Fused Deposition Modelling (FDM) is an actively growing additive manufacturing (AM) technology due to its ability to produce complex shapes in a short time. AM, also known as 3-dimensional printing (3DP), creates the desired shape by adding material, preferably by layering contoured layers on top of each other. The need for low cost, design flexibility and automated manufacturing processes in industry has triggered the development of FDM. However, the mechanical properties of FDM printed parts are still weaker compared to conventionally manufactured products. Numerous studies and research have already been carried out to improve the mechanical properties of FDM printed parts. Reinforce polymer matrix with fiber is one of the possible solutions. Furthermore, reinforcement can enhance the thermal and electrical properties of FDM printed parts. Various types of fibers and manufacturing methods can be adopted to reinforce the polymer matrix for different desired outcomes. This review emphasizes the fiber types and fiber insertion techniques of FDM 3D printed fiber reinforcement polymer composites. A brief overview of fused deposition modelling, polymer sintering and voids formation during FDM printing is provided, followed by the basis of fiber reinforced polymer composites, type of fibers (synthetic fibers vs. natural fibers, continuous vs. discontinuous fiber) and the composites’ performance. In addition, three different manufacturing methods of fiber reinforced thermoplastics based on the timing and location of embedding the fibers, namely ‘embedding before the printing process (M1)’, ‘embedding in the nozzle (M2)’, and ‘embedding on the component (M3)’, are also briefly reviewed. The performance of the composites produced by three different methods were then discussed.

A 3D printed composite via the fused filament fabrication (FFF) technique has potential to enhance the mechanical properties of FFF 3D printed parts. The most commonly employed techniques for 3D composite printing (method 1) utilized premixed composite filaments, where the fibers were integrated into thermoplastic materials prior to printing. In the second method (method 2), short fibers and thermoplastic were mixed together within the extruder of a 3D printer to form a composite part. However, no research has been conducted on method 3, which involves embedding short fibers into the printed object during the actual printing process. A novel approach concerning 3D printing in situ fiber-reinforced polymer (FRP) by embedding glass fibers between deposited layers during printing was proposed recently. An experimental investigation has been undertaken to evaluate the tensile behavior of the composites manufactured by the new manufacturing method. Neat polylactic acid (PLA) and three different glass fiber-reinforced polylactic acid (GFPLA) composites with 1.02%, 2.39%, and 4.98% glass fiber contents, respectively, were 3Dprinted. Tensile tests were conducted with five repetitions for each sample. The fracture surfaces of the samples were then observed under scanning electron microscopy (SEM). In addition, the porosities of the 3D printed samples were measured with a image processing software (ImageJ 1.53t). The result shows that the tensile strengths of GFPLA were higher than the neat PLA. The tensile strength of the composites increased from GFPLA-1 (with a 1.02% glass fiber content) to GFPLA-2.4 (with a 2.39% glass fiber content), but drastically dropped at GFPLA-5 (with a 4.98% glass fiber content). However, the tensile strength of GFPLA-5 is still higher than the neat PLA. The fracture surfaces of tensile samples were observed under scanning electron microscopy (SEM). The SEM images showed the average line width of the deposited material increased as glass fiber content increased, while layer height was maintained. The intralayer bond of the deposited filaments improved via the new fiber embedding method. Hence, the porosity area is reduced as glass fiber content increased.

In this study, tensile test specimens were fabricated using a material extrusion 3D-printer at various printing temperatures to evaluate the development of physical bonds within the same layer as well as in between previous layers. The tensile test specimens were fabricated using PLA material, with printing temperatures ranging from 180 °C to 260 °C. Experimental investigations were conducted to investigate the dimensional accuracy and physical appearance of the parts across printing temperatures. Uniaxial tensile tests were conducted at a strain rate of 1 mm/min and repeated five times for each variable in accordance with the ASTM D638-14 standard. Results showed that increasing the printing temperatures yielded parts with better tensile properties. An approximate difference of 40% in tensile strength was observed between specimens fabricated under the two most extreme conditions (180 °C and 260 °C). The changes in tensile properties were attributed to bonding mechanisms related to interlayer bonding strength and a reduction in voids within the internal geometry. Analysis of the fracture surface using scanning electron microscopy (SEM) revealed fewer and smaller voids within the internal geometry for parts printed at higher temperature. The percentage area of voids reduced significantly when the printing temperature was increased from 180 °C to 220 °C. The tensile properties continuously improved with the printing temperature, with parts printed at 220 °C exhibiting the highest dimensional accuracy. The findings offer insight into the impact of the printing temperature on both the external physical bonds between printed roads, affecting the physical appearance and dimensional accuracy, and the internal bonds, affecting the tensile properties of the fabricated parts.

Fused filament fabrication (FFF) 3D-printed parts are mostly used as prototypes instead of functional parts because they have a weaker mechanical strength compared to their injection molded counterparts. Various methods including a fiber-reinforced polymer composite were proposed to enhance the properties of FFF 3D-printed parts. A new concept to fabricate a polymer composite via FFF 3D printing is proposed, where fiber is deposited during printing, instead of using a premixed composite filament. In order to investigate the workability of this concept, a new device is needed. Firstly, the design requirements were identified, and a fiber doser that can be mounted on a commercial 3D printer was designed. Prototype testing was conducted to improve the design. The improved fiber doser was able to deposit varied fiber contents during FFF 3D printing. Thermogravimetric analysis (TGA) was used to quantify the fiber contents of the fabricated composites. With this newly designed doser, short glass fiber–polylactic acid (PLA) composites with three different fiber contents (1.02 wt.%, 2.39 wt.%, and 4.98 wt.%) were successfully manufactured. A new technique to manufacture a polymer composite is proven; nevertheless, the mechanical and tribological properties of the newly fabricated composites are under investigation and will be reported in a subsequent article.