## 1 Introduction
### Literature Review and Previous Work
It is believed that further research on MCFA-AM could help to produce a viable next-generation CFRP manufacturing process. As explained in the original patent document [9], the MCFA-AM method prints laminates in free space rapidly, without molds. [PERSON] et al. proved the feasibility of this method in their study [18], in which MCFA-AM samples showed improvements of 8% and 9% in ILSS compared to those manufactured by hand layup and by tension-tape-placement-without-compaction additive manufacturing (TTP-WOC-AM, which is similar to the concept of FDM), respectively. The ILSS of the MCFA-AM-printed C-CFRP samples was still 7% lower than the OOA-VBO produced C-CFRP samples. This was probably due to the tightly controlled temperature and vacuum advantages of the OOA-VBO process, while the MCFA-AM's feasibility-prototype printhead was operated by hand [18]. There is hope for a substantial amount of improvement in the properties and strength of the printed composite parts when the MCFA-AM method is implemented with a novel nanocomposite, such as carbon nanofiber (CNF) z-threaded CFRP (ZT-CFRP), as the feedstock for printing. This will hopefully overcome the processing disadvantages of reduced pressure and temperature control and the lack of vacuum source during the \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline  & \multicolumn{2}{c}{**3D Printed Thermoplastic C-CFRP**} & \multicolumn{2}{c}{**3D Printed Thermoset C-CFRP Examples**} \\ \hline Material & CF/Nylon [16] & CF/Epoxy (E-20) [17] & CF/Epoxy (EPIKOTETM TRAC 06170) [18] \\ \hline Fiber Volume Fraction (\%) & 35 & 48 & N.A. \\ \hline Void (\%) & 3.0 & 2.5 & N.A. \\ \hline ILSS (MPa) & N.A. & 49 & 70.5 \\ \hline ILSS change (\%) vs. baseline value & N.A. & \(-\)54\% & \(-\)7\% (vs. OOA-VBO baseline); +9\% (vs. FDM baseline) \\ \hline Tensile strength (MPa) & 1031 & 1476 & N.A. \\ \hline Tensile strength change (\%) vs. baseline value & +29\% & \(-\)32\% & N.A. \\ \hline Flexural strength (MPa) & 945 & 858 & N.A. \\ \hline Flexural strength change (\%) vs. baseline value & +75\% & \(-\)50\% & N.A. \\ \hline
3D printing method used in the literature & 3 D Compaction Printing (3 DCP); hot compaction-roller during FDM & Protrusion modified FDM to pre-from the sample; followed by powder resin melt infusion into the sample’s porosity and post cured the sample & MCFA-AM; a handheld MCFA-AM printing head; average magnetic compaction pressure 2.1 bar \\ \hline Baseline manufacturing method(s) compared in the literature & Filament manufacturer’s data sheet of samples printed with a typical FDM process. & Carbon fiber manufacturer’s data sheet of samples produced by traditional Autoclave process with full vacuum inside the vacuum bag. (\(-\)\(-\)1 bar) and autoclave pressure 5.52–6.89 bars (85–100 psi) outside the vacuum bag. & 1. Traditional OOA-VBO process; full vacuum (\(-\)\(-\)1 bar) applied inside the vacuum bag. \\ \hline \end{tabular}
\end{table} 
Table 2: Performance comparison of reported improved 3D-printing-method-produced C-CFRP samples verses their counterparts produced by either traditional composite processing or typical FDM-based 3D-printing processing [16; 17; 18]. rapid curing required for MCFA-AM. Figure 1 gives a basic representation of the ZT-CFRP structure with the CNFs threaded in the z-direction through arrays of carbon fibers, forming a mechanically interlocked 3D fiber-reinforcement network [20]. According to the literature, ZT-CFRP laminates have significantly improved mechanical properties (e.g., mode-I interlaminar fracture toughness [21]), thermal properties (e.g., through-thickness thermal conductivity [22]), electrical properties (e.g., through-thickness DC electrical conductivity [23; 24]), interlaminar shear strength (ILSS) [25], and longitudinal compressive strength [20], even with low CNF concentrations (0.3 wt% to 2.0 wt%) when dispersed in an epoxy matrix. [PERSON] et al.