## 1 Introduction  
### Motivation  
Additive manufacturing (AM), or 3D printing, has yet to reach its full potential in the field of high-strength-composite manufacturing for numerous reasons. Some of its limitations (e.g., the lack of structural strength and related properties) are holding the technology back and preventing it from competing with the composites manufactured by using traditional methods. Hence, composite parts manufactured using these current AM methods are inferior in strength and stiffness to composites manufactured through traditional methods. The major issues include the low reinforcing fiber content with respect to the resin, physical gaps between the fibers, air traps, voids in the layer-to-layer interface,etc. The voids and agglomerates in the polymer matrix significantly decrease composite products' mechanical and electrical properties [1; 2]. Taking the subpar performance of 3D-printed composites into account, although traditional CFRP manufacturing methods (e.g., the autoclave process, resin-transfer molding (RTM), out-of-autoclave vacuum-bag-only (OOA-VBO) process) use molding or injection processes to produce strong laminates, they encounter obstacles such as poor energy efficiency, high cost, long curing cycles, and size constraints on their composite parts [3]. To better appreciate the potential advantages of the 3D printing of CFRPs, a quick overview of the shortfalls of traditional CFRP manufacturing methods is worthy of discussion. For example, the OOA-VBO process, a newer thermoset CFRP-manufacturing method, requires an oven and a low-pressure, lightweight, one-sided mold (rather than an autoclave or an expensive and bulky high-pressure RTM mold) to produce thermoset continuous carbon-fiber-reinforced polymer (C-CFRP) composite laminate parts, reducing production costs and enabling the manufacturing of larger parts. However, the OOA-VBO process suffers from long curing times, size constraints due to the mold and oven, and high production costs associated with the development, handling, repair, cleaning, and storage of the mold. Continuous fiber-reinforced thermoplastic composites (CFRTCs) are traditionally manufactured by filament winding, vacuum forming, pultrusion, compression molding, and bladder-assisted molding. The high cost of molds and dies, as well as their inferior ability to produce complex geometries and special fiber arrangements, are noteworthy limitations of these methods, and they hinder the wider application of CFRTCs in industrial production [4; 5; 6; 7]. The disadvantages of traditional composite-manufacturing methods could potentially be resolved by an appropriate and innovative 3D-printing process if it were capable of producing 3D-printed CFRPs with equivalent or superior properties to those made by traditional means, and of removing the dependency on molds or the supporting printer bed plate, which limits the sizes of the printed parts, the fiber layup, and the reinforcing direction. There is a need for an alternative AM technology, which can overcome the drawbacks of the aforementioned traditional manufacturing methods and produce stronger CFRP parts. This paper is focused on such a novel 3D-printing method, namely, magnetic compaction force-assisted additive manufacturing (MCFA-AM), which has been proven to require shorter production cycles with the use of a fast resin-blend technique and to completely remove the need for molds or supporting printer beds [8]. This patented 3D-printing method [9] utilizes an attraction force produced by a magnetic field emitter and a backing article attracted to the emitter to rapidly print, compact, and support C-CFRP parts in free space. Through the integration of the MCFA-AM printhead with a robotic arm and fast-curing C-CFRP prepreg, lightweight C-CFRP parts of various sizes can be swiftly printed with great complexity, functionality, and strength [8; 9].