforced samples absorbed significantly increased maximum load relative to multi-axis and XY-planar SCF-PLA (5.8 × and 8.2 × improvement, respectively), highlighting the effectiveness of multi-axis CFR deposition for producing high-strength parts.