Thermal Characterization of Continuous Pitch Carbon Fiber 3D-Printed using a 6-Axis Robot Arm

Initial research into the 3D-printing of continuous pitch carbon fiber composites for heat exchanger applications has showed promise however, measured thermal conductivities were significantly lower than those predicted by theoretical models due to fiber breakage during the printing process. Prior studies in which the carbon fiber was printed at 45° from the printing bed showed through thermal testing and microscopic images that the angle of the nozzle was not enough the stop the breakage. A sample at a fiber volume percentage of 10.4% was expected to have a conductivity of 83.2 W/mK, yet experimental results showed only 36.6 W/mK. At other fiber volume percentages, a similar decrease in thermal conductivity of around 55% was found. In the present study, the effect of fiber extrusion angle on the thermal conductivity of the printed rasters is investigated using a redesigned extruder and hotend mounted to a 6-axis robot arm. The thermal conductivity of individual printed rasters was characterized using a heat flow apparatus and compared to those of un-broken and specified values. Overall, it is shown that printed fiber thermal conductivity increases from 442 W/mK at a printing angle of 45° to 621 W/mK at an angle of 60°. Future directions of this process and technology are discussed.