Composite materials have significantly influenced various industries due to their exceptional reliability and effectiveness. As technology advances, new types of composite reinforcements, such as novel chemical-based and bio-based, and new fabrication techniques are utilized to develop high-performance composite materials. AM, a widely popular concept poised to shape the development of Industry 4.0, is also being utilized in the production of composite materials. Comparing AM-based manufacturing processes to traditional methods reveals significant variations in the performance of the resulting composites.
Additive manufacturing (AM) has emerged as an advanced and innovative technique within the manufacturing industry. This technique, is also known as 3D printing, it has proven to be highly effective in utilizing reinforcements such as fillers and fibers in the fabrication of polymers and metals. By employing a layer-by-layer material deposition approach, AM enables the creation of composites, while conventional methods relying on subtractive manufacturing are used for comparable product development 
. The utilization of AM offers several significant advantages, including cost-effectiveness and the ability to design and fabricate complex structures with precision and high quality. These advantages have positioned AM as a preferred technique, particularly in the aerospace and automotive sectors, where intricate and accurate products are in high demand. The development of 3D-printed composites has witnessed substantial progress over the last decade, and it is expected that these materials will play a pivotal role in revolutionizing diverse industries in the future 
The utilization of AM technology is widespread in aerospace, electrical, and biomedical applications 
. However, in areas such as architecture and the construction industry, its implementation is still limited 
. One notable advantage of AM is its ability to reduce material waste and lead times, offering a flexible manufacturing approach. Incorporating waste or natural fibers as additives hold great promise for enhancing the environmental impact of composite materials in these fields 
. It is important to highlight that manufacturing natural fiber-reinforced composites using the AM process presents certain challenges. Factors such as fiber interactions, weight percentage, type, orientation, and length need to be carefully considered during composite material development. Nonetheless, AM serves as an excellent method for producing innovative and complex composite materials 
2. Fabrication of Composite Materials
Composite materials produced using additive manufacturing (AM) techniques have undergone significant advancements throughout the years. Initially, AM methods such as stereolithography (SLA) and Fused Deposition Modeling (FDM) were utilized to create plastic prototypes. Subsequently, there was a development towards developing polymers and metal matrix-based composites using AM, primarily due to their ability to manufacture intricately shaped structures 
. Further to enhance performance, high-performance composites were developed using carbon fiber and graphene, which exhibit improved thermal and electrical properties. Moreover, the AM concept extended to lightweight structural applications through the use of glass particles as reinforcement, combined with synthetic foam 
. Among AM methods, FDM is particularly well-suited for fabricating polymer-based composites. Thermoplastic filaments are commonly employed in the FDM process. This method offers advantages such as low cost and the ability to vary chemical and mechanical properties. In addition to FDM, other familiar AM techniques used for manufacturing polymer-based composites include sheet lamination, material extrusion, photopolymerization, and powder bed fusion. Photopolymerization provides finer resolution compared to other methods. Material extrusion, on the other hand, is the simplest and most cost-effective method, making fabrication easier.
Metal composites-based additive manufacturing (AM) techniques are a specialized subset of additive manufacturing that focuses on fabricating components using metal matrix composites. These techniques involve the incorporation of reinforcement materials, such as ceramic or carbon fibers, within a metallic matrix. By combining the unique properties of different materials, metal composites offer enhanced mechanical strength, improved thermal properties, and increased lightweight capabilities 
. Metal composites-based AM techniques, such as powder bed fusion (PBF) and directed energy deposition (DED), enable the production of complex and high-performance metal composite parts with precise control over material composition and fiber distribution. Several notable metal AM techniques are:
Powder Bed Fusion (PBF): PBF includes selective laser melting (SLM) and electron beam melting (EBM). In SLM, a high-powered laser selectively fuses metal powder particles layer by layer to create the desired metal part. EBM, on the other hand, uses an electron beam to melt the metal powder and form the object 
. PBF techniques offer high precision, intricate geometries, and excellent material properties.
Directed Energy Deposition (DED): DED techniques, such as laser metal deposition (LMD) and electron beam freeform fabrication (EBF3), involve depositing molten metal layer by layer onto a substrate or previous layers. This method is particularly useful for repairing or adding features to existing parts, as well as fabricating large-scale components 
Binder Jetting (BJ): Binder jetting utilizes a liquid binder to selectively bond metal powder particles together. The printed part is then subjected to a secondary process, such as sintering or infiltrating, to achieve the desired mechanical properties. BJ is known for its high productivity and suitability for producing complex geometries 
Wire Arc Additive Manufacturing (WAAM): WAAM involves melting and depositing a metal wire using an electric arc. This technique is cost-effective and can be used for large-scale manufacturing. WAAM is commonly used in the aerospace, automotive, and maritime industries 
Ultrasonic Additive Manufacturing (UAM): UAM employs ultrasonic vibrations to join layers of metal foils together. This technique allows for the integration of dissimilar metals and can be used for fabricating lightweight structures 
These metal-based AM techniques offer numerous advantages, including design freedom, reduced material waste, faster prototyping, and the ability to create complex and customized metal parts. They find applications in various industries, including aerospace, automotive, medical, and tooling, among others 
. Continuous research and development efforts in metal AM are further advancing the capabilities and expanding the possibilities of metal-based additive manufacturing.
The motivation for producing polymer-based materials through additive manufacturing (AM) is to enhance their properties and expand their applications across various sectors. Natural fibers such as wool, hemp, flax, kenaf, and vegetable fibers have been successfully utilized as replacements for artificial fibers in composite manufacturing using AM. AM is a manufacturing process that allows for the creation of complex shapes with minimal material waste and time. Different types of polymers, including thermoplastics, liquid polymers, and reactive polymers, are used in AM, with recent advancements focusing on incorporating fillers such as nanotubes, carbon fibers, nanofibers, nanoparticles, and synthetic fibers into polymeric products 
. The production of lightweight polymeric products presents challenges in engineering industries, and the development of AM techniques has alleviated some of these burdens in composite manufacturing 
. Notably, AM-based technology has demonstrated superior performance, particularly in Fiber-Reinforced Polymer (FRP) materials, resulting in the production of high-performance structural components